A novel monoclonal antibody, Mar 1, directed specifically against mononuclear phagocyte system cells in rats.

Three different monoclonal antibodies (mAb), designated Mar 1, Mar 2, and Mar 3, recognizing three distinct novel antigen molecules expressed preferentially in rat macrophages, were produced by the hybridoma technique. Binding of these mAb to isolated cells or fixed cells was detected by radioactive binding assay, immunohistochemical technique and flow cytometry. Mar 1 binds specifically to the cells constituting the mononuclear phagocyte system (MPS), but not to granulocytes nor endocytosis-positive cells from non-lymphoid tissues. Mar 2 and Mar 3 recognize both the former and the latter. The isotypes of Mar 1, Mar 2 and Mar 3 were defined as IgG1, IgG1 and IgG2b, respectively. These mAb were species specific, allo-non-specific and not cytotoxic for rat peritoneal macrophages. Immunoelectron microscopic observation demonstrated that Mar 1-3 antigens are located on both surface membrane and cytoplasmic membrane structures of peritoneal macrophages, particularly on the limiting membrane of phagocytic small vesicles and large phagosomes. Immunoprecipitation experiments demonstrated that the apparent molecular weights (MW) of the reactive antigens of Mar 1, Mar 2 and Mar 3 are 95,000, 100,000 and 55,000 and 27,000, respectively. These findings indicate that all of Mar 1-3 mAb have considerable value in the identification of rat phagocytes and that, of the three kinds of antigens detected with Mar 1-3, Mar 1 antigen is a specific marker for identification of the cells constituting the MPS and may offer the means to assess the functional capability and differentiation process of the macrophage populations.