Velocity difference between l-selectfn and p-selectin dependent neutrophil rolling in venules of the mouse cremaster muscle

Leukocyte rolling is initially normal in L-selectin deficient mice (L-) and reduced at later times while in P-selectin deficient mice (P-), leukocyte rolling is initially absent, but induced within 60 min. of tissue trauma. This study uses intravital microscopy to investigate the velocity distribution of rolling leukocytes in the venules of the exteriorized cremaster muscle of wild type (wt) and P- and L-selectin deficient mice to examine the possibility that P- and L-selectin support rolling at different characteristic velocities. We measured the velocities of rolling leukocytes in 30 venules (diameter 25-40mm, blood flow velocity l-2.5mm/s, wall shear rate 400-800 s"1). Trauma-induced rolling in P-selectin deficient mice was found to occur at significantly higher velocities (I29±89mm/s) than in wild type mice (49±23mm/s) at time after exteriorization > 50 min. This rolling was L-selectin dependent since it could be blocked by L-selectin antibodies and E-selectin expression in the absence of TNF-a stimulation was minimal. In L-selectin deficient mice, rolling is completely P-selectin dependent and the distribution of rolling velocities is similar to wild type mice. In.addition, a small population of fast-rolling leukocytes occurred at 60 min. after exteriorization which was not seen in wild type mice. The histological investigation of Giemsa stained wholemount preparations of the cremaster muscle to differentiate the leukocytes present in the investigated venules revealed that the majority of rolling cells under all conditions studied were granulocytes (92% in wt, 91% in L-, 87% in P-). Thus, P-selectin efficiently mediates neutrophil rolling during early phase of rolling, while L-selectin can only produce more rapid rolling at later time periods. This early P-selectin dependent rolling is also consistent with our finding that P-selectin is expressed at high levels in venules of whole-mount mouse cremaster muscles within minutes after exteriorization. The P-selectin expression was seen using immunoperoxidase staining of the whole mount mouse cremaster muscles. We conclude that P-selectin is required for efficient leukocyte rolling in this model, and Lselectin can only mediate more rapid rolling.