MUM-4, A MONOCLONAL-ANTIBODY REACTING WITH RESIDENT PERITONEAL MOUSE MACROPHAGES

A new rat monoclonal antibody, MUM-4, which recognizes a murine antige n/epitope that is absent on monocytes, strongly expressed on resident peritoneal macrophages and almost completely absent from peritoneal ma crophages 4 days after an intraperitoneal injection of thioglycollate or heat-killed Propionibacterium acnes organisms, is described. Immuno cytochemistry and flow cytometry have been used to characterize the sp ecificity of the antibody. MUM-4 did not react with blood granulocytes , peritoneal exudate granulocytes, lymphocytes from blood or peritoneu m, isolated spleen dendritic cells, or veiled cells from the thoracic duct of mesenteric lymphadenectomized mice. The MUM-4 antibody reacted with resident peritoneal macrophages from all the mouse strains studi ed. MUM-4 appears to represent a new specificity. The MUM-4 antibody i s of the rat IgG2c isotype and exhibits complement-mediated cytotoxici ty with rabbit complement. The staining achieved with MUM-4 by FACS or immunocytochemical methods is intense on most resident peritoneal mac rophages and the antibody should be a valuable addition to the panel o f monoclonal antibodies available for studies on mouse macrophages.