Immunologic basis for development of keratoconjunctivitis sicca in systemic autoimmune diseases: Role of innate immune sensors.

The literature is filled with citations reporting an increased incidence of chronic dry eye disease, also known as keratoconjunctivitis sicca, in patients with systemic autoimmune diseases such as rheumatoid arthritis, Sjögren's Syndrome, systemic sclerosis and lupus. As the most environmentally exposed mucosal surface of the body, the conjunctiva constantly responds to environmental challenges which are typically self limited, but when persistent and unresolved may provoke pathogenic innate and adaptive immune reactions. Our understanding of the pathophysiological mechanisms by which systemic autoimmune diseases cause dry eye inducing ocular surface inflammation continues to evolve. Conjunctival immune tone responds to self or foreign danger signals (including desiccating stress) on the ocular surface with an initial non-specific innate inflammatory response. If unchecked, this can lead to activation of dendritic cells that present antigen and prime T and B cells resulting in an adaptive immune reaction. These reactions generally resolve, but dysfunctional, hyper-responsive immune cells found in systemic autoimmune diseases that are recruited to the ocular surface can amplify inflammatory stress responses in the ocular surface and glandular tissues and result in autoimmune reactions that disrupt tear stability and lead to chronic dry eye disease. We here propose that unique features of the ocular surface immune system and the impact of systemic immune dysregulation in autoimmune diseases, can predispose to development of dry eye disease, and exacerbate severity of existing dry eye.

Effect of Withdrawing Chronic Topical Immune Modulating Treatment on Schirmer Tear Test Values in Dogs with Dry Eye Disease: Relevance to Dry Eye Studies.

Purpose: To determine the effect of discontinuing chronic topical immune modulating (IM) treatment on Schirmer tear test (STT) values in dogs with dry eye disease (DED). Methods: Serial measurements of STTs from 14 dogs (16 eyes) previously diagnosed with DED were obtained before and after discontinuation of topical IM agents. Dogs with moderate to severe DED that had been well controlled with a topical IM treatment were included. After initial assessment topical IM treatment was discontinued, but topical lubricant was continued, and STT values were obtained sequentially. A mixed-effects regression model was used to evaluate the effects of age, gender, breed, clinical score, frequency of treatment, baseline STT value, and drug type on final STT values after IM withdrawal. P < 0.05 was considered statistically significant. Results: During the follow-up period after the IM treatment had been discontinued (136 ± 29 days), 50% of the eyes (n = 8) exhibited STT values that never decreased to <10 mm/min. In the other 50% (n = 8), STT values decreased from 15.9 ± 4.7 mm/min to 6.1 ± 0.9 mm/min. In this group, the time it took to decrease the STT to <10 mm/min was 21.1 ± 9.5 days. Severe clinical signs of DED and low baseline STT pre-IM treatment significantly affected STT post-IM treatment withdrawal (P < 0.05). Conclusions: The duration that a residual effect of topical IM treatment persists needs to be taken into consideration when studies are designed utilizing dogs with previous IM treatment for DED.

Utility of lymphocyte phenotype profile to differentiate primary Sjögren's syndrome from sicca syndrome.

OBJECTIVE: To assess the potential diagnostic utility of advanced lymphocyte profiling to differentiate between primary Sjögren's Syndrome (pSS) and non-Sjögren Sicca syndrome. METHODS: Distribution of peripheral lymphocyte subpopulations was analysed by flow cytometry in 68 patients with pSS, 26 patients with sicca syndrome and 23 healthy controls. The ability to discriminate between pSS and sicca syndrome was analysed using the area under the curve (AUC) of the receiver operating characteristic curve of the different lymphocyte subsets. RESULTS: The ratio between naïve/memory B cell proportions showed an AUC of 0.742 to differentiate pSS and sicca syndrome, with a sensitivity of 76.6% and a specificity of 72% for a cut-off value of 3.4. The ratio of non-switched memory B cells to activated CD4+ T cells percentage (BNSM/CD4ACT) presented the highest AUC (0.840) with a sensitivity of 83.3% and specificity of 81.7% for a cut-off value <4.1. To differentiate seronegative pSS patients from sicca patients, the BNSM/CD4ACT ratio exhibited an AUC of 0.742 (sensitivity 75%, specificity 66.7%, cut-off value <4.4), and the number of naïve CD4 T cells had an AUC of 0.821 (sensitivity 76.9%, specificity 88.9%, cut-off value <312/mm3). CONCLUSION: Patients with pSS show a profound imbalance in the distribution of circulating T and B lymphocyte subsets. The ratio BNSM/CD4ACT is useful to discriminate between pSS and sicca syndrome.

