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Complement factor I, also known as C3b/C4b inactivator, is a protein that in humans is encoded by the CFI gene. Complement factor I (factor I) is a protein of the complement system , first isolated in 1966 in guinea pig serum , [ 5 ] that regulates complement activation by cleaving cell-bound or fluid phase C3b and C4b. [ 6 ]
The classical and alternative complement pathways. Alternative pathway. (Some labels are in Polish.) 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.
Complement deficiency is an immunodeficiency of absent or suboptimal functioning of one of the complement system proteins. [4] Because of redundancies in the immune system, many complement disorders are never diagnosed. Some studies estimate that less than 10% are identified. [5]
Complement is responsible for immune inflammatory response in adipose tissues which has been implicated in the development of obesity. [8] Obesity in turn results in an abnormally high level of complement activation via production of the C1 component of the classical pathway, which can lead to tissue inflammation and eventually insulin ...
Properdin (Factor P) is the only known positive regulator of complement activation that stabilizes the alternative C3 convertase (C3bBb). Properdin deficient individuals are sensitive to pyogenic infections. Properdin also promotes association of C3b with Factor B and thus it inhibits the Factor H mediated cleavage of C3b by Factor I. [6]
First, the proteolytic component of the convertase, Bb, is removed by complement regulatory proteins having decay-accelerating factor (DAF) activity. Next, C3b is broken down progressively to first iC3b, then C3c + C3dg, and then finally C3d. Factor I is the protease cleaves C3b but requires a cofactor (e.g Factor H, CR1, MCP or C4BP) for activity.
There are three types of hereditary angioedema (HAE). HAE types I and II are both caused by a deficiency of complement C1-inhibitor (C1-INH), a plasma protein that is an important inhibitor of several serine proteases, specially of the complement system and the contact activation/kallikrein-kinin pathway, but also the fibrinolytic system.
One can interpret the CH50 value along with the individual's complement factor values to help determine the etiology. For example, if and individual has normal C3/C4 values but a decreased CH50, that can indicate a terminal complement pathway deficiency while if one has low C3 and CH50 values that can indicate an autoimmune condition such as ...