CD8 T cells mediate transient herpes stromal keratitis in CD4-deficient mice

The Dilemma of HSV-1 Oncolytic Virus Delivery: The Method Choice and Hurdles

Oncolytic viruses (OVs) have emerged as effective gene therapy and immunotherapy drugs. As an important gene delivery platform, the integration of exogenous genes into OVs has become a novel path for the advancement of OV therapy, while the herpes simplex virus type 1 (HSV-1) is the most commonly used. However, the current mode of administration of HSV-1 oncolytic virus is mainly based on the tumor in situ injection, which limits the application of such OV drugs to a certain extent. Intravenous administration offers a solution to the systemic distribution of OV drugs but is ambiguous in terms of efficacy and safety. The main reason is the synergistic role of innate and adaptive immunity of the immune system in the response against the HSV-1 oncolytic virus, which is rapidly cleared by the body's immune system before it reaches the tumor, a process that is accompanied by side effects. This article reviews different administration methods of HSV-1 oncolytic virus in the process of tumor treatment, especially the research progress in intravenous administration. It also discusses immune constraints and solutions of intravenous administration with the intent to provide new insights into HSV-1 delivery for OV therapy.

The atypical chemokine receptor-2 fine-tunes the immune response in herpes stromal keratitis

Herpes stromal keratitis (HSK) is a blinding corneal disease caused by herpes simplex virus-1 (HSV-1), a common pathogen infecting most of the world's population. Inflammation in HSK is chemokine-dependent, particularly CXCL10 and less so the CC chemokines. The atypical chemokine receptor-2 (ACKR2) is a decoy receptor predominantly for pro-inflammatory CC chemokines, which regulates the inflammatory response by scavenging inflammatory chemokines thereby modulating leukocyte infiltration. Deletion of ACKR2 exacerbates and delays the resolution of the inflammatory response in most models. ACKR2 also regulates lymphangiogenesis and mammary duct development through the recruitment of tissue-remodeling macrophages. Here, we demonstrate a dose-dependent upregulation of ACKR2 during corneal HSV-1 infection. At an HSV inoculum dose of 5.4 x 105 pfu, but not at higher dose, ACKR2 deficient mice showed prolonged clinical signs of HSK, increased infiltration of leukocytes and persistent corneal neovascularization. Viral clearance and T cell activation were similar in ACKR2-/- and wild type mice, despite a transient diminished expression of CD40 and CD86 in dendritic cells. The data suggest that ACKR2 fine-tunes the inflammatory response and the level of neovascularization in the HSK.

Sensory Nerve Retraction and Sympathetic Nerve Innervation Contribute to Immunopathology of Murine Recurrent Herpes Stromal Keratitis

Purpose

Herpes stromal keratitis (HSK) represents a spectrum of pathologies which is caused by herpes simplex virus type 1 (HSV-1) infection and is considered a leading cause of infectious blindness. HSV-1 infects corneal sensory nerves and establishes latency in the trigeminal ganglion (TG). Recently, retraction of sensory nerves and replacement with “unsensing” sympathetic nerves was identified as a critical contributor of HSK in a mouse model where corneal pathology is caused by primary infection. This resulted in the loss of blink reflex, corneal desiccation, and exacerbation of inflammation leading to corneal opacity. Despite this, it was unclear whether inflammation associated with viral reactivation was sufficient to initiate this cascade of events.

Methods

We examined viral reactivation and corneal pathology in a mouse model with recurrent HSK by infecting the cornea with HSV-1 (McKrae) and transferring (intravenous [IV]) human sera to establish primary infection without discernible disease and then exposed the cornea to UV-B light to induce viral reactivation.

Results

UV-B light induced viral reactivation from latency in 100% of mice as measured by HSV-1 antigen deposition in the cornea. Further, unlike conventional HSK models, viral reactivation resulted in focal retraction of sensory nerves and corneal opacity. Dependent on CD4⁺ T cells, inflammation foci were innervated by sympathetic nerves.

Conclusions

Collectively, our data reveal that sectoral corneal sensory nerve retraction and replacement of sympathetic nerves were involved in the progressive pathology that is dependent on CD4⁺ T cells after viral reactivation from HSV-1 latency in the UV-B induced recurrent HSK mouse model.

Mucosal immunology of the ocular surface

The eye is a sensory organ exposed to the environment and protected by a mucosal tissue barrier. While it shares a number of features with other mucosal tissues, the ocular mucosal system, composed of the conjunctiva, Meibomian glands, and lacrimal glands, is specialized to address the unique needs of (a) lubrication and (b) host defense of the ocular surface. Not surprisingly, most challenges, physical and immunological, to the homeostasis of the eye fall into those two categories. Dry eye, a dysfunction of the lacrimal glands and/or Meibomian glands, which can both cause, or arise from, sensory defects, including those caused by corneal herpes virus infection, serve as examples of these perturbations and will be discussed ahead. To preserve vision, dense neuronal and immune networks sense various stimuli and orchestrate responses, which must be tightly controlled to provide protection, while simultaneously minimizing collateral damage. All this happens against the backdrop of, and can be modified by, the microorganisms that colonize the ocular mucosa long term, or that are simply transient passengers introduced from the environment. This review will attempt to synthesize the existing knowledge and develop trends in the study of the unique mucosal and immune elements of the ocular surface.

Intramuscular Vaccination With the HSV-1(VC2) Live-Attenuated Vaccine Strain Confers Protection Against Viral Ocular Immunopathogenesis Associated With γδT Cell Intracorneal Infiltration

Herpes simplex virus type-1 (HSV-1) ocular infection is one of the leading causes of infectious blindness in developed countries. The resultant herpetic keratitis (HK) is caused by an exacerbated reaction of the adaptive immune response that persists beyond virus clearance causing substantial damage to the cornea. Intramuscular immunization of mice with the HSV-1(VC2) live-attenuated vaccine strain has been shown to protect mice against lethal ocular challenge. Herein, we show that following ocular challenge, VC2 vaccinated animals control ocular immunopathogenesis in the absence of neutralizing antibodies on ocular surfaces. Ocular protection is associated with enhanced intracorneal infiltration of γδ T cells compared to mock-vaccinated animals. The observed γδ T cellular infiltration was inversely proportional to the infiltration of neutrophils, the latter associated with exacerbated tissue damage. Inhibition of T cell migration into ocular tissues by the S1P receptors agonist FTY720 produced significant ocular disease in vaccinated mice and marked increase in neutrophil infiltration. These results indicate that ocular challenge of mice immunized with the VC2 vaccine induce a unique ocular mucosal response that leads into the infiltration of γδ T cells resulting in the amelioration of infection-associated immunopathogenesis.

