Changes of cellular markers during differentiation of HL-60 promyelocytes to macrophages as induced by T lymphocyte conditioned medium

Human promyelocytes from a cell line HL-60 of acute promyelocytic leukemia origin were examined in suspension culture in response to conditioned medium (CM) derived from allogeneic lymphocyte or phytohemagglutinin (PHA) stimulated lymphocytes. Within 24 h of exposure to CM, some cells became adherent and aggregates of cells were seen in suspension. A reduction in proliferating cells in suspension occurred, as detected by cell cycle analysis using flow cytometry. The total cellular RNA content was then reduced as determined through simultaneous fluorescence measurement of the DNA and RNA content of single cells. The cells subsequently developed a monocyte-macrophage morphology correlating with the decrease in RNA content. By day six to eight of incubation with CM, almost all the cultured cells were macrophage-like. During this development, the proportion of cells possessing complement receptors became maximal and the reactivity with alphanapthyl esterase staining and the phagocytic capacity were acquired. From these cellular changes, we can infer that the interaction between the inducer and the promyelocytes resulted in suppression of DNA replication with the parallel induction of differentiation. Activated T lymphocytes were demonstrated to be important in providing the maturation inducer. The interaction between lymphoid and promyelocytes in differentiation is discussed.