Expression of complement factor H on the cell surface of the human monocytic cell line U937.
Binding assays and immunocytochemical staining with monoclonal antibodies against the human serum complement protein factor H indicate that factor H antigen is present on the surface of more than 95% of the cells of the human monocytic cell line U937. The antigen is uniformly distributed and there are 10 000-15 000 copies/cell. Factor H antigen is strongly associated with the cell surface and is not removed by hypotonic or hypertonic washes. Factor H antigen has been isolated from surface radioiodinated and 35S biosynthetically labeled cells using polyclonal anti-factor H-Sepharose columns. The antigen is indistinguishable from serum factor H in molecular weight. Secretion of factor H by U937 cells was not detected using sensitive tests in which factor H secretion by monocytes was apparent. Phorbol myristate acetate stimulation of the cells had no effect on the average number of factor H molecules expressed. We conclude that factor H is synthesized by U937 cells, but is not secreted, and remains strongly associated with the cell surface. The surface-bound factor H may function as a C3b receptor.
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D000911:Antibodies, Monoclonal; D000954:Antigens, Surface / Q000032:analysis* / Q000096:biosynthesis / Q000276:immunology; D001666:Binding Sites, Antibody; D002457:Cell Extracts / Q000032:analysis; D002460:Cell Line; D003180:Complement C3b Inactivator Proteins / Q000032:analysis* / Q000096:biosynthesis / Q000276:immunology; D017242:Complement Factor H; D006801:Humans; D007124:Immunoenzyme Techniques; D009000:Monocytes / Q000276:immunology* / Q000378:metabolism; D013194:Staining and Labeling
D000911:Antibodies, Monoclonal; D000954:Antigens, Surface; C493495:CFH protein, human; D002457:Cell Extracts; D003180:Complement C3b Inactivator Proteins; D017242:Complement Factor H