Early cytokine synthesis in the excised mouse cornea

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.

Polluted Air Exposure Compromises Corneal Immunity and Exacerbates Inflammation in Acute Herpes Simplex Keratitis

Air pollution is a serious environmental issue worldwide in developing countries’ megacities, affecting the population’s health, including the ocular surface, by predisposing or exacerbating other ocular diseases. Herpes simplex keratitis (HSK) is caused by the herpes simplex virus type 1 (HSV-1). The primary or recurring infection in the ocular site causes progressive corneal scarring that may result in visual impairment. The present study was designed to study the immunopathological changes of acute HSK under urban polluted air, using the acute HSK model combined with an experimental urban polluted air exposure from Buenos Aires City. We evaluated the corneal clinical outcomes, viral DNA and pro-inflammatory cytokines by RT-PCR and ELISA assays, respectively. Then, we determined the innate and adaptive immune responses in both cornea and local lymph nodes after HSV-1 corneal by immunofluorescence staining and flow cytometry. Our results showed that mice exposed to polluted air develop a severe form of HSK with increased corneal opacity, neovascularization, HSV-1 DNA and production of TNF-α, IL-1β, IFN-γ, and CCL2. A high number of corneal resident immune cells, including activated dendritic cells, was observed in mice exposed to polluted air; with a further significant influx of bone marrow-derived cells including GR1+ cells (neutrophils and inflammatory monocytes), CD11c+ cells (dendritic cells), and CD3+ (T cells) during acute corneal HSK. Moreover, mice exposed to polluted air showed a predominant Th1 type T cell response over Tregs in local lymph nodes during acute HSK with decreased corneal Tregs. These findings provide strong evidence that urban polluted air might trigger a local imbalance of innate and adaptive immune responses that exacerbate HSK severity. Taking this study into account, urban air pollution should be considered a key factor in developing ocular inflammatory diseases.

IL-1α Modulates IFN-γ-Induced Production of CXCL9/MIG during Herpes Simplex Virus Type-1 Corneal Infection

PURPOSE

Investigating the modulation of neutrophil production of MIG and IP-10 during the inflammatory response to HSV-1 infection.

MATERIALS AND METHODS

An ex vivo model of human corneal infection by HSV-1 was used for this study. This model permits the study of cytokine production by human corneal buttons in the presence, or absence, of gradient purified human neutrophils, under conditions of HSV-1 infection. All experimental samples were stimulated with a baseline concentration of recombinant human IFN-γ at 1 ng/mL. The relative levels of production for 12 pro-inflammatory mediators were screened using a multi-analyte ELISA assay. Neutrophil production of chemokines MIG and IP-10, under conditions of IFN-γ and/or HSV-1 stimulation were measured by quantitative ELISA. Lastly, antibody neutralization (goat IgG anti-human IL-1α, 2 µg/mL) of de novo production of IL-1α by corneal tissue was performed to investigated the effect on MIG and IP-10 production in the ex vivo model for HSV-1 infection.

RESULTS

Four of the 12 pro-inflammatory mediators screened (IL-8, IL-6, IL-1α and IL-1β) demonstrated elevated levels of production during corneal cell infection with HSV-1 and communication with neutrophils. Neutrophils were demonstrated to produce significant levels of both MIG and IP-10 under conditions of IFN-γ stimulation, and production of MIG was further upregulated by co-stimulation with IFN-γ and HSV-1. Neutralization of de novo IL-1α production in the model resulted in increased production of the chemokine production MIG but had no observable effect on IP-10 production.

CONCLUSIONS

Our data provide evidence demonstrating the potential for expression patterns of MIG and IP-10 to be modulated by IL-1α, during the inflammatory response to HSV-1 corneal infection. Both corneal cells and neutrophils contribute to the production of T cell recruiting chemokines. However, IL-1α has the potential to upregulate MIG production by corneal cells while down-regulating MIG production by neutrophils.

CCR6-Positive γδ T Cells Provide Protection Against Intracorneal HSV-1 Infection

Purpose

γδ T cells offer an important early immune defense against many different pathogens, both bacterial and viral. Herein, we examined the capacity of γδ T cell subsets to provide protection in the cornea against herpes simplex virus-1 (HSV-1).

Methods

C57Bl/6 (wild-type [WT]), γδ T-cell deficient (TCRδ-/-) and CCR6-deficient (CCR6-/-) mice were infected intracorneally with HSV-1. At multiple time points following infection, corneas were excised, and cells were immunostained for surface markers, intracellular cytokines, and analyzed using flow cytometry. WT and CCR6-/- γδ T cells were adoptively transferred into TCRδ-/- mice and corneal scores and survival were measured.

