Currently, there is no available test for monitoring the clinical effect of active tuberculosis (TB) disease treatment. Therefore, we studied the usefulness of two commercial IFN-γ assays (QuantiFERON TB-2G (QFT-2G) and T-SPOT.TB tests) for monitoring clinical efficacy.

The subjects were 40 patients with active TB disease. These two commercial IFN-γ assays were carried out every three months during active TB disease treatment.

While the positive response rate of QFT-2G test significantly decreased from 83% at treatment initiation to 58% at treatment completion, that of T-SPOT.TB decreased from 90% at treatment initiation to 63% at treatment completion. Although there was a significant decrease in patients with TB infection showing positive responses for ESAT-6 only or CFP-10 only antigens on both IFN-γ assays, there was no significant decrease in patients showing positive responses for both ESAT-6 and CFP-10 antigens on both IFN-γ assays. On both QFT-2G test and T-SPOT.TB test, the mean values of the IFN-γ levels in the pre- and post-treatment responses showed significantly decreased responses to CFP-10. On the other hand, smear conversion results of clinical specimens were obtained in all patients at treatment completion.

Antituberculous treatment induced a significant decrease in T-cell responses to separate ESAT-6 and CFP-10 antigens as measured by both IFN-γ assays. Although IFN-γ assays might be later than smear conversion results of clinical specimens, the quantitative responses especially to CFP-10 may be one of the useful monitoring markers of clinical efficacy for active TB disease treatment.