Local Immune Control of Latent Herpes Simplex Virus Type 1 in Ganglia of Mice and Man

Herpes simplex virus type 1 (HSV-1) is a prevalent human pathogen. HSV-1 genomes persist in trigeminal ganglia neuronal nuclei as chromatinized episomes, while epithelial cells are typically killed by lytic infection. Fluctuations in anti-viral responses, broadly defined, may underlay periodic reactivations. The ganglionic immune response to HSV-1 infection includes cell-intrinsic responses in neurons, innate sensing by several cell types, and the infiltration and persistence of antigen-specific T-cells. The mechanisms specifying the contrasting fates of HSV-1 in neurons and epithelial cells may include differential genome silencing and chromatinization, dictated by variation in access of immune modulating viral tegument proteins to the cell body, and protection of neurons by autophagy. Innate responses have the capacity of recruiting additional immune cells and paracrine activity on parenchymal cells, for example via chemokines and type I interferons. In both mice and humans, HSV-1-specific CD8 and CD4 T-cells are recruited to ganglia, with mechanistic studies suggesting active roles in immune surveillance and control of reactivation. In this review we focus mainly on HSV-1 and the TG, comparing and contrasting where possible observational, interventional, and in vitro studies between humans and animal hosts.

Production of the Cytokine VEGF-A by CD4+ T and Myeloid Cells Disrupts the Corneal Nerve Landscape and Promotes Herpes Stromal Keratitis

Herpes simplex virus type 1 (HSV-1)-infected corneas can develop a blinding immunoinflammatory condition called herpes stromal keratitis (HSK), which involves the loss of corneal sensitivity due to retraction of sensory nerves and subsequent hyperinnervation with sympathetic nerves. Increased concentrations of the cytokine VEGF-A in the cornea are associated with HSK severity. Here, we examined the impact of VEGF-A on neurologic changes that underly HSK using a mouse model of HSV-1 corneal infection. Both CD4⁺ T cells and myeloid cells produced pathogenic levels of VEGF-A within HSV-1-infected corneas, and CD4⁺ cell depletion promoted reinnervation of HSK corneas with sensory nerves. In vitro, VEGF-A from infected corneas repressed sensory nerve growth and promoted sympathetic nerve growth. Neutralizing VEGF-A in vivo using bevacizumab inhibited sympathetic innervation, promoted sensory nerve regeneration, and alleviated disease. Thus, VEGF-A can shape the sensory and sympathetic nerve landscape within the cornea, with implications for the treatment of blinding corneal disease.

Pathogenesis of Herpes Stromal Keratitis: Immune Inflammatory Response Mediated by Inflammatory Regulators

Herpes stromal keratitis (HSK) is one of the primary diseases that cause vision loss or even blindness after herpes simplex virus (HSV)-1 infection. HSK-associated vision impairment is predominantly due to corneal scarring and neovascularization caused by inflammation. In the infected cornea, HSV can activate innate and adaptive immune responses of host cells, which triggers a cascade of reactions that leads to the release of inflammatory cytokines, chemokines, microRNA, and other regulatory factors that have stimulating or inhibitory effects on tissue. Physiologically, host cells show homeostasis. In this review, we summarize the factors involved in HSK pathogenesis from the perspective of immunity, molecules, and pathological angiogenesis. We also describe in detail the pathogenesis of chronic inflammatory lesions of the corneal stroma in response to HSV-1 infection.

NLRP3, NLRP12, and IFI16 Inflammasomes Induction and Caspase-1 Activation Triggered by Virulent HSV-1 Strains Are Associated With Severe Corneal Inflammatory Herpetic Disease

The crosstalk between the host's inflammasome system and the invading virulent/less-virulent viruses determines the outcome of the ensuing inflammatory response. An appropriate activation of inflammasomes triggers antiviral inflammatory responses that clear the virus and heal the inflamed tissue. However, an aberrant activation of inflammasomes can result in a harmful and overwhelming inflammation that could damage the infected tissue. The underlying host's immune mechanisms and the viral virulent factors that impact severe clinical inflammatory disease remain to be fully elucidated. In this study, we used herpes simplex virus type 1 (HSV-1), the causative agent of corneal inflammatory herpetic disease, as a model pathogen to determine: (i) Whether and how the virulence of a virus affects the type and the activation level of the inflammasomes; and (ii) How triggering specific inflammasomes translates into protective or damaging inflammatory response. We showed that, in contrast to the less-virulent HSV-1 strains (RE, F, KOS, and KOS63), corneal infection of B6 mice with the virulent HSV-1 strains (McKrae, 17 or KOS79): (i) Induced simultaneous expression of the NLRP3, NLRP12, and IFI16 inflammasomes; (ii) Increased production of the biologically active Caspase-1 and pro-inflammatory cytokines IL-1β and IL-18; (iii) Heightened recruitment into the inflamed cornea of CD45highLy6C+Ly6G-F4/80+CD11b+CD11c- inflammatory monocytes and CD45highCD11b+F4/80-Ly6GhiLy6Cmed neutrophils; and (iv) This intensified inflammatory response was associated with a severe corneal herpetic disease, irrespective of the level of virus replication in the cornea. Similarly, in vitro infection of human corneal epithelial cells and human monocytic THP-1 cells with the virulent HSV-1 strains triggered a synchronized early expression of NLRP3, NLRP12 and IFI16, 2 h post-infection, associated with formation of single and dense specks of the adapter molecule ASC in HSV(+) cells, but not in the neighboring bystander HSV(-) cells. This was associated with increased cleavages of Caspase-1, IL-1β, and IL-18. These findings suggest a previously unappreciated role of viral virulence in a synchronized early induction of the NLRP3, NLRP12, and IFI16 inflammasomes that lead to a damaging inflammatory response. A potential role of common virus virulent factors that stimulate this harmful inflammatory corneal disease is currently under investigation.

Application of our understanding of pathogenesis of herpetic stromal keratitis for novel therapy

HSV-1 ocular infection can cause herpes stromal keratitis (SK), an immunopathological lesion. Frequent recurrences can lead to progressive corneal scaring which can result in vision impairment if left untreated. Currently, the acute and epithelial forms of SK are usually controlled using anti-viral drugs. However, chronic forms of SK which are inflammatory in nature, require the addition of a topical corticosteroid to the anti-viral treatment regimen. In this review, we highlight the essential events involved in SK pathogenesis which can be targeted for improved therapy. We also examine some approaches which can be combined with the current treatments to effectively control SK.

