Immunology & Public Health Specific Cellular Defences

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

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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Action of T lymphocytes Cytotoxic T cells (Tc cells): Have receptors specific to antigens - once antigens are presented, receptors bind to them and 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

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

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

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

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

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