Kinetics of inflammatory bleeding in thrombocytopenic mice during reverse passive Arthus reaction. (A) Photographs of progressing rpA in the dorsal skinfold chamber. In the absence of platelets, petechial bleeding was clearly visible after 2 hours and increased with time. In nondepleted animals there were virtually no petechial spots. Window diameter was 12 mm. (B) Microscopic view of the progressing rpA in a thrombocytopenic mouse. Petechial bleeding was detected at 20 minutes, with further growth of the spot at 40 minutes. Bar = 200 μm. (C) Petechial spots visible to the eye (∼ 100 μm) were counted during rpA in thrombocytopenic and control animals. The difference in incidence of petechiae became statistically significant within 1 hour (P < .01; n = 4). At t = 4 hours, the petechiae became confluent, impairing quantification. Error bars represent SEM.