notes & notes basic science immunology (1)

__________________________________________________________________________________________________ Notes & Notes for mrcp Dr.Yousif Abdallah Hamad

Notes & Notes For MRCP part 1 & 11

By

Dr. Yousif Abdallah Hamad

Basic science

Immunology

Contains:

1/ Passmedicine 2015 (white & black fields)

2/ on examination 2015 (green fields)

3/ pastest 2015 (yellow fields)


بسم هللا الرحمن الرحيم

Preface ‘How do I get started?’ ‘Which books should I read?’ ‘Which are the best

Self-assessment questions bank?’ ‘Passmedicine alone? Is it enough?’ or should I add other

source? Should I add on-examination or pastest?

These are the usual questions asked by the MRCP candidates. For all these questions, and

depending on thorough follow up of a lot of candidates results , feedbacks and comments, rather

than my personal experience, and after consultations of a wide range of mrcp experts, I decide

to create a very concise notes collected from the most popular three mrcp sources :

- Passmedicine 2015 (in black & white fields)

Onexamination 2015 (in green fields) -

And pastest 2015 (in yellow fields)

Occasionally, I add a few facts from previous exams, last guidelines and uptodate

source.

How to use this ''notes & notes''?

I recommend candidates to follow these steps:

- First off all go carefully through this notes 2 times aiming to build a bulky knowledge

of mrcp syllabus.

- then start to practice questions from Passmedicine , onexam and pastest , you will find

it very easy to answer , and if you face any difficult question you have to open your

''notes & notes'' and read the topic again before returns to question banks , this is

crustily helpful to fix the idea.

- In the last few days before your exam, return to this notes and read it once again.

You will find some information written by red or big font, those are the answers of

questions, which are tested in above sources and previous exams. I hope this

collection will be enough to help you get through mrcp part 1 and give you a good grip

before interring part 11.

Dr. Yousif Abdallah Hamad


HLA associations

HLA antigens are encoded for by genes on short arm of chromosome 6.

HLA A, B and C are class I antigens whilst DP, DQ, DR are class II antigens.

Class-I molecules (subtypes A, B and C) are expressed on all cell types except erythrocytes and trophoblasts

They interact with CD8-positive T-cells and are involved in driving cytotoxic reactions

Class II matching is particularly important when it comes to transplant matching,

Studies in renal transplantation indicate that mismatches at the A, B, and DR loci are associated with worse allograft survival.

Anti-HLA antibodies are typically not naturally occurring, only occur post transplantation

MHC class II is only expressed on immune cells. MHC I is expressed on any cell type.

Questions are often based around which diseases have strong HLA associations. The most important associations are listed below:

Associated diseases

HLA type

Hemochromatosis HLA-A3

Behcet's disease HLA B51 is a split of B5 HLA-B5

21-hydroxylase deficiency HLA-B47

psoriasis HLA-CW6

Diabetes mellitus type 1(but more with HLA-DR4) HLA-DR3 + DR4 combined

Narcolepsy Goodpasture's

HLA-DR2

Felty's syndrome (90% ) => most common

Rheumatoid arthritis (70%) Diabetes mellitus type 1 (> DR3) Drug-induced SLE IgA nephropathy HOCM

HLA-DR4

Ankylosing spondylitis Postgonococcal arthritis Reiter's syndrome (reactive arthritis) Acute anterior uveitis

HLA-B27

Autoimmune hepatitis

Primary biliary cirrhosis Coeliac disease (95% associated with HLA-DQ2) Diabetes mellitus type 1 Primary Sjögren syndrome Dermatitis herpetiformis

HLA-DR3


Rheumatoid arthritis - HLA DR4

Around 70% of patients with rheumatoid arthritis are HLA-DR4. Patients with Felty's syndrome (a triad of rheumatoid arthritis, splenomegaly and neutropaenia) are even more strongly associated with 90% being HLA-DR4

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Clusters of differentiation

Function and usage of CDs:

- Commonly used as cell markers in immuno-phenotyping, allowing cells to be defined based on what molecules are present on their surface.

- often acting as receptors or ligands (the molecule that activates a receptor) - cell signaling: Errors in cellular information processing are responsible for diseases such

as cancer, autoimmunity, and DM - Cell adhesion: essential for the pathogenesis of infectious organisms. Eg: Plasmodium

falciparum uses adhesion molecules to bind to liver cells and RBCs. Cancer metastases by mechanisms of cell adhesion. Adhesion of bacteria is the first step in colonization and regulates tropism (tissue- or cell-specific interactions).

*viruses also have adhesion molecules required for viral binding to host cells. For example, influenza virus has a hemagglutinnin on its surface that is required for recognition of the sugar sialic acid on host cell surface molecules. HIV has an adhesion molecule termed gp120 that binds to its ligand CD4, which is expressed on lymphocyte.

Leukocyte adhesion deficiency-1 (LAD-1) is an example of genetic diseases caused

by an inability to express a specific adhesion molecule (β2-integrin subunit

precursor).This integrin is required for leukocytes to adhere to the blood vessel wall

during inflammation in order to fight infection. The leukocytes from LAD-I patients

fail to adhere and patients exhibit serious infections. * Pemphigus is the result of auto-antibodies which target desmosomal cadherins, resulting in loss of cell adhesion.


The table below lists the major clusters of differentiation (CD) molecules

Cluster of

differentiation Function

CD1 MHC molecule that presents lipid molecules

CD2 Found on thymocytes, T cells, and some natural killer cells that acts as a ligand for

CD58 and CD59 and is involved in signal transduction and cell adhesion

CD3 The signalling component of the T cell receptor (TCR) complex

CD4 Found on helper T cells.

Co-receptor for MHC class II

Used by HIV to enter T cells

CD5 Found in the majority of mantle cell lymphomas

CD8 Found on cytotoxic T cells.

Co-receptor for MHC class I Found on a subset of myeloid dendritic cells

CD14 Cell surface marker for macrophages

CD15 Expressed on Reed-Sternberg cells (along with CD30)

CD28 Interacts with B7 on antigen presenting cell as costimulation signal

CD95 Acts as the FAS receptor, involved in apoptosis

The number of CD4 and CD8 T cells in blood is often used to monitor the progression of HIV infection.


CD4:

encoded by a gene on chromosome 12.

CD4+ T helper cells are white blood cells that are an essential part of the human immune

system. They are often referred to as CD4 cells, T-helper cells or T4 cells.

They are called helper cells because one of their main roles is to send signals to other types of immune cells, including CD8 killer cells, which then destroy the infectious particle.

If CD4 cells become depleted, for example in untreated HIV infection, or following immune suppression prior to a transplant, the body is left vulnerable to a wide range of infections that it would otherwise have been able to fight.

CD4 uses its D1 domain to interact with the β2-domain of MHC class II molecules.

T cells expressing CD4 molecules (and not CD8C) on their surface, therefore, are specific for antigens presented by MHC II and not by MHC class I (they are MHC class II-restricted).

Normal values for CD4 cells being 500-1200 cells/mm3

A CD4 count measures the number of T cells expressing CD4.

Patients often undergo treatments when the CD4 counts reach a level of 350 cells per microliter in Europe but usually around 500cpm in the US; people with less than 200 cells per microliter are at high risk of contracting AIDS defined illnesses. The newest National Institute of Health guidelines recommend treatment of any HIV-positive individuals, regardless of CD4 count.

CD4 continues to be expressed in most neoplasm derived from T-helper cells. It is therefore possible to use CD4 immunohistochemistry on tissue biopsy samples to identify most forms of peripheral T cell lymphoma and related malignant conditions. The antigen has also been associated with a number of autommune diseases such as vitiligo and type I diabetes mellitus

PCP, disseminated fungal disease, and CMV infection almost always occur when the CD4 counts are very low, usually below 200 cells/mm3.

CD8:

encoded by genes on chromosome 2

CD8 binds to a major histocompatibility complex (MHC) molecule, but is specific for the

class I MHC protein

CD8+ T lymphocytes are otherwise known as cytotoxic T lymphocytes.

http://en.wikipedia.org/wiki/CD8


The T cell receptor on the surface of the CD8+ T cell recognises virus peptides in the

context of self HLA class I molecules on the surface of virus infected antigen presenting

cells. The infected cell is then lysed.

The CD8 co-receptor is predominantly expressed on the surface of cytotoxic T class

cytotoxic T cells, but can also be found on natural killer cells, cortical thymocytes,

and dendritic cells.

Dendritic cells are professional antigen presenting cells presenting antigen to CD4+ helper cells and

CD8+ T cells, but have no cytotoxic potential.

Macrophages are also antigen presenting cells and are also involved in recognition and eradication

of certain intracellular pathogens but in a non-HLA restricted manner.