Sjögren Syndrome without Focal Lymphocytic Infiltration of the Salivary Glands.

OBJECTIVE: Primary Sjögren syndrome (SS) is characterized by a focal lymphocytic infiltrate in exocrine glands. We describe patients who lacked this key feature. METHODS: We evaluated patients with sicca in a comprehensive clinic at which medical, dental, and ophthalmological examinations were performed. All subjects underwent a minor salivary gland biopsy with focus score calculation. Extraglandular manifestations were also determined. We categorized subjects as high, intermediate, or low in terms of expression of interferon (IFN)-regulated genes. RESULTS: About 20% (51 of 229, 22%) of those classified as having primary SS had a focus score of zero. Compared to those with anti-Ro positivity and a focus score > 1.0, the patients with focus score of zero (who by classification criteria must be anti-Ro-positive) were statistically less likely to have anti-La (or SSB) and elevated immunoglobulin, as well as less severe corneal staining. The focus score zero patients were less likely to have elevated expression of IFN-regulated genes in peripheral blood mononuclear cells than anti-Ro-positive SS patients with a focal salivary infiltrate. CONCLUSION: There are only a few clinical differences between patients with primary SS with focus score zero and those with both anti-Ro and a focus score > 1.0. The small subset of focus score zero patients tested did not have elevated expression of IFN-regulated genes, but did have systemic disease. Thus, extraglandular manifestations are perhaps more related to the presence of anti-Ro than increased IFN. This may have relevance to pathogenesis of SS.

Mesenchymal Stem Cells Extract (MSCsE)-Based Therapy Alleviates Xerostomia and Keratoconjunctivitis Sicca in Sjogren's Syndrome-Like Disease.

Sjogren's syndrome (SS) is an autoimmune disease that manifests primarily in salivary and lacrimal glands leading to dry mouth and eyes. Unfortunately, there is no cure for SS due to its complex etiopathogenesis. Mesenchymal stem cells (MSCs) were successfully tested for SS, but some risks and limitations remained for their clinical use. This study combined cell- and biologic-based therapies by utilizing the MSCs extract (MSCsE) to treat SS-like disease in NOD mice. We found that MSCsE and MSCs therapies were successful and comparable in preserving salivary and lacrimal glands function in NOD mice when compared to control group. Cells positive for AQP5, AQP4, α-SMA, CK5, and c-Kit were preserved. Gene expression of AQP5, EGF, FGF2, BMP7, LYZ1 and IL-10 were upregulated, and downregulated for TNF-α, TGF-ß1, MMP2, CASP3, and IL-1ß. The proliferation rate of the glands and serum levels of EGF were also higher. Cornea integrity and epithelial thickness were maintained due to tear flow rate preservation. Peripheral tolerance was re-established, as indicated by lower lymphocytic infiltration and anti-SS-A antibodies, less BAFF secretion, higher serum IL-10 levels and FoxP3+ Treg cells, and selective inhibition of B220+ B cells. These promising results opened new venues for a safer and more convenient combined biologic- and cell-based therapy.

Phenotypic features and predictors of the clinical severity of keratoconjunctivitis sicca and salivary gland dysfunction in patients with Sjögren's syndrome: a longitudinal analysis of the Korean Initiative of primary Sjögren's Syndrome (KISS) cohort.

