CD4 and tuberculosis: Although only partially defined (6), the protective components of M. tuberculosis-specific immunity include appropriate and efficient CD4 T-cell responses associated with type 1 cytokine secretion (gamma interferon [IFN-γ] and tumor necrosis factor alpha [TNF-α]), since IFN-γ receptor deficiency is associated with increased susceptibility to mycobacterial infections (7, 8) and anti-TNF-α therapy is associated with increased risk of TB reactivation (9).