Complement receptor 1-related gene/protein y (Crry) is a murine membrane protein that regulates the activity of both classical and alternative complement pathways. We used a recombinant soluble form of Crry fused to the hinge, CH2, and CH3 domains of mouse IgG1 (Crry-Ig) to determine whether inhibition of complement activation prevents and/or reverses mesenteric ischemia/reperfusion-induced injury in mice. Mice were subjected to 30 min of ischemia, followed by 2 h of reperfusion. Crry-Ig was administered either 5 min before or 30 min after initiation of the reperfusion phase. Pretreatment with Crry-Ig reduced local intestinal mucosal injury and decreased generation of leukotriene B(4) (LTB(4)). When given 30 min after the beginning of the reperfusion phase, Crry-Ig resulted in a decrease in ischemia/reperfusion-induced intestinal mucosal injury comparable to that occurring when it was given 5 min before initiation of the reperfusion phase. The beneficial effect of Crry-Ig administered 30 min after the initiation of reperfusion coincided with a decrease in PGE(2) generation despite the fact that it did not prevent local infiltration of neutrophils and did not have a significant effect on LTB(4) production. These data suggest that complement inhibition protects animals from reperfusion-induced intestinal damage even if administered as late as 30 min into reperfusion and that the mechanism of protection is independent of neutrophil infiltration or LTB(4) inhibition.