Group 2 innate lymphoid cells mediate the activation of CD4+T cells and aggravate Th1/Th2 imbalance via MHC II molecules during respiratory syncytial virus infection

Respiratory syncytial virus (RSV) infection induces the activation of CD4+ T cells. However, the underlying mechanism of CD4+ T-cell activation induced by RSV infection is not fully understood. In the present study, we found that depletion of CD4+ T cells can obviously reduce airway inflammation caused by RSV infection. Meanwhile, adoptive transfer of group 2 innate lymphocytes (ILC2s) significantly enhanced the number of CD4+ T cells and promoted their differentiation to Th2 in lung. In fact, RSV infection increased the expression of major histocompatibility complex-II (MHC II) molecules on the surface of pulmonary ILC2s. In vitro coculture experi-ments showed that ILC2s may act as promoters to promote the expansion and differentiation of RSV-infected CD4+ T cells. However, blocking the interaction between CD4+ T cells and ILC2s with anti-MHC-II mAbs significantly reduced CD4+ T-cell expansion. These results suggest that pulmonary ILC2s may function as antigen-presenting cells to induce the activation of CD4+ T cells through the MHC II pathway during RSV infection.