Immune System

• Phagocytosis is where white blood cells engulf pathogens, lysosomes approach the phagosome and fuse, releasing lysozymes which hydrolyse the pathogen
• An antigen is any molecule which is identified by the immune system as non self
• Examples of antigens include glycoproteins, organelles and glycolipids on the cell surface membrane
• Antigenic variability is where a pathogen mutates to change its antigens, this prevents immunity
• When a phagocyte has engulfed a pathogen, it may present its antigens on its cell surface membrane and travel to the lymph nodes to activate the cell mediated response
• The cell mediated response is where a antigen presenting cell travels to the lymph nodes and undergoes clonal selection
• Clonal selection is where a certain T cell has complimentary antigens to those presented on the APC, the antigens bind and cytokines are released, stimulating mitosis
• T cells can become T helper cells for the humoral response, T memory cells in cases of reinfection and cytotoxic T cells
• Phagocytes can detect chemical trails of pathogens which alerts them to begin phagocytosis by extending their pseudopods
• Cytotoxic T cells will bind to the pathogen with complimentary antigens to their own and release perforin to punch holes in the pathogen, they will then release cytotoxins to kill the cell
• Helper T cells travel further into the lymph nodes and undergo clonal selection with a B cell presenting the pathogens antigens, they will bind and cytokines will be released, stimulating mitosis
• B cells can divide into B plasma cells which will release antibodies complimentary to the pathogens antigens
• B cells can divide into B memory cells which will remain in the bloodstream in cases of reinfection
• In the humoral response, a pathogen or its antigens may reach the lymph nodes and enter a B cell with complimentary antigens via endocytosis, their antigens will be presented on the cell surface membrane of the B cell
• Both T and B cells grow in the bone marrow but T cells mature in the thymus
• Antibodies can perform agglutination by binding pathogens together for easier phagocytosis
• Antibodies can neutralise a pathogen, preventing functioning or access to a cell
• Antibodies can mark pathogens for phagocytosis
• Antibodies have a variable region with an antigen binding site and a constant region, its polypeptide chains are joined by disulphide bridges
• Monoclonal antibodies are specific to one antigen and can be used to deliver drugs to cancer, prevent cancer growth and stimulate the immune system
• Eliza testing is where an antigen is attached to a well and is flooded with the blood sample, if a complimentary antibody is in the bloodstream, it will bind to the antigen on the well
• The ELIZA wells are flushed with water to remove any unbound antibodies if the patient does not have the disease, if they do, when a secondary antibody, attached to an enzyme and complimentary to the first antibody binds to the first and a dye substrate is added, colour is released indicating a positive result
• A vaccine can be an attenuated pathogen to make the pathogen harmless, a non toxic or dead version of the pathogen or antigens can be removed from the pathogen
• Herd immunity is where the majority of a population is immune, decreasing the frequency of infection
• Vaccines have ethical issues such as animal testing, side effects, human testing, they are also expensive to distribute to a population to eradicate a disease
• Antibiotics can work by interfering with the bacterial cell wall causing osmotic lysis or binding to ribosomes preventing protein synthesis
• Ethical issues of monoclonal antibodies include side effects, death of animals, need of clinical trials on both animals and humans as well as double blind trials
• Eliza tests can also take the form of a test strip, the control line is dyed when the solvent reaches it, monoclonal antibodies with an enzyme bind to the molecule being tested for, these are carried up the strip to the test line where a second monoclonal antibody binds to the first, the enzyme on the first antibody is held close to a substrate if positive, leading to a dyed line and positive result
• Antibodies can bind to a toxin, agglutinate and destroy them, preventing damage to the body