What Are Antibodies Effective Against?

Antibodies, also known as immunoglobin molecules, are the effector molecules of the immune system that target foreign substances for destruction and removal from the body. These substances can include bacteria, viruses, cellular remnants, molecules and the body's own dying cells.

Characterization of Antibodies

• Although immunoglobins, or antibodies, vary widely in their specific functions, they all share the same basic form. For example, immunoglobin G, commonly referred to as IgG, consists of two sets of amino acid chains; the heavy, H, set and the light, L, set, which take the appearance of a doubled letter "Y." The four ends of the open part of the "Y" are used for the recognition of either "self" or "nonself" molecules. Those that are "self" are normally left alone; however, those that are foreign, or "nonself," referred to as antigens, react with the antibodies and are marked for destruction and removal by white blood cells.

Location of Antibodies

• Antibodies are produced by specific white blood cells, called plasma cells, and take one of two forms. They can exist as either a free-flowing, or secreted, form or an alternative membrane-bound form on the surface of another type of white blood cell, called a B-cell, which are then called B-cell receptor molecules.

Diversity of Antibody Molecules

• There are five recognized types of antibody molecules: IgA, IgD, IgE, IgG and IgM. Due to the interchangeability at the ends of the antibody molecules and variable genetic expression combined with random mutations, they are able to recognize up to 1018 different combinations or sequences of chemical compounds. According to Alberts in "Molecular Biology of the Cell," there are 250 to 1000 different chain sequences possible for the H-chains of the antibody and 250 known for the L-chains. These combinations taken together explain the vast diversity of antibody molecules, which are called isotopes, in the process of acquired immunity.

Actions of Antibodies

• Once an antibody comes in contact with a foreign particle, the molecule becomes activated and signals other molecules and cells to aid in the fight against possible invasion. Activated antibodies on the surface of B-cells often recruit the assistance of another type of white blood cell, called a helper T-cell. The B-cell will then become activated and initiate production of further antibodies, which are secreted into the interstitial fluid and blood. In this way, the antibodies serve a role as a molecular communication system in the recruitment of further defensive cells and molecules to continue surveillance of invading microorganisms.

Natural Antibodies

• All higher animals have an innate, or natural, immune system complete with their own antibodies. These antibodies do not target a particular antigen, but rather, recognize a variety of foreign antigens or other natural debris, such as cell fragments that need to be eliminated to maintain stability in the body. These antibodies are produced without previous exposure to foreign antigens in a process known as passive immunity.