Differentiation of human leukemic cell lines (HL60, U937) toward macrophages is accompanied by production of colony-stimulating activity (CSA).

Human macrophages have been shown to produce colony-stimulating activity (CSA), a glycoprotein capable of promoting the growth of granulocyte-macrophage colonies (CFU-GM) from target nonadherent human bone marrow cells (BM). Two human leukemic cell lines, HL60 (promyelocytic) and U937 (monocytic), that do not routinely produce CSA were studied. Induction of differentiation toward macrophages was followed by acquisition of new cell-surface antigenic determinants characteristic of normal monocyte-macrophages (Mo); this change was accompanied by CSA production. With two monoclonal antihuman-monocyte antibodies (OKM1 and 63D3) it was shown that unstimulated HL60 cells did not express these antigens, but 56% of the HL60-derived macrophages were positive for OKM1 and 51% for 63D3 antibody. Expression of the OKM1 antigen increased from 25% in the unstimulated U937 cells to 47% in the stimulated U937-derived macrophages. In addition, HL60- and U937-derived macrophages were found to produce CSA. This CSA has properties similar to those of the one produced by normal human Mo, in that it is heat labile and protease sensitive. The colonies produced by HL60 CSA were predominantly (68%) of the macrophage type.