Novel animal models for Sjögren's syndrome: expression and transfer of salivary gland dysfunction from regulatory T cell-deficient mice

How gut microbiota may impact ocular surface homeostasis and related disorders

Changes in the bacterial flora in the gut, also described as gut microbiota, are readily acknowledged to be associated with several systemic diseases, especially those with an inflammatory, neuronal, psychological or hormonal factor involved in the pathogenesis and/or the perception of the disease. Maintaining ocular surface homeostasis is also based on all these four factors, and there is accumulating evidence in the literature on the relationship between gut microbiota and ocular surface diseases. The mechanisms involved are mostly interconnected due to the interaction of central and peripheral neuronal networks, inflammatory effectors and the hormonal system. A better understanding of the influence of the gut microbiota on the maintenance of ocular surface homeostasis, and on the onset or persistence of ocular surface disorders could bring new insights and help elucidate the epidemiology and pathology of ocular surface dynamics in health and disease. Revealing the exact nature of these associations could be of paramount importance for developing a holistic approach using highly promising new therapeutic strategies targeting ocular surface diseases.

Regulatory T cells and IFN-γ-producing Th1 cells play a critical role in the pathogenesis of Sjögren's Syndrome

Objectives

Sjögren's Disease (SjD) is an autoimmune disorder characterized by progressive dysfunction, inflammation and destruction of salivary and lacrimal glands, and by extraglandular manifestations. Its etiology and pathophysiology remain incompletely understood, though a role for autoreactive B cells has been considered key. Here, we investigated the role of effector and regulatory T cells in the pathogenesis of SjD.

Methods

Histological analysis, RNA-sequencing and flow cytometry were conducted on glands, lungs, eyes and lymphoid tissues of mice with regulatory T cell-specific deletion of stromal interaction proteins (STIM) 1 and 2 ( Stim1/2 Foxp3 ), which play key roles in calcium signaling and T cell function. The pathogenicity of T cells from Stim1/2 Foxp3 mice was investigated through adoptively transfer into lymphopenic host mice. Additionally, single-cell transcriptomic analysis was performed on peripheral blood mononuclear cells (PBMCs) of patients with SjD and control subjects.

Results

Stim1/2 Foxp3 mice develop a severe SjD-like disorder including salivary gland (SG) and lacrimal gland (LG) inflammation and dysfunction, autoantibodies and extraglandular symptoms. SG inflammation in Stim1/2 Foxp3 mice is characterized by T and B cell infiltration, and transcriptionally by a Th1 immune response that correlates strongly with the dysregulation observed in patients with SjD. Adoptive transfer of effector T cells from Stim1/2 Foxp3 mice demonstrates that the SjD-like disease is driven by interferon (IFN)-γ producing autoreactive CD4 + T cells independently of B cells and autoantiboodies. scRNA-seq analysis identifies increased Th1 responses and attenuated memory Treg function in PBMCs of patients with SjD.

Conclusions

We report a more accurate mouse model of SjD while providing evidence for a critical role of Treg cells and IFN-γ producing Th1 cells in the pathogenesis of SjD, which may be effective targets for therapy.

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.

Regulatory T cells: a new therapeutic link for Sjögren syndrome?

Great advancements have been made in understanding the pathogenesis of SS, but there remain unmet needs for effective and targeted treatments. Glandular and extraglandular dysfunction in SS is associated with autoimmune lymphocytic infiltration that invades the epithelial structures of affected organs. Regulatory T (Treg) cells are a subset of CD4+ T lymphocytes that maintain self-tolerance during physiological conditions. Besides inhibiting excessive inflammation and autoimmune response by targeting various immune cell subsets and tissues, Treg cells have also been shown to promote tissue repair and regeneration in pathogenic milieus. The changes of quantity and function of Treg cells in various autoimmune and chronic inflammatory disorders have been reported, owing to their effects on immune regulation. Here we summarize the recent findings from murine models and clinical data about the dysfunction of Treg cells in SS pathogenesis and discuss the therapeutic strategies of direct or indirect targeting of Treg cells in SS. Understanding the current knowledge of Treg cells in the development of SS will be important to elucidate disease pathogenesis and may guide research for successful therapeutic intervention in this disease.

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.

Immune complexome analysis reveals the presence of immune complexes and identifies disease-specific immune complex antigens in saliva samples from patients with Sjögren's syndrome

Sjögren's syndrome (SS) is a chronic autoimmune disease that mainly damages the salivary and lacrimal glands. Immune complex (IC) formation triggers local inflammation through IC deposition and decreased antigen function. Some ICs can leak from the lesion and into the saliva, but no salivary ICs have been reported to date. We used immune complexome analysis to comprehensively identify antigens incorporated into IC (IC-antigens) in saliva samples from patients with SS (n = 9) or with xerostomia (n = 7). Neutrophil defensin 1 (67%), small proline-rich protein 2D (67%), myeloperoxidase (44%), neutrophil elastase (44%), cathepsin G (33%), nuclear mitotic apparatus 1 (33%) and phosphatidylinositol 4-phosphate 3-kinase C2 domain-containing subunit gamma (33%) were identified as new IC-antigens specifically and frequently detected in the saliva of SS patients. Of these, neutrophil defensin 1, myeloperoxidase, neutrophil elastase and cathepsin G are neutrophil intracellular proteins, which suggests that repeated destruction of neutrophils due to abnormal autoimmunity may be involved in the pathogenesis of SS. We also analyzed serum samples from three SS patients. There was little overlap of IC-antigens between two of the samples (fewer than 30% of the IC-antigens in the saliva samples), suggesting that many ICs are formed locally and independently of the circulation. In addition, we found that four SS-specific salivary antigens show sequence homology with several proteins of oral microbiomes but no antigen has homology with Epstein-Barr virus proteins. The homology between some IC-antigens and oral microbiome proteins may indicate the impact of oral infection on local autoimmunity through molecular mimicry theory.

A Novel Experimental Approach for In Vivo Analyses of the Salivary Gland Microvasculature

Microvascular dysfunction plays a fundamental role in the pathogenesis of salivary gland disorders. Restoring and preserving microvascular integrity might therefore represent a promising strategy for the treatment of these pathologies. The mechanisms underlying microvascular dysfunction in salivary glands, however, are still obscure, partly due to the unavailability of adequate in vivo models. Here, we present a novel experimental approach that allows comprehensive in vivo analyses of the salivary gland microvasculature in mice. For this purpose, we employed different microscopy techniques including multi-photon in vivo microscopy to quantitatively analyze interactions of distinct immune cell subsets in the submandibular gland microvasculature required for their infiltration into the surrounding parenchyma and their effects on microvascular function. Confocal microscopy and multi-channel flow cytometry in tissue sections/homogenates complemented these real-time analyses by determining the molecular phenotype of the participating cells. To this end, we identified key adhesion and signaling molecules that regulate the subset- and tissue-specific trafficking of leukocytes into inflamed glands and control the associated microvascular leakage. Hence, we established an experimental approach that allows in vivo analyses of microvascular processes in healthy and diseased salivary glands. This enables us to delineate distinct pathogenetic factors as novel therapeutic targets in salivary gland diseases.

