Unrestricted C3 activation occurs in Crry-deficient kidneys and rapidly leads to chronic renal failure.

Deficiency of the C3 convertase regulator Crry is embryonic lethal in mice unless C3 also is absent. For evaluation of the effect of local kidney Crry deficiency in the setting of an intact complement system, Crry(-/-)C3(-/-) mouse kidneys were transplanted into syngeneic C57BL/6 wild-type mice. These Crry-deficient kidneys developed marked inflammatory cell infiltration, tubular damage, and interstitial fibrosis, whereas similar changes were absent in control transplanted kidneys. Strong C3 deposition in the vessels and tubules that correlated significantly with measures of disease supported that complement activation was pathogenic in this model. Microarray studies showed upregulation of a number of chemokine and extracellular matrix genes, which were validated for CCL2 and CXCL10 mRNA and collagen III protein. The functional significance of these pathophysiologic findings was evaluated by removing both native kidneys, so the transplanted kidney alone provided renal function. Within 21 d of transplantation, seven of eight Crry-deficient kidneys in complement-sufficient wild-type hosts failed, compared with two of 13 controls (P = 0.001), with final blood urea nitrogen levels of 133.9 +/- 33.0 and 55.6 +/- 8.3 mg/dl, respectively (P = 0.015). These data show that mouse Crry is a critical complement regulator in the kidney. When absent, unrestricted complement activation occurs and quickly leads to marked inflammation and progressive renal failure, with features relevant to human diseases with underlying defects in complement regulation, such as hemolytic uremic syndrome.