B and T lymphocyte attenuator down-regulation by HIV-1 depends on type I interferon and contributes to T-cell hyperactivation

Background. Nonspecific T-cell hyperactivation is the main driving force for human immunodeficiency virus (HIV)-1 disease progression, but the reasons why the excess immune response is not properly shut off are poorly defined. Methods. Eighty-five HIV-1-infected individuals were enrolled to characterize B and T lymphocyte attenuator (BTLA) expression and function. Infection and blockade assays were used to dissect the factors that influenced BTLA signaling in vitro. Results. BTLA expression on overall CD4⁺ and CD8 ⁺ T cells was progressively decreased in HIV-1 infection, which was directly correlated with disease progression and CD4⁺ T-cell differentiation and activation. BTLA⁺CD4⁺ T cells from HIV-1-infected patients also displayed an altered immune status, which was indicated by reduced expression of naive markers but increased activation and exhaustion markers. Cross-linking of BTLA can substantially decrease CD4 ⁺ T-cell activation in vitro. This responsiveness of CD4⁺ T cells to BTLA-mediated inhibitory signaling was further found to be impaired in HIV-1-infected patients. Furthermore, HIV-1 NL4-3 down-regulated BTLA expression on CD4⁺ T cells dependent on plasmacytoid dendritic cell (pDC)-derived interferon (IFN)-α. Blockade of IFN-α or depletion of pDCs prevents HIV-1-induced BTLA downregulation. Conclusions. HIV-1 infection potentially impairs BTLA-mediated signaling dependent on pDC-derived IFN-α, which may contribute to broad T-cell hyperactivation induced by chronic HIV-1 infection.