An Ocular Commensal Protects against Corneal Infection by Driving an Interleukin-17 Response from Mucosal γδ T Cells

Microbiological Profile of Ocular Infection: A Large Retrospective Study

BACKGROUND

We aimed to elucidate the pathogenic bacterial and fungal profiles of specimens obtained from suspected ocular infections at Farabi Eye Tertiary Referral Hospital, Tehran, Iran.

METHODS

In this cross-sectional study, we collected data from ocular specimens taken during the seven-year period of 2011 to 2018, and the results were then retrospectively analyzed. Samples had been obtained from patients who were investigated for ocular infections.

RESULTS

Overall, 16,656 ocular samples were evaluated. The mean patient age was 48.31 ± 26.62 years. Most patients were men (60.33%), and men in the 7th decade of life were the largest represented group. The seasonal distributions of specimen collection sites followed the overall distribution of collection sites by year. Specimens obtained from the cornea were the most common (49.24%), also representing the largest number of specimens in all seasons. The most commonly isolated fungal microorganisms were Fusarium spp., followed by Aspergillus spp. and Candida albicans. Of the 6,556 specimens with positive bacterial cultures, 59% produced gram-positive bacteria, while the remainder produced gram-negative pathogens. The most commonly isolated bacteria were Pseudomonas aeruginosa (17.77%), Staphylococcus epidermidis (13.80%), Streptococcus pneumoniae (13.27%), S. viridans (12.23%), and S. aureus (11.18%).

CONCLUSION

Most submitted specimens were obtained from the cornea. The most commonly isolated fungal microorganisms were Fusarium spp., followed by Aspergillus spp. and C. albicans. The most commonly isolated bacteria were P. aeruginosa, followed by S. epidermidis and S. pneumoniae.

Crosstalk between Body Microbiota and the Regulation of Immunity

The microbiome corresponds to the genetic component of microorganisms (archaea, bacteria, phages, viruses, fungi, and protozoa) that coexist with an individual. During the last two decades, research on this topic has become massive demonstrating that in both homeostasis and disease, the microbiome plays an important role, and in some cases, a decisive one. To date, microbiota have been identified at different body locations, such as the eyes, lung, gastrointestinal and genitourinary tracts, and skin, and technological advances have permitted the taxonomic characterization of resident species and their metabolites, in addition to the cellular and molecular components of the host that maintain a crosstalk with local microorganisms. Here, we summarize recent studies regarding microbiota residing in different zones of the body and their relationship with the immune system. We emphasize the immune components underlying pathological conditions and how they interact with local (and distant) microbiota.

Molecular Characteristics and Distribution of Adult Human Corneal Immune Cell Types

Background

The limbus is located at a 2-mm-wide area between the bulbar conjunctiva and the cornea and has been suggested to be the niche of corneal epithelial stem cells and immune cells. Like the skin and intestines, the cornea is also an important mucosal surface, and immune cells on the cornea play critical roles in immune surveillance to ensure barrier surface homeostasis and protection from various environmental damage and infections. Single-cell RNA sequencing (scRNA-seq) analysis of protein tyrosine phosphatase receptor type C positive (PTPRC⁺) hematopoietic cells from the corneal limbus could provide a single cell atlas of all the immune cell subsets.

Methods

We performed single-cell RNA sequencing to generate transcriptomic profile for 804 sort-purified hematopoietic cells from the corneal limbus of three healthy donors.

Results

Our analysis identified a primary transcriptomic pattern for multiple immune cell subtypes, including naive T cells, antiviral effector CD8⁺ T cells, and innate immune cells such as IDO1⁺ mature regulatory dendritic cells (mregDCs), macrophages, monocytes, and basophils in the human corneal limbus.

Conclusion

Overall, single-cell transcriptomic analysis of limbal immune cells suggested the possible contribution of these cells on the adaptive and innate immune response of the human cornea.

Profiling of the Conjunctival Bacterial Microbiota Reveals the Feasibility of Utilizing a Microbiome-Based Machine Learning Model to Differentially Diagnose Microbial Keratitis and the Core Components of the Conjunctival Bacterial Interaction Network

Both healthy and diseased human ocular surfaces possess their own microbiota. If allowed, opportunistic pathogens within the ocular microbiota may cause microbial keratitis (MK). However, the nonpathogenic component of the ocular microbiota has been proven to undermine the performance of culture, the gold standard of the etiological diagnosis for MK. As the conjunctival bacterial microbiota generates unique alterations with various oculopathies, this study aimed to evaluate the feasibility of distinguishing MK using machine learning based on the characteristics of the conjunctival bacterial microbiome associated with various types of MK. This study also aimed to reveal which bacterial genera constitute the core of the interaction network of the conjunctival bacterial microbiome. Conjunctival swabs collected from the diseased eyes of MK patients and the randomly chosen normal eyes of healthy volunteers were subjected for high-throughput 16S rDNA sequencing. The relative content of each bacterial genus and the composition of bacterial gene functions in every sample were used to establish identification models with the random forest algorithm. Tenfold cross validation was adopted. Accuracy was 96.25% using the bacterial microbiota structure and 93.75% using the bacterial gene functional composition. Therefore, machine learning with the conjunctival bacterial microbiome characteristics might be used for differentiation of MKs as a noninvasive supplementary approach. In addition, this study found that Actinobacteria, Lactobacillus, Clostridium, Helicobacter, and Sphingomonas constitute the core of the interaction network of the conjunctival bacterial microbiome.

Autonomic nervous system receptor-mediated regulation of mast cell degranulation modulates the inflammation after corneal epithelial abrasion

Mast cells (MCs) regulate wound healing and are influenced by the autonomic nervous system (ANS). However, the underlying mechanisms affecting wound healing outcomes remain elusive. Here, we explored the specific role of the ANS by regulating MC degranulation following corneal epithelium abrasion. A mouse model of corneal abrasion was established by mechanically removing a 2-mm central epithelium. Wound closure, neutrophil infiltration, and transcription of injured corneas were investigated using whole-mount immunostaining, flow cytometry, and RNA-sequencing analysis, respectively. Inhibition of MC degranulation by the MC stabilizers cromolyn sodium and lodoxamide tromethamine increased the infiltration of neutrophils and delayed healing of abraded corneas. Moreover, transcriptomic profiling analysis showed that purified MCs from the limbus expressed adrenergic and cholinergic receptors. Pharmacological manipulation and sympathectomy with 6-hydroxydopamine confirmed that sympathetic nervous system signaling inhibited MC degranulation after corneal abrasion, whereas parasympathetic nervous system signaling enhanced MC degranulation. We conclude that normal degranulation of MCs in the corneal limbus and crosstalk between the ANS and MCs are crucial for the appropriate control of inflammation and the repair progress of wounded corneas. This suggests a potential approach for improving defective corneal wound healing by the administration of clinically available autonomic activity-modulating agents.

Ocular Microbiome in a Group of Clinically Healthy Horses

The ocular microbiome in horses is poorly described compared to other species, and most of the information available in the literature is based on traditional techniques, which has limited the depth of the knowledge on the subject. The objective of this study was to characterize and predict the metabolic pathways of the ocular microbiome of a group of healthy horses. Conjunctival swabs were obtained from both eyes of 14 horses, and DNA extraction was performed from the swabs, followed by next generation sequencing and bioinformatics analyses employing DADA2 and PICRUSt2. A total of 17 phyla were identified, of which Pseudomonadota (Proteobacteria) was the most abundant (59.88%), followed by Actinomycetota (Actinobacteria) (22.44%) and Bacteroidota (Bacteroidetes) (16.39%), totaling an average of 98.72% of the communities. Similarly, of the 278 genera identified, Massilia, Pedobacter, Pseudomonas, Sphingomonas, Suttonella and Verticia were present in more than 5% of the samples analyzed. Both Actinobacteria and Bacteroides showed great heterogeneity within the samples. The most abundant inferred metabolic functions were related to vital functions for bacteria such as aerobic respiration, amino acid, and lipid biosynthesis.

