41,42 Many studies have demonstrated that complement activation contributes to kidney MLN0128 clinical trial IRI.43–45 The mechanisms by which complement is triggered during IR and the effectors that are responsible for renal IRI remains to be fully elucidated, but loss or reduced function of complement regulators are likely to play a role. Accordingly, patients with one or more of their regulators deficient or defective may be at increased risk

of suffering from IRI. In a study of mice deficient in DAF and CD59, either alone or in combination, Yamada et al. have shown that both regulators are important in preventing catastrophic renal IRI.46 Thus, although DAF-deficient, but not CD59-deficient, mice were significantly more susceptible to renal IRI than wild-type mice, DAF/CD59 double deficiency caused a much greater degree of renal pathology

and functional impairment, suggesting that CD59 deficiency in the context of DAF deficiency exacerbated renal injury even though CD59 deficiency alone was inconsequential.46 One of the consequences of ischaemia may be cell membrane disruption, resulting in the transient find more loss of membrane regulators such as DAF and CD59. Both of these proteins attach to the cell membrane via a GPI anchor and are known to be capable of shedding from and reincorporating into the lipid bilayer of the cell membrane.47 Positional and functional disruption of transmembrane regulators may also occur as has been shown for mouse Crry during renal IR.48 It has been demonstrated that Crry, normally found on the basolateral side of

tubular cells along the basement membrane, was sequestered in the tubular lumen upon ischaemic insult, allowing increased complement deposition and injury on these cells.48 Additionally, changes in the cell membrane structural integrity and exposure of neoepitopes may alter the binding kinetics of the fluid-phase complement regulator fH, which can also impact on complement activation and renal IRI.49,50 Although both classical and lectin pathways have been implicated in IRI of other organs, likely through binding of natural antibodies and MBL to neoepitopes exposed on ischaemic cells, most animal modelling Ribose-5-phosphate isomerase studies in mice have suggested that renal IRI is mediated by the AP.43 Nevertheless, there is evidence that CP and MBL activation may be important contributors to IRI in some cases of transplant rejection as renal biopsies from these patients showed numerous deposits of C3d and C4d.51,52 Clinical studies have also shown that while injury can decrease complement regulation in some cells, there are cases where inhibitor expression actually increases in response to injury, which can offer enhanced protection from complement-mediated injury.53–56 A recent study with patients experiencing allograft rejection presented evidence that increased DAF expression correlated with increased allograft survival.