Immune complex

As an antigen -antibody reaction, a part of the immune response is known in biochemistry, immunology, and related sciences, in which a complex of antigen and antibodies is formed. This is referred to as antigen -antibody complex, or immune complex The part of the surface of the antigen, the antibody specifically recognizes and binds to, called epitope or antigenic determinant. Different antibodies may be directed against different epitopes of the same antigen ( polyclonality ). Small immune complexes are formed in the body every day, so when in contact with bacteria, which come in banal injuries in the bloodstream, where they bind to antibodies. Even with viral infections, this relationship is known. The immune complexes are retained by binding of complement components in a soluble form. They bind to the complement receptor CR1 on erythrocytes and are transported to the liver and broken down there. Large prone to deposition of immune complexes occur when high, almost equimolar concentrations of antigens and antibodies meet. Then, antigens and antibodies bind together and form large, highly cross-linked immune complexes which are soluble and precipitate in the plasma no longer. In certain cases (eg, autoimmune diseases), the immune complex is also auto-antigen and auto- antibody (eg lupus erythematosus ). The deposition of immune complexes in the blood vessels leads to complement activation and neutrophil chemotaxis as well as consecutive decay of apoptotic neutrophils ( leukocytoclasia ) (eg, leukocytoclastic vasculitis). The classic representative of an immune complex disease is the serum sickness.

As some types of antibodies are able to bind a plurality of identical antigens simultaneously ( up to ten in the case of IgM) and vice versa, an antigen can be reception among a number of antibodies ( see above), an immune complex can in certain circumstances of substantially more than two objects put together. Antigen -antibody reactions in vivo serve to protect the body against foreign substances such as toxins or bacteria, they are eliminated by the reticuloendothelial system in the normal case.

In some cases, immune complexes can have harmful, pathogenic, deadly to effects. Examples are blood transfusion in blood group incompatibility ( transfusion reaction ), or certain autoimmune diseases, and immune pathogenesis, for example, the immune complex nephritis by Bence Jones proteins, or immune-complex vasculitis.

Use in the laboratory

In vitro, complexes form only visible under optimal conditions. They are precipitated as the so-called precipitate. Usable this is to quantify the antigen, in rare cases, of the antibody. An important role this reaction plays in immune assays are used to detect antigens or antibodies. Another use is the Präzipitintest with which one measures the degree of relationship between two animals.