ANCAs induce postcapillary venular hemorrhage. Intravital microscopy was performed on WKY rats 6 to 7 weeks after immunization with hMPO (EAV rats) or HSA (control rats) (C) or on naive WKY rats with infusion of ANCA-rich or ANCA-negative Ig (D). A representative macroscopic image of petechiae around a mesenteric arcade is shown in panel A (× 4; image captured with a Canon IXUS 400; Canon, Tokyo, Japan). The microscopic appearance of this is shown in panel B (H&E stain, UplanApo 20×/0.70 NA). In the active immunization model (C), superfusion with 3 × 10^-9 M CXCL1 was maintained for 90 minutes, and hemorrhage was quantified by expressing the number of hemorrhagic venular segments as the percentage of total segments studied at each time point. The data represent the median, interquartile range (box), and range (error bars, n = 11 in control group and 13 in EAV group). Of note, although minor degrees of hemorrhage were seen in the control group, the median remained at zero throughout the experiment. In the passive transfer model (D) superfusion fluid was changed in some experiments from Tyrode solution to CXCL1 30 minutes after Ig infusion, and hemorrhage was quantified after a further 90 minutes using a global mesenteric visual/analog score (n = 4-10 separate rats in each group). Statistically significant differences between groups of rats are shown by asterisks, ^*P < .05. Data in panels C and D are mean ± SEM.