Antibody (an'ti-bod-ee)

Simple - A protein produced by a plasma cell in the Iymphatic system or bone marrow. An antibody binds to the specific antigen that has stimulated the immune system. Once bound, the antigen can be destroyed by other cells of the immune system.

Extended- An antibody or immunoglobulin is a large Y-shaped protein used by the immune system to identify and neutralize foreign objects like bacteria and viruses. Each antibody recognizes a specific antigen unique to its target. This is because the two tips of the "Y" of the antibody contain a paratope (a structure analogous to a lock) that is specific for one particular epitope (analogous to a key) on an antigen, allowing these two structures to precisely bind together. This precise binding mechanism allows an antibody to tag a microbe or an infected cell for attack by other parts of the immune system, or to directly neutralize its target (i.e. by blocking a part of a microbe that is essential for its invasion and survival). The production of antibodies is the main function of the humoral immune system.

Antibodies are soluble glycoproteins of the immunoglobulin superfamily. The terms antibody and immunoglobulin are often used interchangeably. When attached to the surface of the B cell, the membrane-bound form of the immunoglobulin is sometimes referred to as the B cell receptor (BCR). Soluble antibodies are found in the blood and tissue fluids, as well as many secretions. In structure, they are globulins (in the ã-region of protein electrophoresis). They are synthesized and secreted by plasma cells that are derived from the B cells of the immune system. Membrane-bound immunoglobulins are only found on the surface of B cells and facilitate the activation of these cells following binding of their specific antigen, and their subsequent differentiation into plasma cells for antibody generation, or memory cells that will remember the foreign antigen during future exposure. In most cases, interaction of the B cell with a T helper cell is necessary to produce full activation of the B cell and, therefore, antibody generation following antigen binding.