Astrocytes play important roles in the central nervous system (CNS) during health and disease. Through genome-wide analyses we detected a transcriptional response to type I interferons (IFN-I) in astrocytes during experimental CNS autoimmunity and also in CNS lesions from multiple sclerosis (MS) patients. IFN-I signaling in astrocytes reduces inflammation and experimental autoimmune encephalomyelitis (EAE) disease scores via the ligand-activated transcription factor aryl hydrocarbon receptor (AhR) and suppressor of cytokine signaling 2 (SOCS2). The anti-inflammatory effects of nasally administered IFN-β are partly mediated by AhR. Dietary tryptophan is metabolized by the gut microbiota into AhR agonists that act on astrocytes to limit CNS inflammation. EAE scores were increased following ampicillin treatment during the recovery phase, and CNS inflammation was reduced in antibiotic-treated mice by supplementation with the tryptophan metabolites indole, indoxyl-3-sulfate (I3S), indole-3-propionic acid (IPA) and indole-3-aldehyde (IAld), or the bacterial enzyme tryptophanase. In individuals with MS, the circulating levels of AhR agonists were decreased. These findings suggest that IFN-I produced in the CNS act in combination with metabolites derived from dietary tryptophan by the gut flora to activate AhR signaling in astrocytes and suppress CNS inflammation.

The clinical benefit conferred by vascular endothelial growth factors (VEGF)-targeted therapies is variable, and tumors from treated patients eventually reinitiate growth. Here, we identify a glycosylation-dependent pathway that compensates for the absence of cognate ligand and preserves angiogenesis in response to VEGF blockade. Remodeling of the endothelial cell (EC) surface glycome selectively regulated binding of galectin-1 (Gal1), which upon recognition of complex N-glycans on VEGFR2, activated VEGF-like signaling. Vessels within anti-VEGF-sensitive tumors exhibited high levels of α2-6-linked sialic acid, which prevented Gal1 binding. In contrast, anti-VEGF refractory tumors secreted increased Gal1 and their associated vasculature displayed glycosylation patterns that facilitated Gal1-EC interactions. Interruption of β1-6GlcNAc branching in ECs or silencing of tumor-derived Gal1 converted refractory into anti-VEGF-sensitive tumors, whereas elimination of α2-6-linked sialic acid conferred resistance to anti-VEGF. Disruption of the Gal1-N-glycan axis promoted vascular remodeling, immune cell influx and tumor growth inhibition. Thus, targeting glycosylation-dependent lectin-receptor interactions may increase the efficacy of anti-VEGF treatment.

Summary Intact interkeulin-10 receptor (IL-10R) signaling on effector and regulatory T (Treg) cells are each independently required to maintain immune tolerance. Here we show that IL-10 sensing by innate immune cells, independent of its effects on T cells, was critical for regulating mucosal homeostasis. Following wild-type CD4+ T cell transfer, Rag2−/−Il10rb−/− mice developed severe colitis in association with profound defects in generation and function of Treg cells. Moreover, loss of IL-10R signaling impaired the generation and function of anti-inflammatory intestinal and bone marrow-derived macrophages, and their ability to secrete IL-10. Importantly, transfer of wild-type but not Il10rb−/− anti-inflammatory macrophages ameliorated colitis induction by wild-type CD4+ T cells in Rag2−/−Il10rb−/− mice. Similar alterations in the generation and function of anti-inflammatory macrophages were observed in IL-10R-deficient patients with very early-onset inflammatory bowel disease. Collectively, our studies define innate immune IL-10R signaling as a key factor regulating mucosal immune homeostasis in mice and humans.

Astrocytes play complex roles in the response to trauma, infection or inflammation in the central nervous system (CNS). Thus, it is important to characterize the mechanisms regulating astrocyte function, as well as potential targets for the therapeutic modulation of astrocyte activity. Here we report that lactosylceramide (LacCer) levels are up-regulated in the CNS during chronic experimental autoimmune encephalomyelitis (EAE), an experimental model of multiple sclerosis (MS). We found that LacCer synthesized by β-1,4-galactosyltransferase 6 (B4GALT6) in astrocytes acts in an autocrine manner to trigger transcriptional programs that promote the recruitment and activation of CNS-infiltrating monocytes and microglia, and neurodegeneration. We also detected increased B4GALT6 expression and LacCer levels in CNS MS lesions. Finally, the inhibition of LacCer synthesis suppressed local CNS innate immunity and neurodegeneration in EAE, and interfered with the activation of human astrocytes in vitro. Thus, B4GALT6 is a potential therapeutic target for MS and other neuroinflammatory disorders.

