Immune response

• An antigen is a protein or glycoprotein capable of stimulating an immune response.
• A pathogen, is a disease forming microorganism.
• A phagocyte is attracted to a foreign antigen. It engulfs the antigen by extending its cell membrane. The pathogen is in a phagocytic vacuole, which the lysosome fuses to. Lysozymes are secreted and they hydrolyse the pathogen. The antigen is presented on the cell membrane.
• The receptor proteins on a specific T cell are complementary to the presented antigen. Binds to activate T Helper Cell. Divide using mitosis to produce identical clones. Differentiate into cytotoxic and helper cells.
• Helper cells stimulate phagocytes, B cells and more cytotoxic T cells.
• Cytotoxic cells, bind directly to the pathogen and release a toxic substance that kills the pathogen by causing it to burst.
• An antibody, is a quaternary protein made in response to a foreign antigen by Plasma B Cells. They have 2 variable regions and cause agglutination of foreign antigens.
• Humoral Response. Specific receptor proteins of B cells are complementary to antigen presented by pathogen. These bind and are stimulated by T Helper Cells. It divides by mitosis and produce Plasma and Memory B Cells.
• Identical antibodies are produced, specific to the antigen. These are released into the blood and bond to antigens causing agglutination. This immobilises the pathogen allowing the phagocytes to engulf and destroy them.
• Retained in the blood. if they encounter antigen again, they differentiate and divide to form plasma b cells and make more antibodies.
• Vaccines contain a weakened or dead form of the pathogen but always contain its antigens. So the body can form memory b cells without causing a disease.
• Herd immunity, most people have been vaccinated, those not vaccinated are less likely to catch the disease.
• Ethics: production of monoclonal antibodies involves harming of animals, presence of animal products, reliance on herd immunity without getting immune yourself, unethical to rely on completely tested drugs for carriers of disease i.e. HIV
• Monoclonal antibodies bind to the cancer cells' antigens as they're complementary. The drug is therefore delivered to a specific area and will destroy fewer healthy cells.
• Indirect ELISA test - an antigen is mounted in a well. A sample of the patient's plasma is taken and added to the well. The the specific antibody should bind if the disease is present in the patient's body. The excess is washed away. A secondary antibody with an enzyme attached it added, this should bind to the primary antibody. The excess is washed away. A substrate is added, a colour change should be visible if the patient has the disease.