Mb1, a plasma membrane antigen selectively expressed by U-937 cells
A Biondi, JA Roach, JD Griffin and RF Todd
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.
Volume 66,
Issue 1,
pp. 135-142,
07/01/1985
Copyright © 1985 by The American Society of Hematology
