T Cell-Derived Granulocyte-Macrophage Colony-Stimulating Factor Contributes to Dry Eye Disease Pathogenesis by Promoting CD11b+ Myeloid Cell Maturation and Migration

Substance P and neurokinin 1 receptor boost the pathogenicity of granulocyte-macrophage colony-stimulating factor-producing T helper cells in dry eye disease

Dry eye disease (DED) is an inflammatory disorder in which CD4+ T cells play a significant role in its pathogenesis. A CD4+ T cell subset termed granulocyte-macrophage colony-stimulating factor-producing T helper (ThGM) cells would contribute to DED pathogenesis. However, the mechanisms by which the activity of ThGM cells is modulated are not thoroughly understood. In this research, we characterized the effects of neurokinin 1 receptor (NK1R) and neurokinin 2 receptor (NK2R) on ThGM cells and T helper 1 (Th1) cells in a murine DED model. We found that ThGM cells expressed NK1R and NK2R, whereas Th1 cells predominantly expressed NK1R. Furthermore, substance P and neurokinin A (NKA), the ligands of NK1R and NK2R, were upregulated in post-DED LNs and conjunctivae. Substance P significantly promoted granulocyte-macrophage colony-stimulating factor (GM-CSF) expression while mildly upregulating the expression of interferon-gamma (IFN-γ) and interleukin 2 (IL-2) in ThGM cells. By contrast, NKA did not change GM-CSF expression but significantly increased IFN-γ expression in ThGM cells. Importantly, the adoptive transfer of NK1R-expressing ThGM cells significantly exacerbated DED, whereas the transfer of NK1R-knockdown ThGM cells weakly aggravated DED. NK2R knockdown in ThGM cells did not affect DED progression. In conclusion, this study identifies the substance P-NK1R axis as a novel mechanism that reinforces the pathogenicity of ThGM cells in DED.

Profiling migration of human monocytes in response to chemotactic and barotactic guidance cues

Monocytes are critical to innate immunity, participating in chemotaxis during tissue injury, infection, and inflammatory conditions. However, the migration dynamics of human monocytes under different guidance cues are not well characterized. Here, we developed a microfluidic device to profile the migration characteristics of human monocytes under chemotactic and barotactic guidance cues while also assessing the effects of age and cytokine stimulation. Human monocytes preferentially migrated toward the CCL2 gradient through confined microchannels, regardless of donor age and migration pathway. Stimulation with interferon (IFN)-γ, but not granulocyte-macrophage colony-stimulating factor (GM-CSF), disrupted monocyte navigation through complex paths and decreased monocyte CCL2 chemotaxis, velocity, and CCR2 expression. Additionally, monocytes exhibited a bias toward low-hydraulic-resistance pathways in asymmetric environments, which remained consistent across donor ages, cytokine stimulation, and chemoattractants. This microfluidic system provides insights into the unique migratory behaviors of human monocytes and is a valuable tool for studying peripheral immune cell migration in health and disease.

AS101 regulates the Teff/Treg balance to alleviate rabbit autoimmune dacryoadenitis through modulating NFATc2

Sjögren's syndrome (SS) dry eye can cause ocular surface inflammation and lacrimal gland (LG) damage, leading to discomfort and potential vision problems. The existing treatment options for SS dry eye are currently constrained. We investigated the possible therapeutic effect and the underlying mechanism of AS101 in autoimmune dry eye. AS101 was injected subconjunctivally into a rabbit model of autoimmune dacryoadenitis and its therapeutic effects were determined by evaluating clinical and histological scores. The expressions of effector T cells (Teff)/regulatory T cells (Treg)-related transcription factors and cytokines, inflammation mediators, and transcription factor NFATc2 were measured by quantitative real-time PCR and/or Western blot both in vivo and in vitro. Additionally, the role of NFATc2 in the immunomodulatory effects of AS101 on T cells was explored by co-culturing activated peripheral blood lymphocytes (PBLs) transfected with NFATc2 overexpression lentiviral plasmid with AS101. AS101 treatment potently ameliorated the clinical severity and reduced the inflammation of LG. Further investigation revealed that AS101 treatment led to decreased expression of Th1-related genes (T-bet and IFN-γ) and Th17-related genes (RORC, IL-17A, IL-17F, and GM-CSF) and increased expression of Treg-related gene Foxp3 in vivo and in vitro. Meanwhile, AS101 suppressed the expression of TNF-α, IL-1β, IL-23, IL-6, MMP-2, and MMP-9. Mechanistically, AS101 downregulated the expression of NFATc2 in inflamed LGs. Overexpression of NFATc2 in activated PBLs partially blunted the effect of AS101 on Teff suppression and Treg promotion. In conclusion, AS101 is a potential regulator of Teff/Treg cell balance and could be an effective treatment agent for SS dry eye.