Frontline Science: Aspirin-triggered resolvin D1 controls herpes simplex virus-induced corneal immunopathology

Stromal keratitis (SK) is a chronic immunopathological lesion of the eye, caused by HSV-1 infection, and a common cause of vision impairment in humans. The inflammatory lesions in the cornea are primarily caused by neutrophils with the active participation of CD4⁺ T cells. Therefore, the targeting of these immune cell types and their products represents a potentially valuable form of therapy to reduce the severity of disease. Resolvin D1 (RvD1) and its epimer aspirin-triggered RvD1 (AT-RvD1) are lipid mediators derived from docosahexaenoic acid (DHA) and were shown to promote resolution in several inflammatory disease models. In this report, we examined whether AT-RvD1 administration, begun before infection or at a later stage after ocular infection of mice with HSV-1, could control the severity of SK lesions. Treatment with AT-RvD1 significantly diminished the extent of corneal neovascularization and the severity of SK lesions. AT-RvD1-treated mice had fewer numbers of inflammatory cells that included neutrophils as well as Th1 and Th17 cells in the infected cornea. The mechanisms by which AT-RvD1 acts appear to be multiple. These include inhibitory effects on proinflammatory mediators, such as IL-1β, IL-6, IL-12, CXCL1, MCP-1, MIP-2, vascular endothelial growth factor (VEGF)-A, matrix metalloproteinase 9 (MMP-9), and proinflammatory miRNA, such as miR-155, miR-132, and miR-223, which are involved in SK pathogenesis and corneal neovascularization. In addition, AT-RvD1 attenuated STAT1, which plays an important role in Th1 cell differentiation and IFN-γ expression. These findings demonstrate that AT-RvD1 treatment could represent a useful strategy for the management of virus-induced immunopathological lesions.

Bolstering the Number and Function of HSV-1-Specific CD8+ Effector Memory T Cells and Tissue-Resident Memory T Cells in Latently Infected Trigeminal Ganglia Reduces Recurrent Ocular Herpes Infection and Disease

HSV type 1 (HSV-1) is a prevalent human pathogen that infects >3.72 billion individuals worldwide and can cause potentially blinding recurrent corneal herpetic disease. HSV-1 establishes latency within sensory neurons of trigeminal ganglia (TG), and TG-resident CD8⁺ T cells play a critical role in preventing its reactivation. The repertoire, phenotype, and function of protective CD8⁺ T cells are unknown. Bolstering the apparent feeble numbers of CD8⁺ T cells in TG remains a challenge for immunotherapeutic strategies. In this study, a comprehensive panel of 467 HLA-A*0201-restricted CD8⁺ T cell epitopes was predicted from the entire HSV-1 genome. CD8⁺ T cell responses to these genome-wide epitopes were compared in HSV-1-seropositive symptomatic individuals (with a history of numerous episodes of recurrent herpetic disease) and asymptomatic (ASYMP) individuals (who are infected but never experienced any recurrent herpetic disease). Frequent polyfunctional HSV-specific IFN-γ⁺CD107^a/b+CD44^highCD62L^lowCD8⁺ effector memory T cells were detected in ASYMP individuals and were primarily directed against three "ASYMP" epitopes. In contrast, symptomatic individuals have more monofunctional CD44^highCD62L^highCD8⁺ central memory T cells. Furthermore, therapeutic immunization with an innovative prime/pull vaccine, based on priming with multiple ASYMP epitopes (prime) and neurotropic TG delivery of the T cell-attracting chemokine CXCL10 (pull), boosted the number and function of CD44^highCD62L^lowCD8⁺ effector memory T cells and CD103^highCD8⁺ tissue-resident T cells in TG of latently infected HLA-A*0201-transgenic mice and reduced recurrent ocular herpes following UV-B-induced reactivation. These findings have profound implications in the development of T cell-based immunotherapeutic strategies to treat blinding recurrent herpes infection and disease.

Immune response of T cells during herpes simplex virus type 1 (HSV-1) infection

Herpes simplex virus type 1 (HSV-1), a neurotropic member of the alphaherpes virus family, is among the most prevalent and successful human pathogens. HSV-1 can cause serious diseases at every stage of life including fatal disseminated disease in newborns, cold sores, eye disease, and fatal encephalitis in adults. HSV-1 infection can trigger rapid immune responses, and efficient inhibition and clearance of HSV-1 infection rely on both the innate and adaptive immune responses of the host. Multiple strategies have been used to restrict host innate immune responses by HSV-1 to facilitate its infection in host cells. The adaptive immunity of the host plays an important role in inhibiting HSV-1 infections. The activation and regulation of T cells are the important aspects of the adaptive immunity. They play a crucial role in host-mediated immunity and are important for clearing HSV-1. In this review, we examine the findings on T cell immune responses during HSV-1 infection, which hold promise in the design of new vaccine candidates for HSV-1.

Subclinical Herpes Simplex Virus Type 1 Infections Provide Site-Specific Resistance to an Unrelated Pathogen

HSV-1 infections of the cornea range in severity from minor transient discomfort to the blinding disease herpes stromal keratitis, yet most patients experience a single episode of epithelial keratitis followed by re-establishment of a clear cornea. We asked whether a single transient episode of HSV-1 epithelial keratitis causes long-term changes in the corneal microenvironment that influence immune responses to subsequent corneal infection or trauma. We showed that C57BL/6 mouse corneas infected with HSV-1 KOS, which induces transient herpes epithelial keratitis without herpes stromal keratitis sequelae, possessed a significant leukocytic infiltrate composed primarily of CD4⁺ T cells and macrophages along with elevated chemokines and cytokines that persisted without loss of corneal clarity (subclinical inflammation). Chemokine and cytokine expression was CD4⁺ T cell dependent, in that their production was significantly reduced by systemic CD4⁺ T cell depletion starting before infection, although short-term (3-d) local CD4⁺ T cell depletion postinfection did not influence chemokine levels in cornea. Corneas with subclinical inflammation developed significantly greater trauma-induced inflammation when they were recipients of syngeneic corneal transplants but also exhibited significantly increased resistance to infections by unrelated pathogens, such as pseudorabies virus. The resistance to pseudorabies virus was CD4⁺ T cell dependent, because it was eliminated by local CD4⁺ T cell depletion from the cornea. We conclude that transient HSV-1 corneal infections cause long-term alterations of the corneal microenvironment that provide CD4-dependent innate resistance to subsequent infections by antigenically unrelated pathogens.

