A significant decrease in leukocyte rolling velocity and increased adhesion of Adam17^−/− leukocytes in vivo may contribute to their accelerated neutrophil emigration in the peritonitis model. (A) To investigate possible mechanisms involved in the accelerated neutrophil influx, leukocyte rolling velocity was analyzed by intravital microscopy of the exteriorized cremaster muscle of Adam17-null and WT chimeras. The cumulative frequency of velocities of rolling leukocytes in Adam17^−/− (▵) and Adam17^+/+ (●) chimeras demonstrated a significant reduction in rolling velocity in vivo in Adam17-null chimeras (P < .05). Rolling velocities of at least 75 cells per group (n ≥ 4 mice) were measured. (B) Addition of a hydroxamate metalloproteinase inhibitor diminished the rolling velocity in WT chimeras; however, the inhibitor had no effect on rolling velocity of Adam17^−/− chimeras. To model the inflammatory response, TNF-α was administered 2 hours before intravital microscopy and the cumulative frequency of leukocyte rolling velocity was determined (C). (D) Leukocyte rolling velocity was also determined for Adam17^+/+ and Adam17^−/− chimeras in the presence of Fab fragments of L-selectin antibody MEL-14. The presence or absence of L-selectin MEL-14 Fab fragments was also used to analyze the rolling flux fraction (the number of rolling leukocytes as a fraction of total leukocytes flowing through the venule/unit time; *P = .01 relative to Adam17^+/+ chimeras and P = .02 relative to Adam17^−/− chimeras with MEL-14; E), and adhesion for Adam17^+/+ and Adam17^−/− chimeras (**P < .0001 relative to all other parameters; F). (G) Leukocyte extravasation was investigated using reflected light oblique transillumination microscopy. Emigrated cells were determined in an area reaching out 75 mm to each side of the vessel over a distance of 100-mm vessel length (***P = .0002). Data in panels B, E, F, and G are expressed as means ± SD.