1. Immunology & Public Health
Specific Cellular Defences

2. Lymphocytes Derived from bone marrow
Carry out the specific immune response
2 types:
- T lymphocytes (T cells) – mature in the thymus
- B lymphocytes (B cells) – mature in the bone marrow
Lymphocytes are attracted to sites of infection by cytokines
Act in response to antigens
- a “foreign” molecule (e.g. surface protein)
Each lymphocyte is specific to an antigen
- antigens are said to “select” a lymphocyte
- lymphocytes then make clones of themselves to fight the antigens
- known as the clonal selection theory

3. Action of T lymphocytes
Phagocytes present antigens of destroyed pathogen
-phagocyte is an antigen presenting cell (APC)
Helper T cells (TH cells)
bind with antigens
trigger cloning of:
memory cells
activated TH cells
- these secrete cytokines
- this stimulates other immune cells

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5. Action of T lymphocytes
Cytotoxic T cells (Tc cells):
Have receptors specific to antigens
- once antigens are presented, receptors bind to them
- activate the Tc cell
This will then clone more activated Tc cells and memory cells
Active Tc cells move towards infection site
- influenced by cytokines
Tc cells destroy infected cells by
- apoptosis
- lysis

6. Action of B lymphocytes (B cells)
Helper T cells recognise a foreign antigen
- they then release cytokines
This then produces:
- active B cells
- memory B cells
Active B cells then produce antibodies
- these have binding sites
- specific to each antigen

7. Action of B lymphocytes (ctd.)
Antibodies combine with antigens
- form an antigen-antibody complex
This inactivates the pathogen
- antigens now susceptible to phagocytosis by macrophage

8. Immunological Memory
On first infection, the body responds by producing antibodies
This response is gradual
- relatively few antibodies are produced
- this is the primary response
Individual often suffers from the infection
Upon re-exposure, the disease is usually prevented:
- response is much more rapid
- much higher concentration of antibodies produced
- high concentration maintained for a long time
- this is the secondary response
- this is due to the presence of memory cells
- these clone multiple copies of T cells and B cells

9. Self/Non-self
All body cells have a characteristic set of cell surface proteins
- the antigen signature
Recognised as self
If a signature is recognised as foreign (non-self), an immune response is generated
- carried out by lymphocytes
- lymphocytes shouldn’t act on body’s own cells

10. Autoimmunity & Allergy
When “self” cells are attacked by body’s own cells
E.g. rheumatoid arthritis, type 1 diabetes, M.S.
- this is autoimmunity
Sometimes, the immune system “over-reacts”
- in response to a harmless substance
E.g. pollen, dust, penicillin
- this is called an allergy
E.g. hay fever, anaphylactic shock