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.
Lateral mobility of class I histocompatibility antigens in B lymphoblastoid cell membranes: modulation by cross-linking and effect of cell density.
B E Bierer, S H Herrmann, C S Brown, S J Burakoff, D E Golan; Lateral mobility of class I histocompatibility antigens in B lymphoblastoid cell membranes: modulation by cross-linking and effect of cell density.. J Cell Biol 1 September 1987; 105 (3): 1147–1152. doi: https://doi.org/10.1083/jcb.105.3.1147
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