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COMPLEMENT PATHWAYS A cascade of sequential activation converts each proenzyme into its active state and amplifies

the response. Activation may occur via two main pathways.

1. Classical pathway:

- Triggered by antigen-antibody complexes containing lgM or lgG.

- C1 is the initiating protein, and after binding to an Fc is able to activate C4 and

C2, which in turn activate multiple C3 molecules.

2. Alternative pathway:

- Initiated by certain antigens (lipopolysaccharide, endotoxin) and lgA complexes

on cell surfaces which activate C3.

- Generates early innate response that does not require antibody for activation.

3. Lectin pathway :Mannose-binding lectin (MBL) is a collectin that is able to bind through

its lectin proteins on to carbohydrates present on bacteria. This indirectly activates the

next complement components. C2 and C4.

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Mannose-binding lectin (MBL)

*A child has recurrent pyogenic infection. What is the most likely diagnosis?

Mannose binding lectin deficiency

Mannose-binding lectin (MBL) is a protein involved in complement activation via the lectin

pathway.low MBL result from mutations in MBL2 gene (3 - 5 % of population. Heterozygosity in 30 % of population. ).MBL binds to carbohydrates on microbes or unwanted material and triggers the activation of the lectin pathway, but it does not recognize self carbohydrates. deficiency of MBL is associated with an increased frequency of pyogenic infections, especially encapsulated bacteria, due to defective opsonization. alo leads to an increase severity of chronic inflammatory conditions.


Complement activation IgG and IgM are the main antibody classes that activate the classical pathway

C1q binds to the Fc (Fc, crystallisable fragment)

The membrane-attack complex involves polymerisation of C7

Clotting of blood can lead to complement activation, and hence complement conversion products must be measured on plasma and not serum

the alternative, (not the classical ) C3, convertase enzyme involves C3b

C2 is involved in activation via the classical pathway


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Complement deficiencies

Whilst C3 deficiency is associated with recurrent bacterial infections, C5 deficiency is more characteristically associated with disseminated meningococcal infection

Complement is a series of proteins that circulate in plasma and are involved in the inflammatory and

immune reaction of the body. Complement proteins are involved in chemotaxis, cell lysis and

opsonisation.

C1 inhibitor (C1-INH) protein deficiency

causes hereditary angioedema

C1-INH is a multifunctional serine protease inhibitor

probable mechanism is uncontrolled release of bradykinin resulting in oedema of tissues

C1q, C1rs, C2, C4 deficiency (classical pathway components)

predisposes to immune complex disease

e.g. SLE, Henoch-Schonlein Purpura

mechanism

- complement activity is associated with => clearance of circulating immune complexes


- If immune complexes are not cleared, they undergo => tissue deposition where an

inflammatory process is triggered,leading to SLE

C3 deficiency

causes recurrent bacterial infections

Deficiencies of C3 is more commonly associated with haemolytic uraemic syndrome

C5 deficiency

predisposes to Leiner disease

recurrent diarrhoea, wasting and seborrhoeic dermatitis

C5-9 deficiency

encodes the membrane attack complex (MAC)

particularly prone to Neisseria meningitidis infection

Deficiencies in C1r, s, and 2-4 result in vasculitidies

Deficiencies in C2, 3 and 5-8 are associated with an increased risk of septicaemia.

Decay-accelerating factor (DAF) deficiency is associated with Paroxysmal nocturnal

haemoglobinuria (PNH).

*Post splenectomy what type of immunodeficiency is occurs?

Humoral . Post splenectomy there is increased susceptibility to H. Influenzae, N. Meningitidis

and Strep pneumonia which are encapsulated organisms due to the loss of splenic macrophages

which are part of the humoral response.

* If adenosine deaminase is absent from a cell i.e. in severe combined immunodeficiency

disease, what does this result in?

Leads to accumulation of deoxyadenosine. Adenosine deaminase enzyme leads to the

breakdown of deoxyadenosine, which is a breakdown product of DNA. Deoxyadenosine is toxic to

lymphocytes, thus accumulation of this leads to apoptosis of lymphocytes.


How to exclude antibody deficiency?

Presence of Specific antibodies to haemophilus and pneumococci

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Hereditary angioedema Hereditary angioedema - C1-INH

deficiency

Hereditary angioedema - C4 is the best screening test inbetween

attacks

Hereditary angioedema is an autosomal dominant condition associated with low plasma levels of the C1 inhibitor (C1-INH) protein. C1-INH is a multifunctional serine protease inhibitor - the probable mechanism behind attacks is uncontrolled release of bradykinin resulting in oedema of tissues. Pathophysiology

Low levels of the C1 inhibitor allow C1 to act on C4 and C2

This in turn produces kinin-like products that cause the angio-oedema

Investigation

C1-INH level is low during an attack

Low C2 and C4 levels are seen, even between attacks.

Serum C4 is the most reliable and widely used screening tool

Symptoms

attacks may be proceeded by painful macular rash

painless, non-pruritic swelling of subcutaneous/submucosal tissues

may affect upper airways, skin or abdominal organs (can occasionally present as abdominal

pain due to visceral oedema)

urticaria is not usually a feature

Membrane-attack complex deficiencies leave patients particularly susceptible to neisserial

infection

Triggers include stress, infection and menstruation


Management

acute: IV C1-inhibitor concentrate (1000-1500 units given intravenously over 20-30 min),

- fresh frozen plasma (FFP) if this is not available

prophylaxis: anabolic steroid Danazol may help

Other Causes of angioedema Angioedema associated with angiotensin-converting enzyme (ACE) inhibitors is the

commonest cause of these swellings involving the face and tongue; it often begins several years after starting an ACE inhibitor

Salicylate- and/or aspirin-associated angioedema more likely to coexist with urticaria

Idiopathic angioedema

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Hypersensitivity

The Gell and Coombs classification divides hypersensitivity reactions into 4 types

Type I - Anaphylactic

antigen reacts with IgE bound to mast cells

anaphylaxis, atopy (e.g. asthma, eczema and hayfever).

Diagnosed by plasma tryptase (protease released from mast cell).

*What is the hallmark signs of mast cell degranulation?

Classical wheal and flare

Type II - Cell bound

IgG or IgM binds to antigen on cell surface

autoimmune haemolytic anaemia, ITP, Goodpasture's, pernicious anemia, acute hemolytic

transfusion reactions, rheumatic fever, bullous pemphigoid, pemphigus vulgaris


Type III - Immune complex

free antigen and antibody (IgG, IgA) combine

serum sickness, systemic lupus erythematosus, post-streptococcal glomerulonephritis,

extrinsic allergic alveolitis (especially acute phase)

Type IV - Delayed hypersensitivity

T cell mediated

tuberculosis, tuberculin skin reaction, graft versus host disease, allergic contact dermatitis,

scabies, extrinsic allergic alveolitis (especially chronic phase), multiple sclerosis, Guillain-

Barre syndrome

In recent times a further category has been added:

Type V

antibodies that recognise and bind to the cell surface receptors, either stimulating them or

blocking ligand binding

Graves' disease, myasthenia gravis

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Anaphylaxis Anaphylaxis may be defined as a severe, life-threatening, generalised or systemic

hypersensitivity reaction.

These reactions are mediated by histamine 1 receptor stimulation.

Anaphylaxis can be associated with leukotrienes B4, C4, D4 and E4

The first three(B4, C4, D4 )are the mediators that make up the slow-reacting substance of anaphylaxis (SRSA)

Usually takes 15-30 minutes from the time of exposure to the antigen.

Flushing, warmth and tingling are typical initial symptoms

At least 50% of fatalities are due to respiratory complications, and more than 20% of patients will have a second episode within 8 hours

antigen production of IgE initiates events

Anaphylaxis may be exacerbated by exercise

Plasma tryptase activity is the most likely investigation to confirm the nature of the reaction


The greater the severity of anaphylaxis, the more likely that serum tryptase levels will be

elevated.

Elevated serum tryptase levels demonstrate that mast cell activation with mediator release has

occurred whether triggered by IgE-mediated anaphylaxis or non-IgE-mediated anaphylactoid

reactions.

Tryptase levels peak at 1-2 hours, and return to baseline by 6 hours.

Adrenaline is by far the most important drug in anaphylaxis and should be given as soon as

possible. The recommended doses for adrenaline, hydrocortisone and chlorphenamine are as

follows:

Adrenaline Hydrocortisone Chlorphenamine

< 6 months 150 micrograms (0.15ml 1 in 1,000) 25 mg 250 micrograms/kg

6 months - 6 years 150 micrograms (0.15ml 1 in 1,000) 50 mg 2.5 mg

6-12 years 300 micrograms (0.3ml 1 in 1,000) 100 mg 5 mg

Adult and child > 12

years

500 micrograms (0.5ml 1 in 1,000) 200 mg 10 mg

Adrenaline can be repeated every 5 minutes if necessary. The best site for IM injection is the

anterolateral aspect of the middle third of the thigh.