Autoantibodies targeting TRIM72 compromise membrane repair and contribute to inflammatory myopathy

Idiopathic inflammatory myopathies (IIM) involve chronic inflammation of skeletal muscle and subsequent muscle degeneration due to an uncontrolled autoimmune response; however, the mechanisms leading to pathogenesis are not well understood. A compromised sarcolemmal repair process could promote an aberrant exposure of intramuscular antigens with the subsequent initiation of an inflammatory response that contributes to IIM. Using an adoptive transfer mouse model of IIM, we show that sarcolemmal repair is significantly compromised in distal skeletal muscle in the absence of inflammation. We identified autoantibodies against TRIM72 (also known as MG53), a muscle-enriched membrane repair protein, in IIM patient sera and in our mouse model of IIM by ELISA. We found that patient sera with elevated levels of TRIM72 autoantibodies suppress sarcolemmal resealing in healthy skeletal muscle, and depletion of TRIM72 antibodies from these same serum samples rescues sarcolemmal repair capacity. Autoantibodies targeting TRIM72 lead to skeletal muscle fibers with compromised membrane barrier function, providing a continuous source of autoantigens to promote autoimmunity and further amplifying humoral responses. These findings reveal a potential pathogenic mechanism that acts as a feedback loop contributing to the progression of IIM.

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.

The gut-eye-lacrimal gland-microbiome axis in Sjögren Syndrome

The bacterial communities that collectively inhabit our body are called the microbiome. Virtually all body surface harbors bacteria. Recent advances in next-generation sequencing that have provided insight into the diversity, composition of bacterial communities, and their interaction are discussed in this review, as well as the current knowledge of how the microbiome promotes ocular health. The ocular surface is a site of low bacterial load. Sjögren Syndrome is an autoimmune disease that affects the exocrine glands, causing dry mouth and dry eye. Systemic antibiotic treatment and germ-free mice have demonstrated that commensal bacteria have a protective role for the ocular surface and lacrimal gland. The existence of a gut-eye-lacrimal gland axis-microbiome is discussed.

Interferons and Dry Eye in Sjögren's Syndrome

Various cytokines, including interferon (IFN)-γ and IL-17, are augmented, and autoreactive T cells and B cells are activated in the immune pathogenesis of Sjögren's syndrome (SS). In particular, IFNs are involved in both the early stages of innate immunity by high level of type I IFN in glandular tissue and sera and the later stages of disease progression by type I and type II IFN producing T cells and B cells through B cell activating factor in SS. Genetically modified mouse models for some of these molecules have been reported and will be discussed in this review. New findings from human SS and animal models of SS have elucidated some of the mechanisms underlying SS-related dry eye. We will discuss IFN-γ and several other molecules that represent candidate targets for treating inflammation in SS-related dry eye.

Calcium signaling defects underlying salivary gland dysfunction

Salivary glands secrete saliva, a mixture of proteins and fluids, which plays an extremely important role in the maintenance of oral health. Loss of salivary secretion causes a dry mouth condition, xerostomia, which has numerous deleterious consequences including opportunistic infections within the oral cavity, difficulties in eating and swallowing food, and problems with speech. Saliva secretion is regulated by stimulation of specific signaling mechanisms within the acinar cells of the gland. Neurotransmitter-stimulated increase in cytosolic [Ca²⁺] ([Ca²⁺]_i) in acinar cells is the primary trigger for salivary fluid secretion from salivary glands, the loss of which is a critical factor underlying dry mouth conditions in patients. The increase in [Ca²⁺]_i regulates multiple ion channel and transport activities that together generate the osmotic gradient which drives fluid secretion across the apical membrane. Ca²⁺ entry mediated by the Store-Operated Ca²⁺ Entry (SOCE) mechanism provides the essential [Ca²⁺]_i signals to trigger salivary gland fluid secretion. Under physiological conditions depletion of ER-Ca²⁺ stores is caused by activation of IP3R by IP3 and this provides the stimulus for SOCE. Core components of SOCE in salivary gland acinar cells are the plasma membrane Ca²⁺ channels, Orai1 and TRPC1, and STIM1, a Ca²⁺-sensor protein in the ER, which regulates both channels. In addition, STIM2 likely enhances the sensitivity of cells to ER-Ca²⁺ depletion thereby tuning the cellular response to agonist stimulation. Two major, clinically relevant, conditions which cause irreversible salivary gland dysfunction are radiation treatment for head-and-neck cancers and the autoimmune exocrinopathy, Sjögren's syndrome (pSS). However, the exact mechanism(s) that causes the loss of fluid secretion, in either condition, is not clearly understood. A number of recent studies have identified that defects in critical Ca²⁺ signaling mechanisms underlie salivary gland dysfunction caused by radiation treatment or Sjögren's syndrome (pSS). This chapter will discuss these very interesting and important studies.

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.

Salivary-gland-protective regulatory T-cell dysfunction underlies female-specific sialadenitis in the non-obese diabetic mouse model of Sjögren syndrome

Immune cell-mediated destruction of salivary glands is a hallmark feature of Sjögren syndrome. Similar to the female predominance in humans, female non-obese diabetic (NOD) mice develop spontaneous salivary gland autoimmunity. However, in both humans and mice it is unclear what factors contribute to the initial immune infiltration of the salivary glands. Here, we used an adoptive transfer model of Sjögren syndrome to determine if female mice harbor a sex-specific defect in salivary-gland-protective regulatory T (Treg) cells. Transfer of cervical lymph node (LN) cells from female NOD mice into sex-matched NOD-severe combined immunodeficient (SCID) recipients resulted in sialadenitis, regardless of the presence or absence of Treg cells. In contrast, transfer of cervical LN cells from male NOD mice into sex-matched NOD-SCID recipients only resulted in sialadenitis when Treg cells were depleted before transfer, suggesting that male NOD mice have functional salivary-gland-protective Treg cells. Notably, the host environment affected the ability of Treg cells to prevent sialadenitis with testosterone promoting salivary gland protection. Treg cells from male mice did not protect against sialadenitis in female recipients. Testosterone treatment of female recipients of bulk cervical LN cells decreased sialadenitis, and Treg cells from female mice were capable of protecting against development of sialadenitis in male recipients. Hence, our data demonstrate that female NOD mice develop sialadenitis through a defect in salivary-gland-protective Treg cells that can be reversed in the presence of testosterone.

