Expression of toll-like receptors in the healthy and herpes simplex virus-infected cornea

The immunobiology of corneal HSV-1 infection and herpetic stromal keratitis

SUMMARYHuman alphaherpesvirus 1 (HSV-1) is a highly successful neurotropic pathogen that primarily infects the epithelial cells lining the orofacial mucosa. After primary lytic replication in the oral, ocular, and nasal mucosal epithelial cells, HSV-1 establishes life-long latency in neurons within the trigeminal ganglion. Patients with compromised immune systems experience frequent reactivation of HSV-1 from latency, leading to virus entry in the sensory neurons, followed by anterograde transport and lytic replication at the innervated mucosal epithelial surface. Although recurrent infection of the corneal mucosal surface is rare, it can result in a chronic immuno-inflammatory condition called herpetic stromal keratitis (HSK). HSK leads to gradual vision loss and can cause permanent blindness in severe untreated cases. Currently, there is no cure or successful vaccine to prevent latent or recurrent HSV-1 infections, posing a significant clinical challenge to managing HSK and preventing vision loss. The conventional clinical management of HSK primarily relies on anti-virals to suppress HSV-1 replication, anti-inflammatory drugs (such as corticosteroids) to provide symptomatic relief from pain and inflammation, and surgical interventions in more severe cases to replace damaged cornea. However, each clinical treatment strategy has limitations, such as local and systemic drug toxicities and the emergence of anti-viral-resistant HSV-1 strains. In this review, we summarize the factors and immune cells involved in HSK pathogenesis and highlight alternate therapeutic strategies for successful clinical management of HSK. We also discuss the therapeutic potential of immunoregulatory cytokines and immunometabolism modulators as promising HSK therapies against emerging anti-viral-resistant HSV-1 strains.

Sensing of an HIV-1-Derived Single-Stranded RNA-Oligonucleotide Induces Arginase 1-Mediated Tolerance

Small synthetic oligodeoxynucleotides (ODNs) can mimic microbial nucleic acids by interacting with receptor systems and promoting immunostimulatory activities. Nevertheless, some ODNs can act differently on the plasmacytoid dendritic cell (pDC) subset, shaping their immunoregulatory properties and rendering them suitable immunotherapeutic tools in several clinical settings for treating overwhelming immune responses. We designed HIV-1-derived, DNA- and RNA-based oligonucleotides (gag, pol, and U5 regions) and assessed their activity in conferring a tolerogenic phenotype to pDCs in skin test experiments. RNA-but not DNA-oligonucleotides are capable of inducing tolerogenic features in pDCs. Interestingly, sensing the HIV-1-derived single-stranded RNA-gag oligonucleotide (RNA-gag) requires both TLR3 and TLR7 and the engagement of the TRIF adaptor molecule. Moreover, the induction of a suppressive phenotype in pDCs by RNA-gag is contingent upon the induction and activation of the immunosuppressive enzyme Arginase 1. Thus, our data suggest that sensing of the synthetic RNA-gag oligonucleotide in pDCs can induce a suppressive phenotype in pDCs, a property rendering RNA-gag a potential tool for therapeutic strategies in allergies and autoimmune diseases.

The Host-Pathogen Interplay: A Tale of Two Stories within the Cornea and Posterior Segment

Ocular infectious diseases are an important cause of potentially preventable vision loss and blindness. In the following manuscript, we will review ocular immunology and the pathogenesis of herpesviruses and Pseudomonas aeruginosa infections of the cornea and posterior segment. We will highlight areas of future research and what is currently known to promote bench-to-bedside discoveries to improve clinical outcomes of these debilitating ocular diseases.

Role of Innate Interferon Responses at the Ocular Surface in Herpes Simplex Virus-1-Induced Herpetic Stromal Keratitis

Herpes simplex virus type 1 (HSV-1) is a highly successful pathogen that primarily infects epithelial cells of the orofacial mucosa. After initial lytic replication, HSV-1 enters sensory neurons and undergoes lifelong latency in the trigeminal ganglion (TG). Reactivation from latency occurs throughout the host's life and is more common in people with a compromised immune system. HSV-1 causes various diseases depending on the site of lytic HSV-1 replication. These include herpes labialis, herpetic stromal keratitis (HSK), meningitis, and herpes simplex encephalitis (HSE). HSK is an immunopathological condition and is usually the consequence of HSV-1 reactivation, anterograde transport to the corneal surface, lytic replication in the epithelial cells, and activation of the host's innate and adaptive immune responses in the cornea. HSV-1 is recognized by cell surface, endosomal, and cytoplasmic pattern recognition receptors (PRRs) and activates innate immune responses that include interferons (IFNs), chemokine and cytokine production, as well as the recruitment of inflammatory cells to the site of replication. In the cornea, HSV-1 replication promotes type I (IFN-α/β) and type III (IFN-λ) IFN production. This review summarizes our current understanding of HSV-1 recognition by PRRs and innate IFN-mediated antiviral immunity during HSV-1 infection of the cornea. We also discuss the immunopathogenesis of HSK, current HSK therapeutics and challenges, proposed experimental approaches, and benefits of promoting local IFN-λ responses.

