title: Receptor patching and capping of platelet membranes induced by monoclonal antibodies.
abstract: Redistribution of glycoproteins (GP) Ib, glycocalicin, IIb, and IIIa on the surface of human platelets in response to stimulation with corresponding monoclonal antibodies (MoAb) and a polyclonal antiglycocalicin antibody was studied by immunofluorescence, immunoelectron microscopy, and a quantitative radioimmune assay. Immobilization of the antigens by prefixation with formaldehyde showed a uniform distribution over the surface of the platelet. Incubation of unfixed platelets with specific MoAb against various epitopes on GPIIb and/or IIIa resulted in a time-dependent patching, subsequent capping, and after prolonged exposure to the antibody/label complex, internalization of the complex, possibly by endocytosis. In contrast, GPIb could not be shown to cap. From these results we conclude that platelet GPIIb and/or IIIa undergo spatial rearrangement in a manner analogous to that observed in lymphocytes, whereas GPIb does not. Since both GPIb and GPIIb and/or IIIa seem to be transmembraneous GP associated with the cytoskeleton, a special, though unidentified, role of GPIIb/IIIa in the induction of lateral membrane mobility is postulated.
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology*; D001792:Blood Platelets / Q000276:immunology*; D004705:Endocytosis; D005404:Fixatives; D005455:Fluorescent Antibody Technique; D006023:Glycoproteins / Q000276:immunology*; D006046:Gold; D006801:Humans; D007152:Immunologic Capping; D007158:Immunologic Techniques; D008565:Membrane Proteins / Q000276:immunology*; D008854:Microscopy, Electron; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins
chemical_list: D000911:Antibodies, Monoclonal; D005404:Fixatives; D006023:Glycoproteins; D008565:Membrane Proteins; D019038:Platelet Glycoprotein GPIb-IX Complex; D010980:Platelet Membrane Glycoproteins; C023592:glycocalicin; D006046:Gold