Differential Roles of Selectins and the α₄-Integrin in Acute, Subacute, and Chronic Leukocyte Recruitment in Vivo

Adhesion blocking mAbs specific for rat P-, E-, and L-selectin and the α₄-integrin were used to characterize leukocyte recruitment mechanisms in models of LTC₄ (acute), LPS (subacute), and adjuvant-induced (chronic) inflammation. Intravital microscopy was employed to measure leukocyte rolling and adhesion in rat mesenteric venules. Superfusing the mesentery with 20 nM LTC₄ elicited an increase in leukocyte rolling (66.8 ± 3.8 vs 18.2 ± 3.2 cells/min control) that was completely eliminated by an anti-rat P-selectin mAb. Superfusion with 1 μg/ml LPS induced a significant increase in leukocyte rolling within 15 min (73 ± 8 vs 33 ± 6 cells/min control). Rolling increased further starting at 105 min and peaked by 150 min (141 ± 23 cells/min). LPS-induced leukocyte rolling was eliminated during the first 90 min by the P-selectin mAb. The later increase in leukocyte rolling was not prevented by a second treatment with P-selectin mAb or a function-blocking mAb against rat E-selectin. This later phase of leukocyte rolling was blocked by treatments with mAbs against either the α₄-integrin or L-selectin. Twelve days following Mycobacterium butyricum immunization, 300 to 500 rolling cells/min were observed. This could be reduced ∼50 to 60% by mAb against either the α₄-integrin or L-selectin. The combination of both mAbs eliminated ∼90% of rolling. Neither the P- nor E-selectin mAbs reduced rolling in this chronic inflammatory model. This study highlights differences in leukocyte adhesive mechanisms elicited by different stimuli and at different time points within the same vascular bed.