For Research Use Only in the United States. Not for use in diagnostic procedures.

The MicroVue C4d Enzyme Immuno***** measures the amount of C4d-containing fragments present in human plasma, serum and other biological or experimental samples.

Complement Component C4 is unique to the classical complement pathway. Classical pathway activation is triggered upon the binding of the C1q component of C1 to IgG or IgM containing immune complexes or other activating substances (retroviruses, certain bacteria, parasites, transformed cells, subcellular membranes, DNA and CRP/phosphorylcholine complexes). Binding of C1 to one of these activators results in the conversion of the C1s zymogen to an active proteolytic enzyme. Activated C1s can then cleave C4 at peptide bond 77 to yield C4a, an anaphylatoxin, and C4b. Both fragments have important functions in vivo. As an anaphylatoxin, C4a has a short half life and is bound by cells with the appropriate receptors. C4b mediates opsonization of target cells and can participate in the classical pathway convertase.

The expression of C4b activity is strictly regulated. C4b is rapidly cleaved by Factor I (with CR1 or C4 Binding Protein as cofactor). Cleavage by Factor I yields inactive C4b or C4bi. Further degradation by Factor I yields the fragments C4c and C4d.

C4d has been measured in human serum and plasma. The levels of C4d, normalized by the levels of native C4 can be significantly elevated in specimens obtained from patients with RA, HAE, SLE and chronic urticaria with hypercomplementemia. C4d levels may also be elevated in plasma from patients with a variety of humoral autoimmune diseases in which classical complement activation is known to occur. Because C4 is unique to the classical complement pathway, the C4d activation fragment of C4 is an excellent marker for classical complement pathway activation.

An EIA for the measurement of C4d -containing fragments in experimental samples.