How Antibodies Attach to Foreign Bodies are out to make you sick, and your immune system must assemble a mighty army to fight them. A key weapon are antibodies, Y-shaped proteins that bind to specific sections of proteins, called antigens, on invading pathogens and mark the beginning of an immune response.

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The Y-shaped structure of an antibody consists of two heavy chains and two light chains, stacked together with disulfide bonds that stabilize the overall shape. Each chain contains a variable region, which is responsible for binding to specific antigens. The binding of an antigen to an antibody initiates the immune response, and a chain of events unfolds that leads to the elimination of the germ.

First, antigens bind to certain white blood cells (called B cells), which then transform into plasma cells, which secrete millions of antibodies into the bloodstream. These antibodies circulate through the body and blood-lymph systems, searching for antigens. If, by a one-in-a-million chance, an antibody finds an antigen, it binds to the antigen in a highly specific interaction that’s analogous to a lock and key.

Once bound to antigens, antibodies can carry out a number of important functions. Some antibodies can neutralize the foreign particle, preventing it from interacting with cells and causing cellular damage and invasion. Antibodies can also act as tags, attracting specialized immune cellular mediators that engulf and eliminate the particle through phagocytosis. Alternatively, some antibodies can destabilize organisms, rendering them noninfectious. For example, an antibody to the surface protein gp120 of HIV-1 can induce conformational changes in the viral particle that renders it less infectious (10). Some antibodies can also interfere with the lifecycle or expression of gene material by blocking cell entry or by targeting specific cellular receptors.