CD99 deficiency impairs leukocyte adhesion and extravasation in the inflamed cremaster. (A-D) WT mice (red bars) and CD99^−/− mice (blue bars) were analyzed by intravital microscopy of cremaster tissue after 2 hours of TNF-α stimulation for (A) rolling flux fraction, (B) rolling velocity, (C) adherent leukocytes, and (D) extravasated leukocytes. Results are displayed as mean ± standard error of the mean (SEM) for 5 animals per group (n = 34 for WT and n = 39 for CD99^−/− mice, with n being the number of vessels). **P < .01 and ***P < .001 (supplemental Table 1 shows hemodynamic parameters). (E-F) Confocal intravital microscopy of the cremaster of Ly-EGFP bone marrow–transplanted WT and CD99^−/− mice, stimulated intrascrotally with 500 ng of TNF-α for 90 minutes, followed by intravenous injection of Alexa 555–coupled PECAM monoclonal antibody, and captured in 30-minute videos. The tracking tool in the Imaris software (Bitplane) was used to determine (E) duration of intraluminal crawling and (F) transendothelial migration (minutes:seconds) in WT (red) and CD99^−/− (blue) mice. Results are displayed as mean ± SEM (n = 8 WT mice, leukocytes = 18; n = 7 CD99^−/− mice, leukocytes = 13). Not significant (n.s.), as per Student t test. (G) Chemokine-driven arrest of leukocytes in postcapillary venules of the cremaster was analyzed in WT mice (red dots) and CD99^−/− mice (blue dots). Videos were made 15 seconds before and every minute from 1 to 15 minutes after injection of CXCL1 (600 ng) into the carotid artery. Data are shown as mean ± SEM (n = 5 WT mice; n = 6 CD99^−/− mice). *P < .05 and ***P < .001; n.s. as per Student t test.