Neutrophil and T-Cell Homeostasis in the Closed Eye

Investigation of the rhythmic recruitment of tear neutrophils to the ocular surface and their phenotypes

Hundreds of thousands of polymorphonuclear neutrophils (PMNs) are collected from the ocular surface upon waking, while few are harvested during daytime. This study aimed to investigate potential factors contributing to the circadian infiltration of tear PMNs, including changes in IL-8 and C5a in tears, and their phenotypes across different time points in a 24-h cycle. Tear PMNs were collected using a gentle eyewash after 2-h and 7-h of sleep (eye closure, EC) at night, after 2-h EC during the day, and towards the end of the afternoon. Significantly fewer cells were collected after 2-h EC during the day compared to 2-h EC at night. A positive correlation between IL-8 and PMN numbers existed, but not with C5a. Tear PMNs collected after 2-h EC at night were less degranulated and possessed a larger activation potential compared to 7-h EC. Tear PMNs from 7-h EC at night exhibited hyper-segmented nuclei and more NETosis compared to 2 h EC night, indicating an aged and activated phenotype. The diurnal-nocturnal recruitment pattern of tear PMNs may be driven by increased IL-8 in nighttime tears. Higher degranulation and NETs point to the significant activation of tear PMNs on the ocular surface during prolonged eye closure at night.

Beyond host defense and tissue injury: the emerging role of neutrophils in tissue repair

Neutrophils, the most abundant immune cells in human blood, play a fundamental role in host defense against invading pathogens and tissue injury. Neutrophils carry potentially lethal weaponry to the affected site. Inadvertent and perpetual neutrophil activation could lead to nonresolving inflammation and tissue damage, a unifying mechanism of many common diseases. The prevailing view emphasizes the dichotomy of their function, host defense versus tissue damage. However, tissue injury may also persist during neutropenia, which is associated with disease severity and poor outcome. Numerous studies highlight neutrophil phenotypic heterogeneity and functional versatility, indicating that neutrophils play more complex roles than previously thought. Emerging evidence indicates that neutrophils actively orchestrate resolution of inflammation and tissue repair and facilitate return to homeostasis. Thus, neutrophils mobilize multiple mechanisms to limit the inflammatory reaction, assure debris removal, matrix remodeling, cytokine scavenging, macrophage reprogramming, and angiogenesis. In this review, we will summarize the homeostatic and tissue-reparative functions and mechanisms of neutrophils across organs. We will also discuss how the healing power of neutrophils might be harnessed to develop novel resolution and repair-promoting therapies while maintaining their defense functions.

Leger AJ, Galor A. Living with your biome: how the bacterial microbiome impacts ocular surface health and disease

Introduction

Microbiome research has grown exponentially but the ocular surface microbiome (OSM) remains an area in need of further study. This review aims to explore its complexity, disease-related microbial changes, and immune interactions, and highlights the potential for its manipulation as a therapeutic for ocular surface diseases.

Areas Covered

We introduce the OSM by location and describe what constitutes a normal OSM. Second, we highlight aspects of the ocular immune system and discuss potential immune microbiome interactions in health and disease. Finally, we highlight how microbiome manipulation may have therapeutic potential for ocular surface diseases.

Expert Opinion

The ocular surface microbiome varies across its different regions, with a core phyla identified, but with genus variability. A few studies have linked microbiome composition to diseases like dry eye but more research is needed, including examining microbiome interactions with the host. Studies have noted that manipulating the microbiome may impact disease presentation. As such, microbiome manipulation via diet, oral and topical pre and probiotics, and hygienic measures may provide new therapeutic algorithms in ocular surface diseases.