OBJECTIVE: The aim was to investigate prevalence and degree of ocular and oral involvement in patients with primary Sjögren's syndrome (PSS). METHOD: We analysed 134 participants from the Korean Initiative of PSS cohort who completed a 2 year follow-up oral and ocular sign test. The severity of keratoconjunctivitis sicca (KCS) was determined with the Schirmer I test value (STV) [abnormal (AB) ≤ 5 mm/5 min; normal (N) > 5 mm/5 min]. Salivary gland dysfunction (SGD) was determined by unstimulated whole salivary (UWS) flow rate [moderate to severe (MS) < 0.1 mL/min; mild (Mi) ≥ 0.1 mL/min]. Subgroups were divided into three groups according to STV and severity of SGD: AB-STV/MS-SGD, AB-STV/Mi-SGD, and N-STV/MS-SGD groups. We analysed the changes in STV and SGD during the follow-up period. RESULTS: Among the 134 participants enrolled in this study, 105 (78%) were placed in the AB-STV/MS-SGD group, 16 (12%) in the AB-STV/Mi-SGD, and 13 (10%) in the N-STV/MS-SGD at the 2 year follow-up. The AB-STV/Mi-SGD group was younger than the other two groups, and had a lower Xerostomia Inventory score and lower level of ß2-microglobulin. Participants in the N-STV/MS-SGD group had less hyperimmunoglobulinaemia, rheumatoid factor (RF), and antinuclear antibodies (ANAs). Patients and those with positive RF or ANA ≥ 1:320 at baseline were more likely to have abnormal STV at the 2 year follow-up. CONCLUSIONS: Patients with PSS and positive RF or ANA ≥ 1:320 at baseline may benefit from regular ophthalmology examinations, even if they do not have KCS at baseline or dry eye symptoms.

Novel Sjögren's autoantibodies found in fibromyalgia patients with sicca and/or xerostomia.

INTRODUCTION: A significant proportion of patients with fibromyalgia (FM) complain of dry eyes and mouth. Many Sjögren's syndrome (SS) patients also complain of FM symptoms, and there is literature that suggests that there is interplay between these two disorders. Recently, the presence of novel tissue specific autoantibodies (TSAs), SP-1, CA6, and PSP, has been observed in the early stages of SS. These early markers present themselves before the classic autoantibodies, such as SS-A/Ro, SS-B/La, ANA, and RF. OBJECTIVE: This study aims to examine the relationship between SS and FM by testing patients with FM who also complain of xerostomia and sicca symptoms, for SS- related biomarkers. METHODS: A cohort of 185 patients who met both the 1990 and 2010 preliminary diagnostic criteria for FM and who admitted to symptoms of sicca and/or xerostomia were selected for this study. Serum from 151 study patients was sent to a tertiary lab, Immco Diagnostics, for testing of the classic autoantibodies (SS-A/Ro, SS-B/La, ANA and RF) and TSAs (SP-1, CA6, PSP), while the rest (34 patients) were tested for TSAs only. RESULTS: Of the 151 patients who were evaluated for both the early and classic SS markers, 49 (32%) tested positive for SS autoantibodies. Of those, 4 (3%) tested positive for the classic SS markers only, 40 (26%) of the patients tested positive for the early SS markers only, and 5 (3%) tested positive for both the early and classic SS markers. Of the 34 patients who were tested for early SS markers only, 10 (29%) tested positive and 24 (71%) tested negative. Further analysis of all the patients that tested positive for the TSAs (n = 55), found 83.6% (46) were positive for SP-1, 12.7% (7) were positive for CA6 and 20.0% (11) were positive for PSP. 85.5% (47) of these patients were positive for only one of the TSAs and 14.5% (8) were positive for more than one TSA. CONCLUSION: Approximately 1/3 of FM patients that were tested for both the TSAs and classic Sjögren's markers tested positive for a SS biomarker, and the majority of those patients tested positive for one or more of the TSAs. This suggests that autoimmunity, specifically early- stage Sjögren's syndrome, may be involved in the pathophysiology of fibromyalgia.

Suppression of Th1-Mediated Keratoconjunctivitis Sicca by Lifitegrast.

PURPOSE: Increased interferon gamma (IFN-γ) expression in dry eye causes ocular surface epithelial disease termed keratoconjunctivitis sicca (KCS). The purpose of this study was to investigated the effects of the LFA-1 antagonist, lifitegrast, in a mouse desiccating stress (DS) dry eye model that develops KCS similar to Sjögren syndrome. METHODS: Mice were treated with vehicle or lifitegrast twice daily for 5 days and expression of Th1 family genes (IFN-γ, CXCL9, and CXCL11) was evaluated by real-time polymerase chain reaction. Cornea barrier function was assessed by Oregon Green dextran staining and goblet cell number and area were measured. RESULTS: Compared to the vehicle-treated group, the lifitegrast-treated group had significantly lower expression of Th1 family genes, less corneal barrier disruption, and greater conjunctival goblet cell density/area. CONCLUSIONS: These findings indicate that lifitegrast inhibits DS-induced IFN-γ expression and KCS. This suggests that ICAM-LFA-1 signaling is involved with generation of Th1 inflammation in KCS.