Results

Intracorneal infection of mice lacking γδ T cells exhibited increased corneal opacity scores, elevated viral titers, and higher mortality compared with WT mice. Both CCR6+ and CCR6neg γδ T cell subsets were observed in corneas after virus infection. CCR6+ γδ T cells produced IL-17A and were predominantly CD44+CD62L+, consistent with natural IL-17+ γδ T cells. In contrast IL-17A production by CCR6neg γδ T cells was infrequent, and this subset was largely single positive for CD62L or CD44. The CCR6+ subset appeared to provide protection against HSV-1 as follows: (1) CCR6-/- mice had more severe corneal opacity compared with WT mice; and (2) adoptive transfer of γδ T cells from WT mice restored protection in TCRδ-/- mice whereas transfer of γδ T cells from CCR6-/- mice did not.

Conclusions

γδ T cells in the cornea can be divided into CCR6+ and CCR6neg subsets with the former conferring protection early after intracorneal HSV-1 infection.

Inhibition of NUCKS Facilitates Corneal Recovery Following Alkali Burn

Corneal wound healing involves a complex cascade of cytokine-controlled cellular events, including inflammatory and angiogenesis responses that are regulated by transcriptional chromatin remodeling. Nuclear Ubiquitous Casein and cyclin-dependent Kinase Substrate (NUCKS) is a key chromatin modifier and transcriptional regulator of metabolic signaling. In this study, we investigated the role of NUCKS in corneal wound healing by comparing its effects on corneal alkali burn in NUCKS knockout (NKO) and NUCKS wild-type (NWT) mice. Our data showed that following alkali-injury, inhibition of NUCKS (NKO) accelerated ocular resurfacing and suppressed neovascularization; the cytokine profile of alkali burned corneas in NKO mice showed suppressed expression of inflammation cytokines (IL1A & IL1B); upregulated expression of antiangiogenic factor (Pigment Epithelium-derived Factor; PEDF); and downregulated expression of angiogenic factor (Vascular Endothelial Growth Factor, VEGF); in vitro, following LPS-induced NFκB activation, NKO corneal cells showed reduced expression of IL6, IP10 and TNFα. In vitro, corneal epithelial cells showed reduced NF-κb activation on silencing of NUCKS and corresponding NFκB-mediated cytokine expression was reduced. Here, we illustrate that inhibition of NUCKS played a role in cytokine modulation and facilitated corneal recovery. This reveals a potential new effective strategy for ocular burn treatment.

The inflammasome NLRP3 plays a protective role against a viral immunopathological lesion

Herpes simplex 1 infection of the eye can cause blindness with lesions in the corneal stroma largely attributable to inflammatory events that include components of both adaptive and innate immunity. Several innate immune responses are triggered by herpes simplex 1, but it is unclear how such innate events relate to the subsequent development of stromal keratitis. In this study, we compared the outcome of herpes simplex 1 ocular infection in mice unable to express NLRP3 because of gene knockout (NLRP3(-/-)) to that of wild-type mice. The NLRP3(-/-) mice developed more-severe and earlier stromal keratitis lesions and had higher angiogenesis scores than did infected wild-type animals. In addition, NLRP3(-/-) mice generated an increased early immune response with heightened chemokines and cytokines, including interleukin-1β and interleukin-18, and elevated recruitment of neutrophils. Increased numbers of CD4(+) T cells were seen at later stages of the disease in NLRP3(-/-) animals. Reduction in neutrophils prevented early onset of the disease in NLRP3(-/-) animals and lowered levels of bioactive interleukin-1β but did not lower bioactive interleukin-18. In conclusion, our results indicate that NLRP3 has a regulatory and beneficial role in herpetic stromal keratitis pathogenesis.

Kinetics of viral replication and induction of host responses in ferrets differs between ocular and intranasal routes of inoculation

While influenza viruses are typically considered respiratory pathogens, the ocular system represents a secondary entry point for virus to establish a productive respiratory infection and the location for rare instances of virus-induced conjunctivitis. We used the ferret model to conduct a side-by-side comparison of virus infectivity, kinetics of viral replication, and induction of host responses following inoculation by either the intranasal or ocular routes with two viruses, A/Netherlands/230/03 (H7N7) and A/Panama/2007/99 (H3N2). We show that ocular inoculation resulted in delayed virus replication and reduced levels of proinflammatory cytokine and chemokine transcript in respiratory tract but not ocular tissues compared with intranasally inoculated animals. We identified numerous proinflammatory mediators with known roles in ocular disease elicited in ferret eye tissue following influenza virus infection. These findings provide a greater understanding of the modulation of host responses following different inoculation routes and underscore the risk associated with ocular exposure to influenza viruses.

Resident Corneal Cells Communicate with Neutrophils Leading to the Production of IP-10 during the Primary Inflammatory Response to HSV-1 Infection

In this study we show that murine and human neutrophils are capable of secreting IP-10 in response to communication from the HSV-1 infected cornea and that they do so in a time frame associated with the recruitment of CD8⁺ T cells and CXCR3-expressing cells. Cellular markers were used to establish that neutrophil influx corresponded in time to peak IP-10 production, and cellular depletion confirmed neutrophils to be a significant source of IP-10 during HSV-1 corneal infection in mice. A novel ex vivo model for human corneal tissue infection with HSV-1 was used to confirm that cells resident in the cornea are also capable of stimulating neutrophils to secrete IP-10. Our results support the hypothesis that neutrophils play a key role in T-cell recruitment and control of viral replication during HSV-1 corneal infection through the production of the T-cell recruiting chemokine IP-10.

