12.6

• Antigens are proteins molecules on the surfaces of cells that can trigger an immune response
• Antibodies are Y-shaped glycoproteins (immunoglobulins) which bind to a specific antigen on the pathogen/toxin
• The antibody of the antigen-antibody complex acts as an opsonin so is easily engulfed & digested by phagocytes
• Most pathogens cannot effectively invade host cells once part of an antigen-antibody complex
• Antibodies can act as Agglutins which causes pathogens carrying complexes to clump together
• Antibodies can act as anti-toxins by binding to toxins produced by pathgens and making them harmless
• T Lymphocytes are made in the bone marrow and mature in the thymus gland
• T Helper cells have CD4 receptors on cell surface membranes which bind to surface antigens on APCs and produce interleukins which stimulate activity of B cells & production of other T cells
• T Killer cells produce perforin which kills pathogens by making holes in the cell membrane
• T Memory cells are part of the immunological memory as if they meet an antigen a second time they divide rapidly to form many clones of T Killer cells
• T Regulator cells stop the immune response once a pathogen has been eliminated, and make sure the body recognises self-antigens
• B Lymphocytes are produced and mature in the bone marrow
• Plasma cells produce antibodies for a particular antigen and release them into circulation
• B Effector cells divide to form the plasma cell clones
• B Memory cells are part of the immunological memory as they are programmed to remember a specific antigen and enable a rapid response when pathogen is encountered again
• Autoimmune diseases occur when the immune system stops recognising self antigens and attacks healthy body tissue
• Autoimmune diseases can be treated with immunosupressant drugs
• Cell-mediated immunity is the response to cells of an organism that have been changed e.g. from viruses and protists
• Cell Mediated Immunity: Macrophages digest pathogens and produce antigen-presenting cells, receptors on T helper cells fit antigens and become activated to produce interleukins, which stimulate mitosis to produce clones of T cells
• Cloned T cells may: develop into T memory cells, produce interleukins that stimulate phagocytosis, produce interleukins that stimulate divisiom of B cells, stimulate development of cloned T killer cells for antigen, T regulator cells
• Humoral Immunity is the response to antigens found outside of cells
• Humoral Immunity: T helper cells bind to B cell APC (clonal selection), Interleukins produced by T helper activate B cells, Clonal expansion, Primary immune response, Secondary immune response
• In Clonal Expansion the activated B cell divides by mitosis to give clones of plasma & B memory cells
• In the Primary Immune Response the clones plasma cells produce antibodies that bind to antigens and disable them or act as opsonins/agglutins
• In the Secondary Immune Response some cloned B cells develop into B memory cells which can divide to form plasma cell clones if infected by pathogen again