TH17 cells mediate inflammation in a novel model of spontaneous experimental autoimmune lacrimal keratoconjunctivitis with neural damage.

BACKGROUND: Dry eye disease (DED) affects one third of the population worldwide. In prior studies, experimental autoimmune lacrimal keratoconjunctivitis (EALK) induced by desiccating stress in mice has been used as a model of DED. This model is complicated by a requirement for exogenous epithelial cell injury and administration of anticholinergic agents with broad immunologic effects. OBJECTIVE: We sought to develop a novel mouse model of EALK and to demonstrate the responsible pathogenic mechanisms. METHODS: CD4+CD45RBhigh naive T cells with and without CD4+CD45RBlow regulatory T cells were adoptively transferred to C57BL/10 recombination-activating gene 2 (Rag2)-/- mice. The eyes, draining lymph nodes, lacrimal glands, and surrounding tissues of mice with and without spontaneous keratoconjunctivitis were evaluated for histopathologic changes, cellular infiltration, and cytokine production in tissues and isolated cells. Furthermore, the integrity of the corneal nerves was evaluated using whole-tissue immunofluorescence imaging. Gene-deficient naive T cells or RAG2-deficient hosts were evaluated to assess the roles of IFN-γ, IL-17A, and IL-23 in disease pathogenesis. Finally, cytokine levels were determined in the tears of patients with DED. RESULTS: EALK developed spontaneously in C57BL/10 Rag2-/- mice after adoptive transfer of CD4+CD45RBhigh naive T cells and was characterized by infiltration of CD4+ T cells, macrophages, and neutrophils. In addition to lacrimal keratoconjunctivitis, mice had damage to the corneal nerve, which connects components of the lacrimal functional unit. Pathogenic T-cell differentiation was dependent on IL-23p40 and controlled by cotransferred CD4+CD45RBlow regulatory T cells. TH17 rather than TH1 CD4+ cells were primarily responsible for EALK, even though levels of both IL-17 and IFN-γ were increased in inflammatory tissues, likely because of their ability to drive expression of CXC chemokines within the cornea and the subsequent influx of myeloid cells. Consistent with the findings of this model, the tears of patients with DED had increased levels of inflammatory cytokines, including IL-17A and TNF-α. CONCLUSION: We describe a novel model of spontaneous EALK that supports a role for TH17 cells in disease pathogenesis and that will contribute to our understanding of autoimmune lacrimal keratoconjunctivitis in many human eye diseases, including DED.

[Anatomy and immunology of the eye]. / Anatomie und Immunologie des Auges.

The eye has all the mechanisms necessary for detection and processing (afferent immune reaction) as well as adequate initiation of an (efferent) immune response. Apart from the typical antigen-processing cells, locally present elements (e.g. glial cells and retinal pigment epithelium) can also be involved in the afferent reaction. For the efferent mechanisms a complex regulative system exists, which includes cellular and humoral responses and is essentially determined by surface molecules. In addition, the ocular environment is rich in immunosuppressive molecules that contribute to the regulation of immune cells. The adaptation of the anatomical and biochemical mechanisms for the creation of an immune-privileged microenvironment makes this sense organ unique. The purpose of this article is to highlight the specific features of the eye and to establish a reference to frequent ocular manifestations in rheumatic diseases.

Pathological Analysis of Ocular Lesions in a Murine Model of Sjögren's Syndrome.

Sjögren's syndrome (SS) is a systemic autoimmune disease characterized by severe inflammation of exocrine glands such as the salivary and lacrimal glands. When it affects the lacrimal glands, many patients experience keratoconjunctivitis due to severely dry eyes. This study investigated the pathological and immunological characteristics of ocular lesions in a mouse model of SS. Corneal epithelial injury and hyperplasia were confirmed pathologically. The number of conjunctival mucin-producing goblet cells was significantly decreased in the SS model mice compared with control mice. Expression levels of transforming growth factor (TGF)-ß, interleukin (IL)-6, tumor necrosis factor (TNF)-α, and C-X-C motif chemokine (CXCL) 12 were significantly higher in the corneal epithelium of the SS model mice than in control mice. Inflammatory lesions were observed in the Harderian, intraorbital, and extraorbital lacrimal glands in the SS model mice, suggesting that the ocular glands were targeted by an autoimmune response. The lacrimal glands of the SS model mice were infiltrated by cluster of differentiation (CD)4⁺ T cells. Real-time reverse transcription-polymerase chain reaction (RT-PCR) revealed significantly increased mRNA expression of TNF-α, TGF-ß, CXCL9, and lysozyme in the extraorbital lacrimal glands of the SS model mice compared with control mice. These results add to the understanding of the complex pathogenesis of SS and may facilitate development of new therapeutic strategies.