Late-phase reaction

Hydrocortisone blocks the generation of leukotrienes and prostaglandins, and hence

prevents the late-phase reaction often characterised by asthma

Approximately 30% of deaths related to anaphylaxis occur as a consequence of this late-

phase reaction

Common identified causes of anaphylaxis.

Mast cell mediator release can be triggered by both IgE and non-IgE-mediated factors. Therefore,

anaphylaxis may be termed anaphylaxis (IgE mediated) or anaphylactoid (non--IgE mediated).

1. anaphylaxis (IgE mediated) :

food (e.g. Nuts) - the most common cause in children

drugs


- The most common IgE-mediated triggers are drugs, typically penicillin or other beta-

lactam antibiotics,

- Neuromuscular blocking agents (eg vecuronium) are responsible for 60-70% of

allergic reactions related to anaesthesia. The antigen responsible is thought to be

the quaternary ammonium group that is found in other drugs, foods, cosmetics and hair

products

venom (e.g. Wasp sting)

2. Anaphylactoid (non--IgE mediated).

Non-IgE-mediated causes include factors causing marked complement activation such as plasma proteins or compounds, which act directly on the mast cell membrane, such as vancomycin, quinolone antibiotics, or radiographic contrast media

Is it IgE- mediated? sensitization required? Can reaction occur in first exposure? How much exposure is needed to elicit reaction? Is reaction predicted by skin allergy test? Yes No very little usually more than for anaphylaxis

Anaphylactoid reactions, which do not act through immunoglobulin E- (IgE-) related mechanisms, may follow ingestion of aspirin or other non-steroidal anti-inflammatory drugs or by the injection of radiocontrast media, metabisulfites, or opiates.

Is it anaphylactic OR anaphylactoid reaction?

Anaphylactic Anaphylactoid

Is sensitization required? Yes No

Can reaction occur in first

exposure?

No Yes

How much exposure is needed

to elicit reaction?

very little (dose independent) usually more than for

anaphylaxis

Is reaction predicted by skin

allergy test?

Yes No

*In IgE mediated reactions such as asthma or anaphylaxis what therapy inhibits the important late-phase reaction?

The late phase reaction is due to attraction of T cell and the release of leukotrienes and prostaglandins and this is prevent by the administration of steroids.


Mediators involved in the development of anaphylaxis include histamine, leukotrienes,

prostaglandins and platelet aggregating factor, which are generated by mast cell degranulation.

Additional factors include

Tryptase

Chimase

Heparin

Chondroitin sulphate

IL4

IL13.

IL4 and IL13 are thought to be important in driving the onward cascade of inflammation to other

immune system cells and contribute to the severity of anaphylaxis.

Th2 CD4 positive lymphocytes are involved in the pathogenesis of anaphylaxis, via the production of

IL-4/IL-13 that act on B cells to increase IgE production and precipitate the development of acute

hypersensitivity.

IL-4 also exacerbates anaphylaxis by acting synergistically with other vasoactive mediators to

increase vascular permeability.

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Allergy Birch-associated oral allergy syndrome

- occurs with stoned fruits, apples, carrots and potatoes - However, this only happens with the raw form as cooking denatures the allergen - The birch-tree pollen season is usually in April/May, giving the typical rhinitis symptoms

Latex allergy can be associated with certain foods such as bananas, avocado, kiwi and melon, but this allergen is heat-stable

Most apples contain a considerable amount of salicylate, which can induce urticaria in aspirin-sensitive individuals; however, this is not usually associated with pharyngeal itching

Allergic contact dermatitis is caused by a type 4 delayed hypersensitivity reaction to a chemical in contact with the skin

Initial sensitisation can occur 7-10 days after first contact with a potent allergen However, it is more usually a consequence of many months or years of exposure to small

amounts of the allergen Once sensitised, contact with the allergen can produce dermatitis within 24-48 h, and all areas

of the body are equally susceptible


Urticaria is a common condition and usually responds very well to systemic antihistamines

which are the correct first line treatment. Oral steroids can be given for severe cases but

only as a last resort.

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Latex allergy Nearly 1 in 5 anaphylactic reactions may be due to latex allergy, (more common than

peanuts allergy)

Sensitivity to latex may cause a number of problems:

- type I hypersensitivity (anaphylaxis)

- type IV hypersensitivity (allergic contact dermatitis)

- irritant contact dermatitis

Latex allergy is more common in children with myelomeningocele spina bifida.

Latex-fruit syndrome

It is recognised that many people who are allergic to latex are also allergic to fruits,

particularly banana, pineapple, avocado, chestnut, kiwi fruit, mango, passion fruit and

strawberry. However, bananas are the most commonly associated with latex/rubber

allergy

Latex can induce allergy through IgE bound to mast cells

Morphine, radiocontrast media and colloid plasma expanders induce histamine release

via their direct effects on mast cells

____________________________________________________________

Peanut allergy The sensitivity of a negative skin prick test to foods is high: that is, for all nuts, skin prick tests

miss only 0.5% of cases, whereas specific IgE will miss 22%

Less than 20% of individuals will grow out of peanut allergy, but they are usually those in whom the reactions are mild and started under 1 year of age

The wheal size resulting from the skin prick test is an excellent predictor of a positive food challenge to peanuts


Allergy tests

Skin prick test

Most commonly used test as easy to perform and inexpensive.

the first line for detection of allergen-specific IgE

Drops of diluted allergen are placed on the skin after which the skin is pierced using a needle.

A large number of allergens can be tested in one session.

Normally includes a histamine (positive) and sterile water (negative) control.

A wheal will typically develop if a patient has an allergy.

Can be interpreted after 15 minutes

Useful for food allergies and also pollen

It can induce anaphylaxis, and must therefore be done in an environment where resuscitation facilities are available.

Radioallergosorbent test (RAST)

Determines the amount of IgE that reacts specifically with suspected or known allergens, for example IgE to egg protein.

Results are given in grades from 0 (negative) to 6 (strongly positive)

Useful for food allergies, inhaled allergens (e.g. Pollen) and wasp/bee venom

Blood tests may be used when skin prick tests are not suitable, for example if there is extensive eczema or if the patient is taking antihistamines

Skin patch testing Useful for contact dermatitis.

Around 30-40 allergens are placed on the back.

Irritants may also be tested for.

The patches are removed 48 hours later with the results being read by a dermatologist after a further 48 hours

If a history of anaphylaxis is given it would not be appropriate to perform a skin prick test, thus Radioallergosorbent test (RAST) is the most appropriate first-line test to investigate the cause of the reaction

Reasons for a false negative RAST test:

Immediately following anaphylaxis / allergic reaction (transient drop in IgE)

Waning of allergen-specific IgE with time following a reaction.

Unstable allergens in the RAST substrates (especially food allergens)


Immune system


Immune system cells: innate immune response

The following cells are mostly involved in the innate immune response:

Cell type Functions and properties

Neutrophil Primary phagocytic cell in acute inflammation

Granules contain myeloperoxidase and lysozyme

Most common type of white blood cell

Multi-lobed nucleus

Basophil Releases histamine during allergic response

Granules contain histamine and heparin

Expresses IgE receptors on the cell surface

Bi-lobed nucleus

Mast cell Present in tissues and are similar in function to basophils but derived from different cell

lines

Granules contain histamine and heparin

Expresses IgE receptors on the cell surface

Eosinophil Defends against protozoan and helminthic infections

Bi-lobed nucleus

Monocyte Diffferentiates into macrophages

Kidney shaped nucleus

Macrophage Involved in phagocytosis of cellular debris and pathogens

Acts as an antigen presenting cell

Major source of IL-1

Natural killer

cell

Induce apoptosis in virally infected and tumour cells

Dendritic cell Acts as an antigen presenting cell


Innate (non-specific system) Adaptive (acquired system)

Components Components 1. Anatomical and physiological barriers 2. Inflammatory response with leakage of antibacterial serum proteins (acute-phase proteins) and phagocytic cells 3. Phagocytosis by neutrophils and macrophages

4. Complement system

Components 1. Cell-mediated response effected by T cells

2. Humeral immune response effected by B cells

Properties 1. Rapid: responds within minutes to infection 2. No antigenic specificity, i.e. the same molecules and cells respond to range of pathogens 3. No memory, i.e. the response does not change after repeated exposure exposure 4. Preformed or rapidly formed components

Properties

1. Slow: response over days to weeks

2. Antigenic specificity i.e. each cell is a

programmed genetically to respond to a single

antigen

3. Immunological memory, i.e. on repeated the

response is faster, stronger and qualitatively

different

4. Diversity: ability to recognize and respond to a vast number of different antigens 5. Self/non-self recognition: i.e. lack of response (tolerance) to self-antigens but response to foreign antigens


Immunoglobulins

The table below summarises the characteristics of the 5 types of immunoglobulin found in the body:

IgG 75% Monomer Enhance phagocytosis of bacteria and viruses, pass to fetal circulation

IgA 15% Monomer/

dimer

Found in secretions, provide localized protection on mucous membranes

IgM 10% Pentamer first to be secreted, anti-A, B blood antibodies

IgD 1% Monomer Involved in activation of B cells

IgE 0.1% Monomer Involved in allergic reactions

Each day an average adult produces approximately 3gm of antibodies, about two-thirds of this IgA

1. IgG IgG makes up approximately 75% of the serum antibodies. It comprises the majority of

circulating antibody in serum

It is the major antibody produced in the secondary immune response.