Clinical Characteristics and Tear Film Biomarkers in Patients With Chronic Dry Eye Disease After Femtosecond Laser-Assisted Laser in Situ Keratomileusis

PURPOSE

To investigate clinical characteristics and tear film biomarkers of patients with chronic dry eye disease (DED) following femtosecond laser-assisted laser in situ keratomileusis (FS-LASIK).

METHODS

Patients were divided into the chronic DED after FS-LASIK (n = 36), DED without FS-LASIK (n = 39), and normal control (without FS-LASIK; n = 34) groups. Dry eye, pain, and psychological-related symptoms were evaluated using the Ocular Surface Disease Index (OSDI), Numerical Rating Scale (NRS), Neuropathic Pain Symptom Inventory Modified for the Eye (NPSI-Eye), and Hamilton Anxiety Rating Scale (HAMA) questionnaires. Ocular surface parameters, tear cytokines, and neuropeptide concentrations were evaluated with specific tests.

RESULTS

The DED after FS-LASIK group showed higher corneal fluorescein staining scores, but lower OSDI and NPSI-Eye scores than the DED without FS-LASIK group (all P < .05). Corneal sensitivity and nerve density decreased in the DED after FS-LASIK group (all P < .01). Granulocyte-macrophage colony-stimulating factor (GM-CSF), interleukin (IL)-17A, IL-23, alpha-melanocyte stimulating hormone (α-MSH), oxytocin, and substance P levels were highest in the DED after FS-LASIK group, followed by the DED without FS-LASIK and normal control groups (all P < .05). Interferon-γ and neurotensin levels were only significantly higher in the DED after FS-LASIK group (all P < .05).

CONCLUSIONS

Patients with chronic DED after FS-LASIK showed milder ocular symptoms, greater epithelial damage, and higher levels of tear inflammatory cytokines and neuropeptides than patients with DED without FS-LASIK, indicating that the nervous and immune systems may play significant roles in FS-LASIK-related chronic DED development. [J Refract Surg. 2023;39(8):556-563.].

Extending the use of biologics to mucous membranes by attachment of a binding domain

Biologics are almost exclusively administered systemically, but localized delivery is preferable as it minimizes off-target exposure and allows more aggressive treatments. Topical application of biologics to epithelia is generally ineffective because most are covered with fluids and biologics are washed out too quickly to have significant therapeutic effects. Here we explore the idea that attaching a binding domain can serve as an "anchor" to extend the residency time of biologics on wet epithelia, allowing their effective use even with infrequent applications. We use topical application to the ocular surface as a challenging test since foreign substances are washed out especially efficiently by tear flow and blinking. Our results demonstrate that conjugation of antibodies to wheat germ agglutinin, which binds GlcNAc and sialic acid that are ubiquitously present in tissues, increases their half-life 350-fold upon application to the ocular surface in a mouse model of dry eye, a common and onerous disease in humans. Importantly, antibodies to IL-17A, IL-23, and IL-1β conjugated to the agglutinin reduces manifestations of dry eye, even when applied just once daily. In contrast, unconjugated antibodies are ineffective. Attaching an anchor to biologics is a simple means to overcome washout and to extend their therapeutic use.

The Future of Targeted Treatment of Primary Sjögren's Syndrome: A Focus on Extra-Glandular Pathology

