SPATIAL-DISTRIBUTION OF L-SELECTIN (CD62L) HUMAN-LYMPHOCYTES AND TRANSFECTED MURINE L1-2 CELLS

We have examined the topographical distribution of L-selectin on surfa ce membrane domains of human lymphocytes and murine L1-2 cells transfe cted to express human L-selectin. L-selectin was immunolocalized using murine monoclonal DREG 200 Fab antibody and a 12 nm colloidal gold-co njugated secondary antibody. Cell surface morphology and surface distr ibution of gold-labelled L-selectin were visualized using backscatter electron images obtained by high-resolution, field emission scanning e lectron microscopy. The topographical morphologies of lymphocytes of b oth types were complex. The surface of human lymphocytes was composed of both microvilli and ruffles; that of the murine cells was composed of long microvilli and few, if any, ruffles. L-selectin on human lymph ocytes was observed primarily as focal clusters on the apical surfaces of ruffles and microvilli. Similarly, on the transfected murine cells , L-selectin was detected predominantly on the apical surface of micro villi. We conclude that L-selectin has a common spatial distribution a nd clustered organization on all leukocytes examined to-date, and that these features of receptor expression likely facilitate rolling of ci rculating leukocytes on the endothelial surface.