Here, we report that PstS1 exclusively activated memory T cells but did not stimulate naïve cells. Thus, the ability of PstS1 to induce expression of co-stimulatory molecules and/or release of IL-6 and IL-1β by DCs, as better discussed below, may account for the Ag-independent activation of memory T lymphocytes. However, although unlikely, a contribution for TCR cross-reactivity, which may exist even between apparently unrelated peptide Ag [35] cannot

be excluded. Activation of T lymphocytes by unrelated Ags occurs frequently during infectious processes but the significance of this phenomenon is still a matter of debate. It is thought to be involved in homeostatic turnover, maintenance of immunological memory, or amplification of inflammatory responses [36]. PstS1 is released by replicating Mtb, especially during the acute phase of infection, as indicated by increased levels of anti-PstS1 mAbs in the sera of see more most patients with multibacillary or advanced pulmonary TB [37, 38]. Therefore, PstS1

released by Mtb may be exploited by the bacterium itself to facilitate inflammation during active TB disease. It may promote IFN-γ, IL-17, and IL-22 release by memory T cells specific for other Mtb Ags, such as Ag85B and Ag85A. IFN-γ and IL-17 are induced during primary TB [2-6] and are both capable of inducing chemokines that promote cell recruitment and granuloma organization throughout infection [39]. While many clinical and experimental data indicate a central role for the IFN-γ response in protection Atezolizumab manufacturer against Mtb infection, the role of IL-17 is not yet fully elucidated. Th17 cells per se may contribute to the early control of Mtb infection, although they may increase tissue damage [4, 5]. Similarly, IFN-γ-producing T cells may directly cause lung damage and may alter the efficacy of protective TB

immunity unless tightly controlled [9, 10, 40], suggesting that excessive activation of IFN-γ response may be deleterious for the host. Thus, during TB infection, a balance between Th1 and Th17 responses Arachidonate 15-lipoxygenase needs to be achieved so as to control bacterial growth and limit immunopathology. Recently, a growing body of evidences suggests a role for IL-22 in TB. In healthy humans exposed to mycobacteria, IL-22-expressing CD4+ T cells were reported as being distinct from Th17 and Th1 cells [41]. Moreover, unlike IL-17, IL-22 was found in BALF of TB patients, suggesting that these two cytokines may have distinct roles in TB infection and disease outcome [41, 42]. Nevertheless, considering that the amplification of IFN-γ, IL-17, and IL-22 responses are a double-edge sword for the host [6-10, 42], further investigations are required to determine whether PstS1 release during infection is of benefit to the host or the mycobacteria. Moreover, it remains to be elucidated whether induction and amplification of Ag-unrelated memory Th1 or Th17/22 responses mediated by PstS1 are short term or long lasting.