P-selectin expression in arterioles and venules of mouse small intestine. Cryostat sections of intestinal specimens were incubated with a MoAb against P-selectin and stained using the peroxidase-antiperoxidase technique as described in the Materials and Methods. Counterstaining was performed using Mayer's hemalaun. In control animals (A, C, and E), P-selectin was weakly expressed by vascular endothelium of arterioles (C) and venules (E). In contrast, I/R (B, D, and F) markedly enhanced immunoreactivity for P-selectin in both arterioles (D) and venules (F). Formation of platelet aggregates, identified by an intense staining for P-selectin, was a prominent phenomenon after I/R (arrowheads). The magnification of the objective was 40× in (A) and (B) and 100× in (C) through (F), respectively.