Antibody and Antigen

An antigen is any foreign substance in the body that stimulates the immune system to action. An antibody is a protein made by the body that locks on, or marks, a particular type of antigen so that it can be destroyed by other cells. Antibodies are an essential part of the immune system of vertebrates (animals with a backbone) and enable the body to resist disease-causing organisms.

All vertebrates have an immune system that produces antibodies. The immune system is able to distinguish "self" from "nonself" and recognizes when an antigen (foreign cell) has invaded the body. The immune system then produces special chemicals called antibodies to fight and help kill the invader. The immune system is also able to "remember" these specific invaders, and if they ever return, it is able to respond even faster using specific antibodies whose job is to lock on to that particular type of antigen. After locking on, or binding with it, the antibodies get help from other cells and proteins that destroy the antigen or at least neutralize it.

Antibodies really work after the fact. When an antigen, such as a virus, invades the body, two things can happen. However, if this invader is new to the body and has never entered it before, the body has no antibodies to combat it. In such a case, it is the body's large white blood cells known as macrophages that will attack and try to destroy the antigen. If this virus has entered the host before, then specific antibodies already exist. These antibodies will immediately recognize the virus as "nonself" and bind to it like a key in a lock. Once they lock on to the antigen, they have marked the invader as a target for the body's killer cells. An antibody will only recognize and help destroy one kind of organism or antigen. If a new and different organism enters the body, a new type of antibody must be produced.

Although scientists were aware of antibodies in the 1890s, it was not until the late 1930s that scientists came to discover what they really were. In 1938 antibodies were identified as proteins of the gamma globulin portion of the plasma (the liquid portion of the blood). Later it was found that antibodies are produced by special white blood cells called Blymphocytes.

Immunization, sometimes called vaccination, uses the ability of the immune system to remember a previous invader. For example, a child is immunized against certain diseases, like measles, mumps, rubella, diphtheria, whooping cough, tetanus, polio, and chicken pox, through a vaccine. Vaccines contain dead or weakened disease-causing organisms that stimulate the body's immune system without actually causing the disease. Before vaccination, these diseases were common among children and responsible for many deaths. Now, routine vaccination of children has virtually eliminated these diseases. Vaccination works because once a certain antibody is produced in the body, it usually remains for many years. The case of immunization is an excellent example of how an understanding of the body's systems and operations allows scientists to better use the body's own natural defense mechanisms to the advantage of the individual.

[See alsoBlood; Blood Types; Immune System; Immunization; Rh Factor ]