Epstein-Barr Virus and Human herpes virus 6 Type A DNA Enhance IL-17 Production in Mice

Several studies have shown a potential association between the Herpesviridae members, the Epstein-Barr virus (EBV) and Human herpes virus 6 (HHV-6), and an increased risk of autoimmune disease development. Because of the ability of these viruses to cause recurrent infections, various viral antigens, including viral DNA, are consistently shed. These antigens may then play a role in triggering autoimmune processes or contributing to autoimmune mechanisms. Therefore, this study examined whether the DNA of EBV or that of HHV-6A is capable of triggering IL-17, the autoimmune-associated cytokine, in mice. BALB/c mice were intraperitoneally injected with various copy numbers of either EBV or HHV-6A DNA. One group was injected with sterile water (the DNA solvent), and another was left uninjected. A mouse group that was administered DNA obtained from Staphylococcus epidermidis was included to ensure that any observed effects would pertain to the viral DNA tested. Mice were sacrificed and their sera were examined using an enzyme-linked immunosorbent assay for IL-17 and IL-23, as pro-autoimmune cytokines, IL-10, as an anti-inflammatory cytokine, and IFN-γ, as a pro-inflammatory cytokine, on days 3, 6, and 9 post-injection. All mouse groups injected with different copy numbers of EBV DNA or HHV-6A DNA displayed higher IL-17 levels than did the group injected with water on days 3, 6, and 9 post-injection. The highest IL-17 levels appeared to coincide with a marked increase in IL-23 and a decrease in IL-10 levels. Unlike the S. epidermidis DNA, which increased IFN-γ levels but not IL-17 or IL-23 levels, the viral DNA tested increased all three mediators, indicating that triggering Th17 responses is a specific property of EBV and HHV-6A DNA. In conclusion, EBV and HHV-6A viral DNA are capable of enhancing the production of the pro-inflammatory cytokine IL-17, which has been shown to play a role in autoimmune diseases.