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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 ]
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]
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]
Complement control proteins are proteins that interact with components of the complement system. 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."
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. 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.
Fibrinogen deficiency, also known as factor I deficiency, is a rare inherited bleeding disorder related to fibrinogen function in the coagulation cascade. It is typically subclassified into four distinct fibrinogen disorders : afibrinogenemia, hypofibrinogenemia, dysfibrinogenemia, and hypodysfibrinogenemia.
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 ...