EXPRESSION AND FUNCTION OF THE HUMAN GRANULOCYTE-MACROPHAGE COLONY-STIMULATING FACTOR-RECEPTOR ALPHA-SUBUNIT

To determine the expression and function of the granulocyte-macrophage colony-stimulating factor (GM-CSF) receptor alpha chain (GMR alpha) d uring hematopoiesis and on leukemic cells, monoclonal antibodies were raised by immunizing mice with cells expressing high levels of human G MR alpha. A pool of five antibodies isolated from three different mice was used to characterize GMR alpha. This antibody pool (anti-GMR alph a) immunoprecipitated a protein with the expected molecular weight of GMR alpha from COS cells transiently transfected with the GMR alpha ge ne. In factor-dependent cells, GMR alpha existed as a phosphoprotein, However, its phosphorylation was not stimulated by the presence of GM- CSF, Anti-GMR alpha inhibited the GM-CSF-dependent growth of cell line s and normal bone marrow cells and inhibited the binding of iodinated GM-CSF to its receptor, Cell surface expression of GMR alpha was exami ned using anti-GMR alpha and flow cytometry. GMR alpha was readily det ectable on both blood monocytes and neutrophils. In adherence-depleted normal bone marrow, two separate populations expressed GMR alpha. The most positive cells were predominantly macrophages, whereas the cells that expressed less GMR alpha were largely myelocytes and metamyelocy tes, A small population of lin(-)CD34(+) or CD34(+)CD38(-) cells also expressed GMR alpha, but they were not capable of significant growth i n colony-forming assays. In contrast, the majority of lin(-)CD34(+) an d CD34(+)CD38(-) cells were GMR alpha(-), yet they produced large numb ers of myeloid and erythroid colonies in the same assay. Malignant cel ls from patients with leukemia were also tested for GMR alpha expressi on, All of the myeloid leukemias and only rare lymphoid leukemias surv eyed tested positive for GMR alpha. These results show that anti-GMR a lpha is useful for the functional characterization of the GMR alpha an d for the detection of myeloid leukemia and that GMR alpha is expresse d on certain lineages throughout hematopoietic development; however, p rogenitors that express the receptor may have a reduced capacity to pr oliferate in response to hematopoietic growth factors. (C) 1994 by The American Society of Hematology.