title: Ligand binding by the p150,95 antigen of U937 monocytic cells: properties in common with complement receptor type 3 (CR3).
abstract: U937 cells (a monocytic cell line) grown in the presence of phorbol myristate acetate were surface labeled with 125I and the iC3b-binding proteins isolated by affinity chromatography on iC3b-Sepharose in the presence of divalent cations. Three polypeptides of 170, 150 and 95 kDa were found to bind specifically to iC3b-Sepharose. The polypeptides of 170 and 95 kDa were identified as the alpha and the beta subunits of CR3 by immunoprecipitation with OKM1 monoclonal antibody. The 150-kDa polypeptide was not immunoprecipitated by antibodies to the alpha subunit of CR3 or LFA-1. However, the 150-kDa polypeptide, together with the 95-kDa polypeptide, was immunoprecipitated with an anti-beta subunit-specific antibody IB4, which immunoprecipitates LFA-1, CR3 and p150,95. These results indicated that the 150-kDa polypeptide is the alpha subunit of the p150,95 antigen. The binding of p150,95 and CR3 to iC3b-Sepharose is specific as neither binds to C3u-Sepharose. A monoclonal antibody, 3.9, which immunoprecipitated the 150 and a 95-kDa polypeptide from U937 cells was characterized as being directed against the alpha-subunit of the p150,95 antigen. Phorbol myristate acetate-stimulated U937 cells from rosettes with EAC3b and EAiC3b but not with EAC3d cells. Monoclonal antibody 3.9 does not inhibit either type of rosetting, but we were unable to exclude a role for p150,95 in adherence of iC3b-coated particles. Since there is no rosetting with C3d-bearing particles it is unlikely that p150,95 is a receptor for C3d, a role for p150,95 which has been suggested by others (Wright, S.D., Licht, M.R. and Silverstein, S.C., Fed. Proc. 1984. 43: 413).
mesh_terms: D000911:Antibodies, Monoclonal / Q000276:immunology; D000954:Antigens, Surface / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D002460:Cell Line; D002846:Chromatography, Affinity; D003179:Complement C3b / Q000276:immunology / Q000378:metabolism; D006023:Glycoproteins / Q000276:immunology / Q000378:metabolism*; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1; D016177:Macrophage-1 Antigen; D008565:Membrane Proteins / Q000276:immunology / Q000302:isolation & purification / Q000378:metabolism*; D011951:Receptors, Complement / Q000032:analysis* / Q000378:metabolism; D012397:Rosette Formation; D013755:Tetradecanoylphorbol Acetate / Q000494:pharmacology
chemical_list: D000911:Antibodies, Monoclonal; D000954:Antigens, Surface; D006023:Glycoproteins; D008024:Ligands; D016169:Lymphocyte Function-Associated Antigen-1; D016177:Macrophage-1 Antigen; D008565:Membrane Proteins; D011951:Receptors, Complement; D003179:Complement C3b; D013755:Tetradecanoylphorbol Acetate