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Scheme of the complement system. The complement system, also known as complement cascade, is a part of the humoral, innate immune system and enhances (complements) the ability of antibodies and phagocytic cells to clear microbes and damaged cells from an organism, promote inflammation, and attack the pathogen's cell membrane. [1]
[1] [4] [5] The complement system activation may be due to mutations in the complement regulatory proteins (factor H, factor I, or membrane cofactor protein (CD46)), [6] [5] [7] or occasionally due to acquired neutralizing autoantibody inhibitors of these complement system components (e.g. anti–factor H antibodies).
[3] An example of complement dependent type II hypersensitivity is an acute hemolytic transfusion reaction following transfusion of ABO incompatible blood. [4] Preformed antibody (predominantly IgM) against donor red cell antigens not found in an individual of a particular blood group (e.g. anti-A IgM in an individual with blood group B), bind to the donor red cell surface and lead to rapid ...
Three biochemical pathways activate the complement system: the classical complement pathway, the alternate complement pathway, and the mannose-binding lectin pathway. [9] These processes differ only in the process of activating C3 convertase, [10] which is the initial step of complement activation, and the subsequent process are eventually the ...
The classical complement pathway is one of three pathways which activate the complement system, which is part of the immune system. The classical complement pathway is initiated by antigen-antibody complexes with the antibody isotypes IgG and IgM .
The alternative pathway is a type of cascade reaction of the complement system and is a component of the innate immune system, a natural defense against infections. The alternative pathway is one of three complement pathways that opsonize and kill pathogens. The pathway is triggered when the C3b protein directly binds a microbe. It can also be ...
The complement system is tightly regulated by a network of proteins known as "regulators of complement activation (RCA)" that help distinguish target cells as "self" or "non-self." A subset of this family of proteins, complement control proteins (CCP), are characterized by domains of conserved repeats that direct interaction with components of ...
Complement component 3, often simply called C3, is a protein of the immune system that is found primarily in the blood. It plays a central role in the complement system of vertebrate animals and contributes to innate immunity. In humans it is encoded on chromosome 19 by a gene called C3. [5] [6]