CD4 and bronchiolitis: In these RSV-infected mice, IN treatment given 5 days prior to infection also significantly increased the proportion of the CD4+ IFN-γ+ Th1 cell and FoxP3+ Treg cell populations in the lung and prevented the RSV-induced increase of the innate lymphoid cell 2 (ILC2) proportions, cells known to be associated with Th2 type of immune response and with more severe RSV-bronchiolitis (Figure 2B) (39, 40).