Antibodies (also called immunoglobulins) are large Y-shaped proteins that can stick to the surface of bacteria and viruses. They are found in the blood or other body fluids of vertebrates. Antibodies are the key element in the adaptive immune system.
The antibody recognizes a unique part of the foreign target called an antigen. Each tip of the "Y" of an antibody contains a structure (like a lock) that fits one particular key-like structure on an antigen. This binds the two structures together.
Using this binding mechanism, an antibody can tag a microbe or an infected cell for attack by other parts of the immune system, or can neutralize its target directly. The production of antibodies is the main function of humoral immunity.
Each antibody is different. They are all designed to attack only one kind of antigen (in practice, this means virus or bacteria). For instance, an antibody designed to destroy smallpox is unable to hit the bubonic plague or the common cold.
Though the general structure of all antibodies is very similar, that small region at the tip of the protein is extremely variable. This allows millions of antibodies with different tip structures to exist. Each of these variants can bind to a different antigen. This enormous diversity of antibodies allows the immune system to recognize an equally wide variety of antigens.
Relationship Between White Blood Cells and Antibodies
There are two types of white blood cells: Phagocytes and Lymphocytes.
Phagocytes are a type of white blood cell. Once the antibodies attach to the pathogen the phagocytes bind to and engulf the pathogens. Once the pathogen is surrounded, the phagocyte then breaks down the cell using enzymes in its body. Phagocytes rely on antibodies to flag down pathogens in the blood system.
The other type of white blood cell is called a Lymphocyte. These white blood cells are the ones that are in charge of producing antibodies. The Lymphocytes can detect what pathogen is in your body at that given moment and the Lymphocyte will produce a specific type of antibody to specifically attack that pathogen. These antibodies help group pathogens together into one mass so that the phagocytes can just engulf them whole, rather than going around and individually finding pathogens. They produce antibodies that are specific to the pathogen. It takes a while for lymphocytes to produce these specific antibodies. In addition, some lymphocytes produce toxins that counteract the effect of pathogenic exotoxins in the body.
Immunoglobulin diversity
Basic issue
Although a huge variety of different antibodies is made in a single individual, the number of genes available to make these proteins is limited by the size of the genome.
There are a vast number of microbe strains, and so vertebrates need millions of different antibodies. Actually, humans generate about 10 billion different antibodies, each capable of binding a distinct antigen site. This must be done with a very much smaller number of genes: the total human genome has only about 20,000 genes.
Several complex genetic mechanisms have evolved. These allow vertebrate B cells to generate a huge pool of antibodies from a relatively small number of antibody genes. The full details are not presented here, just a summary.
The variety of antibodies is got by combining segments from a pool of genes in many different ways. Then, hyper-mutations occur in the binding site area of the antibody gene. This creates further diversity.
Heavy chains
Antibodies are glycoproteins belonging to the immunoglobulin superfamily; the terms antibody and immunoglobulin are often used interchangeably. Antibodies are typically made of basic structural units—each with two large heavy chains and two small light chains. There are several different types of antibody heavy chains, and several different kinds of antibodies, which are grouped into different isotypes based on which heavy chain they possess. Five different antibody isotypes are known in mammals. They help direct the appropriate immune response for each different type of foreign object they encounter.