IL-2 is secreted by Ag-activated CD4+ T cells during the primary immune response, and is clearly essential for the differentiation and expansion of naïve T cells into IFN-γ-producing effector cells in TB, indicating that continuous expression of IL-2 is required to confer resistance to TB progression (Uhlin et al., 2012; Clifford et al., 2015). This evidence concerns the gene CD4 and tuberculosis.