Ocular infection of mice with influenza A (H7) viruses: a site of primary replication and spread to the respiratory tract

Avian H7 influenza viruses have been responsible for poultry outbreaks worldwide and have resulted in numerous cases of human infection in recent years. The high rate of conjunctivitis associated with avian H7 subtype virus infections may represent a portal of entry for avian influenza viruses and highlights the need to better understand the apparent ocular tropism observed in humans. To study this, mice were inoculated by the ocular route with viruses of multiple subtypes and degrees of virulence. We found that in contrast to human (H3N2 and H1N1) viruses, H7N7 viruses isolated from The Netherlands in 2003 and H7N3 viruses isolated from British Columbia, Canada, in 2004, two subtypes that were highly virulent for poultry, replicated to a significant titer in the mouse eye. Remarkably, an H7N7 virus, as well as some avian H5N1 viruses, spread systemically following ocular inoculation, including to the brain, resulting in morbidity and mortality of mice. This correlated with efficient replication of highly pathogenic H7 and H5 subtypes in murine corneal epithelial sheets (ex vivo) and primary human corneal epithelial cells (in vitro). Influenza viruses were labeled to identify the virus attachment site in the mouse cornea. Although we found abundant H7 virus attachment to corneal epithelial tissue, this did not account for the differences in virus replication as multiple subtypes were able to attach to these cells. These findings demonstrate that avian influenza viruses within H7 and H5 subtypes are capable of using the eye as a portal of entry.

The role of infections in autoimmune disease

Autoimmunity occurs when the immune system recognizes and attacks host tissue. In addition to genetic factors, environmental triggers (in particular viruses, bacteria and other infectious pathogens) are thought to play a major role in the development of autoimmune diseases. In this review, we (i) describe the ways in which an infectious agent can initiate or exacerbate autoimmunity; (ii) discuss the evidence linking certain infectious agents to autoimmune diseases in humans; and (iii) describe the animal models used to study the link between infection and autoimmunity.

IL-17 receptor signaling influences virus-induced corneal inflammation

IL-17 has been associated with selected inflammatory and autoimmune diseases. We characterized the expression of this proinflammatory cytokine following HSV-1 corneal infection and investigated whether IL-17R signaling modulated the host response to the viral pathogen at early time-points postinfection. IL-17 was elevated in the murine cornea 24 h after high-dose virus infection and subsequently persisted at low levels during the first week. Immunofluorescent studies showed that the IL-17R was expressed by cultured mouse corneal fibroblasts. Exposure of corneal cells to IL-17 led to production of IL-6 and MIP-2 in vitro and in vivo, indicating that the IL-17R was functional. Mice lacking IL-17R displayed significantly reduced neutrophil infiltration and corneal opacity. However, this effect was transient, as corneal pathology and neutrophil influx resembled that of wild-type (WT) hosts 4 days postinfection. HSV-1 growth and clearance in IL-17R(-/-) hosts were similar to that of the WT controls. Infection of IFN-gamma gene knockout mice was associated with elevated IL-17 levels and accelerated corneal opacity, suggesting that IFN-gamma negatively regulated IL-17 expression. Collectively, our results establish that IL-17 is rapidly produced in the cornea after HSV-1 infection and is regulated at least in part by IFN-gamma. The absence of IL-17 signaling results in a transient decrease in the expression of proinflammatory mediators, neutrophil migration, and corneal pathology, but control of virus growth in the cornea and trigeminal ganglia is not compromised. Thus, IL-17 actively influences early virus-induced corneal inflammation.

Local thermal injury elicits immediate dynamic behavioural responses by corneal Langerhans cells

Langerhans cells (LCs) represent a special subset of immature dendritic cells (DCs) that reside in epithelial tissues at the environmental interfaces. Although dynamic interactions of mature DCs with T cells have been visualized in lymph nodes, the cellular behaviours linked with the surveillance of tissues for pathogenic signals, an important function of immature DCs, remain unknown. To visualize LCs in situ, bone marrow cells from C57BL/6 mice expressing the enhanced green fluorescent protein (EGFP) transgene were transplanted into syngeneic wild-type recipients. Motile activities of EGFP(+) corneal LCs in intact organ cultures were then recorded by time lapse two-photon microscopy. At baseline, corneal LCs exhibited a unique motion, termed dendrite surveillance extension and retraction cycling habitude (dSEARCH), characterized by rhythmic extension and retraction of their dendritic processes through intercellular spaces between epithelial cells. Upon pinpoint injury produced by infrared laser, LCs showed augmented dSEARCH and amoeba-like lateral movement. Interleukin (IL)-1 receptor antagonist completely abrogated both injury-associated changes, suggesting roles for IL-1. In the absence of injury, exogenous IL-1 caused a transient increase in dSEARCH without provoking lateral migration, whereas tumour necrosis factor-alpha induced both changes. Our results demonstrate rapid cytokine-mediated behavioural responses by LCs to local tissue injury, providing new insights into the biology of LCs.