Analysis of Conjunctival Sac Microbiome in Dry Eye Patients With and Without Sjögren's Syndrome

Purpose

To analyze the conjunctival sac microbial communities in patients with Sjögren's syndrome-associated dry eyes (SSDE) and non-Sjögren's syndrome-associated dry eyes (NSSDE), compared with normal controls (NC).

Methods

Conjunctival sac swab samples from 23 eyes of SSDE, 36 eyes of NSSDE, and 39 eyes of NC were collected. The V3–V4 region of the 16S ribosomal RNA (rRNA) gene high-throughput sequencing was performed on an Illumina MiSeq platform and analyzed using Quantitative Insights Into Microbial Ecology (QIIME). Alpha diversity was employed to analyze microbiome diversity through Chao1 and Shannon indexes. Beta diversity was demonstrated by the principal coordinates analysis (PCoA) and Partial Least Squares Discrimination Analysis (PLS-DA). The relative abundance was bioinformatically analyzed at the phylum and genus levels.

Results

The alpha diversity was lower in patients with dry eye disease (Shannon index: NC vs. SSDE: P = 0.020, NC vs. NSSDE: P = 0.029). The beta diversity showed divergent microbiome composition in different groups (NC vs. SSDE: P = 0.001, NC vs. NSSDE: P = 0.001, NSSDE vs. SSDE: P = 0.005). The top 5 abundant phyla were Firmicutes, Proteobacteria, Actinobacteriota, Bacteroidota, and Cyanobacteria in all three groups. The top five abundant genera included Acinetobacter, Staphylococcus, Bacillus, Corynebacterium, and Clostridium_sensu_stricto_1. The relative microbiome abundance was different between groups. The Firmicutes/Bacteroidetes (F/B) ratio was 6.42, 7.31, and 9.71 in the NC, NSSDE, and SSDE groups, respectively (NC vs. SSDE: P = 0.038, NC vs. NSSDE: P = 0.991, SSDE vs. NSSDE: P = 0.048).

Conclusion

The diversity of conjunctival sac microbiome in patients with NSSDE and SSDE was diminished compared with NC. The main microbiome at the phylum and genus level were similar between groups, but the relative abundance had variations. The Firmicutes/Bacteroidetes ratio was higher in the SSDE group.

Gut Microbiota From Sjögren syndrome Patients Causes Decreased T Regulatory Cells in the Lymphoid Organs and Desiccation-Induced Corneal Barrier Disruption in Mice

Sjögren syndrome (SS) is an autoimmune inflammatory disorder characterized by secretory dysfunction in the eye and mouth; in the eye, this results in tear film instability, reduced tear production, and corneal barrier disruption. A growing number of studies show that homeostasis of the ocular surface is impacted by the intestinal microbiome, and several 16S sequencing studies have demonstrated dysbiosis of the intestinal microbiota in SS patients. In this study, we utilized metagenomic sequencing to perform a deeper analysis of the intestinal microbiome using stools collected from sex- and age-matched healthy (n = 20), dry eye (n = 4) and SS (n = 7) subjects. The observed Operational Taxonomic Units (OTUs) and Shannon alpha diversity were significantly decreased in SS compared to healthy controls, and there was a significant inverse correlation between observed OTUs and ocular severity score. We also identified specific bacterial strains that are differentially modulated in SS vs. healthy subjects. To investigate if the differential composition of intestinal microbiome would have an impact on the immune and eye phenotype, we performed functional studies using germ-free mice colonized with human intestinal microbiota from SS patients and healthy controls. Flow cytometry analysis demonstrated reduced frequency of CD4+ FOXP3+ cells in ocular draining cervical lymph nodes (CLN) in mice colonized with SS patient intestinal microbiota 4 weeks post-colonization. We also found that offspring of SS-humanized mice also have fewer CD4+FOXP3+ cells in the CLN as well as spleen, demonstrating vertical transmission. SS-humanized mice subjected to desiccating stress exhibited greater corneal barrier disruption as compared to healthy control humanized mice under the same conditions. Taken together, these data support the hypothesis that the intestinal microbiota can modulate ocular surface health, possibly by influencing development of CD4+ FOXP3+ regulatory T cells (Tregs) in the ocular draining lymph nodes.

Characterization of Conjunctival Sac Microbiome from Patients with Allergic Conjunctivitis

Conjunctival sac microbiome alterations have been reported to be closely associated with many ocular diseases. However, the characteristic of conjunctival sac microbiome in allergic conjunctivitis (AC) was scarcely described. In this study, we aimed to identify the differences of the conjunctival sac microbiome composition in AC patients compared with normal controls (NCs) using high-throughput 16S rDNA sequencing metagenomic analysis. The conjunctival sac microbiome samples from 28 AC patients and 39 NC patients were collected. The V3-V4 region of 16S rRNA gene high-throughput sequencing was performed on the illumina MiSeq platform. Alpha diversity, beta diversity and the relative abundance at the phylum and genus levels were analyzed using QIIME. Alpha diversity demonstrated by Chao1, Observed_species and PD_whole_tree indexes did not show significant difference between the AC and NC groups, while the Shannon index was higher in the AC group. Beta diversity showed divergent microbiome composition in different groups (p < 0.005). The top five abundant phyla were Firmicutes, Proteobacteria, Actinobacteriota, Bacteroidota and Cyanobacteria in both groups. The top five abundant genera were Bacillus, Staphylococcus, Corynebacterium, Acinetobacter and Ralstonia in the AC group and Acinetobacter, Staphylococcus, Bacillus, Clostridium_sensu_stricto_1, Corynebacterium and Geobacillus in the NC group. The Firmicutes/Bacteroidetes (F/B) ratio at the phylum level was similar between groups (p = 0.144). The Bacillus/Acinetobacter (B/A) ratio at the genus level was higher in the AC group (p = 0.021). The dysbiosis detected in this study might provide further evidence to investigate the mechanism and treatment methods for allergic conjunctivitis.

Bacterial distribution on the ocular surface of patients with primary Sjögren's syndrome

Many studies have shown that gut microbial dysbiosis is a major factor in the etiology of autoimmune diseases but none have suggested that the ocular surface (OS) microbiome is associated with Sjögren’s syndrome (SS). In this prospective study, we analyzed bacterial distribution on the OS in patients with primary SS. Among the 120 subjects included in this study, 48 patients (group A) had primary SS, whereas 72 subjects (group B) had dry eye symptoms that were unrelated to SS. We evaluated clinical dry eye parameters such as the OS disease index, ocular staining score (OSS), Schirmer’s I test, and tear break-up time (TBUT). Conjunctival swabs were used to analyze the microbial communities from the two groups. Bacterial 16S rRNA genes were sequenced using the Illumina MiSeq platform, and the data were analyzed using the QIIME 1.9.1 program. The Shannon index was significantly lower in group A than in group B microbiota (p < 0.05). An analysis of similarity using the Bray–Curtis distance method found no difference in beta-diversity between the two groups (p > 0.05). In group A, Actinobacteria at the phylum level and Corynebacteria at the genus level exhibited low abundance than group B, but the differences were not statistically significant (p > 0.05). SS apparently decreases the diversity of the OS microbial community. These observations may be related to the pathophysiology of SS and should be investigated in future studies.