Host Molecules That Promote Pathophysiology of Ocular Herpes

Herpes simplex virus type-1 (HSV-1) is a human virus that causes lifelong infections in a large population worldwide. Recurrence of HSV-1 from latency in trigeminal ganglion (TG) is the trigger of the morbidities seen with this virus. In addition to causing fever blisters and cold sores, occasionally the virus can also cause corneal lesions resulting in blindness in untreated individuals. Several host cell proteins play important roles in HSV-1 infection of the eye. HSV-1 enters into the corneal epithelial cells via its interactions with cell surface receptors. In parallel, the Toll-like receptors sense viral invasion and activate defense mechanisms to fight the infection. New data shows that Optineurin, a host autophagy receptor is also activated to degrade viral particles. In contrast, activation of heparanase, a host enzyme, induces an immune-inflammatory response, which triggers pro-inflammatory and pro-angiogenic environment and ultimately results in many of the clinical features seen with HSV-1 infection of the cornea. Rarely, HSV-1 can also spread to the central nervous system causing serious diseases. In this review, we summarize the latest knowledge on host molecules that promote pathophysiological aspects of ocular herpes.

Advancing Our Understanding of Corneal Herpes Simplex Virus-1 Immune Evasion Mechanisms and Future Therapeutics

Herpes stromal keratitis (HSK) is a disease that commonly affects the cornea and external eye and is caused by Herpes Simplex Virus type 1 (HSV-1). This virus infects approximately 66% of people worldwide; however, only a small portion of these people will develop symptoms in their lifetime. There is no cure or vaccine available for HSV-1; however, there are treatments available that aim to control the inflammation caused by the virus and prevent its recurrence. While these treatments are beneficial to those suffering with HSK, there is a need for more effective treatments to minimise the need for topical steroids, which can have harmful effects, and to prevent bouts of disease reactivation, which can lead to progressive corneal scarring and visual impairment. This review details the current understanding of HSV-1 infection and discusses potential novel treatment options including microRNAs, TLRs, mAbs, and aptamers.

Foundational concepts in the biology of bacterial keratitis

Bacterial infections of the cornea, or bacterial keratitis (BK), are notorious for causing rapidly fulminant disease and permanent vision loss, even among treated patients. In the last sixty years, dramatic upward trajectories in the frequency of BK have been observed internationally, driven in large part by the commercialization of hydrogel contact lenses in the late 1960s. Despite this worsening burden of disease, current evidence-based therapies for BK - including broad-spectrum topical antibiotics and, if indicated, topical corticosteroids - fail to salvage vision in a substantial proportion of affected patients. Amid growing concerns of rapidly diminishing antibiotic utility, there has been renewed interest in urgently needed novel treatments that may improve clinical outcomes on an individual and public health level. Bridging the translational gap in the care of BK requires the identification of new therapeutic targets and rational treatment design, but neither of these aims can be achieved without understanding the complex biological processes that determine how bacterial corneal infections arise, progress, and resolve. In this chapter, we synthesize the current wealth of human and animal experimental data that now inform our understanding of basic BK pathophysiology, in context with modern concepts in ocular immunology and microbiology. By identifying the key molecular determinants of clinical disease, we explore how novel treatments can be developed and translated into routine patient care.

Pathobiology and treatment of viral keratitis

Keratitis is one of the most prevalent ocular diseases manifested by partial or total loss of vision. Amongst infectious (viz., microbes including bacteria, fungi, amebae, and viruses) and non-infectious (viz., eye trauma, chemical exposure, and ultraviolet exposure, contact lens) risk factors, viral keratitis has been demonstrated as one of the leading causes of corneal opacity. While many viruses have been shown to cause keratitis (such as rhabdoviruses, coxsackieviruses, etc.), herpesviruses are the predominant etiologic agent of viral keratitis. This chapter will summarize current knowledge on the prevalence, diagnosis, and pathobiology of viral keratitis. Virus-mediated immunomodulation of host innate and adaptive immune components is critical for viral persistence, and dysfunctional immune responses may cause destruction of ocular tissues leading to keratitis. Immunosuppressed or immunocompromised individuals may display recurring disease with pronounced severity. Early diagnosis of viral keratitis is beneficial for disease management and response to treatment. Finally, we have discussed current and emerging therapies to treat viral keratitis.

