Clonal Selection Theory,Lymphocyte Cells,Proliferation,Plasma Cells,B-Lymphocytes,proteins,RNA

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	Clonal Selection Theory - Various theories have been proposed regarding the formation of antibodies, although only the clonal selection theory seems to be acceptable in most situations. According to this theory, lymphocyte cells are able to make a specific antibody against a specific antigen. The cell may not be making the antibody continuously but may get transformed into an antibody synthesizing cell when the antigen contacts the proper lymphocyte cell. B cells, while not engaged in active synthesis of antibodies, carry specific antibodies on their surfaces. Due to these surface bound antibodies, a specific antigen may get bound with specific B cells and may thus trigger the proliferation and maturation of that particular B cell.
The cell responds with repeated cell divisions until a clone of antibody synthesizing cells called plasma cells is formed. These cells then form large number of same antibodies, at a rate of 16,000 molecules per second per cell. The antibodies are produced by B-lymphocytes, and there is a specific antibody for each specific antigen. Antibodies are also produced by other cells in the body, such as I-lymphocytes, macro phages, granulocytes and must cells, which, like B- lymphocytes also differentiate from stem cells in bone marrow. A concerted effort of all these cells is required to produce the immune, response. When an animal first encounters an antigen, it produces a low primary response, since only few B cells or T cells can respond to antigen. However, the next encounter with the same antigen leads to a far more rapid and intense response called secondary response, since many cells are now available for response.
Due to first exposure to antigen, not only mature antibody producing B cells are produced, but immature B and T memory cells are also produced, which can respond on a second ,exposure to the antigen. About 10,000 different antibodies are known to exist in a human body at a given time (there are 1012 lymphocytes with 106 -108 specificities). Obviously thousands of plasma cells throughout the circulatory system are in operation for the production of antibodies at any given time. About 90-95% of the protein produced in plasma cells gives rise to antibodies, which are sometimes stored in large quantities in these cells, and can be visible as crystals within the cell. With the introduction of an antigen inside the body, the antibody producing plasma cells increase in number, their RNA content increases and the entire protein synthesizing machinery is activated for use in antibody production.