Unveiling the Web: Exploring the Multifaceted Role of Neutrophil Extracellular Traps in Ocular Health and Disease

Neutrophil extracellular traps (NETs) play an essential role in antimicrobial defense. However, NETs have also been shown to promote and mediate a wide spectrum of diseases, including cancer, diabetes mellitus, cardiovascular diseases, and ocular diseases. Data regarding NETs in ocular diseases remain limited. In physiological conditions, NETs protect the eye from debris and cleave proinflammatory cytokines, including several interleukins. On the other hand, NETs play a role in corneal diseases, such as dry eye disease and ocular graft-versus-host disease, where they promote acinar atrophy and delayed wound healing. Additionally, NET levels positively correlate with increased severity of uveitis. NETs have also been described in the context of diabetic retinopathy. Although increased NET biomarkers are associated with an increased risk of the disease, NETs also assist in the elimination of pathological blood vessels and the regeneration of normal vessels. Targeting NET pathways for the treatment of ocular diseases has shown promising outcomes; however, more studies are still needed in this regard. In this article, we summarize the literature on the protective roles of NETs in the eye. Then, we describe their pathogenetic effects in ocular diseases, including those of the cornea, uvea, and retinal blood vessels. Finally, we describe the therapeutic implications of targeting NETs in such conditions.

Persistent Neutrophil Infiltration and Unique Ocular Surface Microbiome Typify Dupilumab-Associated Conjunctivitis in Patients with Atopic Dermatitis

Objective

To elucidate the pathogenesis of dupilumab (Dupixent®)-associated ocular surface disease (DAOSD).

Design

Prospective single-center cohort study.

Subjects

Twenty patients with moderate-to-severe atopic dermatitis (AD) who received dupilumab and 10 age- and sex-matched healthy controls were enrolled in the study.

Methods

The study cohort underwent a thorough slit-lamp and entire-body dermatologic examination. Conjunctival swabs and smears were collected at baseline, 4 and 16 weeks after treatment initiation, and during the conjunctivitis episode. To analyse the ocular surface microbiome, 16S ribosomal RNA sequencing was performed, smears were hematoxylin and eosin stained, and serum cytokines were measured by using a multiplex immunobead assay.

Main Outcome Measures

Composition of ocular surface microbiome and cellular component as well as serum cytokine levels.

Results

Six of the 20 patients with AD developed DAOSD after dupilumab initiation; these patients responded after a delay to treatment as quantified by Eczema Area and Severity Index and Investigator's Global Assessment score. Conjunctival smears showed massive neutrophilic infiltration and serum analysis revealed increased systemic levels of neutrophil-priming proinflammatory cytokines, in particular interleukin-1β and tumor necrosis factor α, in patients with DAOSD compared with those without it. The ocular surface microbiome of patients with DAOSD was characterized by a diverse and persistent microbial colonization, particularly by Acetobacter aceti. In contrast, microbial diversity decreased in patients with AD without DAOSD after the initiation of dupilumab treatment, especially the abundance of Staphylococcus aureus. In vitro experiments substantiated the potential role of the microbiome, showing increased growth of A. aceti and decreased growth of S. aureus in presence of dupilumab.

Conclusions

Persistent neutrophilic infiltration and a unique microbial landscape on the ocular surface associated with elevated levels of systemic proinflammatory cytokines typify DAOSD.

Financial Disclosures

Proprietary or commercial disclosure may be found after the references.

Contact lens-induced corneal parainflammation involving Ly6G+ cell infiltration requires IL-17A and γδ T cells

PURPOSE

Previously, using a murine model, we reported that contact lens (CL) wear induced corneal parainflammation involving CD11c+ cells after 24 h and Ly6G+ cells (neutrophils) after 5-6 days. Here, we investigated the role of IL-17 and γδ T cells in the CL-induced neutrophil response.

METHODS

CL-wearing C57BL/6 wild-type (WT) mice were compared to lens-wearing IL-17A/F single or double gene knock-out mice, or mice treated with UC7-13D5 monoclonal antibody to functionally deplete γδ T cells. Contralateral eyes served as no lens wear controls. Corneal Ly6G+ and γδ T cell responses were quantified as was expression of genes encoding pro-inflammatory cytokines IL-17A/F, IL-β, IL-18 and expression of IL-17A/F protein.

RESULTS

After 6 days lens wear, WT corneas showed Ly6G+ cell infiltration while remaining free of visible pathology. In contrast, lens-wearing corneas of IL-17AF (-/-), IL-17A (-/-) mice and γδ T cell-depleted mice showed little or no Ly6G+ cell infiltration. No Ly6G+ cell infiltration was detected in contralateral eye controls. Lens-wearing WT corneas also showed a significant increase in γδ T cells after 24 h that was maintained after 6 days of wear, and significantly increased cytokine gene expression after 6 days versus contralateral controls: IL-18 & IL-17A (∼3.9 fold) and IL-23 (∼6.5-fold). Increased IL-17A protein (∼4-fold) was detected after 6 days lens wear. γδ T cell-depletion abrogated these lens-induced changes in cytokine gene and protein expression.

