Why do we have an immune

system?

Non specific immunity

Inflammatory Response

Non-specific Cellular

response

Physical & chemical barriers

Specific immunity

Immunological surveillance

Clonal Selection theory

T cellsB cells

Infectious Disease

Transmission Epidemiology

Vaccination Public Health

Immune system diseases

Disease survival mechanisms

Big picture

NK cells phagocytes

Cells of the Immune System – many cells we will look specifically at these ….. Bone graft

Multipotentialstem cell

Hematopoieticstem cell

Platelets

Macrophage

Erythrocytes

Eosinophil

Neutrophil

Megakaryocyte

Mast cell

Basophil

T lymphocyte

Natural killer cell

Dendritic cell

B lymphocyte

Lymphoid progenitor cell

Myeloid progenitor

cell

Monocyte

Marrow

Bone

The human body has the capacity to protect itself against pathogens, some toxins and cancer cells through the immune system

GLOSSARY TERMS;

•PATHOGEN – DISEASE CAUSING ORGANISMS

•TOXINS – POISONS PRODUCED BY ORGANISMS

•IMMUNITY – BODY’S ABILITY TO RESIST INFECTION BY A PATHOGEN OR DESTROY THE ORGANISM IF IT SUCCEEDS

Learning outcomes

• Distinguish between the non-specific and specific immune system

• Identify the three lines of defence

• Explain the non-specific defences

Immune system organisationSPLIT INTO 2 AREAS –

NON SPECIFIC AND SPECIFIC

1.NON-SPECIFIC IMMUNITY WORKS AGAINST ANY TYPE OF DISEASE-CAUSING AGENT

2.SPECIFIC IMMUNITY WORKS AGAINST A PARTICULAR PATHOGEN

Non-specific physical barriers

EPITHIAL cells

• The first line of defence against infection.

• Line the surfaces and cavities of the entire body.

• Form sheets/ layers of closely packed cells.

SECRETIONS

• Some Epithelial cells produce secretions such as enzymes, hormones and lubricating fluids that can defend against infection.

• Mucus traps dirt and germs, preventing them from entering the blood.

• Various glands produce antimicrobial secretions that help kill microbes.

Other physical defences

• TINY HAIRS AT THE ENTRANCE TO THE NOSE.

• COUGH AND SNEEZE REFLEXES.

• ‘FRIENDLY’

BACTERIA.

Non-specific immunity• First line of defence are physical and chemical barriers

Line of defenc

e

Specific (s) or non-specific

(ns)

Mechanism employed Function

1st NS Skin barrier Epithelial cells intact

1st NS Mucus

Cilia

Traps microbes in respiratory and gastrointestinal tractRemove microbe by sweeping

1st NS Acid Contains hydrochloric acid at pH 1.5 - 2.5 which has a disinfecting action on the stomach wall and contents.

1st NS Sweat and sebaceous Low pH inhibits microbial growth

1st NS Saliva and tears Enzymes lysozyme digests bacterial walls so it destroys them

Remember lysozyme - ZZZZZ for sleep in your

eye!

Immune system organisation• Second line of defence is the Inflammatory response

• This occurs if the first line are breached, by a cut/ piercing or an invasion of an infectious organisms

Immune system organisation• Second line of defence is the Inflammatory response

• This occurs if the first line are breached, by a cut/ piercing or an invasion of an infectious organisms

Mast cells histamine vasodilation and increased capillary permeability secrete cytokines phagocytosis complement / antimicrobial proteins clotting and tissue repair

phagocytosisA phagocyte is motile (moves towards pathogen when chemicals detected or antigens). It then engulfs

pathogen (endocytosis) – forming a phagocytic vesicle (vacuole) which merges with a lysosome. Lysosomes

contain digestive enzymes, which disposes of the pathogen and released by exocytosis.

The phagocyte releases more cytokines – positive feedback

Natural killer cells1. Protein from NK cell inserts a pore into the target cell membrane

2. Signal molecule from NK enters cell

3. Signal relayed and genes

switched on

5. “suicide” protein function to make degradative enzymes (protease / DNAase). Destroying vital proteins/DNA

4. “suicide” proteins made

Outer membrane on target

cell

12

3

3

4

4

5

5DNAase

protease

DNA

Useless fragments of DNA

vital cell protein

Useless fragments of protein

Natural killer (NK) cells

FINAL NON-SPECIFIC DEFENCE

• FOR VIRUS AND TUMOUR CELLS PREDOMINANTLY

• DISTINCT CLASS OF LYMPHOCYTES WHICH CAN WORK WITH ANTIBODY-DEPENDENT CELLULAR CYTOTOXITY HOWEVER THEY ARE NOT SPECIFIC – WILL ATTACK CELLS (DECIDE SELF/FOREIGN BY LACK OF SELF ANTIGEN (MHC).

