LFA-1 and L-selectin regulation of recirculating lymphocyte tethering and rolling on lung microvascular endothelium.

Recirculating lymphocytes migrate into areas of lung inflammation by binding to microvascular endothelium and transmigrating into extravascular tissue. In this report, we examined the multiple-step paradigm using a unique system: recirculating lymphocytes from sheep peripheral lymphatics adhering to activated lung microvascular endothelium in conditions of physiologic flow. Video microscopy demonstrated that recirculating lymphocytes formed abrupt adhesions, without requisite rolling, on the lung microvascular endothelial cells. Lymphocyte velocity was unchanged within 100 ms of the development of firm adhesions. To dissect the adhesion mechanism, the lymphocytes were pretreated with anti-LFA-1 or anti-L-selectin monoclonal antibody (mAb). Both mAb decreased the incidence of firm adhesions. The mechanism of this inhibition was investigated using time-lapse topographic reconstructions of cell movement after pretreatment with mAb. Time-lapse analysis of the movement of lymphocytes pretreated with anti-LFA-1 mAb suggested that abortive adhesion was manifested by a characteristic saltatory movement and a sustained reduction in cell velocity (rolling) to <25 microns/s. In contrast, abortive adhesions of lymphocytes pretreated with anti-L-selectin mAb demonstrated transient arrest (tethering) but minimal rolling before resumption of baseline velocity in the flow stream. These observations provide insights into selectin and integrin regulation of lymphocyte transmigration into the lung. Further, the results of mAb inhibition suggest that the mechanism of lymphocyte migration may have some unique features not observed in studies of neutrophil transmigration.