Herpes Simplex Virus-1 (HSV) infection of the cornea leads to a blinding immuno-inflammatory lesion of the eye termed stromal keratitis (SK). Recently, IL-17 producing CD4+ T cells (Th17) were shown to play a prominent role in many autoimmune conditions, but the role of IL-17 and/or of Th17 cells in virus immunopathology is unclear. Here we show that, after HSV infection of the cornea, IL-17 is upregulated in a biphasic manner with an initial peak production around day 2 pi and a second wave starting from day 7 pi with a steady increase until day 21 pi, a time point when clinical lesions are fully evident. Further studies demonstrated that innate cells particularly, γδ T cells, were major producers of IL-17 early after HSV infection. However, during the clinical phase of SK, the predominant source of IL-17 was Th17 cells which infiltrated the cornea only after the entry of Th1 cells. By ex-vivo stimulation, the half fraction of IFN-γ producing CD4+ T (Th1) cells were HSV specific, whereas very few Th17 cells responded to HSV stimulation. The delayed influx of Th17 cells in the cornea was attributed to the local chemokine and cytokine milieu. Finally, HSV infection of IL-17 receptor knockout mice, as well as IL-17 neutralization in WT mice showed diminished SK severity. In conclusion, our results show that IL-17 and Th17 cells contribute to the pathogenesis of SK, the most common cause of infectious blindness in the western world.

In this communication, we demonstrate that galectin (Gal)-9 acts to constrain CD8+ T cell immunity to Herpes Simplex Virus (HSV) infection. In support of this, we show that animals unable to produce Gal-9, because of gene knockout, develop acute and memory responses to HSV that are of greater magnitude and better quality than those that occur in normal infected animals. Interestingly, infusion of normal infected mice with α-lactose, the sugar that binds to the carbohydrate-binding domain of Gal-9 limiting its engagement of T cell immunoglobulin and mucin (TIM-3) receptors, also caused a more elevated and higher quality CD8+ T cell response to HSV particularly in the acute phase. Such sugar treated infected mice also had expanded populations of effector as well as memory CD8+ T cells. The increased effector T cell responses led to significantly more efficient virus control. The mechanisms responsible for the outcome of the Gal-9/TIM-3 interaction in normal infected mice involved direct inhibitory effects on TIM-3+ CD8+ T effector cells as well as the promotion of Foxp3+ regulatory T cell activity. Our results indicate that manipulating galectin signals, as can be achieved using appropriate sugars, may represent a convenient and inexpensive approach to enhance acute and memory responses to a virus infection.

Tumors actively suppress antitumor immunity creating formidable barriers to successful cancer immunotherapy. The molecular mechanisms underlying tumor-induced immune tolerance are largely unknown. In the present study, we show that dendritic cells (DCs) in the tumor microenvironment (TME) acquire the ability to metabolize vitamin A to produce retinoic acid (RA), which drives T regulatory responses and immune tolerance. Tolerogenic responses were dependent on induction of vitamin A-metabolizing enzymes via the β-catenin/T Cell Factor (TCF) pathway in DCs. Consistent with this observation, DC-specific deletion of β-catenin in mice markedly reduced T regulatory responses and delayed melanoma growth. Pharmacological inhibition of either vitamin A metabolizing enzymes or the β-catenin/TCF4 pathway in vivo had similar effects on tumor growth and T regulatory responses. Hence, β-catenin/TCF4 signaling induces local regulatory DC and regulatory T cell phenotypes via the RA pathway, identifying this pathway as an important target for anticancer immunotherapy.

Breakdown in immunological tolerance to self-antigens or uncontrolled inflammation results in autoimmune disorders. Dendritic cells (DCs) play an important role in regulating the balance between inflammatory and regulatory responses in the periphery. However, factors in the tissue microenvironment and the signaling networks critical for programming DCs to control chronic inflammation and promote tolerance are unknown. Here, we show that wnt ligand-mediated activation of β-catenin signaling in DCs is critical for promoting tolerance and limiting neuroinflammation. DC-specific deletion of key upstream (LRP5/6) or downstream mediators (β-catenin) of canonical wnt-signaling in mice exacerbated experimental autoimmune encephalomyelitis (EAE) pathology. Mechanistically, loss of LRP5/6-β-catenin-mediated signaling in DCs led to an increased Th1/ Th17 cell differentiation whereas reduced regulatory T cell response. This was due to increased production of pro-inflammatory cytokines and decreased production of anti-inflammatory cytokines such as IL-10 and IL-27 by DCs lacking LRP5/6-β-catenin signaling. Consistent with these findings, pharmacological activation of canonical wnt/β-catenin signaling delayed EAE onset and diminished CNS pathology. Thus, the activation of canonical wnt signaling in DCs limits effector T cell responses and represents a potential therapeutic approach to control autoimmune neuroinflammation.