CONCLUSION

Together, these data show that IL-17A and γδ T cells are required for Ly6G+ cell (neutrophil) infiltration of the cornea during contact lens-induced parainflammation.

Effect of Deposition and Protease Digestion on the Ex Vivo Activity of Antimicrobial Peptide-Coated Contact Lenses

A clinical study of antimicrobial contact lenses containing the cationic peptide Mel4 was conducted. The few adverse events that occurred with this lens occurred on or after 13 nights of wear. The current study examined whether the Mel4 contact lenses lost activity during wear and the mechanism of this loss. Participants wore contact lenses for up to 13 nights. Lenses were tested for their ability to reduce the adhesion of Pseudomonas aeruginosa and Staphylococcus aureus. The amount of protein and lipid extracted from lenses was measured. The ability of trypsin to affect the antimicrobial activity of Mel4-coated contact lenses was measured. Mel4-coated contact lenses lost their antimicrobial activity at six nights of wear for both bacteria. The amount of lipids (13 ± 11 vs. 21 ± 14 μg/lens at 13 nights wear) and proteins (8 ± 4 vs. 10 ± 3 mg/lens at 13 nights of wear) extracted from lenses was not different between Mel4-coated and uncoated lenses, and was not different after three nights when antimicrobial activity was maintained and thirteen nights when they had lost activity (lipid: 25 ± 17 vs. 13 ± 11, p = 0.2; protein: 8 ± 1 vs. 8 ± 4 mg/lens, p = 0.4). Trypsin digestion eliminated the antimicrobial activity of Mel4-coated lenses. In summary, Mel4-coated contact lenses lost antibacterial activity at six nights of wear, and the most likely reason was proteolytic digestion of the peptide. Future studies will design and test proteolytically stable peptide mimics as coatings for contact lenses.

Increase in the level of oral neutrophils with gingival inflammation - A population survey

Objectives

Host responses to oral inflammation include a continuous and substantive response with the influx of polymorphonuclear leukocytes (PMN). PMN, referred to as first responders, migrate rapidly from the circulatory system through the connective tissue to mitigate stimuli and localize in the saliva. This study examined the relationship between the well-established clinical indices of gingivitis and dental plaque and the PMN level.

Materials and Methods

This study enrolled adults aged 18-75 years, who provided voluntary informed consent. Oral rinse samples were collected from 159 participants to estimate the PMN levels prior to the full-mouth assessment for gingivitis and dental plaque using the respective clinical indices.

Results

The gingival index and dental plaque index scores were in the range of 0.098-2.71 and 0.73-4.78, respectively. Regardless of the age and gender, higher number of PMN was observed with higher gingival index and dental plaque index scores. Our analyses indicated a significant correlation between the oral PMN level and gingival index with a correlation coefficient of 0.66 (p < 0.0001). Similarly, the correlation between the PMN level and dental plaque index was statistically significant with a correlation coefficient of 0.57 (p < 0.0001). Regression analysis identified a significant relationship between the PMN level and clinical indices (p < 0.0005).

Conclusions

Increase in the PMN levels with increasing clinical scores (gingival and dental plaque indices) reflect the oral inflammatory burden, irrespective of age or gender. These observations warrant future studies on participants stratified by health status and research directed toward examining the effects of interventions.

Neutrophils, functions beyond host defense

Neutrophils are the most abundant, ephemeral cell type in human blood. As the first line of defense in the host immune system, neutrophils mature in the bone marrow after undergoing multiple stages of development and then are released into the peripheral blood and conduct a surveillance function. Recent advances in cutting-edge techniques such as single-cell sequencing have uncovered the complexity and plasticity of neutrophils under homeostatic and inflammatory conditions. The exploration of neutrophil heterogeneity and function under disease and homeostasis settings has revealed many unexpected roles of neutrophils beyond a phagocyte. Furthermore, neutrophils are known to actively communicate with innate and adaptive immunocytes via direct or indirect interactions, allowing the modulation of various immune cells. In this review, we will discuss the versatile identities of neutrophils that have been discovered in recent decades, as well as the interplay between neutrophils and other cells.

