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.

The precise role of each of the seven individual CD11c؉ dendritic cell subsets (DCs) identified to date in the response to viral infections is not known. DCs serve as critical links between the innate and adaptive immune responses against many pathogens, including herpes simplex virus type 1 (HSV-1). The role of DCs as mediators of resistance to HSV-1 infection was investigated using CD11c-diphtheria toxin (DT) receptor-green fluorescent protein transgenic mice, in which DCs can be transiently depleted in vivo by treatment with low doses of DT. We show that ablation of DCs led to enhanced susceptibility to HSV-1 infection in the highly resistant C57BL/6 mouse strain. Specifically, we showed that the depletion of DCs led to increased viral spread into the nervous system, resulting in an increased rate of morbidity and mortality. Furthermore, we showed that ablation of DCs impaired the optimal activation of NK cells and CD4؉ and CD8 ؉ T cells in response to HSV-1. These data demonstrated that DCs were essential not only in the optimal activation of the acquired T-cell response to HSV-1 but also that DCs were crucial for innate resistance to HSV-1 infection.Based on serological evidence, it is estimated that 60 to 80% of the adult population is infected with herpes simplex virus type 1 (HSV-1) (46). Most infected individuals remain asymptomatic. Of symptomatic individuals, clinical presentation ranges from mild illness, such as the development of orofacial vesicular lesions, all the way to life-threatening systemic complications, such as hepatitis and encephalitis (39). The outcome of infection is known to be influenced by both specific and nonspecific genetically linked host defense mechanisms (32). The immune system is particularly important in controlling HSV-1 infection in both the periphery and the nervous system, although the events that initiate this immunity in humans are not very well understood. Underlying immunosuppression does not appear to explain the distinct outcomes of host-virus interaction. Rather, the observed range in clinical outcomes appears to reflect differences in intrinsic resistance to infection.Studies using inbred strains of mice have revealed critical insights into the immunological basis for resistance to . Specifically, a range in innate resistance to systemic, lethal HSV-1 infection exists and has subsequently led to the grouping of inbred mice into resistant, moderately susceptible, and susceptible categories based upon the levels of virus required to cause death. In all cases examined, mice of the C57 background (C57BL/6 and C57BL/10) are most resistant and best able to effectively control HSV-1 infection (35).Human and murine studies suggest that the innate immune response, specifically the ability to produce elevated levels of type I interferon (IFN) at early time points, provides a threshold of resistance to acute HSV-1 infection (44).

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.

MicroRNAs (miRNAs) are small regulatory molecules that control diverse biological processes that include angiogenesis. Herpes simplex virus (HSV) causes a chronic immuno-inflammatory response in the eye that may result in corneal neovascularization during blinding immunopathological lesion stromal keratitis (SK). miR-132 is a highly conserved miRNA that is induced in endothelial cells in response to growth factors, such as vascular endothelial growth factor (VEGF). In this study, we show that miR-132 expression was up-regulated (10- to 20-fold) after ocular infection with HSV, an event that involved the production of both VEGF-A and IL-17. Consequently, blockade of VEGF-A activity using soluble VEGF receptor 1 resulted in significantly lower levels of corneal miR-132 after HSV infection. In addition, low levels of corneal miR-132 were detected in IL-17 receptor knockout mice after HSV infection. In vivo silencing of miR-132 by the provision of anti-miR-132 (antagomir-132) nanoparticles to HSV-infected mice led to reduced corneal neovascularization and diminished SK lesions. The anti-angiogenic effect of antagomir-132 was reflected by a reduction in angiogenic Ras activity in corneal CD31-enriched cells (presumably blood vessel endothelial cells) during SK. To our knowledge, this is one of the first reports of miRNA involvement in an infectious ocular disease. Manipulating miRNA expression holds promise as a therapeutic approach to control an ocular lesion that is an important cause of human blindness.