Ageing and ocular surface immunity.

The prevalence of ocular surface immunopathologies is enhanced in the elderly. This increased prevalence has been attributed to age-related dysregulation of innate and adaptive immune system responses. Age-related changes in ocular surface immunity have similar and distinct characteristics to those changes seen in other mucosal tissues. This mini review provides a brief outline of key findings in the field of ocular ageing, draws comparisons with other mucosal tissues and, finally, discusses age-related changes in the context of immunopathogenesis of infectious keratitis and dry eye disease, two of the most common inflammatory disorders of the ocular surface.

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.H2b 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.

Dry eye disease and uveitis: A closer look at immune mechanisms in animal models of two ocular autoimmune diseases.

Understanding the immunopathogenesis of autoimmune and inflammatory diseases is a prerequisite for specific and effective therapeutical intervention. This review focuses on animal models of two common ocular inflammatory diseases, dry eye disease (DED), affecting the ocular surface, and uveitis with inflammation of the inner eye. In both diseases autoimmunity plays an important role, in idiopathic uveitis immune reactivity to intraocular autoantigens is pivotal, while in dry eye disease autoimmunity seems to play a role in one subtype of disease, Sjögren' syndrome (SjS). Comparing the immune mechanisms underlying both eye diseases reveals similarities, and significant differences. Studies have shown genetic predispositions, T and B cell involvement, cytokine and chemokine signatures and signaling pathways as well as environmental influences in both DED and uveitis. Uveitis and DED are heterogeneous diseases and there is no single animal model, which adequately represents both diseases. However, there is evidence to suggest that certain T cell-targeting therapies can be used to treat both, dry eye disease and uveitis. Animal models are essential to autoimmunity research, from the basic understanding of immune mechanisms to the pre-clinical testing of potential new therapies.

Autoimmunity in the pathogenesis and treatment of keratoconjunctivitis sicca.

Dry eye is a chronic corneal disease that impacts the quality of life of many older adults. Keratoconjunctivitis sicca (KCS), a form of aqueous-deficient dry eye, is frequently associated with Sjögren's syndrome and mechanisms of autoimmunity. For KCS and other forms of dry eye, current treatments are limited, with many medications providing only symptomatic relief rather than targeting the pathophysiology of disease. Here, we review proposed mechanisms in the pathogenesis of autoimmune-based KCS: genetic susceptibility and disruptions in antigen recognition, immune response, and immune regulation. By understanding the mechanisms of immune dysfunction through basic science and translational research, potential drug targets can be identified. Finally, we discuss current dry eye therapies as well as promising new treatment options and drug therapy targets.

Dry eye disease: an immune-mediated ocular surface disorder.

Dry eye disease is a multifactorial disorder of the tears and ocular surface characterized by symptoms of dryness and irritation. Although the pathogenesis of dry eye disease is not fully understood, it is recognized that inflammation has a prominent role in the development and propagation of this debilitating condition. Factors that adversely affect tear film stability and osmolarity can induce ocular surface damage and initiate an inflammatory cascade that generates innate and adaptive immune responses. These immunoinflammatory responses lead to further ocular surface damage and the development of a self-perpetuating inflammatory cycle. Herein, we review the fundamental links between inflammation and dry eye disease and discuss the clinical implications of inflammation in disease management.

Punctal occlusion is safe and efficient for the treatment of keratoconjunctivitis sicca in patients with ocular GvHD.

