title: Lateral mobility of class I histocompatibility antigens in B lymphoblastoid cell membranes: modulation by cross-linking and effect of cell density.
abstract: We have studied the lateral mobility of class 1 major histocompatibility complex (MHC) proteins in the membranes of human Epstein-Barr virus-transformed B cells using fluorescence photobleaching recovery. Class I MHC antigens were labeled with either W6/32 monoclonal antibody or its Fab fragment directly conjugated to fluorescein isothiocyanate. The diffusion coefficient of class I antigens labeled with Fab fragments of W6/32 was identical to that of a lipid analogue, fluorescein phosphatidylethanolamine, and was 10-fold greater than that of antigens labeled with intact W6/32. Furthermore, antigens labeled with Fab fragments but not with intact W6/32 had fractional mobilities identical to that of the lipid probe. The lateral mobility of class I antigens was dependent on the time of incubation with fluorescent antibody and on the presence of antibody microaggregates. Finally, class I MHC proteins labeled with intact W6/32 but not with Fab fragments were immobilized in the membranes of most cells grown in suspension at high cell density. These results suggest that, in the unperturbed state, class I MHC antigens diffuse as rapidly as membrane lipid, i.e., without cytoskeletal constraint. Cross-linking with bivalent ligand and growth to high cell density may trigger membrane events leading to slowing and immobilization of these proteins.
mesh_terms: D000911:Antibodies, Monoclonal / Q000302:isolation & purification; D001402:B-Lymphocytes / Q000276:immunology*; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology; D004058:Diffusion; D016650:Fluorescein-5-isothiocyanate; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006680:HLA Antigens / Q000276:immunology; D006801:Humans; D013861:Thiocyanates
chemical_list: D000911:Antibodies, Monoclonal; D005452:Fluoresceins; D005456:Fluorescent Dyes; D006680:HLA Antigens; D013861:Thiocyanates; D016650:Fluorescein-5-isothiocyanate