Diurnal Variation of Corneal Dendritic Cell Density

Purpose: To measure variation in corneal dendritic cell density, and percentage of mature to total dendritic cells, in healthy individuals during the sleep/wake cycle.Methods: Using in vivo confocal microscopy, images of the subbasal nerve plexus were captured from 19 healthy, noncontact lens wearing participants. The central cornea and inferior whorl were imaged three times (midday, before sleep, upon awakening). Dendritic cell counts from the images were categorized according to perceived maturity (immature vs mature). Dendritic cell density and percentage of mature to total cells were compared between time points.Result: The median and interquartile range (IQR) of total dendritic cell density in the central cornea was 32.0 (7.0-131.3) cells/mm² at midday, 37.1 (8.2-103.9) cells/mm² before sleep, and 19.5 (7.0-83.2) cells/mm² on awakening. Corresponding values for immature cells were 28.1 (5.8-112.5) cells/mm², 22.3 (7.4-84.0) cells/mm² and 18.0 (2.9-64.8) cells/mm², and for mature cells, 3.1 (0.0-6.6) cells/mm², 2.0 (0.8-16.8) cells/mm², and 1.6 (0.2-8.2) cells/mm². At the inferior whorl, total dendritic cell density was 38.5 (18.4-84.5) cells/mm², 34.4 (9.4-82.3) cell/mm², and 32.3 (15.2-96.1) cells/mm². Immature cell density was 32.8 (18.4-80.9) cells/mm², 34.4 (8.6-81.0) cells/mm², and 32.3 (12.6-78.5) cells/mm². Mature cell density was 1.6 (0.0-6.3) cells/mm², 1.6 (0.0-3.1) cells/mm², and 1.8 (0.0-6.3) cells/mm². There was no significant difference between time points for total cell density (p > 0.05), but the percentage of mature cells upon awakening was significantly greater, compared to midday, at the central cornea (p = 0.02).Conclusion: In healthy individuals, overall corneal dendritic cell density is reasonably constant during the sleep/wake cycle, but the relative number of mature cells tends to increase overnight.

The Role of Neutrophil Extracellular Traps in the Ocular System

Purpose: Neutrophils remain at the top of congenital and adaptive immune systems. The past 20 years witnessed a steep rise in the interest in neutrophil extracellular traps (NETs), which are a novel type of anti-pathogen mechanism coordinated with neutrophils. However, accumulating data revealed that excessive NETs in the host were associated with exacerbated inflammation, thrombosis, and autoimmunity. Increasing evidence found the participation of NETs in the pathophysiological process of many infectious and sterile diseases in the ocular system. Therefore, we discussed the role of neutrophil extracellular traps in the ocular system in this review.Methods: Articles were searched on PubMed, Embase and Web of science up to December 2021.Results: In this review, we exhibited the protective role of neutrophils patrolling the ocular surface from invading pathogens and their contribution to exacerbated inflammation and thrombogenesis in some ocular diseases. We also discussed the physiological and pathological processes of NET generation to identify novel biomarkers and therapeutic targets to interrupt immoderate NET formation and alleviate NET-induced harmful effects.Conclusions: Neutrophils and NETs are quite important for immune responses in the ocular system, while their negative effects on ocular tissue should also be emphasized, which could serve as novel biomarkers and potential therapeutic targets.