Pathogenesis of herpes simplex keratitis: The host cell response and ocular surface sequelae to infection and inflammation

Herpes simplex virus type 1 (HSV) keratitis is a leading cause of infectious blindness. Clinical disease occurs variably throughout the cornea from epithelium to endothelium and recurrent HSV stromal keratitis is associated with corneal scarring and neovascularization. HSV keratitis can be associated with ocular pain and subsequent neutrophic keratopathy. Host cell interactions with HSV trigger an inflammatory cascade responsible not only for clearance of virus but also for progressive corneal opacification due to inflammatory cell infiltrate, angiogenesis, and corneal nerve loss. Current antiviral therapies target viral replication to decrease disease duration, severity and recurrence, but there are limitations to these agents. Therapies directed towards viral entry into cells, protein synthesis, inflammatory cytokines and vascular endothelial growth factor pathways in animal models represent promising new approaches to the treatment of recurrent HSV keratitis.

Activation of Toll-like receptor 3 promotes pathological corneal neovascularization by enhancement of SDF-1-mediated endothelial progenitor cell recruitment

Toll-like receptors (TLRs) play an important role in inflammatory and immunological responses, which are intimately related to neovascularization. However, the precise mode of action of TLR3 in neovascularization still remains ambiguous. In this study, we sought to investigate the role of TLR3 in pathological corneal neovascularization (CNV) using a mouse model of alkali-induced CNV. CNV was attenuated in TLR3-deficient mice, and the absence of TLR3 led to decreased production of stromal cell-derived factor 1 (SDF-1), a well-characterized cytokine that regulates the recruitment of endothelial progenitor cells (EPCs) to the sites of neo-angiogenic niches in the injured tissues. Topical administration of polyinosinic-polycytidylic acid [poly (I:C)], a synthetic ligand for TLR3, to the injured cornea promoted CNV in wild type (WT) mice but not in TLR3-deficient mice. In addition, the effect of poly (I:C) on WT mice was abolished by addition of SDF-1 receptor antagonist AMD 3100. Furthermore, poly (I:C) treatment in vitro enhanced the migration of EPCs, whereas the enhanced migration was abolished by AMD 3100. These results indicate an essential role of TLR3 signalling in CNV that involves upregulating SDF-1 production and recruiting EPCs to the sites of injury for neovascularization. Thus, targeting the TLR3 signalling cascade may constitute a novel therapeutic approach for treating neovascularization-related diseases.

Transcriptional Profile and Integrative Analyses of Long Noncoding RNAs in Primary Human Corneal Epithelial Cells in Response to HSV-1 Infection

PURPOSE

Long noncoding RNAs (lncRNAs) have been demonstrated to have important regulatory functions in diverse cellular processes; however, the role of lncRNAs in the pathogenesis of herpes simplex keratitis (HSK) remains poorly understood.

METHODS

Primary human corneal epithelial cells (HCECs) were infected with herpes simplex virus-1 (HSV-1) and the total RNAs extracted from both the infected group and the mock-infected group subjected to microarray analysis to identify the differential expression of lncRNAs and mRNAs. We also performed bioinformatic analysis including gene ontology (GO) analysis, pathway analysis and co-expression network analysis.

RESULTS

Compared with mock-infected group, the expression of thousands of lncRNAs and mRNAs were significantly changed, and the microarray results were validated by qRT-PCR. The most enriched GOs targeted by up-regulated transcripts were defense response, intrinsic component of plasma membrane and cytokine activity，and the most enriched GOs targeted by the down-regulated transcripts were cellular metabolic process, intracellular part and poly (A) RNA binding. Pathway analysis indicated that the most correlated pathways for up- and down-regulated transcripts were cytokine-cytokine receptor interaction and RNA transport, respectively.

CONCLUSIONS

Our study identified the genome-wide profile of lncRNAs and mRNAs expression in primary corneal epithelial cells with HSV-1 infection. These transcriptomic data together with subsequent bioinformatic analysis will provide us with novel clue to the insight into molecular mechanism and potential therapeutic targets of HSK. Further studies are expected to verify the potentially functional genes and pathways and explore the critical lncRNAs.