Severe Dry Eye in CD25 Deficiency Syndrome

CD25 deficiency (Interleukin-2 receptor alpha deficiency) is a rare subtype of combined B- and T-cell immunodeficiency. Recurrent infections and lymphocyte infiltration of multiple tissues are the main clinical presentations. Only four patients have been reported in whom ophthalmological findings were not described. In this article, ocular findings of CD25 deficiency in a 12-year-old child are highlighted.

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.

ALX/FPR2 Modulates Anti-Inflammatory Responses in Mouse Submandibular Gland

Activation of the G-protein coupled formyl peptide receptor 2 (ALX/FPR2) by the lipid mediators lipoxin A4 and resolvin D1 (RvD1) promotes resolution of inflammation. Our previous in vitro studies indicate that RvD1 activation of ALX/FPR2 resolves cytokine-mediated inflammatory responses in mammalian cells. However, the impact of ALX/FPR2 activation on salivary gland function in vivo is unknown. The objective of this study was to determine whether submandibular glands (SMG) from ALX/FPR2(-/-) mice display enhanced inflammatory responses to lipopolysaccharides (LPS) stimulation. For these studies, C57BL/6 and ALX/FPR2(-/-) mice at age 8-12-week-old were treated with LPS by i.p for 24 h. Salivary gland structure and function were analyzed by histopathological assessment, saliva flow rate, quantitative PCR, Western blot analyses and immunofluorescence. Our results showed the following events in the ALX/FPR2(-/-) mice treated with LPS: a) upregulated inflammatory cytokines and decreased M3R (Muscarinic Acetylcholine receptor M3) and AQP5 (Aquaporin 5) protein expression, b) decreased saliva secretion, c) increased apoptosis, d) alteration of tight junction and neuronal damage. Overall, our data suggest that the loss of ALX/FPR2 results in unresolved acute inflammation and SMG dysfunction (xerostomia) in response to LPS that is similar to human salivary gland dysfunction induced by bacterial infection.

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.

The coexistence of Sjögren's syndrome and primary biliary cirrhosis: a comprehensive review

Organ-specific and systemic autoimmune diseases share numerous features and often coexist in the same patient. Autoimmune cholangitis/primary biliary cirrhosis and Sjogren syndrome represent paradigmatic examples of the common grounds of different autoimmunity phenotypes based on similarities in clinical manifestations and immunopathogenesis. In fact, primary biliary cirrhosis and Sjogren's syndrome have both been coined as an autoimmune epithelitis in which apoptosis may be in both cases the key element to explain the organ-specific immune-mediated injury against the biliary and exocrine gland epithelia, respectively. Further, growing evidence supports in both diseases the view that B cells, T cytotoxic cells, and T helper cells are involved in chronic inflammation, likely via the altered expression of pro-inflammatory cytokines. The presence of estrogen receptors on the biliary and exocrine gland epithelia has been advocated as a key to the female predominance encountered in primary biliary cirrhosis and Sjogren's syndrome. Sadly, despite available data, therapeutic approaches remain largely unsatisfactory and recent studies with mechanistic approaches (as in the case of B cell depletion with rituximab) have been of partial benefit only. Future studies should focus on new molecular tools (single-cell transcriptomics, microRNA, epigenetics) to provide unique insights into common mechanisms.

Reversible lacrimal gland-protective regulatory T-cell dysfunction underlies male-specific autoimmune dacryoadenitis in the non-obese diabetic mouse model of Sjögren syndrome

CD4(+) CD25(+) Foxp3(+) regulatory T (Treg) cells are required to maintain immunological tolerance; however, defects in specific organ-protective Treg cell functions have not been demonstrated in organ-specific autoimmunity. Non-obese diabetic (NOD) mice spontaneously develop lacrimal and salivary gland autoimmunity and are a well-characterized model of Sjögren syndrome. Lacrimal gland disease in NOD mice is male-specific, but the role of Treg cells in this sex-specificity is not known. This study aimed to determine if male-specific autoimmune dacryoadenitis in the NOD mouse model of Sjögren syndrome is the result of lacrimal gland-protective Treg cell dysfunction. An adoptive transfer model of Sjögren syndrome was developed by transferring cells from the lacrimal gland-draining cervical lymph nodes of NOD mice to lymphocyte-deficient NOD-SCID mice. Transfer of bulk cervical lymph node cells modelled the male-specific dacryoadenitis that spontaneously develops in NOD mice. Female to female transfers resulted in dacryoadenitis if the CD4(+) CD25(+) Treg-enriched population was depleted before transfer; however, male to male transfers resulted in comparable dacryoadenitis regardless of the presence or absence of Treg cells within the donor cell population. Hormone manipulation studies suggested that this Treg cell dysfunction was mediated at least in part by androgens. Surprisingly, male Treg cells were capable of preventing the transfer of dacryoadenitis to female recipients. These data suggest that male-specific factors promote reversible dysfunction of lacrimal gland-protective Treg cells and, to our knowledge, form the first evidence for reversible organ-protective Treg cell dysfunction in organ-specific autoimmunity.

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.

Regulatory T cell-deficient scurfy mice develop systemic autoimmune features resembling lupus-like disease

Introduction

Scurfy mice are deficient in regulatory T cells (Tregs), develop a severe, generalized autoimmune disorder that can affect almost every organ and die at an early age. Some of these manifestations resemble those found in systemic lupus erythematosus (SLE). In addition, active SLE is associated with low Treg numbers and reduced Treg function, but direct evidence for a central role of Treg malfunction in the pathophysiology of lupus-like manifestations is still missing. In the present study, we characterize the multiorgan pathology, autoantibody profile and blood count abnormalities in scurfy mice and show their close resemblances to lupus-like disease.

Methods

Scurfy mice have dysfunctional Tregs due to a genetic defect in the transcription factor Forkhead box protein 3 (Foxp3). We analyzed skin, joints, lung and kidneys of scurfy mice and wild-type (WT) controls by conventional histology and immunofluorescence (IF) performed hematological workups and tested for autoantibodies by IF, immunoblotting and enzyme-linked immunosorbent assay. We also analyzed the intestines, liver, spleen and heart, but did not analyze all organs known to be affected in scurfy mice (such as the testicle, the accessory reproductive structures, the pancreas or the eyes). We transferred CD4⁺ T cells of scurfy or WT mice into T cell-deficient B6/nude mice.

Results

We confirm previous reports that scurfy mice spontaneously develop severe pneumonitis and hematological abnormalities similar to those in SLE. We show that scurfy mice (but not controls) exhibited additional features of SLE: severe interface dermatitis, arthritis, mesangioproliferative glomerulonephritis and high titers of anti-nuclear antibodies, anti-double-stranded DNA antibodies, anti-histone antibodies and anti-Smith antibodies. Transfer of scurfy CD4⁺ T cells (but not of WT cells) induced autoantibodies and inflammation of lung, skin and kidneys in T cell-deficient B6/nude mice.