Primary Sjögren's syndrome (pSS) is a chronic, systemic autoimmune disease defined by exocrine gland hypofunction resulting in dry eyes and dry mouth. Despite increasing interest in biological therapies for pSS, achieving FDA-approval has been challenging due to numerous complications in the trials. The current literature lacks insight into a molecular-target-based approach to the development of biological therapies. This review focuses on novel research in newly defined drug targets and the latest clinical trials for pSS treatment. A literature search was conducted on ClinicalTrials.gov using the search term "Primary Sjögren's syndrome". Articles published in English between 2000 and 2021 were included. Our findings revealed potential targets for pSS treatment in clinical trials and the most recent advances in understanding the molecular mechanisms underlying the pathogenesis of pSS. A prominent gap in current trials is in overlooking the treatment of extraglandular symptoms such as fatigue, depression, and anxiety, which are present in most patients with pSS. Based on dryness and these symptom-directed therapies, emerging biological agents targeting inflammatory cytokines, signal pathways, and immune reaction have been studied and their efficacy and safety have been proven. Novel therapies may complement existing non-pharmacological methods of alleviating symptoms of pSS. Better grading systems that add extraglandular symptoms to gauge disease activity and severity should be created. The future of pSS therapies may lie in gene, stem-cell, and tissue-engineering therapies.

Change in Ocular Surface Staining during Eyelid Warming Is Related to Tear Cytokine Levels

Purpose

To investigate the changes in the tear cytokine profile of patients with meibomian gland dysfunction (MGD) treated with eyelid warming and to correlate these changes with clinical parameters for dry eye disease (DED).

Methods

Seventy patients with MGD were included and treated with the warming of eyelids. Of these, 61 still used the treatment three months after baseline, while 48 completed the whole treatment period of six months. The concentrations of 39 cytokines in the tear fluid were measured at baseline and after three and six months of treatment. All participants were examined with tests for DED, including tear film break-up time (TBUT), ocular surface staining (OSS), and the self-reporting Ocular Surface Disease Index (OSDI). Changes in cytokine concentrations were assessed from baseline to three months, from three to six months, and from baseline to six months. Correlation analyses were performed between changes in the cytokine concentrations and changes in TBUT, OSS, and OSDI during the same time intervals.

Results

No significant changes were found in the concentrations of the 39 cytokines during any of the three treatment intervals. However, several correlations were detected between changes in the level of cytokines and OSS from baseline to three months of treatment. Decreasing concentrations of granulocyte chemotactic protein 2 (GCP-2/CXCL6, mean effect 2.36, p=0.042), interleukin 10 (IL-10, mean effect 1.04, p=0.045), and IL-16 (mean effect 1.36, p=0.035) were associated with decreasing OSS. Decreasing concentrations of granulocyte macrophage colony-stimulating factor (GM-CSF, mean effect −2.98, p=0.024), IL-8 (IL-8/CXCL8, mean effect −1.35, p=0.026), and macrophage migration inhibitory factor (MIF, mean effect −2.44, p=0.033) were related to increasing OSS.

Conclusions

Warming of eyelids did not change the concentration of cytokines in the tear fluid of patients with MGD significantly. However, alterations in the level of several cytokines were associated with changes in the OSS. This finding indicates a close connection between tear cytokines and OSS in MGD patients treated with eyelid warming.

Porcine Corneas Incubated at Low Humidity Present Characteristic Features Found in Dry Eye Disease

Dry eye is a multifactorial disease that affects the ocular surface and tear fluid. Current treatment options include lubricant eye drop application several times a day. However, these eye drops often cause local side effects like ocular allergies or blurred vision after the application. To test new treatment options, a robust dry eye model is needed. Here, a porcine ex vivo model was established by means of incubation of porcine corneas in low humidity (LH) and characterized by histological damage evaluation, epithelial thickness and by relevant dry eye markers, such as interleukin 1 beta (IL-1β), nuclear factor kappa-light-chain-enhancer of activated B cells (NF-κB), occludin and galectin-3. In the dry eye model proposed, an increased secretion of IL-1β was observed, as well as an upregulation of NF-κB, occludin and galectin-3 mRNA expression. Moreover, the model presented a higher rate of cell death in comparison to the controls. These effects could be reversed with successful treatment of dexamethasone (dexa) and partially reversed with hyaluronic acid (HA) containing eye drops. Furthermore, medium-molecular-weight HA stimulated an increase in IL-1β in the model proposed. In conclusion, this dry eye model mimics the in vivo condition and hence allows for animal-free testing of novel dry eye treatments.