Mucosal-associated invariant T cells have therapeutic potential against ocular autoimmunity

Autoimmune uveitis is a sight-threatening disease induced by pathogenic T cells that recognize retinal antigens; it is observed in disorders including Vogt-Koyanagi-Harada disease (VKH). The roles of specific T cell subsets and their therapeutic potential against autoimmune uveitis are not fully understood. Here we conducted multi-parametric single-cell protein quantification which shows that the frequency of CD161^highTRAV1-2⁺ mucosal-associated invariant T (MAIT) cells that recognize vitamin B2 metabolite-based antigens is decreased in relapsing VKH patients compared to individuals without active ocular inflammation. An experimental autoimmune uveitis (EAU) mouse model revealed that genetic depletion of MAIT cells reduced the expression of interleukin (Il) 22 and exacerbated retinal pathology. Reduced IL-22 levels were commonly observed in patients with relapsing VKH compared to individuals without active ocular inflammation. Both mouse and human MAIT cells produced IL-22 upon stimulation with their antigenic metabolite in vitro. An intravitreal administration of the antigenic metabolite into EAU mice induced retinal MAIT cell expansion and enhanced the expressions of Il22, as well as its downstream genes related to anti-inflammatory and neuroprotective effects, leading to an improvement in both retinal pathology and visual function. Taken together, we demonstrate that a metabolite-driven approach targeting MAIT cells has therapeutic potential against autoimmune uveitis.

Mechanism of the Gut Microbiota Colonization Resistance and Enteric Pathogen Infection

The mammalian gut microbial community, known as the gut microbiota, comprises trillions of bacteria, which co-evolved with the host and has an important role in a variety of host functions that include nutrient acquisition, metabolism, and immunity development, and more importantly, it plays a critical role in the protection of the host from enteric infections associated with exogenous pathogens or indigenous pathobiont outgrowth that may result from healthy gut microbial community disruption. Microbiota evolves complex mechanisms to restrain pathogen growth, which included nutrient competition, competitive metabolic interactions, niche exclusion, and induction of host immune response, which are collectively termed colonization resistance. On the other hand, pathogens have also developed counterstrategies to expand their population and enhance their virulence to cope with the gut microbiota colonization resistance and cause infection. This review summarizes the available literature on the complex relationship occurring between the intestinal microbiota and enteric pathogens, describing how the gut microbiota can mediate colonization resistance against bacterial enteric infections and how bacterial enteropathogens can overcome this resistance as well as how the understanding of this complex interaction can inform future therapies against infectious diseases.

High fat diet induced gut dysbiosis alters corneal epithelial injury response in mice

PURPOSE

Commensal microbiome secretes various metabolites that can exert important effects on the host immunity and inflammation and can alter cellular functions. However, little is known regarding the effect of microbiome on corneal immunity and genetic expression. The purpose of this study is to describe the effect of diet-induced gut dysbiosis on corneal immunity and corneal gene expression after wounding.

METHODS

This study is approved by the Animal Care and Use of the University of Illinois. Six-week-old female C57BL6 mice were fed on a normal chow diet (ND), isocaloric low-fat control diet (LFD), or a 21% milk high-fat diet (HFD) for six weeks. 2 mm corneal epithelial debridement was performed (n = 10). Fecal samples from mice were used for microbial diversity analysis (n > 3). Immunofluorescence staining of corneal wholemount tissue post-debridement was used to visualize immune cell distribution. RNA Seq was performed on tissue samples from corneas following debridement.

RESULTS

Mice fed differing diets had significant alterations in gut microbial diversities. After corneal debridement, HFD mice experienced delayed wound healing in comparison to LFD mice and ND mice groups. However, fecal transplantation led to normalization of wound closure rates. Increased γδTCR staining was observed in the LFD group, and decreased LY6G was observed in HFD group (p < 0.05). Gene Ontology terms of differentially expressed genes included response to external stimulus, cell proliferation, migration, adhesion, defense response and leukocyte migration. Top over-represented pathways included ECM-receptor interaction, Cytokine-cytokine receptor interaction, Focal adhesion and Leukocyte trans-endothelial migration.

CONCLUSIONS

Gut microbial dysbiosis alters corneal immune cell distribution, corneal response to injury, and genes related to epithelial function and corneal immunity.

[Visualization of normal ocular surface microflora via impression cytology sample using scanning electron microscopy with lanthanide contrasting]

PURPOSE

To determine the possibilities of impression cytology (IC) with subsequent visualization of the sample on a scanning electron microscope in assessment of normal microflora of the ocular surface.

MATERIALS AND METHODS

The article presents a visual characteristic of the microorganisms of the ocular surface (OS) captured during impression cytology (IC) in individuals without signs of inflammatory and degenerative eye diseases. The original method of staining the sample with heavy metal salts made it possible to identify the individual signs of the microorganisms in their subsequent visualization by scanning electron microscopy (SEM).

RESULTS

The paper presents photomicrographs of the microorganisms most common for the OS obtained with the help of SEM, confirming and supplementing the data of non-visual methods of studying the ocular microflora. It was shown that the detection frequency of the microbial component of the OS by the visual method presented in this study is comparable with the detection frequency when using the microbial cultivation method (<80%). Coccoid and rod-shaped microorganisms were detected with relatively equal frequency, with the coccoid organisms mainly represented in association with epithelial cells. The morphological diversity of rod-shaped microorganisms is shown.

CONCLUSION

The results of the study can be used as a visual reference for the normal microbiome of the eye.

Mucosal immunology of the ocular surface

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

Commensals Serve as Natural Barriers to Mammalian Cells during Acanthamoeba castellanii Invasion

Acanthamoeba castellanii is a free-living, pathogenic ameba found in the soil and water. It invades the body through ulcerated skin, the nasal passages, and eyes and can cause blinding keratitis and granulomatous encephalitis. However, the mechanisms underlying the opportunistic pathogenesis of A. castellanii remain unclear. In this study, we observed that commensal bacteria significantly reduced the cytotoxicity of the ameba on mammalian cells. This effect occurred in the presence of both Gram-positive and Gram-negative commensals. Additionally, commensals mitigated the disruption of cell junctions. Ex vivo experiments on mouse eyeballs further showed that the commensals protected the corneal epithelial layer. Together, these findings indicate that A. castellanii is pathogenic to individuals with a dysbiosis of the microbiota at infection sites, further highlighting the role of commensals as a natural barrier during parasite invasion. IMPORTANCE Acanthamoeba castellanii, an opportunistic protozoan widely present in the environment, can cause Acanthamoeba keratitis and encephalitis in humans. However, only a few reports describe how the ameba acts as an opportunistic pathogen. Our study showed that the normal microbiota interfered with the cytotoxicity of Acanthamoeba, persevered during Acanthamoeba invasion, and reduced corneal epithelium peeling in the mouse eyeball model. This suggests that commensals may act as a natural barrier against Acanthamoeba invasion. In future, individuals who suffer from Acanthamoeba keratitis should be examined for microbiota absence or dysbiosis to reduce the incidence of Acanthamoeba infection in clinical settings.

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.

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

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

Microbiota and Ocular Diseases

Recent advances have identified significant associations between the composition and function of the gut microbiota and various disorders in organ systems other than the digestive tract. Utilizing next-generation sequencing and multiomics approaches, the microbial community that possibly impacts ocular disease has been identified. This review provides an overview of the literature on approaches to microbiota analysis and the roles of commensal microbes in ophthalmic diseases, including autoimmune uveitis, age-related macular degeneration, glaucoma, and other ocular disorders. In addition, this review discusses the hypothesis of the "gut-eye axis" and evaluates the therapeutic potential of targeting commensal microbiota to alleviate ocular inflammation.