IgG has a half-life of 7-23 days depending on the subclass.

IgG is a monomer and has 2 epitope-binding sites

The Fc portion of IgG can activate the classical complement pathway.

The Fc portion of IgG can bind to macrophage and neutrophils for enhanced phaGocytosis.

The Fc portion of IgG can bind to NK cells for antibody-dependent cytotoxicity (ADCC).

The Fc portion of IgG enables it to cross the placenta. (IgG is the only class of antibody that can

cross the placenta and enter the fetal circulation).

Acute organ rejection is due to anti-IgG antibodies to the human leukocyte antigen (HLA) incompatible tissues with primary activation of T cells.

Rhesus antibodies are IgG , wherese ABO antibodies are IgM


2. IgA IgA makes up approximately 15% of the serum antibodies, it has a half-life of ≈ 5 days.

IgA is found mainly in body secretions (saliva, mucous, tears, colostrum and milk) as secretory IgA

(sIgA) where it protects internal body surfaces exposed to the environment by blocking the

attachment of bacteria and viruses to mucous membranes.

Secretory IgA is the most immunoglobulin produced.

IgA is made primarily in the mucosal-associated lymphoid tissues (MALT).

IgA appears as a dimer of 2 "Y"-shaped molecules and has 4 epitope-binding sites and a secretory

component to protect it from digestive enzymes in the secretions

The Fc portion of secretory IgA binds to components of mucous and contributes to the

ability of mucous to trap microbes.

IgA can activate the alternative complement pathway. (IgA ≈ Alternate)

Low levels of IgA are associated with an increased incidence of Coeliac Disease.

3. IgM IgM makes up approximately 10% of the serum antibodies and is the first antibody produced

during an immune response.

IgM is the major antibody produced during the primary response.

IgM has a half-life of about 5 days.

IgM is a pentamer and has 10 epitope-binding sites

The Fc portions of IgM are able to activate the classical complement pathway (most efficient)

Monomeric forms of IgM are found on the surface of B-lymphocytes as B-cell receptors or sIg.

4. IgD IgD makes up approximately 1% of the serum antibodies.

IgD is a monomer and has 2 epitope-binding sites.

IgD is found on the surface of B-lymphocytes (along with monomeric IgM) as a B-cell receptor

or sIg where it may control of B-lymphocyte activation and suppression.

IgD may play a role in eliminating B-lymphocytes generating self-reactive autoantibodies.

Hyper-lgD is associated with periodic fever (attacks of fever every 4-8 weeks, with

each attack lasting 3-7 days)

5. IgE ( produced by plasma cells)

IgE makes up about 0.002% of the serum antibodies with a half-life of 2 days.

Most IgE is tightly bound to basophils and mast cells via its Fc region.

IgE is a monomer and has 2 epitope-binding sites.

IgE is made in response to parasitic worms (helminths) and arthropods. It is also often made in

response to allergens.


IgE may protect external mucosal surfaces by promoting inflammation, enabling IgG,

complement proteins, and leucocytes to enter the tissues.

The Fc portion of IgE can bind to mast cells and basophils where it mediates many allergic

reactions. Cross linking of cell-bound IgE by antigen triggers the release of vasodilators for an

inflammatory response.

IgE is involved in arming mast cells and basophils.

IgE causes mast cells to release vasoactive amines, such as histamine, producing an inflammatory response which can result in a type I hypersensitivity reaction.

The Fc portion of IgE made against parasitic worms and arthropods can bind to eosinophils

enabling opsonization. This is a major defense against parasitic worms and arthropods.

increased in the serum of atopic individuals, but serum IgE does not rise acutely during an asthmatic attack.

Commonly recognized immunoglobulin changes in liver disease

(usually accompanied by a decrease in albumin) are:

• lgG ↑ in: chronic active hepatitis, cryptogenic cirrhosis

• lgM ↑ in: 1° biliary cirrhosis, alcoholic cirrhosis

• lgA ↑ in: alcoholic cirrhosis.

Which one of the immunoglobulin structure forms antigen binding site? The variable region of one heavy and one light chain

Complement fixation

• IgA can fix complement via the alternative pathway • IgG and IgM can fix complement via the classical pathway through the Fc portion of the

immunoglobulin

____________________________________________________________

Antibody deficiency The most common type of primary immunodeficiency (>50% of cases) involves being deficient

in antibody production

Selective IgG deficiencies include the decreased production of IgA and/or the various IgG subclasses and impaired antibody responses to polysaccharide antigens

Normal immunoglobulin serum levels, including subclasses, do not exclude antibody deficiency

Hence in patients with a good history of recurrent (proven) bacterial infections, IgG responses to Haemophilus

influenzae, Pneumococcus spp. and tetanus toxoid should all be assessed, as should postimmunisation responses if required

Good IgG antibody responses to immunisations excludes IgG subclass deficiency.


Which disease occurring during pregnancy is most likely to lead to the neonate having low immunoglobulin levels and hence being prone to bacterial infections? Intestinal lymphangiectasia

____________________________________________________________

Selective IgA deficiency selective IgA deficiency (SlgAD), is the most common primary antibody deficiencies

IgA deficiency predisposes to pernicious anaemia and hence gastric carcinoma

The possibility of lgG2 deficiency should always be investigated in IgA-deficient individuals with a history of recurrent bacterial infections, but Staphylococcus aureus is the exception

Patients with SlgAD have a 10-fold increased risk of coeliac disease

individuals of Arab and Spanish origin have a particularly high incidence of SlgAD

There is an increased incidence of gluten-sensitive enteropathy (GSE) in people with selective IgA deficiency

Allergy and autoimmune conditions are more common in IgA-deficient individuals

some cases of IgAD may progress to common variable immune deficiency (involving low

levels of both IgA and IgG, and sometimes also IgM),

Treatment: - no specific treatment - identification of comorbid conditions, - preventative measures to reduce the risk of infection, - and effective treatment of infections - Replacement therapy is not practical because of the short half-life of IgA and the relative

paucity of IgA in commercial immunoglobulin preparations

____________________________________________________________

Isolated IgD deficiency No specific signs or symptoms

increased viral respiratory tract infections, - IgE deficiency leads to both viral and parasitic infections

IgA, IgG and IgM levels are entirely normal

isolated IgD deficiency has been identified amongst people of Basque origin,hence the link to northern Spain

not require any specific treatment

____________________________________________________________

The patient with IgG deficiency In IgG subclass deficiency, the overall level of IgG may be normal or slightly reduced

lgG2 deficiency increase susceptibility to infections with polysaccharide-coated bacteria, including Haemophilus influenzae, multiple presentations with otitis media and respiratory tract infections


If these patients are vaccinated with Pneumovax, they are still unable to mount a response to S. pneumoniae antigens

lgG3 deficiency increase susceptibility to infections with Moraxella catarrhalis,frequent chronic sinusitis

lgG1 deficiency normally occurs as part of a wider picture of common variable immunodeficiency

____________________________________________________________

Hyper-IgM syndrome

• also known as CD40 ligand deficiency

• is an X-linked condition

• is a T-cell defect

• presenting in a similar way to X-linked agammaglobulinaemia with recurrent sinopulmonary

disease

• affected individuals are susceptible to - Pneumocystis jirovecii pneumonia - chronic Cryptosporidia! infection, leading to sclerosing cholangitis and liver failure - increased risk of malignancy, particularly abdominal cancers

____________________________________________________________

Hypergammaglobulinaemia

Causes of polyclonal hypergammaglobulinaemia: 1. Artefactual, e.g. prolonged venous stasis before venepuncture

2. Haemoconcentration secondary to dehydration

3. Chronic infection, e.g. TB, infective endocarditis, leishmaniasis

4. Autoimmune disease, e.g. SLE, rheumatoid arthritis

5. Ulcerative colitis and Crohn's disease

6. Sarcoidosis 7. Hepatic disease.

Causes of monoclonal hypergammaglobulinaemia

1. Multiple myeloma, Waldenstrom's macroglobulinaemia and heavy chain

disease (Table 3.15)