The use of punctal plugs in the treatment of keratoconjunctivitis sicca (KCS) in inflammatory eye disease remains controversial because of the potentially increased retention time of tears enriched with inflammatory cytokines that may aggravate eye inflammation. We describe the safety and efficacy of punctal occlusion in a retrospective analysis of 19 patients (16 men) with KCS due to chronic GvHD (cGvHD). Efficacy and safety were assessed by subjective and objective criteria (symptoms, corneal fluorescein staining, tear film break-up time (BUT), Schirmer I test, Jones test and visual acuity). Follow-up was from plug insertion until maximum one year after punctal occlusion. After punctal occlusion, patients reported a significant increase in subjective comfort (1.10 vs 0.59 on a scale ranging from no symptoms (0) to severe impairment (2), P<0.001). Pathological corneal fluorescein staining decreased significantly (P<0.001) and tear film BUT remained unchanged (5.98 vs 4.0 s, P=0.79). Measurement of tear secretion or retention time showed a non-significant trend for improvement in the Schirmer I (3.0 vs 3.40 mm, P=0.08) and Jones (1.36 vs 2.8 mm, P=0.08) tests. The logMAR visual acuity remained unchanged. Punctal occlusion achieved a significant improvement in subjective symptoms and objective findings in ocular GvHD without increasing ocular inflammation.

Ocular surface APCs are necessary for autoreactive T cell-mediated experimental autoimmune lacrimal keratoconjunctivitis.

As specialized sentinels between the innate and adaptive immune response, APCs are essential for activation of Ag-specific lymphocytes, pathogen clearance, and generation of immunological memory. The process is tightly regulated; however, excessive or atypical stimuli may ignite activation of APCs in a way that allows self-Ag presentation to autoreactive T cells in the context of the necessary costimulatory signals, ultimately resulting in autoimmunity. Studies in both animal models and patients suggest that dry eye is a chronic CD4(+) T cell-mediated ocular surface autoimmune-based inflammatory disease. Using a desiccating stress-induced mouse model of dry eye, we establish the fundamental role of APCs for both the generation and maintenance of ocular-specific autoreactive CD4(+) T cells. Subconjunctival administration of liposome-encapsulated clodronate efficiently diminished resident ocular surface APCs, inhibited the generation of autoreactive CD4(+) T cells, and blocked their ability to cause disease. APC-dependent CD4(+) T cell activation required intact draining cervical lymph nodes, as cervical lymphadenectomy also inhibited CD4(+) T cell-mediated dry eye disease. In addition, local depletion of peripheral conjunctival APCs blocked the ability of dry eye-specific CD4(+) T cells to accumulate within the ocular surface tissues, suggesting that fully primed and targeted dry eye-specific CD4(+) T cells require secondary activation by resident ocular surface APCs for maintenance and effector function. These data demonstrate that APCs are necessary for the initiation and development of experimental dry eye and support the standing hypothesis that dry eye is a self-Ag-driven autoimmune disease.

The complexity of Sjögren's syndrome: novel aspects on pathogenesis.

In Sjögren's syndrome, like in most other autoimmune diseases, the enigma leading to a pathogenic attack against self has not yet been solved. By definition, the disease must be mediated by specific immune reactions against endogenous tissues to qualify as an autoimmune disease. In Sjögren's syndrome the autoimmune response is directed against the exocrine glands, which, as histopathological hallmark of the disease, display persistent and progressive focal mononuclear cell infiltrates. Clinically, the disease in most patients is manifested by two severe symptoms: dryness of the mouth (xerostomia) and the eyes (keratoconjunctivitis sicca). A number of systemic features have also been described and the presence of autoantibodies against the ubiquitously expressed ribonucleoprotein particles Ro (Sjögren's-syndrome-related antigen A - SSA) and La (SSB) further underline the systemic nature of Sjögren's syndrome. The original explanatory concept for the pathogenesis of Sjögren's syndrome proposed a specific, self-perpetuating, immune mediated loss of acinar and ductal cells as the principal cause of salivary gland hypofunction. Although straightforward and plausible, the hypothesis, however, falls short of accommodating several Sjögren's syndrome-related phenomena and experimental findings. Consequently, researchers considered immune-mediated salivary gland dysfunction prior to glandular destruction and atrophy as potential molecular mechanisms underlying the symptoms of dryness in Sjögren's syndrome. Accordingly, apoptosis, fibrosis and atrophy of the salivary glands would represent consequences of salivary gland hypofunction. The emergence of advanced bio-analytical platforms further enabled the identification of potential biomarkers with the intent to improve Sjögren's syndrome diagnosis, promote the development of prognostic tools for Sjögren's syndrome and the long-term goal to identify possible processes for therapeutic treatment interventions. In addition, such approaches allowed us to glimpse at the apparent complexity of Sjögren's syndrome.