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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]
Classical and alternative pathways shown with their corresponding proteins. 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. [1] [2]
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 classical and alternative complement pathways. C3b is the larger of two elements formed by the cleavage of complement component 3, and is considered an important part of the innate immune system. C3b is potent in opsonization: tagging pathogens, immune complexes (antigen-antibody), and apoptotic cells for phagocytosis.
The classical and alternative complement pathways. Complement-pathways. C3 convertase (C4bC2b, formerly C4b2a) belongs to family of serine proteases and is necessary in innate immunity as a part of the complement system which eventuate in opsonisation of particles, release of inflammatory peptides, C5 convertase formation and cell lysis.
All four complement receptors can bind to fragments of complement component 3 or complement component 4 coated on pathogen surface, but the receptors trigger different downstream activities. [1] Complement receptor (CR) 1, 3, and 4 function as opsonins which stimulate phagocytosis, whereas CR2 is expressed only on B cells as a co-receptor.
[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 ...
Activation of the C1 complex initiates the classical complement pathway. This occurs when C1q binds to antigen-antibody complexes. The antibodies IgM or certain subclasses of IgG complexed with antigens are able to initiate the complement system: a single pentameric IgM can initiate the pathway, while several monomeric IgG molecules are needed. [3]