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

An X-ray inactivated vaccine against Pseudomonas aeruginosa Keratitis in mice

Pseudomonas aeruginosa (P. aeruginosa) is one of the most prevalent pathogens of bacterial keratitis. Bacterial keratitis is a major cause of blindness worldwide. The rising incidence of multidrug resistance of P. aeruginosa precludes treatment with conventional antibiotics. Herein, we evaluated the protective efficiency and explored the possible underlying mechanism of an X-ray inactivated vaccine (XPa) using a murine P. aeruginosa keratitis model. Mice immunized with XPa exhibit reduced corneal bacterial loads and pathology scores. XPa vaccination induced corneal macrophage polarization toward M2, averting an excessive inflammatory reaction. Furthermore, histological observations indicated that XPa vaccination suppressed corneal fibroblast activation and prevented irreversible visual impairment. The potency of XPa against keratitis highlights its potential utility as an effective and promising vaccine candidate for P. aeruginosa.

Suppurative Meningoencephalitis by Pseudomonas aeruginosa from Direct Extension of Chronic Otitis in a Gir Cow

This paper aims to report clinical, laboratory and pathological features in a case of suppurative meningoencephalitis by P. aeruginosa from the direct extension of chronic otitis in a Gir cow. The cow was recumbent during physical examination, and neurological examination revealed depression, absence of left eyelid and auricular motor reflex, and hypotonic tongue. Hematology revealed hemoconcentration, leukocytosis by neutrophilia, and hyperfibrinogenemia. Cerebrospinal fluid was slightly turbid, and presented polymorphonuclear pleocytosis, and hyperproteinorrachia. Grossly, the skull floor showed a purulent green-yellow exudate that drained from the left inner ear to the cisterna magna. There was diffuse congestion of the telencephalon, and meninges showed severe hyperemia, moderate thickening, and opacity with the deposition of fibrinosuppurative material ventrally, extending to the cerebellum and brainstem. The left cerebellar hemisphere showed an approximately 1.5 cm in diameter liquefaction area surrounded by a hemorrhagic halo. Histologically, cerebellar, mesencephalic, thalamic, and brain base meninges were intensely thickened and showed severe suppurative inflammation and fibrin deposition. Small multifocal suppurative areas were observed in the cerebellum and brainstem, characterized by a necrotic core, a number of neutrophils, and Gram-negative intralesional bacillary myriads. Pure cultures of P. aeruginosa were obtained and identified in the suppurative CNS lesions, meninges, and inner ear samples. This report highlights an uncommon clinical evolution of secondary P. aeruginosa suppurative meningoencephalitis, probably triggered by recurrent parasitic otitis in an adult Gir cow. Veterinarians, practitioners, and farmers must be aware of the risk of CNS infections after unresolved media and inner otitis, especially in cattle breeds more prone to developing parasitic otitis, such as the Gir and Indubrasil breeds.

Association of Single-Nucleotide Polymorphisms in Interleukin Genes with Microbial Keratitis in a South Indian Population

BACKGROUND

To examine the relationship between single-nucleotide polymorphisms (SNPs) in interleukin (IL) genes and keratitis and its clinical manifestations.

METHODS

SNPs in IL1B, IL6, CXCL8, IL10, and IL12B were analysed. Differences in frequencies of alleles, genotypes and haplotypes between cases and controls as well as associations between SNPs and clinical variables were calculated by χ2 tests with odds ratios.

RESULTS

The minor homologous genotype in IL1B rs16944 (p = 0.036; odds ratio (OR) = 2.063, 95% confidence interval (CI): 1.048-4.061) and CXCL8 rs4073 (p = 0.041; OR = 0.463, 95% CI: 0.224-0.956) and the heterologous genotypes in IL6 rs1800795 (p = 0.046; OR = 0.563, 95% CI: 0.326-0.972) and IL12B rs2569254 (p = 0.0446; OR = 0.557, 95% CI: 0.314-0.989) or rs730691 (p = 0.0051; OR = 0.451, 95% CI: 0.260-0.784) were associated with keratitis. The minor genotype of rs16944 was associated with severe infection (p = 0.046). The heterologous genotype in rs2569254 was associated with hospital admission, photophobia, and mode of contact lens wear (p ≤ 0.041). The heterologous genotype in rs730691 was associated with blurred vision, discharge, anterior chamber reaction, and mode of wear (p ≤ 0.047).

CONCLUSIONS

This study demonstrates that SNPs in IL1B and CXCL8 are associated with risk of developing keratitis. The study also found relationships between SNPs and clinical measures of keratitis. The potential for ethnic differences in frequency of SNPs and their association with keratitis should be followed up using different populations.

USP22 promotes pro‑inflammatory responses in Pseudomonas aeruginosa‑induced keratitis by targeting TRAF6

Pseudomonas aeruginosa (PA)‑induced keratitis is characterized by inflammatory epithelial edema, stromal infiltration, corneal ulceration and can lead to vision loss. The present study aimed to study the effect of ubiquitin‑specific protease 22 (USP22) on PA‑induced keratitis. Using RT‑qPCR and western blotting, significantly increased expression of USP22 was identified in mouse corneas and cultured RAW264.7 cells following PA stimulation. In addition, the results of in vivo experiments, western blot assay and ELISA suggested that the silencing of USP22 attenuated disease progression, downregulated the NF‑κB pathway and suppressed the expression of pro‑inflammatory cytokines following PA stimulation. Notably, it was identified that the expression of tumor necrosis factor receptor‑associated factor 6 (TRAF6) was decreased by silencing of USP22 and USP22 was found to remove lysine 48‑linked poly‑ubiquitination chains from TRAF6 to stabilize TRAF6 expression and these effects were clearly aggravated following PA infection.

The dose-dependent effect of a stabilized cannabidiol nanoemulsion on ocular surface inflammation and intraocular pressure

Cannabidiol (CBD) is a phytocannabinoid that has a great clinical therapeutic potential. Few studies have been published on its efficacy in ocular inflammations while its impact on intraocular pressure (IOP), a major risk factor for glaucoma, remains unclear. Moreover, due to its lability and high lipophilicity, its formulation within a prolonged stable topical ophthalmic solution or emulsion able to penetrate the highly selective corneal barrier is challenging. Therefore, various CBD nanoemulsions (NEs) were designed and evaluated for stability in accelerated conditions. Further, the optimal formulation was tested on a murine LPS-induced keratitis inflammation model. Lastly, increasing CBD concentrations were topically applied, for two weeks, on mice eyes, for IOP measurement. CBD NEs exhibited optimal physicochemical characteristics for ocular delivery. A specific antioxidant was required to obtain the stable, final, formulation. In vivo, 0.4 to 1.6% CBD w/v reduced the levels of key inflammatory cytokines, depending on the concentration applied. These concentrations decreased or did not affect the IOP. Our results showed that a well-designed CBD ocular dosage form can be stabilized for an extended shelf life. Furthermore, the significant decrease in inflammatory cytokines levels could be exploited, provided that an adequate therapeutic dosage regimen is identified in humans.

Prophylactic Knockdown of the miR-183/96/182 Cluster Ameliorates Pseudomonas aeruginosa-Induced Keratitis

Purpose

Previously, we demonstrated that miR-183/96/182 cluster (miR-183C) knockout mice exhibit decreased severity of Pseudomonas aeruginosa (PA)-induced keratitis. This study tests the hypothesis that prophylactic knockdown of miR-183C ameliorates PA keratitis indicative of a therapeutic potential.

Methods

Eight-week-old miR-183C wild-type and C57BL/6J inbred mice were used. Locked nucleic acid-modified anti-miR-183C or negative control oligoribonucleotides with scrambled sequences (NC ORNs) were injected subconjunctivally 1 day before and then topically applied once daily for 5 days post-infection (dpi) (strain 19660). Corneal disease was graded at 1, 3, and 5 dpi. Corneas were harvested for RT-PCR, ELISA, immunofluorescence (IF), myeloperoxidase and plate count assays, and flow cytometry. Corneal nerve density was evaluated in flatmounted corneas by IF staining with anti-β-III tubulin antibody.

Results

Anti-miR-183C downregulated miR-183C in the cornea. It resulted in an increase in IL-1β at 1 dpi, which was decreased at 5 dpi; fewer polymorphonuclear leukocytes (PMNs) at 5 dpi; lower viable bacterial plate count at both 1 and 5 dpi; increased percentages of MHCII+ macrophages (Mϕ) and dendritic cells (DCs), consistent with enhanced activation/maturation; and decreased severity of PA keratitis. Anti-miR-183C treatment in the cornea of naïve mice resulted in a transient reduction of corneal nerve density, which was fully recovered one week after the last anti-miR application. miR-183C targets repulsive axon-guidance receptor molecule Neuropilin 1, which may mediate the effect of anti-miR-183C on corneal nerve regression.

