IC3b

iC3b is a protein molecule that is used in medical research because of its ability to bind to specific target cells. This is useful for basic research, and in some cases it is possible to get the immune system to attack those cells, thus opening the possibility of new cancer treatments.

iC3b is a proteolytically inactive product of the complement cleavage fragment C3b that still opsonizes microbes, but cannot associate with factor B, thus preventing amplification of the complement cascade or activation through the alternative pathway.