Conclusion

Our observations support the hypothesis that lupus-like autoimmune features develop in the absence of functional Tregs.

A crucial role of RORγt in the development of spontaneous Sialadenitis-like Sjögren's syndrome

The nuclear receptor retinoic acid-related orphan receptor (ROR)γt is required for the generation of Th17 cells, which are involved in various autoimmune diseases, including Sjögren's syndrome (SS). However, the pathological role of RORγt in SS remains to be elucidated. The present study was designed to clarify the role of RORγt in the pathogenesis of sialadenitis-like SS. Histological analysis of RORγt transgenic (Tg) mice was determined, and then Tg mice developed severe spontaneous sialadenitis-like SS. The analysis of infiltrating cells showed that most infiltrating cells were CD4(+) T cells. RORγt-overexpressing CD4(+) T cells induced sialadenitis as a result of transferred CD4(+) T cells from Tg mice into Rag2(-/-) mice. The examination of IL-17-deficient Tg mice indicated that IL-17 was not essential for the development of sialadenitis. The number of CD4(+)CD25(+)Foxp3(+) regulatory T (Treg) cells was significantly decreased in Tg mice, and CD25 expression and IL-2 stimulated STAT5 activation were inhibited in Treg cells. The inhibitory function of Treg cells of Tg mice was equal to that of wild-type mice in vitro. The abundant Treg cells of Tg mice could suppress the development of sialadenitis, but the reduced Treg cells of Tg mice could not inhibit the induction of sialadenitis in Rag2(-/-) mice transferred with effector cells from Tg mice. These results suggest that both RORγt-overexpressed CD4(+) T cells and reduced Treg cells might contribute to the development of SS-like sialadenitis.

A chimeric human-mouse model of Sjögren's syndrome

Despite recent advances in the understanding of Sjögren's Syndrome (SjS), the pathogenic mechanisms remain elusive and an ideal model for early drug discovery is not yet available. To establish a humanized mouse model of SjS, peripheral blood mononuclear cells (PBMCs) from healthy volunteers or patients with SjS were transferred into immunodeficient NOD-scid IL-2rγ(null) mouse recipients to produce chimeric mice. While no difference was observed in the distribution of cells, chimeric mice transferred with PBMCs from SjS patients produced enhanced cytokine levels, most significantly IFN-γ and IL-10. Histological examination revealed enhanced inflammatory responses in the lacrimal and salivary glands of SjS chimeras, as measured by digital image analysis and blinded histopathological scoring. Infiltrates were primarily CD4+, with minimal detection of CD8+ T-cells and B-cells. These results demonstrate a novel chimeric mouse model of human SjS that provides a unique in vivo environment to test experimental therapeutics and investigate T-cell disease pathology.

Aberrant muscle antigen exposure in mice is sufficient to cause myositis in a Treg cell-deficient milieu

Objective

Myositis is associated with muscle-targeted inflammation and is observed in some Treg cell–deficient mouse models. Because an autoimmune pathogenesis has been strongly implicated, the aim of this study was to investigate the hypothesis that abnormal exposure to muscle antigens, as observed in muscle injury, can induce autoimmune-mediated myositis in susceptible hosts.

Methods

FoxP3 mutant (scurfy) mice were mated to synaptotagmin VII (Syt VII) mutant mice, which resulted in a new mouse strain that combines impaired membrane resealing with Treg cell deficiency. Lymphocyte preparations from double-mutant mice were adoptively transferred intraperitoneally, with or without purified Treg cells, into recombination-activating gene 1 (RAG-1)–null recipients. Lymph node cells from mice with the FoxP3 mutation were transferred into RAG-1–null mice either 1) intraperitoneally in conjunction with muscle homogenate or purified myosin protein or 2) intramuscularly with or without cotransfer of purified Treg cells.

Results

FoxP3-deficient mouse lymph node cells transferred in conjunction with myosin protein or muscle homogenate induced robust skeletal muscle inflammation. The infiltrates consisted predominantly of CD4+ and CD8+ T cells, a limited number of macrophages, and no B cells. Significant inflammation was also seen in similar experiments using lymph node cells from FoxP3/Syt VII double-mutant mice but was absent in experiments using adoptive transfer of FoxP3 mutant mouse cells alone. The cotransfer of Treg cells completely suppressed myositis.

Conclusion

These data, derived from a new, reproducible model, demonstrate the critical roles of Treg cell deficiency and aberrant muscle antigen exposure in the priming of autoreactive cells to induce myositis. This mouse system has multifaceted potential for examining the interplay in vivo between tissue injury and autoimmunity.

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.

Interleukin-7 enhances the Th1 response to promote the development of Sjögren's syndrome-like autoimmune exocrinopathy in mice

OBJECTIVE

Although elevated interleukin-7 (IL-7) levels have been reported in patients with primary Sjögren's syndrome (SS), the role of IL-7 in this disease remains unclear. We undertook this study to characterize the previously unexplored role of IL-7 in the development and onset of primary SS using the C57BL/6.NOD-Aec1Aec2 (B6.NOD-Aec) mouse model, which recapitulates human primary SS.

METHODS

For gain-of-function studies, recombinant IL-7 or control phosphate buffered saline was injected intraperitoneally (IP) into 12-week-old B6.NOD-Aec mice for 8 weeks. For loss-of-function studies, anti-IL-7 receptor α-chain (anti-IL-7Rα) antibody or its isotype control IgG was administered IP into 16-week-old B6.NOD-Aec mice. Salivary flow measurement, histologic and flow cytometric analysis of salivary glands, and serum antinuclear antibody assay were performed to assess various disease parameters.

RESULTS

Administration of exogenous IL-7 accelerated the development of primary SS, whereas blockade of IL-7Rα signaling almost completely abolished the development of primary SS, based on salivary gland inflammation and apoptosis, autoantibody production, and secretory dysfunction. IL-7 positively regulated interferon-γ (IFNγ)-producing Th1 and CD8+ T cells in the salivary glands without affecting IL-17. Moreover, IL-7 enhanced the expression of CXCR3 ligands in a T cell- and IFNγ-dependent manner. Accordingly, IFNγ induced a human salivary gland epithelial cell line to produce CXCR3 ligands. IL-7 also increased the level of tumor necrosis factor α, another Th1-associated cytokine that can facilitate tissue destruction and inflammation.

CONCLUSION

IL-7 plays a pivotal pathogenic role in SS, which is underpinned by an enhanced Th1 response and IFNγ/CXCR3 ligand-mediated lymphocyte infiltration of target organs. These results suggest that targeting the IL-7 pathway may be a potential future strategy for preventing and treating SS.