Conclusions

Prophylactic miR-183C knockdown is protective against PA keratitis through its regulation of innate immunity, corneal innervation, and neuroimmune interactions.

Paradox of complex diversity: Challenges in the diagnosis and management of bacterial keratitis

Bacterial keratitis continues to be one of the leading causes of corneal blindness in the developed as well as the developing world, despite swift progress since the dawn of the "anti-biotic era". Although, we are expeditiously developing our understanding about the different causative organisms and associated pathology leading to keratitis, extensive gaps in knowledge continue to dampen the efforts for early and accurate diagnosis, and management in these patients, resulting in poor clinical outcomes. The ability of the causative bacteria to subdue the therapeutic challenge stems from their large genome encoding complex regulatory networks, variety of unique virulence factors, and rapid secretion of tissue damaging proteases and toxins. In this review article, we have provided an overview of the established classical diagnostic techniques and therapeutics for keratitis caused by various bacteria. We have extensively reported our recent in-roads through novel tools for accurate diagnosis of mono- and poly-bacterial corneal infections. Furthermore, we outlined the recent progress by our group and others in understanding the sub-cellular genomic changes that lead to antibiotic resistance in these organisms. Finally, we discussed in detail, the novel therapies and drug delivery systems in development for the efficacious management of bacterial keratitis.

Targeting Inflammation Driven by HMGB1 in Bacterial Keratitis-A Review

Pseudomonas (P.) aeruginosa is a Gram-negative bacteria that causes human infectionsinfections. It can cause keratitis, a severe eye infection, that develops quickly and is a major cause of ulceration of the cornea and ocular complications globally. Contact lens wear is the greatest causative reason in developed countries, but in other countries, trauma and predominates. Use of non-human models of the disease are critical and may provide promising alternative argets for therapy to bolster a lack of new antibiotics and increasing antibiotic resistance. In this regard, we have shown promising data after inhibiting high mobility group box 1 (HMGB1), using small interfering RNA (siRNA). Success has also been obtained after other means to inhinit HMGB1 and include: use of HMGB1 Box A (one of three HMGB1 domains), anti-HMGB1 antibody blockage of HMGB1 and/or its receptors, Toll like receptor (TLR) 4, treatment with thrombomodulin (TM) or vasoactive intestinal peptide (VIP) and glycyrrhizin (GLY, a triterpenoid saponin) that directly binds to HMGB1. ReducingHMGB1 levels in P. aeruginosa keratitis appears a viable treatment alternative.

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.

Topical tacrolimus nanocapsules eye drops for therapeutic effect enhancement in both anterior and posterior ocular inflammation models

Tacrolimus has shown efficacy in eye inflammatory diseases. However, due to the drug lability, its formulation into a stable ophthalmic product remains a challenge. Tacrolimus-loaded nanocapsules (NCs) were designed for ocular instillation. Further, the stability and effects of the formulation were analyzed under different experimental conditions. Physicochemical characterization of the NCs revealed suitable homogeneous size and high encapsulation efficiency. Moreover, the lyophilized formulation was stable at ICH long term and accelerated storage conditions, for at least 18 and 3 months, respectively. The tacrolimus NCs did not elicit any eye irritation in rabbits after single- and multiple-dose applications. Additionally, ex vivo penetration assays on isolated porcine cornea and pharmacokinetics analyses in various rabbit eye compartments demonstrated the superiority of the NCs in retention and permeation into the anterior chamber of the eye compared to the free drug dissolved in oil. Moreover, multiple dose ocular instillation of the NCs in rats allowed high tacrolimus levels in the eye with very low plasma concentrations. Finally, the developed delivery system achieved a significant decrease in four typical inflammatory markers in a murine model of keratitis, an anterior chamber inflammation. Furthermore, these NCs, applied as eye drops, displayed clinical and histological efficacy in the mainly posterior chamber inflammation model of murine, experimental auto-immune uveitis.

Understanding clinical and immunological features associated with Pseudomonas and Staphylococcus keratitis

Pseudomonas aeruginosa and Staphylococcus aureus are the two dominant Gram-negative and -positive species, respectively, isolated from patients with contact lens-related bacterial keratitis. The clinical features of bacterial keratitis vary, such that timely differential diagnosis can be challenging, which may cause a delay in diagnosis resulting in poorer outcome. This review aims to explore the current understanding of clinical and immunological features associated with contact lens-related P. aeruginosa and S. aureus keratitis based on currently available evidence. Firstly, the review characterises contact lens-related P. aeruginosa and S. aureus keratitis, based on clinical features and prognostic factors. Secondly, the review describes the primary immune response associated with a bacterial infection in in-vivo non-scratch contact lens-wearing animal models, colonised by bacteria on contact lens and topical administration of bacteria on the cornea. Finally, the review discusses the role of macrophage inflammatory protein-2 (MIP-2) and intercellular adhesion molecule (ICAM-1) in neutrophil recruitment based on both in-vivo scratch models of bacterial keratitis and bacterial challenged in cell culture models.

Stimulator of Interferon Genes Promotes Host Resistance Against Pseudomonas aeruginosa Keratitis

Pseudomonas aeruginosa (PA) is the leading cause of bacterial keratitis, especially in those who wear contact lens and who are immunocompromised. Once the invading pathogens are recognized by pattern recognition receptors expressed on the innate immune cells, the innate immune response is stimulated to exert host defense function, which is the first line to fight against PA infection. As a converging point of cytosolic DNA sense signaling, stimulator of interferon genes (STING) was reported to participate in host–pathogen interaction. However, the role of STING in regulating PA-induced corneal inflammation and bacterial clearance remains unknown. Our data demonstrated that STING was activated in murine model of PA keratitis and in in vitro-cultured macrophages, indicated by Western blot, immunostaining, and flow cytometry. To explore the role of STING in PA keratitis, we used siRNA to silence STING and 2′,3′-cGAMP to activate STING in vivo and in vitro, and the in vivo data found out that STING promoted host resistance against PA infection. To investigate the reason why STING played a protective role in PA keratitis, the inflammatory cytokine secretion and bacterial load were measured by using real-time PCR and bacterial plate count, respectively. Our data demonstrated that STING suppressed the production of inflammatory cytokines and enhanced bacterial elimination in murine model of PA keratitis and in PA-infected macrophages. To further investigate the mechanism beneath, the phosphorylation of mitogen-activated protein kinase, the nuclear translocation of nuclear factor-κB (NF-κB) and the bactericidal mechanism were measured by western-blot, immunofluorescence, and real-time PCR, respectively. Our data indicated that STING suppressed inflammatory cytokine expressing via restraining NF-κB activity and enhanced inducible NO synthase expression, an oxygen-dependent bactericidal mechanism. In conclusion, this study demonstrated that STING promoted host resistance against PA keratitis and played a protective role in PA-infected corneal disease, via inhibiting corneal inflammation and enhancing bacterial killing.

Esculentin-1a derived peptides kill Pseudomonas aeruginosa biofilm on soft contact lenses and retain antibacterial activity upon immobilization to the lens surface

Contact lens (CL) wear is a risk factor for development of microbial keratitis, a vision threatening infection of the eye. Adverse events associated with colonization of lenses, especially by the multi-drug resistant and biofilm forming bacterium Pseudomonas aeruginosa remain a major safety issue. Therefore, novel strategies and compounds to reduce the onset of CL-associated ocular infections are needed. Recently, the activity of the frog skin-derived antimicrobial peptide Esc(1-21) and its diastereomer Esc(1-21)-1c was evaluated against both planktonic and sessile forms of this pathogen. Furthermore, Esc(1-21) was found to significantly reduce the severity of P. aeruginosa keratitis in a mouse model and preserve antipseudomonal activity in the presence of human basal tears. Here, we have analyzed the activity of the peptides on P. aeruginosa biofilm formed on soft CLs. Microbiological assays and scanning electron microscopy analysis indicated that the peptides were able to disrupt the bacterial biofilm, with the diastereomer having the greater efficacy (up to 85% killing vs no killing at 4 μM for some strains). Furthermore, upon covalent immobilization to the CL, the two peptides were found to cause more than four log reduction in the number of bacterial cells within 20 minutes and to reduce bacterial adhesion to the CL surface (77%-97% reduction) in 24 hours. Importantly, peptide immobilization was not toxic to mammalian cells and did not affect the lens characteristics. Overall, our data suggest that both peptides have great potential to be developed as novel pharmaceuticals for prevention and treatment of CL-associated P. aeruginosa keratitis.

