{"type":"root","children":[{"type":"paragraph","children":[{"type":"text","value":"Complement component 4, or C4, plays a central role in the complement system. C4d is the final proteolytic remnant of deposited C4b on endothelium and remains covalently attached to endothelium for little more than a week. It is easily detectable by immunohistochemistry. According to literature C4d expression is important in predicting kidney graft survival and likelihood of rejection."}]}]}