Current Aspects of Pathogenesis in Sjögren's Syndrome

Sjögren's syndrome is a chronic autoimmune process that primarily affects the exocrine glands and leads to their functional impairment. The exocrine gland involvement is characterized by a focal, mononuclear cell infiltrate which is accumulated around ducts and, in some patients, extends and replaces the secretory functional units. The mechanisms of this autoimmune 'exocrinopathy' are not fully understood. The immune attack that follows activation or apoptosis of glandular epithelial cells exposing autoantigens in genetically predisposed individuals may drive the immune-mediated tissue injury. Abnormalities related to the upregulation of type I interferon-regulated genes (interferon signature), abnormal expression of B-cell-activating factor (BAFF) and activation of the IL-23/TH17 pathway are among the immune mediators implicated in the pathogenesis of autoimmune lesions within the salivary glands. Such abnormalities demonstrate the complex interplay between innate and adaptive immunity that contributes to autoimmune 'exocrinopathy'.

STIM1 and STIM2 protein deficiency in T lymphocytes underlies development of the exocrine gland autoimmune disease, Sjogren's syndrome

Primary Sjögren's Syndrome (pSS) is an autoimmune disease involving salivary and other exocrine glands that leads to progressive lymphocytic infiltration into the gland, tissue damage, and secretory defects. The mechanism underlying this disease remains poorly understood. Here we report that mice with T-cell-targeted deletion of Stromal Interaction Molecule (STIM) 1 and STIM2 [double-knockout (DKO)] mice develop spontaneous and severe pSS-like autoimmune disease, displaying major hallmarks of the disease. In DKO mice, diffuse lymphocytic infiltration was seen in submandibular glands, a major target of pSS, by age 6 wk, progressing to severe inflammation by age 12 wk. Sjögren's syndrome-specific autoantibodies (SSA/Ro and SSB/La) were detected in the serum, and progressive salivary gland destruction and loss of fluid secretion were also seen. Importantly, we report that peripheral blood mononuclear cells as well as lymphocytic infiltrates in submandibular glands from patients with pSS demonstrated significant reductions in STIM1 and STIM2 proteins. Store-operated calcium entry was also reduced in peripheral blood mononuclear cells from pSS patients compared with those from healthy controls. Thus, deficiency of STIM1 and STIM2 proteins in T cells, and consequent defects in Ca(2+) signaling, are associated with salivary gland autoimmunopathy in DKO mice and pSS patients. These data reveal a previously unreported link between STIM1 and STIM2 proteins and pSS.

The Biology of Autoimmune Response in the Scurfy Mice that Lack the CD4+Foxp3+ Regulatory T-Cells

Due to a mutation in the Foxp3 transcription factor, Scurfy mice lack regulatory T-cells that maintain self-tolerance of the immune system. They develop multi-organ inflammation (MOI) and die around four weeks old. The affected organs are skin, tail, lungs and liver. In humans, endocrine and gastrointestinal inflammation are also observed, hence the disease is termed IPEX (Immunodysregulation, Polyendocrinopathy, Enteropathy, X-linked) syndrome. The three week period of fatal MOI offers a useful autoimmune model in which the controls by genetics, T-cell subsets, cytokines, and effector mechanisms could be efficiently investigated. In this report, we will review published work, summarize our recent studies of Scurfy double mutants lacking specific autoimmune-related genes, discuss the cellular and cytokine controls by these genes on MOI, the organ-specificities of the MOI controlled by environments, and the effector mechanisms regulated by specific Th cytokines, including several newly identified control mechanisms for organ-specific autoimmune response.

Activation of innate immunity accelerates sialoadenitis in a mouse model for Sjögren's syndrome-like disease

OBJECTIVE

Sjögren's syndrome is a chronic autoimmune disorder characterized by progressive lymphocytic infiltration within the salivary and lacrimal glands. This study was undertaken to investigate the effects of innate immunity activation on sialoadenitis in a mouse strain genetically susceptible for development of SS-like disease.

METHODS

Female New Zealand Black X New Zealand White F1 mice were repeatedly treated with toll-like 3 receptor agonist poly(I:C). Submandibular glands were investigated at different time points for sialoadenitis by immunohistochemistry and for gene expression of different chemokines by quantitative PCR. Submandibular gland-infiltrating cells were characterized by flow cytometry.

RESULTS

Poly(I:C) treatment significantly upregulated the expression of multiple chemokines within the submandibular glands. The severity and incidence of sialoadenitis was considerably higher in poly(I:C)-treated mice. There was a preponderance of dendritic cells and NK cells in the initial inflammatory cell infiltrates, and these were followed by CD4+ T cells.

CONCLUSIONS

Our data clearly demonstrate that systemic activation of innate immunity accelerates sialoadenitis in a mouse model for SS-like disease. These findings suggest that chronic activation of innate immunity can influence certain features of SS.

Sjögren's syndrome: studying the disease in mice

Sjögren's syndrome (SS), a systemic autoimmune disease, is characterized by inflammation of exocrine tissues accompanied by a significant loss of their secretory function. Clinical symptoms develop late and there are no diagnostic tests enabling early diagnosis of SS. Thus, particularly to study these covert stages, researchers turn to studying animal models where mice provide great freedom for genetic manipulation and testing the effect of experimental intervention. The present review summarizes current literature pertaining to both spontaneous and extrinsic-factor induced SS-like diseases in mouse models, discussing advantages and disadvantages related to the use of murine models in SS research.

Spontaneous autoimmune dacryoadenitis in aged CD25KO mice

To investigate time-related immunopathological changes in the lacrimal glands (LGs) of CD25KO mice, we examined LGs of C57BL/6 (wild-type) and CD25KO mice at 8, 12, and 16 weeks of age. T cell infiltration was quantified by flow cytometry, and gland function by tear peroxidase activity and epidermal growth factor mRNA expression. T helper (Th)-1, -2 and -17-associated cytokine expression was evaluated by real-time PCR. Epithelial apoptosis was assessed by terminal deoxynucleotidyl transferase dUTP nick-end labeling assay and activated caspase-3 staining. Eight-week-old CD25KO mice demonstrated significantly increased numbers of CD4 and CD8 T cells infiltrating the LGs. This peaked at 12 weeks of age. No peroxidase secretion was detected, and epidermal growth factor mRNA expression was barely detected in CD25KO mice. Ductal epithelial apoptosis was noted in CD25KO mice. Young CD25KO LGs had higher Th-17- (interleukin [IL]-23R, transforming growth factor-beta1, IL-17A, CC chemokine attractant ligand-20) and Th-1-associated cytokine transcripts (interferon-gamma, T-bet, IL-12, IL-2, IL-18) than young wild-type LGs. There was also a significant time-related decrease in IL-17A and CC chemokine attractant ligand-20 in CD25KO LGs. Taken together, autoimmune LG infiltration with loss of LG function was observed in CD25KO mice as early as 8 weeks of age. Time-related switch from Th-17 to Th-1 inflammation was noted in CD25KO mice.

