Abstract
Mitogen-stimulated mononuclear blood cells produce differentiation-inducing factors (DIFs) for the human myeloid leukemia cells. We report here that human fibroblasts also produce a DIF distinguished from leukocyte DIFs. WI-38, a human diploid cell line derived from fetal lung, was used for preparing fibroblast conditioned medium (FCM) . Differntiation inducing activity in the FCM was assayed by determining several differentiation. associated properties of U937, a human monoblastic leukemia cell line derived from a patient with hystiocytic lymphoma. FCM induced NBT reducing activity and phagocytic activity, and the differentiated cells were classified as macrophage-like by morphology and lineage-specific a-naphthyl acetate esterase stain. The factor in FCM was stable at pH 2, at 70°C for 30 min and sensitive to trypsin digestion. The molecular weight was approximately 80, 000 by the analysis of gel filtration, Factor (s) in FCM induced NBT reducing activity remarkably of monocytic leukemic lines, but was almost ineffective on myeloid leukemic lines. These results suggest that fibroblasts produce a proteinaceous factor which induces differentiation of monoblastic leukemia cells to monocyte/macrophage lineage.
