Antigen-antibody reaction
In biochemistry , immunology , infectious diseases and related sciences , the antigen-antibody reaction ( AAR ) is a component of the immune reaction in which a complex of antigen and antibody is formed. This is known as the antigen-antibody complex or immune complex . The part of the surface of the antigen that the antibody specifically recognizes and binds is called the epitope or antigenic determinant. Different antibodies can be directed against different epitopes of the same antigen ( polyclonality ). Small immune complexes arise in the body every day, for example when they come into contact with bacteria, which in the case of trivial injuries get into the bloodstream and bind to antibodies there. This relationship is also known for viral infections. The immune complexes are kept in soluble form by binding complement components. They bind to the complement receptor CR1 on erythrocytes and are transported to the liver and broken down there. Large immune complexes, which tend to deposit, arise when high, almost equimolar concentrations of antigens and antibodies come together. Then antigens and antibodies bind to each other and form large, strongly cross-linked immune complexes that are no longer soluble in the plasma and precipitate. In certain cases (e.g. in autoimmune diseases ) the immune complex also consists of autoantigen and autoantibodies (e.g. in lupus erythematosus ). The deposition of immune complexes in the vessels leads to complement activation and consecutive neutrophil chemotaxis as well as apoptotic disintegration of the neutrophil leukocytes (leukocytoclasia) (e.g. in leukocytoclastic vasculitis ). The classic representative of an immune complex disease is serum sickness .
Since some types of antibodies are able to bind several antigens of the same kind at the same time (up to ten in the case of IgM ) and, conversely, an antigen can be occupied by several antibodies (see above), an immune complex can under certain circumstances become significantly different Put more than two objects together. Antigen-antibody reactions serve in vivo to protect the organism against foreign bodies such as toxins or bacteria ; they are normally eliminated by the reticuloendothelial system .
Immune complexes can have damaging, pathogenic and even fatal effects. Examples are blood transfusions with blood group incompatibilities ( transfusion reaction ), or certain autoimmune diseases and immune pathogenesis , for example, the immune complex nephritis by Bence Jones proteins , or immune-complex vasculitis . Antipaternal antibodies may create some form of infertility .
Use in the laboratory
Visible complexes are only formed in vitro under optimal conditions. They are precipitated out as a so-called precipitate . This can be used to quantify the antigen, and in rare cases also the antibody. This reaction plays an important role in immunassays that are used to detect antigens or antibodies. Another use is the precipitin test , with which one measures the degree of relationship between two animals.
literature
- Charles Janeway , Paul Travers, Mark Walport, Mark Shlomchik: Immunology. 5th edition, Spektrum Akademischer Verlag, Heidelberg 2002, ISBN 3-8274-1079-7 . Table of contents and free searchable text. 5th edition, 2001 (English).
- Volker Kiefel, Christian Müller-Eckhardt (ed.): Transfusion medicine and immunohematology: Basics - Therapy - Methodology. Springer, Berlin / Heidelberg / New York 2010, ISBN 3-6421-2764-9 , p. 79 f
- Reinhold Eckstein, Robert Zimmermann: Immunohematology and clinical transfusion medicine: theory and practice compact paperback. Edition 7, Urban & Fischer Verlag / Elsevier, Munich 2015, ISBN 3-4373-1681-8 , p. 13
Individual evidence
- ↑ a b Peter Altmeyer , Volker Paech: Immunkomplexe . In: Encyclopedia Dermatology, Allergology, Environmental Medicine . Springer 2013, ISBN 978-3-540-89542-8 .