Age-related T-cell cytokine profile parallels corneal disease severity in Sjogren's syndrome-like keratoconjunctivitis sicca in CD25KO mice

OBJECTIVES

IL-2ralpha (CD25)(-/-) mice develop autoimmunity and lymphoproliferative disorders, including SS-like disease. The objective of this study was to evaluate the severity of corneal epithelial disease and T-cell cytokine profile in the ocular surface tissues of CD25KO mice.

METHODS

CD25KO mice were evaluated at 8, 12 and 16 weeks of age. Corneal epithelial smoothness and corneal permeability were measured. Phenotype of infiltrating lymphocytes was evaluated by immunohistochemistry. Th-1, -2 and -17 associated factors were measured by real-time PCR in cornea and conjunctiva and by Luminex immunobead assay in tears.

RESULTS

Compared with 8-week-old wild-type (WT) mice, CD25KO mice of the same age had significantly greater corneal irregularity and a significant increase in the number of CD4(+) and CD8(+) T cells infiltrating the conjunctiva. CD25KO mice had significantly higher levels of IL-6, TGF-beta1, IL-23R, IL-17A, IL-17F, IL-21, CCL20, IL-10, GATA-3 and IFN-gamma mRNA transcripts in their cornea and conjunctiva than WT mice at 8 weeks. IL-17A and IL-17F mRNA transcripts peaked at 12 weeks, whereas IFN-gamma spiked at 16 weeks in CD25KO mice. Increased expression of IL-17A and IL-17F at 12 weeks in CD25KO mice was accompanied by a worsening of corneal surface parameters and an increase of CD4(+) T cell infiltrating the cornea.

CONCLUSIONS

Disruption of IL-2 signalling in CD25KO mice results in age-dependent SS-like autoimmune lacrimal-keratoconjunctivitis. A mix of Th-1 and Th-17 cytokines was detected. The peak severity of corneal epithelial disease corresponded to the peak of IL-17 expression.

The numbers of Foxp3 + Treg cells are positively correlated with higher grade of infiltration at the salivary glands in primary Sjogren's syndrome

This study was designed to investigate whether Foxp3( +) regulatory T (Treg) cells play a role in the histopathologic changes of primary Sjögren's Syndrome (pSS) and to evaluate other factors possibly associated with Foxp3(+) Treg cells in pSS patients. The number of FoxP3-expressing T cells in peripheral blood (PB) of 39 patients with pSS, 40 patients with rheumatoid arthritis (RA), and 28 healthy controls was measured by flow-cytometer analysis. FoxP3-expressing CD4(+)CD25(+) Treg cells were analyzed in minor salivary gland (SG) tissues of 39 pSS patients. Histopathologic changes were examined by light microscopy according to Chisholm's classification. Immunohistochemistry and immunofluorescence were performed to assess the Foxp3(+) Treg in SG biopsy specim-ens. The numbers of CD4(+) T cells and FoxP3-expressing CD4(+) T cells in PB were similar in all groups. Expression of CD25 on CD4(+) T cells in PB of patients with pSS and RA was significantly higher than in healthy controls, especially for RA patients. Immunohistochemistry and immunofluorescence showed that FoxP3(+) Treg were enriched in the SGs of pSS patients, with a positive correlation between the increase in FoxP3(+) Treg in SG and the Chisholm score in pSS (p < 0.001, r = +0.605). The increase of FoxP3( +) Treg cells in the SGs of pSS patients, which is correlated with gland infiltration, suggests that natural regulatory T cells play an important role in the pathogenesis of pSS. Further studies are required to explore the mechanisms that mediate the relationship between Treg and the pathogenesis of pSS.

Characteristics of the minor salivary gland infiltrates in Sjögren's syndrome

Sjögren's syndrome (SS) is a chronic autoimmune exocrinopathy associated with variable degree of lymphocytic infiltration of the affected organs (primarily salivary and lacrimal glands) and broad clinical manifestations. Minor salivary gland (MSG) lesions mainly consist of T and B cells, while antigen-presenting cells have been reported in heavy infiltrates. Evidence suggests that the infiltrate composition differs according to lesion severity; however, these differences are not well-defined. To investigate the differential distribution of the major infiltrating mononuclear cell (MNC) types in SS-lesions of variable severity, total-T, CD4(+)-T, CD8(+)-T, Treg, and B cell, macrophage (MPhi), interdigitating (iDC) and follicular dendritic cell (fDC), and natural-killer (NK)-cell incidence (%-total infiltrating MNC) was analyzed in MSG biopsies with mild (n = 11), intermediate (n = 13) or severe (n = 15) lesions. T cells, CD4(+)-T cells and Tregs, B lymphocytes, MPhis and iDCs were significantly different among MSG tissues with mild, intermediate or severe inflammatory lesions, while CD8(+)-T cell, fDC and NK cell incidence was not correlated with lesion severity. T cell, CD4(+)-T cell, T/B cell ratio and iDC incidence was negatively, whereas B cell and MPhi incidence was positively correlated with infiltration grade and biopsy focus score. Tregs predominated in intermediate lesions. Multivariate analysis revealed several associations between the incidence of each infiltrating MNC-type and disease manifestations, implying an involvement of local immune responses in systemic disease features. Our findings support that the distribution of infiltrating MNCs at the SS-lesions varies according to lesion severity and correlates with disease manifestations. The significance of this differential distribution and the underlying aetiopathogenic factors need to be elucidated.

Cleavage of functional IL-2 receptor alpha chain (CD25) from murine corneal and conjunctival epithelia by MMP-9

BACKGROUND

IL-2 has classically been considered a cytokine that regulates T cell proliferation and differentiation, signaling through its heterotrimeric receptor (IL-2R) consisting of alpha (CD25), beta (CD122), gamma chains (CD132). Expression of IL-2R has also been detected in mucosal epithelial cells. Soluble IL-2Ralpha (CD25) has been reported as an inflammatory marker. We evaluated the expression of CD25 and CD122 in the ocular surface epithelium and investigated the mechanism of proteolytic cleavage of CD25 from these cells.

METHODS

Desiccating stress (DS) was used as an inducer of matrix metalloproteinase 9 (MMP-9). DS was created by subjecting C57BL/6 and MMP-9 knockout (BKO) mice and their wild-type littermates (WT) mice to a low humidity and drafty environment for 5 days (DS5). A separate group of C57BL/6 mice was subjected to DS5 and treatment with topical 0.025% doxycycline, a MMP inhibitor, administered QID. The expression of CD25 and CD122 was evaluated in cryosections by dual-label laser scanning confocal microscopy. Western blot was used to measure relative levels of CD25 in epithelial lysates. Gelatinase activity was evaluated by in situ zymography. Soluble CD25 in tear fluid was measured by an immunobead assay.

