IL-9 as a mediator of Th17-driven inflammatory disease

We report that like other T cells cultured in the presence of transforming growth factor (TGF) beta, Th17 cells also produce interleukin (IL) 9. Th17 cells generated in vitro with IL-6 and TGF-beta as well as purified ex vivo Th17 cells both produced IL-9. To determine if IL-9 has functional consequences in Th17-mediated inflammatory disease, we evaluated the role of IL-9 in the development and progression of experimental autoimmune encephalomyelitis, a mouse model of multiple sclerosis. The data show that IL-9 neutralization and IL-9 receptor deficiency attenuates disease, and this correlates with decreases in Th17 cells and IL-6-producing macrophages in the central nervous system, as well as mast cell numbers in the regional lymph nodes. Collectively, these data implicate IL-9 as a Th17-derived cytokine that can contribute to inflammatory disease.

Central nervous system demyelinating disease protection by the human commensal Bacteroides fragilis depends on polysaccharide A expression

The importance of gut commensal bacteria in maintaining immune homeostasis is increasingly understood. We recently described that alteration of the gut microflora can affect a population of Foxp3(+)T(reg) cells that regulate demyelination in experimental autoimmune encephalomyelitis (EAE), the experimental model of human multiple sclerosis. We now extend our previous observations on the role of commensal bacteria in CNS demyelination, and we demonstrate that Bacteroides fragilis producing a bacterial capsular polysaccharide Ag can protect against EAE. Recolonization with wild type B. fragilis maintained resistance to EAE, whereas reconstitution with polysaccharide A-deficient B. fragilis restored EAE susceptibility. Enhanced numbers of Foxp3(+)T(reg) cells in the cervical lymph nodes were observed after intestinal recolonization with either strain of B. fragilis. Ex vivo, CD4(+)T cells obtained from mice reconstituted with wild type B. fragilis had significantly enhanced rates of conversion into IL-10-producing Foxp3(+)T(reg) cells and offered greater protection against disease. Our results suggest an important role for commensal bacterial Ags, in particular B. fragilis expressing polysaccharide A, in protecting against CNS demyelination in EAE and perhaps human multiple sclerosis.

A commensal symbiotic factor derived from Bacteroides fragilis promotes human CD39(+)Foxp3(+) T cells and Treg function

Polysaccharide A (PSA) derived from the human commensal Bacteroides fragilis is a symbiosis factor that stimulates immunologic development within mammalian hosts. PSA rebalances skewed systemic T helper responses and promotes T regulatory cells (Tregs). However, PSA-mediated induction of Foxp3 in humans has not been reported. In mice, PSA-generated Foxp3(+) Tregs dampen Th17 activity thereby facilitating bacterial intestinal colonization while the increased presence and function of these regulatory cells may guard against pathological organ-specific inflammation in hosts. We herein demonstrate that PSA induces expression of Foxp3 along with CD39 among naïve CD4 T cells in vitro while promoting IL-10 secretion. PSA-activated dendritic cells are essential for the mediation of this regulatory response. When cultured with isolated Foxp3(+) Tregs, PSA enriched Foxp3 expression, enhanced the frequency of CD39(+)HLA-DR(+) cells, and increased suppressive function as measured by decreased TNFα expression by LPS-stimulated monocytes. Our findings are the first to demonstrate in vitro induction of human CD4(+)Foxp3(+) T cells and enhanced suppressive function of circulating Foxp3(+) Tregs by a human commensal bacterial symbiotic factor. Use of PSA for the treatment of human autoimmune diseases, in particular multiple sclerosis and inflammatory bowel disease, may represent a new paradigm in the approach to treating autoimmune disease.

