Isolation and immunocytochemical characterization of human bone marrow stromal macrophages in hemopoietic clusters.

Stromal macrophages (M phi) have been localized in situ and isolated within erythroid clusters from human marrow. Stromal M phi arborize in an extensive network uniformly distributed throughout marrow interstitium, and express the phenotype CD4+, CD11a+, CD11c+, CD13+, CD14+, CD16+, CD18+, CD31+, CD32+, FcRI+, HLA-DR+, and CD35-, transferrin receptor-negative, and CD11b (weak). They express endocytic receptor antigens, but show significant differences in myeloid antigen expression compared with freshly harvested or cultured monocytes. Human stromal M phi are therefore specialized mature marrow M phi that are accessible for further investigations in infectious, storage, or hemopoietic disorders.