Antibodies: Protein Warfare

Antibodies, which are called immunoglobulins (Ig), are proteins produced by B-cells, often within the spleen or thymus (an image of this process is located here.They are in charge of all humoral immune responses. Antibodies are shaped in the form of a Y. The base of the "arms" determines how the antibody destroys the antigen, while the "arms" themselves bind to the antigen directly. The base of the "arms" categorizes antibodies into five classes: IgG, IgA, IgM, IgD, and IgE.

B-cells always make IgM antibodies first during a humoral response. The other classes appear several days after. Exactly which classes are made is determined by the type of interleukins the B-cells receive from the T-cells. IgM and IgG antibodies can trigger a group of proteins that can cut holes in the plasma membranes of cells, making them disintegrate. This is called the complement system. It is used to fight against extremely resistant bacteria. These antibodies work best in the circulatory system.

IgA antibodies can appear in the bloodstream as well as other bodily fluids. Because of this, IgA is extremely important in fighting infection in the intestine and lungs, which contain mucusal surfaces. IgA is can also be found in mother's milk and may held nursing babies to resist disease.

Antibodies can help destroy antigens in a process called opsonization. During this process, antibodies prepare an antigen to be ingested by a macrophage by coating its surface. Antigens that have been coated with antibodies are more likely to be ingested, since macrophages have a receptor that sticks to the bases of antibodies.

Antibodies can also cease an antigen's disease-causing activities. It binds the antigen, therefore preventing it from interfering with the body cells' normal activities. This process is called neutralization.