The monoclonal antibody ER-MP23 specifically reacts with the macrophage galactose-specific lectin (MGL), a 38 kDa single chain surface glycoprotein. MGL is found on murine mature macrophages in the connective tissue neighboring epithelia of e.g. salivary glands, capsule of lymph nodes, thymus and various other organs. MGL is present on the surface of connective tissue macrophages and their precursor cells in bone marrow. Also, MGL is expressed in macrophage cell lines (e.g. J774-1.6, RAW309Cr.1 and WR19M.1). Expression levels of MGL are increased in mature macrophages. The antigen is co expressed with the antigen recognized by monoclonal antibody BM8 (HM1066). The monoclonal antibody ER-MP23 has been raised after immunization of rats with mouse macrophage cell lines. Blocking studies demonstrated that the monoclonal antibody ER-MP23 is able to block mouse MGL.