Single-cell transcriptional profiling of murine conjunctival immune cells reveals distinct populations expressing homeostatic and regulatory genes

Immune cells in the exposed conjunctiva mucosa defend against environmental and microbial stresses. Expression profiling by single-cell RNA sequencing was performed to identify conjunctival immune cell populations expressing homeostatic and regulatory genes. Fourteen distinct clusters were identified, including myeloid cells (neutrophils, monocytes, macrophages), dendritic cells (DC), and lymphoid cells (B, T, γδT, ILC2, and NK) lineages. Novel neutrophil [lipocalin (Lcn2) high and low), and MHCII^lo macrophage (MP) clusters were identified. More than half of the cells map to myeloid and dendritic cell populations with differential expression profiles that include genes with homeostatic and regulatory functions: Serpinb2 (MHCII^lo macrophage), Apoe (monocyte), Cd209a (macrophage), Cst3 (cDC1), and IL4i1 in migratory DC (mDC). ILC2 expresses the goblet cell trophic factor IL-13. Suppressed inflammatory and activated anti-inflammatory/regulatory pathways were observed in certain myeloid and DC populations. Confocal immunolocalization of identity markers showed mDC (CCR7, FASCIN1) located on or within the conjunctival epithelium. Monocyte, macrophage, cDC1 and IL-13/IL-5⁺ ILC2 were located below the conjunctival epithelium and goblet cells. This study found distinct immune cell populations in the conjunctiva and identified cells expressing genes with known homeostatic and immunoregulatory functions.

Is dry eye disease the same in young and old patients? A narrative review of the literature

Advanced age is one of the most evident risk factors for dry eye disease (DED), with male/female sex, chronic drug consumption, and prolonged device use. This article aims to review the literature about the changes of the ocular surface associated with DED in the elderly and patients < 40 years. The pathophysiologic changes of the ocular surface responsible for eye dryness are linked with inflammation and neurosensory abnormalities and may occur with a different feature in young patients compared with elders. Peculiar treatment strategies may be needed for young and older subjects with DED.

Erxian Decoction modulates Th17/Treg cells differentiation through LFA-1/ICAM-1/STAT3 pathway in menopausal dry eye disease

With the development of modern societies and the ageing of the population, the treatment of menopausal dry eye disease (MDED) has become a thorny issue for the medical profession. Erxian Decoction (EXD) is a traditional Chinese medicine prescription, which has performed good clinical effect on dry eye disease. In this research, we purposed to investigate the molecular mechanisms of EXD for the treatment of MDED. A MDED rat model was established, the results indicated that high concentration of EXD could significantly improve the tear secretion and tear film stability of the animal model. Next, we found that EXD worked through the LFA-1/ICAM-1/STAT3 pathway in the body, and EXD could regulate IL-17, IL-10, CTLA-4 and TGF-β1 to get Th17/Treg balance. In vitro experiments, the results indicated that EXD affected the differentiation of CD4⁺ T cells into Th17/Treg cells by inhibiting the expression and activation of LFA-1 on CD4⁺ T cells, thus exerting immunotherapy effect. Our research provided the experimental basis and associated mechanisms for the clinical application of EXD in dry eye disease.

Therapeutic Potential of „Derived-Multiple Allogeneic Proteins Paracrine Signaling-D-Mapps” in the Treatment of Dry Eye Disease

Dry eye disease (DED) is a chronic inflammatory disease of the lacrimal system and ocular surface. Considering the important role of inflammation in DED development, the main treatment strategy has shifted from hydration and lubrication of dry ocular surface to the immunomodulation and immunoregulationapproach that should address the main pathologic processes responsible for disease progression. Due to their capacity for production of immunosuppressive factors, mesenchymal stem cells (MSCs) and their secretome have been considered as potentially new agents in DED therapy. We recently developed an immunomodulatory ophthalmic solution “derived- Multiple Allogeneic Proteins Paracrine Signaling (d-MAPPS)” which activity is relied on immunosuppressive capacity of MSC-derived secretome. d-MAPPS contains MSC-derived exosomes, growth factors and immunosuppressive cytokines that are able to efficiently suppress generation of inflammatory phenotype in T cells and macrophages. Herewith, we demonstrated that d-MAPPS protected human corneal epithelial cells from chemical injury and efficiently alleviated ocular discomfort and pain in 131 DED patients during the 12-month follow-up, indicating d-MAPPS eye drops as potentially new remedy for the treatment of DED patients.

