CD4 and infection: Lung CD4+ T-cell subsets were then examined at 2 and 4 days post-secondary infection: GM-CSF+ CD4+ T cells (Figures 3A,E, respectively), IL-4+ CD4+ T cells (Figures 3B,F, respectively), IFN-γ+ CD4+ T cells (Figures 3C,G, respectively), and IL-17+ CD4+ T cells (Figures 3D,H, respectively).