Protective effect of pilin protein with alum+naloxone adjuvant against acute pulmonary Pseudomonas aeruginosa infection

Pseudomonas aeruginosa is an important opportunistic human pathogen that causes a wide variety of severe nosocomial infections. Type IV pili of P. aeruginosa are made up of polymerized pilin that aids in bacterial adhesion, biofilm formation and twitching motility. The aim of this study was to evaluate the efficacy of alum and naloxone (alum+NLX) as an adjuvant for P. aeruginosa recombinant PilA (r-PilA) as a vaccine candidate in the improvement of humoral and cellular immunity. Primary immunization with r-PilA in combination with alum+NLX followed by two booster shots was sufficient to generate robust cellular and humoral responses, which were Th1 and Th2 type responses consisting of IgG1 and IgG2a subtypes. Analysis of the cytokine response among immunized mice showed an increased production of IL-4, INF-γ and IL-17 by splenocytes upon stimulation by r-PilA. These sera were also able to reduce bacterial load in the lung tissue of challenged mice. The reduction of systemic bacterial spread resulted in increased survival rates in challenged immunized mice. In conclusion, immunization with r-PilA combined with alum+NLX evokes cellular and humoral immune responses, which play an important role in providing protection against acute P. aeruginosa lung infection among immunized mice.

Flagellin and pilin immunization against multi-drug resistant Pseudomonas aeruginosa protects mice in the burn wound sepsis model

Pseudomonas aeruginosa is a formidable pathogen and a major threat to burn patients. Antimicrobial therapy is often unsuccessful because P. aeruginosa can develop multi-drug resistance; thus, immunotherapy and vaccine can be a rational alternative. Flagella and type IV pili have been identified as important virulence factors in the colonization and pathogenesis of P. aeruginosa in burn wound infections. Immunogenicity and efficacy of mixed recombinant full-length type b flagellin (r-b-flagellin) and recombinant PilA (r-PilA) as candidate vaccines were assessed by measuring humoral and cellular responses, using an experimental burned mouse model. Primary immunization with "r-b-flagellin+r-PilA" followed by two booster shots was sufficient to generate a robust humoral response, which was predominantly a Th2 response consisting mainly of subtype IgG1 and low levels of IgG2a. Analysis of the cytokine response among immunized mice showed an increased production of IL-4, INF-γ and IL-17 by splenocytes upon stimulation by "r-b-flagellin+r-PilA". Opsonophagocytosis assays confirmed the enhanced killing of bacteria by anti "r-b-flagellin+r-PilA" immune sera. These antibodies were also able to reduce bacterial load in the site of original infection into the liver and spleen of challenged mice. The reduction of systemic bacterial spread resulted in an increased survival rate of challenged immunized mice. In conclusion, immunization with "r-b-flagellin+r-PilA" proteins provides a better protective response against P. aeruginosa infection in the burn mouse model.

Inactivation of the miR-183/96/182 Cluster Decreases the Severity of Pseudomonas aeruginosa-Induced Keratitis

PURPOSE

The microRNA-183/96/182 cluster (miR-183/96/182) plays important roles in sensory organs. Because the cornea is replete with sensory innervation, we hypothesized that miR-183/96/182 modulates the corneal response to bacterial infection through regulation of neuroimmune interactions.

METHODS

Eight-week-old miR-183/96/182 knockout (ko) mice and their wild-type littermates (wt) were used. The central cornea of anesthetized mice was scarred and infected with Pseudomonas aeruginosa (PA), strain 19660. Corneal disease was graded at 1, 3, and 5 days postinfection (dpi). Corneal RNA was harvested for quantitative RT-PCR. Polymorphonuclear neutrophils (PMN) were enumerated by myeloperoxidase assays; the number of viable bacteria was determined by plate counts, and ELISA assays were performed to determine cytokine protein levels. A macrophage (Mϕ) cell line and elicited peritoneal PMN were used for in vitro functional assays.

RESULTS

MicroRNA-183/96/182 is expressed in the cornea, and in Mϕ and PMN of both mice and humans. Inactivation of miR-183/96/182 resulted in decreased corneal nerve density compared with wt mice. Overexpression of miR-183/96/182 in Mϕ decreased, whereas knockdown or inactivation of miR-183/96/182 in Mϕ and PMN increased their capacity for phagocytosis and intracellular killing of PA. In PA-infected corneas, ko mice showed decreased proinflammatory neuropeptides such as substance P and chemoattractant molecules, MIP-2, MCP1, and ICAM1; decreased number of PMN at 1 and 5 dpi; increased viable bacterial load at 1 dpi, but decreased at 5 dpi; and markedly decreased corneal disease.

CONCLUSIONS

MicroRNA-183/96/182 modulates the corneal response to bacterial infection through its regulation of corneal innervation and innate immunity.

Wnt3a suppresses Pseudomonas aeruginosa-induced inflammation and promotes bacterial killing in macrophages

Pseudomonas aeruginosa (PA) is a common Gram‑negative bacterium and can cause serious infections, including hospital‑acquired pneumonia, suppurative bacterial keratitis and acute burn wound infection. The pathogenesis of PA infections is closely associated with excessive inflammatory responses and bacterial virulence factors. Wingless‑type MMTV integration site family, member 3A (Wnt3a), an upstream mediator in the canonical Wnt signaling pathway, has been implicated as a regulator of inflammation. However, its role in PA‑induced inflammation and bacterial clearance remains unknown. In the present study, the efficacy of Wnt3a conditioned media (Wnt3a‑CM) was assessed using western blotting and immunofluorescence, which showed that β‑catenin, a downstream molecule of Wnt3a, was upregulated and translocated to the nucleus following exposure to 50% Wnt3a‑CM for 6 h. To explore the role of Wnt3a in PA‑induced inflammation, the mRNA levels of pro‑inflammatory cytokines and apoptosis in macrophages were measured using reverse transcription‑quantitative polymerase chain reaction and flow cytometry, respectively. This indicated that Wnt3a suppressed inflammation by reducing the production of pro‑inflammatory cytokines and by promoting apoptosis in macrophages. Furthermore, the mechanism of macrophage‑mediated bacterial killing was investigated, and the results indicated that Wnt3a enhanced macrophage‑mediated intracellular bacterial killing via the induction of the production of cathelicidin‑related antimicrobial peptide and β‑defensins 1. Taken together, the current study explored the role of Wnt3a in inflammation and bacterial invasion, which may provide an improved understanding of host resistance to PA infection.

A proof-of-concept model for the identification of the key events in the infection process with specific reference to Pseudomonas aeruginosa in corneal infections

BACKGROUND

It is a common medical practice to characterise an infection based on the causative agent and to adopt therapeutic and prevention strategies targeting the agent itself. However, from an epidemiological perspective, exposure to a microbe can be harmless to a host as a result of low-level exposure or due to host immune response, with opportunistic infection only occurring as a result of changes in the host, pathogen, or surrounding environment.

METHODS

We have attempted to review systematically the key host, pathogen, and environmental factors that may significantly impact clinical outcomes of exposure to a pathogen, using Pseudomonas aeruginosa eye infection as a case study.

RESULTS AND DISCUSSION

Extended contact lens wearing and compromised hygiene may predispose users to microbial keratitis, which can be a severe and vision-threatening infection. P. aeruginosa has a wide array of virulence-associated genes and sensing systems to initiate and maintain cell populations at the corneal surface and beyond. We have adapted the well-known concept of the epidemiological triangle in combination with the classic risk assessment framework (hazard identification, characterisation, and exposure) to develop a conceptual pathway-based model that demonstrates the overlapping relationships between the host, the pathogen, and the environment; and to illustrate the key events in P. aeruginosa eye infection.

CONCLUSION

This strategy differs from traditional approaches that consider potential risk factors in isolation, and hopefully will aid the identification of data and models to inform preventive and therapeutic measures in addition to risk assessment. Furthermore, this may facilitate the identification of knowledge gaps to direct research in areas of greatest impact to avert or mitigate adverse outcomes of infection.

