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

111111

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

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