A monoclonal antibody, RbM2, specific for a lysosomal membrane antigen of rabbit monocyte/macrophages.

An anti-macrophage monoclonal antibody (mAb), RbM2, was produced using thioglycolate-elicited rabbit peritoneal macrophages as immunogen. The immunohistochemical approach revealed an intense reactivity of this mAb to macrophages, particularly those engaged in phagocytosis, in different organs and tissues, and to peripheral blood monocytes. Immunoelectron microscopy demonstrated reaction products of RbM2 in the lysosomes of macrophages and monocytes. This selective reactivity with the mAb was further confirmed in various experiments by endocytosis of Latex particles with different diameters or IgG-coated sheep erythrocytes. The results indicate that RbM2 recognizes a lysosomal membrane antigen of 50,000 molecular weight (MW). In contrast, dendritic cells, such as follicular dendritic cells (FDC) of lymphoid follicles, interdigitating cells (IDC) of lymphoid T zones, or epidermal Langerhans' cells, were not reactive with the antibody. Thus, RbM2 is useful not only in differentiating the phagocytic macrophages from the immunologically accessory dendritic cell populations but also in identifying lysosomes and their related structures in macrophages.