Aspergillus fumigatus triggers innate immune response via NOD1 signaling in human corneal epithelial cells

Fungal keratitis is a serious vision-threatening disease caused by fungi after corneal epithelium damage. We have previously shown a role of cell surface TLRs in Aspergillus fumigatus (A. fumigatus) keratitis. In the present study we showed that Human telomerase-immortalized corneal epithelial cells (HCECs) exposed to A. fumigatus elicited an inflammatory response consisting in increased interleukin-6 (IL-6), IL-8 and tumor necrosis factor (TNF)-α expression and innate defense molecules hBD2 and LL37 in a time-dependent manner. In this study we further investigated the role of intracellular nucleotide-binding oligomerization domain-containing protein (NOD)-like receptors, NOD1 in innate immune and inflammatory response to A. fumigatus. We showed that NOD1 and its downstream signaling molecules RIP2 and NF-κB p65 are expressed in HCECs challenged with either NOD1 specific ligand iE-DAP or A. fumigatus. More importantly, NOD1 knockdown attenuated A. fumigatus-triggered the expression of NOD1, and downstream signaling effectors RIP2 and NF-κB p65, as well as the secretion of IL-6, IL-8 and TNF-α, and the production of hBD2 and LL37. In conclusion, our results demonstrated that NOD1 is a prominent factor of innate immune and inflammatory response in HCECs against A. fumigatus, suggesting that NOD1 might be a potential novel therapeutic target for the treatment of fungal keratitis.

β-Catenin promotes host resistance against Pseudomonas aeruginosa keratitis

OBJECTIVE

To explore the role of β-catenin in Pseudomonas aeruginosa (PA) keratitis.

METHODS

Western-blot and immunostaining assay were used to determine the β-catenin protein expression in C57BL/6 (B6) corneas and in in vitro cultured murine cells including macrophage-like RAW264.7 cells, bone marrow-derived neutrophils and A6(1) corneal epithelial cells. B6 mice were subconjunctivally injected with lentivirus expressing active mutant of β-catenin (β-cat-lentivirus) vs appropriate control (Ctl-lentivirus), and then infected with PA. Pro-inflammatory cytokine levels were examined using real-time PCR and ELISA, and bacterial burden was assessed using plate count assays both in vivo and in vitro.

RESULTS

β-Catenin protein expression was decreased in B6 corneas, murine macrophage-like RAW264.7 cells, mouse bone marrow-derived neutrophils and mouse A6(1) corneal epithelial cells after PA infection. Over-expression of β-catenin in B6 corneas significantly reduced the severity of corneal disease after PA infection, by decreasing pro-inflammatory cytokine expression and bacterial burden. In vitro data further demonstrated that over-expression of β-catenin suppressed pro-inflammatory cytokine production but enhanced bacterial clearance in macrophages and neutrophils.

CONCLUSIONS

β-Catenin reduces the severity of PA keratitis by decreasing corneal inflammation and bacterial burden.

HIF-1α is essential for effective PMN bacterial killing, antimicrobial peptide production and apoptosis in Pseudomonas aeruginosa keratitis

Hypoxia-inducible factor (HIF)-1α, is a transcription factor that controls energy metabolism and angiogenesis under hypoxic conditions, and a potent regulator of innate immunity. The studies described herein examined the role of HIF-1α in disease resolution in BALB/c (resistant, cornea heals) mice after ocular infection with Pseudomonas (P.) aeruginosa. Furthermore, the current studies focused on the neutrophil (PMN), the predominant cell infiltrate in keratitis. Using both siRNA and an antagonist (17-DMAG), the role of HIF-1α was assessed in P. aeruginosa-infected BALB/c mice. Clinical score and slit lamp photography indicated HIF-1α inhibition exacerbated disease and corneal destruction. Real time RT-PCR, immunohistochemistry, ELISA, Greiss and MPO assays, bacterial load, intracellular killing, phagocytosis and apoptosis assays further tested the regulatory role of HIF-1α. Despite increased pro-inflammatory cytokine expression and increased MPO levels after knocking down HIF-1α expression, in vivo studies revealed a decrease in NO production and higher bacterial load. In vitro studies using PMN provided evidence that although inhibition of HIF-1α did not affect phagocytosis, both bacterial killing and apoptosis were significantly affected, as was production of antimicrobial peptides. Overall, data provide evidence that inhibition of HIF-1α converts a normally resistant disease response to susceptible (corneal thinning and perforation) after induction of bacterial keratitis. Although this inhibition does not appear to affect PMN transmigration or phagocytosis, both in vivo and in vitro approaches indicate that the transcriptional factor is essential for effective bacterial killing, apoptosis and antimicrobial peptide production.

TREM-2 promotes host resistance against Pseudomonas aeruginosa infection by suppressing corneal inflammation via a PI3K/Akt signaling pathway

PURPOSE

To explore the role of triggering receptor expressed on myeloid cells 2 (TREM-2) in Pseudomonas aeruginosa (PA) keratitis.

METHODS

BALB/c mice were routinely infected with PA and evaluated at various postinfection time points for corneal expression of TREM-2, by real-time PCR, Western blot, and flow cytometry. Next, BALB/c and C57BL/6 mice were respectively treated with TREM-2 siRNA or agonistic anti-TREM-2 antibody, to determine the role of TREM-2 in PA keratitis. Bacterial load and neutrophil infiltration were tested by plate count and myeloperoxidase assay, respectively. Th1-/Th2-type and proinflammatory cytokine expression were tested by real-time PCR and ELISA after in vivo and in vitro silencing of TREM-2. Moreover, phosphorylated Akt levels were tested by Western blot in murine macrophages after treatment with agonistic anti-TREM-2 antibody. mRNA levels of proinflammatory cytokines were examined in murine macrophages after TREM-2 activation and lipopolysaccharide stimulation, following pretreatment with inhibitors for PI3K or Akt, to determine whether PI3K/Akt is required in TREM-2-mediated immune modulation. In addition, BALB/c mice were treated with wortmannin and analyzed for bacterial load and proinflammatory cytokine expression.

RESULTS

TREM-2 expression was elevated in the infected BALB/c corneas at 3 or 5 days postinfection. Silencing of TREM-2 accelerated disease progression by enhancing bacterial load and corneal inflammation, whereas activation of TREM-2 promoted host resistance to PA keratitis. PI3K/Akt signaling is required in the TREM-2-mediated immune modulation, and inhibition of PI3K resulted in worsened disease after PA corneal infection.

CONCLUSIONS

TREM-2 promoted host resistance to PA infection by suppressing corneal inflammation via activation of the PI3K/Akt pathway.

Increased resistance to Staphylococcus aureus endophthalmitis in BALB/c mice: Fas ligand is required for resolution of inflammation but not for bacterial clearance

FasL was recently shown be required for bacterial clearance in C57BL/6 mice that express the FasL.1 allotype. The FasL.2 allotype is expressed in BALB/c mice and exhibits increased binding affinity to and increased cytotoxic activity against Fas(+) target cells. Therefore, we hypothesized that BALB/c mice would be more resistant to Staphylococcus aureus-induced endophthalmitis. To test this hypothesis, C57BL/6, BALB/c, and BALB(gld) mice received intravitreal injections of 2,500 CFU of S. aureus (RN6390). Clinical examinations, electroretinography (ERG), histology, and bacterial quantification were performed at 24, 48, 72, and 96 h postinjection. The myeloperoxidase (MPO) assay was used to quantitate neutrophil infiltration. At 96 h postinfection, 86% of C57BL/6 mice presented with complete destruction of the eye, compared to only 29% of BALB/c mice with complete destruction. To our surprise, in the absence of Fas ligand, BALB(gld) mice showed no difference in bacterial clearance compared to BALB/c mice. However, histology and ERG analysis revealed increased retinal damage and significant loss of retinal function. MPO analysis revealed equal numbers of neutrophils in BALB(gld) and BALB/c mice at 24 h postinfection. However, at 48 h, the neutrophil numbers remained significantly elevated in BALB(gld) mice, correlating with the increased retinal damage observed in BALB(gld) mice. We conclude that the increased resistance to S. aureus induced endophthalmitis in BALB/c mice is not dependent upon the FasL. However, in contrast to C57BL/6 mice, FasL is required for resolution of inflammation and protecting host tissue from nonspecific damage in BALB/c mice.

Topical neutralization of interleukin-17 during experimental Pseudomonas aeruginosa corneal infection promotes bacterial clearance and reduces pathology

The proinflammatory cytokine interleukin-17 (IL-17) is involved in neutrophilic tissue infiltration, contributing to both microbial clearance as well as inflammation-associated tissue damage. Its role during bacterial corneal infections is unknown. We hypothesized that IL-17 responses would be detrimental in this setting and tested the impact of IL-17 receptor deficiency or antibody-mediated neutralization of IL-17 in a murine model of Pseudomonas aeruginosa ulcerative keratitis after scratch injury. We found that, compared with infected corneas from wild-type mice, those from IL-17 receptor (IL-17R)-deficient mice had significantly lower corneal pathology scores, neutrophil influx, and intracellular bacterial levels. Infected IL-17R-deficient corneas had low intercellular adhesion molecule 1 (ICAM-1) expression, and ICAM-1-deficient mice were similarly resistant to infection. Topical treatment with polyclonal antibodies to IL-17 resulted in significant reductions in corneal pathology and also lowered bacterial counts after infection with six different laboratory or clinical P. aeruginosa strains, including both invasive and cytotoxic strains. Thus, neutralization of IL-17 during P. aeruginosa corneal infection reduces neutrophil influx and pathology without compromising bacterial clearance and offers a promising new avenue for therapy of these potentially sight-threatening infections.

