Mouse Monoclonal. Ready-to-use. Intended for in vitro diagnostic (IVD) use. Complement 4d (C4d) is the most clinically used marker for humoral rejection. It is a degradation product of the activated complement factor C4b. C4d is typically initiated by binding of antibodies to specific target molecules. Following activation and degradation of the C4 molecule, thio-ester groups are exposed, which allow transient, covalent binding of the degradation product C4d to endothelial cell surfaces and extracellular matrix components of vascular basement membranes near the sites of C4 activation. C4d is also found in intracytoplasmic vacuoles of endothelial cells. Covalent binding renders C4d a stable molecule that can easily be detected by Immunohistochemistry. References 1. Collins AB et. al. J Am Soc Nephrol. 1999;10(10):2208-14. 2. Racusen LC et. al. Am J Transplant. 2003;3(6):708-14. 3. Sacks SH et. al. Curr Opin Nephrol Hypertens. 2002;11(6):627-8.