Multiple sclerosis (MS) is a demyelinating disease of the central nervous system. We and others have shown that there is enrichment or depletion of some gut bacteria in MS patients compared to healthy controls (HC), suggesting an important role of the gut bacteria in disease pathogenesis. Thus, specific gut bacteria that are lower in abundance in MS patients could be used as a potential treatment option for this disease. In particular, we and others have shown that MS patients have a lower abundance of Prevotella compared to HC, whereas the abundance of Prevotella is increased in patients that receive disease-modifying therapies such as Copaxone® (Glatiramer acetate-GA). This inverse correlation between the severity of MS disease and the abundance of Prevotella suggests its potential for use as a therapeutic option to treat MS. Notably we have previously identified a specific strain , Prevotella histicola ( P. histicola ), that suppresses disease in the animal model of MS, experimental autoimmune encephalomyelitis (EAE) compared with sham treatment. In the present study we analyzed whether the disease suppressing effects of P. histicola synergize with those of the disease-modifying drug Copaxone® to more effectively suppress disease compared to either treatment alone. Treatment with P. histicola was as effective in suppressing disease as treatment with Copaxone®, whereas the combination of P. histicola plus Copaxone® was not more effective than either individual treatment. P. histicola -treated mice had an increased frequency and number of CD4 + FoxP3 + regulatory T cells in periphery as well as gut and a decreased frequency of pro-inflammatory IFN-γ and IL17-producing CD4 T cells in the CNS, suggesting P. histicola suppresses disease by boosting anti-inflammatory immune responses and inhibiting pro-inflammatory immune responses. In conclusion, our study indicates that the human gut commensal P. histicola can suppress disease as efficiently as Copaxone® and may provide an alternative treatment option for MS patients.

Gut microbiota has emerged as an important environmental factor in the pathobiology of multiple sclerosis (MS), an inflammatory demyelinating disease of the central nervous system (CNS). Both genetic and environmental factors have been shown to play an important role in MS. Among genetic factors, the human leukocyte antigen (HLA) class II allele such as HLA-DR2, DR3, DR4, DQ6, and DQ8 show the association with the MS. We have previously used transgenic mice expressing MS susceptible HLA class II allele such as HLA-DR2, DR3, DQ6, and DQ8 to validate significance of HLA alleles in MS. Although environmental factors contribute to 2/3 of MS risk, less is known about them. Gut microbiota is emerging as an imporatnt environmental factor in MS pathogenesis. We and others have shown that MS patients have distinct gut microbiota compared to healthy control (HC) with a lower abundance of Prevotella. Additionally, the abundance of Prevotella increased in patients receiving disease-modifying therapies (DMTs) such as Copaxone and/or Interferon-beta (IFNβ). We have previously identified a specific strain of Prevotella (Prevotella histicola), which can suppress experimental autoimmune encephalomyelitis (EAE) disease in HLA-DR3.DQ8 transgenic mice. Since Interferon-β-1b [IFNβ (Betaseron)] is a major DMTs used in MS patients, we hypothesized that treatment with the combination of P. histicola and IFNβ would have an additive effect on the disease suppression. We observed that treatment with P. histicola suppressed disease as effectively as IFNβ. Surprisingly, the combination of P. histicola and IFNβ was not more effective than either treatment alone. P. histicola alone or in combination with IFNβ increased the frequency and number of CD4+FoxP3+ regulatory T cells in the gut-associated lymphoid tissue (GALT). Treatment with P. histicola alone, IFNβ alone, and in the combination decreased frequency of pro-inflammatory IFN-γ and IL17-producing CD4+ T cells in the CNS. Additionally, P. histicola alone or IFNβ alone or the combination treatments decreased CNS pathology, characterized by reduced microglia and astrocytic activation. In conclusion, our study indicates that the human gut commensal P. histicola can suppress disease as effectively as commonly used MS drug IFNβ and may provide an alternative treatment option for MS patients.

Despite extensive studies on IL-17A in MS and its animal model EAE, the role of IL-17 in disease development and maintenance is unclear. We have previously established proteolipid protein-(PLP)91–110 induce EAE model in HLA-DR3 transgenic mice. In the present study, we investigated the role of IL-17A in disease development and severity utilizing HLA-DR3 transgenic mice lacking IL-17A (IL-17A−/−). We observed that HLA-DR3.IL17A−/− mice develop milder EAE than HLA-DR3 mice suggesting that IL17 is redundant for the development of EAE but might be required for the disease severity. Milder disease in HLA-DR3.IL17A−/− mice were due to an increase in CD4+CD25+FoxP3+ Treg frequency and suppressive function of Treg cells. Depletion of Tregs using anti-CD25 neutralizing antibody abrogated milder disease phenotype in HLA-DR3.IL17A−/− mice. As gut microbiota play an important role in the generation of Treg cells, we asked whether an absence of IL17A altered gut microbiota towards Treg promoting bacteria. Our 16s rRNA analysis of gut microbiota confirmed that IL-17 deficient mice had distinct gut microbiota than IL-17 sufficient mice with an increased abundance of Treg promoting bacteria such as Lactobacillus and Clostridia. Fecal transplantation studies are underway to confirm the role of Treg promoting gut bacteria. We next investigated whether IL-17F and GM-CSF can compensate for the absence of IL-17A. Interestingly blockage of both IL-17F and GM-CSF led to increased disease severity suggesting a protective role for IL-17F and GM-CSF. Thus our study suggests that there is a bidirectional link between the gut microbiota and IL-17A and the inverse relationship between IL-17A and Tregs might determine the susceptibility vs protection from EAE.

Multiple sclerosis (MS) is an inflammatory demyelinating disease of the central nervous system. Despite IL-17A being linked to the immunopathogenesis of MS, the mechanism of IL-17A in disease development and maintenance is unclear. In the present study, we investigated the association of IL-17A and gut microbiota in disease development and severity, utilizing HLA-DR3 transgenic mice lacking IL-17A (IL-17A−/−). We found that HLA-DR3.IL-17A−/− mice had a higher frequency of CD4+CD25+FoxP3+ Treg cells and develop milder EAE compared to IL-17A suffcient HLA-DR3 mice. Utilizing 16S metagenocmic sequencing and analysis of gut microbiota we observed that HLA-DR3.IL-17A−/− mice had an increased abundance of regulatory T cells promoting bacteria in the gut such as Lactobacillus and Clostridia. Fecal transplantation followed by co-housing of HLA.DR3 mice with HLA-DR3.IL17A−/− resulted in development of milder EAE and an increase in CD4+CD25+FoxP3+ Treg cells in HLA-DR3 mice. Further whole-genome shotgun metagenomic analysis showed modulation of pathogen-associated molecular patterns (PAMPs) and O-antigen pathways linked with the host innate immune responses in HLA-DR3.IL-17A−/− mice. Thus our study suggests that gut microbiota changes due to the absence of IL17A induce regulatory T cells and suppresses disease in an animal model of MS by modulating the host-bacterial dynamics via PRR-PAMPS interactions.