Gut, bugs, and brain: role of commensal bacteria in the control of central nervous system disease

The mammalian gastrointestinal track harbors a highly heterogeneous population of microbial organisms that are essential for the complete development of the immune system. The gut microbes or "microbiota," coupled with host genetics, determine the development of both local microbial populations and the immune system to create a complex balance recently termed the "microbiome." Alterations of the gut microbiome may lead to dysregulation of immune responses both in the gut and in distal effector immune sites such as the central nervous system (CNS). Recent findings in experimental autoimmune encephalomyelitis, an animal model of human multiple sclerosis, suggest that altering certain bacterial populations present in the gut can lead to a proinflammatory condition that may result in the development of autoimmune diseases, in particular human multiple sclerosis. In contrast, other commensal bacteria and their antigenic products, when presented in the correct context, can protect against inflammation within the CNS.

A commensal bacterial product elicits and modulates migratory capacity of CD39(+) CD4 T regulatory subsets in the suppression of neuroinflammation

Tolerance established by host-commensal interactions regulates host immunity at both local mucosal and systemic levels. The intestinal commensal strain Bacteroides fragilis elicits immune tolerance, at least in part, via the expression capsular polysaccharide A (PSA). How such niche-specific commensal microbial elements regulate extra-intestinal immune responses, as in the brain, remains largely unknown. We have recently shown that oral treatment with PSA suppresses neuro-inflammation elicited during experimental autoimmune encephalomyelitis (EAE), an animal model for multiple sclerosis. This protection is dependent upon the expansion of immune-regulatory CD4 T cells (Treg) expressing CD39, an ectonucleotidase. Here, we further show that CD39 modulation of purinergic signals enhances migratory phenotypes of both total CD4 T cells and Foxp3(+) CD4 Tregs at central nervous system (CNS) lymphoid-draining sites in EAE in vivo and promotes their migration in vitro. These changes are noted during PSA treatment, which leads to heightened accumulation of CD39(+) CD4 Tregs in the CNS. Deficiency of CD39 abrogates accumulation of Treg during EAE, and is accompanied by elevated Th1/Th17 signals in the CNS and in gut-associated lymphoid tissues. Our results demonstrate that immune-modulatory commensal bacterial products impact the migratory patterns of CD4 Treg during CNS autoimmunity via the regulation of CD39. These observations provide clues as to how intestinal commensal microbiome is able to modulate Treg functions and impact host immunity in the distal site.

Downregulation of IL-17 and IL-6 in the central nervous system by glatiramer acetate in experimental autoimmune encephalomyelitis

T helper 17 (Th17) cells are pivotal in the immune pathogenesis of EAE. Glatiramer acetate (GA) can enhance Treg FOXp3 expression. We demonstrate that GA downregulates the expression of both IL-17 and IL-6 in two different EAE models. Increased mRNA expression in CNS for ROR gamma t, IL-17, IL-12/IL-23, IL-6, TNF-alpha, STAT4 and Th1 cytokines were significantly reduced by GA with a concomitant rise in SMAD3. The increased expression of TNF-alpha, IL-6, and IL-17 in CNS of CD25+ depleted animals was suppressed by GA treatment. This study demonstrates that both Th1 polarization and Th17 expression are modulated by GA.

Increased expression of B cell-associated regulatory cytokines by glatiramer acetate in mice with experimental autoimmune encephalomyelitis

B cells are of increasing importance as a target for multiple sclerosis treatment. Here we show that GA treatment of mice with experimental autoimmune encephalomyelitis (EAE) biases cytokine production by B cells towards cytokines associated with regulation in MS including interleukin (IL)-4, -10 and -13 and reduces pro-inflammatory IL-6, IL-12, and TNF alpha levels. GA also down-regulates expression of B cell-activating factor (BAFF) of the TNF family and a proliferation-inducing ligand (APRIL), as well as the BAFF receptor in mice with EAE. Thus, GA impacts both B cell survival and B cell cytokine production during CNS inflammatory disease in an EAE model.

Induction of gut regulatory CD39+ T cells by teriflunomide protects against EAE

Objective:

To determine whether as an orally delivered treatment, teriflunomide, an inhibitor of the mitochondrial enzyme dihydroorotate dehydrogenase approved to treat relapsing forms of multiple sclerosis, could affect gut-associated lymphoid tissue (GALT) immune responses functionally.