Autoimmunity in dry eye disease - An updated review of evidence on effector and memory Th17 cells in disease pathogenicity

The classic Th1/Th2 dogma has been significantly reshaped since the subsequent introduction of several new T helper cell subsets, among which the most intensively investigated during the last decade is the Th17 lineage that demonstrates critical pathogenic roles in autoimmunity and chronic inflammation - including the highly prevalent dry eye disease. In this review, we summarize current concepts of Th17-mediated disruption of ocular surface immune homeostasis that leads to autoimmune inflammatory dry eye disease, by discussing the induction, activation, differentiation, migration, and function of effector Th17 cells in disease development, highlighting the phenotypic and functional plasticity of Th17 lineage throughout the disease initiation, perpetuation and sustention. Furthermore, we emphasize the most recent advance in Th17 memory formation and function in the chronic course of dry eye disease, a major area to be better understood for facilitating the development of effective treatments in a broader field of autoimmune diseases that usually present a chronic course with recurrent episodes of flare in the target tissues or organs.

α-MSH ameliorates corneal surface dysfunction in scopolamine-induced dry eye rats and human corneal epithelial cells via enhancing EGFR expression

Dry eye (DE) is a chronic, multifactorial ocular surface disease associated with visual disturbance, tear film instability, hyperosmolarity, ocular surface inflammation and damage. Effective intervention is necessary to control this disease. In this study we topically applied α-melanocyte stimulating hormone (α-MSH) on the ocular surface of scopolamine-induced DE rats and found that it promoted tear secretion, reduced tear breakup time and fluorescein sodium staining and increased the number of conjunctival goblet cells. To investigate the mechanism, protein array was conducted, which showed that α-MSH exerted its effects via epithelial growth factor receptor (EGFR) in the JAK-STAT signaling pathway. Furthermore, in vitro experiments showed that α-MSH protected human corneal epithelial cells (hCECs) by maintaining their migration ability and viability and decreasing apoptosis. However, blockade of EGFR abolished these protective effects. Moreover, α-MSH decreased the level of autophagy in benzalkonium chloride (BAC)-stressed hCECs via EGFR. These results demonstrated that α-MSH ameliorated lesions and restored ocular surface functions by upregulating EGFR expression.

Desiccation Induced Conjunctival Monocyte Recruitment and Activation - Implications for Keratoconjunctivitis

Background

Lacrimal gland secretory dysfunction in Sjögren syndrome (SS) causes ocular surface desiccation that is associated with increased cytokine expression and number of antigen-presenting cells (APCs) in the conjunctiva. This study evaluated the hypothesis that desiccating stress (DS) alters the percentage and gene expression of myeloid cell populations in the conjunctiva.

Methods

DS was induced by pharmacologic suppression of tear secretion and exposure to drafty low humidity environment. Bone marrow chimeras and adoptive transfer of CD45.1⁺ bone marrow cells to CD45.2⁺ C-C chemokine receptor 2 knockout (CCR2^-/-) mice were used to track DS-induced myeloid cell recruitment to the conjunctiva. Flow cytometry evaluated myeloid cell populations in conjunctivae obtained from non-stressed eyes and those exposed to DS for 5 days. CD11b⁺ myeloid lineage cells were gated on monocyte (Ly6C), macrophage (CD64, MHCII) and DC (CD11c, MHCII) lineage markers. NanoString immune arrays were performed on sorted MHCII⁺ and MHCII^- monocyte/macrophage cell populations.

Results

DS significantly increased the recruitment of adoptively transferred MHCII positive and negative myeloid cells to the conjunctiva in a CCR2 dependent fashion. The percentage of resident conjunctival monocytes (Ly6C⁺CD64^-) significantly decreased while CD64⁺MHCII⁺ macrophages increased over 5 days of DS (P<0.05 for both). Comparison of gene expression between the MHCII^- monocyte and MHCII⁺ populations in non-stressed conjunctiva revealed a ≥ 2 log² fold increase in 95 genes and decrease in 46 genes. Upregulated genes are associated with antigen presentation, cytokine/chemokine, M1 macrophage and NLRP3 inflammasome pathways. DS increased innate inflammatory genes in monocytes and MHCII⁺ cells and increased M1 macrophage (Trem1, Ido1, Il12b, Stat5b) and decreased homeostasis (Mertk) and M2 macrophage (Arg1) genes in MHCII⁺ cells.

Conclusions

There are myeloid cell populations in the conjunctiva with distinct phenotype and gene expression patterns. DS recruits myeloid cells from the blood and significantly changes their phenotype in the conjunctiva. DS also alters expression of an array of innate inflammatory genes. Immature monocytes in the unstressed conjunctiva appear to cascade to MHCII⁺ macrophages during DS, suggesting that DS promotes maturation of monocytes to antigen presenting cells with increased expression of inflammatory genes that may contribute to the pathogenesis of SS keratoconjunctivitis sicca.