Keratoconus patients exhibit a distinct ocular surface immune cell and inflammatory profile

Inflammatory factors have been considered to contribute to keratoconus (KC) pathogenesis. This study aims to determine the immune cells subsets and soluble inflammatory factor profile on the ocular surface of KC patients. 32 KC subjects (51 eyes) across different grades of severity and 15 healthy controls (23 eyes) were included in the study. Keratometry and pachymetry measurements were recorded. Ocular surface immune cells (collected by ocular surface wash) immunophenotyped using flow cytometry include leukocytes, neutrophils, macrophages, natural killer (NK) cells, pan-T cells, gamma delta T (γδT) cells and NKT cells. Tear fluid collected using Schirmer's strip was used to measure 50 soluble factors by multiplex ELISA. Proportions of activated neutrophils, NK cells and γδT cells were significantly increased in KC patients. Significantly higher levels of tear fluid IL-1β, IL-6, LIF, IL-17A, TNFα, IFNα/β/γ, EPO, TGFβ1, PDGF-BB, sVCAM, sL-selectin, granzyme-B, perforin, MMP2, sFasL and IgE, along with significantly lower levels of IL-1α and IL-9 were observed in KC patients. Alterations observed in few of the immuno-inflammatory parameters correlated with grades of disease, allergy, eye rubbing and keratometry or pachymetry measurements. The observation implies a distinct immuno-inflammatory component in KC pathogenesis and its potential as an additional therapeutic target in KC management.

Crosstalk between γδ T cells and the microbiota

The role of the microbiota in the development and function of γδ T cells-a T cell subset characterized by a T cell receptor composed of one γ-chain and one δ-chain-has been investigated in multiple organs in mice and humans. Interactions between the microbiota and γδ T cells affect both tissue homeostasis and disease pathologies. Notably, microbiota-induced interleukin-17 (IL-17)-producing-γδ T cells can mediate a range of immunological processes, from metabolic disorders to neuroinflammation via the gut-brain axis. However, the bidirectional interactions between γδ T cells and the microbiota have not been fully determined. In this Perspective, we dissect the roles of microbiota in modulating γδ T cell development and function, and evaluate the evidence for γδ T cell selection of commensal communities. We also discuss the potential implications of these cells in health and disease and the major open questions and research avenues in the field.

Alternative Therapeutic Interventions: Antimicrobial Peptides and Small Molecules to Treat Microbial Keratitis

Microbial keratitis is a leading cause of blindness worldwide and results in unilateral vision loss in an estimated 2 million people per year. Bacteria and fungus are two main etiological agents that cause corneal ulcers. Although antibiotics and antifungals are commonly used to treat corneal infections, a clear trend with increasing resistance to these antimicrobials is emerging at rapid pace. Extensive research has been carried out to determine alternative therapeutic interventions, and antimicrobial peptides (AMPs) are increasingly recognized for their clinical potential in treating infections. Small molecules targeted against virulence factors of the pathogens and natural compounds are also explored to meet the challenges and growing demand for therapeutic agents. Here we review the potential of AMPs, small molecules, and natural compounds as alternative therapeutic interventions for the treatment of corneal infections to combat antimicrobial resistance. Additionally, we have also discussed about the different formats of drug delivery systems for optimal administration of drugs to treat microbial keratitis.

Short-Term High Fructose Intake Impairs Diurnal Oscillations in the Murine Cornea

Purpose

Endogenous and exogenous stressors, including nutritional challenges, may alter circadian rhythms in the cornea. This study aimed to determine the effects of high fructose intake (HFI) on circadian homeostasis in murine cornea.

Methods

Corneas of male C57BL/6J mice subjected to 10 days of HFI (15% fructose in drinking water) were collected at 3-hour intervals over a 24-hour circadian cycle. Total extracted RNA was subjected to high-throughput RNA sequencing. Rhythmic transcriptional data were analyzed to determine the phase, rhythmicity, unique signature, metabolic pathways, and cell signaling pathways of transcripts with temporally coordinated expression. Corneas of HFI mice were collected for whole-mounted techniques after immunofluorescent staining to quantify mitotic cell number in the epithelium and trafficking of neutrophils and γδ-T cells to the limbal region over a circadian cycle.

Results

HFI significantly reprogrammed the circadian transcriptomic profiles of the normal cornea and reorganized unique temporal and clustering enrichment pathways, but did not affect core-clock machinery. HFI altered the distribution pattern and number of corneal epithelial mitotic cells and enhanced recruitment of neutrophils and γδ-T cell immune cells to the limbus across a circadian cycle. Cell cycle, immune function, metabolic processes, and neuronal-related transcription and associated pathways were altered in the corneas of HFI mice.

Conclusions

HFI significantly reprograms diurnal oscillations in the cornea based on temporal and spatial distributions of epithelial mitosis, immune cell trafficking, and cell signaling pathways. Our findings reveal novel molecular targets for treating pathologic alterations in the cornea after HFI.

Evolved to protect, designed to destroy: IL-17-producing γδ T cells in infection, inflammation, and cancer

T cells of the gamma delta (γδ) lineage are evolutionary conserved from jawless to cartilaginous and bony fish to mammals and represent the "swiss army knife" of the immune system capable of antigen-dependent or independent responses, memory, antigen presentation, regulation of other lymphocytes, tissue homeostasis, and mucosal barrier maintenance, to list a few. Over the last 10 years, γδ T cells that produce the cytokine IL-17 (γδT17) have taken a leading position in our understanding of how our immune system battles infection, inflicts tissue damage during inflammation, and gets rewired by the tumor microenvironment. A lot of what we know about γδT17 cells stems from mouse models, however, increasing evidence implicates these cells in numerous human diseases. Herein, we aim to give an overview of the most common mouse models that have been used to study the role of γδT17 cells in infection, inflammation, and cancer, while at the same time we will evaluate evidence for their importance in humans. We hope and believe that in the next 10 years, means to take advantage of the protective and destructive properties of γδ T and in particular γδT17 cells will be part of our standard immunotherapy toolkit.

Clearance of Gram-Negative Bacterial Pathogens from the Ocular Surface by Predatory Bacteria

It was previously demonstrated that predatory bacteria are able to efficiently eliminate Gram-negative pathogens including antibiotic-resistant and biofilm-associated bacteria. In this proof-of-concept study we evaluated whether two species of predatory bacteria, Bdellovibrio bacteriovorus and Micavibrio aeruginosavorus, were able to alter the survival of Gram-negative pathogens on the ocular surface. Clinical keratitis isolates of Pseudomonas aeruginosa (strain PAC) and Serratia marcescens (strain K904) were applied to the ocular surface of NZW rabbits followed by application of predatory bacteria. At time intervals, surviving pathogenic bacteria were enumerated. In addition, B. bacteriovorus and S. marcescens were applied to porcine organ culture corneas under contact lenses, and the ocular surface was examined by scanning electron microscopy. The ocular surface epithelial layer of porcine corneas exposed to S. marcescens, but not B. bacteriovorus was damaged. Using this model, neither pathogen could survive on the rabbit ocular surface for longer than 24 h. M. aeruginosavorus correlated with a more rapid clearance of P. aeruginosa but not S. marcescens from rabbit eyes. This study supports previous evidence that predatory bacteria are well tolerated by the cornea, but suggest that predatory bacteria do not considerably change the ability of the ocular surface to clear the tested Gram-negative bacterial pathogens from the ocular surface.

Ocular Surface Microbiome Alterations Are Found in Both Eyes of Individuals With Unilateral Infectious Keratitis

Purpose

To analyze the ocular surface microbiome (OSM) profile in both eyes of individuals with unilateral keratitis.