Induction of TNF-alfa and CXCL-2 mRNAs in different organs of mice infected with pathogenic Leptospira

The role of innate immune response in protection against leptospirosis is poorly understood. We examined the expression of the chemokine CXCL2/MIP-2 and the cytokine TNF-α in experimental resistant and susceptible mice models, C3H/HeJ, C3H/HePas and BALB/c strains, using a virulent strain of Leptospira interrogans serovar Copenhageni. Animals were infected intraperitoneally with 10(7) cells and the development of the disease was followed. Mortality of C3H/HeJ mice was observed whereas C3H/HePas presented jaundice and BALB/c mice remained asymptomatic. The infection was confirmed by the presence of leptospiral DNA in the organs of the animals, demonstrated by PCR. Sections of the organs were analyzed, after H&E stain. The relative expression of mRNA of chemokine CXCL2/MIP-2 and cytokine TNF-α was measured in lung, kidney and liver of the mice by qPCR. The concentrations of these proteins were measured in extracts of tissues and in serum of the animals, by ELISA. Increasing levels of transcripts and protein CXCL2/MIP-2 were detected since the first day of infection. The highest expression was observed at third day of infection in kidney, liver and lung of BALB/c mice. In C3H/HeJ the expression of CXCL2/MIP-2 was delayed, showing highest protein concentration in lung and kidney at the 5th day. Increasing in TNF-α transcripts were detected after infection, in kidney and liver of animals from the three mice strains. The expression of TNF-α protein in C3H/HeJ was also delayed, being detected in kidney and lung. Our data demonstrated that Leptospira infection stimulates early expression of CXCL2/MIP-2 and TNF-α in the resistant strain of mice. Histological analysis suggests that the expression of those molecules may be related to the influx of distinct immune cells and plays a role in the naturally acquired protective immunity.

Characterization of protease IV expression in Pseudomonas aeruginosa clinical isolates

Expression of protease IV by Pseudomonas aeruginosa during ocular infections contributes significantly to tissue damage. However, several P. aeruginosa strains isolated from ocular infections or inflammatory events produce very low levels of protease IV. The aim of the present study was to characterize, genetically and phenotypically, the presence and expression of the protease IV gene in a group of clinical isolates that cause adverse ocular events of varying degrees, and to elucidate the possible control mechanisms of expression associated with this virulence factor. Protease IV gene sequences from seven clinical isolates of P. aeruginosa were determined and compared to P. aeruginosa strains PAO1 and PA103-29. Production and enzyme activity of protease IV were measured in test strains and compared to that of quorum-sensing gene (lasRI) mutants and the expression of other virulence factors. Protease IV gene sequence similarities between the isolates were 97.5-99.5 %. The strains were classified into two distinct phylogenetic groups that correlated with the presence of exo-enzymes from type three secretion systems (TTSS). Protease IV concentrations produced by PAOΔlasRI mutants and the two clinical isolates with a lasRI gene deficiency were restored to levels comparable to strain PAO1 following complementation of the quorum-sensing gene deficiencies. The protease IV gene is highly conserved in P. aeruginosa clinical isolates that cause a range of adverse ocular events. Observed variations within the gene sequence appear to correlate with presence of specific TTSS genes. Protease IV expression was shown to be regulated by the Las quorum-sensing system.

TREM-1 amplifies corneal inflammation after Pseudomonas aeruginosa infection by modulating Toll-like receptor signaling and Th1/Th2-type immune responses

As a novel family of cell surface receptors, triggering receptors expressed on myeloid cells (TREMs) play an important role in inflammatory responses. However, the role of TREMs in the ocular immune system remains unknown. In this study, we examined the expression and function of TREM-1 in Pseudomonas aeruginosa keratitis, one of the most common sight-threatening ocular diseases. TREM-1 was significantly increased in human corneas after P. aeruginosa infection. Consistent with TREM-1 expression at the human ocular surface, TREM-1 levels (mRNA and protein) were also elevated in the infected corneas of C57BL/6 (B6) mice at 1, 3, and 5 days postinfection. To determine whether TREM-1 dictates the outcome of P. aeruginosa keratitis in susceptible mice, TREM-1 signaling in B6 mice was blocked with a soluble mTREM-1/Fc fusion protein. The results indicated that blockade of TREM-1 reduced the severity of corneal disease, polymorphonuclear neutrophil infiltration, Th1/proinflammatory cytokine expression and Toll-like receptor (TLR) activation but enhanced the production of Th2 cytokines, murine β-defensin 2 (mBD2), single Ig interleukin-1R-related molecule (SIGIRR), and ST2. Furthermore, we also used agonistic anti-mTREM-1 antibody to activate TREM-1 signaling in B6 mice and found that TREM-1 activation resulted in worsened disease and earlier corneal perforation in infected B6 mouse corneas and elevated production of proinflammatory cytokines and TLR signaling molecules but reduced expression of mBD2, SIGIRR, and ST2. To the best of our knowledge, this study provides the first evidence that TREM-1 functions as an inflammatory amplifier in P. aeruginosa keratitis by modulating TLR signaling and Th1/Th2 responses.

Nona-D-arginine amide suppresses corneal cytokines in Pseudomonas aeruginosa keratitis

PURPOSE

Nona-D-arginine (D9R) amide suppressed interleukin 1β production during Pseudomonas aeruginosa corneal infection. The purpose of this study was to determine the cellular disposition of D9R and its effect on other inflammatory mediators induced by infection.

METHODS

Mouse eyes received 5 μL of either phosphate-buffered saline (PBS, pH 7.4) or 100-μM D9R hourly for 5 hours (total of 6 drops per eye) immediately after corneal wounding and infection with 1 × 10 colony-forming units (CFUs) of P. aeruginosa strain PAO1. At 6, 12, and 24 hours postinfection, eyes were scored on a scale of 0 (normal eye) to +4 (corneal perforation). After scoring, mice were killed and eyes enucleated. Whole eyes were used for determining viable CFUs per eye. Corneas were excised for quantitation of tumor necrosis factor α, interferon γ, interleukin 10, and granulocyte-macrophage colony-stimulating factor. The fate of D9R in cells was determined using a labeled peptide.

RESULTS

Eyes treated with D9R had significantly lower disease scores (P ≤ 0.001) and fewer CFUs (P ≤ 0.01) than those in PBS-treated eyes. No corneal cytokines were detected in any D9R-treated eyes. In contrast, beginning at 12 hours postinfection, increasing amounts of tumor necrosis factor alpha, interleukin 10, and granulocyte-macrophage colony-stimulating factor were detectible in corneas of PBS-treated eyes. Within 60 minutes, D9R accumulated in the cell nucleus and nucleolus and remained for over 24 hours.

CONCLUSION

D9R reduces the severity of P. aeruginosa ocular infection in part by reducing bacterial burden and in part by controlling a destructive proinflammatory response. D9R might be a useful alternative to steroids in treating other inflammation-mediated pathologies of the eye.

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.

Increased Langerhan cell density and corneal nerve damage in diabetic patients: role of immune mechanisms in human diabetic neuropathy

AIM/HYPOTHESIS

Immune mechanisms have been proposed to play a role in the development of diabetic neuropathy. We employed in vivo corneal confocal microscopy (CCM) to quantify the presence and density of Langerhans cells (LCs) in relation to the extent of corneal nerve damage in Bowman's layer of the cornea in diabetic patients.

METHODS

128 diabetic patients aged 58 ± 1 yrs with a differing severity of neuropathy based on Neuropathy Deficit Score (NDS-4.7 ± 0.28) and 26 control subjects aged 53 ± 3 yrs were examined. Subjects underwent a full neurological evaluation, evaluation of corneal sensation with non-contact corneal aesthesiometry (NCCA) and corneal nerve morphology using corneal confocal microscopy (CCM).