Therapeutic effect of secretome from TNF-α stimulated mesenchymal stem cells in an experimental model of corneal limbal stem cell deficiency

AIM

To explore the secretome efficacy in tumor necrosis factor (TNF)-α stimulated mouse mesenchymal stem cells (MSCs) in a murine model of corneal limbal alkali injury.

METHODS

Corneal limbal stem cell deficiency (LSCD) was created in the eyes of male C57 mice. Concentrated conditioned medium from TNF-α stimulated MSCs (MSC-CMT) was applied topically for 4wk, with basal medium and conditioned medium from MSCs as controls. Corneal opacification, corneal inflammatory response, and corneal neovascularization (NV) were evaluated. Corneal epithelial cell apoptosis, corneal conjunctivation, and inflammatory cell infiltration were assessed with TUNEL staining, CK3 and Muc-5AC immunostaining, and CD11b immunofluorescence staining, respectively. The effect of TSG-6 was further evaluated by knockdown with short hairpin RNA (shRNA).

RESULTS

Compared to the controls, topical administration of MSC-CMT significantly ameliorated the clinical symptoms of alkali-induced LSCD, with restrained corneal NV, reduced corneal epithelial cell apoptosis, and inhibition of corneal conjunctivation. In addition, MSC-CMT treatment significantly reduced CD11b⁺ inflammatory cell infiltration, and inhibited the expression of pro-inflammatory cytokines (IL-1β, TNF-α and IL-6). Furthermore, the promotion of corneal epithelial reconstruction by MSC-CMT was largely abolished by TSG-6 knockdown.

CONCLUSION

Our study provides evidence that MSC-CMT enhances the alleviation of corneal alkali injuries, partially through TSG-6-mediated anti-inflammatory protective mechanisms. MSC-CMT may serve as a potential strategy for treating corneal disorders.

GM-CSF in inflammation

GM-CSF is a potential therapeutic target in inflammation and autoimmunity. This study reviews the literature on the biology of GM-CSF, in particular that describing the research leading to clinical trials targeting GM-CSF and its receptor in numerous inflammatory/autoimmune conditions, such as rheumatoid arthritis.

Granulocyte–macrophage colony-stimulating factor (GM-CSF) has many more functions than its original in vitro identification as an inducer of granulocyte and macrophage development from progenitor cells. Key features of GM-CSF biology need to be defined better, such as the responding and producing cell types, its links with other mediators, its prosurvival versus activation/differentiation functions, and when it is relevant in pathology. Significant preclinical data have emerged from GM-CSF deletion/depletion approaches indicating that GM-CSF is a potential target in many inflammatory/autoimmune conditions. Clinical trials targeting GM-CSF or its receptor have shown encouraging efficacy and safety profiles, particularly in rheumatoid arthritis. This review provides an update on the above topics and current issues/questions surrounding GM-CSF biology.

The role of Th17 immunity in chronic ocular surface disorders

Th17 cells have been implicated in the pathogenesis of numerous inflammatory and autoimmune conditions. At the ocular surface, Th17 cells have been identified as key effector cells in chronic ocular surface disease. Evidence from murine studies indicates that following differentiation and expansion, Th17 cells migrate from the lymphoid tissues to the eye, where they release inflammatory cytokines including, but not limited to, their hallmark cytokine IL-17A. As the acute phase subsides, a population of long-lived memory Th17 cells persist, which predispose hosts both to chronic inflammation and severe exacerbations of disease; of great interest is the small subset of Th17/1 cells that secrete both IL-17A and IFN-γ in acute-on-chronic disease exacerbation. Over the past decade, substantial progress has been made in deciphering how Th17 cells interact with the immune and neuroimmune pathways that mediate chronic ocular surface disease. Here, we review (i) the evidence for Th17 immunity in chronic ocular surface disease, (ii) regulatory mechanisms that constrain the Th17 immune response, and (iii) novel therapeutic strategies targeting Th17 cells.

Antigen-presenting cells in ocular surface diseases

PURPOSE

To review the role of antigen-presenting cells (APC) in the pathogenesis of ocular surface diseases (OSD).

