Differential expression of granulocyte-macrophage colony-stimulating factor and IL-3 receptor subunits on human CD34+...

Cytokines transduce their signals through specific receptors. Receptors for granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-3, and IL-5 share the common signal transducing subunit (beta c), whereas the alpha subunits function as specific ligand binding components. In this study we prepared specific mouse monoclonal antibodies against human GM-CSF receptor-alpha subunit (hGMR alpha) by immunizing mice with Ba/F3 cells transfected with hGMR alpha complementary DNA. Using these anti-hGMR alpha antibodies in combination with antibodies against IL-3 receptor-alpha (IL-3R alpha), beta c subunits, and c-kit, we examined expression patterns and modulation of these receptor subunits on several human hematopoietic cells, including CD34+ cells and leukemic cell lines. GMR alpha and IL-3R alpha were expressed on GM-CSF- and IL-3-responsive cell lines, such as TF-1 and UT-7, whereas the expression levels were much lower on UT-7E, a GM-CSF- and IL-3-unresponsive subline of UT-7. The GMR alpha subunit was expressed only on mature granulocytes and monocytes, and IL-3R alpha was expressed on monocytes but not on mature granulocytes, and none of these subunits were expressed on lymphocytes. For CD34+ cells, GMR alpha was expressed more abundantly on CD34+ CD33high cells than on CD34+ CD33low cells, whereas IL-3R alpha was expressed more abundantly on CD34+ CD33low cells than on CD34+ CD33high and CD34+ CD33neg cells. Slight but significant expression of the beta c subunit was detected on CD34+ cells. Expression of not only GMR alpha and IL-3R alpha subunits but also c-kit was specifically downregulated by 48-hour incubation with their respective ligands. Receptor transmodulation between GM-CSF, IL-3, and stem cell factor (or kit ligand) was not detected on CD34+ cells in 48-hour cultures. We also detected upregulation of these alpha subunits by IL-1 alpha and interferon-gamma on leukemic cell lines. Our study showed expression levels for each receptor subunit--including GMR, IL-3R, and c-kit on human bone marrow and peripheral blood cells and leukemic cell lines--and revealed differential regulation of the expression of the receptor subunits.