High-affinity receptors for human granulocyte macrophage colony- stimulating factor (GM-CSF), interleukin-3 (IL-3), and IL-5 are composed of two distinct subunits, alpha and beta. Each receptor has its own ligand-specific alpha subunit, and the three receptors share the common beta subunit, beta c. Using a transfectant of NIH3T3 cells expressing the high-affinity human GM-CSF receptor, monoclonal antibodies (MoAbs) against beta c were generated. These MoAbs specifically bound to cells bearing beta c and immunoprecipitated the beta c protein of 120 Kd. Using these MoAbs, expression of beta c was examined. It is known that IL-1 augments the proliferative response of a human factor-dependent hematopoietic cell line TF-1 to either GM-CSF, IL-3, or IL-5, and that it upregulates the high-affinity receptors for GM-CSF, IL-3, and IL-5. Antibody binding and immunoprecipitation demonstrated that IL-1 increased cell surface expression of beta c. This enhancement by IL-1 was accompanied by an increased level of beta c mRNA. In addition, we found that tumor necrosis factor-alpha (TNF- alpha) also increased the expression of beta c, although it did not augment the proliferative response of TF-1 to GM-CSF, IL-3, and IL-5.

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