Introduction: Inflammatory vascular syndromes (IVS) are rare but devastating arterial disorders. A lethal IVS model can be induced by mouse gamma herpesviral (MHV68) infection in interferon gamma receptor knockout mice (IFNγR-/-). Previously, a serine protease inhibitor (serpin), virus-derived Serp-1 protein and Serp-1 reactive center loop (RCL) peptide S-7 (G305TTASSDTAITLIPR319) significantly improved survival and reduced aortic inflammation after MHV68 infection. As the microbiome is reported to have profound effects on immune response, we investigated the role of the gut bacteria in MHV68-infected IVS mouse models with and without treatment.
Method: IFNγR-/- mice (N=56) were split into control or 10-day antibiotic groups prior to infection with MHV68. Mice were treated with saline, Serp-1 or RCL peptides S-2, S-7, S-8 or modified S-7 peptides MPS-8 and MPS-9. Fecal pellets were collected and 16S rRNA was Illumina sequenced from genomic DNA extracts.
Results: Suppression of gut bacteria accelerated mortality and reduced survival from 60 to 20 days (P=0.036) in MHV68 IVS. Survival was reduced from 70% at 150 days to 20% at 30 days with Serp-1 treatment (P=0.003) and 0% at 30 days with S-7 treatment (P<0.0001), while S-2 was inactive and S-8 trended towards improvement (N=14). In contrast, modified MPS-8 and MPS-9 improved survival after suppression of gut bacteria (P<0.001, N=10). Both Serp-1 and S-7 significantly altered microbiome community structure (beta-diversity), while S-7 also altered community richness (alpha-diversity), in the large intestine versus saline controls. Lactobacillales were significantly reduced and Streptophyta increased in MHV68 infection with saline treatment, while Bacillales were significantly reduced and Lactobacillales increased in Serp-1 treatments.
Conclusion: Microbiome richness, structure, or sub-population composition, may play a crucial role in modulating lethal vasculitic syndromes and treatment response. Serp-1 and S-7 show significant therapeutic benefit in MHV68 infection-induced IVS in mice, which is abolished by gut microbiome suppression. MPS-8 and MPS-9 recover efficacy in this model. Significant microbiome changes occurred in Serp-1- and S-7-treated, gut bacteria-suppressed mice.