Chlorhexidine Improves Hygiene Reducing Oral Polymorphonuclear Leukocytes with Antimicrobial Effects at Distinct Microenvironments amongst Subjects Stratified by Health Status

Oral conditions such as gingivitis and oral malodor are commonly reported globally. Objective: This investigation clinically stratified subjects to healthy, malodor and gingivitis groups and enumerated oral polymorphonuclear leukocytes (PMN) as a measure of inflammation prior to and after rinsing with a chlorhexidine (CHX) mouthwash. The study also assessed clinical outcomes (dental plaque and gingival bleeding indices), malodor (halimeter scores, organoleptic and tongue coat index and microbiological parameters (anaerobic and malodor organisms of dental plaque, tongue surface and saliva) for a comprehensive assessment of the oral inflammatory burden. Methods: Consenting adults were stratified into control (n = 17), gingivitis (n = 19) and halitosis (n = 17) groups based on clinical criteria. At baseline, oral samples were examined for PMN in addition to microbiological analysis of dental plaque, saliva and tongue scrapings for anaerobic and malodor bacteria. Subjects were issued a commercially available fluoride toothpaste and a chlorhexidine mouthwash for two-week use prior to post-treatment assessments identical to baseline. Results: At baseline, PMN were lowest in the control that increased amongst the halitosis subjects, with the gingivitis group registering the highest levels (p < 0.05) with these outcomes corresponding with clinical parameters (p < 0.05). CHX use improved outcomes with a 56−61% reduction in PMN with significant differences between groups (p < 0.05). Dental plaque and bleeding indices were lower by 57−78% with oral malodor, demonstrating reductions of 33−59% (p < 0.05). Significant reductions in anaerobic and malodor organisms ranging from 78−96% and 76−94%, respectively, were noted after CHX use (p < 0.05). Conclusions: At study enrollment, PMN scores were lowest in healthy subjects, with increasing numbers amongst halitosis followed by gingivitis. Amongst all subject groups, CHX use significantly reduced oral PMN and corroborated with corresponding decreases in clinical, malodor and bacterial outcomes. Together, these results demonstrate the significant reductions in the oral inflammatory burden following CHX use.

The Differential Reactive Oxygen Species Production of Tear Neutrophils in Response to Various Stimuli In Vitro

A large number of polymorphonuclear neutrophils (PMNs) invade the ocular surface during prolonged eye closure (sleep); these leukocytes are commonly referred as tear PMNs. PMNs contribute to homeostasis and possess an arsenal of inflammatory mediators to protect against pathogens and foreign materials. This study examined the ability of tear PMNs to generate reactive oxygen species (ROS), an essential killing mechanism for PMNs which can lead to oxidative stress and imbalance. Cells were collected after sleep from healthy participants using a gentle eye wash. ROS production in stimulated (phorbol-12-myristate-13-acetate (PMA), lipopolysaccharides (LPS) or N-Formylmethionyl-leucyl-phenylalanine (fMLP)) and unstimulated tear PMNs was measured using luminol-enhanced chemiluminescence for 60 min. A high level of constitutive/spontaneous ROS production was observed in tear PMNs in the absence of any stimulus. While tear PMNs were able to produce ROS in response to PMA, they failed to appropriately respond to LPS and fMLP, although fMLP-stimulated tear PMNs generated ROS extracellularly in the first three minutes. Higher ROS generation was observed in isolated tear PMNs which may be due to priming from the magnetic bead cell separation system. The differential responses of tear PMNs in ROS generation provide further evidence of their potential inflammatory roles in ocular complications involving oxidative stress.

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.

Does Orthokeratology Wearing Affect the Tear Quality of Children?

Orthokeratology is currently known as one of the most effective methods of myopia control in the process of rapid deterioration of the global myopia prevalence. As orthokeratology is widely used, it is necessary to evaluate its complications reasonably and accurately. Eye surface problems in children, such as dry eyes, have received increasing attention. At present, there is no conclusive evidence on how orthokeratology affects the ocular surface, especially the tears. To our knowledge, this is the first study to explore the relationship between orthokeratology lenses and tears through meta-analysis. However, it is still challenging to get a convincing conclusion and a higher level of evidence in this meta-analysis. Reasons for this include limitation of study design, lack of clarity on important confounding factors, lack of appropriate statistical tools, and other biases. This paper will analyze the dilemma existing in the current research from different perspectives to provide meaningful information for future studies in this field.