RESULTS

CD25 and CD122 were abundantly expressed in cornea (all layers) and conjunctiva epithelia (apical and subapical layers) in nonstressed control mice. After desiccating stress, we found that immunoreactivity to CD25, but not CD122, decreased by the ocular surface epithelia and concentration of soluble CD25 in tears increased as MMP-9 staining increased. CD25 was preserved in C57BL/6 mice topically treated with an MMP-9 inhibitor and in MMP-9 knock-out mice. MMP-9 treatment of human cultured corneal epithelial cells decreased levels of CD25 protein in a concentration dependent fashion.

CONCLUSION

Our results indicate that functional IL-2R is produced by the ocular surface epithelia and that CD25 is proteolytic cleaved to its soluble form by MMP-9, which increases in desiccating stress. These findings provide new insight into IL-2 signaling in mucosal epithelia.

X-linked Foxp3 (Scurfy) mutation dominantly inhibits submandibular gland development and inflammation respectively through adaptive and innate immune mechanisms

Scurfy (Foxp3(Sf)/Y), Il2(-/-), and Il2ralpha(-/-) mice are deficient in CD4(+)Foxp3(+) regulatory T cells (Treg), but only the latter two develop inflammation in the submandibular gland (SMG), a critical target of Sjögren's syndrome. In this study, we investigated the reason that SMG of Scurfy (Sf), Sf.Il2(-/-), Sf.Il2ralpha(-/-), and the long-lived Sf.Fas(lpr/lpr) mice remained free of inflammation, even though their lymph node cells induced SMG inflammation in Rag1(-/-) recipients. A strong correlation was observed between the development of the granular convoluted tubules (GCT) of the SMG in these mice and SMG resistance to inflammation. Moreover, GCT development in Sf.Rag1(-/-) mice was not impeded, indicating a role of adaptive immunity. In the Sf.Fas(lpr/lpr) mice, this block was linked to atrophy and inflammation in the accessory reproductive organs. Testosterone treatment restored GCT expression, but did not induce SMG inflammation, indicating GCT is not required for inflammation and additional mechanisms were controlling SMG inflammation. Conversely, oral application of LPS induced SMG inflammation, but not GCT expression. LPS treatment induced up-regulation of several chemokines in SMG with little effect on the chemokine receptors on CD4(+) T cells in Sf mice. Our study demonstrates that Sf mutation affects SMG development through adaptive immunity against accessory reproductive organs, and the manifestation of SMG inflammation in Sf mice is critically controlled through innate immunity.

Regulatory T cells suppress innate immunity in kidney ischemia-reperfusion injury

Both innate and adaptive mechanisms participate in the pathogenesis of kidney ischemia-reperfusion injury (IRI), but the role of regulatory immune mechanisms is unknown. We hypothesized that the anti-inflammatory effects of CD4(+)CD25(+)FoxP3(+) regulatory T cells (Tregs) protect against renal IRI. Partial depletion of Tregs with an anti-CD25 mAb potentiated kidney damage induced by IRI. Reducing the number of Tregs resulted in more neutrophils, macrophages, and innate cytokine transcription in the kidney after IRI but did not affect CD4(+) T cells or B cells. We performed adoptive transfer of lymph node cells from wild-type mice or FoxP3-deficient Scurfy mice into T cell- and B cell-deficient RAG-1 knockout mice to generate mice with and without FoxP3(+) Tregs, respectively. FoxP3(+) Treg-deficient mice accumulated a greater number of inflammatory leukocytes after renal IRI than mice containing Tregs. To confirm that a lack of Tregs potentiated renal injury, we co-transferred isolated Tregs and Scurfy lymph node cells; Treg repletion significantly attenuated IRI-induced renal injury and leukocyte accumulation. Furthermore, although adoptive transfer of wild-type Tregs into RAG-1 knockout mice was sufficient to prevent kidney IRI, transfer of IL-10-deficient Tregs was not. Taken together, these results demonstrate that Tregs modulate injury after kidney IRI through IL-10-mediated suppression of the innate immune system.

Regulation of multi-organ inflammation in the regulatory T cell-deficient scurfy mice

Scurfy mice display the most severe form of multi-organ inflammation due to total lack of the CD4+Foxp3+ regulatory T cells (Treg) resulted from a mutation of the X-linked transcription factor Foxp3. A large repertoire of Treg-suppressible, inflammation-inducing T cells was demonstrated by adoptive transfer experiments using Rag1-/- mice as recipients and by prolongation of lifespan through breeding with Faslpr/lpr mutant. Inflammation in the ear, eyes, skin, tail, salivary glands, lungs, stomach, pancreas, liver, small intestine, colon, skeletal muscle, and accessory reproductive organs are identified. Genetic and cellular regulations of specific organ inflammation are described. Sf mice may be useful for the identification of organ-specific antigens and Treg capable of suppressing inflammation in an organ-specific manner. Sf mice are also useful to determine the important inflammation process at the checkpoint after Treg regulation using genetic analysis through breeding.

Deficiency in regulatory T cells results in development of antimitochondrial antibodies and autoimmune cholangitis

There have been several descriptions of mouse models that manifest select immunological and clinical features of autoimmune cholangitis with similarities to primary biliary cirrhosis in humans. Some of these models require immunization with complete Freund's adjuvant, whereas others suggest that a decreased frequency of T regulatory cells (Tregs) facilitates spontaneous disease. We hypothesized that antimitochondrial antibodies (AMAs) and development of autoimmune cholangitis would be found in mice genetically deficient in components essential for the development and homeostasis of forkhead box 3 (Foxp3)(+) Tregs. Therefore, we examined Scurfy (Sf) mice, animals that have a mutation in the gene encoding the Foxp3 transcription factor that results in a complete abolition of Foxp3(+) Tregs. At 3 to 4 weeks of age, 100% of animals exhibit high-titer serum AMA of all isotypes. Furthermore, mice have moderate to severe lymphocytic infiltrates surrounding portal areas with evidence of biliary duct damage, and dramatic elevation of cytokines in serum and messenger RNAs encoding cytokines in liver tissue, including tumor necrosis factor alpha, interferon-gamma, interleukin (IL)-6, IL-12, and IL-23.

CONCLUSION

The lack of functional Foxp3 is a major predisposing feature for loss of tolerance that leads to autoimmune cholangitis. These findings reflect on the importance of regulatory T cells in other murine models as well as in patients with primary biliary cirrhosis.

