Expression and modulation of cellular receptors for interferon-gamma, tumour necrosis factor, and Fas on human bone marrow CD34+ cells.

Interferon-gamma (IFN-gamma), tumour necrosis factor-alpha (TNF-alpha) and Fas-ligand can mediate potent inhibitory signals in haemopoietic cells. Clinical and laboratory studies have suggested the involvement of these cytokines in the regulation of normal haemopoiesis and in the pathophysiology of bone marrow (BM) failure syndromes. As the effects of cytokines may also be regulated at the cellular receptor level, we studied the expression and modulation of TNF receptor (TNFR), IFN-gammaR and Fas-R on haemopoietic progenitor cells. In freshly isolated BM, using flow cytometry, TNFR1 (p55), TNFR2 (p75), IFN-gammaR, and Fas-R were detected on 5-12% of mononuclear cells. Two-colour staining showed comparable receptor expression on a CD34+ population, which includes haemopoietic progenitor and stem cells. Using reverse transcriptase-PCR (RT-PCR) transcription of mRNA coding for these receptors was demonstrated in fresh, highly purified CD34+ cells. These findings indicate that the effects of these factors on progenitor cells may be directly mediated. In cultured BM cells, expression of TNFR1 was not influenced by IFN-gamma, TNF-alpha or apoptosis-inducing anti-Fas monoclonal antibody (mAb). IFN-gamma decreased CD34+ cell TNFR2 expression. CD34+ cell Fas-R expression was increased by IFN-gamma and TNF-alpha. IFN-gammaR expression was enhanced by anti-Fas mAb and to lesser degree with TNF-alpha. Similar results were obtained with RT-PCR analysis in cultured CD34+ cells. Potentiation of anti-Fas mAb-mediated inhibition of haemopoietic colony formation by IFN-gamma and TNF-alpha was observed. Similarly, anti-Fas mAb enhanced the inhibitory effects of IFN-gamma. These results suggest that, in addition to interacting at the level of intracellular signalling pathways, IFN-gamma, TNF-alpha or Fas-ligand may potentiate or antagonize their effects through modulation of cytokine receptor expression.