HUMORAL IMMUNITY
Humoral immunity involves the resistance against diseases involving the production of specific antibodies to bind to specific antigens by. Antibodies are proteins that are produced by B cells (a type of lymphocyte/white blood cell that originate in the bone marrow but them migrates to the lymph nodes, capable of producing antibodies) designed only to attach to a specific antigen. Different B cells must produce different antibodies for different invading pathogens. An antibody has four chains, 2 light and 2 heavy chains Two antigen binding sites are present on each antibody, one at the end of each light-heavy chain region so therefore each antibody can bind to two antigens. The only variable regions of an antibody are its antigen binding sites B cells can usually have antibodies on their cell membranes. Millions of B cells exist hence why millions of antibodies can exist. When the antibody is stimulated/primed upon the recognition of a particular antigen, mitosis (clonal expansion) occurs, resulting in the many clones. Replication is also stimulated from the release of cytokines by helper t cells. Upon replication, specialisation may occur. These cells may form plasma cells which produce specific antibodies and some memory cells. Antibodies that have been produced to fight infection remain in the body for long periods of time and attach to memory cells which form a memory of the pathogen and increase the response time of the immune system upon re-exposure to the pathogen. Antibodies can bind to antigens to immobilze them to enhance phagocytic responses, neutralize the toxins produced by thee pathogens, form antibody-antigen complexes when they bind with the antigen and form agglutination (clumping) allowing phagocytes to engulf it. Complement proteins can also be stimulated to lyse the pathogen's cell membrane.
Immunological Memory Because the adaptive immune response is dependent on clonal expansion to create sufficiently large amounts of antibodies, there is a delay between initial exposure and the production of antibodies When B and T cells divide and differentiate in order to produce antibodies, a small proportion of clones will differentiate into memory cells Memory cells remain in the body for years (or even a lifetime) If a second infection with the same antigen occurs, the memory cells react faster and more vigorously than the initial immune response, such that the symptoms of the infection do not normally appear Because the individual no longer presents with the symptoms of infection upon exposure, the individual is thus said to be immune
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