immunology in haematology (part 2)

8/14/2019 Immunology in Haematology (Part 2)

1/55

Dr C G Lopez

Ex Transfusion Medicine Unit

University Malaya Medical Centre


2/55

Innate Non SpecificImmune Response


3/55

Innate immune defensesNon-specific

This system does not confer long-lastingimmunity against a pathogen.

The innate immune system is the dominant

system of host defense


4/55

Innate immune defensesInvolves the following:

phagocytic cells (neutrophils, monocytes,

and macrophages)cells that release inflammatory mediators

(basophils, mast cells, and eosinophils)

natural killer cells (NK cells)

complement proteins

cytokines


5/55

anatomical barriers

mechanical removal

bacterial antagonism

phagocytosis

pattern-recognition receptors,

antigen-nonspecific defense chemicals,

complement pathways

Innate immune defenses


6/55

Innate ImmunityDesigned to recognize molecules ( PAMPS) shared by groups

of related microbes. Pathogen-Associated Molecular Patterns

( PAMPS ) include

- LPS from the gram-negative cell wall,

- peptidoglycan and lipotechoic acids from the gram-positive cell wall

- bacterial and viral unmethylated DNA

- bacterial flagellin,

the amino acid N-formylmethionine found in bacterial proteins,

double-stranded and single-stranded RNA from viruses

glucans from fungal cell walls.

unique molecules displayed on stressed, injured, infected, or

transformed human cells also act as PAMPS.


7/55

Response triggered when

microbes are identified by pattern

recognition receptors common to broadgroups of microorganisms

damaged, injured or stressed cells send outalarm signals, many of which (but not all) arerecognized by the same receptors as thosethat recognize pathogens.

Innate Response


8/55

Response

njured or infected cells release eicosanoids

and cytokinesrostaglandins inflammation ( redness andswelling )

eicosanoids)

ytokines

eucotrenes attract WBC s to site of


9/55

Tcells

B cells

Eosinophils

Killercells

Neutrophils

MACROPHAG

E

PLASMACELLS


10/55

NeutrophilsMost abundant type of leukocytes in body

Highly effective in killing most bacteria and fungi.

PMNs contain many cytotoxic compounds that are non-specific needs to be regulated

PMN turnover regulated by apoptosis, a process of cell

death and safe removal by macrophages.

Apoptosis is accelerated following phagocytosis ofbacteria, a process that appears important for the

resolution of infection and inflammation.

neutrophils which have receptors for C3b


11/55

Specific ImmuneResponse


12/55

Cluster of genes MHC

or HLA region

encode HLA antigens ,

complement

components


13/55

MHC Class l AntigensClass I molecules expressed by almost all the cells

of the body .Surface heterodimers that primarily present

peptides derived from the cytosol (viral bacteria,pollen, self peptides) to circulating CD8+ T cells.

Act as ligands for killer immunoglobulin receptors

(KIR), which regulate the cytotoxic activity ofnatural killer (NK) cells.

Epitopes that are part of class I histocompatibilitymolecules bind to CD8+ T cells


14/55

Class II moleculesClass II molecules - Only specialized antigen-

presenting cells express these i.e dendriticcells phagocytic cells like macrophages and Bcells

alpha-beta heterodimer presents primarily

exogenously derived peptides (bacteria andchemical toxins) to circulating CD4+ T cells.

Epitopes that are part of class II

histocompatibility molecules bound to CD4+


15/55

On almost all nucleated

cells and platelets

Soluble HLA antigens

found in plasma

B activated T

lymphocytes, dendritic

lymphocytes, macrophages

Alpha chainencoded by class 1

genes

Encoded by gene on

Chr 15 . May beconcerned with trans

membrane signaling

Alpha and beta

chains encoded

by class ll genes

CLASS I and II

HLA Antigens


16/55

Stimulation through CD28 in addition to

the TCR provides a potent co-stimulatory

signal to T cells for the production of

various interleukins (IL-2 and IL-6 in

particular).

CD28


17/55

Cytotoxic T cell Class 1Pathway

CD8+ T cells bind epitopes

part of class I

histocompatibility molecules ).

Almost all the cells of the

body express class I

molecules.


18/55

Pathway

CD4+ T cells

bind epitopes

part of class ll

histocompatibility

molecules

The alpha-beta

heterodimer presents

primarily exogenously

derived peptides

(bacteria and

chemical toxins)to

circulating CD4+ T

cells.


