Spontaneous autoimmune dacryoadenitis in aged CD25KO mice

Aged regulatory T cells fail to control autoimmune lacrimal gland pathogenic CD4+ T cells

CD25KO mice are a model of Sjögren disease. CD25KO mice have severe inflammation and infiltrating lymphocytes to the lacrimal glands (LG). Whether the pathogenicity of CD25KO CD4+ T cells can be controlled in vivo by Tregs is unknown. Eight-week-old B6 and CD25KO mice LGs were submitted for RNA bulk sequencing. A total of 3481 genes were differentially expressed in CD25KO LG compared to B6. Tear washing analysis identified CD25KO mice had elevated protein levels of TNF, IFN-γ, and CCL5 and decreased protein levels of IL-12p40 and VEGF-A. Co-adoptive transfer of CD25KO CD4+ T cells with either young or aged B6 Tregs was performed in RAG1KO mice. Recipients of CD25KO CD4+ T cells alone had higher LG inflammation than naive mice. However, in recipients of young B6 Tregs plus CD25KO CD4+ T cells, LGs had significantly reduced inflammation. Recipients of CD25KO CD4+ T cells with aged B6 Tregs had more inflamed LGs than young Tregs, suggesting aged Tregs have less suppressive capacity in vivo. Altogether, CD25KO mice have phenotypic and genetic changes resulting in increased inflammation and severe lymphocytic infiltration in the LGs. However, this autoimmunity can be controlled by the addition of young, but not aged, Tregs, suggesting that aging Tregs have dysfunctional suppression.

Ocular Surface Involvements in the Development of Sjögren's Syndrome-Associated Dry Eye in the IL14α Transgenic Mouse

Purpose

To investigate the ocular surface changes during progress of the Sjögren's Syndrome (SS), using a previously described IL14α transgenic mice (IL14α TG) SS model.

Methods

The ocular surface of IL14α TG and C57BL/6 wild-type (WT) female mice were evaluated at the age of six, nine, 12, 15, and 18 months. Slit lamp microscopy observation, Oregon green dextran staining, Schirmer test, and periodic-acid-Schiff staining were assessed. Immunohistochemistry, immunofluorescence, and associated gene expression analysis by qPCR and ELISA were performed in cornea, conjunctiva, and lacrimal grand at different ages of the mice. Masson's trichome staining was conducted on lacrimal gland cryosections.

Results

Compared with C57BL/6 WT mice, IL14α TG mice showed corneal barrier function damage and losses in conjunctival goblet cell density starting at nine months, whereas decreases in tear secretion started at 18 months of age. Significant increases in CD4+ T cell infiltration in the conjunctiva of IL14α TG mice was first observed at 6 months. Higher expression levels of inflammatory cytokines IL-17A, IFN-γ, IL-1β, and TNF-α in the conjunctiva, whereas MUC5AC and MUC5B had lower expression levels at nine months in the IL14α TG mice. However, lacrimal gland function-associated gene expression levels mostly decreased in IL14α TG mice at 12 months of age.

Conclusions

Ocular surface tissue changes were involved in SS-like dry eye in a time-dependent manner in IL14α TG mice, and conjunctival T-cell infiltration may contribute to ocular surface pathological changes in an early stage of SS-related dry eye.

Inhibition of Cathepsin S in Autoimmune CD25KO Mouse Improves Sjögren Disease-Like Lacrimal Gland Pathology

Purpose

CD25KO mice are a model of Sjögren disease (SjD) driven by autoreactive T cells. Cathepsin S (CTSS) is a protease crucial for major histocompatibility complex class II presentation that primes T cells. We investigated if a diet containing CTSS inhibitor would improve autoimmune signs in CD25KO mice.

Methods

Four-week female CD25KO mice were randomly chosen to receive chow containing a CTSS inhibitor (R05461111, 262.5 mg/kg chow) or standard chow for 4 weeks. Cornea sensitivity was measured. Inflammatory score was assessed in lacrimal gland (LG) histologic sections. Flow cytometry of LG and ocular draining lymph nodes (dLNs) investigated expression of Th1 and Th17 cells. Expression of inflammatory, T- and B-cell, and apoptotic markers in the LG were assessed with quantitative PCR. The life span of mice receiving CTSS inhibitor or standard chow was compared. CD4+ T cells from both groups were isolated from spleens and adoptively transferred into RAG1KO female recipients.

Results

Mice receiving CTSS inhibitor had better cornea sensitivity and improved LG inflammatory scores. There was a significant decrease in the frequency of CD4+ immune cells and a significant increase in the frequency of CD8+ immune cells in the dLNs of CTSS inhibitor mice. There was a significant decrease in Th1 and Th17 cells in CTSS inhibitor mice in both LGs and dLNs. Ifng, Ciita, and Casp8 mRNA in CTSS inhibitor mice decreased. Mice that received the CTSS inhibitor lived 30% longer. Adoptive transfer recipients with CTSS inhibitor-treated CD4+ T cells had improved cornea sensitivity and lower inflammation scores.

Conclusions

Inhibiting CTSS could be a potential venue for the treatment of SjD in the eye and LG.

Conditional deletion of CD25 in the corneal epithelium reveals sex differences in barrier disruption

PURPOSE

IL-2 promotes activation, clonal expansion, and deletion of T cells. IL-2 signals through its heterotrimeric receptor (IL-2R) consisting of the CD25, CD122 and CD132 chains. CD25 knockout (KO) mice develop Sjögren Syndrome-like disease. This study investigates whether corneal CD25/IL-2 signaling is critical for ocular health.

METHODS

Eyes from C57BL/6 mice were collected and prepared for immunostaining or in-situ hybridization. Bulk RNA sequencing was performed on the corneal epithelium from wild-type and CD25KO mice. We generated a conditional corneal-specific deletion of CD25 in the corneal epithelium (CD25Δ/ΔCEpi). Corneal barrier function was evaluated based on the uptake of a fluorescent dye. Mice were subjected to unilateral corneal debridement, followed by epithelial closure over time.

