title: Characterization of three monoclonal antibodies to membrane co-factor protein (MCP) of the complement system and quantification of MCP by radioassay.
abstract: MCP is a widely distributed regulatory glycoprotein of the complement system which binds C3b and C4b and has factor I-dependent co-factor activity. Monoclonal antibodies raised to lymphocytes (E4.3), chorionic microvilli (GB24) and an embryonal carcinoma cell line (TRA-2-10) recognize MCP (CD46). GB24 inhibited both the binding of MCP to its ligand iC3 and co-factor activity; E4.3 and TRA-2-10 did not. The binding of GB24 to cells bearing MCP was not cross-inhibited by E4.3 or TRA-2.10, but TRA-2-10 blocked binding and displaced pre-bound E4.3. Using these antibodies, we developed a radioassay for quantifying the number of MCP molecules/cells. Human peripheral blood mononuclear (PBMC) and polymorphonuclear cells (PMN) had about 10,000 MCP cell; platelets had about 600/cell, and no MCP was found on erythrocytes. Neoplastic hematopoietic cell lines, of myelocytic and T lymphocytic origin, had several-fold more (20-60,000) molecules cell than peripheral blood cells or B cell lines (about 12,000). Malignant epithelial cell lines. HeLa (about 100,000/cell) and HEp-2 (about 250,000 cell) had the highest MCP expression of any cells examined. These monoclonal antibodies--especially GB24, which blocks MCP function--and the direct binding assay will facilitate the further analysis of the biology of this complement regulatory protein.
authors.affiliation: Howard Hughes Medical Institute, Washington University School of Medicine, St Louis, MO.
authors.forename: S W
authors.initials: SW
authors.lastname: Cho
authors.forename: T J
authors.initials: TJ
authors.lastname: Oglesby
authors.forename: B L
authors.initials: BL
authors.lastname: Hsi
authors.forename: E M
authors.initials: EM
authors.lastname: Adams
authors.forename: J P
authors.initials: JP
authors.lastname: Atkinson
mesh_terms: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; D003165:Complement System Proteins / Q000032:analysis*; D006801:Humans; D007457:Iodine Radioisotopes; D051916:Membrane Cofactor Protein; D008562:Membrane Glycoproteins / Q000032:analysis* / Q000276:immunology; D011233:Precipitin Tests
chemical_list: D000911:Antibodies, Monoclonal; D015703:Antigens, CD; C497857:CD46 protein, human; D007457:Iodine Radioisotopes; D051916:Membrane Cofactor Protein; D008562:Membrane Glycoproteins; D003165:Complement System Proteins