METHODS

A thorough literature search was performed in PubMed database. An additional search was made in Google Scholar to complete the collected items.

RESULTS

APCs have the ability to initiate and direct immune responses and are found in most lymphoid and non-lymphoid tissues. APCs continuously sample their environment, present antigens to T cells and co-ordinate immune tolerance and responses. Many different types of APCs have been described and there is growing evidence that these cells are involved in the pathogenesis of OSD. OSD is a complex term for a myriad of disorders that are often characterized by ocular surface inflammation, tear film instability and impairment of vision.

CONCLUSIONS

This review summarizes the current knowledge concerning the immunotopographical distribution of APCs in the normal ocular surface. APCs appear to play a critical role in the pathology of a number of conditions associated with OSD including infectious keratitis, ocular allergy, dry eye disease and pterygium.

Evaluation of Corneal Damage After Lacrimal Gland Excision in Male and Female Mice

Purpose

Lacrimal gland excision (LGE) has been utilized in several studies to model aqueous tear deficiency, yet sex as a biological variable has not been factored in to these reports. This study compared corneal pathology in male and female mice following LGE-induced dry eye.

Methods

An LGE of either the extraorbital lacrimal gland (single LGE) or both the extraorbital and intraorbital lacrimal glands (double LGE) was performed in male and female C57BL/6J and Balb/cJ mice to produce dry eye of graded severity. Following excision, tearing was evaluated with phenol red thread, and corneal fluorescein staining was scored to quantify the severity of damage. Corneas were evaluated for apoptosis by the TUNEL assay and for cell proliferation using Ki67 staining. Furthermore, corneas were harvested and analyzed for macrophages via flow cytometry.

Results

Baseline tearing levels were similar in male and female mice, and LGE resulted in comparable reductions in tearing with the lowest levels recorded after double LGE. As determined by fluorescein staining, LGE produced more severe damage to the cornea in female C57BL/6J and Balb/cJ mice. Double LGE increased TUNEL and Ki67 staining in the cornea, with greater increases found in female mice. Furthermore, LGE produced a greater increase in the total number of corneal macrophages in female mice.

Conclusions

These results indicate that female mice are more susceptible to LGE-induced corneal damage. The mechanisms involved in producing these sex differences still need to be elucidated but may involve increased inflammation and macrophage infiltration.

Dry Eye Disease: Emerging Approaches to Disease Analysis and Therapy

Dry eye disease (DED) is among the most common ocular disorders affecting tens of millions of individuals worldwide; however, the condition remains incompletely understood and treated. Valuable insights have emerged from multidisciplinary approaches, including immunometabolic analyses, microbiome analyses, and bioengineering. Furthermore, we have seen new developments in clinical assessment approaches and treatment strategies in the recent past. Here, we review the emerging frontiers in the pathobiology and clinical management of DED.

Diquafosol Sodium Inhibits Apoptosis and Inflammation of Corneal Epithelial Cells Via Activation of Erk1/2 and RSK: In Vitro and In Vivo Dry Eye Model

Purpose

To evaluate the effect of diquafosol on corneal epithelium in a dry eye model using Transwell culture and a scopolamine-induced dry eye rat model.

Methods

Desiccation stress induced in an in vitro dry eye model using human corneal epithelial cells was used, and the cells were incubated with or without diquafosol media diluted at 1:100. Reactive oxygen species (ROS) generation was measured using 2',7'-dichlorofluorescein diacetate (DCFH-DA). Apoptosis was analyzed, and levels of phosphorylated Erk1/2, phosphorylated p90RSK, phosphorylated Akt, IκB-α, and NF-κB-p65 were determined. Levels of IL-1β, TNF-α, IL-6, IL-8, and GM-CSF were quantified. To investigate the in vivo effects of diquafosol, we induced dry eye in Wistar rats using scopolamine hydrobromide. The rats were divided into three groups: control, dry eye, and dry eye diquafosol; topical DIQUAS was applied four times daily for 28 days. We used immunohistochemistry to detect the levels of phosphorylated Erk1/2, phosphorylated p90RSK, and IL-1β, and used the TUNEL assay in corneal tissue.

