Previously, polyfunctional T cells producing IFN-γ, TNF-α and IL-2 have been suggested find more as possible markers of protective immunity, based on observations that vaccine-induced triple positive T cells correlated well with protection 18–24. However, other studies reported that such T cells were associated with active TB disease 25–28. The nature of Mtb DosR antigen-responsive CD4+ and CD8+ T-cell subsets in untreated Mtb-exposed donors who had been infected several decades ago, yet never developed any signs or symptoms of active TB (ltLTBIs), was studied here. In vitro purified protein derivative of Mtb (PPD) negative (PPD−) donors were included as uninfected controls. PBMCs of ltLTBIs and PPD−

donors were stimulated with Mtb DosR-regulon-encoded antigens or corresponding peptide pools and the responses were analyzed using multi-parameter flow cytometry (Supporting Information Fig. S1A and S1B). Donors were considered positive when the frequency of a double or poly learn more functional T-cell subset population was ≥0.2%, which is equivalent to ≥200 events. In ltLTBIs high percentages of IFN-γ, TNF-α and/or IL-2 cytokine-producing CD4+ and CD8+ T cells were found in response to PPD (0.23–7.91% and 0.25–7.55%, respectively), Rv2031c protein (0.21–19.71% and 0.25–20.35%, respectively) and the

Rv2031c peptide pool (0.2–16.28% and 0.23–32.92%, respectively), whereas no such responses were observed in PPD− controls (Fig. 1A). The highest frequencies were consistently found within the single cytokine-producing CD4+ and CD8+ T-cell populations. Interestingly, many double producing T cells were identified within the CD8+ T-cell population, as shown by Fig. 1B, which depicts the proportions of polyfunctional as well as double and single cytokine-producing T cells. For Mtb DosR antigen Rv1733c, two peptide pools

were tested (Fig. 1C). Again high CD4+ and CD8+ T-cell responses were observed (0.43–14.41% and 0.2–14.25%, respectively), with single positive cells being the most frequent. In addition, substantial numbers of double cytokine-producing CD4+ and CD8+ T cells were present in both peptide pool responsive CD4+ and CD8+ T-cell populations, IFN-γ+TNF-α+ CD8+ T cells being the most frequent (Fig. 1D). Low to no Rv1733c-specific responses were identified within the PPD− controls (Fig. 1C). Miconazole A comparable pattern was observed for Rv2029c (0.29–8.41% CD4+ T cells and 0.36–9.55% CD8+ T cells). Unlike Rv1733c, the Rv2029c protein induced a considerable fraction of IFN-γ+TNF-α+ CD8+ T cells. Some responses to Rv2029c peptide pool 1 were also observed in the PPD− group, but no responses were seen to peptide pools 2 and 3 (Fig. 1E and F). Of note, stimulation of PBMCs with Staphylococcus enterotoxin B induced high percentages of CD4+ and CD8+ T cells producing single (0.3–26.44% CD4+ T cells and 0.29–12.6% CD8+ T cells), double (0.23–22.26% CD4+ T cells and 0.