Phenotypic analysis of human bone marrow macrophages.

Bone marrow macrophages have been isolated for phenotypic analysis by their ability to bind erythroblasts in erythroid clusters. In situ, when labeled for CD68 antigen, they are seen to form an arborizing network uniformly distributed throughout the hemopoietic marrow. Marrow macrophages isolated within erythroid clusters are acid phosphatase and alpha-naphthol butyrate esterase positive. Immunophenotypically, they are highly reactive for CD4, phagocytic receptors FcRI, II, and III, for HLA-Dr and CD31, as well as for the integrins CD11a, CD11c, and CD18, but negative for CD35 and transferrin receptor epitopes. Comparison of their phenotype with blood monocytes and cultured macrophages reveals significant differences, which indicate that marrow macrophages are specialized, differentiated mononuclear phagocytes that selectively associate with developing erythroblasts.