Herpes simplex virus 1 infection induces the expression of proinflammatory cytokines, interferons and TLR7 in human corneal epithelial cells

Herpetic epithelial and stromal keratitis is a sight-threatening ocular infection. To study the role of the epithelium in the innate response to herpes simplex virus 1 (HSV-1) infection of the cornea, we used a telomerase-immortalized human corneal epithelial cell (HCEC) line, HUCL, and primary HCECs as a model and infected the cells with HSV-1 (KOS strain). HSV-1 infection of HCECs resulted in a two-phase activation of nuclear factor-kappaB (NF-kappaB), JNK and p38, with the first peak at 1-4 hr and a second peak at 8 hr. Concomitant with the first peak of activation, transcriptional expression of interleukin (IL)-6, IL-8, tumour necrosis factor (TNF)-alpha and interferon (IFN)-beta was rapidly induced in HSV-1-infected cells. HSV-1 infection also induced the production of IL-6, IL-8, and TNF-alpha in both HUCL cells and primary HCECs. Coincident with the second phase of NF-kappaB activation in HSV-1-infected HCECs, the expression of Toll-like receptor 7 (TLR7) was induced, whereas the level of TLR3 was greatly down-regulated. Thus, in response to HSV-1 infection, HCECs produce proinflammatory cytokines, leading to infiltration, and IFNs to enhance the antiviral activity in the cornea, probably through sequential activation of TLRs.

Involvement of IL-6 in the paracrine production of VEGF in ocular HSV-1 infection

Following ocular HSV-1 infection, neovascularisation of the avascular cornea is a critical event in the pathogenesis of herpetic stromal keratitis. This present study evaluates the role of proinflammatory cytokines such as IL-6 in corneal angiogenesis following virus infection. Both in vivo and in vitro data indicate that IL-6 produced from virus-infected cells can stimulate noninfected resident corneal cells and other inflammatory cells in a paracrine manner to secrete VEGF, a potent angiogenic factor. Antibody neutralisation of IL-6 resulted in a significant decrease in the number of VEGF producing cells in the cornea. Thus, our results further demonstrate the close relationship between proinflammatory cytokines and VEGF-induced corneal neovascularisation.

Molecular mimicry versus bystander activation: herpetic stromal keratitis

Herpes stromal keratitis (HSK) is a significant inflammatory disease of the cornea as a result of herpes simplex virus (HSV) infection often progressing to vision loss if left untreated. However, even with immunosuppressive compounds and anti-viral drug treatment, HSV continues to be the leading cause of infectious corneal blindness in the industrialized world. The inflammatory nature of the disease is the root of the pathogenic process characterized by irreversible corneal scarring, neovascularization of the avascular cornea, and infiltration of activated leukocytes. Experimental evidence using mice suggest HSK is the result of either molecular mimicry or a bystander activation phenomenon. This review will revisit the basis of HSK focusing on issues that pertain to the autoimmune component versus collateral damage as a result of non-specific activation as a means to explain the pathologic manifestations of the disease.

Early events in HSV keratitis--setting the stage for a blinding disease

The last decade has seen herpes simplex virus (HSV)-induced stromal keratitis (SK) research shift from being a topic only of interest to vision researchers to one that fascinates the general field of inflammatory disease. Studies on experimental mouse lesions have uncovered several fundamental processes that explain lesion development. In this model, the chronic immuno-inflammatory lesions are mainly orchestrated by CD4+ T cells, but multiple early events occur that set the stage for the subsequent pathology. These include virus replication, the production of key cytokines and chemokines, neovascularization of the avascular cornea and the influx of certain inflammatory cell types. Many of these early events are subject to modulation, providing an approach to controlling this important cause of human blindness. We also comment on events ongoing during chronic SK, debating whether or not these represent virus-induced or autoimmune lesions.

Corneal response to Pseudomonas aeruginosa infection

Pseudomonas aeruginosa (P. aeruginosa) is a common organism associated with bacterial keratitis, especially in those who use extended wear contact lenses. Recent advances in our understanding of host innate and adaptive immune responses to experimental infection have been made using a variety of animal models, including inbred murine models that are classed as resistant (cornea heals) vs. susceptible (cornea perforates). Evidence has been provided that sustained IL-12-driven IFN-gamma production in dominant Th1 responder strains such as C57BL/6 (B6) contributes to corneal destruction and perforation, while IL-18-driven production of IFN-gamma in the absence of IL-12 is associated with bacterial killing and less corneal destruction in dominant Th2 responder strains such as BALB/c. The critical role of IL-1 and chemotactic cytokines such as MIP-2 in PMN recruitment and the critical role of this cell in the innate immune response to bacterial infection is reviewed. Regulation of PMN persistence is also discussed and evidence provided that persistence of PMN in B6 cornea is regulated by CD4+ T cells, while macrophages regulate PMN number in the cornea of BALB/c mice. The studies provide a better understanding of the inflammatory mechanisms that are operative in the cornea after P. aeruginosa challenge and are consistent with long-term goals of providing targets for alternative or adjunctive treatment for this disease. Future studies will be aimed at better defining the role of Toll receptors, neuropeptides (as unconventional modulators of the immune response) and exploitation of disease control by new techniques, such as RNA silencing.

