immunoglobulin
(im‵yŭ-nō-glob'yŭ-lĭn 
, im-ū‵nō-glob'yŭ-lĭn)
[immuno- + globulin]
ABBR: Ig, IG
- Any of a diverse group of plasma polypeptides that bind antigenic proteins and serve as one of the body's primary defenses against disease. Two different forms exist. The first group of immunoglobulins lies on the surface of mature B cells, enabling them to bind to thousand s of antigens. When the antigens are bound, the B plasma cells secrete the second type of immunoglobulins, antigen-specific antibodies, which circulate in the blood and accumulate in lymphoid tissue, esp. the spleen and lymph nodes, binding and destroying specific foreign antigens and stimulating other immune activity. Antibodies also activate the complement cascade, neutralize bacterial toxins and viruses, and function as opsonins, stimulating phagocytosis.
- Immune globulin.
Immunoglobulins are formed by light and heavy (depending on molecular weight) chains of polypeptides made up of about 100 amino acids. These chains determine the structure of antigen-binding sites and , therefore, the specificity of the antibody to one antigen. The five types of immunoglobulins (IgA, IgD, IgE, IgG, IgM) account for approximately 30% of all plasma proteins. Antibodies are one of the three classes of globulins (plasma proteins) in the blood that contribute to maintaining colloidal oncotic pressure.SYN: antibody.
SEE: antigen; B cell.
ABBR: IgA
The principal immunoglobulin in exocrine secretions such as milk, respiratory and intestinal mucin, saliva, and tears. It prevents pathogenic bacteria and viruses from invading the body through the mucosa of the gastrointestinal, pulmonary, and genitourinary tracts. Its presence in colostrum and breast milk helps prevent infection in breast-feeding infants.ABBR: IgD
An immunoglobulin that is present on the surface of B lymphocytes and acts as an antigen receptor.ABBR: IgE
An immunoglobulin that attaches to mast cells in the respiratory and intestinal tracts and plays a major role in allergic reactions. About 50% of patients with allergies have increased IgE levels. IgE is also important in the formation of reagin, a type of immunoglobulin gamma E (IgGE), found in the blood of individuals with an atopic hypersensitivity.ABBR: IgG
The principal immunoglobulin in human serum. Because IgG moves across the placental barrier, it is important in producing immunity in the infant before birth. It is the major antibody for antitoxins, viruses, and bacteria. It also activates complement and serves as an opsonin. As gamma globulin, IgG may be given to provide temporary resistance to hepatitis or other diseases.ABBR: IVIG
A solution containing concentrated human immunoglobulins (antibodies), primarily immunoglobulin G. IVIG has numerous uses in health care, including as replacement therapy for patients with primary immune deficiencies; as a treatment for those with Kawasaki disease, bullous pemphigoid, Guillain-Barré syndrome, idiopathic thrombocytopenic purpura, chronic inflammatory demyelinating polyneuropathy, and other immune-mediated illnesses. It also serves as a means of providing patients with passive immunity against infectious diseases.ABBR: IgM
An immunoglobulin formed in almost every immune response during the early period of the reaction. IgM controls the A, B, and O blood group antibody responses and is the most efficient antibody in stimulating complement activity. Its size prevents it from moving across the placenta to the fetus.