Human mononuclear phagocyte differentiation: a study of the U-937 cell line by ultrastructural cytochemistry and surface antigen analysis.

U-937 represents a well-established permanent human haematopoietic cell line, which exhibits characteristics of the monocyte/macrophage series. U-937 cells were investigated by peroxidase ultrastructural cytochemistry in order to determine the normal developmental stage to which they correspond. This study was performed in non- and TPA-stimulated cells, in conjunction with surface analysis by monoclonal antibodies. It is concluded: (1) peroxidase-positive U-937 cells are monoblasts and promonocytes involved in myeloperoxidase synthesis; (2) TPA-stimulation caricatures transformation of these cells into monocytes but not into resident macrophages, as far as peroxidase cytochemistry is concerned; (3) the reactivity of myeloperoxidase present in the endoplasmic reticulum of synthesizing cells is inhibited by glutaraldehyde fixation.