Effect of IR injury on renal polymorphonuclear (PMN) cell infiltration. PMN infiltration was assessed by (A) measuring renal myeloperoxidase activity and (B) counting PMN cells on H&E-stained tissue sections of WT (n = 16), low-TF (n = 7), WT mice treated with hirudin (n = 7) and PAR-1^−/− (n = 16) mice undergoing 25 minutes of bilateral ischemia followed by 24 hours of reperfusion or WT mice undergoing sham surgery. WT mice undergoing IR had significantly increased MPO and PMN counts compared with sham-operated mice (*P < .001). Low-TF, WT mice treated with hirudin and PAR-1^−/− mice had significantly reduced renal PMN accumulation compared with WT (**P < .001). Data are expressed as mean ± SEM.