ABBREVIATIONS

Long noncoding RNAs: lncRNAs; herpes simplex virus-1: HSV-1; herpes simplex virus keratitis: HSK; human corneal epithelial cells: HCECs.

Toll-like receptors 4, 5, 6 and 7 are constitutively expressed in non-human primate retinal neurons

The purpose of this study was to characterize cell-specific expression patterns of Toll-like receptors (TLR) in non-human primate (NHP) neural retina tissue. TLR 4, 5, 6, and 7 proteins were detected by immunblotting of macaque retina tissue lysates and quantitative PCR (qPCR) demonstrated TLRs 4-7 mRNA expression. Immunofluorescence (IF) microscopy detected TLRs 4-7 in multiple cell types in macaque neural retina including Muller, retinal ganglion cells (RGC), amacrine, and bipolar cells. These results demonstrate that TLRs 4-7 are constitutively expressed by neurons in the NHP retina raising the possibility that these cells could be involved in retinal innate inflammatory responses.

Inhibitory Effects of Tranilast on Cytokine, Chemokine, Adhesion Molecule, and Matrix Metalloproteinase Expression in Human Corneal Fibroblasts Exposed to Poly(I:C)

Purpose/Aim: Viral infection of the cornea can result in inflammation and scarring and eventually cause blindness. Polyinosinic-polycytidylic acid [poly(I:C)], an analog of viral double-stranded RNA, induces the synthesis of various cytokines, chemokines, adhesion molecules, and matrix metalloproteinases (MMPs) in corneal fibroblasts. The effects of tranilast on the expression of these molecules in human corneal fibroblasts were examined.

MATERIALS AND METHODS

Human corneal fibroblasts were cultured with or without poly(I:C) or tranilast. The release of the proinflammatory cytokine interleukin (IL)-6 and of the chemokines IL-8 and monocyte chemotactic protein-1 (MCP-1) was measured with enzyme-linked immunosorbent assays. The expression of intercellular adhesion molecule-1 (ICAM-1), vascular cell adhesion molecule-1 (VCAM-1), MMP-1, and MMP-3 was evaluated by immunoblot or immunofluorescence analysis. The phosphorylation of mitogen-activated protein kinases (MAPKs), c-Jun (a component of the transcription factor AP-1), and IκB-α (an endogenous inhibitor of the transcription factor NF-κB) was examined by immunoblot analysis.

RESULTS

Tranilast inhibited in a concentration- and time-dependent manner the production of IL-6, IL-8, MCP-1, ICAM-1, VCAM-1, MMP-1, and MMP-3 by corneal fibroblasts exposed to poly(I:C). It also inhibited the poly(I:C)-induced phosphorylation of c-Jun and the MAPK JNK without affecting that of IκB-α or the MAPKs ERK and p38.

CONCLUSIONS

Tranilast inhibited proinflammatory cytokine, chemokine, adhesion molecule, and MMP expression in human corneal fibroblasts exposed to poly(I:C), with these effects likely being mediated by attenuation of JNK-AP-1 signaling. Tranilast might therefore be expected to limit immune cell infiltration and stromal degradation associated with viral infection of the cornea.

Granulocytes in Ocular HSV-1 Infection: Opposing Roles of Mast Cells and Neutrophils

PURPOSE

The contributions of mast cells (MCs) to immunologic defense against pathogens in the eye are unknown. We have characterized pericorneal MCs as tissue-resident innate sentinels and determined their impact on the immune response to herpes simplex virus type-1 (HSV-1), a common ocular pathogen.

METHODS

The impact of mast cells on the immune response to HSV-1 infection was investigated using MC-deficient Kit(W-sh) mice. Virus titers, inflammatory cytokine production, eicosanoid profiles, cellular immune responses, and ocular pathology were evaluated and compared with C57BL/6J mice during an acute corneal HSV-1 infection.

RESULTS

Corneas of Kit(W-sh) mice have higher viral titers, increased edema, and greater leukocyte infiltration following HSV-1 infection. Following infection, cytokine profiles were slightly elevated overall in Kit(W-sh) mice. Eicosanoid profiles were remarkably different only when comparing uninfected corneas from both groups. Neutrophils within infected corneas expressed HSV-1 antigen, lytic genes, and served as a disease-causing vector when adoptively transferred into immunocompromised animals. Myeloid-derived suppressor cells did not infiltrate into the cornea or suppress the expansion, recruitment, or cytokine production by CD8+ T cells following acute HSV-1 infection.

