CD4+CD25+ Tregs purified from LCMV-immune mice were exposed in vitro to DCs obtained from mice recently challenged with LCMV, which we and others found to harbor an activated phenotype and carry LCMV particles (data not shown, and 38). After 6 days in culture, the Tregs were separated from the DCs and adoptively transferred into B6 RIP-GP Cabozantinib nmr mice in which autoimmune diabetes was triggered simultaneously by LCMV infection. While the capacity of LCMV-exposed, WT CD4+CD25+ T cells to protect B6 RIP-GP mice from T1D was enhanced after culture with DCs from WT

LCMV-infected mice (Fig. 7B), TLR2−/− Tregs cultured with TLR2−/− DCs had no effect on disease development. These results indicated that MK 2206 LCMV-mediated Treg enhancement could be conferred by DCs and depended on TLR2. Our observations indicate that triggering of TLR2 in a naïve context or upon viral infection confers protection from autoimmune diabetes by promoting the expansion of invigorated CD4+CD25+ Tregs, possibly via DCs. Since P3C-induced signaling occurs through heterodimerization of TLR2 with TLR1, further studies should assess the contribution of TLR1 in induction of immunoregulation and protection from T1D. We did not observe Treg enhancement after treatment of NOD mice with Pam2CSK4 (data not shown), thus

excluding a role for TLR6-TLR2 heterodimerization in this phenomenon. TLR2 was previously shown to promote rather than hinder T1D, notably by inducing TNF-α production by APCs 18. On the other hand, a requirement for TLR2 in the development of T1D was

ID-8 not supported by a recent study 32. Such opposing roles of TLR2 in this disease might reflect the importance of β-cell antigen release concomitant to TLR signaling for autoimmunity to develop. TLR stimulation indeed causes autoimmune diabetes when triggered in the presence of β-cell antigens 16, 17, but otherwise prevents the disease 24–27. Our previous 12 and present findings suggest that this might be due to the capacity of immunostimulatory factors to enhance immunoregulation. Another, possibly related, important aspect might be the timing at which TLRs, and subsequent release of inflammatory cytokines, are triggered during the prediabetic phase 39. In this regard, previous studies by us and others have shown that TNF-α differentially affects the outcome of T1D depending on the time of action 10, 40, 41. TNF-α may also have opposing effects on CD4+CD25+ Tregs 41–43, which play a crucial role in T1D. Other inflammatory cytokines such as IFNs can also differentially affect autoimmune processes in T1D, as supported by our previous work 12. Finally, while TLR2 delivers pro-inflammatory signals, its engagement also causes the release of anti-inflammatory/immunoregulatory cytokines such as IL-10 44, 45.