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/cell. Human peripheral blood mononuclear (PBMC) and polymorphonuclear cells (PMN) had about 10000 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 (20–60000) molecules/cell than peripheral blood cells or B cell lines (about 12000). Malignant epithelial cell lines, HeLa (about 100000/cell) and HEp‐2 (about 250000/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.
|Number of pages||5|
|Journal||Clinical & Experimental Immunology|
|State||Published - Feb 1991|
- membrane co‐factor protein (CD46)