Fas antigen expression on CD34+ human marrow cells is induced by interferon γ and tumor necrosis factor α and potentiates cytokine-mediated hematopoietic suppression in vitro

Abstract

Activation of Fas antigen, a cell surface receptor molecule, by its ligand results in transduction of a signal for cell death. The Fas system has been implicated in target cell recognition, clonal development of immune effector cells, and termination of the cellular immune response. Fas antigen expression on lymphocytes is regulated by interferon γ (IFNγ) and tumor necrosis factor α (TNFα), cytokines that also have inhibitory effects on hematopoiesis. We investigated Fas antigen expression on human marrow cells and the effects of Fas activation on hematopoiesis in vitro. Freshly isolated immature hematopoietic cells, as defined by the CD34 marker, did not express Fas antigen at levels detectable by fluorescent staining. CD34+ cells, which include progenitors and stem cells, showed low levels of Fas expression in culture, even in the presence of growth factors. Stimulation by TNFα and IFNγ markedly increased Fas antigen expression on CD34+ cells. Anti-Fas antibody, which mimics the action of the putative ligand, enhanced IFNγ- and TNFα-mediated suppression of colony formation by bone marrow (BM) in a dose- dependent manner. This effect did not require the presence of accessory cells. Colony formation from mature (CD34+ CD38+) and immature (CD34+CD38-) progenitor cells and long-term culture initiating cells were susceptible to the inhibitory action of anti-Fas antibody in the presence of IFNγ and TNFα. Apoptosis assays performed on total BM cells and CD34+ cells showed that anti-Fas antibody induced programmed cell death of CD34+ BM cells. Fas antigen may be expressed as part of the differentiation program of hematopoietic cells. Fas antigen and its ligand may play a role in the pathophysiology of marrow failure states and in the elimination of abnormal hematopoietic cells in the course of an immune response.