Patching and capping of LFA-1 molecules on human lymphocytes

The distribution and dynamics of LFA-I molecules over the surface of human lymphocytes were analysed using immunogold label-fracture and fracture-flip methods. Patching and capping were induced by incubation at 37-degrees-C with antibodies directed against the alpha and beta chains respectively of the heterodimeric LFA-1 molecule, and were followed by immunofluorescence. Treatment with 12-O-tetradecanoylphorbol-13-acetate (TPA) to link LFA-1 molecules to the cytoskeleton increased the percentage of capped cells, implying a faster and more efficient process of capping. At all times of clustering or upon phorbol ester treatment, the concentration of LFA-1 in patches and then in caps was not accompained by a parallel concentration of membrane particles on the freeze-fractured plasma membranes. Our results support the role of the cytoskeleton in regulating the capping phenomenon and in controlling the structural organization of the plasma membranes.