DIFFERENTIAL REGULATION OF CD95 (FAS APO-1) EXPRESSION IN HUMAN BLOODEOSINOPHILS/

CD95 (Fas, APO-1) is a cell surface receptor expressed on many cells i ncluding eosinophils which mediates apoptosis when ligated by agonisti c antibodies or its natural ligand FasL. Since inhibition of apoptosis may play an important role in controlling tissue eosinophilia, we inv estigated the expression of CD95 on purified peripheral blood eosinoph ils from normal donors. Freshly isolated eosinophils expressed CD95 on the cell surface as well as CD95-specific mRNA at low levels which di d not change during 24-h culture. Incubation of eosinophils with IL-3, IL-5 and granulocyte-macrophage colony-stimulating factor (GM-CSF) di d not modulate the basal expression of CD95. IFN-gamma as well as TNF- alpha, however, induced a significant, dose- and time-dependent increa se in CD95 mRNA and cell surface expression as measured by reverse tra nscription-PCR and flow cytometry. Co-stimulation with IFN-gamma and T NF-alpha had synergistic effects on the CD95 surface expression on eos inophils. Addition of IL-3, IL-5 or GM-CSF to lFN-gamma- and TNF-alpha -stimulated eosinophils caused in a reduction of CD95 expression. Func tional activity for CD95 following incubation with IFN-gamma and TNF-a lpha was demonstrated by increased apoptosis in response to cross-link ing with Fast. From these data, we conclude that IFN-gamma and TNF-alp ha can up-regulate cell surface expression of CD95 on eosinophils, whi ch leads to an increased susceptibility of eosinophils to Fas-mediated apoptosis. Thus, our results suggest that receptors involved in eosin ophil apoptosis can be regulated by antagonistic cytokines.