Inhibition of Th1 activation and differentiation by dietary guar gum ameliorates experimental autoimmune encephalomyelitis

Dietary fibers are potent modulators of immune responses that can restrain inflammation in multiple disease contexts. However, dietary fibers encompass a biochemically diverse family of carbohydrates, and it remains unknown how individual fiber sources influence immunity. In a direct comparison of four different high-fiber diets, we demonstrate a potent ability of guar gum to delay disease and neuroinflammation in experimental autoimmune encephalomyelitis, a T cell-mediated mouse model of multiple sclerosis. Guar gum-specific alterations to the microbiota are limited, and disease protection appears to be independent of fiber-induced increases in short-chain fatty acid levels or regulatory CD4⁺ T cells. Instead, CD4⁺ T cells of guar gum-supplemented mice are less encephalitogenic due to reduced activation, proliferation, Th1 differentiation, and altered migratory potential. These findings reveal specificity in the host response to fiber sources and define a pathway of fiber-induced immunomodulation that protects against pathologic neuroinflammation.

A dietary fiber limits autoimmune neuroinflammation by restricting Th1 activation, polarization, and migration

Dietary fibers and their breakdown products have been shown to limit inflammation in multiple disease contexts. However, the term “dietary fiber” encompasses a biochemically diverse family of carbohydrates, and it remains unknown how different fiber sources influence immune cell function. To address this question, we assessed the immunomodulatory capacity of different fiber types in a mouse model of multiple sclerosis, experimental autoimmune encephalomyelitis (EAE). C57BL/6 mice were fed a control diet (5% cellulose) or diets enriched (30%) with resistant starch, inulin, pectin, or guar gum for 2 weeks prior to EAE induction. A diet rich in guar gum uniquely ameliorated the clinical, pathological, and immunological features of EAE. Limited central nervous system (CNS) infiltration of IFNγ+CD4+ T cells (Th1s) in guar gum-fed mice could be attributed to T cell-intrinsic impairment Th1 activation and polarization. Nanostring nCounter transcriptional analyses revealed downregulation of migration-associated markers in CD4+ T cells isolated from guar gum/EAE mice, which was supported by reduced cell-surface expression of integrins involved in migration into the CNS. Functionally, this translated to limited migration of guar gum-derived encephalitogenic Th1s into the CNS upon adoptive transfer into control-fed recipients, which reduced incidence and severity of EAE. However, the 16S rRNA microbiome signature and short chain fatty acid profiles were not unique in comparison to other fiber-supplemented diets, indicating a novel mechanism of action from those previously ascribed in high fiber diet studies. These data confirm the individuality of dietary fibers and identify a novel immunomodulatory function of guar gum.

This project was supported by the endMS doctoral studentship program (Multiple Sclerosis Society of Canada) (NMF, JRA), the Canadian Institutes for Health Research (PJT-148909), and the Canada Research Chair program (LCO).

Restriction of viral replication, rather than T cell immunopathology, drives lethality in MNV CR6-infected STAT1-deficient mice

Recent evidence indicates that viral components of the microbiota can contribute to intestinal homeostasis and protection from local inflammatory or infectious insults. However, host-derived mechanisms that regulate the virome remain largely unknown. Here, we used colonization of C57BL6/J mice with the model commensal murine norovirus (MNV CR6) to interrogate host-directed mechanisms of viral regulation, and show that STAT1 is a central coordinator of both viral replication and antiviral T cell responses. In STAT1-sufficient mice MNV CR6 is asymptomatic and restricted to the colon, despite the persistence of high viral loads. However, in the absence of STAT1 viral replication is disseminated and observed in key innate and adaptive immune populations.

STAT1-deficient mice develop dysregulated inflammatory CD8+ and CD4+ T cell responses, which coincide with weight loss and severe necrosis of the spleen and liver. Despite these altered T cell responses which resemble those that mediate lethal immunopathology following other model viral infections of STAT1-deficient mice, depletion of adaptive immune cells and their associated effector functions had no effect on CR6-induced disease. In contrast, therapeutic administration of an antiviral compound limited viral replication, preventing viral-induced tissue damage and death despite ongoing inflammatory antiviral T cell responses. Collectively, our data show that STAT1 restricts MNV CR6 replication within the intestinal mucosa. Unlike other model viral infections, CR6 induces disease in STAT1-deficient mice via uncontrolled viral replication rather than the concomitant development of dysregulated antiviral T cell responses.