Our understanding of the pathways that regulate lymphocyte metabolism, as well as the effects of metabolism and its products on the immune response, is still limited. We report that a metabolic program controlled by the transcription factors hypoxia inducible factor-1α (HIF1-α) and aryl hydrocarbon receptor (AHR) supports the differentiation of type 1 regulatory (Tr1) cells. HIF1-α controls the early metabolic reprograming of Tr1 cells. At later time points, AHR promotes HIF1-α degradation and takes control of Tr1 cell metabolism. Extracellular adenosine triphosphate (eATP) and hypoxia, linked to inflammation, trigger AHR inactivation by HIF1-α and inhibit Tr1 cell differentiation. Conversely, CD39 promotes Tr1 cell differentiation by depleting eATP. CD39 also contributes to Tr1 suppressive activity by generating adenosine in cooperation with CD73 expressed by responder T cells and antigen presenting cells. These results suggest that HIF1-α and AHR integrate immunological, metabolic and environmental signals to regulate the immune response.

Dendritic cells (DCs) control the balance between effector and regulatory T cells in vivo. Hence, the study of DCs might identify mechanisms of disease pathogenesis and guide new therapeutic approaches for immune-mediated disorders. We found that IL-27 signaling in murine DCs limits the generation of effector TH1 and TH17 cells and the development of experimental autoimmune encephalomyelitis (EAE). The effects of IL-27 were mediated, at least partially, through the induction of the immunoregulatory molecule ENTPD1 (CD39) in DCs. IL-27-induced ENTPD1 decreased extracellular ATP levels, down-regulating nucleotide-dependent NLRP3 inflammasome activation. Finally, therapeutic vaccination with IL-27-conditioned DCs suppressed established relapsing-remitting EAE. Thus, IL-27 signaling in DCs limits pathogenic T cell responses and the development of autoimmunity.

SUMMARY Inflammation-mediated neurodegeneration occurs in the acute and the chronic phases of multiple sclerosis (MS) and its animal model experimental autoimmune encephalomyelitis (EAE). Classically-activated (M1) microglia are key players mediating this process. Here we identified Galectin-1 (Gal1), an endogenous glycan-binding protein, as a pivotal regulator of M1 microglia activation, targeting the activation of p38MAPK-, CREB-, and NF-κB-dependent signaling pathways and hierarchically supressing downstream pro-inflammatory mediators such as iNOS, TNF and CCL2. Gal1 bound to core 2 O-glycans on CD45, favoring retention of this glycoprotein on the microglial cell surface and augmenting its phosphatase activity and inhibitory function. Gal1 was highly expressed in the acute phase of EAE and its targeted deletion resulted in pronounced inflammation-induced neurodegeneration. Adoptive transfer of Gal1-secreting astrocytes or administration of recombinant Gal1 suppressed EAE through mechanisms involving microglia de-activation. Thus, Gal1-glycan interactions are essential in tempering microglia activation, brain inflammation and neurodegeneration with critical therapeutic implications for MS.

SUMMARY Seasonal changes in disease activity have been observed in multiple sclerosis, an autoimmune disorder that affects the central nervous system. These epidemiological observations suggest that environmental factors influence the disease course. Here we report that melatonin levels, whose production is modulated by seasonal variations in night length, negatively correlate with multiple sclerosis activity in humans. Treatment with melatonin ameliorates disease in an experimental model of multiple sclerosis and directly interferes with the differentiation of human and mouse T cells. Melatonin induces the expression of the repressor transcription factor Nfil3, blocking the differentiation of pathogenic Th17 cells as well as boosts the generation of protective Tr1 cells via Erk1/2 and the transactivation of the IL-10 promoter by ROR-α. These results suggest that melatonin is another example of how environmental-driven cues can impact on T cell differentiation and have implications for autoimmune disorders such as multiple sclerosis.