Human macrophage maturation and heterogeneity: Analysis with a newly generated set of monoclonal antibodies to differentiation antigens

Abstract

We have analyzed the expression of late differentiation antigens during terminal in vitro maturation of human macrophages (MØ) from blood monocytes (MO) in comparison to their distribution among mature MØ residing in various tissue sites. By immunizing mice with MØ derived from blood MO by culture on hydrophobic Teflon foils, monoclonal antibodies (mAbs) were developed (MAX.1, MAX.2, MAX.3, MAX.11) that reacted with lineage-restricted differentiation antigens. These antigens were expressed exclusively on MØ or were markedly increased after in vivo differentiation. The only overlap to another hemopoietic cell lineage was observed with MAX.3, which is shared by platelets and megakaryocytes. In the course of MØ maturation in vitro, the MAX.1 and MAX.3 antigens are detected within the cytoplasm two days before they appear on the cell surface. In contrast, the MAX.11 antigen is expressed simultaneously in the cytoplasm and at the cell surface, is found in varying degrees on a minor portion of blood MO and U937 cells, and is expressed rapidly at high density during early MØ differentiation in vitro. Among conventional mAbs that do not react with MO we found those against the transferrin (TF)-receptor, the BA-2, and the PCA1 antigen to label MØ. MØ matured in vivo and isolated from body fluids were positive with some but not all MAX mAbs. Distinctive patterns were observed with pulmonary MØ, exudate MØ from pleural and peritoneal effusions, synovial fluids, and early lactation milk. MØ from the alveolar space, for example, constantly expressed the MAX.2 antigen but not the MAX.3 antigen. Pleural effusion MØ, however, did not react with the MAX.1 mAb, but in most cases, it did react with the MAX.3 mAb. The detection of novel differentiation antigens, all expressed on monocyte-derived MØ but differently expressed on site-specific MØ in situ, underlies the remarkable heterogeneity among human MØ. The expression of these antigens is flexible because those MAX antigens that were not expressed in situ could be induced if cells from distinct tissue sites were cultured in vitro for several days. MAX mAbs may be of potential value to study both the sequential stages of maturation within the MØ lineage as well as differential developments induced by various culture conditions in parallel to environmental factors in vivo.