RESULTS

The proportion of individuals with LCs was significantly increased in diabetic patients (73.8%) compared to control subjects (46.1%), P = 0.001. Furthermore, LC density (no/mm(2)) was significantly increased in diabetic patients (17.73 ± 1.45) compared to control subjects (6.94 ± 1.58), P = 0.001 and there was a significant correlation with age (r = 0.162, P = 0.047) and severity of neuropathy (r = -0.202, P = 0.02). There was a progressive decrease in corneal sensation with increasing severity of neuropathy assessed using NDS in the diabetic patients (r = 0.414, P = 0.000). Corneal nerve fibre density (P < 0.001), branch density (P < 0.001) and length (P < 0.001) were significantly decreased whilst tortuosity (P < 0.01) was increased in diabetic patients with increasing severity of diabetic neuropathy.

CONCLUSION

Utilising in vivo corneal confocal microscopy we have demonstrated increased LCs in diabetic patients particularly in the earlier phases of corneal nerve damage suggestive of an immune mediated contribution to corneal nerve damage in diabetes.

Inhibition of macrophage migration inhibitory factor ameliorates ocular Pseudomonas aeruginosa-induced keratitis

Pseudomonas aeruginosa causes severe sight-threatening corneal infections, with the inflammatory response to the pathogen being the major factor resulting in damage to the cornea that leads to loss of visual acuity. We found that mice deficient for macrophage migration inhibitory factor (MIF), a key regulator of inflammation, had significantly reduced consequences from acute P. aeruginosa keratitis. This improvement in the outcome was manifested as improved bacterial clearance, decreased neutrophil infiltration, and decreased inflammatory responses when P. aeruginosa-infected MIF knock out (KO) mice were compared to infected wild-type mice. Recombinant MIF applied to infected corneas restored the susceptibility of MIF deficient mice to P. aeruginosa-induced disease, demonstrating that MIF is necessary and sufficient to cause significant pathology at this immune privileged site. A MIF inhibitor administered during P. aeruginosa-induced infection ameliorated the disease-associated pathology. MIF regulated epithelial cell responses to infection by enhancing synthesis of proinflammatory mediators in response to P. aeruginosa infection and by promoting bacterial invasion of corneal epithelial cells, a correlate of virulence in the keratitis model. Our results uncover a host factor that elevates inflammation and propagates bacterial cellular invasion, and further suggest that inhibition of MIF during infection may have a beneficial therapeutic effect.

IL-10 induction by Bordetella parapertussis limits a protective IFN-gamma response

Bordetella parapertussis causes the prolonged coughing illness known as pertussis or whooping cough, persisting for weeks within the respiratory tracts of infected hosts but inducing a very poor T cell response relative to that induced by Bordetella pertussis, the more common cause of pertussis. In this study, we examine the contributions of cytokines involved in the clearance of B. parapertussis and immunomodulation that delays effective clearance. The slow elimination of this pathogen from the respiratory tracts of mice coincides with the gradual accumulation of CD4(+) T cells in the lungs and B. parapertussis-responsive IFN-gamma-producing cells in the spleen. IFN-gamma-deficient mice were defective in the accumulation of leukocytes in lungs and in clearance of B. parapertussis from the lungs. In vitro B. parapertussis-stimulated macrophages produced IL-10, which inhibited the generation of the IFN-gamma response that is required for protection in vivo. As compared with wild-type mice, IL-10-deficient mice produced significantly higher levels of IFN-gamma, had higher numbers of leukocytes accumulated in the lungs, and cleared B. parapertussis more rapidly. Together, these data indicate that B. parapertussis induces the production of IL-10, which facilitates its persistence within infected hosts by limiting a protective IFN-gamma response.

MyD88 regulation of Fusarium keratitis is dependent on TLR4 and IL-1R1 but not TLR2

The fungal pathogens Fusarium solani and Fusarium oxysporum cause severe corneal disease in the United States and worldwide and were the causative organisms in a recent outbreak of contact lens-associated keratitis. To characterize innate immunity in Fusarium keratitis, we developed a murine model in which conidia are injected into the corneal stroma. Immunocompetent C57BL/6 mice rapidly developed severe corneal opacification associated with neutrophil infiltration and clearance of Fusarium hyphae. In contrast, neutrophil infiltration was delayed in MyD88-/- mice, resulting in uncontrolled growth of Fusarium hyphae in the corneal stroma and anterior chamber, and eventually resulting in corneal perforation. Corneal opacification scores in TLR2-/-, TLR4-/-, and TLR2/4-/- mice were similar to those of C57BL/6 mice; however, TLR4-/- and TLR2/4-/- mice had impaired antifungal responses. The phenotype of infected IL-1R1-/- mice was similar to that of MyD88-/- mice, with uncontrolled fungal growth resulting in corneal perforation. IL-1R1-/- mice also produced significantly less CXCL1/KC in the corneal stroma compared with C57BL/6 mice consistent with delayed neutrophil recruitment to the corneal stroma. Together, these findings indicate that IL-1R1 and MyD88 regulate CXC chemokine production and neutrophil recruitment to the cornea, and that TLR4 has an important role in controlling growth and replication of these pathogenic fungi.

Cathelicidin-deficient (Cnlp -/- ) mice show increased susceptibility to Pseudomonas aeruginosa keratitis

PURPOSE

To examine the clinical progression and innate immune responses during Pseudomonas aeruginosa (PA) keratitis in cathelicidin-deficient (KO) mice.

METHODS

PA (ATCC 19660) keratitis was induced in KO mice and wild-type (WT) littermates generated on a 129/SVJ background. Clinical score and histopathology were used to monitor the progression of infection at postinfection (PI) days 1, 3, 7, 14, and 21. Mouse corneas were harvested for viable bacteria quantitation, and myeloperoxidase (MPO) assays were performed to determine the number of infiltrating neutrophils. ELISA was used to quantitate interleukin (IL)-1beta, IL-6, macrophage inflammatory peptide (MIP)-2, keratinocyte-derived chemokine (KC), tumor necrosis factor (TNF)-alpha, and vascular endothelial growth factor (VEGF) levels in the corneas.

RESULTS

WT mice were resistant (cornea healed), whereas KO mice showed increased susceptibility (corneas failed to recover by 21 days or perforated) to PA infection. Clinical scores were significantly elevated in the infected corneas of KO mice versus WT mice at 7, 14, and 21 days PI. Absence of cathelicidin resulted in significantly delayed clearance of PA in the cornea and an increased number of infiltrating neutrophils at 1, 3, 7, and 14 days PI. KO mice also exhibited differential expression of protein levels for IL-1beta, IL-6, MIP-2, KC, TNF-alpha, and VEGF up to day 21 PI compared with the WT mice.

CONCLUSIONS

Cathelicidin-deficient mice showed considerable susceptibility to PA keratitis. The present study demonstrates direct in vivo evidence that endogenous expression of cathelicidin provides defense against corneal PA infection indicating its importance in host innate immunity at the ocular surface.

Human corneal epithelial cells synthesize ELR(-)alpha-chemokines in response to proinflammatory mediators

The purpose of this study was to characterize the synthesis of alpha-chemokines IP-10, MIG, and I-TAC by human corneal epithelial cells (HCE) following exposure to proinflammatory mediators. Supernatants were collected from HCE cultures stimulated with individual or combinations of TNF-alpha, IL-1alpha, and IFN-gamma, and assayed for alpha-chemokines by ELISA. RT-PCR was used to detect IFN-gamma receptor mRNA. Activation of STAT 1 was determined by Western blotting. Stimulation of HCE with either IL-1alpha or TNF-alpha increased IP-10 protein synthesis up to 6-fold, whereas insignificant levels of MIG and I-TAC were induced. The epithelial cells were found to express IFN-gamma receptors constitutively. Exposure to the ligand resulted in STAT 1 phosphorylation and production of nanogram amounts of IP-10, I-TAC, and MIG. When HCE were stimulated with combinations of TNF-alpha and IFN-gamma, or IL-1alpha and IFN-gamma, the levels of IP-10 and I-TAC secreted were > 150-fold higher than that produced following exposure to a single cytokine. In contrast, MIG protein synthesis was not enhanced upon stimulation with cytokine combinations. The abundant production of ELR(-)alpha -chemokines following appropriate stimulation suggests that HCE may play an important role in the recruitment of effector cells such as activated T-lymphocytes to inflamed corneal tissue. The data also indicate that the synthesis of IP-10, I-TAC, and MIG are differentially regulated in HCE.

Inhibition of inflammatory cytokine production in human corneal cells by dexamethasone, but not cyclosporin

PURPOSE

To evaluate the modulatory effects of anti-inflammatory agents, dexamethasone (Dex) and cyclosporin A (CsA), on the production of cytokines and chemokines by human corneal cells in vitro following stimulation by the pro-inflammatory cytokine after interleukin 1beta (IL-1beta).

