Neutrophils are the cause of skin bleeding in thrombocytopenic and GPVI^−/− mice during the cutaneous rpA reaction. (A) Intravital microscopy imaging of the cutaneous rpA reaction in a thrombocytopenic mouse injected with rhodamine-6G for staining of leukocytes. Bright-field color image showing that bleeding originated from capillaries and postcapillary venules (left). Arterioles (A) and venules (V) were identified by whether they collected or distributed blood from/to lower caliber vessels. Merged image of bright-field and corresponding rhodamine-6G image showing that bleeding occurred from vessels in which leukocytes accumulated (white asterisks) (right). Scale bar, 200 µm. (B) Representative images of the inner layer of the skin subjected to the rpA reaction from control (100% platelets), thrombocytopenic (<3% platelets), GPVI^−/− mice, and thrombocytopenic and GPVI^−/− that were immunodepleted for neutrophils prior to the induction of the rpA reaction. Images were taken 4 hours after inducing the rpA reaction. (C) Hemoglobin content in skin biopsy specimens from control and rpA reaction areas from the various groups of mice, as indicated. n = 6-18 mice per group. # indicates a statistically significant increase (P < .05) in hemoglobin content as compared with control spots from control wild-type mice.