Mice Transgenic for IL-1 Receptor Antagonist Protein Are Resistant to Herpetic Stromal Keratitis: Possible Role for IL-1 in Herpetic Stromal Keratitis Pathogenesis

Ocular infection with HSV may result in the blinding immunoinflammatory lesion stromal keratitis (SK). This represents a CD4+ T cell-mediated immunopathologic lesion in both humans and a mouse model. Early events in the pathogenesis that set the stage for SK are poorly understood. The present study evaluates the role of IL-1 using a transgenic mouse that overexpresses the IL-1 receptor antagonist (IL-1ra) protein. Such transgenic mice were markedly resistant to SK compared with IL-1ra(-/-) and C57BL/6 control animals. The resistance was shown to be the consequence of reduced expression of molecules such as IL-6, macrophage-inflammatory protein-2, and vascular endothelial growth factor, normally up-regulated directly or indirectly by IL-1. A critical event impaired in IL-1ra transgenic mice was vascular endothelial growth factor production with a consequent marked reduction in angiogenesis, an essential step in SK pathogenesis. Targeting IL-1 could prove to be a worthwhile therapeutic approach to control SK, an important cause of human blindness.

Pathogenic mechanisms of P. aeruginosa keratitis: a review of the role of T cells, Langerhans cells, PMN, and cytokines

The aim of this article is to review our current understanding of the role of cytokines, chemokines, T cells, Langerhans cells, and neutrophils (PMN) and their interactions in vivo in the host response to Pseudomonas aeruginosa ocular challenge. The cellular/cytokine network in vivo has begun to be unraveled, and the data discussed provide substantive evidence for a regulatory role of CD4(+) T cells (Th1 type) contributing directly to persistence of PMN in the cornea of susceptible C57BL/6 (cornea perforates) versus resistant BALB/c (cornea heals) mice. Additionally, in the susceptible mouse model, CD4(+) T cells interact with Langerhans cells and B7/CD28 ligation appears critical for antigen presentation and the susceptibility response. Various cytokines and chemokines (e.g., MIP-1alpha, IL-1beta, MIP-2, IL-12, and IFN-gamma) and their pattern of sustained upregulation after infection in susceptible versus resistant mice also will be discussed in light of an in vivo cytokine network. T-cell-mediated pathogenic mechanisms are of importance in development of the susceptible response to P. aeruginosa ocular infection. In the absence of T-cell infiltration into the cornea, PMN do not persist in the stroma, and cytokines and chemokines are better balanced, resulting in decreased stromal destruction and the resistance response.

Signal transducers and activators of transcription (Stat) are detectable in mouse trigeminal ganglion neurons

We studied signal transducers and activators of transcription (Stat) expression in mouse trigeminal ganglia (TG) to gain an understanding of herpes simplex virus (HSV) infection and reactivation. Mouse TG were harvested and were either frozen for Western blot analysis or preserved in 4% paraformaldehyde for subsequent immunohistochemistry study. The thawed specimens were homogenized, and nuclear/cytoplasmic extractions were performed for Western blots and immunoprecipitation. Immunohistochemistry showed that Stat1, Stat3, Stat4, Stat5b, and phosphotyrosine Stat3 localized to TG neurons, not surrounding satellite cells. Western blot of TG nuclear and cytoplasmic extracts confirmed the presence of these Stat at the appropriate molecular weights. Stat2 was undetectable in TG by these methods. Immunoprecipitation of TG nuclear extracts did not confirm the presence of Stat-Stat dimers in these specimens. These studies show that several Stat, including phosphotyrosine Stat3, are present in TG neurons, the site of HSV latency, where they could act upon latent viral DNA to effect reactivation.

Predictive value of in vitro model systems in toxicology

The application of in vitro model systems to evaluate the toxicity of xenobiotics has significantly enhanced our understanding of drug- and chemical-induced target toxicity. From a scientific perspective, there are several reasons for the popularity of in vitro model systems. From the public perspective, in vitro model systems enjoy increasing popularity because their application may allow a reduction in the number of live animals employed in toxicity testing. In this review, we present an overview of the use of in vitro model systems to investigate target organ toxicity of drugs and chemicals, and provide selective examples of these model systems to better understand cutaneous and ocular toxicity and the role of drug metabolism in the hepatotoxicity of selected agents. We conclude by examining the value and use of in vitro model systems in industrial development of new pharmaceutical agents.

