ULTRASTRUCTURAL EVIDENCE OF DISTINCTIVE BEHAVIOR OF L-SELECTIN AND LFA-1 (ALPHA(L)BETA(2) INTEGRIN) ON LYMPHOCYTES ADHERING TO THE ENDOTHELIAL SURFACE OF HIGH ENDOTHELIAL VENULES IN PERIPHERAL LYMPH-NODES

Using an immunoelectron microscopic technique, we demonstrated the dis tinctive localization of L-selectin, alpha(L) and beta(2) integrins (L FA-I) on lymphocytes adhering to high endothelial venules (HEVs) of pe ripheral lymph nodes. Immunogold staining clearly demonstrated the pre ferential localization of L-selectin on the faintly adherent microvill i to endothelial surfaces. Often, the particles of L-selectin were fou nd around those microvilli with a dispersed distribution. Examination by antibody-coated latex beads showed that the localization of L-selec tin was not restricted to the lymphocyte surface but also found on end othelial cells. These data suggest the molecular shedding from lymphoc ytes and its transfer to the HEV surface as the 'molecular footprints' of rolling cells. Concomitant with the dispersion of L-selectin, the gold particles of alpha(L) and beta(2) integrins showed significant ca pping and clustering images on the adherent border of lymphocytes. Thi s redistribution of LFA-1 may be important for inducing the transition of the molecule into the active state to facilitate effective binding to its endothelial ligands. These morphological findings revealed the characteristic behavior of L-selectin and LFA-1 on lymphocytes, and t hey confirm their respective molecular roles in the current adhesion c ascade model between lymphocytes and HEVs.