Methods

In this prospective, cross-sectional study, the conjunctival OSM of adults (>18 years old) presenting to an ophthalmic emergency department with acute unilateral keratitis and controls without an acute infectious process was sampled. Samples underwent DNA amplification and 16S sequencing using Illumina MiSeq 250 and were analyzed using Qiime. Statistical analysis was performed using a two-sided Student t-test, diversity indices, and principal coordinate analysis. The main outcome measures included relative abundance and α and β diversity.

Results

Bacterial DNA was recovered from all 34 eyes of 17 individuals with keratitis (mean age, 49.3 ± 17.5 years) and 16 eyes of controls (mean age, 56.6 ± 17.0 years). In the two culture-positive eyes, 16S aligned with culture results. Significant differences in α diversities were noted when comparing both eyes of individuals with keratitis to control eyes (all P < 0.05), but no significant differences between the eyes of an individual with keratitis. Principal coordinate analysis plots confirmed this finding, demonstrating separation between either eye of patients with keratitis and controls (both P < 0.01), however not between eyes in patients with unilateral keratitis. Both eyes of individuals with keratitis had greater abundance of Pseudomonas compared with controls both on compositional analysis and linear discriminant analysis.

Conclusions

Alterations in the OSM profile are detected in both eyes of individuals with unilateral keratitis compared with controls. Beyond the causative organism, a greater abundance of potential pathogens and lesser abundance of commensal organisms were found.

Translational Relevance

The OSM profile is altered in both eyes of individuals with unilateral keratitis, which may lend insight into the role of the microbiome in the pathophysiology of disease.

Ocular Surface Microbiota in Contact Lens Users and Contact-Lens-Associated Bacterial Keratitis

Our objectives were to investigate whether the conjunctival microbiota is altered by contact lens wear and/or bacterial keratitis and to explore the hypothesis that commensals of conjunctival microbiota contribute to bacterial keratitis. Swab samples from both eyes were collected separately from the inferior fornix of the conjunctiva of non-contact-lens users (n_participants = 28) and contact lens users (n_participants = 26) and from patients with contact-lens-associated bacterial keratitis (n_participants = 9). DNA from conjunctival swab samples was analyzed with 16S rRNA gene amplicon sequencing. Pathogens from the corneal infiltrates were identified by cultivation. In total, we identified 19 phyla and 283 genera; the four most abundant genera were Pseudomonas, Enhydrobacter, Staphylococcus, and Cutibacterium. Several pathogens related to bacterial keratitis were identified in the conjunctival microbiota of the whole study population, and the same bacteria were identified by both methods in the conjunctiva and cornea for four patients with contact-lens-associated bacterial keratitis. The overall conjunctival microbiota profile was not altered by contact lens wear or bacterial keratitis; thus, it does not appear to contribute to the development of bacterial keratitis in contact lens users. However, in some individuals, conjunctival microbiota may harbor opportunistic pathogens causing contact-lens-associated bacterial keratitis.

Profiling of Diagnostic Information of and Latent Susceptibility to Bacterial Keratitis From the Perspective of Ocular Bacterial Microbiota

The ocular surface possesses its own bacterial microbiota. Once given a chance, opportunistic pathogens within ocular microbiota may lead to corneal infection like bacterial keratitis (BK). To reveal the possible factor that makes people vulnerable to BK from the perspective of ocular bacterial microbiota, as well as to compare diagnostic information provided by high-throughput 16S rDNA sequencing and bacterial culture, 20 patients with BK and 42 healthy volunteers were included. Conjunctival swabs and corneal scrapings collected from the diseased eyes of BK patients were subjected for both high-throughput 16S rDNA sequencing and bacterial culture. Conjunctival swabs collected from the normal eyes of BK patients and healthy volunteers were sent only for sequencing. For identifying the pathogens causing BK, high-throughput 16S rDNA sequencing presented a higher positive rate than bacterial culture (98.04% vs. 17.50%), with 92.11% reaching the genus level (including 10.53% down to the species level). However, none of the sequencing results was consistent with the cultural results. The sequencing technique appears to challenge culture, and could be a complement for pathogen identification. Moreover, compared to the eyes of healthy subjects, the ocular microbiota of three sample groups from BK patients contained significantly less Actinobacteria and Corynebacteria (determinate beneficial symbiotic bacteria), but significantly more Gammaproteobacteria, Pseudomonas, Bacteroides, and Escherichia-Shigella (common ocular pathogenic bacteria). Therefore, it is speculated that the imbalance of protective and aggressive bacteria in the ocular microbiota of healthy people may trigger susceptibility to BK. Based on this speculation, it seems promising to prevent and treat infectious oculopathy through regulating ocular microbiota.

Comparative analysis of ocular surface tissue microbiome in human, mouse, rabbit, and guinea pig

Animal models are a critical element of ocular surface research for investigating therapeutic drops, surgical implants, and infection research. This study was a comparative analysis of the microbial communities on conjunctival tissue samples from humans compared to several commonly used laboratory animals (BALB/c mice, New Zealand white rabbits and IMVS colored stock guinea pigs). Microbial communities were analyzed by extracting total DNA from conjunctival tissue and sequencing the 16 S rRNA gene using the Illumina MiSeq platform. Sequences were quality filtered using the UNOISE pipeline in USEARCH and taxonomically classified using GTDB database. Sequences associated with blank extraction and sampling negative controls were removed with the decontam R software package prior to downstream analysis. There was a difference in the diversity measures of richness (P = 0.0124) and Shannon index (P = 0.0002) between humans and rabbits but not between human, mouse and guinea pigs. There was a difference between the human and any animal for bacterial community structure (P = 0.006). There was a higher degree of similarity between the bacterial composition of the human and mouse samples with each dominated by the phyla Proteobacteria and Firmicutes. The use of mouse models may be more appropriate for studies investigating changes to the ocular microbiome due to interventions such as application of antibiotics due to greater similarities in bacterial community structure and composition to humans.

Control of Immunity by the Microbiota

The immune system has coevolved with extensive microbial communities living on barrier sites that are collectively known as the microbiota. It is increasingly clear that microbial antigens and metabolites engage in a constant dialogue with the immune system, leading to microbiota-specific immune responses that occur in the absence of inflammation. This form of homeostatic immunity encompasses many arms of immunity, including B cell responses, innate-like T cells, and conventional T helper and T regulatory responses. In this review we summarize known examples of innate-like T cell and adaptive immunity to the microbiota, focusing on fundamental aspects of commensal immune recognition across different barrier sites. Furthermore, we explore how this cross talk is established during development, emphasizing critical temporal windows that establish long-term immune function. Finally, we highlight how dysregulation of immunity to the microbiota can lead to inflammation and disease, and we pinpoint outstanding questions and controversies regarding immune system-microbiota interactions.

Unconventional T cells - New players in antifungal immunity

Life-threatening invasive fungal diseases (IFD) are increasing in incidence, especially in immunocompromised patients and successful resolution of IFD requires a variety of different immune cells. With the limited repertoire of available antifungal drugs there is a need for more effective therapeutic strategies. This review interrogates the evidence on the human immune response to the main pathogens driving IFD, with a focus on the role of unconventional lymphocytes e.g. natural killer (NK) cells, gamma/delta (γδ) T cells, mucosal associated invariant T (MAIT) cells, invariant natural killer T (iNKT) cells and innate lymphoid cells (ILC). Recent discoveries and new insights into the roles of these novel lymphocyte groups in antifungal immunity will be discussed, and we will explore how an improved understanding of antifungal action by lymphocytes can inform efforts to improve antifungal treatment options.

Altered ocular surface immune cell profile in patients with dry eye disease

PURPOSE

Aberrant inflammation and immune dysregulation are known pathogenic contributors in dry eye disease (DED). Aim of the study was to determine the proportions of immune cell subsets on the ocular surface (OS) of DED patients.