CONCLUSIONS

Collectively, these findings provide new insight into host defense in the cornea and the pathogenesis of HSV-1 infection by identifying previously unacknowledged MCs as protective innate sentinels for infection of the ocular surface and reinforcing that neutrophils are detrimental to corneal infection.

Dry eye modulates the expression of toll-like receptors on the ocular surface

We aimed to determine if toll-like receptor (TLR) expression is modulated in response to dry eye-associated conditions and in dry eye syndrome (DES). Primary human corneal epithelial cells (HCEC), an SV40 HCEC cell line or a normal human conjunctival epithelial cell line (IOBA-NHC) were cultured under hyperosmolar stress (HOS) (400-500 mOsm/kg) or with DES associated cytokines (IL-1α/β, TNFα or TGFβ) at concentrations ranging from 1 to 1000 ng/ml for up to 24 h. Epithelial cells were harvested from a human cornea organ culture model following 24 h of desiccation. Conjunctival impression cytology samples were harvested from subjects with DES and age and gender-matched normal subjects. TLR4, TLR5 or TLR9 mRNA or protein was examined by quantitative RT-PCR, western blotting or flow cytometry. TLR functionality was evaluated in terms of addition of TLR agonists and quantitation of secreted inflammatory cytokines by the use of ELISA and Luminex assays. In SV40 HCEC, HOS significantly increased TLR4 by 8.18 fold, decreased TLR9 by 0.58 fold, but had no effect on TLR5 mRNA expression. TLR4 and TLR9 protein were decreased by 67.7% and 72% respectively. TLR4 mRNA was also significantly up-regulated by up to 9.70 and 3.36 fold in primary HCEC and IOBA-NHC respectively. DES associated cytokines had no effect on TLR4, TLR5 and TLR9 expression. In response to desiccation, TLR4 and TLR5 mRNA were significantly up-regulated by 4.81 and 2.51 fold respectively, while TLR9 mRNA was down-regulated by 0.86 fold in HCEC. A similar trend for TLR4 and TLR9 protein was observed. TLR9 mRNA was significantly down-regulated by almost 59.5% in DES subjects. In conclusion, changes in TLR expression occur in dry eye and could have an important role in ocular surface susceptibility to inflammation and infection.

Immunological aspects of acute and recurrent herpes simplex keratitis

Herpes simplex keratitis (HSK) belongs to the major causes of visual morbidity worldwide and available methods of treatment remain unsatisfactory. Primary infection occurs usually early in life and is often asymptomatic. Chronic visual impairment and visual loss are caused by corneal scaring, thinning, and vascularization connected with recurrent HSV infections. The pathogenesis of herpetic keratitis is complex and is still not fully understood. According to the current knowledge, corneal scarring and vascularization are the result of chronic inflammatory reaction against HSV antigens. In this review we discuss the role of innate and adaptive immunities in acute and recurrent HSV ocular infection and present the potential future targets for novel therapeutical options based on immune interventions.

Who pays the toll for solving the enigma of corneal herpes?

In herpetic stromal keratitis (HSK), herpes simplex virus type-1 DNA fragments and herpes simplex virus-immunoglobulin G immune complexes are present in corneas long after the infective virus has disappeared. These viral components are highly immunogenic and potentiate the production of proinflammatory cytokines and chemokines via Toll-like receptors expressed on corneal cells and macrophages. In addition, angiogenic factors, such as the vascular endothelium growth factor and the tissue-damaging enzyme, matrix metalloproteinase 9, are induced by corneal cells and macrophages through the recognition of these viral components in the pathogenesis of HSK. Upon neovascularization, robust infiltration of leukocytes via leaky new vessels is elicited. Activated polymorphonuclear leukocytes (PMNs) secrete hydrogen peroxide and myeloperoxidase, which inhibit viral growth. PMNs also produce tumor necrosis factor, monokine-induced by interferon-γ (CXCL9), and nitric oxide. These factors provide a local environment that can induce the differentiation of peripheral CD4* T cells to induce Th1-predominant immunopathology. Thus, strategies developed to alter these pathways should lead to new preventative and therapeutic measures for the treatment of HSK.

