However, the generation of effective antiviral or autoreactive adaptive learn more immune responses requires blocking of immunosuppression by Tregs. In this study, we show that TLR7 ligands reduce the number of Tregs generated

de novo from naïve murine T cells in vitro and in vivo. In the presence of TLR7-activated splenic DCs, Foxp3 was transiently induced in naïve T cells by TGF-β but was downregulated at later time points. Neutralization experiments revealed that loss of Foxp3 after initial induction was mostly dependent on IL-6 produced in the DC–T-cell cocultures containing TLR7 ligands. Thus, under the influence of TLR7 ligands fewer Tregs were generated and these expressed lower levels of Foxp3 correlating with a reduced capacity to suppress responder T-cell proliferation. Thus, we provide evidence that TLR7

ligands affect Treg-dependent immune regulation and may thereby contribute to the development of autoimmune diseases such as systemic lupus erythematosus. Viral RNA as well as self-RNA present in nuclear autoantigens of patients with autoimmune diseases such as systemic lupus erythematosus (SLE) activate Toll-like receptor (TLR) 7 1–6. Accordingly, TLR7 has been shown to play an important role in antiviral defense 7 as well as autoimmunity, as was shown in several mouse models of SLE 8–13. DCs and B cells which are directly activated by TLR7 ligands support the activation and expansion of effector T and B lymphocytes directed against viral antigens 7 or autoantigens

Rapamycin datasheet 10. In addition, TLR7 activation could be involved in breaking peripheral tolerance mediated by Tregs, which has to be overcome in order to generate protective antiviral immune responses 14 or pathogenic autoreactive immunity. In several murine models of SLE and in patients with active Olopatadine SLE, reduced frequencies and suppressive functions of Tregs have been observed 15–18, supporting the concept that defects in the Treg compartment are critical factors in the pathogenesis of this autoimmune disease. We propose that in addition to the direct stimulatory effects on APCs, TLR7 activation by exogenous and endogenous TLR7 ligands impairs Treg generation and function. However, the studies investigating the effect of TLR7 ligands on Treg suppressive function have yielded controversial results 19, 20 and the influence of TLR7 activation on the de novo generation of Tregs from naïve T cells has not been examined. We show that TGF-β induces Foxp3 expression in naïve T cells even in the presence of TLR7 ligand and DCs; however, Foxp3 expression is only transient and is downregulated at later time points. Loss of Foxp3 expression is dependent on soluble factors – mainly IL-6 – produced in DC–T-cell cocultures in response to TLR7 ligands. Upon exposure to TLR7 ligands, reduced numbers of Tregs are generated which additionally express lower levels of Foxp3 and have a reduced capacity to inhibit the proliferation of responder T cells.