METHODS

15 healthy controls (22 eyes) and 48 DED subjects (36 eyes with evaporative DED - EDED; 60 eyes with aqueous deficient DED - ADED) were included in the study. Tear break up time (TBUT), Schirmer's test 1 (ST1), corneal staining (CS) and ocular surface disease index (OSDI) scoring were recorded. OS wash was used to collect immune cells on the OS of study subjects. The cells immunophenotyped using flow cytometry include leukocytes, neutrophils, macrophages, natural killer-NK cells and T cell subsets (CD4; CD8; double positive-DP; gamma delta-γδ and NK T cells).

RESULTS

Significantly higher proportions of leukocytes, neutrophils, CD4 T cells, CD8 T cells, DP T cells and CD4/CD8 T cells ratio were observed in EDED and/or ADED patients. Significantly higher proportions of neutrophils and lower proportions of NK cells were observed in ADED subjects with corneal staining compared to those without and controls. Neutrophils/NK cells ratio was significantly higher in EDED and ADED subjects compared to controls. Correlation analysis revealed pathological relationships between proportions of leukocytes, neutrophils, CD4 T cells and Neutrophil/NK cells ratio with DED clinical parameters.

CONCLUSION

OS immune cell subset proportion changes in DED patients were associated with DED types and severity. The data suggests the potential for a new generation of therapies targeting immune cells on the ocular surface.

The ocular microbiome and microbiota and their effects on ocular surface pathophysiology and disorders

The ocular surface flora perform an important role in the defense mechanisms of the ocular surface system. Its regulation of the immunological activity and the barrier effect against pathogen invasion are remarkable. Composition of the flora differs according to the methods of investigation, because the microbiome, composed of the genetic material of bacteria, fungi, viruses, protozoa, and eukaryotes on the ocular surface, differs from the microbiota, which are the community of microorganisms that colonize the ocular surface. The observed composition of the ocular surface flora depends on harvesting and examining methods, whether with traditional culture or with more refined genetic analysis based on rRNA and DNA sequencing. Environment, diet, sex, and age influence the microbial flora composition, thus complicating the analysis of the baseline status. Moreover, potentially pathogenic organisms can affect its composition, as do various disorders, including chronic inflammation, and therapies applied to the ocular surface. A better understanding of the composition and function of microbial communities at the ocular surface could bring new insights and clarify the epidemiology and pathology of ocular surface dynamics in health and disease. The purpose of this review is to provide an up-to-date overview of knowledge about this topic.

The ocular surface immune system through the eyes of aging

Since the last century, advances in healthcare, housing, and education have led to an increase in life expectancy. Longevity is accompanied by a higher prevalence of age-related diseases, such as cancer, autoimmunity, diabetes, and infection, and part of this increase in disease incidence relates to the significant changes that aging brings about in the immune system. The eye is not spared by aging either, presenting with age-related disorders of its own, and interestingly, many of these diseases have immune pathophysiology. Being delicate organs that must be exposed to the environment in order to capture light, the eyes are endowed with a mucosal environment that protects them, the so-called ocular surface. As in other mucosal sites, immune responses at the ocular surface need to be swift and potent to eliminate threats but are at the same time tightly controlled to prevent excessive inflammation and bystander damage. This review will detail how aging affects the mucosal immune response of the ocular surface as a whole and how this process relates to the higher incidence of ocular surface disease in the elderly.

Host-derived lipids orchestrate pulmonary γδ T cell response to provide early protection against influenza virus infection

Innate immunity is important for host defense by eliciting rapid anti-viral responses and bridging adaptive immunity. Here, we show that endogenous lipids released from virus-infected host cells activate lung γδ T cells to produce interleukin 17 A (IL-17A) for early protection against H1N1 influenza infection. During infection, the lung γδ T cell pool is constantly supplemented by thymic output, with recent emigrants infiltrating into the lung parenchyma and airway to acquire tissue-resident feature. Single-cell studies identify IL-17A-producing γδ T (Tγδ17) cells with a phenotype of TCRγδhiCD3hiAQP3hiCXCR6hi in both infected mice and patients with pneumonia. Mechanistically, host cell-released lipids during viral infection are presented by lung infiltrating CD1d+ B-1a cells to activate IL-17A production in γδ T cells via γδTCR-mediated IRF4-dependent transcription. Reduced IL-17A production in γδ T cells is detected in mice either lacking B-1a cells or with ablated CD1d in B cells. Our findings identify a local host-immune crosstalk and define important cellular and molecular mediators for early innate defense against lung viral infection.

Deletion of Irf4 in T Cells Suppressed Autoimmune Uveitis and Dysregulated Transcriptional Programs Linked to CD4+ T Cell Differentiation and Metabolism

Interferon regulatory factor-4 (IRF4) and IRF8 regulate differentiation, growth and functions of lymphoid and myeloid cells. Targeted deletion of irf8 in T cells (CD4-IRF8KO) has been shown to exacerbate colitis and experimental autoimmune uveitis (EAU), a mouse model of human uveitis. We therefore generated mice lacking irf4 in T cells (CD4-IRF4KO) and investigated whether expression of IRF4 by T cells is also required for regulating T cells that suppress autoimmune diseases. Surprisingly, we found that CD4-IRF4KO mice are resistant to EAU. Suppression of EAU derived in part from inhibiting pathogenic responses of Th17 cells while inducing expansion of regulatory lymphocytes that secrete IL-10 and/or IL-35 in the eye and peripheral lymphoid tissues. Furthermore, CD4-IRF4KO T cells exhibit alterations in cell metabolism and are defective in the expression of two Ikaros zinc-finger (IKZF) transcription factors (Ikaros, Aiolos) that are required for lymphocyte differentiation, metabolism and cell-fate decisions. Thus, synergistic effects of IRF4 and IkZFs might induce metabolic reprogramming of differentiating lymphocytes and thereby dynamically regulate relative abundance of T and B lymphocyte subsets that mediate immunopathogenic mechanisms during uveitis. Moreover, the diametrically opposite effects of IRF4 and IRF8 during EAU suggests that intrinsic function of IRF4 in T cells might be activating proinflammatory responses while IRF8 promotes expansion of immune-suppressive mechanisms.

Identification of an intraocular microbiota

The current dogma in ophthalmology and vision research presumes the intraocular environment to be sterile. However, recent evidence of intestinal bacterial translocation into the bloodstream and many other internal organs including the eyes, found in healthy and diseased animal models, suggests that the intraocular cavity may also be inhabited by a microbial community. Here, we tested intraocular samples from over 1000 human eyes. Using quantitative PCR, negative staining transmission electron microscopy, direct culture, and high-throughput sequencing technologies, we demonstrated the presence of intraocular bacteria. The possibility that the microbiome from these low-biomass communities could be a contamination from other tissues and reagents was carefully evaluated and excluded. We also provide preliminary evidence that a disease-specific microbial signature characterized the intraocular environment of patients with age-related macular degeneration and glaucoma, suggesting that either spontaneous or pathogenic bacterial translocation may be associated with these common sight-threatening conditions. Furthermore, we revealed the presence of an intraocular microbiome in normal eyes from non-human mammals and demonstrated that this varied across species (rat, rabbit, pig, and macaque) and was established after birth. These findings represent the first-ever evidence of intraocular microbiota in humans.

Comparative profile of ocular surface microbiome in vernal keratoconjunctivitis patients and healthy subjects

PURPOSE

To compare ocular surface microbiome and its antibiotic sensitivity in vernal keratoconjunctivitis (VKC) with normal ocular surface.