Resistance to HSV-1 infection in the epithelium resides with the novel innate sensor, IFI-16

Toll-like receptors (TLRs) are innate sentinels required for clearance of bacterial and fungal infections of the cornea, but their role in viral immunity is currently unknown. We report that TLR signaling is expendable in herpes simplex virus (HSV)-1 containment as depicted by plaque assays of knockout mice (MyD88(-/-), Trif(-/-) and MyD88(-/-) Trif(-/-) double knockout) resembling wild-type controls. To identify the key sentinel in viral recognition of the cornea, in vivo knockdown of the DNA sensor IFI-16/p204 in the corneal epithelium was performed and resulted in a loss of IFN-regulatory factor-3 (IRF-3) nuclear translocation, interferon-α production, and viral containment. The sensor seems to have a similar function in other HSV clinically relevant sites such as the vaginal mucosa in which a loss of p204/IFI-16 results in significantly more HSV-2 shedding. Thus, we have identified an IRF-3-dependent, IRF-7- and TLR-independent innate sensor responsible for HSV containment at the site of acute infection.

Expression of Toll-like receptors 2, 3, 4, 6, 9, and MD-2 in the normal equine cornea, limbus, and conjunctiva

OBJECTIVE

Human corneal cells have detectable levels of TLRs 1-10. TLRs 2 and 4 are the major corneal receptors, recognizing the PAMPs associated with fungal invasion in humans. The conjunctiva and limbus contain TLRs 2, 4, and 9. Our purpose was to determine the expression of TLRs 2, 3, 4, 6, 9, and MD-2 in the normal equine cornea, conjunctiva, and limbus.

METHODS

Corneal, limbal, and conjunctival tissues were collected from seven euthanized horses having no evidence of ocular disease. RNA extraction with DNase-1 digestion was performed followed by RT-PCR to determine expression of TLRs 2, 3, 4, 6, 9, and MD-2. Products were resolved by electrophoresis on 1.5% agarose gels and visualized using ethidium bromide staining.

RESULTS

Expression of TLRs 2, 3, 4, 6, 9, and MD-2 was present in the cornea, limbus, and conjunctiva of each horse, except one horse, where TLR3 expression was unable to be demonstrated in the dorsal and ventral conjunctiva.

CONCLUSIONS

Confirming the expression of TLRs in equine ocular tissues is an initial step in identifying how they play a role in infectious keratitis, particularly fungal. The results further support the use of equine ocular tissues as a model for human fungal keratitis. Studies of the TLR expression together with their cytokine profile induced during equine fungal keratitis may help further clarify the pathogenesis of the disease and possibly lead to the development of new treatment protocols for both equines and humans.

Engagement of TLR2 reverses the suppressor function of conjunctiva CD4+CD25+ regulatory T cells and promotes herpes simplex virus epitope-specific CD4+CD25- effector T cell responses

PURPOSE. The authors recently reported that Foxp3(+)CD4(+) CD25(+(Bright)) "natural" regulatory T cells (nT(reg) cells) are abundant in rabbit conjunctiva and suppress herpes simplex virus (HSV)-1-specific CD4(+) and CD8(+) effector T cells (T(eff) cells). However, little is known about the overall regulatory mechanisms of these nT(reg) cells. The authors investigate the regulation of conjunctiva-resident nT(reg) cells through Toll-like receptors (TLRs) and their effect on ocular mucosal T(eff) cell immunity. METHODS. CD4(+)CD25(+) nT(reg) cells were purified from naive rabbit conjunctivas, and their TLR expression profile was determined. The effects of TLR engagement on nT(reg) cell-mediated suppression of CD4(+) T(eff) cells were determined in vitro and in vivo. RESULTS. The authors found that conjunctiva-resident nT(reg) cells express high levels of TLR2 and TLR9; exposure to the TLR2 ligand lipoteichoic acid (LTA) led to the increased activation and proliferation of nT(reg) cells, and the addition of autologous APCs further increased nT(reg) cell expansion; in contrast, the TLR9 ligand CpG(2007) inhibited the proliferation of nT(reg) cells, and the addition of autologous APCs had no effect on such inhibition; nT(reg) cells treated with LTA, but not with CpG(2007), expressed IFN-γ and IL-10 mRNA, but not TGF-β; consistent with in vitro data, rabbits immunized by topical ocular drops of HSV-gD peptides + TLR2 ligand (LTA) displayed enhanced CD4(+)CD25(-) T(eff) cell immune responses when compared with HSV-gD peptides + TLR9 ligand (CpG(2007)). CONCLUSIONS. Although conjunctiva-resident CD4(+)CD25(+) nT(reg) cells express high level of TLR2 and TLR9, their suppressive function is more significantly reversed after the administration of TLR2 ligand (LTA; P < 0.005) than of TLR9 ligand (CpG(200); P > 0.005). These findings will likely help optimize the topical ocular administration of immunotherapies.