Controlling chronic immunoinflammatory diseases such as lesions in eye caused by infection with herpes simplex virus (HSV) represents therapeutic challenge. Since CD4+ T cells are the primary orchestrators of lesions, targeting activated CD4+ T cell subsets and increasing the representation of cells that express regulatory function would be a logical therapeutic approach. We show that this outcome can be achieved by therapy, systemic or local, with the lectin-family member galectin-9. This molecule, which is a natural product of many cell types, acts as a ligand to the inhibitory molecule TIM-3 that is expressed by activated but not naïve T cells. We show that 50% or more of T cells in ocular lesions caused by HSV in mice express TIM-3 and that blocking signals from its natural ligand with a monoclonal antibody results in more severe lesions. More importantly the provision of additional galectin-9, either systemically or more effectively by local subconjuctival administration, diminished the severity of SK lesions as well as the extent of corneal neovascularization. Multiple mechanisms were involved in inhibitory effects. These included apoptosis of the orchestrating effector T cells with consequent reduction of proinflammatory cytokines, an increase in the representation of two separate subtypes of regulatory cells as well as inhibitory effects on the production of molecules involved in neovascularization, an essential component of SK pathogenesis. Our results indicate that galectin-9 therapy may represent a useful approach to control HSV induced lesions, the commonest cause of infectious blindness in the Western World.

At mucosal sites such as the intestine, the immune system launches robust immunity against invading pathogens while maintaining a state of tolerance to commensal flora and ingested food Ags. The molecular mechanisms underlying this phenomenon remain poorly understood. In this study, we report that signaling by GPR81, a receptor for lactate, in colonic dendritic cells and macrophages plays an important role in suppressing colonic inflammation and restoring colonic homeostasis. Genetic deletion of GPR81 in mice led to increased Th1/Th17 cell differentiation and reduced regulatory T cell differentiation, resulting in enhanced susceptibility to colonic inflammation. This was due to increased production of proinflammatory cytokines (IL-6, IL-1β, and TNF-α) and decreased expression of immune regulatory factors (IL-10, retinoic acid, and IDO) by intestinal APCs lacking GPR81. Consistent with these findings, pharmacological activation of GPR81 decreased inflammatory cytokine expression and ameliorated colonic inflammation. Taken together, these findings identify a new and important role for the GPR81 signaling pathway in regulating immune tolerance and colonic inflammation. Thus, manipulation of the GPR81 pathway could provide novel opportunities for enhancing regulatory responses and treating colonic inflammation.

Stromal keratitis (SK) is a chronic immunopathological lesion of the eye caused by herpes simplex virus-1 (HSV-1) infection and a common cause of blindness in humans. The inflammatory lesions are primarily perpetuated by neutrophils with the active participation of CD4+ T cells. Therefore, targeting these immune cell types represents a potentially valuable form of therapy to reduce the severity of disease. Resolvin E1 (RvE1), an endogenous lipid mediator, was shown to promote resolution in several inflammatory disease models. In the present report, we determined if RvE1 administration begun at different times after ocular infection of mice with HSV could influence the severity of SK lesions. Treatment with RvE1 significantly reduced the extent of angiogenesis and SK lesions that occurred. RvE1 treated mice had fewer numbers of inflammatory cells that included Th1 and Th17 cells as well as neutrophils in the cornea. The mechanisms by which RvE1 acts appear to be multiple. These included reducing the influx of neutrophils and pathogenic CD4+ T cells, increasing production of the anti-inflammatory cytokine IL-10, and inhibitory effects on the production of pro-inflammatory mediators and molecules such as IL-6, IFN-γ, IL-17, KC, VEGF-A, MMP-2 and MMP-9, that are involved in corneal neovascularization and SK pathogenesis. These findings are the first to show that RvE1 treatment could represent a novel approach to control lesion severity in a virally induced immunopathological disease.

The Wnt/β-catenin pathway is an evolutionarily conserved signaling pathway critical for several biological processes. An aberrant Wnt/β-catenin signaling is linked to several human diseases. Emerging studies have highlighted the regulatory role of the Wnt/β-catenin signaling pathway in normal physiological processes of parenchymal and hematopoietic cells. Recent studies have shown that the activation of Wnt/β-catenin pathway in dendritic cells (DCs) play a critical role in mucosal tolerance and suppression of chronic autoimmune pathologies. Alternatively, tumors activate Wnt/β-catenin pathway in DCs to induce immune tolerance and thereby evade antitumor immunity through suppression of effector T cell responses and promotion of regulatory T cell responses. Here, we review our work and current understanding of how Wnt/β-catenin signaling in DCs shapes the immune response in cancer and autoimmunity and discuss how Wnt/β-catenin pathway can be targeted for successful therapeutic interventions in various human diseases.