Research in the Osborne lab is supported by the Natural Sciences and Engineering Research Council of Canada, the Canadian Institutes of Health Research, the Canada Research Chair program and scholarships from the University of British Columbia.

STAT1-dependent tolerance of intestinal viral infection

The diverse commensal ecosystem present in the mammalian intestine requires the host immune system to maintain a tolerogenic environment. The virome is an understudied component of the microbiota which promotes intestinal homeostasis and protection from injury, but the host mechanisms that regulate tolerance to viral commensals are poorly described. The antiviral signal transducer STAT1 has previously been shown to mediate tolerance to systemic viral pathogens by suppressing adaptive immune responses and protecting the host from immunopathology, but we sought to characterize its role in the context of a commensal intestinal viral infection.

We used a persistent strain of murine norovirus (MNV CR6) to interrogate host mechanisms of viral tolerance and commensalism, as CR6 has previously been shown to promote intestinal homeostasis. While CR6 infections of wildtype mice were asymptomatic and limited to the colon, STAT1-deficient mice exhibited virus-induced weight loss and mortality accompanied by systemic viral spread, colonic bacterial dysbiosis, CD4+ T cell dysfunction and hyperaccumulation of CD8+ T cells. However, clinical manifestation of virus-induced disease in STAT1-deficient mice was independent of T cells and the bacterial microbiota. Instead, therapeutic control of viral replication was sufficient to prevent virus-induced disease despite ongoing T cell dysregulation. Collectively, our data indicate that STAT1 maintains tolerance to a viral component of the intestinal microbiota by control of viral replication rather than immunopathology, suggesting that STAT1 uses distinct strategies to tolerate pathogenic and commensal viruses.

Recirculating Intestinal IgA-Producing Cells Regulate Neuroinflammation via IL-10

Plasma cells (PC) are found in the CNS of multiple sclerosis (MS) patients, yet their source and role in MS remains unclear. We find that some PC in the CNS of mice with experimental autoimmune encephalomyelitis (EAE) originate in the gut and produce immunoglobulin A (IgA). Moreover, we show that IgA⁺ PC are dramatically reduced in the gut during EAE, and likewise, a reduction in IgA-bound fecal bacteria is seen in MS patients during disease relapse. Removal of plasmablast (PB) plus PC resulted in exacerbated EAE that was normalized by the introduction of gut-derived IgA⁺ PC. Furthermore, mice with an over-abundance of IgA⁺ PB and/or PC were specifically resistant to the effector stage of EAE, and expression of interleukin (IL)-10 by PB plus PC was necessary and sufficient to confer resistance. Our data show that IgA⁺ PB and/or PC mobilized from the gut play an unexpected role in suppressing neuroinflammation.

Atomic vapor cells for chip-scale atomic clocks with improved long-term frequency stability

A novel technique for microfabricating alkali atom vapor cells is described in which alkali atoms are evaporated into a micromachined cell cavity through a glass nozzle. A cell of interior volume 1 mm3, containing 87Rb and a buffer gas, was made in this way and integrated into an atomic clock based on coherent population trapping. A fractional frequency instability of 6 x 10(-12) at 1000 s of integration was measured. The long-term drift of the F=1, mF=0-->F=2, mF=0 hyperfine frequency of atoms in these cells is below 5 x 10(-11)/day.

Compact diode-laser based rubidium frequency reference

The performance of a simple microwave frequency reference based on Raman scattering in an atomic vapor is examined. This reference has the potential to be compact, low-power, and insensitive to acceleration. Several design architectures have been evaluated with a table-top experiment in order to guide the future development of a compact system. Fractional frequency deviations of </=5x10(-11) appear to be feasible.

Frozen raspberries and hepatitis A

An outbreak of 24 cases of hepatitis A in Aberdeen was traced to a large hotel in the city by epidemiological investigation. Food-specific questioning of those affected, their fellow diners and hotel staff, coupled with serological studies, implicated raspberry mousse prepared from frozen raspberries as the source of the infection. The raspberries were probably contaminated at the time of picking.