Characterization of regulatory T cells identified as CD4+CD25highCD39+ in patients with active tuberculosis

Forkhead box P3 (FoxP3) is a transcription factor whose expression characterizes regulatory T cells (T-reg), but it is also present on activated T cells, thus hindering correct T-reg identification. Using classical markers for T-reg recognition, discordant results were found in terms of T-reg expansion during active tuberculosis (TB) disease. Recently CD39 has been shown to be an accurate marker for T-reg detection. The objectives of this study were: (i) to identify T-reg expressing CD39 in patients with TB and to compare the results with those obtained by the standard phenotypic markers; (ii) to evaluate if T-reg are expanded in vitro by exogenous interleukin (IL)-2 or by antigen-specific stimulation; and (iii) to characterize T-reg function on the modulation of antigen-specific responses. We enrolled 13 patients with pulmonary TB and 12 healthy controls. T-reg were evaluated by flow cytometry ex vivo and after antigen-specific in vitro stimulation using CD25, FoxP3, CD127 and CD39 markers. Results indicate that CD39(+) cells within the CD4(+)CD25(high) cells have T-reg properties (absence of interferon-gamma production and transforming growth factor-beta 1 release upon stimulation). Ex vivo analysis did not show significant differences between TB patients and controls of T-reg by classical or novel markers. In contrast, a significantly higher percentage of T-reg was found in TB patients after antigen-specific stimulation both in the presence or absence of IL-2. Depletion of CD39(+) T-reg increased RD1-specific responses significantly. In conclusion, CD39 is an appropriate marker for T-reg identification in TB. These results can be useful for future studies to monitor Mycobacterium tuberculosis-specific response during TB.