Toll-like receptors in ocular surface diseases: overview and new findings

The ocular surface is the first line of defence in the eye against environmental microbes. The ocular innate immune system consists of a combination of anatomical, mechanical and immunological defence mechanisms. TLRs (Toll-like receptors), widely expressed by the ocular surface, are able to recognize microbial pathogens and to trigger the earliest immune response leading to inflammation. Increasing evidence highlights the crucial role of TLRs in regulating innate immune responses during ocular surface infective and non-infective inflammatory conditions. In addition, recent observations have shown that TLRs modulate the adaptive immune response, also playing an important role in ocular autoimmune and allergic diseases. One of the main goals of ocular surface treatment is to control the inflammatory reaction in order to preserve corneal integrity and transparency. Recent experimental evidence has shown that specific modulation of TLR pathways induces an improvement in several ocular inflammatory conditions, such as allergic conjunctivitis, suggesting new therapeutic anti-inflammatory strategies. The purpose of the present review is to summarize the current knowledge of TLRs at the ocular surface and to propose them as potential targets of therapy for ocular inflammatory conditions.

Toll-like receptor activation modulates antimicrobial peptide expression by ocular surface cells

The ability of the ocular surface to respond to pathogens is in part attributed to toll-like receptors (TLRs) that recognize conserved motifs on various microbes. This study examines TLR expression on various ocular surface cells, if TLR agonists can modulate the expression of antimicrobial peptides (AMPs), human beta defensins (hBD) and cathelicidin (hCAP-18/LL-37) which maybe functionally active against Pseudomonas aeruginosa (PA) and if TLR agonists or AMPs can modulate TLR mRNA expression. TLR1-10 mRNA expression was examined in corneal epithelial, corneal stromal cells and conjunctival epithelial cells by RT-PCR. To confirm protein expression flow cytometry or immunostaining was performed for selected TLRs on some cell cultures. Ocular surface cells were cultured with a range of TLR agonists and then hBD-1, 2, 3, or hCAP-18 mRNA and protein expression was determined by RT-PCR and immunoblotting. In some experiments, cells were cultured with a cocktail of agonists for TLR3, 5 and 6/2 and the antimicrobial activity of the culture media was tested against PA. TLR mRNA expression was also examined in primary human corneal epithelial cells (HCEC) treated with either 3 μg/ml of hBD-2, 5 μg/ml of LL-37 or TLR4, 5 and 9 agonists. Overall, the ocular surface cells expressed mRNA for most of the TLRs but some differences were found. TLR2 was not detected in corneal fibroblasts, TLR4 was not detected in primary cultured or freshly isolated HCEC, TLR5 was not detected in conjunctival epithelial cells (IOBA-NHC) and corneal fibroblasts, TLR7 was not detected in freshly isolated HCEC and TLR10 was not detected in HCEC and IOBA-NHC. TLR8 mRNA was not expressed by any of the samples tested. Immunostaining of cadaver corneas revealed TLR5 and 9 expression throughout the cornea while TLR3 was significantly expressed only in the epithelium. Flow cytometry and immunostaining revealed cultured fibroblasts expressed TLR9 but had no significant TLR3 expression. hBD-2 expression was upregulated by TLR1/2, 3, 4, 5 and 6/2 agonists depending on the cell type, whereas only the TLR3 agonist upregulated the expression of hCAP-18 in primary HCEC. The combination of TLR3, 5 and 6/2 agonists in primary HCEC, upregulated hBD-2 and hCAP-18 mRNA and peptide expression and secretion into the culture media, which significantly killed PA. This antimicrobial activity was primarily attributed to LL-37. TLR agonists did not modulate TLR expression itself, however, LL-37 or hBD-2 downregulated TLR5, 7 and/or 9 mRNA depending on the cell type. TLRs are expressed on the ocular surface and TLR agonists trigger the production of LL-37 and hBD-2, with LL-37 being particularly important for protecting the ocular surface against PA infection.

Toll-like receptors in ocular surface disease

The ability of the ocular surface to mount an immune response is in part attributed to a family of proteins called toll-like receptors (TLRs). The latter are evolutionary conserved receptors that recognize and respond to various microbes and endogenous ligands. In addition to their recognition function, TLR activation triggers a complex signal transduction cascade that induces the production of inflammatory cytokines and co-stimulatory molecules, thus initiating innate and adaptive immunity. Toll-like receptor expression at the ocular surface is modulated during infection (e.g. Herpes simplex, bacterial keratitis and fungal keratitis) as well as during various inflammatory conditions (allergic conjunctivitis and dry-eye syndrome). Here recent findings regarding TLR expression and their involvement in various ocular surface diseases are discussed.

