Abrogation of cell rolling by IM7 is dependent on leukocyte CD44 and requires CD44 cross-linking. (A) The graph shows the changes in the frequency of rolling leukocytes in synovial venules of CD44 KO mice (○, full CD44 KO), or of chimeric mice lacking CD44 in leukocytes (, Leuko CD44 KO) or in endothelial cells (●, Endo CD44 KO) after IM7 (200 μg) injection. Results are expressed as ratios of changes in leukocyte rolling frequency over time in mice treated with IM7 relative to rat IgG-treated controls (n = 8 mice/treatment group, *P < .05). (B) Comparison of the effects of (●) whole IM7 antibody and its (□) F(ab′)₂ or (▽) Fab fragments on leukocyte rolling in WT mice. IVM records were made before and up to 30 minutes after injection of antibodies (200 μg each). For secondary cross-linking of CD44, goat anti–rat IgG (GAR; 100 μg) was administered intravenously at 25 minutes. , GAR alone served as a negative control. Results are expressed as ratios of changes in cell rolling, as described for panel A (n = 5 mice/group).