2. Leukaemia, lymphoma or carcinoma

3. Bence Jones proteinuria

4. 'Benign' paraproteinaemia

5. Amyloidosis.


Cryoglobulinaemia Immunoglobulins which undergo reversible precipitation at 4 deg C, dissolve when warmed to 37 deg

C. One third of cases are idiopathic

Three types

type I (25%): monoclonal

type II (25%): mixed monoclonal and polyclonal: usually with RF

type III (50%): polyclonal: usually with RF

Type I

monoclonal - IgG or IgM

associations: multiple myeloma, Waldenstr�m macroglobulinaemia

Type II

mixed monoclonal and polyclonal: usually with RF

associations: hepatitis C, RA, Sjogren's, lymphoma

Type III

polyclonal: usually with RF

associations: RA, Sjogren's

Symptoms (if present in high concentrations)

Raynaud's only seen in type I

cutaneous: vascular purpura, distal ulceration, ulceration

arthralgia

renal involvement (diffuse glomerulonephritis)


Tests

low complement (esp. C4)

high ESR

Treatment

immunosuppression

plasmapheresis

____________________________________________________________

Immunoglobulins: therapeutics

The Department of Health issued guidelines on the use of intravenous immunoglobulins in May 2008

Uses

primary and secondary immunodeficiency

idiopathic thrombocytopenic purpura

myasthenia gravis

Guillain-Barre syndrome

Kawasaki disease

toxic epidermal necrolysis

pneumonitis induced by CMV following transplantation

low serum IgG levels following haematopoietic stem cell transplant for malignancy

dermatomyositis

chronic inflammatory demyelinating polyradiculopathy

Basics

formed from large pool of donors (e.g. 5,000)

IgG molecules with a subclass distribution similar to that of normal blood

half-life of 3 weeks


Leukotrienes Function

mediators of inflammation and allergic reactions

cause bronchoconstriction, mucous production (an important consideration in the

pathophysiology of bronchial asthma)

increase vascular permeability, attract leukocytes

leukotriene D4 has been identified as the SRS-A (slow reacting substance of anaphylaxis)

which causes bronchial wall and intestinal smooth muscle contraction

Production

secreted by leukocytes

formed from arachidonic acid by action of lipoxygenase

it is thought that the NSAID induced bronchospasm in asthmatics is secondary to the express

production of leukotrienes due to the inhibition of prostaglandin synthetase

____________________________________________________________

Acute phase proteins Acute phase proteins

CRP

procalcitonin

ferritin

fibrinogen

alpha-1 antitrypsin

caeruloplasmin

serum amyloid A

serum amyloid P component*

haptoglobin

complement

During the acute phase response the liver decreases the production of other proteins (sometimes

referred to as negative acute phase proteins). Examples include:

albumin

transthyretin (formerly known as prealbumin)


transferrin

retinol binding protein

cortisol binding protein

*plays a more significant role in other mammals such as mice

____________________________________________________________

ANCA There are two main types of anti-neutrophil cytoplasmic antibodies (ANCA) - cytoplasmic (cANCA)

and perinuclear (pANCA)

For the exam, remember:

cANCA - Wegener's granulomatosis

pANCA - Churg-Strauss syndrome + others (see below)

cANCA

most common target serine proteinase 3 (PR3) (Proteinase-3 is a neutral serine proteinase

present in azurophil granules of human neutrophils)

some correlation between cANCA levels and disease activity

Wegener's granulomatosis, positive in > 90%

In Wegener's, the level of PR3 antibody and ANCA titre are related to disease activity and the

antibodies typically disappear when the disease is in remission.

microscopic polyangiitis, positive in 40%

pANCA

most common target is myeloperoxidase (MPO)

cannot use level of pANCA to monitor disease activity

associated with immune crescentic glomerulonephritis (positive in c. 80% of patients)

microscopic polyangiitis, positive in 50-75%

Churg-Strauss syndrome, positive in 60%

primary sclerosing cholangitis, positive in 60-80%

Wegener's granulomatosis, positive in 25%


Other causes of positive ANCA (usually pANCA)

inflammatory bowel disease (UC > Crohn's)

connective tissue disorders: RA, SLE, Sjogren's

autoimmune hepatitis

Rheumatoid factor (RF)

Rheumatoid factor is an IgM antibody against IgG

Rheumatoid factor (RF) is a circulating antibody (usually IgM) which reacts with the Fc portion of the patients own IgG.

Rheumatoid factor is an antibody with reactivity to the heavy chain of IgG.

The rheumatoid factor may be of IgM, IgG or IgA class.

The conventional (agglutination) test, detects only IgM RF. RF can be detected by either:

Rose-Waaler test: sheep red cell agglutination

Latex agglutination test (less specific)

RF is positive in 70-80% of patients with rheumatoid arthritis, high titre levels are associated with severe progressive disease (but NOT a marker of disease activity), Other conditions associated with a positive RF include:

Sjogren's syndrome (around 100%)

Felty's syndrome (around 100%)

infective endocarditis (= 50%)

SLE (= 20-30%)

systemic sclerosis (= 30%)

general population (= 5%)

rarely: TB, HBV, EBV, leprosy


Anti-smooth muscle antibody

Positive in:

1. Chronic active hepatitis (40-90%)

2. Primary biliary cirrhosis (30-70%)

3. Idiopathic cirrhosis (25-30%)

4. Viral infections (80%)

Anti-mitochondrial antibody

Positive in:

1. Primary biliary cirrhosis (60-94%)

2. Chronic active hepatitis (2~0%)

3. Idiopathic cirrhosis (25-30%)

Gastric parietal cell antibody

Positive in:

1. Pernicious anaemia (>90%)

2. Atrophic gastritis('? 60%, c3 15-20%)

3. Autoimmune thyroid disease (33%)

Thyroid autoantibodies (microsomal and thyroglobulin)

Positive in:

1. Hashimoto's thyroiditis (70-90% microsomal: 75-95% thyroglobulin)

2. Graves' disease (50-80% microsomal; 33-75% thyroglobulin) ·

3. Hypothyroidism (40-65% microsomal; 50-80% thyroglobulin)

4. Pernicious anaemia (55% microsomal)


Antireticulin antibody

Positive in:

1. Coeliac disease (37%)

2. Crohn's disease (24%)

3. Dermatitis herpetiformis (17-22%)

The only two auto-antibodies which have a role in monitoring disease activity (there is correlation between levels and disease activity)

1. Anti-ds DNA antibodies in systemic lupus erythematosus (SLE)

2. Circulating anti-neutrophil cytoplasmic antibody (cANCA) in Wegener's granulomatosis.

ANTINUCLEAR ANTIBODIES (ANA) lgG or lgM antibody directed against a variety of nuclear constituents, e.g. DNA, RNA or nucleolar material.

Younger women often have low-titred antinuclear antibodies (ANAs) and the titres increase with age

ANA positivity with antiphospholipid antibody syndrome (APL) suggests secondary APL, ie in association with a connective tissue disease

The common tests used for detecting and screening ANAs are indirect immunofluorescence and enzyme-linked immunosorbent assay (ELISA).

In immunofluorescence, the level of autoantibodies is reported as a titre. This is the highest dilution of the serum at which autoantibodies are still detectable.

- Positive autoantibody titres at a dilution equal to or greater than 1:160 are usually considered as clinically significant.

- Positive titres of less than 1:160 are present in up to 20% of the healthy population, especially the elderly.

- Although positive titres of 1:160 or higher are strongly associated with autoimmune disorders, they are also found in 5% of healthy individuals


ANA subtypes • Anti-Ro and anti-La antibodies, also known as SS-A and SS-B, respectively, are commonly

found in primary Sjögren's syndrome and SLE.

- Anti-Ro antibodies alone are found in 50–70% of Sjögren's syndrome and 30% of SLE

with cutaneous involvement,

- During pregnancy, anti-Ro antibodies can cross the placenta and cause neonatal lupus in babies.

• Anti-Smith (Anti-Sm) antibodies are a very specific marker for SLE. Approximately 99% of individuals without SLE lack anti-Sm antibodies, but only 20% of people with SLE have the antibodies.

- They are associated with central nervous system involvement, kidney disease, lung fibrosis and pericarditis in SLE, but they are not associated with disease activity.

• Anti-nuclear ribonucleoprotein (anti-nRNP) antibodies, also known as anti-U1-RNP antibodies, are found in 30–40% of SLE.

- highly associated with mixed connective tissue disease. • Anti-Scl-70 antibodies are linked to scleroderma.

- The sensitivity of the antibodies for scleroderma is approximately 34%, but is higher for cases with diffuse cutaneous involvement (40%), and lower for limited cutaneous involvement (10%).