High-Risk Corneal Graft Rejection in the Setting of Previous Corneal Herpes Simplex Virus (HSV)-1 Infection

Purpose

The “high-risk phenotype” of corneal graft recipients is considered to be related to preexisting vascularization such as that associated with herpes simplex virus-1 (HSV-1) keratitis (HSK). The purpose of this study was to investigate the immunologic mechanisms underlying accelerated corneal graft rejection using a mouse model of HSK.

Methods

Herpes simplex virus type 1 keratitis was induced in BALB/c mice. Syngeneic and allogeneic (C57BL/6 mice) corneal grafts were performed in mice with HSK at different times after infection. Some grafts were performed on HSV-infected CD4 T cell–deficient BALB/c mice. Clinical, histologic, immunologic, and virus detection studies were performed on samples of cornea, draining lymph node (LN), and trigeminal ganglion (TG) cells.

Results

Corneal grafts in mice with HSK rejected with higher frequency and more rapid tempo compared with grafts in uninfected mice. In corneas with HSK and vascularization at the time of grafting, both syngeneic and allogeneic corneal grafts failed with similar frequency and tempo. However, in the absence of preexisting inflammation and vascularization, syngeneic grafts were accepted when the grafts were performed at a late time point after HSV infection (42 days), whereas allografts were rejected at this time. In contrast, syngeneic grafts in nonvascularized HSV-infected recipients failed if they were performed within 10 days of HSV infection, an effect that was dependent on CD4 T cells, as demonstrated using CD4 deficient mice. Importantly, a variably sustained but strongly positive anti-HSV T-cell response was detected in allografted HSK recipients with a similar but lesser response in syngeneic hosts.

Conclusions

A previous HSV-1 corneal infection predisposes donor grafts to a high risk of failure by both innate and adaptive immune mechanisms in which an anti-HSV CD4 T-cell response plays a prominent role.

A Highly Efficacious Herpes Simplex Virus 1 Vaccine Blocks Viral Pathogenesis and Prevents Corneal Immunopathology via Humoral Immunity

Correlates of immunologic protection requisite for an efficacious herpes simplex virus 1 (HSV-1) vaccine remain unclear with respect to viral pathogenesis and clinical disease. In the present study, mice were vaccinated with a novel avirulent, live attenuated virus (0ΔNLS) or an adjuvanted glycoprotein D subunit (gD-2) similar to that used in several human clinical trials. Mice vaccinated with 0ΔNLS showed superior protection against early viral replication, neuroinvasion, latency, and mortality compared to that of gD-2-vaccinated or naive mice following ocular challenge with a neurovirulent clinical isolate of HSV-1. Moreover, 0ΔNLS-vaccinated mice exhibited protection against ocular immunopathology and maintained corneal mechanosensory function. Vaccinated mice also showed suppressed T cell activation in the draining lymph nodes following challenge. Vaccine efficacy correlated with serum neutralizing antibody titers. Humoral immunity was identified as the correlate of protection against corneal neovascularization, HSV-1 shedding, and latency through passive immunization. Overall, 0ΔNLS affords remarkable protection against HSV-1-associated ocular sequelae by impeding viral replication, dissemination, and establishment of latency.

IMPORTANCE

HSV-1 manifests in a variety of clinical presentations ranging from a rather benign "cold sore" to more severe forms of infection, including necrotizing stromal keratitis and herpes simplex encephalitis. The present study was undertaken to evaluate a novel vaccine to ocular HSV-1 infection not only for resistance to viral replication and spread but also for maintenance of the visual axis. The results underscore the necessity to reconsider strategies that utilize attenuated live virus as opposed to subunit vaccines against ocular HSV-1 infection.

Host immune cellular reactions in corneal neovascularization

Corneal neovascularization (CNV) is a global important cause of visual impairment. The immune mechanisms leading to corneal heme- and lymphangiogenesis have been extensively studied over the past years as more attempts were made to develop better prophylactic and therapeutic measures. This article aims to discuss immune cells of particular relevance to CNV, with a focus on macrophages, Th17 cells, dendritic cells and the underlying immunology of common pathologies involving neovascularization of the cornea. Hopefully, a thorough understanding of these topics would propel the efforts to halt the detrimental effects of CNV.

Dendritic Cell Autophagy Contributes to Herpes Simplex Virus-Driven Stromal Keratitis and Immunopathology

Herpetic stromal keratitis (HSK) is a blinding ocular disease that is initiated by HSV-1 and characterized by chronic inflammation in the cornea. Although HSK immunopathology of the cornea is well documented in animal models, events preceding this abnormal inflammatory cascade are poorly understood. In this study, we have examined the activation of pathological CD4⁺ T cells in the development of HSK. Dendritic cell autophagy (DC-autophagy) is an important pathway regulating major histocompatibility complex class II (MHCII)-dependent antigen presentation and proper CD4⁺ T cell activation during infectious diseases. Using DC-autophagy-deficient mice, we found that DC-autophagy significantly and specifically contributes to HSK disease without impacting early innate immune infiltration, viral clearance, or host survival. Instead, the observed phenotype was attributable to the abrogated activation of CD4⁺ T cells and reduced inflammation in HSK lesions. We conclude that DC-autophagy is an important contributor to primary HSK immunopathology upstream of CD4⁺ T cell activation.

Herpetic stromal keratitis (HSK) is the leading cause of infectious blindness in the United States and a rising cause worldwide. HSK is induced by herpes simplex virus 1 but is considered a disease of inappropriately sustained inflammation driven by CD4⁺ T cells. In this study, we investigated whether pathways preceding CD4⁺ T cell activation affect disease outcome. We found that autophagy in dendritic cells significantly contributed to the incidence of HSK. Dendritic cell autophagy did not alter immune control of the virus or neurological disease but specifically augmented CD4⁺ T cell activation and pathological corneal inflammation. This study broadens our understanding of the immunopathology that drives HSK and implicates the autophagy pathway as a new target for therapeutic intervention against this incurable form of infectious blindness.

