HTLV-I-Infected T Cells Evade the Antiproliferative Action of IFN-β

AbstractHuman T-cell lymphotropic virus type I (HTLV-I)-infected T-cell clones enter the S-phase of the cell cycle in the absence of exogenous IL-2. The pathway by which HTLV-I activates the host T cell may circumvent normal immunoregulatory mechanisms and thus be important for the pathogenesis of HTLV-I-induced diseases. The early control of viral infections is in part mediated by interferons (IFNs), which possess both antiviral and antiproliferative functions. In order to investigate the antiproliferative effect of IFN-β on HTLV-I-induced T-cell activation, we generated T-cell clones from patients with HTLV-I-associated myelopathy/tropical spastic paraparesis by single-cell cloning under limiting dilution conditions. Here we demonstrate that HTLV-I-induced T-cell proliferation is resistant to the antiproliferative action of IFN-β. Moreover, HTLV-I-infected T-cell clones continue to constitutively secrete IFN-γ in the presence of high doses of IFN-β. HTLV-I-infected T cells express normal levels of IFNAR1 and are able to respond to IFN-β by phosphorylation of STAT1 on Tyr701, although they display a relative increase in phosphorylation of the transcriptionally inactive STAT1β when compared with STAT1α. Thus, HTLV-I promotes cell cycle progression in G1by a mechanism that overcomes inhibitory signals, thereby circumventing an innate immune defense mechanism