Fluorescence Microscopy Digital Image GalleryTransformed African Green Monkey Kidney Fibroblast Cells (COS-7 Line)
The acquired immune system is capable of producing antibodies and T-cells which recognize a very large number of different molecules with remarkable specificity. It has been estimated that mammals can produce about a million different antibodies, and the mechanism able to achieve this generation of diversity has been a primary field of immunological research. It is also known that antibodies can be produced against synthetic substances which do not occur in nature. Early theories seeking to explain this diversity considered that an “instructive” process, involving the “induced fit” of antibody with antigens was the basis of specificity.
This theory has been largely abandoned as no convincing biological basis for its action has been conceived or discovered. It is now known that immunoglobulins are produced by reorganization and joining of several genes, and that somatic mutation of genetic material occurs during the development of acquired immunity. This especially affects the highly variable portions of the immunoglobulin protein that make up the antigen recognition site.
Such processes play a significant role in the generation of diversity and specificity of the immune system. Development of humoral immunity involves interaction of antigens with IgM or IgD molecules present on the B-cell surface. This triggers B-cell activation which (if sufficient help from T-cells and other systems is available) results in maturation of the response and secretion of appropriate antibodies. This concept was put forward by the pioneering German immunologist Paul Ehrlich decades before it was proven by experimentation. T-cells interact with antigens via T-cell receptors, which show structural similarities with immunoglobulins.