19/55

NK cellsUnlike B and T cells, NK cells do not express

unique clonally distributed receptors for specific

antigens, rather they express many differentpromiscuous stimulatory and inhibitory receptors

that can be divided into at least four

the killer immunoglobulin-like receptors (KIRs)

the C-type lectin receptors

the natural cytotoxicity receptors (NCRs)

toll-like receptors (TLRs)


20/55

(KIRs) are Killer cell immunoglobulin-like receptors forclassical MHC I (HLA-A, HLA-B, HLA-C) molecules. Some

KIRs are specific for certain HLA subtypes

Provides the first line of defense against virus infection andtumor transformation.

KIRs - interacts with MHC class I molecules

- regulate the cytotoxic activity of natural killer (NK)

cells

- distinguish the tumor and virus infected

cells from normal body cells.

.

NK cells: KIR receptors


21/55

SpecificClonal

Receptors

Non clonalReceptors


22/55

LargegranularKiller Cellswith no T or Bmarkers

Killer Cells haveFc receptors . Canbind Ab alreadybound to tumourtargetProbably perforin

release mechanismkills cells

NK Cells bindtumour targets

NK Cells bind targetsby unknown mechanism. Kill cells thru perforin

release mechanism


23/55

B cells B lymphocytes are both antigen-receiving and antigen-

presenting cells.

They can come in contact with these antigens by

- encountering them in the surrounding lymph

- being presented them by macrophages or

dendritic cells.

They bind intact antigens (e.g., virus particles, proteins)with their B cell receptor (BCR).

B lymphocytes process antigen by the class II

pathway for presentation to T cells.

Macrophage with Ag


24/55

Macrophage with Agpresentedto T helper lymphocyte

B CELL

B CELL

Activated by cytokines

More Helper T cellsMore Cytotoxic T clls( CTLs)B cells to Plasma cells


25/55

The Complement System


26/55

Series of proteins found in fresh, normal serum.

Categorized as a beta globulin. Found in the beta region on protein electrophoresis C3 is complement component that is found in thehighest

concentration

Characteristics ofComplement

Complement components are identified by C andtheir number: C1, C2, C3 etcComplement products resulting from the splitting of

these proteins during the activation process arefollowed by a lower case letter: C3a, C3b, C1qIf complement complexes develop that haveenzymatic activity are written with a bar above the

top: C5b678


27/55

Cell destruction through lysis Cell destruction through opsonization (enhanced

phagocytosis) especially with C3b Chemotaxis via certain split products acting as

chemical signals to the phagocytic cells Anaphylaxis again through the split products (C5a and

C3a), which promote inflammation. C5a and C3a

can bind with mast cells and basophils leading to

the release of histamine. This is turn:

Increases vascular permeability Smooth muscle contraction to preserve blood for vital

organs Increases cellular membrane adhesion

Complement controls various biological processes


28/55

Complement and Innate Immune Response

Complement proteins bind to

- carbohydrates on the surfaces of microbes ( C4b)

- antibodies attached to these microbes or cells

Complement protease activity activated producing acatalytic cascade that amplifies the initial signal

Cascade results in production of peptides - attract immune

cells, increase vascular permeability, and opsonize (coat)

pathogen surface marking it for destruction.

Complement can kill cells directly by disrupting their

plasma membrane


29/55


30/55

Comprises the :-

Classical pathway

Activated by antigen-antibody complexes and may

require all nine complement proteins.

Lectin pathway

Initiated by bacterial surface sugars (mannose) through the

mannose-binding lectin (MBL) protein and subsequent interaction

with mannose-binding lectin-activated serine proteases.

After that point pathway functions identically to classical pathway.

Alternative pathway

activated by LPS.

Complement Activation


31/55

MASP: MBL-associatedserineproteinaseMBL: mannan-

binding lectin;MCP:

Alternative Pathway

Activated by C3b bound

to surface components

of microbes


32/55

Proteins of the Classical pathway

CIin plasma as complex of - 6 mol CIq, 2 mol CIr,

2 mol Cls

Binding ofCIq - activates CIr , Cls

Activated Cl (serine protease ) cleaves C4 into

large fragment C4b and small C4 fragment

which diffuses away

C4b binds covalently to sugar residues on cell

surface glycoproteins


33/55

Cleaved to C2b ( C2a diffuses away ) which

binds non- covalently to the large fragment C4b

Complex C4b*2a = C3 Convertase

C2


34/55

C3b binds to covalently to

glycoproteins on phagocytese.g.

macrophages, neutrophils which

have receptors for C3b.

