Complement—here, there and everywhere, but what about the transplanted organ?

• Importance of peripheral and central complement.
• Complement in Ischaemia-Reperfusion Injury in Kidney Transplantation can be targeted.
• Modulation of complement and its regulators affect rejection and induction of tolerance in kidney transplant recipients.
• New complement therapeutic agents and Biomarkers are changing the field.

The part of the innate immune system that communicates and effectively primes the adaptive immune system was termed “complement” by Ehrlich to reflect its complementarity to antibodies having previously been described as “alexine” (i.e protective component of serum) by Buchner and Bordet. It has been established that complement is not solely produced systemically but may have origin in different tissues where it can influence organ specific functions that may affect the outcome of transplanted organs. This review looks at the role of complement in particular to kidney transplantation. We look at current literature to determine whether blockade of the peripheral or central compartments of complement production may prevent ischaemic reperfusion injury or rejection in the transplanted organ.We also review new therapeutics that have been developed to inhibit components of the complement cascade with varying degrees of success leading to an increase in our understanding of the multiple triggers of this complex system. In addition, we consider whether biomarkers in this field are effective markers of disease or treatment.