- Found in 5% of individuals with SLE. - The antigenic target of anti-Scl-70 antibodies istopoisomerase I

• Anti-double stranded DNA (anti-dsDNA) antibodies - very specific marker for SLE, with some studies quoting nearly 100%. - Data on sensitivity ranges from 25–85%. - Correlate with disease activity in SLE; high levels indicate more active lupus. - also linked with lupus nephritis and there is evidence they are the cause.

• Anti-histone antibodies found in 75–95% of people with drug induced lupus and 75% of idiopathic SLE.

- Unlike anti-dsDNA antibodies in SLE, these antibodies do not fix complement. - Although they are most commonly found in drug induced lupus, they are also found in

some cases of SLE, scleroderma, rheumatoid arthritis and undifferentiated connective tissue disease.

• anti-glycoprotein-210 (anti-gp210) and anti-nucleoporin 62 (anti-p62) antibodies - found in primary biliary cirrhosis (PBC). - Each antibody is present in approximately 25–30% of PBC. - are antibodies to components of the nuclear membrane

• Anti-centromere antibodies are associated with limited cutaneous systemic sclerosis, also known as CREST syndrome, primary biliary cirrhosis and proximal scleroderma

• Anti-sp100 antibodies are found in approximately 20–30% of primary biliary cirrhosis (PBC). - They are found in few individuals without PBC, and therefore are a very specific

marker of the disease. • Anti-PM-Scl antibodies are found in up to 50% of polymyositis/systemic sclerosis (PM/SSc)

overlap syndrome. - Around 80% of individuals with antibodies present in their blood serum will have the

disorder. - linked to limited cutaneous involvement of PM/SSc overlap syndrome.


Interleukin

Interleukin are a group of cytokines (secreted proteins and signal molecules) that were first seen to be

expressed by white blood cells (leukocytes).

The function of the immune system depends in a large part on interleukins,

The majority of interleukins are synthesized by helper CD4 T lymphocytes, as well as

through monocytes, macrophages, and endothelial cells.

They promote the development and differentiation of T and B lymphocytes,

and hematopoietic cells.

Interleukin receptors on astrocytes in the hippocampus are also known to be involved in the

development of spatial memories in mice

Mnemonic Hot T-Bone stEAk

IL-1: fever (Hot)

IL-2: stimulates T lymphocytes

IL-3: stimulates Bone marrow

IL-4: stimulates IgE

IL-5: stimulates IgA

Interleukin 1 (IL-1) (α, β)

Interleukin 1 (IL-1) is a key mediator of the immune response.

It is secreted mainly by macrophages and monocytes and acts as a costimulator of T cell

and B cell proliferation. (Stimulation of acute phase response)

Other effects include increasing the expression of adhesion molecules on the endothelium.

By stimulating the release by the endothelium of vasoactive factors such as PAF (platelet-

activating factor), nitric oxide and prostacyclin it also causes vasodilation and increases

vascular permeability.

It is therefore one of the mediators of shock in sepsis.

Along with IL-6 and TNF, it acts on the hypothalamus causing pyrexia.

IL-1 β levels in the circulation are only detectable in the following situations:

- after strenuous exercise,

- in ovulating women,

- sepsis,

- acute organ rejection,

- acute exacerbation of rheumatoid arthritis.

IL-1 play a role in the formation of the atherosclerotic plaque.

The uptake of oxidized low-density lipoproteins (LDL) by vascular endothelial cells results in

IL-1 expression stimulates the production of platelet-derived growth factor.


Interleukin-2 (IL-2)

IL-2 is a member of a cytokine family. It is a protein that regulates the activities of white blood

cells (leukocytes, often lymphocytes) that are responsible for immunity.

IL-2 is part of the body's natural response to microbial infection, and in discriminating between

foreign ("non-self") and "self".

Through its role in the development of T cell immunologic memory, it also has a key role in

enduring cell-mediated immunity.

there is some evidence that IL-2 may be involved in itchy psoriasis

High-dose interleukin-2 can produce a high rate of response and durable remissions in

patients with metastatic renal cancer.

Other important interleukins

Interleukin 3 (IL3)

is a cytokine that regulates blood-cell production by controlling the production, differentiation

and function of granulocytes and macrophages

It is thought that the genetic change of the cell line to constitutive production of IL3 is the key

event in development of myelomonocytic leukaemia

Interleukin 5 (IL5)

Interleukin 5 (IL5), also known as eosinophil differentiation factor (EDF), is a lineage-specific

cytokine for eosinophilpoiesis.

It regulates eosinophil growth and activation, and thus plays an important role in diseases

associated with increased levels of eosinophils, including asthma.

Interleukin 6 (IL6)

also referred to as B-cell stimulatory factor-2 (BSF-2) and interferon beta-2,

It plays an essential role in the final differentiation of B cells into IG-secreting cells.

Inducing myeloma/plasmacytoma growth, nerve cell differentiation, and, in hepatocytes, acute-

phase reactants

Interleukin 10 (IL-10)

is a protein that inhibits the synthesis of a number of cytokines, including IFN-gamma, IL-2, IL-

3, TNF, and GM-CSF produced by activated macrophages and by helper T cells.

IL-10 is highly similar to the Human herpesvirus 4 (Epstein-Barr virus) BCRF1 protein, which

inhibits the synthesis of gamma-interferon



stimulates megakaryocytopoiesis, resulting in increased production of platelets,

Activating osteoclasts, inhibiting epithelial cell proliferation and apoptosis, and inhibiting

macrophage mediator production.


It is involved in the stimulation and maintenance of Th1 cellular immune responses, including

the normal host defence against various intracellular pathogens, such as Leishmania,

Toxoplasma, Measles virus, and Human immunodeficiency virus 1 (HIV).

IL-12 also has an important role in enhancing the cytotoxic function of NK cells and role in

pathological Th1 responses, such as in inflammatory bowel disease and multiple sclerosis.

Suppression of IL-12 activity in such diseases may have therapeutic benefit.

On the other hand, administration of recombinant IL-12 may have therapeutic benefit in

conditions associated with pathological Th2 responses

____________________________________________________________

Cytokine disorders

Both cytokine overexpression and underexpression or their receptors 'can be

pathogenic:

1. Septic shock: production of IL-1, IL-6 and TNF due to endotoxin stimulation of macrophages following Gram-negative infection.

2. Toxic shock syndrome: massive release of cytokines due to super antigen stimulation of T-cells by TSST-1, a bacterial exotoxin.

3. Chagas' disease (T. cruzi infection): causes reduced expression of IL-2 receptor, leading to marked immune suppression.

____________________________________________________________

Interferon Interferons (IFN) are cytokines released by the body in response to viral infections and neoplasia.

They are classified according to cellular origin and the type of receptor they bind to. IFN-alpha and

IFN-beta bind to type 1 receptors whilst IFN-gamma binds only to type 2 receptors.

IFN-alpha

produced by leucocytes

antiviral action

useful in hepatitis B & C, Kaposi's sarcoma, metastatic renal cell cancer, hairy cell leukaemia

adverse effects include flu-like symptoms and depression


IFN-beta

produced by fibroblasts

antiviral action

reduces the frequency of exacerbations in patients with relapsing-remitting MS

IFN-gamma

produced by T lymphocytes & NK cells

weaker antiviral action, more of a role in immunomodulation particularly macrophage activation

may be useful in chronic granulomatous disease and osteopetrosis

____________________________________________________________

Nitric oxide

Previously known as endothelium derived relaxation factor, nitric oxide (NO) has emerged as a molecule which is integral to many physiological and pathological processes.

It is formed from L-arginine and oxygen by nitric oxide synthetase (NOS). An inducible form of NOS has been shown to be present in macrophages. Nitric oxide has a very short half-life (seconds), being inactivated by oxygen free radicals

Effects

acts on guanylate cyclase leading to raised intracellular cGMP levels and therefore decreasing

Ca2+ levels

vasodilation, mainly venodilation

inhibits platelet aggregation

Clinical relevance

underproduction of NO is implicated in hypertrophic pyloric stenosis

lack of NO is thought to promote atherosclerosis

in sepsis increased levels of NO contribute to septic shock

organic nitrates (metabolism produces NO) is widely used to treat cardiovascular disease (e.g.

angina, heart failure)

sildenafil is thought to potentiate the action of NO on penile smooth muscle and is used in the

treatment of erectile dysfunctions


Tumour necrosis factor (TNF) Tumour necrosis factor (TNF) is a pro-inflammatory cytokine with multiple roles in the immune system

TNF is secreted mainly by macrophages and has a number of effects on the immune system, acting

mainly in a paracrine fashion:

activates macrophages and neutrophils

acts as costimulator for T cell activation

key mediator of bodies response to Gram negative septicaemia

similar properties to IL-1

anti-tumour effect (e.g. phospholipase activation) is a key cytokine in the pathogenesis of multi-organ failure. exerts an interferon-like effect against viruses

. Enhanced HLA class I expression

Stimulation of acute phase response

TNF-alpha binds to both the p55 and p75 receptor. These receptors can induce apoptosis. It also

cause activation of NFkB

Endothelial effects include increase expression of selectins and increased production of platelet

activating factor, IL-1 and prostaglandins

TNF promotes the proliferation of fibroblasts and their production of protease and collagenase. It is

thought fragments of receptors act as binding points in serum

Systemic effects include pyrexia, increased acute phase proteins and disordered metabolism leading

to cachexia

TNF is important in the pathogenesis of rheumatoid arthritis - TNF blockers (e.g. infliximab,

etanercept) are now licensed for treatment of severe rheumatoid

TNF blockers

infliximab: monoclonal antibody, IV administration

etanercept: fusion protein that mimics the inhibitory effects of naturally occurring soluble TNF

receptors, subcutaneous administration

adalimumab: monoclonal antibody, subcutaneous administration

adverse effects of TNF blockers include reactivation of latent tuberculosis and demyelination

Infliximab is also used in active Crohn's disease unresponsive to steroids


Growth factors Transforming growth factor-beta (TGF-β)

Generally limits inflammatory response.

