Leukocyte-endothelium interactions in arthritic mouse ankle synovium are differentially affected by CD44 deficiency and anti-CD44 (mAb IM7) treatment. In comparison with WT mice (■), CD44 KO mice (□) showed (A) significantly elevated rolling cell number, (B) comparable rolling velocity, and (C) significantly reduced number of firm adherent cells (n = 22 mice/genotype, *P < .05). (D-F) Immediate effects of (D) rat IgG (control) and (E) anti-CD44 (IM7) treatment on the (●) frequency of rolling leukocytes, (○) rolling velocity, and (▲) adherent cell number, in the synovial venules. IVM videos were recorded before (0 minutes, baseline) and at the indicated time points after intravenous injection of rat IgG or IM7 (both at 200 μg). Results are expressed as percentage change (mean ± SE) relative to baseline (100%; n = 8 mice/group, *P < .05). IM7 treatment had reduced the number of rolling cells so drastically that the rolling velocity could not be determined. (F) IVM snapshots of fluorescent leukocytes before (0 minutes, baseline; left) and 5 minutes (right) after injection of IM7. Arrows point to bright rolling cells that appear before (left), but not after (right) IM7 injection. Dotted lines encircle adherent cells that underwent a change in morphology, ie, exhibited a “hairy” (“disheveled”) appearance after IM7 administration.