Complement polymorphisms in kidney transplantation: critical in graft rejection?

The complement system, as part of the innate immune system, plays an important role in renal transplantation. Complement is involved in the protection against foreign organisms and clearance of apoptotic cells but can also cause injury to the renal allograft, for instance, via antibody binding or in ischemia–reperfusion injury. Numerous polymorphisms in complement factors have been identified thus far; some of them result in different functionalities or alter complement levels. In this review, we provide an overview of the literature on the role of complement polymorphisms in renal transplantation. Furthermore, we discuss functional complement polymorphisms that have not yet been investigated in kidney transplantation. By investigating multiple polymorphisms both in donor and recipient at the same time, a complotype can be constructed. Because the combination of multiple polymorphisms is likely to have a greater impact than a single one, this could provide valuable prognostic information.