The infection of T cells by Epstein-Barr virus (EBV) may result in hemophagocytic syndrome (HPS) through enhanced cytokine secretion, particularly tumor necrosis factor- (TNF-α), by EBV latent membrane protein-1 (LMP-1). One bewildering observation of HPS patients is relapsing disease or progression to T-cell lymphoma. This finding raises the question whether EBV LMP-1-expressing T cells may survive and proliferate in the cytokine milieu of HPS. To explore this possibility, we tested the sensitivity of LMP-1-expressing T cells to apoptosis in the presence of TNF-α LMP-1 up-regulated TNF- α through TRAF2,5 and nuclear factor-B pathway in T cells. The LMP-1-expressing T cells then became resistant to TNF-α-induced apoptosis. Interestingly, the expression of TNFR1 was remarkably down-regulated by LMP-1 in T cells. Furthermore, the TNF-/TNFR1 downstream death signal TNFR1-associated death domain protein was constitutively recruited by LMP-1, and the activities of apoptotic caspases 3, 8, and 9 were suppressed. Reconstitution of TNFR1 successfully reversed the TNF-α-induced apoptotic cascades. Therefore, EBV LMP-1 not only activates T cells to proliferate but also confers resistance to TNF-α-mediated apoptosis via down-regulation of TNFR1 in the cytokine milieu of HPS. This finding provides a potential mechanism to explain the disease persistence or progression to T-cell lymphoma in HPS patients.