Investigation of the response of tear-film neutrophils to interleukin 8 and their sensitivity to centrifugation, fixation, and incubation

During eye closure, a large number of neutrophils (polymorphonuclear neutrophils, PMNs) invade the ocular surface and are often referred to as tear-film PMNs. While immunophenotyping experiments have been performed on tear-film PMNs, the impact of commonly used experimental procedures on their phenotype as well as their response to interleukin-8 (IL-8), a physiological inflammatory mediator, have not yet been investigated. A gentle eye wash method was used to collect cells at home. In the morning upon awaking, participants washed their eyes with sterile phosphate buffer saline (PBS) and collected the runoff into a sterile polypropylene tube. The cell collection was then delivered to the lab within two hours. The effects of centrifugation, incubation and fixation with paraformaldehyde (PFA) before (pre-fixed staining) or after (post-fixed staining) incubation with antibodies were characterized. Tear-film PMNs as well as blood PMNs (used for comparison) were also stimulated with IL-8. To assess the reproducibility of cell collection and variability in receptor expression over time, participants were also asked to collect cells three times over a period of a month. The change in expression of surface receptors, CD11b, CD16, CD55, CD66b, important inflammatory and activation markers, and CD45 (PAN leukocyte marker) was assessed by flow cytometry. Fixing tear-film PMNs prior to the staining with antibodies resulted in a significant (fivefold or more) reduction in the expression of CD11b, CD16 and CD45 when compared to unfixed samples, while CD16 was the only receptor to undergo significant downregulation upon post-staining fixation. Furthermore, additional centrifugation step prior to antibody incubation as well as long (4 h) incubation at 37 °C resulted in significant reductions in expression of CD11b, CD16 and CD55 when compared to control samples. As opposed to blood PMNs, stimulating tear-film PMNs with IL-8 did not induce any significant changes in expression of CD11b, CD16, CD55 and CD66b. When working with collected tear-film PMNs, our results suggest that any additional centrifugation and incubation step should be avoided, or at least limited, and post fixation staining is recommended in order to preserve cell phenotype and cell integrity of tear film PMNs. Our study also adds further information on the reproducibility of the gentle eye wash as well as the inability of tear-film PMNs to modulate their surface receptors upon stimulation with IL-8. The latter may be due to prior exposure to IL-8, activation in the closed-eye environment, or a reduced ability to respond to inflammatory stimulus. Further mechanistic studies will be needed to gain a better understanding of the tear-film neutrophil phenotype.

The closed eye harbours a unique microbiome in dry eye disease

Dry eye affects millions of individuals. In experimental models, dry eye disease is associated with T helper cell 17-mediated inflammation of the ocular surface that may cause persistent damage to the corneal epithelium. However, the initiating and perpetuating factors associated with chronic inflammation of the ocular surface remain unclear. The ocular microbiota alters ocular surface inflammation and may influence dry eye disease development and progression. Here, we collected serial samples of tears on awakening from sleep, closed eye tears, during a randomized clinical trial of a non-pharmaceutical dry eye therapy and used 16S rRNA metabarcoding to characterize the microbiome. We show the closed dry eye microbiome is distinct from the healthy closed eye microbiome, and that the microbiome remains distinct despite daily saline eye wash upon awakening. The ocular microbiome was described only recently, and this report implicates a distinct microbiome in ocular disease development. Our findings suggest an interplay between microbial commensals and inflammation on the ocular surface. This information may inform future studies of the pathophysiological mechanisms of dry eye disease.

Identification of Leukocytes Associated With Midday Fogging in the Post-Lens Tear Film of Scleral Contact Lens Wearers

Purpose

Midday fogging is a frequent complaint among scleral contact lens (ScCL) wearers, and the mechanism and cause of this is unknown. The purpose of this investigation was to understand the relation between midday fogging, ocular surface leukocytes, and ScCL fitting characteristics.

Methods

Subjects arrived at a clinical exam having worn ScCLs for at least 4 hours. ScCL were removed, and 150 μL of phosphate-buffered saline (PBS) was used to wash the bowl of the ScCL. Eyes were washed post-ScCL removal with 5 mL PBS per eye. Wash solutions were collected and leukocytes were then isolated and counted, followed by assessment with flow cytometry. Samples from the post-lens tear fluid were stained with fluorescently labeled antibodies to detect leukocyte distributions.