RESULTS

In C57BL/6 mice, CD25 mRNA was expressed in ocular tissues. Protein expression of CD25, CD122, and CD132 was confirmed in the corneal epithelium. Delayed corneal re-epithelization was seen in female but not male CD25KO mice. There were 771 differentially expressed genes in the corneal epithelium of CD25KO compared to wild-type mice. While barrier function is disrupted in CD25Δ/ΔCEpi mice, re-epithelialization rates are not delayed.

CONCLUSIONS

All three chains of the IL-2R are expressed in the corneal epithelium. Our results indicate for the first time, deleting CD25 systemically in all tissues in the mouse and deleting CD25 locally in just the corneal epithelium compromises corneal epithelial barrier function, leading to dry eye disease in female mice. Future studies are needed to delineate the pathways used by IL-2 signaling to influence cornea homeostasis.

Association of Ocular Surface Immune Cells With Dry Eye Signs and Symptoms in the Dry Eye Assessment and Management (DREAM) Study

Purpose

Dry eye disease (DED) is a multifactorial, heterogeneous disease of the ocular surface with one etiology being ocular surface inflammation. Studies using animal models demonstrate the role of ocular surface immune cells in the inflammatory pathway leading to DED, but few have evaluated humans. This study described the white blood cell population from the ocular surface of patients with DED and assessed its association with DED signs and symptoms in participants of the Dry Eye Assessment and Management (DREAM) study.

Methods

Participants were assessed for symptoms using the Ocular Surface Disease Index, signs via corneal staining, conjunctival staining, tear break-up time, and Schirmer test, and Sjögren's syndrome (SS) based on the 2012 American College of Rheumatology classification criteria. Impression cytology of conjunctival cells from each eye was evaluated using flow cytometry: T cells, helper T cells (Th), regulatory T cells (Tregs), cytotoxic T cells, and dendritic cells.

Results

We assessed 1049 eyes from 527 participants. White blood cell subtype percentages varied widely across participants. Significant positive associations were found for Th and conjunctival staining (mean score of 2.8 for 0% Th and 3.1 for >4.0% Th; P = 0.007), and corneal staining (mean score of 3.5 for 0% Th and 4.3 for >4.0% Th; P = 0.01). SS was associated with higher percent of Tregs (median 0.1 vs. 0.0; P = 0.01).

Conclusions

Th were associated with more severe conjunctival and corneal staining, possibly indicating their role in inflammation leading to damage of the ocular surface. There is no consistent conclusion about Tregs in SS, but these results support that Tregs are elevated in SS.

Oxidative Stress in the Protection and Injury of the Lacrimal Gland and the Ocular Surface: are There Perspectives for Therapeutics?

Oxidative stress (OS) is a major disruption in the physiology of the lacrimal functional unit (LFU). Antioxidant enzymes have dual protective activities: antioxidant and antimicrobial activities. Peroxidases have been indistinctly used as markers of the secretory activity of the LFU and implicated in the pathophysiology, diagnosis and treatment of dry eye disease (DED), even though they comprise a large family of enzymes that includes lactoperoxidase (LPO) and glutathione peroxidase (GPO), among others. Assays to measure and correlate OS with other local LFU phenomena have methodological limitations. Studies implicate molecules and reactions involved in OS as markers of homeostasis, and other studies identify them as part of the physiopathology of diseases. Despite these conflicting concepts and observations, it is clear that OS is influential in the development of DED. Moreover, many antioxidant strategies have been proposed for its treatment, including calorie restriction to nutritional supplementation. This review offers a critical analysis of the biological mechanisms, diagnostic outcomes, drug use, dietary supplements, and life habits that implicate the influence of OS on DED.

Immune regulation of the ocular surface

Despite constant exposure to various environmental stimuli, the ocular surface remains intact and uninflamed while maintaining the transparency of the cornea and its visual function. This 'immune privilege' of the ocular surface is not simply a result of the physical barrier function of the mucosal lining but, more importantly, is actively maintained through a variety of immunoregulatory mechanisms that prevent the disruption of immune homeostasis. In this review, we focus on essential molecular and cellular players that promote immune quiescence in steady-state conditions and suppress inflammation in disease-states. Specifically, we examine the interactions between the ocular surface and its local draining lymphoid compartment, by encompassing the corneal epithelium, corneal nerves and cornea-resident myeloid cells, conjunctival goblet cells, and regulatory T cells (Treg) in the context of ocular surface autoimmune inflammation (dry eye disease) and alloimmunity (corneal transplantation). A better understanding of the immunoregulatory mechanisms will facilitate the development of novel, targeted immunomodulatory strategies for a broad range of ocular surface inflammatory disorders.

Application of Animal Models in Interpreting Dry Eye Disease

Different pathophysiologic mechanisms are involved in the initiation, development, and outcome of dry eye disease (DED). Animal models have proven valuable and efficient in establishing ocular surface microenvironments that mimic humans, thus enabling better understanding of the pathogenesis. Several dry eye animal models, including lacrimal secretion insufficiency, evaporation, neuronal dysfunction, and environmental stress models, are related to different etiological factors. Other models may be categorized as having a multifactorial DED. In addition, there are variations in the methodological classification, including surgical lacrimal gland removal, drug-induced models, irradiation impairment, autoimmune antibody-induced models, and transgenic animals. The aforementioned models may manifest varying degrees of severity or specific pathophysiological mechanisms that contribute to the complexity of DED. This review aimed to summarize various dry eye animal models and evaluate their respective characteristics to improve our understanding of the underlying mechanism and identify therapeutic prospects for clinical purposes.