METHODS

In this case-control study, thirty patients each with clinical diagnosis of VKC and age-matched controls with normal ocular surface were enrolled. Tear film samples were collected from each group and subjected to microbial evaluation with microscopy, conventional culture methods, and polymerase chain reaction (PCR). Microbial diversity and antibiotic sensitivity patterns were analyzed.

RESULTS

Most patients (67%) belonged to severe grades (3 and 4) of VKC, and allergic history could be elicited in 20%. On culture, bacteria were isolated in 50% of VKC patients and 47% of control group. Staphylococcus species were identified in 70% VKC group and 57% control group. S. aureus growth was seen in 52% and 21% of VKC patients and controls, respectively. S. pneumoniae was isolated only in controls (29%) (p<0.05). Confluent colonies (≥10 colonies/μl) were seen in 70% of VKC patients and 14% of controls (p<0.05). Fluoroquinolone resistance was more among higher grades of VKC (50%) (p<0.01) and was observed in 46% of VKC patients and 23% of control group (p<0.01). Both groups were negative for HSV-1 DNA and fungal growth.

CONCLUSION

Staphylococcus, the most common ocular surface flora, was predominant in VKC patients. Microbial analysis revealed similar microbial diversity in both groups. However, bacterial load was higher in VKC. Increased fluoroquinolone resistance was observed in VKC patients with more resistance among higher grades. Fungi and HSV-1 were not seen in VKC or normal ocular surface.

American Academy of Optometry Microbial Keratitis Think Tank

SIGNIFICANCE

Think Tank 2019 affirmed that the rate of infection associated with contact lenses has not changed in several decades. Also, there is a trend toward more serious infections associated with Acanthamoeba and fungi. The growing use of contact lenses in children demands our attention with surveillance and case-control studies.

PURPOSE

The American Academy of Optometry (AAO) gathered researchers and key opinion leaders from around the world to discuss contact lens-associated microbial keratitis at the 2019 AAO Annual Meeting.

METHODS

Experts presented within four sessions. Session 1 covered the epidemiology of microbial keratitis, pathogenesis of Pseudomonas aeruginosa, and the role of lens care systems and storage cases in corneal disease. Session 2 covered nonbacterial forms of keratitis in contact lens wearers. Session 3 covered future needs, challenges, and research questions in relation to microbial keratitis in youth and myopia control, microbiome, antimicrobial surfaces, and genetic susceptibility. Session 4 covered compliance and communication imperatives.

RESULTS

The absolute rate of microbial keratitis has remained very consistent for three decades despite new technologies, and extended wear significantly increases the risk. Improved oxygen delivery afforded by silicone hydrogel lenses has not impacted the rates, and although the introduction of daily disposable lenses has minimized the risk of severe disease, there is no consistent evidence that they have altered the overall rate of microbial keratitis. Overnight orthokeratology lenses may increase the risk of microbial keratitis, especially secondary to Acanthamoeba, in children. Compliance remains a concern and a significant risk factor for disease. New insights into host microbiome and genetic susceptibility may uncover new theories. More studies such as case-control designs suited for rare diseases and registries are needed.

CONCLUSIONS

The first annual AAO Think Tank acknowledged that the risk of microbial keratitis has not decreased over decades, despite innovation. Important questions and research directions remain.

Strain heterogeneity, cooccurrence network, taxonomic composition and functional profile of the healthy ocular surface microbiome

BACKGROUND

There is growing evidence indicating that the microbial communities that dwell on the human ocular surface are crucially important for ocular surface health and disease. Little is known about interspecies interactions, functional profiles, and strain heterogeneity across individuals in healthy ocular surface microbiomes.

METHODS

To comprehensively characterize the strain heterogeneity, cooccurrence network, taxonomic composition and functional profile of the healthy ocular surface microbiome, we performed shotgun metagenomics sequencing on ocular surface mucosal membrane swabs of 17 healthy volunteers.

RESULTS

The healthy ocular surface microbiome was classified into 12 phyla, 70 genera, and 140 species. The number of species in each healthy ocular surface microbiome ranged from 6 to 47, indicating differences in microbial diversity among individuals. The species with high relative abundances and high positivity rates were Streptococcus pyogenes, Staphylococcus epidermidis, Propionibacterium acnes, Corynebacterium accolens, and Enhydrobacter aerosaccus. A correlation network analysis revealed a competitive interaction of Staphylococcus epidermidis with Streptococcus pyogenes in ocular surface microbial ecosystems. Staphylococcus epidermidis and Streptococcus pyogenes revealed phylogenetic diversity among different individuals. At the functional level, the pathways related to transcription were the most abundant. We also found that there were abundant lipid and amino acid metabolism pathways in the healthy ocular surface microbiome.

CONCLUSION

This study explored the strain heterogeneity, cooccurrence network, taxonomic composition, and functional profile of the healthy ocular surface microbiome. These findings have important significance for the future development of probiotic-based eye therapeutic drugs.

The cornea IV immunology, infection, neovascularization, and surgery chapter 1: Corneal immunology

PURPOSE

of Review: This review offers an informed and up-to-date insight on the immune profile of the cornea and the factors that govern the regulation of such a unique immune environment.

SUMMARY

The cornea is a unique tissue that performs the specialized task of allowing light to penetrate for visual interpretation. To accomplish this, the ocular surface requires a distinct immune environment that is achieved through unique structural, cellular and molecular factors. Not only must the cornea be able to fend off invasive infectious agents but also control the inflammatory response as to avoid collateral, and potentially blinding damage; particularly of post-mitotic cells such as the corneal endothelium. To combat infections, both innate and adaptive arms of the inflammatory immune response are at play in the cornea. Dendritic cells play a critical role in coordinating both these responses in order to fend off infections. On the other side of the spectrum, the ocular surface is also endowed with a variety of anatomic and physiologic components that aid in regulating the immune response to prevent excessive, potentially damaging, inflammation. This attenuation of the immune response is termed immune privilege. The balance between pro and anti-inflammatory reactions is key for preservation of the functional integrity of the cornea.

RECENT FINDINGS

The understanding of the molecular and cellular factors governing corneal immunology and its response to antigens is a growing field. Dendritic cells in the normal cornea play a crucial role in combating infections and coordinating the inflammatory arms of the immune response, particularly through coordination with T-helper cells. The role of neuropeptides is recently becoming more highlighted with different factors working on both sides of the inflammatory balance.

Microbes of the human eye: Microbiome, antimicrobial resistance and biofilm formation

BACKGROUND

The review focuses on the bacteria associated with the human eye using the dual approach of detecting cultivable bacteria and the total microbiome using next generation sequencing. The purpose of this review was to highlight the connection between antimicrobial resistance and biofilm formation in ocular bacteria.

METHODS

Pubmed was used as the source to catalogue culturable bacteria and ocular microbiomes associated with the normal eyes and those with ocular diseases, to ascertain the emergence of anti-microbial resistance with special reference to biofilm formation.

RESULTS

This review highlights the genetic strategies used by microorganisms to evade the lethal effects of anti-microbial agents by tracing the connections between candidate genes and biofilm formation.

CONCLUSION

The eye has its own microbiome which needs to be extensively studied under different physiological conditions; data on eye microbiomes of people from different ethnicities, geographical regions etc. are also needed to understand how these microbiomes affect ocular health.

Current knowledge on the human eye microbiome: a systematic review of available amplicon and metagenomic sequencing data

Insights in the ocular surface microbiome are still at an early stage and many more questions remain unanswered compared with other human-associated microbial communities. The current knowledge on the human microbiome changed our viewpoint on bacteria and human health and significantly enhanced our understanding of human pathophysiology. Also in ocular medicine, microbiome research might impact treatment. Here, we summarize the current knowledge on ocular microbiome research with a particular focus on potential confounding factors and their effects on microbiome composition. Moreover, we present the ocular surface core microbiome based on current available data and defined it as genera present in almost half of the published control cohorts with a relative abundance of at least 1%.

