Antibodies, or immunoglobulins (Ig), are molecules made by white blood cells (specifically, B cells) and aid in the destruction of infectious organisms, according to BiologyReference.com. Immunoglobulins attach to foreign invaders, and this allows the immune system to target and destroy them. There are different types of immunoglobulins for specific functions throughout the body.
Immunoglobulin D (IgD)
IgD is found only on immature B cells, according to the University of South Carolina School of Medicine. IgD helps B cells mature, but the role IgD plays in the serum is uncertain. There is no evidence that this type of antibody can attach to foreign organisms and aid other white blood cells in the immune response.
Immunoglobulin M (IgM)
IgM is the first type of antibody that is produced against a new germ, according to Merck Manuals. IgM production is called the primary immune response. IgM then attaches to the infectious agent, or antigen, and helps other cells destroy the foreign organism. IgM is most commonly found in the bloodstream, but it rarely enters body tissues.
Immunoglobulin G (IgG)
IgG is most abundant antibody in the blood. This immunoglobulin makes up 75 percent of all immunoglobulins in the blood, according to the University of South Carolina School of Medicine. IgG is the considered the most versatile of antibodies because it exists in blood and also in tissue, and it perform all the functions of any other antibody. IgG also is the only antibody that crosses the placenta. When a baby is born, the only antibodies that protect it are the maternal IgG. It attaches to the antigen and allows other cells of the immune system to ingest and destroy germs.
Immunoglobulin A (IgA)
IgA is the second-most common form of immunoglobulin in the blood. IgA, according to BiologyReference.com, usually is found in secretions such as tears, saliva, sweat, mucous and mother's milk. Since these secretions are the first barriers most germs encounter, IgA is a crucial first-line defense. This type of immunity is called local or mucosal immunity.
Immunoglobulin E (IgE)
IgE are the antibodies that cause immediate allergic reactions, according to Merck Manuals. IgE binds to a specific type of white blood cell called a basophil or mast cell. When basophils or mast cells that have combined with an IgE molecule interact with an allergen (any substance that the patient is allergic to), the cells release substances, such as histamine, that cause inflammation and other allergic responses. This response can be harmful, but it also helps defend against numerous parasitic infections. IgE is found in the bloodstream, and it is more abundant in people with hay fever, asthma, other allergic conditions and parasitic infections.
