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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]
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.
[14] [15] Deficiency in the C1q protein of the classical complement pathway can lead to development of systemic lupus erythematosus. [2] [16] Among the many functions of C1q, C1q triggers clearance of immune complexes and apoptotic cells by activating the classical pathway and binding directly onto phagocytes.
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.
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 ...
In a multicellular organism's immune system, phagocytosis is a major mechanism used to remove pathogens and cell debris. The ingested material is then digested in the phagosome. Bacteria, dead tissue cells, and small mineral particles are all examples of objects that may be phagocytized. Some protozoa use phagocytosis as means to obtain nutrients.
C5a has the highest specific biological activity and is able to act directly on neutrophils and monocytes to speed up the phagocytosis of pathogens. C3a works with C5a to activate mast cells, recruit antibody, complement and phagocytic cells and increase fluid in the tissue, all of which contribute to the initiation of the adaptive immune response.