Persistent elevated expression of cytokine transcripts in ganglia latently infected with herpes simplex virus in the absence of ganglionic replication or reactivation

Infection of mouse trigeminal ganglia by herpes simplex virus induces cytokine expression that persists long after infectious virus or viral antigens become undetectable. To examine mechanisms underlying this phenomenon, we used a thymidine kinase mutant, dlsptk, which fails to replicate in ganglia and does not reactivate upon ganglionic explant. Using quantitative reverse transcriptase-polymerase chain reaction assays, we found that levels of interferon-gamma and tumor necrosis factor-alpha transcripts in dlsptk-infected ganglia were lower than those in wild type-infected ganglia, but were significantly (eight- to 10-fold) higher than those in mock-infected ganglia from Day 3 to Day 100 postinfection. We also studied latency-associated transcript (LAT) negative mutants that exhibit increased expression of productive cycle transcripts in ganglia. Ganglia infected with these mutants contained levels of cytokine transcripts similar to those in wild type-infected ganglia; any increases in viral antigen expression mediated by the LAT deletion were not accompanied by increased cytokine expression. Thus, neither viral replication, the ability to reactivate, nor LAT expression in ganglia is required for persistent elevated cytokine expression. The results provide indirect evidence that low-level expression of viral productive cycle genes in neurons can provide signals that elicit cytokine expression.

Cytokine and chemokine expression kinetics after corneal transplantation

BACKGROUND

Allogeneic rejection is the most common cause of corneal graft failure. The aim of this work was to establish the kinetics of cytokine and chemokine mRNA expression before and after onset of corneal graft rejection.

METHODS

Intracorneal cytokine and chemokine mRNA levels were investigated in the Brown Norway-->Lewis inbred rat model in which rejection onset is observed at 8/9 days after grafting in all animals. Nongrafted corneas and syngeneic (Lewis-->Lewis) corneal transplants were used as controls. Donor and recipient cornea was examined by quantitative competitive reverse transcription-polymerase chain reaction (RT-PCR) for hypoxyanthine phosphoribosyltransferase (HPRT), CD3, CD25, interleukin (IL)-1beta, IL-1RA, IL2, IL-6, IL-10, interferon-gamma (IFN-gamma), tumor necrosis factor (TNF), transforming growth factor (TGF)-beta1, and macrophage inflammatory protein (MIP)-II and by nonquantitative RT-PCR for IL4, IL-5, IL-12 p40, IL-13, TGF-beta2, monocyte chemotactic protein-1 (MCP-1), MIP-1alpha, MIP-1beta, and RANTES (for regulated upon activation normal T cell expressed and secreted).

RESULTS

A biphasic expression of cytokine and chemokine mRNA was found after transplantation. During the early phase (days 3-9), there was an elevation of the majority of the cytokines examined, including IL-1beta, IL-6, IL-10, IL-12 p40, and MIP-II. There was no difference in cytokine expression patterns between allogeneic or syngeneic recipients at this time. In syngeneic recipients, cytokine levels reduced to pretransplant levels by day 13, whereas levels of all cytokines rose after observed rejection onset in the allografts, including TGF-beta1, TGF-beta2, and IL-1RA. The T cell-derived cytokines IL-4, IL-13, and IFN-gamma were detected only during the rejection phase in allogeneic recipients.

CONCLUSIONS

There is an early cytokine and chemokine response to the transplantation process, evident in syngeneic and allogeneic grafts, that probably drives angiogenesis, leukocyte recruitment, and affects leukocyte functions. After an immune response has been generated, allogeneic rejection results in the expression of Th1 cytokines (IL-2, IL-12 p40, IFN-gamma), Th2 cytokines (IL-4, IL-6, IL-10, and IL-13), and antiinflammatory/Th3 cytokines (TGF-beta1/2 and IL-1RA).

Changes of cytochemical markers in the conjunctival and corneal epithelium after corneal debridement

1. The aim of this study was to determine the epithelial changes of the conjunctiva and cornea up to 7 days after corneal debridement and the changes highlighted included (1) proliferation, (2) production of growth factor, (3) changes in calcium binding protein marker, (4) production of cytokine, and (5) maturity of the regeneration corneal epithelium. 2. The cytochemical changes of the corneal and conjunctival epithelia of rabbit were analyzed up to 7 days after debridement. 3. An increase in proliferating cell nuclear antigen (PCNA) was observed in the limbal epithelia 12 hr after lesion and reached a peak by 48 hr. 4. Some proliferating limbal cells also contained epidermal growth factor (EGF) beginning 24 hr after injury. The early limbal cell proliferation and the EGF production and their persistence until 7 days after lesion were likely involved with the process of regeneration. 5. Other positive markers appeared after lesion included tumor necrosis factor (TNFalpha) and calcium binding proteins S100A and S100B, which appeared mainly within the first 48 hr after lesion and then started to decline. The short appearance and the relatively small quantity of TNFalpha indicated that this cytokine was probably not very important in the repair process and its appearance might be related to the injury induced. The presence of S100A and S100B could be associated with both cell death after injury and the proliferation of new epithelium. 6. The cornea epithelium was still immature 7 days after lesion in that it still contained cytokeratin. 7. In conclusion, the critical hours of peak conjunctival and corneal changes after corneal debridement were in the first 2 days.

