Reactivation of latent M tuberculosis (Mtb) infection is a major complication of anti-TNFalpha treatment, but its mechanism is not fully understood. In this work, we evaluated in two conditions the effect of the TNF antagonists infliximab, adalimumab and etanercept on anti-mycobacterial immune responses: with ex vivo studies from patients treated with TNF antagonists, and with the in vitro addition of TNF antagonists to cells stimulated with mycobacteria antigens. In both cases, we analysed the response of CD4+ T lymphocytes to PPD and to CFP-10, an antigen restricted to Mtb. The tests performed were lymphoproliferation and immediate production of IFNgamma (ELISPOT). In the 68 patients with inflammatory diseases (rheumatoid arthritis, spondylarthropathy or Crohn's disease), including 31 patients with a previous or latent tuberculosis (TB), fourteen weeks of anti-TNFalpha treatment had no effect on the proliferation of CD4+ T lymphocytes. In contrast, the number of IFNgamma-releasing CD4+ T lymphocytes decreased, for PPD (p<0.005) and CFP-10 (p<0.01), in patients with previous TB, and for PPD (p<0.05) in other patients (all vaccinated with Bacille Calmette-Guerin). Treatments with infliximab and with etanercept affected IFNgamma release to a similar extent. In vitro addition of TNF antagonists to CD4+T lymphocytes stimulated with mycobacteria antigens inhibited their proliferation and their expression of membrane-bound TNF (mTNF). These effects occurred late in cultures, suggesting a direct effect of TNF antagonists on activated mTNF+ CD4+ T lymphocytes. Infliximab and adalimumab were more efficient than etanercept for these in vitro effects. Therefore, TNF antagonists have a dual action on anti-mycobacteria CD4+ T lymphocytes. Administered in vivo, they decrease the frequency of the subpopulation of anti-mycobacteria memory CD4+ T lymphocytes rapidly releasing IFNgamma upon challenge with mycobacteria antigens. All TNF antagonists are as efficient to induce this decline. Added in vitro, they inhibit the activation of CD4+ T lymphocytes by mycobacteria antigens, with a stronger effect of infliximab and adalimumab than of etanercept. Such a dual effect may explain the increased incidence of TB in patients treated with TNF antagonists as well as possible differences between TNF antagonists for the incidence and the clinical presentation of TB reactivation.