Spatial transcriptomics of the lacrimal gland features macrophage activity and epithelium metabolism as key alterations during chronic inflammation

The lacrimal gland (LG) is an exocrine gland that produces the watery part of the tear film that lubricates the ocular surface. Chronic inflammation, such as Sjögren's syndrome (SS), is one of the leading causes of aqueous-deficiency dry eye (ADDE) disease worldwide. In this study we analyzed the chronic inflammation in the LGs of the NOD.B10Sn-H2b/J (NOD.H-2b) mice, a mouse model of SS, utilizing bulk RNAseq and Visium spatial gene expression. With Seurat we performed unsupervised clustering and analyzed the spatial cell distribution and gene expression changes in all cell clusters within the LG sections. Moreover, for the first time, we analyzed and validated specific pathways defined by bulk RNAseq using Visium technology to determine activation of these pathways within the LG sections. This analysis suggests that altered metabolism and the hallmarks of inflammatory responses from both epithelial and immune cells drive inflammation. The most significant pathway enriched in upregulated DEGs was the "TYROBP Causal Network", that has not been described previously in SS. We also noted a significant decrease in lipid metabolism in the LG of the NOD.H-2b mice. Our data suggests that modulation of these pathways can provide a therapeutic strategy to treat ADDE.

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.

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.

Studying Sjögren's syndrome in mice: What is the best available model?

Sjögren's syndrome (SS) is a common autoimmune disease characterized by lymphocytic infiltration and destruction of exocrine glands. The disease manifests primarily in the salivary and lacrimal glands, but other organs are also involved, leading to dry mouth, dry eyes, and other extra-glandular manifestations. Studying the disease in humans is entailed with many limitations and restrictions; therefore, the need for a proper mouse model is mandatory. SS mouse models are categorized, depending on the disease emergence into spontaneous or experimentally manipulated models. The usefulness of each mouse model varies depending on the SS features exhibited by that model; each SS model has advanced our understanding of the disease pathogenesis. In this review article, we list all the available murine models which have been used to study SS and we comment on the characteristics exhibited by each mouse model to assist scientists to select the appropriate model for their specific studies. We also recommend a murine strain that is the most relevant to the ideal SS model, based on our experience acquired during previous and current investigations.

Ophthalmologic Manifestations of Primary Sjögren's Syndrome

Sjögren’s syndrome (SS) is a chronic, progressive, inflammatory, autoimmune disease, characterized by the lymphocyte infiltration of exocrine glands, especially the lacrimal and salivary, with their consequent destruction. The onset of primary SS (pSS) may remain misunderstood for several years. It usually presents with different types of severity, e.g., dry eye and dry mouth symptoms, due to early involvement of the lacrimal and salivary glands, which may be associated with parotid enlargement and dry eye; keratoconjunctivitis sicca (KCS) is its most common ocular manifestation. It is still doubtful if the extent ocular surface manifestations are secondary to lacrimal or meibomian gland involvement or to the targeting of corneal and conjunctival autoantigens. SS is the most representative cause of aqueous deficient dry eye, and the primary role of the inflammatory process was evidenced. Recent scientific progress in understanding the numerous factors involved in the pathogenesis of pSS was registered, but the exact mechanisms involved still need to be clarified. The unquestionable role of both the innate and adaptive immune system, participating actively in the induction and evolution of the disease, was recognized. The ocular surface inflammation is a central mechanism in pSS leading to the decrease of lacrimal secretion and keratoconjunctival alterations. However, there are controversies about whether the ocular surface involvement is a direct autoimmune target or secondary to the inflammatory process in the lacrimal gland. In this review, we aimed to present actual knowledge relative to the pathogenesis of the pSS, considering the role of innate immunity, adaptive immunity, and genetics.

T cell signaling and Treg dysfunction correlate to disease kinetics in IL-2Rα-KO autoimmune mice

IL-2Rα, in part, comprises the high affinity receptor for IL-2, a cytokine important in immune proliferation, activation, and regulation. IL-2Rα deficient mice (IL-2Rα-KO) develop systemic autoimmune disease and die from severe anemia between 18 and 80 days of age. These mice develop kinetically distinct autoimmune progression, with approximately a quarter dying by 21 days of age and half dying after 30 days. This research aims to define immune parameters and cytokine signaling that distinguish cohorts of IL-2Rα-KO mice that develop early- versus late-stage autoimmune disease. To investigate these differences, we evaluated complete blood counts (CBC), antibody binding of RBCs, T cell numbers and activation, hematopoietic progenitor changes, and signaling kinetics, during autoimmune hemolytic anemia (AIHA) and bone marrow failure. We identified several alterations that, when combined, correlate to disease kinetics. Early onset disease correlates with anti-RBC antibodies, lower hematocrit, and reduced IL-7 signaling. CD8 regulatory T cells (Tregs) have enhanced apoptosis in early disease. Further, early and late end stage disease, while largely similar, had several differences suggesting distinct mechanisms drive autoimmune disease kinetics. Therefore, IL-2Rα-KO disease pathology rates, driven by T cell signaling, promote effector T cell activation and expansion and Treg dysfunction.

Mouse Models of Sjögren's Syndrome with Ocular Surface Disease

Sjögren’s syndrome (SS) is a systemic rheumatic disease that predominantly affects salivary and lacrimal glands resulting in oral and ocular dryness, respectively, referred to as sicca symptoms. The clinical presentation of ocular dryness includes keratoconjunctivitis sicca (KCS), resulting from the inflammatory damage to the ocular surface tissues of cornea and conjunctiva. The diagnostic evaluation of KCS is a critical component of the classification criteria used by clinicians worldwide to confirm SS diagnosis. Therapeutic management of SS requires both topical and systemic treatments. Several mouse models of SS have contributed to our current understanding of immunopathologic mechanisms underlying the disease. This information also helps develop novel therapeutic interventions. Although these models address glandular aspects of SS pathology, their impact on ocular surface tissues is addressed only in a few models such as thrombospondin (TSP)-1 deficient, C57BL/6.NOD.Aec1Aec2, NOD.H2^b, NOD.Aire KO, and IL-2Rα (CD25) KO mice. While corneal and/or conjunctival damage is reported in most of these models, the characteristic SS specific autoantibodies are only reported in the TSP-1 deficient mouse model, which is also validated as a preclinical model. This review summarizes valuable insights provided by investigations on the ocular spectrum of the SS pathology in these models.