Prior Corneal Scarification and Injection of Immune Serum are Not Required Before Ocular HSV-1 Infection for UV-B-Induced Virus Reactivation and Recurrent Herpetic Corneal Disease in Latently Infected Mice

PURPOSE

Blinding ocular herpetic disease in humans is due to spontaneous reactivation of herpes simplex virus type 1 (HSV-1) from latency, rather than to primary acute infection. Mice latently infected with HSV-1 undergo little or no in vivo spontaneous reactivation with accompanying virus shedding in tears. HSV-1 reactivation can be induced in latently infected mice by several in vivo procedures, with UV-B-induced reactivation being one commonly used method. In the UV-B model, corneas are scarified (lightly scratched) just prior to ocular infection to increase efficiency of the primary infection and immune serum containing HSV-1 neutralizing antibodies is injected intraperitoneally (i.p.) to increase survival and decrease acute corneal damage. Since scarification can significantly alter host gene transcription in the cornea and in the trigeminal ganglia (TG; the site of HSV-1 latency) and since injection of immune serum likely modulates innate and adaptive herpes immunity, we investigated eliminating both treatments.

MATERIAL AND METHODS

Mice were infected with HSV-1 with or without corneal scarification and immune serum. HSV-1 reactivation and recurrent disease were induced by UV-B irradiation.

RESULTS

When corneal scarification and immune serum were both eliminated, UV-B irradiation still induced both HSV-1 reactivation, as measured by shedding of reactivated virus in tears and herpetic eye disease, albeit at reduced levels compared to the original procedure.

CONCLUSION

Despite the reduced reactivation and disease, avoidance of both corneal scarification and immune serum should improve the clinical relevance of the UV-B mouse model.

Cornea-infiltrating and lymph node dendritic cells contribute to CD4+ T cell expansion after herpes simplex virus-1 ocular infection

After HSV type 1 corneal infection, CD4(+) T cells are expanded in the draining lymph nodes (DLNs) and restimulated in the infected cornea to regulate the destructive inflammatory disease herpes stromal keratitis (HSK). The contribution of cornea resident, cornea-infiltrating, and DLN resident dendritic cells (DC) to CD4(+) T cell expansion in DLNs and restimulation in corneas is unknown. Cornea resident and cornea-infiltrating DCs were selectively depleted by timed local (subconjunctival) injection of diphtheria toxin (DT) into mice that express high-affinity DT receptors from the CD11c promoter. Corneal and DLN DCs were depleted by systemic (i.p.) DT treatment. We found that: 1) DCs that were resident in the cornea and DLNs at the time of infection or that migrate into the tissues during the first 24 h postinfection were not required for CD4(+) T cell expansion; 2) DCs that infiltrated the cornea >24 h postinfection were responsible for most of the CD4(+) T cell expansion measured in the DLNs at 3 and 7 d postinfection (dpi); 3) non-cornea-derived DCs that infiltrate the DLNs >24 h postinfection made a modest contribution to CD4(+) T cell expansion at 3 dpi but did not contribute at 7 dpi; and 4) surprisingly, HSK development between 7 and 21 dpi did not require corneal DCs. DC-independent HSK development appears to reflect close interactions of CD4(+) T cells with MHC class II(+) corneal epithelial cells and macrophages in infected DC-depleted corneas.

Reversible nerve damage and corneal pathology in murine herpes simplex stromal keratitis

Herpes simplex virus type 1 (HSV-1) shedding from sensory neurons can trigger recurrent bouts of herpes stromal keratitis (HSK), an inflammatory response that leads to progressive corneal scarring and blindness. A mouse model of HSK is often used to delineate immunopathogenic mechanisms and bears many of the characteristics of human disease, but it tends to be more chronic and severe than human HSK. Loss of blink reflex (BR) in human HSK is common and due to a dramatic retraction of corneal sensory nerve termini in the epithelium and the nerve plexus at the epithelial/stromal interface. However, the relationship between loss of BR due to nerve damage and corneal pathology associated with HSK remains largely unexplored. Here, we show a similar retraction of corneal nerves in mice with HSK. Indeed, we show that much of the HSK-associated corneal inflammation in mice is actually attributable to damage to the corneal nerves and accompanying loss of BR and can be prevented or ameliorated by tarsorrhaphy (suturing eyelids closed), a clinical procedure commonly used to prevent corneal exposure and desiccation. In addition, we show that HSK-associated nerve retraction, loss of BR, and severe pathology all are reversible and regulated by CD4(+) T cells. Thus, defining immunopathogenic mechanisms of HSK in the mouse model will necessitate distinguishing mechanisms associated with the immunopathologic response to the virus from those associated with loss of corneal sensation. Based on our findings, investigation of a possible contribution of nerve damage and BR loss to human HSK also appears warranted. Importance: HSK in humans is a potentially blinding disease characterized by recurrent inflammation and progressive scarring triggered by viral release from corneal nerves. Corneal nerve damage is a known component of HSK, but the causes and consequences of HSK-associated nerve damage remain obscure. We show that desiccation of the corneal surface due to nerve damage and associated loss of BR severely exacerbates and prolongs inflammation-induced pathology in mice. Preventing corneal desiccation results in a milder and more transient HSK with variable scarring that mirrors HSK seen in most humans. We further show that nerve damage is reversible and regulated by CD4(+) T cells. Thus, we provide a mouse model that more closely resembles typical human HSK and suggest nerve damage is an important but largely overlooked factor in human disease.

Herpes keratitis

Herpes simplex virus-1 (HSV-1) infects the majority of the world's population. These infections are often asymptomatic, but ocular HSV-1 infections cause multiple pathologies with perhaps the most destructive being herpes stromal keratitis (HSK). HSK lesions, which are immunoinflammatory in nature, can recur throughout life and often cause progressive corneal scaring resulting in visual impairment. Current treatment involves broad local immunosuppression with topical steroids along with antiviral coverage. Unfortunately, the immunopathologic mechanisms defined in animal models of HSK have not yet translated into improved therapy. Herein, we review the clinical epidemiology and pathology of the disease and summarize the large amount of basic research regarding the immunopathology of HSK. We examine the role of the innate and adaptive immune system in the clearance of virus and the destruction of the normal corneal architecture that is typical of HSK. Our goal is to define current knowledge of the pathogenic mechanisms and recurrent nature of HSK and identify areas that require further study.

