A MONOCLONAL-ANTIBODY (ER-HR3) AGAINST MURINE MACROPHAGES .2. BIOCHEMICAL AND FUNCTIONAL-ASPECTS OF THE ER-HR3 ANTIGEN

We describe the purification and intracellular distribution of an anti gen present on a subpopulation of murine macrophages and recognized by monoclonal antibody ER-HR3 against bone marrow-derived haemopoietic r eticulum cells. Using the ER-HR3 antibody as an immobilizing ligand, t wo proteins were isolated as determined by SDS polyacrylamide gel elec trophoresis. Under non-reducing conditions, there was a major band wit h an apparent molecular mass of 69 kDa and a minor band of 55 kDa. Und er reducing conditions, the apparent molecular mass of each band was e stimated as 76 kDa and 67 kDa, respectively. Intracellularly, these pr oteins occurred in close association with membranous structures, as de monstrated with gold-labelled protein A in an electron-microscopic stu dy of the ER-HR3-positive cell line AP284. Some of the antigen was pre sent in vesicles. To gain further insight into the possible function o f the ER-HR3 antigen, its tissue distribution was investigated under d istinct experimental conditions. In mice infected with Bacillus Calmet te Gurerin, ER-HR3-positive cells were observed in many, but not all, granulomata of the spleen, the lung and the liver. The ER-HR3 reactivi ty in these mice clearly differed from that of other antimacrophage mo noclonal antibodies, such as F4/80, M5/114 and M1/70. Furthermore, phe nylhydrazine-induced extramedullary erythropoiesis in the liver was ac companied by ER-HR3 expression on a subpopulation of macrophages. Fina lly, the addition of ER-HR3 to an antigen-specific T cell proliferatio n assay did not inhibit T cell proliferation.