Mucosal treatments for herpes simplex virus: insights on targeted immunoprophylaxis and therapy

Herpes simplex virus (HSV) serotypes 1 and 2 establish lifelong infections that can produce reactivated pools of virus at mucosal sites where primary infections were initiated. No approved vaccines are available. To break the transmission cycle, interventions must either prevent infection or reduce infectivity at mucosal sites. This article discusses the recent experimental successes of immunoprophylactic and therapeutic compounds that enhance resistance and/or reduce viral loads at genital and ocular mucosa. Current data indicate Toll-like receptor agonists and selected immunomodulating compounds effectively increase the HSV infection threshold and hold promise for genital prophylaxis. Similarly, immunization at genital and extragenital mucosal sites is discussed. Finally, preclinical success with novel immunotherapies for ocular HSV that address herpetic keratitis and corneal blindness is reviewed.

Modulation of expression of Toll-like receptors in the human endometrium

PROBLEM

The purpose of the study was to investigate the different expressions of toll-like receptors (TLRs) in the proliferative and the secretory phase of endometrial tissue.

METHOD OF STUDY

Eight infertile women were included in this study. The endometrial tissues of proliferative and secretory phase were obtained from each woman. The tissues were evaluated for the expression of mRNA for TLR1-10 by reverse transcribed polymerase chain reaction (RT-PCR). The proteins of TLR2, 3, 4, and 9 were evaluated by Western blot. The mRNA and protein level of proliferative and secretory endometrial tissue from the same woman was compared. The data were analysed with SPSS15.0.

RESULTS

TLR1-7, 9, and 10 mRNA were expressed throughout the menstrual cycle, but in the same woman, the expression of TLR2-6, 9, and 10 mRNA was higher during the secretory phase than that in the proliferative phase. The Western blot also showed that the protein expression of TLR2, 3, 4, and 9 was stronger in the secretory phase than that in the proliferative phase in the same woman.

CONCLUSION

The expression of TLRs is cycle dependent in human endometrial tissue. The expressions of TLRs were higher in the secretory phase than that in the proliferative phase: this indicated that TLRs may be regulated by sex hormones throughout the menstrual cycle.

Who (what) pays toll for the development of herpetic stromal keratitis (HSK)

In the herpetic stromal keratitis (HSK), HSV DNA fragments and HSV-IgG immune complexes (HSV-IC) are present in most of the corneas long after infective virus has disappeared. These viral components are highly immunogenic and potentiate production of proinflammatory cytokines and chemokines via Toll-like receptors (TLRs) expressed on the corneal cells and macrophages. In addition angiogenic factors, such as vascular endothelium growth factor (VEGF) and the tissue damaging enzyme matrix metalloproteinase 9 (MMP-9) deeply involved in the pathogenesis of HSK, are also induced by corneal cells and macrophages through the recognition of these viral components. These processes elicited by residual viral DNA and HSV-IC are likely one of the sustained driving force in the development of HSK. Hence, strategies developed to alter these pathways should lead to new preventative and therapeutic measures.

Expression of toll-like receptors in the Fusarium solani infected cornea

PURPOSE

To investigate the expression of toll-like receptors (TLRs) in the human cornea with Fusarium solani (F. solani) keratitis.

METHODS

Five human corneas with F. solani keratitis and 5 healthy human corneas were evaluated for TLR1-10 mRNA by reverse transcribed polymerase chain reaction (RT-PCR) and relative real-time PCR. The proteins of TLR2, 4, and 9 were also compared by Western blot. The mean times between these corneas were collected, and the onset of treatment to surgery was 34.4 +/- 12.4 days, ranging from 15 to 47 days. The data were analyzed with SPSS15.0.

RESULTS

TLR1-10 mRNA was expressed in both healthy and F. solani infected human corneas. The expression of TLR2, 4, 6, and 9 mRNA in the F. solani infected human corneas were upregulated. The Western blot showed the protein expression of TLR2, 4, and 9 was also upregulated in the corneas with F. solani keratitis than that of the healthy corneas.

CONCLUSIONS

TLRs are expressed diversely in the F. solani infected human cornea, and TLR2, 4, and 9 may be implicated in the pathogenesis of F. solani infection in the cornea.