CD8+ T cells suppress viral replication in the cornea but contribute to VEGF-C-induced lymphatic vessel genesis

HSV-1 is the leading cause of infectious corneal blindness in the industrialized world. CD4(+) T cells are thought to be the major leukocyte population mediating immunity to HSV-1 in the cornea as well as the likely source of immunopathology that reduces visual acuity. However, the role of CD8(+) T cells in immune surveillance of the cornea is unclear. Thus, we sought to evaluate the role of CD8(+) T cells in ocular immunity using transgenic mice in which >98% of CD8(+) T cells are specific for the immunodominant HSV-1 epitope (gBT-I.1). We found a significant reduction in virus, elevation in HSV-specific CD8(+) T cell influx, and more CD8(+) T cells expressing CXCR3 in the cornea of transgenic mice compared with those in the cornea of wild-type controls yet similar acute corneal pathology. However, by day 30 postinfection, wild-type mice had drastically more blood and lymphatic vessel projections into the cornea compared with gBT-I.1 mice, in which only lymphatic vessel growth in response to VEGF-C could be appreciated. Taken together, these results show that CD8(+) T cells are required to eliminate virus more efficiently from the cornea but play a minimal role in immunopathology as a source of VEGF-C.

Recurrent herpetic stromal keratitis in mice: a model for studying human HSK

Herpes simplex virus 1 (HSV-1) infection of the cornea leads to a potentially blinding disease, termed herpetic stromal keratitis (HSK) that is characterized by lesions of an immunoinflammatory nature. In spite of the fact that HSK typically presents as a recurrent disease due to reactivation of virus which latently infects the trigeminal ganglia, most murine studies of HSK have employed a primary and not recurrent model of the disease. This report documents the several recurrent models of HSK that have been developed and how data generated from these models differs in some important aspects from data generated following primary infection of the cornea. Chief among these differences is the fact that recurrent HSK takes place in the context of an animal that has a preexisting anti-HSV immune response, while primary HSK occurs in an animal that is developing such a response. We will document both differences and similarities that derive from this fundamental difference in these models with an eye towards possible vaccines and therapies that demonstrate promise in treating HSK.

Efficient generation and rapid isolation via stoplight recombination of Herpes simplex viruses expressing model antigenic and immunological epitopes

Generation and isolation of recombinant herpesviruses by traditional homologous recombination methods can be a tedious, time-consuming process. Therefore, a novel stoplight recombination selection method was developed that facilitated rapid identification and purification of recombinant viruses expressing fusions of immunological epitopes with EGFP. This "traffic-light" approach provided a visual indication of the presence and purity of recombinant HSV-1 isolates by producing three identifying signals: (1) red fluorescence indicates non-recombinant viruses that should be avoided; (2) yellow fluorescence indicates cells co-infected with non-recombinant and recombinant viruses that are chosen with caution; (3) green fluorescence indicates pure recombinant isolates and to proceed with preparation of viral stocks. Adaptability of this system was demonstrated by creating three recombinant viruses that expressed model immunological epitopes. Diagnostic PCR established that the fluorescent stoplight indicators were effective at differentiating between the presence of background virus contamination and pure recombinant viruses specifying immunological epitopes. This enabled isolation of pure recombinant viral stocks that exhibited wildtype-like viral replication and cell-to-cell spread following three rounds of plaque purification. Expression of specific immunological epitopes was confirmed by western analysis, and the utility of these viruses for examining host immune responses to HSV-1 was determined by a functional T cell assay.

Circulating herpes simplex type 1 (HSV-1)-specific CD8+ T cells do not access HSV-1 latently infected trigeminal ganglia

Background

Therapeutic vaccines can be designed to enhance existing T cell memory populations for increased protection against re-infection. In the case of herpes simplex virus type 1, recurrent disease results from reactivation of latent virus in sensory ganglia, which is controlled in part by a ganglia-resident HSV-specific memory CD8⁺ T cell population. Thus, an important goal of a therapeutic HSV-1 vaccine would be to enhance this population.

Methods

HSV-1-infected mice were treated with TAK-779 to block CCR5- and CXCR3-mediated CD8⁺ T cell migration during both acute and latent infections. Additionally, HSV-1-specific CD8⁺ T cells were transferred into HSV-1 latently infected mice to mimic the effect of a therapeutic vaccine, and their migration into trigeminal ganglia (TG) was traced during steady-state latency, or during recovery of the TG-resident memory CD8⁺ T cell population following stress-, and corticosterone-induced depletion and HSV-1 reactivation from latency. Bromodeoxy uridine (BrdU) incorporation measured cell proliferation in vivo.

Results

TAK-779 treatment during acute HSV-1 infection reduced the number of infiltrating CD8⁺ T cells but did not alter the number of viral genome copies. TAK-779 treatment during HSV latency did not affect the size of the TG-resident memory CD8⁺ T cell population. Transferred HSV-specific CD8⁺ T cells failed to access latently infected TG during steady-state latency, or during recovery of the TG resident HSV-specific CD8⁺ T cell population following exposure of latently infected mice to stress and corticosterone. Recovery of the HSV-specific CD8⁺ T cell population after stress and corticosterone treatment occurred with homeostatic levels of cell division and did not require CD4⁺ T cell help.

Conclusions

Our findings are consistent with the notion that the CD8⁺ T cells in latently infected TG are a tissue-resident memory (Trm) population that is maintained without replenishment from the periphery, and that when this population is disrupted, it recovers without proliferation or detectable recruitment of HSV-specific CD8⁺ T cells from the blood. The compartmentalization of the HSV-specific CD8⁺ memory T cell population in latently infected TG will complicate the design of therapeutic vaccines.

Reviews for immune privilege in the year 2010: immune privilege and infection

Advances in understanding host innate/adaptive immunity and abrogation of immune privilege in ocular viral and bacterial infections have been accomplished using animal models. In Pseudomonas aeruginosa keratitis, mouse models have shown that IL-12-driven IFN-gamma production in Th1 responder strains such as C57BL/6 contributes to corneal perforation, while IL-18-driven IFN-gamma production is associated with bacterial killing and less disease in Th2 responders (BALB/c). The role of neuropeptides, macrophages, and regulation of neutrophil apoptosis is discussed. The potentially blinding Th1 CD4 T-cell-mediated immunopathology referred to as herpes stromal keratitis (HSK) is characterized by breakdown of the normal barrier to blood and lymph angiogenesis in the cornea, a dramatic increase in mature professional antigen-presenting cells, and a heavy leukocytic infiltrate composed primarily of neutrophils. HSK is more frequent and severe in BALB/c than C57BL/6 mice, and varies in severity with the strain and dose of HSV-1 used to infect the cornea.