• A PORE RELEASED FROM NATURAL KILLER (NK) CELL

• NK CELL THEN RELEASES SIGNALLING MOLECULES

• THIS SIGNALS GENETIC CONTROL OF BOTH SELF DESTRUCTIVE ENZYMES BEING RELEASED AND DNA / VITAL PROTEIN BREAKDOWN

• PROCESS OF “CELL SUICIDE”, PROGRAMMED CELL DEATH IS CALLED APOPTOSIS

NK CELLS

Secondary affect which links to the specific immune system is both NK cells and phagocytes secrete cytokines (interleukins ) that serve to stimulate the specific immune response through the activation of T cells

Natural killer cells1. Protein from NK cell inserts a pore into the target cell membrane

2. Signal molecule from NK enters cell

3. Signal relayed and genes

switched on

5. “suicide” protein function to make degradative enzymes (protease / DNAase). Destroying vital proteins/DNA

4. “suicide” proteins made

Outer membrane on target

cell

12

3

3

4

4

5

5DNAase

protease

DNA

Useless fragments of DNA

vital cell protein

Useless fragments of protein

Complement system

• THE PRESENCE OF BACTERIA AT THE SITE OF INFECTION STIMULATES ANTIMICROBIAL PROTEINS KNOWN AS ‘COMPLEMENT’ TO ARRIVE AT THE SITE OF INFECTION.

• THE COMPLEMENT SYSTEM HELPS THE BODY TO RID ITSELF OF INFECTION BY AMPLIFYING THE IMMUNE

RESPONSE.

Cytokines ....

• Made by damaged tissue / white blood cells

• Enhance migration of phagocytes (chemotaxins - chemoattractants) which engulf/digest pathogen and release more cytokines

• Deliver antimicrobial proteins faster which amplifies immune response

• Deliver blood clotting chemicals (complement) which seals the wound and helps tissue repair

• Have a dual purpose; not only in the non-specific defence but also specific defence system by triggering lymphocytes (next lesson)

Clotting system• The final stage of inflammation is tissue repair.

• What do you remember from unit 2?

• What molecules involved?

• What is prothrombin / fibrinogen?

Non-specific immunity• second line of defence are inflammation cascade and

cellular responses Line of

defenceSpecific (s) or non-specific

(ns)

Mechanism employed Function

2nd NS Inflammatory response Inflammatory response initiated by histamine and serotonin release from basophils/mast cells attractsphagocytes to infected region. Reduces spread of infection throughout organism.

2nd NS Cellular response of phagocytes (phagocytosis)

Ingestion and digestion of foreign particles/microbes by neutrophils, eosinophils, monocytes and macrophages.

2nd NS Cellular response of natural killer cells (NK cells)

Attack virus and cancer cells by releasing molecule which forms a pore in target cells membrane which signals apoptosis by self destroying enzymes

Summary slide

Non-specific defences

Physical defences

• Epithelial cells on the body surface and cavity linings form a physical barrier (skin/trachea/oesophagus etc.)

chemical defences

• Mucus membranes secrete sticky mucus trapping microorganisms

• Acid from epithelial cells in stomach destroy ingested microorganisms

• Skin sebaceous/sweat glands produce low pH secretions that are too low for most microbes to survive

Summary slide

Non-specific defences

Inflammatory response

• Release of histamine by mast cells causes vasodilation and increased capillary permeability.

• The increased blood flow and the secretion of cytokines results in the accumulation of phagocytes and the delivery of antimicrobial proteins and clotting elements to the site of infection.

Summary slide

Non-specific defences

Cellular mechanisms

• A variety of specialised white blood cells provide protection against pathogens.

• Phagocytes recognise surface antigen molecules on pathogens and destroy them by phagocytosis.

• Natural killer (NK) cells induce the pathogen to produce self destructive enzymes in apoptosis.

• Both Phagocytes and NK cells release cytokines which stimulate the specific immune response.

• Complement system amplifies this immune response.