Early expression of proinflammatory cytokines interleukin-1 and tumor necrosis factor-alpha after corneal transplantation

This study's aim was to determine the early postoperative expression of proinflammatory cytokines interleukin-1 (IL-1) and tumor necrosis factor-alpha (TNF-alpha) by corneal grafts. BALB/c (n = 90) and C57BL/6 (n = 90) murine recipients were grafted with donor corneas from either syngeneic or allogeneic mice. At 7 and 14 days after surgery, corneal grafts were excised and the recipient rims separated from the donor tissue. Corneal segments were cultured and assayed for cytokines by enzyme-linked immunosorbent assay (ELISA). There was profound upregulation in expression of both IL-1alpha and TNF-alpha after corneal transplantation. Among both low-rejecting BALB/c and high-rejecting C57BL/6 hosts, levels of IL-1alpha were significantly (p < 0.01) more marked in allogeneic as compared to syngeneic grafts. TNF-alpha overexpression was similarly more marked in allogeneic as compared to syngeneic grafts in both BALB/c and C57BL/6 hosts, although the difference was generally more marked among high-rejecting C57BL/6 recipients. In the case of both IL-1alpha and TNF-alpha, the principal source of cytokine expression in the transplanted tissue was the recipient rim. There is significant overexpression of both IL-1alpha and TNF-alpha during the first 2 weeks after transplantation in both syngeneic and allogeneic orthotopic corneal grafts. However, whereas in syngeneic grafts cytokine expression generally decreases after the first postoperative week, significantly elevated cytokine levels are sustained in allogeneic grafts, implicating IL-1 and TNF-alpha as mediators of the alloimmune response in corneal transplantation.

Expression of interleukin-6 in the cornea in response to infection with different strains of Pseudomonas aeruginosa

Strains of Pseudomonas aeruginosa causing keratitis can be either cytotoxic (6206) or invasive (6294), while a strain (Paer1) causing contact lens-induced acute red eye has been shown to be neither. In situ hybridization was used to examine the location and identity of cells expressing interleukin-6 (IL-6) mRNA in the murine cornea and changes in expression in response to infection with different strains of P. aeruginosa. The number of IL-6-positive cells was determined by image analysis. IL-6 protein levels were measured by an enzyme-linked immunosorbent assay. BALB/c mice were challenged by use of the wounded-cornea model with P. aeruginosa 6294, 6206, or Paer1 (2 x 10(6) CFU). At time intervals up to 24 h, postchallenge corneal tissue was probed for IL-6 mRNA. IL-6 mRNA expression was rapidly elevated in the epithelium in response to strains 6294 and 6206. At the conclusion of the experiments, infiltrating inflammatory cells also stained positively for IL-6 mRNA. In contrast, corneas challenged with strain Paer1 showed significant upregulation of IL-6 mRNA only at 4 h postchallenge. Three distinct patterns of IL-6 mRNA expression in the mouse cornea occur in response to these three ocular isolates of P. aeruginosa. The data obtained for mRNA expression in the cornea for all three strains of P. aeruginosa correlated well with IL-6 protein analysis of whole-eye homogenates. Differences in the cytokine responses to these strains correlate with differences in the pathology associated with each strain and may offer an opportunity to develop strategies for the improved management of ocular inflammation.

Early cytokine and chemokine gene expression during Pseudomonas aeruginosa corneal infection in mice

Using a multiprobe RNase protection assay, we examined cytokine and chemokine mRNAs that were expressed after corneal infection with Pseudomonas aeruginosa in mice. Cytokines that were upregulated included interleukin-1alpha (IL-1alpha) and -1beta, IL-1 receptor antagonist, IL-6, IL-11, granulocyte colony-stimulating factor, granulocyte-macrophage colony-stimulating factor, macrophage colony-stimulating factor, stem cell factor, lymphotoxin beta, transforming growth factor beta1, and tumor necrosis factor alpha. Chemokine transcripts that were upregulated included Eotaxin; gamma-interferon-inducible protein 10; monocyte chemoattractant protein 1; macrophage inflammatory proteins 1alpha, 1beta, and 2; and RANTES. Peak expression of these cytokines and chemokines was observed between 1 and 3 days after infection. These responses returned to or approached baseline preinfection levels by 7 days after ocular challenge. Identification of the various cytokines and chemokines upregulated during corneal infection provides important information relevant to unraveling the pathogenesis induced by this bacterium and provides hope that specific molecules can be targeted for therapy.

