C4d is a stable split product remnant of classical complement activation which becomes covalently bound to endothelium and basement membrane (1). Capillary deposition of complement C4d has been suggested to be a valuable marker for humoral rejection and endothelial C4d deposition in kidney allograft has been associated with inferior graft outcome (1-3). The detection of C4d in formalin-fixed, paraffin-embedded tissue has been documented to be valuable in the evaluation of various inflammatory diseases (4). Membranous nephropathy (MN) is the most common cause of nephrotic syndrome in adults and C4d immunohistochemical staining has been shown to be a very useful tool for MN (5).
In the past, most publications have used polyclonal antibodies against C4d. However, polyclonal antibodies are known to vary from batch to batch. C4d [A24-T] is a rabbit monoclonal antibody suitable for formalin-fixed paraffin-embedded tissues.