A low interleukin-2 receptor signaling threshold supports the development and homeostasis of T regulatory cells

Interleukin-2 receptor (IL-2R) signaling is essential for T regulatory (Treg) cell development and homeostasis. Here, we show that expression of IL-2Rbeta chains that lack tyrosine residues important for the association of the adaptor Shc and the transcription factor STAT5 in IL-2Rbeta-deficient mice resulted in production of a normal proportion of natural Treg cells that suppressed severe autoimmunity related with deficiency in IL-2 or IL-2R. These mutant IL-2Rbeta chains supported suboptimal and transient STAT5 activation that upregulate the transcription factor Foxp3 to normal amounts in natural, but not induced, Treg cells. Nevertheless, gene expression profiling revealed many targets in peripheral natural Treg cells that were IL-2 dependent and a substantial overlap between the Treg cell IL-2-dependent gene program and the Treg cell transcriptional signature. Collectively, these findings demonstrate that a critical, and perhaps minor, subset of IL-2-dependent targets is indexed to a low IL-2R signaling threshold and that a substantial proportion of the Treg cell gene program is regulated by IL-2.

Etiopathogenesis of primary biliary cirrhosis

Primary biliary cirrhosis (PBC) is an autoimmune disease of the liver characterized by progressive bile duct destruction eventually leading to cirrhosis and liver failure. The serological hallmark of the disease is the presence of circulating antimitochondrial antibodies (AMA). These reflect the presence of autoreactive T and B cells to the culprit antigens, the E2 subunits of mitochondrial 2-oxo-acid dehydrogenase enzymes, chiefly pyruvate dehydrogenase (PDC-E2). The disease results from a combination of genetic and environmental risk factors. Genetic predisposition is indicated by the higher familial incidence of the disease particularly among siblings and the high concordance rate among monozygotic twins. Environmental triggering events appear crucial to disrupt a pre-existing unstable immune tolerance of genetic origin allowing, after a long latency, the emergence of clinical disease. Initiating mimotopes of the vulnerable epitope of the PDC-E2 autoantigen can be derived from microbes that utilize the PDC enzyme or, alternatively, environmental xenobiotics/chemical compounds that modify the structure of native proteins to make them immunogenic. A further alternative as a source of antigen is PDC-E2 derived from apoptotic cells. In the effector phase the biliary ductular cell, by reason of its proclivity to express the antigen PDC-E2 in the course of apoptosis, undergoes a multilineage immune attack comprised of CD4⁺ and CD8⁺ T cells and antibody. In this article, we critically review the available evidence on etiopathogenesis of PBC and present interpretations of complex data, new developments and theories, and nominate directions for future research.

A novel role of IL-2 in organ-specific autoimmune inflammation beyond regulatory T cell checkpoint: both IL-2 knockout and Fas mutation prolong lifespan of Scurfy mice but by different mechanisms

Mutation of the Foxp3 transcription factor in Scurfy (Sf) mice results in complete absence of the CD4+Foxp3+ regulatory T cells (Tregs), severe multiorgan autoimmune syndrome, and early death at 4 wk of age. However, Sf mice simultaneously bearing the Il2-/- (Sf.Il2-/-) or Faslpr/lpr gene (Sf.Faslpr/lpr) have extended lifespan despite totally lacking Tregs, indicating a role of IL-2 and CD95 (Fas) signaling pathways in the multiorgan autoimmune syndrome beyond the Treg checkpoint. IL-2 has been implicated in regulating lymphoproliferation and CD178 (FasL) expression. However, Sf.Il2-/- mice have increased lymphoproliferation and FasL expression. Importantly, the pattern of organ-specific autoimmune response of Sf.Il2-/-mice resembled IL-2 knockout mice whereas that of Sf.Faslpr/lpr was similar to Sf mice, indicating that the distinct and weakened autoimmune manifestation in IL-2 knockout mice was not caused by the residual Tregs. Our study demonstrated a novel role of IL-2 in regulating multiorgan autoimmune inflammation beyond the Treg checkpoint and indicated that both Il2-/- and Faslpr/lpr genes prolong the lifespan of Sf mice but by different mechanisms.

Cell damage and autoimmunity: a critical appraisal

In April 2007, an international Colloquium bridging scientific and clinical disciplines was held to discuss the role of cellular and tissue damage in the initiation, development and persistence of autoimmune disease. Five potential etiologic and pathophysiologic processes fundamental to autoimmune disease (i.e. inflammation, infection, apoptosis, environmental exposure and genetics) were the focus of the presentations and integrative discussions at the Colloquium. The information presented on these topics is condensed in this review. Inflammation has close clinico-pathologic associations with autoimmunity, but future analyses will require better definition and metrics of inflammation, particularly for the earliest cellular and molecular components dependent on recruitment of elements of innate immunity. Although infection may be associated with increased levels of autoantibodies, most infections and virtually all vaccinations in humans lack well-established links to autoimmune diseases. Further application of well-designed, long-term epidemiologic and population-based studies is urgently needed to relate antecedent exposures with later occurring stigmata of autoimmunity with a goal of discerning potentially susceptible individuals or subpopulations. Suspect infections requiring closer interrogation include EB virus (SLE and other diseases), HCV (autoimmune hepatitis), beta hemolytic streptococci (rheumatic carditis) and Helicobacter pylori (autoimmune gastritis) among others. And even if a micro-organism was to be incriminated, mechanisms of initiation/perpetuation of autoimmunity continue to challenge investigators. Plausible mechanisms include potentiation and diversion of innate immunity; exposure or spillage of intracellular autoantigens; or provision of autoantigenic mimics. Integrity of apoptosis as a critical safeguard against autoimmunity was discussed in the contexts of over-reactivity causing autoantigens to gain enhanced exposure to the immune system, or under-reactivity producing insufficient elimination of autoreactive clones of lymphocytes. Although environmental agents are widely believed to serve as necessary "triggers" of autoimmune disease in genetically predisposed individuals, only a few such agents (mainly drugs and some nutrients) have been clearly identified and their mechanism of action defined. Finally an essential genetic foundation underlies all these hazards for autoimmunity in the form of risk-associated polymorphisms in immunoregulatory genes. They may be predictive of future or impending disease.

A novel method of bone marrow transplantation (BMT) for intractable autoimmune diseases

We have previously proposed that autoimmune diseases are hemopoietic stem cell (HSC) disorders. In this review article, we provide evidence that most age-associated diseases such as osteoporosis are mesenchymal stem cell (MSC) disorders and, based on this evidence, we propose a new concept of "stem cell disorders (SCDs)", including HSC and MSC disorders. To treat SCDs, we have recently developed a new strategy (intra-bone marrow-bone marrow transplantation: IBM-BMT) for replacing the abnormal stem cells of recipients with donor-derived normal stem cells (both HSCs and MSCs). We here show that this strategy not only can be used to treat SCDs but is also applicable to organ transplantation, since IBM-BMT can induce tolerance (full chimerism) without the need for immunosuppressants even when radiation doses as the conditioning regimen of BMT are reduced to less than 5.0 Gy x 2, which is equivalent to one shot of 8 Gy (a sublethal dose). We believe that this strategy heralds a revolution in the field of transplantation (BMT and organ transplantation) and regeneration therapy.