Cluster Analysis of Dry Eye Disease Models Based on Immune Cell Parameters - New Insight Into Therapeutic Perspective

Dry eye disease (DED) can be represented as a display of disease in the mucosal part of the eye. It is quite distinct from the retinal side of the eye which connects with the neurons and thus represents the neuroimmunological disease. DED can occur either by the internal damage of the T cells inside the body or by microbial infections. Here we summarize the most common animal model systems used for DED relating to immune factors. We aimed to identify the most important immune cell/cytokine among the animal models of the disease. We also show the essential immune factors which are being tested for DED treatment. In our results, both the mechanism and the treatment of its animal models indicate the involvement of Th1 cells and the pro-inflammatory cytokine (IL-1β and TNF-α) related to the Th1-cells. The study is intended to increase the knowledge of the animal models in the field of the ocular surface along with the opening of a dimension of thoughts while designing a new animal model or treatment paradigm for ocular surface inflammatory disorders.

InflammAging at Ocular Surface: Clinical and Biomolecular Analyses in Healthy Volunteers

Purpose

To assess the ocular surface in volunteers who consider themselves as healthy, in order to evaluate how para-inflammatory mechanisms fail with age, and thus investigate the phenomenon of "InflammAging."

Methods

In this observational prospective cohort study, volunteers were categorized into three groups according to age: young (19-40 years), middle-aged (41-60 years), and older adults (61-93 years). Clinical assessments included tear breakup time (T-BUT) and Schirmer test type I. Dry eye symptoms were evaluated by the Ocular Surface Disease Index (OSDI) questionnaire. Conjunctival mRNA and protein expression of intercellular adhesion molecule-1 (ICAM-1), MUC5AC, and IL-8 were measured by real-time PCR and immunofluorescence.

Results

A total of 82 volunteers (38 males and 44 females) were enrolled. T-BUT decreased significantly with increasing age (young: 11.13 ± 0.18 seconds; middle-aged: 10.83 ± 0.56 seconds; older: 9.00 ± 1.00 seconds, P < 0.05). Schirmer test values decreased significantly with age (young: 20.6 ± 1.0 mm; middle-aged: 19.2 ± 1.2 mm; older: 16.0 ± 1.1 mm, P < 0.05). OSDI scores increased with age in both groups, but they were substantially higher in women. Conjunctival expression of inflammatory markers ICAM-1, IL-8, and MUC5AC increased with age.

Conclusions

Clinical signs, symptoms, and biomarkers of chronic inflammation increased with age in a cohort of volunteers who considered themselves healthy, indicating an age-related progressive impairment of ocular surface system function.

Reduced Corneal Innervation in the CD25 Null Model of Sjögren Syndrome

Decreased corneal innervation is frequent in patients with Sjögren Syndrome (SS). To investigate the density and morphology of the intraepithelial corneal nerves (ICNs), corneal sensitivity, epithelial cell proliferation, and changes in mRNA expression of genes that are involved in autophagy and axon targeting and extension were assessed using the IL-2 receptor alpha chain (CD25 null) model of SS. ICN density and thickness in male and female wt and CD25 null corneas were assessed at 4, 6, 8, and 10/11 wk of age. Cell proliferation was assessed using ki67. Mechanical corneal sensitivity was measured. Quantitative PCR was performed to quantify expression of beclin 1, LC3, Lamp-1, Lamp-2, CXCL-1, BDNF, NTN1, DCC, Unc5b1, Efna4, Efna5, Rgma, and p21 in corneal epithelial mRNA. A significant reduction in corneal axon density and mechanical sensitivity were observed, which negatively correlate with epithelial cell proliferation. CD25 null mice have increased expression of genes regulating autophagy (beclin-1, LC3, LAMP-1, LAMP-2, CXCL1, and BDNF) and no change was observed in genes that were related to axonal targeting and extension. Decreased anatomic corneal innervation in the CD25 null SS model is accompanied by reduced corneal sensitivity, increased corneal epithelial cell proliferation, and increased expression of genes regulating phagocytosis and autophagy.

Protective role of commensal bacteria in Sjögren Syndrome

CD25 knock-out (CD25KO) mice spontaneously develop Sjögren Syndrome (SS)-like inflammation. We investigated the role of commensal bacteria by comparing CD25KO mice housed in conventional or germ-free conditions. Germ-free CD25KO mice have greater corneal barrier dysfunction, lower goblet cell density, increased total lymphocytic infiltration score, increased expression of IFN-γ, IL-12 and higher a frequency of CD4⁺IFN-γ⁺ cells than conventional mice. CD4⁺ T cells isolated from female germ-free CD25KO mice adoptively transferred to naive immunodeficient RAG1KO recipients caused more severe Sjögren-like disease than CD4⁺ T cells transferred from conventional CD25KO mice. Fecal transplant in germ-free CD25KO mice reversed the spontaneous dry eye phenotype and decreased the generation of pathogenic CD4⁺IFN-γ⁺ cells. Our studies indicate that lack of commensal bacteria accelerates the onset and severity of dacryoadenitis and generates autoreactive CD4⁺T cells with greater pathogenicity in the CD25KO model, suggesting that the commensal bacteria or their metabolites products have immunoregulatory properties that protect exocrine glands in the CD25KO SS model.

