Effect of Toll-Like Receptor 7 Pathway Inhibition on the Severity of Epstein-Barr virus DNA-Exacerbated Intestinal Inflammation in a Mouse Model of Inflammatory Bowel Disease

Abstract

Background: An Epstein-Barr virus (EBV) infection was proposed to play a role in the pathogenesis of inflammatory bowel disease (IBD), a chronic inflammatory malady with a poorly defined etiology. In recent research conducted by our laboratory, we reported that EBV DNA activates the endosomal Toll-like receptor 7 (TLR7) pathway, leading to an increase in interleukin 17A (IL-17A) levels. We have also reported that EBV DNA exacerbates the severity of intestinal inflammation in a mouse model of IBD. Thus, we aimed at determining whether inhibiting the TLR7 pathway would alleviate some of the severity of EBV DNA-exacerbated intestinal inflammation and the clinical course severity in a mouse model of IBD.

Methods: A C57BL/6J mouse model of dextran sodium sulfate (DSS)-induced acute colitis was employed in this study. A total of forty mice were obtained and distributed amongst four groups of ten. All four groups were administered 1.5% DSS in drinking water from day 0 until day 7. The groups were then rectally administered sterile water or 288 x 103 copies of EBV DNA in sterile water on day 3. On day 4, mice were intraperitoneally injected with sterile water or with 57.5µg of IRS661 (TLR7 inhibitor) in 100µl of sterile water. The effect of TLR7 inhibition on EBV DNA-exacerbated colitis was assessed based on trends in the disease activity index (DAI), macroscopic assessments of the colon, histological damage grading of H&E-stained colon cross sections, systemic IL-17A levels and immunofluorescence staining of pro-inflammatory markers in colon cross sections.

Results: The group that received an intra-peritoneal injection of the TLR7 inhibitor in addition to the EBV DNA injection and DSS administration had a statistically significant decrease in the DAI and histological scores compared to the group that received an intra-rectal injection of EBV DNA in addition to the DSS administration. In line with the DAI and histology scores, the group that received an intra-peritoneal injection of the TLR7 inhibitor in addition to the EBV DNA injection and DSS administration exhibited a significant increase in colon length compared to the group that received an intra-rectal injection of EBV DNA in addition to the DSS administration. Consistent with these findings, the group that received an intraperitoneal injection of the TLR7 inhibitor in addition to the EBV DNA injection and DSS administration had a significant decrease in the number of IL-17A+ IFNγ+ FOXP3+ counts and IL-17A+ FOXP3+ found in the gut compared to the group that received an intra-rectal injection of EBV DNA in addition to the DSS administration.

Conclusion: Our study indicates that TLR7 inhibition alleviates some of the severity of EBV DNA-exacerbated intestinal inflammation in a mouse model of IBD. This suggests a potential therapeutic/prophylactic target in TLR7 for IBD management in EBV-infected individuals. Further studies may assess alternative doses or regimens of this inhibitor as well as other routes of administration.