Microbiology

Microbiology Study Guide

Activity of Cytotoxic T-Lymphocytes The cytotoxic T-lymphocytes migrate from the lymphatic tissues and move to the bloodstream to accumulate at the site of the infection. These cells do not produce any molecule tissues. Once they reach the site of the infection, they fight directly with the different microorganisms and the cells that are infected by these microorganisms. They combat with these cells directly by secreting toxic substances into them that possibly cause their destruction. Other than this, cytotoxic T-lymphocytes also secrete lymphokines that signal and attract phagocytes to the infection site so that phagocytosis can be performed on these infectious microorganisms and the body cells infected by them. These activities help the individual get some relief from the infection caused in the body. Helper and Suppressor T-Lymphocytes The T-cells can further be categorized as helper T-lymphocytes and suppressor T- lymphocytes. The helper T-lymphocytes attract and ignite the function of the B-lymphocytes, which further produces antibodies to fight with the infection in the body. In contrast, the suppressor T-lymphocytes control the activity of the immune system and keep them in a controlled range. There is another category of T- lymphocytes known as natural killer (NK) cells that do not expose the target cells to antigens, but destroy them directly. These cells function on their own without being part of the specific immune response. Another category is delayed hypersensitivity T-lymphocytes, which is responsible for causing inflammation of the local tissues, as they majorly react in the case of hypersensitivity. Antibody-Mediated (Humoral) Immunity B-lymphocytes activate and initiate their function by forming plasma cells only when they are exposed to the antigenic determinants in lymphatic organs. The role of these plasma cells is to synthesize and secrete specific antibodies depending on the nature of antigens. Apart from plasma cells, other B-cells also get activated and take on the form of memory cells. These memory cells help the plasma cells at a later stage by producing antibodies rapidly. This generally happens when the antigen re-enters the body, which leads to the formation of long-term immunity of the body. The plasma cells produce antibodies to combat infections and microorganisms attacking the body. These antibodies are protein substances that are produced by host cells in the host tissues, after receiving signals from the antigens. The antibodies finally react with the antigens. These antibodies are also known as immunoglobulins, which circulate in the bloodstream and are associated with the gamma globulin fraction of the plasma. Structure of Antibodies The structure of antibodies consists of the four protein chains linked by sulfur bonds, arranged in a specific pattern. It is comprised of two chains, each of heavy molecular weight protein (denoted as H chains) and light molecular weight protein (denoted as L chains). A sequence of specific amino acids at the outer arm of the molecule of the antibody exists. The

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