Immunoglobulins (Ig) are a group of proteins (albumin) formed in plasma cells (B cells) that specifically bind as antibodies with foreign substances (antigens) to render them harmless. The specific binding of antibodies to antigens forms an essential part of the defense against invading foreign substances (e.g. pathogens).
The following classes of immunoglobulins can be distinguished:
- Immunoglobulin A (IgA) – secreted on all mucous membranes of the respiratory tract, eyes, gastrointestinal tract, genitourinary tract, and via special glands around the nipple of mothers, where it protects against pathogens; found in blood serum and body secretions.
- Immunoglobulin D (IgD) – occurs in the membrane of B lymphocytes.
- Immunoglobulin E (IgE) – mediates protection against parasites, such as worms. Upon antigen contact, it leads to the release ofHistamines, granzymes, etc.; Occur in the membrane of mast cells and basophilic granulocytes (allergic immediate reaction).
- Immunoglobulin G (IgG) – is formed only in a delayed defense phase (3 weeks) and remains for a long time. Detection of Ig G indicates a passed infection or vaccination; occurrence in blood serum and breast milk; placental.
- Immunoglobulin M (IgM) – is the first class of antibodies formed on initial contact with antigens and indicates the acute infectious phase of a disease; occurrence in blood serum.
Immunoglobulins are composed of two light and two heavy polypeptide chains connected by disulfide bridges.
