C3 Antibody (Polyclonal)

A goat antiserum raised against human C3 protein.

> 40 mg/mL

Goat

Short term (30 days) 4˚C. Long term at or below –20˚C.

C3 plays a central role for the classical, alternative, and lectin pathways of the complement system. The circulating form of C3 is naturally glycosylated and contains two disulfide-bonded chains that weigh approximately 110 kD and 75 kD, respectively. The average concentration of circulating C3 in human serum/plasma is 1.25 mg/mL. Activation of any of the three complement pathways results in the cleavage of C3 into C3a and C3b fragments. C3a is one of the three complement-derived anaphylatoxins. The C3a polypeptide also exhibits immunoregulatory activity. This activity is dependent on the physical binding of C3a to helper T lymphocytes, which results in the inhibition of helper T cell function. C3a also suppresses the production, in vitro, of lymphokines by PHA or Con A simulated human PBL. This suppression is dependent on the presence of the carboxyl terminal arg-77, due to the inactivity of C3a-des-arg. Upon complement activation, the C3b fragment’s reactive site (a thioester bond) becomes accessible to nucleophilic attack by target cell acceptor molecules or non-complement proteolytic enzymes. Such an attack results in a covalent ester bond between the C3b fragment and the target cell surface. This attachment provides the binding site for C5, initiating membrane attack complex assembly. The ability of C3b to continue cleaving C5 is lost upon cleavage into iC3b and C3f by naturally occurring plasma regulator proteins, Factor H and Factor I. iC3b remains bound to the cell surface and can continue to mediate the opsonization of complement-coated target cells by binding CR3 receptors, or in the presence of CR1, iC3b can further be hydrolyzed by a variety of proteolytic enzymes, trypsin, elastase, plasmin or Factor I, into C3c and C3d,g.