Results

Thirty-nine eyes from 19 adapted, full-time, ScCL wearers were included, and 46% presented with midday fogging. ScCL corneal clearance was 246 ± 61 μm for nonfoggers, while it was 308 ± 98 μm for those with fogging (P < 0.05). On average, the number of leukocytes collected from the ScCL bowl (9551 ± 18,926) was greater than the number of leukocytes recovered from the eye wash (2195 ± 4384, P < 0.02). ScCL corneal clearance was associated with the presence of fogging, with an odds ratio of 2.24 (95% confidence interval = 1.48–3.38, P < 0.001).

Conclusions

Leukocytes, predominated by neutrophils, are present in the post-lens tear film of ScCL wearers, and in particular wearers with greater ScCL corneal clearance have greater odds of having midday fogging.

Frontline Science: Aggregated neutrophil extracellular traps prevent inflammation on the neutrophil-rich ocular surface

Eye rheum is a physiological discharge, which accumulates at the medial angle of the healthy eye soon after opening in the morning. Microscopic evaluation of eye rheum revealed the presence of viable neutrophils, bacteria, epithelial cells, and particles, aggregated by neutrophil extracellular traps. We observed that in the evening, during eye closure, high C5a recruited neutrophils to the tear film and activated them. In this hypoxic area rich in CO₂ , neutrophils fight microbial aggressors by degranulation. Immediately after eye opening, the microenvironment of the ocular surface changes, the milieu gets normoxic, and loss of CO₂ induces subtle alkalinization of tear film. These conditions favored the formation of neutrophil extracellular traps (NETs) that initially covers the ocular surface and tend to aggregate by eyelid blinking. These aggregated neutrophil extracellular traps (aggNETs) are known as eye rheum and contain several viable neutrophils, epithelial cells, dust particles, and crystals packed together by NETs. Similar to aggNETs induced by monosodium urate crystals, the eye rheum shows a robust proteolytic activity that degraded inflammatory mediators before clinically overt inflammation occur. Finally, the eye rheum passively floats with the tear flow to the medial angle of the eye for disposal. We conclude that the aggNETs-based eye rheum promotes cleaning of the ocular surface and ameliorates the inflammation on the neutrophil-rich ocular surfaces.

The Neutrophil’s Role During Health and Disease

Neutrophils have always been considered as uncomplicated front-line troopers of the innate immune system equipped with limited proinflammatory duties. Yet recently, the role of the neutrophil has been undergoing a rejuvenation of sorts. Neutrophils are now considered complex cells capable of a significant array of specialized functions, and as an effector of the innate immune response, they are able to regulate many processes such as acute injury and repair, cancer, autoimmunity, and chronic inflammatory processes. Furthermore, evidence exists to indicate that neutrophils also contribute to adaptive immunity by aiding the development of specific adaptive immune responses or guiding the subsequent adaptive immune response. With this revived interest in neutrophils and their many novel functions, it is prudent to review what is currently known about neutrophils and, even more importantly, understand what information is lacking. We discuss the essential features of the neutrophil, from its origins, lifespan, subsets, margination and sequestration of the neutrophil to the death of the neutrophil. We highlight neutrophil recruitment to both infected and injured tissues and outline differences in recruitment of neutrophils between different tissues. Finally, we examine how neutrophils use different mechanisms to either bolster protective immune responses or negatively cause pathological outcomes at different locations.

Imaging the neutrophil: Intravital microscopy provides a dynamic view of neutrophil functions in host immunity

Neutrophils are the first cellular responders of the immune system. They employ their impressive arsenal of microbicidal molecules to provide rapid and efficient defense against pathogens. However, the role of neutrophils extends far beyond microbial destruction to include tissue repair and remodeling, provision of signals to the adaptive immune system and body homeostasis. Intravital imaging has allowed the visualization of neutrophils in their native environment in both health and disease and provided crucial insights into their mechanisms of action. In the last few years the power of intravital imaging has been considerably extended by the introduction of photoconvertible proteins and intracellular signaling reporter mice. This review will highlight recent advances in our understanding of neutrophil biology based on the use of intravital microscopy to visualize their modus operandi in vivo including migration in and out of inflamed tissues, host-pathogen interactions and cell fate.

