Remarkably, the finding that PstS1 stimulates memory T cells specific for TT, suggests the potential exploitation of PstS1 immunomodulatory properties in other infections. Although effects on other APCs cannot be excluded, our study shows that the immunomodulatory properties of PstS1 are linked to its ability to activate DCs in vitro and in vivo. In particular, PstS1 promoted

the expression of IL-6, IL-1β, and, to a minor extent, IL-23. These cytokines were recently reported to drive a fine balance of CD4+ T-cell differentiation in the effector phase of the immune response to Candida albicans and Staphylococcus aureus [44]. Of interest, other cytokines pivotal for the homeostasis of memory T cells, such as IL-7

and IL-15 for CD8+ T cells [45], or IL-12p40 for Th1 check details response [46], were EPZ-6438 not modulated by PstS1 (data not shown). The ability to stimulate DCs was peculiar to PstS1, since other immunodominant Mtb Ags such as Ag85B, Esat-6, or HBHA were unable to activate DCs (Fig. 4 and data not shown) and it was directed preferentially toward CD8α− DCs. The two major DC subsets of mouse spleen, CD8α+ and CD8α−, trigger distinct T-cell responses against pathogens. While CD8α+ DCs are thought to be specialized in antiviral response due to their unique cross-priming ability, CD8α− DCs have been involved in CD4+ T-cell immunity, particularly during bacterial infections [47]. CD8α− DCs efficiently induce CD4+ Y-27632 2HCl T-cell responses through in vivo targeting of Ag via C-type lectin receptors, such as dectin-1 and DCIR-2 [30, 48]. The preferential ability of CD8α− DCs to prime CD4+ T-cell responses has been correlated with their superior capacity to process Ags via MHC class II molecules [30]. Accordingly, we report that PstS1 endowed CD8α− DCs with a strong ability to simulate CD4+ T cells. In particular, CD8α− DCs stimulated by PstS1 were found to produce much higher amounts of IL-6, IL-1β, and IL-23 with respect

to CD8α+ DCs. Moreover, PstS1-pulsed CD8α− DCs were far superior at inducing IFN-γ, IL-17, and IL-22 release by Ag85B-specific memory T cells, compared with CD8α+ DCs. The mechanisms by which PstS1 activates DCs remain to be established. Our data on DCs deficient for TLR2, the main PRR recognized by Mtb components, suggest that this receptor is dispensable. We envisage that the TLR2-independent pathway of DC maturation induced by PstS1 strongly differs from that triggered by the Mtb Ags Rv0577, Rv1196, Rv0978c, and Rv0754, which all recognize TLR2 and induce maturation of DCs leading to either Th1 or Th2 polarization, but not to IL-17 secretion by memory CD4+ T cells [14-18].