Enhances lgA synthesis.

Initiates and terminates tissue repair.

Undergoes autoinduction.

Released by platelets at the site of tissue injury and promotes the formation of extracellular matrix.

Implicated in diseases of tissue fibrosis such as cirrhosis and glomerulosclerosis.

____________________________________________________________

Leukocyte alkaline phosphatase

Raised in

Myelofibrosis

Leukemoid reactions

Polycythemia rubra vera

Infections

Steroids, Cushing's syndrome

Pregnancy, oral contraceptive pill

Low in

Chronic myeloid leukemia

Pernicious anemia

Paroxysmal nocturnal hemoglobinuria

Infectious mononucleosis


Monoclonal antibodies

Rituximab - monoclonal antibody against CD20

Monoclonal antibodies have an increasing role in medicine. They are manufactured by a technique

called somatic cell hybridization. This involves the fusion of myeloma cells with spleen cells from a

mouse that has been immunized with the desired antigen. The resulting fused cells are termed a

hybridoma and act as a 'factory' for producing monoclonal antibodies. The main limitation to this is

that mouse antibodies are immunogenic leading to the formation of human anti-mouse antibodies

(HAMAs). This problem is overcome by combining the variable region from the mouse body with the

constant region from an human antibody.

Clinical examples of monoclonal antibodies:

MONOCLONAL AB TYPE USES

Rituximab Anti-CD20 non-Hodgkin's lymphoma

Infliximab anti-TNF rheumatoid arthritis and Crohn's

Cetuximab anti epidermal growth factor receptor metastatic colorectal cancer and

head and neck cancer

Trastuzumab anti-HER2, anti EGF receptor metastatic breast cancer

Alemtuzumab anti-CD52 chronic lymphocytic leukemia

abciximab anti-glycoprotein IIb/IIIa receptor undergoing PCI, prevention of

ischemic events in patients

OKT3 anti-CD3 prevent organ rejection

Monoclonal antibodies are also used for:

medical imaging when combined with a radioisotope

identification of cell surface markers in biopsied tissue

diagnosis of viral infections


Diagnostic antibody testing

AB Association Anti-Yo antibodies ovarian, breast and lung cancers

Anti-Hu antibodies small-cell lung cancer, neuroblastoma and prostatic cancer

Intrinsic factor antibodies pernicious anaemia, and hence (subacute combined degeneration of the spinal cord) secondary to vitamin B12 deficiency

Anti-Ri neuroblastoma (children) and fallopian or breast cancer (adults), resulting in paraneoplastic opsoclonus myoclonus ataxia (POMA).

Anti-Yo gynaecological tumours and breast cancer,

Anti-Tr Hodgkin's disease, resulting in cerebellar degeneration.

Anti-Ta (Ma2) testicular tumours, and can lead to limbic or brain stem encephalomyelitis.

Antiendomysial antibodies coeliac disease, and related vitamin B-1 deficiency may lead to

Wernicke's encephalopathy and Korsakoff's psychosis

Antimitochondrial antibodies (M2 pattern)

primary biliary cirrhosis (PBC)

double-stranded DNA (ds-DNA) antibodies

highly specific for SLE.

Antibodies that bind single-stranded denatured DNA (ss-DNA)

present in 90% of patients with SLE, but also in drug-induced lupus and other connective tissue disorders.

Antihistone antibody seen in SLE and drug-induced lupus.

Anticentromere antibody present in 70% of patients with CREST and 15% of patients with diffuse scleroderma. CREST syndrome: calcinosis, Raynaud's phenomenon, oesophageal dysfunction, sclerodactyly and telangiectasia.

Tissue transglutaminase antibody ('tTGA') & Endomysial antibody ('EMA')

The most accurate blood tests for coeliac disease

Antiribonucleoprotein (anti-RNP) antibody

seen in high titres with mixed connective tissue disorders and in lower titres with SLE and other connective tissue disorders.

A Glutamic Acid Decarboxylase Autoantibodies test (GAD antibodies test)

Used to differentiate type 1 diabetes(↑↑anti-GAD) from Latent Autoimmune Diabetes of Adulthood (LADA).

useful for adults over 30 who get diabetes where a type 2 diabetes diagnosis is in doubt - such as if the patient is not overweight.

Preferable than c-peptide test, which measures how much insulin is being produced by the body.

Used to determine whether gestational diabetes may be type 1 diabetes.


Lymphocytes

B lymphocytes T lymphocytes Site of production

B cells are produced in the bone marrow. germinal centre of lymph nodes and spleen.

produced in the bone marrow but leave the bone marrow and mature in the thymus Paracortical region of lymph nodes and spleen.

Functions Humoral immunity - antibody production; - control of pyogenic bacteria;

prevention of blood-borne infections;

- neutralization of toxins.

Cell-mediated immunity; - protection against intracellular

organisms, protozoa and fungi; - graft rejection; - control of neoplasms.

% of total lymphocytes:

12%; mainly fixed. 70-80%; mainly circulating; long-lived memory cells.

Immune cell antigen receptors

T and B lymphocytes express receptors on their surface that recognise antigen in a specific manner.

Each individual lymphocyte expresses a single type of receptor with unique specificity (except dual specificity T cells

The receptor on the B lymphocyte is membrane bound immunoglobulin (IgM and IgD isotype) and recognises particulate antigen, whilst the TCR is a heterodimer that recognises peptide fragments presented by MHC molecules.

T cells with dual specificities have been reported although their function is unknown.

____________________________________________________________

B-cells and plasma cells B-cells have surface IgG and major histocompatibility complex (MHC) class II

B cells express immunoglobulin on their surface

B-cells undergo somatic hypermutation and isotype switching (ie switching through the immunoglobulin classes)

Plasma cells are fully differentiated cells from B-cells and hence lack these features

Multiple myeloma is a cause of isolated B-cell immune deficiency

B cells usually require T cell help for full activation.

B cells activated in the primary immune response initially produce IgM. With continuing T cell help B cells then undergo heavy chain class switching and enter germinal centres in secondary lymphoid organs.

The germinal centres are the sites of immunoglobulin affinity maturation and memory B cell formation.


CD40 and CD40L are required for co-stimulation by T cells. Deficiency of either CD40 or CD40L impairs class switching.

Certain antigens can activate B cells in the absence of T cell help - thymus independent antigen. T cell independent B cell responses are mainly to carbohydrate antigen, for example, pneumococcal polysaccharide. These antigens are not processed and presented in association with MHC molecules, and therefore cannot activate T helper cells.

The influenza virus will activate T and B cells, and result in memory cell production.

Affinity maturation of the B cell receptor is an important process initiated during the primary

immune response

IgD are surface receptors of B lymphocytes

Class II MHCs are present on all antigen presenting cells, for example,

B cells

Dendritic cells

Macrophages

Langerhans cells.

They are also present on activated T cells.

CD4 T-cells interact with B-cells via MHC class II

Class I major histocompatibility complexes (MHCs) react with CD 8 on T cells to result in immune system activation

Proteins are displayed on the cell surface by MHC I human leukocyte antigen (HLA) antigens.

If the MHC I is presenting material recognised as foreign, then it is detected and destroyed by CD 8

plus T cells

____________________________________________________________

T cells

Co-operation with other cell types is required for T cell recognition of antigen

T cells recognise antigen only when presented by (self) MHC molecules on an antigen

presenting cell.

Autoreactive T cells exist in the periphery and other mechanisms are responsible for the protection of the body against autoimmunity.


The antigen specificity of T and B cells is generated during development in the thymus (T lymphocytes) and in the bone marrow (B lymphocytes).

