CD4 and tuberculosis: The median PPD-specific IFNγ secretion was 0.15% versus 0.20% (P = 0.37) for total lymphocytes, 1.20% versus 0.58% (P = 0.33) for CD4+ T lymphocytes, and 2.50% versus 2.96% (P = 0.98) for the CD27− CD4+ memory T lymphocytes in the active and non-active TB groups, respectively.