METHODS

A human corneal epithelial (HCE) cell line and human corneal fibroblasts (HCFs) were stimulated in culture with IL-1beta and treated with Dex or CsA. The gene expression for selected cytokines and chemokines was determined by reverse transcriptase-polymerase chain reaction (RT-PCR). The secretion of cytokines and chemokines was measured by enzyme-linked immunosorbent assay.

RESULTS

IL-1beta enhanced the mRNA and/or protein levels of granulocyte-macrophage colony-stimulating factor (GM-CSF), IL-8, and monocyte chemotactic protein (MCP)-1 in HCE and IL-6, IL-8, MCP-3, and regulated on T-cell activation expressed secreted (RANTES) in HCFs. Treatment with CsA did not inhibit cytokine production in either HCE or HCFs. In contrast, Dex treatment inhibited the IL-1beta-induced production of GM-CSF, IL-6, IL-8, MCP-3, and RANTES, but not MCP-1.

CONCLUSION

These results show that Dex, but not CsA, has direct immunosuppressive effects on the resident corneal cells, HCE and HCFs. This suggests that the clinically observed immunosuppressive effects of topical CsA are mediated primarily through the immune cells.

Pseudomonas aeruginosa infection and inflammation during contact lens wear: a review

Infection and inflammation during contact lens wear is often associated with microbial contamination of lenses. Several different types of microbes that colonize lenses can lead to infection and inflammation, but the most common cause of infection (microbial keratitis; MK) remains the Gram-negative bacterium Pseudomonas aeruginosa. P. aeruginosa has a battery of cell-associated and extracellular virulence factors it can use to initiate and maintain infection. Its ability to produce proteases, to either invade or kill corneal cells, and to coordinate expression of virulence factors via quorum-sensing have been shown to be important during MK. Another important factor that contributes to the destruction of the cornea during MK is excessive activation of the host defense system. P. aeruginosa can activate several pathways of the immune system during MK, and activation often involves receptors on the corneal epithelial cells called toll-like receptors (TLRs). These TLRs recognize e.g., lipopolysaccharide or flagella from P. aeruginosa and activate the epithelial cells to produce inflammatory mediators such as cytokines and chemokines. These cytokines or chemokines recruit white blood cells, predominantly polymorphonuclear leukocytes, to the infection in order that they can phagocytose and kill the P. aeruginosa. However, continued recruitment and presence of these polymorphonuclear neutrophils and other white blood cells in the corneal tissue leads to destruction of corneal cells and tissue components. This can ultimately lead to scarring and vision loss.

The corneal response to infection withStaphylococcus aureusin the absence of interleukin‐4

Interleukin-4 (IL-4) has previously been implicated in a protective response to Staphylococcus aureus corneal infection. Consequently, the specific role of IL-4 during S. aureus corneal infection was investigated using IL-4 gene knockout mice. The eyes of IL-4-/- mice and wild-type mice were challenged topically with S. aureus and examined at 24 h post-infection. Keratitis was examined clinically and histologically. Bacterial and polymorphonuclear leucocytes (PMN) numbers were enumerated and cytokine and chemokine levels determined by enzyme-linked immunosorbent assay. Exogenous IL-4 was administered to both IL-4-/- and wild-type mice and clinical parameters were determined. A lack of IL-4 resulted in a significant increase in clinical scores, pathology, bacterial load and neutrophil numbers. The absence of IL-4 also resulted in an upregulation of interferon (IFN)-gamma and a downregulation of IL-6, IL-10 and the chemokines KC and macrophage inflammatory protein-2. Administration of exogenous IL-4 to IL-4-/- mice was protective but time-dependent. This study highlights the protective role of IL-4 during S. aureus infection and emphasizes the balance between IL-4 and IFN-gamma in achieving bacterial control and maintaining the integrity of the cornea. This information may lead to the development of novel therapeutic strategies potentially improving the prognosis for infection of this unique avascular site.

Acute inflammation and loss of retinal architecture and function during experimental Bacillus endophthalmitis

Rapid vision loss and explosive inflammation are devastating consequences of Bacillus endophthalmitis that have not been well defined. We therefore analyzed the evolution of intraocular inflammation and loss of retinal architecture and function during experimental Bacillus endophthalmitis. Mice were intravitreally injected with 100 CFU of B. cereus, and eyes were analyzed for bacterial growth, retinal function, architectural changes and retinal cellular stress, inflammatory cytokines, and infiltrating cells. Retinal electrophysiologic and structural changes began as early as 4 to 6 hr postinfection. Significant declines in retinal function paralleled the loss of retinal architecture. Glial fibrillary acidic protein (GFAP) was detected in retina, indicating potential stress. Polymorphonuclear leukocyte (PMN) infiltration into the vitreous began as early as 4 hr postinfection, coinciding with a significant increase in TNF-alpha in the eye. These results indicated that acute inflammation and detrimental architectural and electrophysiologic changes in the retina began earlier than once thought, suggesting that therapeutic intervention should be given at the earliest possible time to avoid vision loss during Bacillus endophthalmitis.

Vasoactive Intestinal Peptide Balances Pro- and Anti-Inflammatory Cytokines in thePseudomonas aeruginosa-Infected Cornea and Protects against Corneal Perforation

Corneal infection with Pseudomonas aeruginosa perforates the cornea in susceptible C57BL/6 (B6), but not resistant BALB/c, mice. To determine whether vasoactive intestinal peptide (VIP) played a role in development of the resistant response, protein expression levels were tested by immunocytochemistry and enzyme immunoassay in BALB/c and B6 corneas. Both mouse strains showed constitutive expression of corneal VIP protein and nerve fiber distribution. However, disparate expression patterns were detected in the cornea after infection. VIP protein was elevated significantly in BALB/c over B6 mice at 5 and 7 days postinfection. Therefore, B6 mice were injected with rVIP and subsequently demonstrated decreased corneal opacity and resistance to corneal perforation compared with PBS controls. rVIP- vs PBS-treated B6 mice also demonstrated down-regulation of corneal mRNA and/or protein levels for proinflammatory cytokines/chemokines: IFN-gamma, IL-1beta, MIP-2, and TNF-alpha, whereas anti-inflammatory mediators, IL-10 and TGF-beta1, were up-regulated. Treatment with rVIP decreased NO levels and polymorphonuclear neutrophil (PMN) number. To further define the role of VIP, peritoneal macrophages (Mphi) and PMN from BALB/c and B6 mice were stimulated with LPS and treated with rVIP. Treatment of LPS-stimulated Mphi from both mouse strains resulted in decreased IL-1beta and MIP-2 protein levels; PMN responded similarly. Both cell types also displayed a strain-dependent differential response to rVIP, whereby B6 Mphi/PMN responded only to a higher concentration of VIP compared with cells from BALB/c mice. These data provide evidence that neuroimmune regulation of the cytokine network and host inflammatory cells functions to promote resistance against P. aeruginosa corneal infection.

SIGIRR promotes resistance against Pseudomonas aeruginosa keratitis by down-regulating type-1 immunity and IL-1R1 and TLR4 signaling

Pseudomonas aeruginosa keratitis destroys the cornea in susceptible Th1 responder C57BL/6 (B6), but not resistant Th2 responder (BALB/c) mice. To determine whether single Ig IL-1R-related molecule (SIGIRR) played a role in resistance, mRNA and protein expression levels were tested. Both were constitutively expressed in the cornea of the two mouse groups. A disparate mRNA and protein expression pattern was detected in the cornea of BALB/c vs B6 mice after infection. SIGIRR protein decreased significantly in BALB/c over B6 mice at 1 day postinfection. Thus, BALB/c mice were injected with an anti-SIGIRR Ab or IgG control. Anti-SIGIRR Ab over control-treated mice showed increased corneal opacity, stromal damage, and bacterial load. Corneal mRNA levels for IL-1beta, MIP-2, IL-1R1, TLR4, IL-18, and IFN-gamma and protein levels for IL-1beta and MIP-2 also were significantly up-regulated in anti-SIGIRR Ab over control mice, while no changes in polymorphonuclear cell number, IL-4, or IL-10 mRNA expression were detected. To further define the role of SIGIRR, RAW264.7 macrophage-like cells were transiently transfected with SIGIRR and stimulated with heat-killed P. aeruginosa or LPS. SIGIRR transfection significantly decreased mRNA levels for IL-1R1, TLR4, and type 1 immune response-associated cytokines (IL-12, IL-18, and IFN-gamma) as well as proinflammatory cytokines IL-1beta and MIP-2 protein expression. SIGIRR also negatively regulated IL-1 and LPS, but not poly(I:C)-mediated signaling and NF-kappaB activation. These data provide evidence that SIGIRR is critical in resistance to P. aeruginosa corneal infection by down-regulating type 1 immunity, and that it negatively regulates IL-1 and TLR4 signaling.