Proinflammatory cytokine deficiency and pathogenesis of Pseudomonas aeruginosa keratitis in aged mice

Corneal clarity in young adult Swiss (HSD:ICR) mice is restored after Pseudomonas aeruginosa infection. Previous data showed that this response involves a rapid up-regulation of constitutive intercellular cell adhesion molecule-1 (ICAM-1) and migration of inflammatory cells into the cornea. In contrast, in aged mice, there is no up-regulation of corneal ICAM-1, inflammatory cell infiltration into the cornea is delayed, and the cornea perforates. Therefore, the aim of this study was to test whether specific cytokines which up-regulate ICAM-1 expression differ in young and aged mice. Corneas of young (6- to 8-week-old) and aged (1- to 2-year-old) mice were scarified and inoculated with P. aeruginosa. The eyes were graded for pathologic changes (score 0 to +4); at 6, 12, 24, and 48 h postinfection (p.i.), six mice from each age group were sacrificed. Three corneas from each respective group were excised for quantitation of interleukin-1beta (IL-1beta), tumor necrosis factor alpha, and gamma interferon (IFN-gamma) by enzyme-linked immunosorbent assay. The remaining three corneas from each age group were harvested for quantitation of viable bacteria by direct plate count determination and for infiltrating polymorphonuclear leukocytes (PMNs) by a myeloperoxidase (MPO) assay. Compared to those of young mice, the corneas of infected aged mice had less IL-1beta at 6 h p.i. (P < or = 0.04) and less IFN-gamma at 12 to 48 h p.i. (P < or = 0.05). Also, compared to those of young mice, corneas of aged mice had fewer PMNs (P < or = 0.008) by the MPO assay at 6 h p.i. and more viable bacteria (P < or = 0.01) per cornea by plate count determination at 24 h p.i. These data suggest that the lack of up-regulation of ocular ICAM-1 in aged mice may reflect a reduction in both IL-1beta and IFN-gamma levels in the infected cornea. Consequently, a sufficient number of PMNs and other inflammatory cells fail to rapidly migrate into the infected corneas of aged mice, the bacterial load is initially greater than that in young mice, and the cornea perforates.

Astrogliosis in the neonatal and adult murine brain post-trauma: elevation of inflammatory cytokines and the lack of requirement for endogenous interferon-gamma

The relevance of astrogliosis remains controversial, especially with respect to the beneficial or detrimental influence of reactive astrocytes on CNS recovery. This dichotomy can be resolved if the mediators of astrogliosis are identified. We have measured the levels of transcripts encoding inflammatory cytokines in injury systems in which the presence or absence of astrogliosis could be produced selectively. A stab injury to the adult mouse brain using a piece of nitrocellulose (NC) membrane elicited a prompt and marked increase in levels of transcripts for interleukin (IL)-1alpha, IL-1beta, and tumor necrosis factor (TNF)-alpha, which are considered to be microglia/macrophage cytokines. The elevations preceded, or occurred concomitantly with, the rise in glial fibrillary acidic protein mRNA, an early manifestation of astrogliosis. In neonatal mice, IL-1 and TNF-alpha mRNA were elevated to a greater extent by an NC-implant injury, which produced astrogliosis, than after an NC-stab, with minimal astrogliosis. We determined whether endogenous interferon (IFN)-gamma could be responsible for the observed increases in IL-1 and TNF-alpha, because IFN-gamma is a potent microglia/macrophage activator, and because its exogenous administration to rodents enhanced astrogliosis after adult or neonatal insults. A lack of requirement for endogenous IFN-gamma was demonstrated by three lines of evidence. First, no increase in IFN-gamma transcripts could be found at injury. Second, the administration of a neutralizing antibody to IFN-gamma did not attenuate astrogliosis. Third, in IFN-gamma knockout adult mice, astrogliosis and increases in levels of IL-1alpha and TNF-alpha were induced rapidly by injury. The marked elevation of inflammatory cytokines is discussed in the context of astrogliosis and general CNS recovery.

Trauma and alkali burns induce distinct patterns of cytokine gene expression in the rat cornea

Cytokines such as the interleukins (IL) and tumor necrosis factor alpha (TNF alpha) have traditionally been associated with paracrine regulation of immune reactions. These proteins also have properties suggestive of functional roles in the inflammatory and reparative responses to tissue injury. In this study, mRNA levels for IL-1 alpha, IL-1 beta, IL-6, TNF alpha, interferon gamma, transforming growth factor beta 1, and CD4 were monitored in rat corneas at times from 1 hour through 2 weeks after incisional trauma or alkali burns. Transcripts for IL-1 alpha, TNF alpha, and TGF beta 1 were present in most corneal samples; whereas those for IFN gamma and CD4 were not detected. As early as 1 hour following either of these non-immunologic forms of injury, expression of IL-6 mRNA levels was induced. Only in corneas with alkali burns did IL-6 induction persist from days 1 through 7. The alkali-injured corneas also had markedly increased IL-1 beta mRNA levels from days 1 through 7. These observations indicate that cytokine mRNA is induced in the cornea by trauma without an apparent immunologic stimulus. Our data are consistent with the hypothesis that corneal tissues respond to different types of injury with different patterns of cytokine gene expression.