A MONOCLONAL-ANTIBODY (ER-HR3) AGAINST MURINE MACROPHAGES .1. ONTOGENY, DISTRIBUTION AND ENZYME-HISTOCHEMICAL CHARACTERIZATION OF ER-HR3-POSITIVE CELLS

We describe ER-HR3, a monoclonal antibody directed against bone marrow -derived haemopoietic reticulum cells. ER-HR3-positive cells have the electronmicroscopic and enzyme-histochemical characteristics of macrop hages. Additionally, they are able to phagocytoze. The ER-HR3 antigen is expressed by a majority of blood monocytes and is present on a subp opulation of resident macrophages in multiple organs. ER-HR3-positive cells are abundant in the bone marrow, the splenic red pulp, the mesen teric lymphoid paracortex and the interfollicular areas of the Peyer's patch. Few ER-HR3-positive cells have been observed in the thymic cor tex and the connective tissues of the gastro-intestinal tract, the der mis and the renal medulla. Moreover, epidermal Langerhans cells expres s the antigen. No cross-reactivity with other cell types has been foun d. It is concluded that ER-HR3 has a unique distribution pattern disti nct from other macrophage-specific antibodies.