Monocytic origin of the human hematopoietic cell line U‐937 and its convertibility to macrophages evidenced by isoenzyme mapping

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Abstract
U-937 represents a well established permanent human hematopoietic cell line. Electron microscopical and enzyme cytochemical studies as well as the analysis of surface glycoproteins have provided ample evidence for the monocytic origin of U-937. Upon stimulation with the tumour promotor 12-O-tetradecanoylphorbol-13-acetate (TPA), U-937 cells evolve into macrophage-like cells with phagocytic capacities. Since human blood monocytes (BM) are characterized by five acid esterase (AcE; EC 3.1.1.6) isoenzymes which are cell-specific in terms of isoelectric points (pi) and antigenicity, attempts were made in the present study to identify identical isoenzyme patterns in non- and TPA-stimulated U-937 cells. BM, cultured BM, non- and TPA-stimulated U-937 cells, as well as samples of resident human peritoneal macrophages (PM) as clearly-defined functional derivatives of BM, were subjected to isoenzyme analysis using isoelectric focusing (IEF). The five monocyte specific isoenzymes of AcE were identified in both populations of U-937. TPA-stimulated samples showed two additional bands, identical to those appearing in cultured BM after 4 days of glass-adherence and characteristic of resident human PM. Antisera raised against AcE of BM immunoprecipitated the two additional isoenzymes of TPA-stimulated U-937. It is concluded (1) the isoenzyme mapping of AcE documents the monocytic origin of U-937. (2) TPA-stimulation caricatures transformation of BM into resident tissue macrophages as far as pure morphology and AcE isoenzyme patterns are concerned. Thus, AcE isoenzyme mapping is apt for establishing reproducible and standardized criteria of different activation/differentiation states within the monocyte-macrophage lineage.