Marked infiltration of neutrophils at the upper palpebral conjunctiva in patients with chronic graft-versus-host disease

PURPOSE

Neutrophils may be involved in the local pathophysiology of chronic graft-versus-host disease (cGVHD). We evaluated neutrophil infiltration in cGVHD using conjunctival impression cytology (IC) and its clinical correlation with ocular surface status and neutrophil enzyme levels in tears.

METHODS

This cross-sectional observational study included 76 patients with cGVHD. The ocular surface was assessed for the tear break-up time, Schirmer I test, corneal and conjunctival staining score, meiboscore, and the ocular surface disease index questionnaire. Conjunctival IC was performed at the temporal, superior bulbar, and upper palpebral conjunctiva, and the number of neutrophils (cells/high power field [HPF]) was calculated. Neutrophil elastase (NE), myeloperoxidase (MPO), and matrix metalloperoxidase-8 and -9 levels in tear washes were measured in 20 patients.

RESULTS

The number of neutrophils was significantly greater at the upper palpebral conjunctiva (median [range], 16.5 [0 to 147] cells/HPF) than at the temporal and superior bulbar conjunctiva (0 [0 to 70] and 0 [0 to 105] cells/HPF; P < 0.0001). The number of neutrophils at the upper palpebral conjunctiva showed moderate correlations with the corneal staining score and the NE and MPO levels in tears (r = 0.668, 0.553, and 0.563, respectively; P < 0.0001, P = 0.014, and 0.012).

CONCLUSIONS

Our results suggest that neutrophils at the upper palpebral conjunctiva associate with the clinical manifestations and inflammatory status of the ocular surface in cGVHD. Conjunctival neutrophils should be addressed when assessing the inflammatory activity of ocular cGVHD and exploring its pathogenesis.

Leukocyte Distribution in the Open Eye Tears of Normal and Dry Eye Subjects

PURPOSE

Leukocytes accumulate in the eye with sleep, but little is known about the presence or absence of leukocytes in awake, open eye tears. This study sought to compare normal and dry eye subjects for daily variation in open eye leukocyte composition.

MATERIALS AND METHODS

Ten normal subjects and nine dry eye subjects were enrolled. Subjects were trained for self-collection of tear samples using an ocular surface wash with 5 mL of phosphate buffered saline per eye. Subjects performed washes at awakening, between 8 and 9 am, between 11 am and 12 pm, and between 4 pm and 5 pm on four separate days. Leukocytes were isolated from the wash and were counted with a cell counter before staining with an anti-CD45 antibody and viability stain. Stained leukocytes were then analyzed via flow cytometry. Side scatter characteristics were used to distinguish granulocytes from lymphocytes. Results were interpreted both by time of wash as well as time from awakening.

RESULTS

At awakening, dry eye subjects had approximately twice as many recovered leukocytes and had a statistically significantly higher granulocyte-to-lymphocyte ratio as compared to normals. Leukocytes were rapidly cleared from the eye with a significant decrease in leukocyte counts at the 8 am time point as compared to awakening. Leukocyte counts across all open eye time points appeared to be consistent, with no differences between normal and dry eye subjects.

CONCLUSIONS

There is a low level, constitutively expressed population of leukocytes in the open eye tears of normal and dry eye subjects. Higher levels of granulocytes in dry eye disease subjects warrants further investigation into this population of cells, and their role in homeostasis and dysregulation.

The enigmatic neutrophil: what we do not know

The neutrophil appears to be undergoing a renaissance of sorts. While it was for many years thought to be a killing machine brought into tissues to eradicate pathogens, it is now being implicated in many other processes, ranging from acute injury and repair, chronic inflammatory processes, cancer and auto-immunity. Not only is it an effector of the innate immune response, it appears to also potentially contribute to adaptive immunity, implicated in either contributing to the development of specific adaptive immune responses or perhaps even instructing and directing certain adaptive immune responses. With this renewed interest in the neutrophil and its numerous new functions, it is worth examining not what we know but rather what we do not know and what still needs to be more thoroughly examined. In this review, consideration is given to such topics as neutrophil subtypes, neutrophil differentiation, neutrophil as a director of immunity, neutrophil residency and ultimately death of the neutrophil.