Respiratory Syncytial Virus Interferon Antagonist NS1 Protein Suppresses and Skews the Human T Lymphocyte Response

We recently demonstrated that the respiratory syncytial virus (RSV) NS1 protein, an antagonist of host type I interferon (IFN-I) production and signaling, has a suppressive effect on the maturation of human dendritic cells (DC) that was only partly dependent on released IFN-I. Here we investigated whether NS1 affects the ability of DC to activate CD8+ and CD4+ T cells. Human DC were infected with RSV deletion mutants lacking the NS1 and/or NS2 genes and assayed for the ability to activate autologous T cells in vitro, which were analyzed by multi-color flow cytometry. Deletion of the NS1, but not NS2, protein resulted in three major effects: (i) an increased activation and proliferation of CD8+ T cells that express CD103, a tissue homing integrin that directs CD8+ T cells to mucosal epithelial cells of the respiratory tract and triggers cytolytic activity; (ii) an increased activation and proliferation of Th17 cells, which have recently been shown to have anti-viral effects and also indirectly attract neutrophils; and (iii) decreased activation of IL-4-producing CD4+ T cells - which are associated with enhanced RSV disease - and reduced proliferation of total CD4+ T cells. Except for total CD4+ T cell proliferation, none of the T cell effects appeared to be due to increased IFN-I signaling. In the infected DC, deletion of the NS1 and NS2 genes strongly up-regulated the expression of cytokines and other molecules involved in DC maturation. This was partly IFN-I-independent, and thus might account for the T cell effects. Taken together, these data demonstrate that the NS1 protein suppresses proliferation and activation of two of the protective cell populations (CD103+ CD8+ T cells and Th17 cells), and promotes proliferation and activation of Th2 cells that can enhance RSV disease.
Author Summary Respiratory syncytial virus (RSV) is a leading cause of pediatric lower respiratory tract disease. RSV has two IFN-I antagonist proteins, NS1 and NS2. In this study, we infected primary human dendritic cells with recombinant RSV from which the NS1 and/or the NS2 genes were deleted, and evaluated effects on the proliferation of autologous T lymphocytes during co-culture in vitro. We found that NS1, but not NS2, has a suppressive effect on two cell populations, namely CD103+ CD8+ T cells and Th17 cells, which are known to protect against viral respiratory infections, and a stimulatory effect on Th2 cells, which are involved in enhanced disease caused by RSV. We also provide evidence that these effects are not due to suppressed IFN-I production or signaling in dendritic cells or T cells, and that they likely result from reduced maturation of dendritic cells caused by the NS1 protein.