Factor I
Factor I (FI) is a serine protease with narrow specificity restricted to activated complement components C3b and C4b. Supported by appropriate cofactors such as factor H or C4b-binding protein, FI cleaves peptide bonds in C3b/C4b after arginyl residues. By doing so it inhibits further propagation of the complement cascade thus contributing to protection from misguided or excessive complement attac