Results

The distribution of highly fluorescent dichlorofluorescein and the proportion of annexin V- and PI-positive cells decreased in the diquafosol medium. Diquafosol increased the levels of phospho-Erk1/2, phospho-90RSK, phospho-Akt, and IκB-α, whereas it significantly decreased the levels of NF-κB-p65, IL-1β, and TNF-α. In vivo, apoptosis was enhanced in dry eye group. This response was markedly reduced and the level of phosphorylated p90RSK and phosphorylated ERK1/2 were upregulated and IL-1β was downregulated by DIQUAS.

Conclusions

Diquafosol treatment reduced intracellular ROS levels, apoptosis, and inflammation, all of which were increased in the dry eye model through desiccation.

Activation of Dendritic Cells in Dry Eye Mouse Model

Purpose

The immune system plays a major role in the pathogenesis of dry eye diseases (DED), and dendritic cells (DCs) are known to be important initiators of acquired immunity. Thus, the purpose of this study was to determine the contribution of DCs to the development of DED.

Methods

Mouse dry eye model was induced by subcutaneous injections of scopolamine and was euthanized at the baseline, and 2, 4, and 7 days postinjection. The activation of the DCs was determined by the mixed leukocyte reaction (MLR), and the number of activated CD86+ DCs in the lymph nodes was determined by flow cytometry. Upregulation of cytokines in the culture supernatant of MLR was determined by ELISA.

Results

Significantly increased superficial corneal punctate lesions and decreased number of goblet cells in the conjunctiva were observed in scopolamine-injected mice. The number of activated CD86+ DCs was significantly increased in the cervical lymph nodes but not in the inguinal lymph nodes of the dry eye mice. The stimulatory activity of the DCs derived from the cervical lymph nodes of dry eye mice was significantly higher than that of control mice, and upregulations of IL-17, IL-2, and IL-4 were observed in the culture supernatant of MLR. These results indicate that the DCs of the cervical lymph nodes were activated by the scopolamine injections.

Conclusions

Our results indicate that DCs in our dry eye model were sufficiently activated to stimulate the T cells that participate in the onset and progression of DED.

Mast cells contribute to the induction of ocular mucosal alloimmunity

Beyond their historical role as the effector cells in allergic disorders, mast cells have been implicated in regulating both innate and adaptive immune responses. Possessing considerable functional plasticity, mast cells are abundant at mucosal surfaces, where the host and external environments interface. The purpose of this study was to evaluate the contribution of mast cells to allograft rejection at the ocular surface. Using a well-characterized murine model of corneal transplantation, we report that mast cells promote allosensitization. Our data show mast cell frequencies and activation are increased following transplantation. We demonstrate that mast cell inhibition (a) limits the infiltration of inflammatory cells and APC maturation at the graft site; (b) reduces allosensitization and the generation of Th1 cells in draining lymphoid tissues; (c) decreases graft infiltration of alloimmune-inflammatory cells; and (d) prolongs allograft survival. Our data demonstrate a novel function of mast cells in promoting allosensitization at the ocular surface.

Innate and Adaptive Cell Populations Driving Inflammation in Dry Eye Disease

Dry eye disease (DED) is the most common ocular disease and affects millions of individuals worldwide. DED encompasses a heterogeneous group of diseases that can be generally divided into two forms including aqueous-deficient and evaporative DED. Evidence suggests that these conditions arise from either failure of lacrimal gland secretion or low tear film quality. In its secondary form, DED is often associated with autoimmune diseases such as Sjögren's syndrome and rheumatoid arthritis. Current treatment strategies for DED are limited to anti-inflammatory medications that target the immune system as the source of deleterious inflammation and tissue injury. However, there is a lack of understanding of the underlying pathogenesis of DED, and subsequently, there are very few effective treatment strategies. The gap in our knowledge of the etiology of primary DED is in part because the majority of research in DED focused on secondary autoimmune causes. This review focuses on what is currently understood about the contribution of innate and adaptive immune cell populations in the pathogenesis of DED and highlights the need to continue investigating the central role of immunity driving DED.

When Clarity Is Crucial: Regulating Ocular Surface Immunity

The ocular surface is a unique mucosal immune compartment in which anatomical, physiological, and immunological features act in concert to foster a particularly tolerant microenvironment. These mechanisms are vital to the functional competence of the eye, a fact underscored by the devastating toll of excessive inflammation at the cornea - blindness. Recent data have elucidated the contributions of specific anatomical components, immune cells, and soluble immunoregulatory factors in promoting homeostasis at the ocular surface. We highlight research trends at this distinctive mucosal barrier and identify crucial gaps in our current knowledge.