Alterations in the Ocular Surface Microbiome in Traumatic Corneal Ulcer Patients

Purpose

Corneal ulcers are a common eye inflammatory disease that can cause visual impairment or even blindness if not treated promptly. Ocular trauma is a major risk factor for corneal ulcers, and corneal trauma in agricultural work can rapidly progress to corneal ulcers. This study aims to evaluate the changes in the ocular surface (OS) microbiome of patients with traumatic corneal ulcer (TCU).

Methods

Among 20 healthy control (HC) subjects and 22 patients with TCU, 42 eyes were examined to investigate the OS microbial flora using metagenomic shotgun sequencing.

Results

At the taxonomic composition level, our findings showed that dysbiosis (alterations in richness and community structure) occurs in the OS microbiome of patients with TCU. Notably, Pseudomonas was present at a greater than 30% relative abundance in all individuals in the TCU group. At the species level, the abundance of Pseudomonas fluorescens and Pseudomonas aeruginosa was significantly elevated in the TCU group compared to the HC group. At the functional level, we identified significant differences in the HC and TCU groups. We observed that inflammation-related pathways involved in bacterial chemotaxis, flagellar assembly, and biofilm formation were significantly more abundant in the TCU group. Besides, the pathways related to biosynthesis, degradation, and metabolism were also increased significantly in the TCU group.

Conclusions

These findings indicate an altered OS microbiome in the affected eyes of patients with TCU. Further research is needed to determine whether these alterations contribute to the pathogenesis of TCU or impact disease progression.

The Next Generation of Ocular Pathogen Detection

ABSTRACT

Metagenomic next-generation sequencing is a powerful method for pathogen detection that combines advanced genome sequencing technology with cutting-edge bioinformatics to analyze microbial populations. Metagenomic next-generation sequencing has the potential to identify uncommon, unculturable, and even previously unidentified pathogens from a clinical isolate. Of particular interest to ophthalmology, this robust data extraction can occur from very small volume clinical samples. Here we discuss the opportunities and limitations of this technique and their current and future application to ophthalmic diagnostics.

Microbiota-dependent expansion of testicular IL-17-producing Vγ6+ γδ T cells upon puberty promotes local tissue immune surveillance

γδT cells represent the majority of lymphocytes in several mucosal tissues where they contribute to tissue homoeostasis, microbial defence and wound repair. Here we characterise a population of interleukin (IL) 17-producing γδ (γδ17) T cells that seed the testis of naive C57BL/6 mice, expand at puberty and persist throughout adulthood. We show that this population is foetal-derived and displays a T-cell receptor (TCR) repertoire highly biased towards Vγ6-containing rearrangements. These γδ17 cells were the major source of IL-17 in the testis, whereas αβ T cells mostly provided interferon (IFN)-γ in situ. Importantly, testicular γδ17 cell homoeostasis was strongly dependent on the microbiota and Toll-like receptor (TLR4)/IL-1α/IL-23 signalling. We further found that γδ17 cells contributed to tissue surveillance in a model of experimental orchitis induced by intra-testicular inoculation of Listeria monocytogenes, as Tcrδ-/- and Il17-/- infected mice displayed higher bacterial loads than wild-type (WT) controls and died 3 days after infection. Altogether, this study identified a previously unappreciated foetal-derived γδ17 cell subset that infiltrates the testis at steady state, expands upon puberty and plays a crucial role in local tissue immune surveillance.

Safety and Tolerability of an Eye Drop Based on 0.6% Povidone-Iodine Nanoemulsion in Dry Eye Patients

Purpose: To evaluate safety and tolerability on the ocular surface of an anti-septic formulation containing 0.6% povidone–iodine (0.6% PVI) for a 4 week period.

Methods: An observational, prospective study included 20 mild-moderate dry eye disease (DED) patients who enrolled at the Ocular Surface Disease Unit of the University of Messina, receiving 0.6% PVI eye drops for 28 days, 2 drops twice daily (BID). The assessment included the Ocular Surface Disease Index questionnaire; symptoms score (0 = absent to 3 = severe) for burning, ocular dryness, foreign body sensation, watery eyes, tearing, photophobia, and ocular pain; fluorescein tear break-up time (TBUT); and corneal-conjunctival staining, performed at baseline (T0), after 7 (T7) and 28 (T28). Schirmer I-test, corneal endothelial cell count, intraocular pressure, and fundus examination were performed at T0 and T28. The main outcome measures were TBUT and corneal-conjunctival staining as markers of ocular surface homeostasis. For statistical analysis, Student's T-test and Wilcoxon test were used as appropriate.

Results: No significant alterations of the safety parameters were found throughout the study. Further, at T28 a significant improvement of burning, ocular dryness, foreign body sensation, and watery eyes (T0 vs. T28 P < 0.03) were observed; corneal-conjunctival staining improved at T28 (T0 vs. T28 P < 0.0001), and TBUT improved already at T7 (T0 vs. T7 P = 0.0008) lasting so till the end of the study. The only adverse event was mild burning at instillation for the first 3 days of treatment in most of the patients.

Conclusions: The treatment with 0.6% PVI was safe and well tolerated in a group of patients with a damaged ocular surface.

The biology of Acanthamoeba keratitis

Acanthamoeba keratitis (AK) is a rare protozoal infection of the cornea. At least eight species of Acanthamoeba are known to cause this sight-threatening disease of the ocular surface. Acanthamoeba spp. exist in a wide array of niches ranging from thermal springs to under ice and every conceivable habitat in between. Contact lens wear is the leading risk factor for AK and is practiced by over 30 million individuals in the United States, yet the incidence of AK is less than 33 cases per one million contact lens wearers. Serological studies have reported that 90%-100% of individuals with no history of AK possess antibodies specific for Acanthamoeba antigens indicating that exposure to this organism is commonplace, yet disease is remarkably rare. Animal studies have shed light on the pathobiology and immunobiology of AK and indicate that a constellation of factors including the ocular surface microbiome and the microbiome of Acanthamoeba itself contribute to the pathogenesis of AK. Interesting, secretory antibodies produced by the adaptive immune response can prevent the initiation of corneal infection, but once Acanthamoeba trophozoites breach the corneal epithelium the adaptive immune system is helpless in altering the course of AK. It has been almost 50 years since AK was first described, yet many questions remain unanswered about this curious and enigmatic disease of the ocular surface.

Gut-educated IgA plasma cells defend the meningeal venous sinuses

The central nervous system has historically been viewed as an immune-privileged site, but recent data have shown that the meninges-the membranes that surround the brain and spinal cord-contain a diverse population of immune cells1. So far, studies have focused on macrophages and T cells, but have not included a detailed analysis of meningeal humoral immunity. Here we show that, during homeostasis, the mouse and human meninges contain IgA-secreting plasma cells. These cells are positioned adjacent to dural venous sinuses: regions of slow blood flow with fenestrations that can potentially permit blood-borne pathogens to access the brain2. Peri-sinus IgA plasma cells increased with age and following a breach of the intestinal barrier. Conversely, they were scarce in germ-free mice, but their presence was restored by gut re-colonization. B cell receptor sequencing confirmed that meningeal IgA+ cells originated in the intestine. Specific depletion of meningeal plasma cells or IgA deficiency resulted in reduced fungal entrapment in the peri-sinus region and increased spread into the brain following intravenous challenge, showing that meningeal IgA is essential for defending the central nervous system at this vulnerable venous barrier surface.