Sjögren-Like Lacrimal Keratoconjunctivitis in Germ-Free Mice

Commensal bacteria play an important role in the formation of the immune system but their role in the maintenance of immune homeostasis at the ocular surface and lacrimal gland remains poorly understood. This study investigated the eye and lacrimal gland phenotype in germ-free and conventional C57BL/6J mice. Our results showed that germ-free mice had significantly greater corneal barrier disruption, greater goblet cell loss, and greater total inflammatory cell and CD4⁺ T cell infiltration within the lacrimal gland compared to the conventionally housed group. A greater frequency of CD4⁺IFN-γ⁺ cells was observed in germ-free lacrimal glands. Females exhibited a more severe phenotype compared to males. Adoptive transfer of CD4⁺ T cells isolated from female germ-free mice into RAG1KO mice transferred Sjögren-like lacrimal keratoconjunctivitis. Fecal microbiota transplant from conventional mice reverted dry eye phenotype in germ-free mice and decreased CD4⁺IFN-γ⁺ cells to levels similar to conventional C57BL/6J mice. These findings indicate that germ-free mice have a spontaneous lacrimal keratoconjunctivitis similar to that observed in Sjögren syndrome patients and demonstrate that commensal bacteria function in maintaining immune homeostasis on the ocular surface. Thus, manipulation of intestinal commensal bacteria has the potential to become a novel therapeutic approach to treat Sjögren Syndrome.

Goblet cell loss abrogates ocular surface immune tolerance

Intestinal epithelial cells condition tolerogenic properties in DCs. Aqueous-deficient dry eye is associated with goblet cell (GC) loss and increased IFN-γ expression in the conjunctiva. We hypothesized that loss of GCs reduces tolerance-inducing properties of antigen presenting cells (APCs) in the conjunctiva and draining nodes. Mice lacking the SAM pointed domain containing ETS transcription factor (Spdef) that is required for GC differentiation had an increased frequency of macrophages in the conjunctiva and CD11b+CD11c+ DCs in the conjunctiva and draining nodes, and these cells had greater IL-12 expression than WT mice. Conditioned media from cultured WT conjunctival GCs suppressed LPS-induced IL-12 production by conjunctival APCs. OVA antigen-specific OTII CD4+ T cells primed by Spdef-KO draining lymph node APCs showed greater proliferation, lower frequency of Foxp3+, increased frequency of IFN-γ+ and IL-17+ cells, and greater IFN-γ production than those primed by WT APCs. The immune tolerance to OVA antigen topically applied to the conjunctiva measured by cutaneous delayed type hypersensitivity (DTH) reaction, OVA-specific T cell proliferation, Foxp3 induction, and IFN-γ production observed in WT mice was lost in the Spdef-KO mice. We concluded that conjunctival GCs condition tolerogenic properties in APCs that suppress IL-12 production and Th1 polarization.

The Pathophysiology of Dry Eye Disease: What We Know and Future Directions for Research

Clinical and laboratory studies performed over the past few decades have discovered that dry eye is a chronic inflammatory disease that can be initiated by numerous extrinsic or intrinsic factors that promote an unstable and hyperosmolar tear film. These changes in tear composition, in some cases combined with systemic factors, lead to an inflammatory cycle that causes ocular surface epithelial disease and neural stimulation. Acute desiccation activates stress signaling pathways in the ocular surface epithelium and resident immune cells. This triggers production of innate inflammatory mediators that stimulate the production of matrix metalloprotease, inflammatory cell recruitment, and dendritic cell maturation. These mediators, combined with exposure of autoantigens, can lead to an adaptive T cell-mediated response. Cornea barrier disruption develops by protease-mediated lysis of epithelial tight junctions, leading to accelerated cell death; desquamation; an irregular, poorly lubricated cornea surface; and exposure and sensitization of epithelial nociceptors. Conjunctival goblet cell dysfunction and death are promoted by the T helper 1 cytokine interferon gamma. These epithelial changes further destabilize the tear film, amplify inflammation, and create a vicious cycle. Cyclosporine and lifitegrast, the 2 US Food and Drug Administration-approved therapies, inhibit T-cell activation and cytokine production. Although these therapies represent a major advance in dry eye therapy, they are not effective in improving discomfort and corneal epithelial disease in all patients. Preclinical studies have identified other potential therapeutic targets, biomarkers, and strategies to bolster endogenous immunoregulatory pathways. These discoveries will, it is hoped, lead to further advances in diagnostic classification and treatment.

TFOS DEWS II pathophysiology report

The TFOS DEWS II Pathophysiology Subcommittee reviewed the mechanisms involved in the initiation and perpetuation of dry eye disease. Its central mechanism is evaporative water loss leading to hyperosmolar tissue damage. Research in human disease and in animal models has shown that this, either directly or by inducing inflammation, causes a loss of both epithelial and goblet cells. The consequent decrease in surface wettability leads to early tear film breakup and amplifies hyperosmolarity via a Vicious Circle. Pain in dry eye is caused by tear hyperosmolarity, loss of lubrication, inflammatory mediators and neurosensory factors, while visual symptoms arise from tear and ocular surface irregularity. Increased friction targets damage to the lids and ocular surface, resulting in characteristic punctate epithelial keratitis, superior limbic keratoconjunctivitis, filamentary keratitis, lid parallel conjunctival folds, and lid wiper epitheliopathy. Hybrid dry eye disease, with features of both aqueous deficiency and increased evaporation, is common and efforts should be made to determine the relative contribution of each form to the total picture. To this end, practical methods are needed to measure tear evaporation in the clinic, and similarly, methods are needed to measure osmolarity at the tissue level across the ocular surface, to better determine the severity of dry eye. Areas for future research include the role of genetic mechanisms in non-Sjögren syndrome dry eye, the targeting of the terminal duct in meibomian gland disease and the influence of gaze dynamics and the closed eye state on tear stability and ocular surface inflammation.

Age-related spontaneous lacrimal keratoconjunctivitis is accompanied by dysfunctional T regulatory cells

In both humans and animal models, the development of Sjögren syndrome (SS) and non-SS keratoconjunctivitis sicca (KCS) increases with age. Here, we investigated the ocular surface and lacrimal gland (LG) phenotype of NOD.B10.H2^b mice at 7-14, 45-50, and 96-100 weeks. Aged mice develop increased corneal permeability, CD4⁺ T-cell infiltration, and conjunctival goblet cell loss. Aged mice have LG atrophy with increased lymphocyte infiltration and inflammatory cytokine levels. An increase in the frequency of CD4⁺Foxp3⁺ T regulatory cells (Tregs) was observed with age in the cervical lymph node (CLN), spleen, and LG. These CD4⁺CD25⁺ cells lose suppressive ability, while maintaining expression of Foxp3 (forkhead box P3) and producing interleukin-17 (IL-17) and interferon-γ (IFN-γ). An increase of Foxp3⁺IL-17⁺ or Foxp3⁺IFN-γ⁺ cells was observed in the LG and LG-draining CLN. In adoptive transfer experiments, recipients of either purified Tregs or purified T effector cells from aged donors developed lacrimal keratoconjunctivitis, whereas recipients of young Tregs or young T effector cells failed to develop disease. Overall, these results suggest inflammatory cytokine-producing CD4⁺Foxp3⁺ cells participate in the pathogenesis of age-related ocular surface disease.

