title: Mb1, a plasma membrane antigen selectively expressed by U-937 cells.
abstract: To examine the plasma membrane characteristics of an immature monocytic cell capable of proliferation, we have developed a murine monoclonal antibody that identifies an antigen, Mb1, found on the surface of U-937. In immunofluorescence analyses, Mb1 is not expressed by peripheral blood monocytes (freshly isolated, lymphokine-activated, or cultured for seven days), neutrophils, or any other circulating element. It is also absent on human bone marrow mononuclear cells, including the CFU-GM. Among a series of malignant cells from 50 patients with acute myeloid leukemia (including 22 with monocytic or myelomonocytic leukemia), no Mb1 expression was detected. Continuous human cell lines of B or T cell origin were also negative, as were the myeloid lines HL-60 and K562. Apart from U-937, which uniformly expresses Mb1 in high antigen density, only KG-1 (a myeloblastic line) exhibits Mb1 in low antigen density. Exposure of U-937 to phorbol diester (TPA) under conditions that induce features of macrophage differentiation (including the expression of Mo1) results in a significant reduction in Mb1 expression. Mb1 expression is also reduced as a result of culture of U-937 in medium containing anti-Mb1 antibody (antigenic modulation). On sodium dodecyl sulfate-polyacrylamide gel electrophoresis of radiolabeled immunoprecipitates, Mb1 appears to be a dimeric protein with an estimated molecular weight of 80 kd (43 kd under reducing conditions). Antigenic activity on U-937 is destroyed by treatment with trypsin or papain but is regenerated after 24 hours' culture in enzyme-free medium. Mb1 is a constituent plasma membrane protein of U-937, and its degree of expression relates to the state of cellular differentiation.
mesh_terms: D000911:Antibodies, Monoclonal; D000918:Antibody Specificity; D000936:Antigen-Antibody Complex; D000954:Antigens, Surface / Q000276:immunology*; D001853:Bone Marrow / Q000276:immunology; D002454:Cell Differentiation; D002460:Cell Line; D002462:Cell Membrane / Q000276:immunology; D006412:Hematopoietic Stem Cells / Q000276:immunology*; D006801:Humans; D007951:Leukemia, Myeloid / Q000276:immunology; D015470:Leukemia, Myeloid, Acute / Q000276:immunology; D009000:Monocytes / Q000276:immunology*; D010447:Peptide Hydrolases
chemical_list: D000911:Antibodies, Monoclonal; D000936:Antigen-Antibody Complex; D000954:Antigens, Surface; D010447:Peptide Hydrolases