Differences in IL-2/IFN-γ ratio observed in our study are in agreement with previous studies, which indicated that the frequency of IL-2-secreting and IL-2/IFN-γ-dual-secreting CD4+ central memory T-cells increased and the number of IFN-γ-secreting effector memory T-cells was reduced in non-active TB compared with active TB patients[23,24,25]. This evidence concerns the gene CD4 and tuberculosis.