CD4 and tuberculosis: In the T-SPOT.TB assay, there was no statistically significant correlation between the CD4+ T-cell count and interferon-γ response to ESAT-6 or CFP 10 (correlation co-efficient 0.057, p 0.236 and correlation co-efficient 0.077, p = 0.104 respectively) or CD4+ T-cell count and response to mitogen (positive control) (correlation co-efficient 0.057, p = 0.266).