Herpes stromal keratitis: erosion of ocular immune privilege by herpes simplex virus

Herpes stromal keratitis (HSK) is a potentially blinding disease caused by herpes simplex virus corneal infection. Most cases of HSK are due to reactivation of the virus from latency leading to recurrent bouts of corneal inflammation and scarring with progressive loss of vision. Replicating virus is required to initiate HSK, and CD4 T cells of the adaptive immune system appear requisite for stromal inflammation. Corneal neovascularization also contributes significantly to HSK pathogenesis. Combination therapy with topical antivirals and corticosteroids is the current standard of care for human HSK. Future therapies will probably target angiogenesis with anti-VEGF agents to inhibit blood vessel growth into the normally avascular cornea, and target viral reactivation with therapeutic vaccination strategies to inhibit subsequent attacks.

Kinetics of immune cell infiltration in vaccinia virus keratitis

PURPOSE

Vaccinia virus keratitis leading to blindness is a severe complication of smallpox vaccination. The clinical manifestations of vaccinia virus keratitis are similar to those of herpes simplex virus keratitis, a well-studied immunopathologic disease. Vaccinia virus keratitis is likely to involve an immunopathologic component, but little is known about the pathogenesis of the disease. The goal of this study was to determine type and kinetics of immune cell infiltration in the cornea during vaccinia virus keratitis.

METHODS

Rabbit eyes were trephined and inoculated with 1x10(5) pfu of the Dryvax strain of the vaccinia virus. On days 2, 4, 7, 10, 14, and 28 after infection, the animals were scored for clinical disease and eye sections were stained for B cells, CD4+ cells, CD8+ cells, and neutrophils. The eyelid, ciliary body, cornea, iris, iridocorneal angle, and choroid were examined.

RESULTS

Corneal vaccinia virus challenge resulted in the infiltration of B cells, CD4+ cells, CD8+ cells, and neutrophils into the cornea and eyelids. Neutrophils were the predominant cell type on days 2 and 3 after infection, whereas CD4+ cells were the predominant cell type detected in corneas on days 4 through 10. CD8+ cells and B cells peaked on day 10, but at lower levels than CD4+ cells and neutrophils.

CONCLUSIONS

These results suggest that sequential migration of neutrophils, then CD4+ cells, plays an important role in vaccinia virus keratitis.

A novel p40-independent function of IL-12p35 is required for progression and maintenance of herpes stromal keratitis

PURPOSE. Interleukin (IL)-12p40 can couple with IL-12p35 or p19 chains to form the molecules IL-12p70 and IL-23, respectively, which promote T(H)1 cytokine responses. IL-12p35 can bind to EBI3 to form the anti-inflammatory molecule IL-35, but a proinflammatory function of IL-12p35 independent of IL-12p40 has not been described. Here such a function in a mouse model of herpes stromal keratitis (HSK), a CD4(+) T(H)1 cell-dependent corneal inflammation, is demonstrated. METHODS. Corneas of wild-type (WT), IL-12p40(-/-), IL-12p35(-/-), and IL-12p35(-/-)p40(-/-) (double knockout) mice were infected with the RE strain of HSV-1, and HSK was monitored based on corneal opacity, neovascularization, leukocytic infiltrate, and cytokine/chemokine levels. RESULTS. All mouse strains developed moderate HSK by 11 days after infection (dpi). However, from 11 to 21 dpi, HSK progressed in WT and IL-12p40(-/-) mice but regressed in IL-12p35(-/-) and IL-12p35(-/-)p40(-/-) mice. HSK regression was characterized by reductions in neutrophils and CD4(+) T cells and attenuation of blood vessels, which was associated with reduced levels of the chemokines KC (CXCL3), Mip-2 (CXCL2), and MCP-1 (CCL2) and the angiogenic factor vascular endothelial growth factor. CONCLUSIONS. HSK development does not require IL-12p40 and is thus independent of IL-12p70 and IL-23. However, late HSK progression does require a previously unrecognized IL-12p40-independent, proinflammatory function of IL-12p35.

Prolonged microglial cell activation and lymphocyte infiltration following experimental herpes encephalitis

Experimental murine herpes simplex virus (HSV)-1 brain infection stimulates microglial cell-driven proinflammatory chemokine production which precedes the presence of brain-infiltrating systemic immune cells. In the present study, we investigated the phenotypes and infiltration kinetics of leukocyte trafficking into HSV-infected murine brains. Using real-time bioluminescence imaging, the infiltration of luciferase-positive splenocytes, transferred via tail vein injection into the brains of HSV-infected animals, was followed over an 18-day time course. Flow cytometric analysis of brain-infiltrating leukocytes at 5, 8, 14, and 30 days postinfection (d.p.i.), was performed to assess their phenotype. A predominantly macrophage (CD45(high)CD11b(+)Ly6C(high)) and neutrophil (CD45(high)CD11b(+)Ly6G(+)) infiltration was seen early during infection, with elevated levels of TNF-alpha mRNA expression. By 14 d.p.i., the phenotypic profile shifted to a predominantly lymphocytic (CD45(high)CD3(+)) infiltrate. This lymphocyte infiltrate was detected until 30 d.p.i., when infectious virus could not be recovered, with CD8(+) and CD4(+) T cells present at a 3:1 ratio, respectively. This T lymphocyte infiltration paralleled increased IFN-gamma mRNA expression in the brain. Activation of resident microglia (CD45(int)CD11b(+)) was also detected until 30 d.p.i., as assessed by MHC class II expression. Activated microglial cells were further identified as the predominant source of IL-1beta. In addition, infected mice given primed immunocytes at 4 d.p.i. showed a significant increase in mortality. Taken together, these results demonstrate that intranasal infection results in early macrophage and neutrophil infiltration into the brain followed by prolonged microglial activation and T lymphocyte retention. Similar prolonged neuroimmune activation may contribute to the neuropathological sequelae observed in herpes encephalitis patients.