Patients with HIV have a deficiency of T-cells (CD4 T-cell lymphocytes)

T lymphocytes are involved in cell-mediated acquired immune responses, whereas B lymphocytes are involved in humoral immunity and produce immunoglobulins.

T lymphocytes compose the majority of circulating lymphocytes in plasma.

Which is the predominant site in the lymph node that contains T cells?

Paracortex.

Within lymph nodes:

• The paracortical areas contain T cells and accessory cells.

• Cortex B cells are found within the cortex in follicles, which have central areas known

as germinal centres.

• The medulla contains large blood vessels and sinuses, and medullary cords that

contain plasma cells secreting antibody.

____________________________________________________________

T-Helper cells

There are two major subsets of T-Helper cells:

Th1

involved in the cell mediated response and delayed (type IV) hypersensitivity

secrete IFN-gamma, IL-2, IL-3

Th2

involved in mediating humoral (antibody) immunity

e.g. stimulating production of IgE in asthma

secrete IL-4, IL-5, IL-6, IL-10, IL-13

An increase in the Th1:Th2 ratio is associated with a reduction in the risk of allergic/hypersensitivity

reactions.


Mast cells

Mast cells are basophilic cells in the connective and subcutaneous tissues, which are involved in

inflammatory and immune responses.

They contain storage granules that contain lytic enzymes (for example, tryptase) and inflammatory

mediators, for example:

Histamine

Heparin

5-Tryptase hydroxytryptamine (5-HT)

Leukotrienes

Platelet aggregating factor

Leukocyte chemotactic factor

Hyaluronidase.

Release of these mediators occurs during mast cell degranulation, which can be triggered by:

Tissue injury

Drugs

Complement activation

Foreign antigenic material.

An anaphylactic reaction occurs when a previously sensitised individual is re-exposed to the antigen.

It is an IgE mediated immune response.

Mastocytosis occurs when excess mast cells are present in the circulation or as tissue infiltrates. Degranulation releases lytic enzymes and inflammatory mediators from storage granules

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Immunity to viruses Natural killer cells are activated faster than cytotoxic T-cells

Infected non-immune cells produce interferon-α and -β, whereas interferon-γ is produced by T-cells

Influenza virus mutates its surface neuraminidase and haemagglutinin to avoid antibody recognition

Enveloped viruses are susceptible to complement attack

IgA can offer protection at mucosal surfaces


Immunity to bacteria Cellular immunity is essential in protection against intracellular bacteria, eg mycobacteria

Phagocytes interact directly but weakly with bacteria, or strongly if they are complement-opsonised

Endotoxin activates macrophages by binding to CD14

bacteria opsonised by antibodies and complement are more effectively phagocytosed

than those opsonised by antibodies alone

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Primary immunodeficiency

Primary immunodeficiency disorders may be classified according to which component of the immune

system they affect.

Neutrophil disorders

Disorder Underlying defect Notes

Chronic

granulomatous

disease

Lack of NADPH oxidase

reduces ability of

phagocytes to produce

reactive oxygen species

Caused by a failure of intracellular killing (no respiratory

burst).

Causes recurrent pneumonias and abscesses, particularly due

to catalase-positive bacteria (e.g. Staphylococcus aureus and

fungi (e.g. Aspergillus)

Negative nitroblue-tetrazolium test

Screening is by the nitroblue tetrazolium (NBT) test

Abnormal dihydrorhodamine flow cytometry test

Chediak-Higashi

syndrome

Microtubule

polymerization defect

which leads to a

decrease in phagocytosis

Affected children have 'partial albinism' and peripheral

neuropathy. Recurrent bacterial infections are seen

Giant granules in neutrophils and platelets

Leukocyte

adhesion

deficiency

Defect of LFA-1 integrin

(CD18) protein on

neutrophils

Recurrent bacterial infections.

Delay in umbilical cord sloughing may be seen

Absence of neutrophils/pus at sites of infection


B-cell disorders


Common variable

immunodeficiency

Many varying causes Hypogammaglobulinemia is seen. May predispose to

autoimmune disorders and lymphona

Bruton's (x-linked)

congenital

agammaglobulinaemia

Defect in Bruton's

tyrosine kinase

(BTK) gene that

leads to a severe

block in B cell

development

X-linked recessive. Recurrent bacterial infections are

seen

Absence of B-cells with reduce immunoglogulins of all

classes

Selective

immunoglobulin A

deficiency

Maturation defect in

B cells

Most common primary antibody deficiency. Recurrent

sinus and respiratory infections

Associated with coeliac disease and may cause false

negative coeliac antibody screen

T-cell disorders


DiGeorge syndrome 22q11.2 deletion,

failure to develop

3rd and 4th

pharyngeal pouches

Common features include congenital heart disease (e.g.

tetralogy of Fallot), learning difficulties, hypocalcaemia,

recurrent viral/fungal diseases, cleft palate


Combined B- and T-cell disorders

Combined B- and T-cell disorders: SCID WAS ataxic (SCID, Wiskott-Aldrich syndrome, ataxic telangiectasia)


Severe combined

immunodeficiency

Many varying causes.

Most common (X-linked)

due to defect in the

common gamma chain, a

protein used in the

receptors for IL-2 and

other interleukins. Other

causes include adenosine

deaminase deficiency

Recurrent infections due to viruses, bacteria and fungi.

Reduced T-cell receptor excision circles

Stem cell transplantation may be successful

Ataxia

telangiectasia

Defect in DNA repair

enzymes

Autosomal recessive. Features include cerebellar ataxia,

telangiectasia (spider angiomas), recurrent chest

infections and 10% risk of developing malignancy,

lymphoma or leukaemia

Wiskott-Aldrich

syndrome

Defect in WAS gene X-linked recessive. Features include recurrent bacterial

infections, eczema, thrombocytopaenia.

Low IgM levels

Increased risk of autoimmune disorders and malignancy

Severe combinedimmunodeficiency disease (SCID)

Adenosine deaminase is found throughout the body but is most active in lymphocytes

The function of the adenosine deaminase enzyme is to eliminate deoxyadenosine, which is generated when DNA is broken down

Adenosine deaminase converts deoxyadenosine, which is toxic to lymphocytes, in to deoxynosine. It also converts adenosine inosine

Mutations in the adenosine deaminase gene reduce or eliminate the activity of adenosine deaminase and allow the build-up of deoxyadenosine to levels that are toxic to lymphocytes

Immature lymphocytes in the thymus are particularly vulnerable to a toxic build-up of deoxyadenosine

The number of lymphocytes in other lymphoid tissues is also greatly reduced, resulting in the signs and symptoms of SCID


DiGeorge syndrome DiGeorge syndrome - a T-cell disorder

• DiGeorge syndrome is a primary immunodeficiency disorder caused by T-cell deficiency and

dysfunction.

• Results from maldevelopment of thymic epithelial elements derived from the third and fourth

pharyngeal pouches.

• It is an example of a microdeletion syndrome.

• The gene defect mapped to chromosome 22q11.

Features

at risk of viral and fungal infections

parathyroid gland hypoplasia → hypocalcaemic tetany

thymus hypoplasia

T-lymphocyte deficiency/dysfunction

cardiac outflow tract anomalies occur (interrupted aortic arch, truncus arteriosus and tetralogy

of Fallot)

Facial abnormalities may include abnormal ears, a shortened philtrum, micrognathia and

hypertelorism

Affected individuals usually have a small, histologically normal thymus located near the

base of the tongue or in the neck, allowing most patients to develop functional T-cells in

numbers that may or may not be adequate for host defence

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Wiskott-Aldrich syndrome

Wiskott-Aldrich syndrome

recurrent bacterial infections (e.g. Chest)

eczema

thrombocytopaenia


Wiskott-Aldrich syndrome causes primary immunodeficiency due to a combined B- and T-cell

dysfunction.

It is inherited in a X-linked recessive fashion

and is thought to be caused by mutation in the WASP gene.( which responsible for ensuring

proper functioning of the actin cytoskeleton in haematopoietic cells)

Features include:

- recurrent bacterial infections (e.g. chest),

- eczema

- thrombocytopenia

- low IgM levels

- humoral immunodeficiency, autoimmune disease and haematological malignancy

The disease have variable penetrance, which means that life expectancy can range from as low as 6 years of age to as great as 30 years.

Bleeding complications, severe bacterial infection and malignancy are the commonest causes of death

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Acquired lipodystrophy Unlike congenital lipodystrophies, acquired lipodystrophy is not associated with metabolic

abnormalities

It is however associated with reduced levels of C3 and raised levels of C3 nephritic factor

C3 nephritic factor induces lysis of adipocytes that secrete adipsin, which is identical to complement factor D

The pattern of fat loss is thought to follow the pattern of adipsin secretion

Despite the low levels of C3, severe infections are thankfully rare

notes & notes basic science immunology (1)

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