Interferon-γ-Induced Unfolded Protein Response in Conjunctival Goblet Cells as a Cause of Mucin Deficiency in Sjögren Syndrome

Goblet cells (GCs) are specialized secretory cells that produce mucins and a variety of other proteins. Significant conjunctival GC loss occurs in both experimental dry eye models and patients with keratoconjunctivitis sicca due to the induction of interferon (IFN)-γ. With the use of a primary murine culture model, we found that GCs are highly sensitive to IFN-γ with significantly reduced proliferation and altered structure with low concentrations. GC cultures treated with IFN-γ have increased gene expression of Muc2 and Muc5AC but do not express these mucin glycoproteins. We hypothesized that IFN-γ induces endoplasmic reticulum stress and the unfolded protein response (UPR) in GCs. Cultures treated with IFN-γ increased expression of UPR-associated genes and proteins. Increased GRP78 and sXBP1 expression was found in experimental dry eye and Sjögren syndrome models and was GC specific. Increased GRP78 was also found in the conjunctiva of patients with Sjögren syndrome at the gene and protein levels. Treatment with dexamethasone inhibited expression of UPR-associated genes and increased mucin production. These results indicate that induction of UPR by IFN-γ is an important cause of GC-associated mucin deficiency observed in aqueous-deficient dry eye. Therapies to block the effects of IFN-γ on the metabolically active endoplasmic reticulum in these cells might enhance synthesis and secretion of the protective GC mucins on the ocular surface.

Sjögren syndrome: what and where are we looking for?

PURPOSE OF REVIEW

Sjögren's syndrome affects exocrine glands leading to a dry mouth and dry eyes. Dry eye manifestations can precede the diagnosis of Sjögren's syndrome by many years. Innumerous spontaneous and inducible Sjögren's syndrome models have been used to study the pathogenesis of Sjögren's syndrome. This review focuses on recent human data, ocular and extraglandular manifestations of animal models, what is known, what is still unknown and how we need to look, and their correlation correspondence to human disease.

RECENT FINDINGS

Hallmarks of dry eye in Sjögren's syndrome include increased corneal staining, goblet cell loss and low tear volume. Confocal microscopy and impression cytology are able to clarify new markers of the ocular disease. Extraglandular manifestations should be an alert more severe complications in the eye. Some models have strong sex and exocrine gland predilection, whereas aging generally worsens the disease phenotype. Although most models do not display a significant increase in corneal staining or tear secretion impairment, conjunctival infiltration and decrease in goblet cells are frequently seen.

SUMMARY

We have seen great advances in the role of inflammation in ocular, oral and extra-glandular manifestations of Sjögren's syndrome. Several mechanisms and mediators of Sjögren's syndrome have been elucidated in animal model studies.

Age-Related Conjunctival Disease in the C57BL/6.NOD-Aec1Aec2 Mouse Model of Sjögren Syndrome Develops Independent of Lacrimal Dysfunction

PURPOSE

To investigate parameters of ocular surface disease in C57BL/6.NOD-Aec1Aec2 (Aec) mice with aging and their correlation with development of Sjögren syndrome (SS)-like lacrimal gland (LG) disease.

METHODS

Aec and C57BL/6 wild-type (B6) female mice were evaluated at 4, 12, and 20 weeks of age. Whole LG and eyes and adnexa were excised for histology and gene expression analysis and evaluated by flow cytometry and immunohistochemistry. Tear volume and goblet cell density was measured. Quantitative PCR evaluated T-cell-related cytokine expression in cornea and conjunctiva.

RESULTS

Both strains showed age-related conjunctival goblet cell loss that was more pronounced in the Aec strain and significantly greater than in B6 mice at 12 weeks. This was accompanied by CD4+ T-cell infiltration of the conjunctiva that was greater in Aec strain at 20 weeks. Aec mice had higher levels of IL-17A, IL-17R, IL-1α, IL-1β, and TNF-α in the conjunctiva, and they significantly increase with aging. Aec mice had greater lymphocytic infiltration of the LG and conjunctiva at 20 weeks that consisted of a mixture of CD4+ and CD8+ cells. Flow cytometry showed a significant increase in CD4+ T cells in Aec LG compared to B6 mice. Tear volume was significantly increased in both strains at 20 weeks.

CONCLUSIONS

Aec mice developed greater conjunctival goblet cell loss associated with lymphocytic infiltration of the LG and conjunctiva with aging. Increased expression of certain T helper or inflammatory cytokines in these tissues was observed in Aec mice. The conjunctival disease appeared to be due to inflammation and not a decrease in tear volume.

Altered balance of interleukin-13/interferon-gamma contributes to lacrimal gland destruction and secretory dysfunction in CD25 knockout model of Sjögren's syndrome

Introduction

The lacrimal gland (LG) of the CD25^-/^- model of Sjögren’s syndrome (SS) has high interleukin (IL)-17, IL-13 and interferon-gamma (IFN-γ) cytokines. The specific contribution of these cytokines to the onset and severity of dacryoadenitis in the CD25^-/^- mice has not been evaluated.

