1. Immunology & Public Health
Immune System

2. Learning Intentions Identify the role of the immune system
Describe non-specific immune defences (“3 lines of defence”):
- physical and chemical defences
- inflammatory response
- cellular response

3. Immune System Immunity
– the ability to resist infection by a pathogen, toxin, or cancer cell
- OR, ability to destroy it after it infects the body
Pathogen - bacteria, virus, fungi, protozoa, parasites
There are three layers of defence
- two are non-specific

4. Immune System – non-specific
Work against ANY kind of disease causing agent
PHYSICAL & CHEMICAL
- the skin’s epithelial cells provide a physical protection
- some membranes are covered in mucus to trap micro-organisms
E.g. digestive and respiratory tracts
- sweat gland and sebaceous gland secretions lower skin pH
- and provide a layer of protection
- tears and saliva contain lysozyme
– digests bacterial cell walls
- stomach acid destroys many swallowed pathogens

5. Immune System – non-specific
INFLAMMATORY RESPONSE
- in response to a physical injury
- e.g. a cut
- mast cells are activated
- they release histamine
- cause blood vessels to vasodilate
- increased blood flow
- mast cells also release cytokines (complement)
- these attract:
- phagocytes to engulf pathogens
- blood-clotting chemicals
- antimicrobial proteins

6. Summary

7. Immune System – non-specific
CELLULAR RESPONSES
Phagocytosis:
- specialised white blood cells (leukocytes) detect pathogens
- they engulf the pathogen
- form a vacuole (phagocytic vesicle)
- lysosomes fuse with the vesicle
- digestive enzymes released
- pathogen is digested
Natural killer cells (NK cells):
- attack cancer cells OR cells affected by viruses
- NK cells release proteins to form a pore in target cell membrane
- a signal molecule gets through the pore
- “self destructive” enzymes produced by target cell
- triggers apoptosis
Cytokines:
- help to stimulate the “specific” immune response

8. Re-Cap questions 1) What are mast cells responsible for?
2) Why does injured tissue at a cut quickly become red and swollen?
3) Briefly explain what is meant by the term phagocytosis
4) Describe the process of apoptosis