What Is the Role of Antibodies in the Immune System?

Antibodies in the immune system are proteins that are produced by certain white blood cells called lymphocytes. These proteins are specifically programmed to attack and kill invading viruses, bacteria or other foreign microbes, called antigens. There are five subtypes of antibodies, or types of immunoglobulin (Ig). Four of these are found in the free floating form of antibodies IgA, IgE, IgG and IgM. IgD is not as frequently seen and is bound to the outer membrane of B cells.

All antibodies in the immune system are similar in shape and function, but each one has a specific role. Antibodies are Y-shaped proteins with receptor sites at both northern poles, called paratopes, which attract receptive docking sites of antigens, or epitopes. Each individual antibody has two paratopes programmed to bind to two individual epitopes of foreign antigens.

Free-floating antibodies in the immune system navigate through bodily fluids in search of antigens. Antibodies in the immune system that are found primarily in blood are IgG and IgM. The IgG antibody effectively immobilizes the invading antigen with a coating that tags the cell for destruction by other members of the immune system, such as T cells. IgG also has the ability to move into other bodily tissues to serve the same function. IgM locates and kills — with the assistance of T cells — invading bacterium that might be present in the blood stream.

Two other free-floating antibodies in the immune system, IgE and IgA, are designated scouts as well. IgE induces the release of histamines to attack invading allergens. IgA is found in bodily fluids and secretions. This immunoglobulin protects against invading antigens in areas such as the respiratory tract and intestinal tract. It also is found in tears and saliva.

IgD are antibodies in the immune system that are encased in the membrane layer of B cells. This immunoglobulin aids the B cell in identifying antigens. After the specific antigen has been identified, a distress call is released to alert other killer cells in the immune system, typically T cells, that an invader has been discovered. The T cells work together with the B cells to effectively destroy the antigen.

After a B cell has been programmed to identify certain pathogens with the assistance of the IgD immunoglobulin, it emits memory cells as an additional element of the immune system. These memory cells work as antibodies in the immune system by readily identifying foreign antigens that they have been previously programmed to recognize. This allows for a more specific distress call and quicker response by T cells. Inoculations work to prevent disease because B cells initially attacked the injected microbe and created memory cells to fight against the microbe if it were to appear in the body again.