Methods

CD25⁻/⁻IL-17A⁻/⁻, CD25⁻/⁻IL-17⁻/⁻IFN-γ⁻/⁻ and CD25⁻/⁻IFN-γ⁻/⁻ were used at 4, 8, 12, 16 weeks (W). Total lymphocytic infiltration was evaluated by histology and characterized by flow cytometry. Epidermal growth factor (EGF) concentration was measured in tears. Immunofluorescent staining evaluated expression of IFN-γ receptor (IFN-γR) and apoptosis. Real-time PCR evaluated inflammatory and T cell-related cytokines expression in LG. Caspase-3, -8, -9 activities was assayed in LG lysates. T helper cytokines were measured in serum by Luminex assay.

Results

The greatest total LG infiltration at 8 W was seen in CD25⁻/⁻IL-17A⁻/⁻ (95%), followed by CD25⁻/⁻ (71%) and IL-17⁻/⁻ (12%). Tear EGF concentration was in normal range in CD25⁻/⁻ at 4 W and in very low levels in both CD25⁻/⁻ and CD25⁻/⁻IL-17A⁻/⁻. CD25⁻/⁻ had high levels of inflammatory cytokines transcripts in LG compared to IL-17⁻/⁻ mice; however, CD25⁻/⁻IL-17A⁻/⁻ had even higher IL-1β, IFN-γR, caspase-3, -8, -9 mRNA levels, greater immunoreactivity to IFN-γR in LG acini, greater number of apoptotic⁺ cells and greater caspases activities in the LG at 8 W. CD25⁻/⁻IL-17A⁻/⁻ had lower IL-13 concentration and lower IL-13/IFN-γ ratio compared to CD25⁻/⁻ in serum. CD25⁻/⁻IFN-γ⁻/⁻ had lower number of apoptotic⁺ cells and decreased caspase-3 expression in LG. CD25⁻/⁻IL-17⁻/⁻IFN-γ⁻/⁻ had lower total lymphocytic cell infiltration at 8 W (48%), CD4⁺T cell infiltration and expression of IFN-γR and apoptotic⁺ cells in the LG and increased tear EGF concentration in tears.

Conclusions

IFN-γ is critical for LG destruction and secretory dysfunction in the CD25⁻/⁻ model of SS. Altered balance between IFN-γ and IL-13 in the CD25⁻/⁻IL-17A⁻/⁻ mice accelerates LG destruction by increasing glandular apoptosis and facilitating apoptosis through increased expression of IFN-γR by glandular epithelium and activation of caspases. Targeting both IFN-γ and IL-17 may be beneficial for treating the LG inflammation in SS.

Managing Sjögren's Syndrome and non-Sjögren Syndrome dry eye with anti-inflammatory therapy

Dry eye from Sjögren’s syndrome is a multifactorial disease that results in dysfunction of the lacrimal functional unit. Studies have shown changes in tear composition, including inflammatory cytokines, chemokines, and metalloproteinase. T-lymphocytes have been shown to increase in the conjunctiva and lacrimal glands in patient and animal models. This inflammation is in part responsible for the pathogenesis of the disease, which results in symptoms of eye irritation, ocular surface epithelial disease, and loss of corneal barrier function. There are a number of anti-inflammatory approaches for treating this disease. The current study reviews details of immune response and anti–inflammatory therapies used to control this disease.

Ocular surface disease and dacryoadenitis in aging C57BL/6 mice

Dry eye in humans displays increased prevalence in the aged and in women. Here, we investigated the ocular surfaces and lacrimal glands of aged mice of both sexes. We surveyed three different ages [young, middle-aged (6 to 9 months), and elderly] by investigating severity markers of dry eye disease (DED). We observed an age-dependent dry eye phenotype as early as 6 to 9 months: increased corneal surface irregularity, increased corneal barrier disruption, conjunctival CD4(+) T-cell infiltration, and loss of mucin-filled goblet cells. Expression of interferon-γ, IL-17 mRNA transcripts was increased in the conjunctiva and IL-17A, matrix metallopeptidase 9, and chemokine ligand 20 in the corneas of elderly mice. Elderly male mice develop more of a skewed response of type 1 T helper cell, whereas female mice have a bias toward type 17 T helper cell in the conjunctiva. In the lacrimal gland, an increase in CD4(+) and CD8(+) T cells and B cells and a decrease in activated dendritic cells were observed. Adoptive transfer of CD4(+) T cells isolated from elderly mice transferred DED into young immunodeficient recipients, which was more pronounced from male donors. Our findings show the development of DED in aging mice. Pathogenic CD4(+) T cells that develop with aging are capable of transferring DED from older mice to naive immunodeficient recipients. Taken together, our results indicate that age-related autoimmunity contributes to development of DED with aging.

The chemokine receptor CCR7 expressed by dendritic cells: a key player in corneal and ocular surface inflammation

Dendritic cells (DCs) are highly potent stimulators of the immune system, and their contribution as such to the pathogenesis of corneal and ocular surface inflammatory disease has been well established. These vigorous antigen-presenting cells are reliant upon their effective migration from peripheral tissues (e.g., those of the ocular surface) to the lymphoid organs, where immune responses are triggered and can then cause disease. The chemokine receptor CCR7 expressed on DCs has emerged as the master mediator of this highly complex migratory process, and thus it is important in causing corneal and ocular surface inflammation. Furthermore, CCR7 has received considerable attention as a potential therapeutic target, as topically instilled antagonists of this receptor are quite effective therapeutically in a mouse model of ocular allergy. These findings and more are reviewed in the current article. In addition, the understanding regarding CCR7 function in mice and humans, and the biology of DCs that populate the ocular surface are also detailed herein. The involvement of DCs and their expression of CCR7 in corneal and ocular surface diseases such as in ocular allergy, dry eye disease, immune rejection and more, are also reviewed here.