An increase of blood squamous cell carcinoma antigen in Pseudomonas aeruginosa spondylitis

Squamous cell carcinoma antigen (SCCA) is traditionally engaged for detecting and following up malignancy from a squamous cell origin. We encountered an unusual increase of blood SCCA but no other cancer markers in a patient associated with an infective lumbar spondylitis due to Pseudomonas aeruginosa. An overshooting of Th1 expression, such as tumor necrosis factor alpha, bumped up by his uremia as a result of P. aeruginosa infection may hasten SCCA. Therefore, SCCA might additionally serve as a serological marker for infection besides squamous cell cancer, and its false-positive increase also highlights the appropriateness of tumor marker screening.

A live-attenuated Pseudomonas aeruginosa vaccine elicits outer membrane protein-specific active and passive protection against corneal infection

Pseudomonas aeruginosa can cause sight-threatening corneal infections in humans, particularly those who wear contact lenses. We have previously shown that a live-attenuated P. aeruginosa vaccine given intranasally protected mice against acute lethal pneumonia in a lipopolysaccharide (LPS) serogroup-specific manner. In the current study, we evaluated the protective and therapeutic efficacies, as well as the target antigens, of this vaccine in a murine corneal infection model. C3H/HeN mice were nasally immunized with the vaccine (an aroA deletion mutant of strain PAO1, designated PAO1DeltaaroA) or with Escherichia coli as a control and were challenged 3 weeks later by inoculating the scratch-injured cornea with P. aeruginosa. For passive prophylaxis and therapy, we utilized a serum raised in rabbits nasally immunized with PAO1DeltaaroA or E. coli. Outcome measures included corneal pathology scores and, in some experiments, reductions in total and internalized bacterial CFU. We found that both active and passive immunization reduced corneal pathology scores after challenge with a variety of P. aeruginosa strains, including several serogroup-heterologous strains. Even when given therapeutically starting as late as 24 h after infection, the rabbit antiserum to PAO1DeltaaroA was effective at reducing corneal pathology scores. Immunotherapy of established infections also reduced the numbers of total and internalized corneal P. aeruginosa bacteria. Experiments using absorbed sera showed that the protective antibodies are specific to outer membrane proteins. Thus, live-attenuated P. aeruginosa vaccines delivered nasally protect against corneal infections in mice and potentially can be used to prepare passive therapy reagents for the treatment of established P. aeruginosa corneal infections caused by diverse LPS serogroups.

Role of cytokines and chemokines in pseudomonal keratitis

Pseudomonal keratitis usually progresses rapidly, often resulting in corneal perforation and blindness. Remarkable events in pseudomonal keratitis include massive polymorphonuclear leukocyte infiltration in the cornea and various degrees of tissue destruction. With regard to initiation of these inflammatory events, various inflammatory cytokines and chemokines appear to be key substances and have been the subject of several studies. Inflammatory cytokines and chemokines believed to be important in pseudomonal keratitis include interleukin (IL)-1 beta, IL-6, macrophage inflammatory protein (MIP)-2 (homologous to human IL-8), macrophage inhibitory factor (MIF), IL-12, IL-18, interferon (IFN)-gamma, and tumor necrosis factor (TNF)-alpha. In this article, current concepts related to the role of inflammatory cytokines and chemokines in pseudomonal keratitis are reviewed.

Respiratory syncytial virus-induced acute and chronic airway disease is independent of genetic background: an experimental murine model

Background

Respiratory syncytial virus (RSV) is the leading respiratory viral pathogen in young children worldwide. RSV disease is associated with acute airway obstruction (AO), long-term airway hyperresponsiveness (AHR), and chronic lung inflammation. Using two different mouse strains, this study was designed to determine whether RSV disease patterns are host-dependent. C57BL/6 and BALB/c mice were inoculated with RSV and followed for 77 days. RSV loads were measured by plaque assay and polymerase chain reaction (PCR) in bronchoalveolar lavage (BAL) and whole lung samples; cytokines were measured in BAL samples. Lung inflammation was evaluated with a histopathologic score (HPS), and AO and AHR were determined by plethysmography.

Results

Viral load dynamics, histopathologic score (HPS), cytokine concentrations, AO and long-term AHR were similar in both strains of RSV-infected mice, although RSV-infected C57BL/6 mice developed significantly greater AO compared with RSV-infected BALB/c mice on day 5. PCR detected RSV RNA in BAL samples of RSV infected mice until day 42, and in whole lung samples through day 77. BAL concentrations of cytokines TNF-α, IFN-γ, and chemokines MIG, RANTES and MIP-1α were significantly elevated in both strains of RSV-infected mice compared with their respective controls. Viral load measured by PCR significantly correlated with disease severity on days 14 and 21.

Conclusion

RSV-induced acute and chronic airway disease is independent of genetic background.

Surfactant protein D is present in human tear fluid and the cornea and inhibits epithelial cell invasion by Pseudomonas aeruginosa

We have previously shown that human tear fluid protects corneal epithelial cells against Pseudomonas aeruginosa in vitro and in vivo and that protection does not depend upon tear bacteriostatic activity. We sought to identify the responsible tear component(s). The hypothesis tested was that collectins (collagenous calcium-dependent lectins) were involved. Reflex tear fluid was collected from healthy human subjects and examined for collectin content by enzyme-linked immunosorbent assay (ELISA) and Western blot with antibody against surfactant protein D (SP-D), SP-A, or mannose-binding lectin (MBL). SP-D, but not SP-A or MBL, was detected by ELISA of human reflex tear fluid. Western blot analysis of whole tears and of high-performance liquid chromatography tear fractions confirmed the presence of SP-D, most of which eluted in the same fraction as immunoglobulin A. SP-D tear concentrations were calculated at approximately 2 to 5 microg/ml. Depletion of SP-D with mannan-conjugated Sepharose or anti-SP-D antibody reduced the protective effect of tears against P. aeruginosa invasion. Recombinant human or mouse SP-D used alone reduced P. aeruginosa invasion of epithelial cells without detectable bacteriostatic activity or bacterial aggregation. Immunofluorescence microscopy revealed SP-D antibody labeling throughout the corneal epithelium of normal, but not gene-targeted SP-D knockout mice. SP-D was also detected in vitro in cultured human and mouse corneal epithelial cells. In conclusion, SP-D is present in human tear fluid and in human and mouse corneal epithelia. SP-D is involved in human tear fluid protection against P. aeruginosa invasion. Whether SP-D plays other roles in the regulation of other innate or adaptive immune responses at the ocular surface, as it does in the airways, remains to be explored.

[Eye-associated lymphoid tissue (EALT) is continuously spread throughout the ocular surface from the lacrimal gland to the lacrimal drainage system]

INTRODUCTION

Components of the mucosal immune system (MALT) have been identified in the conjunctiva (as CALT) and the lacrimal drainage system (as LDALT). Their structural and functional relation with the established immune protection by the lacrimal gland is unclear.

MATERIAL AND METHODS

Macroscopically normal and complete tissues of the conjunctiva, lacrimal drainage system and lacrimal gland from human body donors were investigated by analysis of translucent whole mounts, and using histology, immunohistology as well as scanning and transmission electron microscopy.

RESULTS

A typical diffuse lymphoid tissue, composed of effector cells of the immune system (T-lymphocytes and IgA producing plasma cells) under an epithelium that contains the IgA transporter SC, is not isolated in the conjunctiva and lacrimal drainage system. It is anatomically continuous from the lacrimal gland along its excretory ducts into the conjunctiva and from there via the lacrimal canaliculi into the lacrimal drainage system. Lymphoid follicles occur in a majority (about 60%) and with bilateral symmetry. The topography of CALT corresponds to the position of the cornea in the closed eye.

CONCLUSION

These results show that the MALT of the lacrimal gland, conjunctiva and lacrimal drainage system constitute an anatomical and functional unit for immune protection of the ocular surface. Therefore it should be integrated as an "eye-associated lymphoid tissue" (EALT) into the MALT system of the body. EALT can detect ocular surface antigens by the lymphoid follicles and can supply other organs and the ocular surface including the lacrimal gland with specific effector cells via the regulated recirculation of lymphoid cells.

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.