CD4 and congenital T-cell immunodeficiency: In contrast with the observed T cell deficiency in the lung (Figure 3A–G), continuous cigarette smoke exposure resulted in an increased number of total CD4+ (Figure 4A) and activated CD4+IFN-γ+ T cells (Figure 4B) in the spleen, while having a minimal effect on numbers of T cells in the MLN (Figure 4C/4D), indicating that cigarette smoke exposure impairs the recruitment of CD4+IFN-γ+ to the lung, rather than suppressing their priming in the peripheral lymphoid tissues.