Dendritic cell-derived thrombospondin-1 is critical for the generation of the ocular surface Th17 response to desiccating stress

TSP-1 is a physiologic activator of TGF-β, a critical induction factor for Th17-mediated immunity. The purpose of this study was to investigate the role of TSP-1 in the induction of the Th17 ocular surface response to DS. TSP-1KO and WT mice were subjected to DS5 and DS10), and parameters of ocular surface disease, including corneal barrier function, conjunctival CD4(+) T cell infiltration, and GC density, were evaluated. TSP-1KO mice subjected to DS had less corneal barrier disruption, reduced loss of PAS+ GC, and decreased CD4(+) T cell infiltration in the conjunctiva. In contrast to WT, TSP-1KO mice failed to up-regulate MMP-3 and MMP-9 mRNA transcripts in the cornea and IL-17A mRNA transcripts in the conjunctiva. RAG-1KO recipients of adoptively transferred CD4(+) T cells isolated from TSP-1KO mice subjected to DS5 showed milder dry-eye phenotype and less conjunctival inflammation than recipients of CD4(+) T cells from DS5 WT control. Reconstitution of TSP-1KO mice with WT DCs prior to DS reversed the resistance of the TSP-1KO to DS-induced immunopathology. In conclusion, DC-derived TSP-1 is critical for generating the Th17 ocular surface response to DS.

T helper cytokines in dry eye disease

Dry eye is an inflammatory disease that results from activation of innate inflammatory pathways in resident ocular surface cells, as well as cytokines produced by recruited T helper (Th) cells. Cytokines produced by the infiltrating Th cells alter the normal cytokine balance on the ocular surface and cause ocular surface epithelial pathology. Changes in levels of Th cytokines on the ocular surface have been measured in dry eye and the biological effects of these cytokines have been documented in experimental culture and mouse model systems. The Th2 cytokine IL-13 has a homeostatic role in promoting goblet cell differentiation. In contrast, The Th1 cytokine IFN-γ antagonizes IL-13 and promotes apoptosis and squamous metaplasia of the ocular surface epithelia. The Th17 cytokine, IL-17 promotes corneal epithelial barrier disruption. The ocular surface epithelium expresses receptors to all of these Th cytokines. Therapies that maintain normal IL-13 signaling, or suppress IFN-γ and IL-17 have potential for treating the ocular surface disease of dry eye.

Deletion of interferon-γ delays onset and severity of dacryoadenitis in CD25KO mice

Introduction

To investigate the role of interferon-gamma (IFN-γ) in the onset and severity of dacryoadenitis in the CD25 knockout (KO) mouse model of Sjögren Syndrome.

Methods

CD25/IFN-γ double KO (γDKO) mice were created by crossbreeding CD25KO and IFN-γKO mice. Mice were used at 8, 12, and 16 weeks. Lacrimal gland (LG) infiltrating lymphocytes were characterized with flow cytometry. Tear epidermal growth factor (EGF) concentration was measured with enzyme-linked immunosorbent assay (ELISA). Quantitative polymerase chain reaction (PCR) evaluated T-cell-related cytokines in LGs. Serum autoantibodies against M3R in LG lysates were detected with Western blot.

Results

γDKO LG showed lower lymphocytic infiltration at 8 weeks than in the CD25KO parental strain (˜20% versus ˜60%, respectively), which increased to CD25KO levels at 16 weeks. Flow-cytometry analysis showed an increase in CD4⁺ and CD8⁺ T cells with aging in γDKO LG, similar to that in CD25KO. γDKO had lower levels of interleukin (IL)-17A, transforming growth-factor (TGF)-β1, IL-21, and CCL20, and higher IL-1β and IL-13 mRNA transcripts in the LG than in the parental CD25KO strain. Autoantibodies to M3R were observed in both strains and significantly increased with aging in both strains. CD25KO mice had very low tear EGF concentrations at all ages, whereas the ear EGF concentration in γDKO mice significantly decreased with aging and inversely correlated with the presence of M3R autoantibodies and the degree of LG CD4 and CD8⁺ T-cell infiltration.

Conclusions

The deletion of IFN-γ in the CD25KO mice strain delays glandular destruction and preserves glandular function. M3R autoantibodies increased with aging in both the γDKO and the CD25KO strains. The decrease in LG function in γDKO correlated with the degree of T-cell infiltration and the presence of M3R autoantibodies.

Disruption of TGF-β signaling improves ocular surface epithelial disease in experimental autoimmune keratoconjunctivitis sicca

BACKGROUND

TGF-β is a pleiotropic cytokine that can have pro- or anti-inflammatory effects depending on the context. Elevated levels of bioactive TGF-β1 in tears and elevated TGF-β1mRNA transcripts in conjunctiva and minor salivary glands of human Sjögren's Syndrome patients has also been reported. The purpose of this study was to evaluate the response to desiccating stress (DS), an experimental model of dry eye, in dominant-negative TGF-β type II receptor (CD4-DNTGFβRII) mice. These mice have a truncated TGF-β receptor in CD4(+) T cells, rendering them unresponsive to TGF-β.

METHODOLOGY/PRINCIPAL FINDINGS

DS was induced by subcutaneous injection of scopolamine and exposure to a drafty low humidity environment in CD4-DNTGFβRII and wild-type (WT) mice, aged 14 weeks, for 5 days. Nonstressed (NS) mice served as controls. Parameters of ocular surface disease included corneal smoothness, corneal barrier function and conjunctival goblet cell density. NS CD4-DNTGFβRII at 14 weeks of age mice exhibited a spontaneous dry eye phenotype; however, DS improved their corneal barrier function and corneal surface irregularity, increased their number of PAS+ GC, and lowered CD4(+) T cell infiltration in conjunctiva. In contrast to WT, CD4-DNTGFβRII mice did not generate a Th-17 and Th-1 response, and they failed to upregulate MMP-9, IL-23, IL-17A, RORγT, IFN-γ and T-bet mRNA transcripts in conjunctiva. RAG1KO recipients of adoptively transferred CD4+T cells isolated from DS5 CD4-DNTGFβRII showed milder dry eye phenotype and less conjunctival inflammation than recipients of WT control.

CONCLUSIONS/SIGNIFICANCE

Our results showed that disruption of TGF-β signaling in CD4(+) T cells causes paradoxical improvement of dry eye disease in mice subjected to desiccating stress.