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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 ]
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.
The complement fixation test is an immunological medical test that can be used to detect the presence of either specific antibody or specific antigen in a patient's serum, based on whether complement fixation occurs. It was widely used to diagnose infections, particularly with microbes that are not easily detected by culture methods, and in ...
The protein encoded by this gene is a type I membrane protein and is a regulatory part of the complement system. The encoded protein has cofactor activity for inactivation (through cleavage) of complement components C3b and C4b by serum factor I, which protects the host cell from damage by complement. [8]
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]
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 ...
Atypical hemolytic uremic syndrome (aHUS), also known as complement-mediated hemolytic uremic syndrome (not to be confused with hemolytic–uremic syndrome), is an extremely rare, life-threatening, progressive disease that frequently has a genetic component. In most cases, it can be effectively controlled by interruption of the complement cascade.
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.