Methods:

C57BL/6 mice were treated orally with teriflunomide and flow cytometric analysis of immune GALT cells performed ex vivo, and adoptive transfer experiments were used to test the protective effects of GALT regulatory T (Treg) cells.

Results:

Teriflunomide reduced the percentages of antigen-presenting cells of Peyer patches when compared to controls. Conversely, a significant increase of the relative frequency of CD39⁺ Treg cells was observed. In vivo, the protective effect of GALT-derived teriflunomide-induced CD39⁺ Treg cells was established by adoptive transfer into recipient experimental autoimmune encephalomyelitis mice.

Conclusions:

Our results identify specific GALT-derived CD39⁺ Treg cells as a mechanism of action that may contribute to the efficacy of teriflunomide during CNS inflammatory demyelination and as an oral therapeutic in relapsing multiple sclerosis.

Apoptosis in Toxoplasma gondii activated T cells: the role of IFNgamma in enhanced alteration of Bcl-2 expression and mitochondrial membrane potential

In the present study we addressed the question whether Toxoplasma gondii could promote apoptosis in T lymphocytes in the acute stage of infection. Using in vivo activated T cells and then culturing them for a short time, we observed activation-induced cell death in T. gondii infected mice. A higher level of activation-induced cell death (AICD) was seen in susceptible C57BL/6 mice than in resistant CBA/J mice following infection with the same P strain of parasite. Apoptosis in T cells of susceptible mice was associated with altered induction of Bcl-2/Bax, loss of Mitochondrial Transmembrane Potential. Both CD4+ and CD8+ T cells were found to be susceptible to apoptosis; CD4+ T cells were sensitive to Fas-mediated death whereas CD8+ T cells were insensitive to this signal. Caspase inhibitors had less effect on DNA fragmentation in CD4+ compared to CD8+ T cells. Exposure of CD4+ T cells to anti-IFNgamma mAb resulted in an increase in the number of T cells that were positive for anti-apoptotic molecule Bcl-2 and DiOC6, a cationic dye that accumulates in intact mitochondria. These changes were less noticeable in CD8+ T cells following treatment with anti-IFNgamma mAb. These findings provide further insight into the mechanisms of T cell apoptosis in T. gondii infection.

The role of CD39-expressing regulatory T cells following treatment with αCD52: an effective therapeutic against central nervous system autoimmunity

Alemtuzumab (αCD52), a novel immunotherapy approved for the treatment of relapsing multiple sclerosis (MS), induces the widescale deletion of lymphocytes, including self-reactive T cells. Using the mouse model of MS, experimental autoimmune encephalomyelitis (EAE), we previously found that following reconstitution of the immune compartment, there was an increased frequency of CD39+Foxp3+ regulatory T cells (Tregs) in the spleen and gut-associated lymphoid tissues of αCD52-treated mice. We hypothesized that the CD39-expressing Tregs that emerge following lymphocyte reconstitution would be suppressive against central nervous system autoimmunity. However, when CD39+ Tregs were purified from αCD52-treated mice and adoptively transferred to naïve recipients, they were unable to reduce the severity of EAE disease. We next used Foxp3/GFP reporter mice treated with αCD52 to compare the suppressive capacity of CD39+Foxp3+ versus CD39+Foxp3− Treg subsets and found that CD39+Foxp3+ Tregs, but not CD39+Foxp3− Tregs, were able to significantly reduce the proliferation of activated naïve T cells in vitro. Finally, we sought to determine if expression of CD39 was required for the therapeutic effects of αCD52 in the EAE model. Preliminary studies using a limited number of CD39 KO mice indicated that treatment with αCD52 was equally effective in both control and KO mice. Thus, our studies have identified potential differences in individual subsets of Tregs emerging after αCD52 treatment and suggest that expression of CD39 is dispensable for the short-term effectiveness of αCD52 in mice. Future studies are required to determine if CD39 expression on Tregs contributes to the long-term suppression of MS disease in patients treated with αCD52.