An increase in herpes simplex virus type 1 in the anterior segment of the eye is linked to a deficiency in NK cell infiltration in mice deficient in CXCR3

In response to ocular herpes simplex virus type 1 (HSV-1) infection in mice, a rapid induction or increase in the local expression of chemokines, including CXCL10, is found. The present study investigated the role of the receptor for CXCL10, CXCR3, in the host response to corneal HSV-1 infection. Mice deficient in CXCR3 (CXCR3(-/-)) were found to have an increase in infectious virus in the anterior segment of the eye by day 7 postinfection. Coinciding with the increase, selective chemokines, including CCL2, CCL3, CCL5, CXCL9, and CXCL10, were elevated in the anterior segment of the HSV-1-infected CXCR3(-/-) mice. In contrast, there was a time-dependent reduction in the recruitment of natural killer (NK) cells (NK1.1(+)CD3(-)) into the anterior segment of CXCR3(-/-) mice. A reduction in NK cells residing in the anterior segment of mice following antiasialoGM1 antibody treatment resulted in an increase in infectious virus. No other leukocyte populations infiltrating the tissue were modified in the absence of CXCR3. Collectively, the loss of CXCR3 expression specifically reduces NK cell mobilization into the cornea in response to HSV-1.

A recombinant herpes simplex virus type 1 expressing two additional copies of gK is more pathogenic than wild-type virus in two different strains of mice

The effect of glycoprotein K (gK) overexpression on herpes simplex virus type 1 (HSV-1) infection in two different strains of mice was evaluated using a recombinant HSV-1 virus that expresses two additional copies of the gK gene in place of the latency-associated transcript (LAT). This mutant virus (HSV-gK3) expressed higher levels of gK than either the wild-type McKrae virus or the parental dLAT2903 virus both in vitro (in cultured cells) and in vivo (in infected mouse corneas and trigeminal ganglia [TG] of BALB/c and C57BL/6 mice). gK transcripts were detected in the TG of both HSV-gK3-infected mouse strains on day 30 postinfection (p.i.), while gB transcripts were detected only in the TG of the HSV-gK3-infected C57BL/6 mice, a finding that suggests that increased gK levels promote chronic infection. C57BL/6 mice infected with HSV-gK3 also contained free virus in their TG on day 30 p.i. Both HSV-gK3-infected mouse strains had significantly higher corneal scarring (CS) than did McKrae-infected mice. T-cell depletion studies in C57BL/6 mice suggested that this CS enhancement in the HSV-gK3-infected mice was mediated by a CD8+ T-cell response. Taken together, these results strongly suggest that increased gK levels promote eye disease and chronic infection in infected mice.

Modulation of CD8+ CTL effector function by fibroblasts derived from the immunoprivileged cornea

PURPOSE

To examine the acquisition of lytic activity and interferon gamma (IFN-gamma) production by herpes simplex virus (HSV) type 1-specific CD8(+) cytotoxic T-lymphocyte precursors (HSV-CTLps) after exposure to in vitro HSV-1-infected fibroblasts derived from the immunoprivileged cornea (HSV-cFb) or nonprivileged skin (HSV-sFb) or to in vitro HSV-1-infected splenocytes (HSV-Spls) obtained from noninfected mice.

METHODS

Chromium release assays were used to assess HSV-CTL cytotoxicity, and flow cytometry was used to assess intracellular granzyme (Gr) B content and lytic granule exocytosis through surface CD107a expression. In addition, the BLT esterase assay was used to assess functional GrA release. [(3)H]-Thymidine incorporation and total CD8(+) cell numbers, as assessed by flow cytometry, were used to assess CTLp proliferation. ELISA and intracellular flow cytometric analysis were used to assess CTL IFN-gamma production and release.

RESULTS

HSV-cFb, HSV-sFb, and HSV-Spl individually induced strong cytotoxic and IFN-gamma responses by HSV-CTL. Simultaneous exposure to HSV-Spl and HSV-cFb virtually abrogated the cytotoxic response while enhancing IFN-gamma production by HSV-CTL. In contrast, exposure to HSV-sFb, in conjunction with HSV-Spl, did not alter the cytotoxic or IFN-gamma response of HSV-CTL compared with stimulation with either cell type alone. Abrogation of the cytotoxic response after simultaneous exposure to HSV-Spl and HSV-cFb was associated with reduced production, storage, or both of GrA and GrB but with unimpaired lytic granule release.

CONCLUSIONS

These findings suggest that an interesting regulatory circuit protects the cornea from the potentially damaging effects of CD8(+) T-cell cytotoxic function while maintaining their ability to control virus replication through enhanced production of the antiviral cytokine IFN-gamma.

CD4+ T cell migration into the cornea is reduced in CXCL9 deficient but not CXCL10 deficient mice following herpes simplex virus type 1 infection

The role of CXCL9 and CXCL10 in the ocular immune response to herpes simplex virus type 1 (HSV-1) infection was investigated using mice deficient in either CXCL9 or CXCL10. CXCL10 but not CXCL9 deficient mice showed an increase in sensitivity to ocular virus infection as measured by an elevation in virus titer recovered in the tear film and corneal tissue. The increase in virus was associated with an increase in the expression of the chemokine CCL2 but no significant change in the infiltration of CD4(+) T cells or NK cells into the corneal stroma. In contrast, a significant reduction in CD4(+) T cell infiltration into the cornea was found in CXCL9 deficient mice following HSV-1 infection consistent with the absence of CXCL9 expression and reduction in expression of other chemokines including CCL3, CCL5, CXCL1, and CXCL10. Collectively, the results suggest a non-redundant role for CXCL9 and CXCL10 in response to ocular HSV-1 infection in terms of controlling virus replication and recruitment of CD4(+) T cells into the cornea.

Expression and function of the OX40/OX40L costimulatory pair during herpes stromal keratitis

Herpes stromal keratitis (HSK) is an immunopathological disease regulated by Th1 CD4 T cells, which require APC and costimulation within the infected cornea to mediate disease. Recent studies suggest the OX40:OX40 ligand (OX40L) interaction enhances effector cell cytokine secretion at inflammatory sites. OX40(+) cells were detected in HSV-1-infected mouse corneas as early as 3 days postinfection (dpi), prior to the onset of HSK, and their frequency increased through 15 dpi, when all mice exhibited severe HSK. OX40L(+) cells were first detected at 7 dpi, coincident with the initiation of HSK. It is interesting that the OX40L(+) cells did not coexpress MHC Class II or the dendritic cell (DC) marker CD11c. Our findings demonstrate rapid infiltration of activated (OX40(+)) CD4(+) T cells into HSV-1-infected corneas and expression of OX40L on MHC Class II-negative cells but surprisingly, not on MHC Class II(+) CD11c(+) DC, which are present in the infected corneas and required for HSK. Moreover, neither local nor systemic treatment of mice with a blocking antibody to OX40L or with a blocking fusion protein altered the course of HSK significantly, possibly as a result of a lack of OX40L expression on functional APC.