Infection with the Epstein-Barr virus (EBV) has been associated with several autoimmune diseases including rheumatoid arthritis (RA). We have previously reported that DNA from this virus enhances production of the pro-autoimmune interleukin 17A (IL-17A) in mice. In this study we assessed the effect of EBV DNA on regulatory T cell programming and examined whether it mediated its effects via Toll-like receptor 9 (TLR9) in mice; moreover, we evaluated whether EBV DNA in humans had similar effects to those seen in mice. For this purpose, we assessed the linearity of the correlation between EBV DNA and IL-17A levels in RA subjects and matched controls. A modulatory effect for the viral DNA was observed for regulatory T cell markers with an inhibitory effect observed for CTLA4 expression in the EBV DNA-treated mice. To examine whether TLR9 mediated the detection of EBV DNA and enhancement of IL-17A production, mouse peripheral blood mononuclear cells were treated with the DNA in the presence or absence of the TLR9 inhibitor ODN 2088. Subsequently, IL-17A production from these cells was assessed. Treatment with the TLR9 inhibitor resulted in a significant decrease in IL-17A production indicating that TLR9 is involved in this pathway. In human subjects, examining the linearity of the correlation between EBV DNA and IL-17A levels in RA subjects showed a propensity for linearity that was not observed in controls. Our data thus indicates that EBV DNA itself acts as a modulator of the Th17 compartment as well as that of regulatory T cell mechanisms. The involvement of TLR9 in the EBV DNA-triggered induction of IL-17A suggests therapeutic targeting of this endosomal receptor in EBV positive subjects with an autoimmune flare-up or possibly for prophylactic purposes.

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Introduction: EBV has long-been associated with autoimmune disorders. We have previously demonstrated that EBV DNA increases the production of IL-17A in mice. This property may play a role in the association of EBV with autoimmune diseases. The objective of this study was to elucidate mechanisms through which EBV DNA modulates IL-17A levels in mice. Methodology: To study the potential role of endosomal receptors in detecting EBV DNA, chloroquine, an endosomal maturation inhibitor, was used to treat mouse peripheral blood mononuclear cells (PBMCs) in the presence or absence of EBV DNA. IL-17A levels were then assessed by ELISA. Subsequently, to determine whether TLR3, 7 or 9 played a role in this pathway, specific inhibitors were used for these TLRs both in mouse PBMCs and in vivo in BALB/c mice treated with the viral DNA; IL-17A levels were then similarly assessed. Results: IL-17A production was enhanced from mouse PBMCs cultured with EBV DNA; pre-incubation of PBMCs with chloroquine significantly reduced its production. When cells were cultured with EBV DNA and a TLR3, 7 or 9 inhibitor, a significant decrease in IL-17A levels was detected. A similar decrease in the EBV DNA-triggered IL-17A production in mice was observed when animals were treated with the TLR inhibitors. Conclusion: Endosomal TLRs appear to be involved in recognizing EBV DNA and subsequently triggering IL-17A production in mice. Targeting these receptors in EBV positive subjects with autoimmunity may be useful pending investigations assessing whether they play a similar role in humans.