Terminal complement effectors in atypical hemolytic uremic syndrome: C5a, C5b-9, or a bit of both?

The role of the terminal complement pathway as the cause of atypical hemolytic uremic syndrome (aHUS) is widely recognized, but the relative contribution of the effectors C5a/C5aR1 and C5b-9 to disease pathogenesis has not been defined. Using FH^R/R mice carrying a factor H mutation that causes cell surface complement alternative pathway dysregulation, Ueda documented that in FH^R/R mice, C5b-9 causes renal thrombotic microangiopathy (TMA) whereas C5a/C5aR drives macrovascular thrombosis. This commentary addresses the implications and limitations of this study.