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antibody, protein produced by the immune system (see immunity) in response to the presence in the body of antigens: foreign proteins or polysaccharides such as bacteria, bacterial toxins, viruses, or other cells or proteins. Such antigens are capable of inflicting damage by chemically combining with natural substances in the body and disrupting the body's processes. The body contains hundreds of thousands of different white blood cells called B lymphocytes, each capable of producing one type of antibody and each bearing sites on its membrane that will bind with a specific antigen. When such a binding occurs, it triggers the B lymphocyte to reproduce itself, forming a clone that manufactures vast amounts of its antibody.

The antibody molecule is composed of four polypeptide chains (see peptide)—two identical light chains and two identical heavy chains—joined by disulfide bridges. The light chains have a variable portion that is different in each type of antibody and is the active portion of the molecule that binds with the specific antigen. Antibodies combine with some antigens, such as bacterial toxins, and neutralize their effect; they remove other substances from circulation in body fluids; they bind certain antigens together, a process known as agglutination; and they activate complement, blood serum proteins that cause the destruction of invading cells.

See also monoclonal antibody.

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A protein found principally in blood serum and characterized by a specific reactivity with the corresponding antigen. Antibodies are important in resistance against disease, in allergy, and in blood transfusions, and can be utilized in laboratory tests for the detection of antigens or the estimation of immune status.

Antibodies are normally absent at birth unless derived passively from the mother through the placenta or colostrum. In time, certain antibodies appear in response to environmental antigens. Antibodies are also induced by artificial immunization with vaccines or following natural infections. The resulting antibody level declines over a period of months, but rapidly increases following renewed contact with specific antigen, even after a lapse of years. This is known as an anamnestic or booster response. See Allergy, Blood groups, Hypersensitivity, Isoantigen, Vaccination

Antibody reactivity results in precipitation of soluble antigens, agglutination of particulate antigens, increased phagocytosis of bacteria, neutralization of toxins, and dissolution of bacterial or other cells specifically sensitive to their action; the antibodies so revealed are termed precipitins, agglutinins, opsonins, antitoxins, and lysins. One antibody may give many such reactions, depending on conditions, so these classifications are not unique or exclusive.

Three principal groups (IgG, IgM, IgA) and two minor groups (IgD, IgE) of antibodies are recognized. These all form part of the wider classification of immunoglobulins. Antibody diversity is generated by amino acid substitutions that result in unique antigen-binding structures. See Cellular Immunology, Immunoglobulin

The development of the technology for producing monoclonal antibodies, which can bind to specific sites on target antigens, revolutionized the uses of antibodies in biology and medicine. Unfortunately, almost all monoclonal antibodies originate in mice, and the murine immunoglobulin serves as an antigen, frequently acting immunogenic in human recipients. See Antigen, Monoclonal antibodies

McGraw-Hill Concise Encyclopedia of Bioscience. © 2002 by The McGraw-Hill Companies, Inc.


A protein, found principally in blood serum, originating either normally or in response to an antigen and characterized by a specific reactivity with its complementary antigen. Also known as immune body.
McGraw-Hill Dictionary of Scientific & Technical Terms, 6E, Copyright © 2003 by The McGraw-Hill Companies, Inc.


any of various proteins produced in the blood in response to the presence of an antigen. By becoming attached to antigens on infectious organisms antibodies can render them harmless or cause them to be destroyed
Collins Discovery Encyclopedia, 1st edition © HarperCollins Publishers 2005
References in periodicals archive ?
It feels like we don't matter in the UK, we are fearful of the future ANCA PITICII who was beaten up by teen yobs
Clinical features and treatment outcomes of otitis media with antineutrophil cytoplasmic antibody (ANCA)-associated vasculitis (OMAAV): A retrospective analysis of 235 patients from a nationwide survey in Japan.
The laboratory profile retrieved included WBC, hemoglobin, platelets count, ESR, Rheumatoid factor, serum creatinine, urine protein, 24 hour urine protein excretion, creatinine clearance and ANCA. ANCA pattern and specificity were also noted, namely c-ANCA, p-ANCA, PR3-ANCA and MPO-ANCA.
De Sousa et al., "ANCA serotype and histopathological classification for the prediction of renal outcome in ANCA-associated glomerulonephritis," Nephrology Dialysis Transplantation , vol.
Merola et al., "The significance of MPOANCA and PR3-ANCA without immunoflorescent ANCA found by routine clinical testing," Journal of Rheumatology, vol.
The diagnosis of AAV is strongly suggested by a positive ANCA test; however, 5-10% of the patients do not develop ANCA, so a negative result does not exclude a diagnosis of AAV [8,11].
Although ANCA-associated necrotizing GN has been widely recognized as "pauci-immune" GN, immune-complex GN and ANCA positivity are not mutually exclusive as evidenced by when immune deposits were seen over half of cases of ANCA-associated crescentic GN [20], signifying that the distinction between immune-complex and pauci-immune GN may no longer allow for a precise delineation of glomerulonephritis.
However, almost no literatures have mentioned how to determine the biopsy site in the limited type of GPA because most cases had positive ANCA or typical symptoms and laboratory changes in the respiratory tract or kidney.
Quantitative measurement of PR3-ANCA antibody serum concentration was performed using the Varelisa[TM] PR3 ANCA EIA kit (Phadia GmbH, Freiburg, Germany).