Ki-M2R, a new specific monoclonal antibody, discriminates tissue macrophages from reticulum cells and monocytes in vivo and in vitro.

Utilizing rat peritoneal macrophages as the immunogen, a new monoclonal antibody enabling differential monitoring of the mononuclear phagocyte system (MPS) by immunohistochemistry has been raised. Designated Ki-M2R, this antigen could be detected with the immune alkaline phosphatase reaction on all macrophages including those of bone marrow, lymphatic sinuses, lymphoid follicles, splenic red pulp, and von Kupffer cells of the liver, as well as on macrophages of connective tissue, renal interstitial tissue, serous cavities, and gastrointestinal tract. Langerhans cells--the MPS-derived reticulum cells of the epidermis--interdigitating reticulum cells, and dendritic reticulum cells of lymphoid follicles were invariably negative. Blood monocytes were rendered positive only after evolving into macrophages upon appropriate stimulation. Thus, Ki-M2R selectively labels monocytes after transformation into macrophages.