Herpes simplex virus (HSV) infection of adult humans occasionally results in life-threatening herpes simplex encephalitis (HSE) for reasons that remain to be defined. An animal system that could prove useful to model HSE could be miR-155 knockout mice (miR-155KO). Thus we observe that mice with a deficiency of miR-155 are highly susceptible to HSE with a majority of animals (75–80%) developing HSE after ocular infection with HSV-1. The lesions appeared to primarily represent the destructive consequences of viral replication and animals could be protected from HSE by acyclovir treatment provided 4 days after ocular infection. The miR-155KO animals were also more susceptible to develop zosteriform lesions, a reflection of viral replication and dissemination within the nervous system. One explanation for the heightened susceptibility to HSE and zosteriform lesions could be because miR-155KO animals develop diminished CD8 T cell responses when the numbers, functionality and homing capacity of effector CD8 T cell responses were compared. Indeed, adoptive transfer of HSV-immune CD8 T cells to infected miR-155KO mice at 24 hours post infection provided protection from HSE. Deficiencies in CD8 T cell numbers and function also explained the observation that miR-155KO animals were less able than control animals to maintain HSV latency. Our observations may be the first to link miR-155 expression with increased susceptibility of the nervous system to virus infection.

Ocular infection with herpes simplex virus (HSV) causes corneal neovascularization (CV), an essential step in the pathogenesis of the blinding immuno-inflammatory lesion, stromal keratitis (SK). The infection results in IL-17A production which contributes to CV in ways that together serve to shift the balance between corneal concentrations of VEGF-A and the soluble receptor molecule sVEGFR-1 which binds to VEGF-A and blocks its function (a so-called VEGF trap). Accordingly, animals lacking responses to IL-17A signaling, either because of IL-17 receptor-A knockout or WT animals that received neutralizing mAb to I L-17A had diminished CV compared to controls. The procedures reduced VEGF-A protein levels, but had no effect on the levels of sVEGFR-1 present. Hence the VEGF trap was strengthened. IL-17A also caused increased CXCL1/KC synthesis, which attracts neutrophils to the inflammatory site. Neutrophils further influenced the extent of CV by acting as an additional source of VEGF-A as well as metalloproteinase (MMP) enzymes that degrade the soluble receptor inhibiting its VEGF blocking activity. Our results indicate that suppressing the expression of IL-17A, or increasing the activity of the VEGF trap, represent useful approaches to inhibit CV and the control of an ocular lesion that is an important cause of human blindness.

After herpes simplex virus type 1 (HSV-1) infection, CD8+ T cells accumulate in the trigeminal ganglion (TG) and participate in the maintenance of latency. However, the mechanisms underlying intermittent virus reactivation are poorly understood. In this study, we demonstrate the role of an inhibitory interaction between Tim-3 expressing CD8+ T cells and galectin 9 (Gal-9) that could influence HSV-1 latency and reactivation. Accordingly, we show that the majority of Kb-gB tetramer specific CD8+T cells in the TG of HSV-1 infected mice express Tim-3, a molecule that delivers negative signals to CD8+ T cells upon engagement of its ligand Gal-9. Gal-9 was also up-regulated in the TG when replicating virus was present as well during latency. This could set the stage for Gal-9/Tim-3 interaction and this inhibitory interaction was responsible for reduced CD8+ T cell effector function in WT mice. Additionally, TG cell cultures exposed to recombinant Gal-9 in the latent phase caused apoptosis of majority of CD8+ T cells. Further, Gal-9 KO TG cultures showed delayed and reduced viral reactivation as compared to wild type cultures demonstrating the greater efficiency of CD8+ T cells to inhibit virus reactivation in the absence of Gal-9. Moreover, the addition of recombinant Gal-9 to ex vivo TG cultures induced enhanced viral reactivation compared to untreated controls. Our results demonstrate that the host homeostatic mechanism mediated by Gal-9/Tim-3 interaction on CD8+ T cells can influence the outcome of HSV-1 latent infection and manipulating Gal-9 signals might represent therapeutic means to inhibit HSV-1 reactivation from latency.