C3b coats particles e.g bacteria

before they are phagocytosed -

acts as opsonin

binds to C5 to form C3/ C5

Convertase

C3a diffuses into

plasma can bind tobasophils, mast cells

which release

vasoactive contents

histamine - acts as

anaphylotoxin )

Cleaved by C3 Convertase (called C4b* 2a before ) to

C3 Most abundant protein - 1.3 mg/ml


35/55

C5

Cleavage of C5 by C3/C5 Convertase produces

set of complement proteins for membrane attack

called Membrane Attack Complex

C5a released into surrounding fluid acts as

anaphylatoxin ( like C3a ) and chemotactic

attractant for neutrophils

C5b serves as anchor for assembly of single

molecule each ofC6, C7, C8.


36/55

Resulting complex C5b *6*7*8 guides C9

polymerisationAs many as 18 molecules of C9 form a

channel into the bi lipid layer of the cell

membrane allowing passage of ions andsmall molecules

Water enters cell by osmosis and cell lysis

Note: Membrane Attack Complex by another C5

convertase produced by theAlternate Pathway


37/55

Contains 74 amino acids

Induces release ofgranular enzymes fromphagocytic cells production in neutrophils ofsuperoxide

anionvasodilatation increased vascular permeability induction ofthymocyte apoptosis duringsepsis

Excessive production of C5a by activationin sepsis can lead to an unregulated pro-inflammatory response, ultimately

resulting in tissue damage and multi-

C5a anaphylatoxin


38/55


39/55


40/55

The Alternate ( Properdin ) Pathway

Does not require specific antibody to recognise potential

pathogens.

6 plasma proteins perform A, (C3), B (C3 proactivator ),

D, H, I, performcontinuous surveillance function

Activated by

- Organisms - bacteria, fungi, certain viruses

- virus infected cells- variety of polysaccharides & lipopolysaccharides

- human RBC lacking Decay Accelerating Factor


41/55

The Alternate ( Properdin ) Pathway

C3b continuously generated in circulation in small

amounts formed from intervention with activators e.g cell

walls of bacteria, fungi, ect also endotoxins

C3b + Factor B ( C3 Proactivator ) forms complex

Complex C3bBbP ( activated Factor B )

Activates large numbers ofC3 molecules


42/55

MASP: MBL-associatedserineproteinaseMBL: mannan-

binding lectin;MCP:

Alternative Pathway

Activated by C3b bound

to surface components of

microbes ( opsonised )


43/55

Proteins of the MBL ( Mannose Binding Lectin )

Pathway

MBL made in liver in response to Macrophage

cytokines

MBL cascade initiated by MBL binding topathogen surface ( microbial carbohydrates)

MBL and 2 serum proteases C4 & C2 function

like CI to form C3 convertase

C3b combines with C5 & C6 to form C5

convertase


44/55


45/55

All pathways converge at level of C3leading to

the cleavage products, C3a and C5a

terminal membrane attack complex,

C5b-9, which forms pores in the

membranes of bacteria and cells,ultimately causing their lysis.


46/55

Summary of Effector Functions of Complement

Opsonization by C3b targets foreign particles for

phagocytosis

Chemotaxis by C5 a attracts phagocytic cells to site

of damage aided by increased permeability of the

capillary beds mediated by C3a and C5a

Assists in catabolism of Ag/Ab complexes and

elimination from body Deficiency of C2 associatedwith Lupus Erythematosis an auto immune disease

Lysis of antibody coated cells


47/55

Immunoglobulins


48/55


49/55

Each

antibodymoleculehas specificAg binding

site


50/55
http://home20.inet.tele.dk/iir/IIR/IIRinfl.htmhttp://home20.inet.tele.dk/iir/home.htm


51/55

Macrophagereceptors bind

here
http://home20.inet.tele.dk/iir/home.htmhttp://f/buttonhttp://home20.inet.tele.dk/iir/home.htm


52/55

Immunoglobin Molecule and Complement

CIq largest six globed structure

fused by shafts to single base

Serves as recognition unit that

binds to Fc region of Immunoglobin

moleculeto Ch2 domain - if IgG

to Ch 4 domain - if IgM


53/55

IgGless efficient at complement binding thanIgM

Two IgG molecules with FcR binding sites

must be in close proximity for CIq to attach andactivate the full complement cascade

IgM has 5 Fc sites. One molecule of IgM is

capable of CIq binding to activate the full

complement cascade

Immunoglobin Molecules and Complement


54/55

CI

Two IgG

moleculesrequiredto bind CIq

One IgMmoleculeable to spandistancebetween cellsand bind CIq


55/55

IgM antibodies able to

span the distance and

bring about direct

agglutination

IgG antibodies unable to span

the distance cells are

sensitized but agglutination

not seen

immunology in haematology (part 2)

Documents