Antibodies

Blood lymphocytes (plasma cells) produce antibodies that destroy disease-causing bacteria and viruses. Immunoglobulins act as effector molecules of humoral immunity. Antigens, entering the body from outside sources (e.g., infections) or forming within the body (endogenous), stimulate antibody synthesis. Typically, antibodies interact specifically with complementary antigens, forming non-covalent bonds. A wide variety of antibodies exists, but each molecule has a unique site that binds to the antigen determinant. B lymphocytes, which make up about 15% of circulating lymphocytes in the blood, synthesize antibodies. The human body produces about 107 clones of B lymphocytes, each producing one of the 107 immunoglobulins. IgG best represents the common structure of all immunoglobulins.

The IgG molecule (monomer) consists of four polypeptide chains: two identical light chains (L), each with a structure of 220 amino acids, and two heavy chains (H), each with about 440 amino acids. Four disulfide bonds and numerous non-covalent bonds link all four chains. There are five classes of heavy chains and, based on them, five classes of immunoglobulins: A, D, E, G, M. Antibodies constitute one of the main blood plasma protein fractions (about 20%). They resist weak acids and alkalis, as well as temperatures of 60°C. Activated B lymphocytes usually transform into plasma cells that produce IgM antibodies (primary response) and generate B memory cells.

Memory cells can circulate in the blood for decades, quickly producing specific antibodies upon re-exposure to the antigen (secondary response). The specific cellular response (cellular immunity) uses T lymphocytes to protect against infected virus cells, parasites, foreign cells, and non-plasma cells. All antibodies are glycoproteins.

Source | Glossary of Most Commonly Used Biomedical Terms and Concepts | Lithuanian University of Health Sciences | Academician Professor Antanas Praškevičius, Professor Laima Ivanovienė