Sjögren's syndrome: immunologic and neuroendocrine mechanisms

Rethinking Sjögren Beyond Inflammation: Considering the Role of Nerves in Driving Disease Manifestations

ABSTRACT

Sjögren syndrome (SS) is a chronic inflammatory autoimmune disease characterized by destruction of mucosal glands resulting in dry eye and dry mouth. Ocular presentations can be heterogenous in SS with corneal nerves abnormalities that are structural, functional, or both. Some individuals present with corneal hyposensitivity, with a phenotype of decreased tear production and epithelial disruption. Others present with corneal hypersensitivity, with a phenotype of neuropathic pain including light sensitivity and pain out of proportion to signs of tear dysfunction. A similar correlate can be found outside the eye, with dry mouth predominating in some individuals while pain conditions predominate in others. Understanding how nerve status affects SS phenotype is an important first step to improving disease management by targeting nerve abnormalities, as well as inflammation.

Pathology of salivary gland dysfunction and restoration of function

In this review, the author shows that simultaneous multiple disorders caused by reactivation of Epstein-Barr virus can lead to salivary gland disorders as part of Sjogren's syndrome (SS). Therefore, clinicians must differentiate SS from other diseases when diagnosing and treating salivary gland disorders. In particular, the author explains how microbial infection in SS overcomes immunological tolerance, leading to pathological changes, and how cytokine overexpression and endocrine disrupters contribute to glandular tissue injury. Also, the author suggests that involvement of reactive oxygen species is a common pathogenesis of salivary gland disorders and SS, so regulation of oxidative stress is an effective treatment for both. The results of clinical studies on restoring salivary gland function and regenerating salivary glands with tissue stem cells may provide clues on elucidating the cause of SS.

Functional effects of proinflammatory factors present in Sjögren's syndrome salivary microenvironment in an in vitro model of human salivary gland

Primary Sjögren’s syndrome (pSS) is an autoimmune exocrinopathy in which the role that the immune response plays in reducing exocrine gland function, including the glandular microenvironment of cytokines, has not been fully understood. Epithelial cells from biopsies of human parotid gland (HPG) were used to establish a model of human salivary gland in vitro. In this model, the functional consequences of several proinflammatory soluble factors present in the pSS glandular microenvironment were assessed. Stimulation with isoproterenol and calcium produced a significant increase in the basal activity of amylase in the HPG cell supernatants. Under these conditions, the presence of TNF-α and CXCL12 increased amylase mRNA cellular abundance, but reduced the amylase activity in the cell-free supernatant in a dose-dependent manner. IL-1β and IFN-γ, but not TGF-β, also diminished amylase secretion by HPG cells. These results suggest that the glandular microenvironment of cytokine, by acting post-transcriptionally, may be responsible, at least in part, for the reduced exocrine function observed in pSS patients. These data may help to a better understanding of the pathogenesis of SS, which in turn would facilitate the identification of new therapeutic targets for this disorder.

Preventive effect of Ophiopogon japonicus polysaccharides on an autoallergic mouse model for Sjogren's syndrome by regulating the Th1/Th2 cytokine imbalance

AIM OF STUDY

Sjogren's syndrome (SS) is an autoimmune disorder characterized by lymphocytic infiltration of salivary and lacrimal glands leading to xerostomia and keratoconjunctivitis sicca. Evidence has accumulated suggesting that a Th1/Th2 cytokine imbalance has a role in the pathogenesis of SS. Currently, only palliative treatment is available. Ophiopogon japonicus, a common Chinese herbal, has been used to treat sicca-associated disorders in traditional Chinese medicine for centuries.

MATERIALS AND METHOD

In this study, we constructed an autoallergic mouse model for SS by immunizing C57BL/6 mouse with submandibular gland (SMG) autoantigen. At the same time, Ophiopogon japonicus polysaccharides (OJP) was administered and hydroxychloroquine was served as positive control. During the 4 weeks' experiment, salivary flow rates were determined every week, body weight, food and water intake were measured every 2 days. After death, serum were collected for IFN-gamma and IL-4 ELISA analysis and the IFN-gamma/IL-4 was calculated, SMG and spleen were harvested for organ index calculation, and part of SMG was examined for histological changes.

RESULTS

Results showed that immunization with SMG autoantigen induced decreased salivary flow and body weight, increased water intake, SMG index, spleen index, IFN-gamma level and IFN-gamma/IL-4 ratio compared with the normal group. However, administration of the OJP could improve these data and the pathological changes of SMG with respect to the model mice, especially the high-dose of OJP group.

CONCLUSIONS

Thus, this study provided a basis for the use of Ophiopogon japonicus in SS.

Microarray analysis of the rat lacrimal gland following the loss of parasympathetic control of secretion

Previous studies showed that loss of muscarinic parasympathetic input to the lacrimal gland (LG) leads to a dramatic reduction in tear secretion and profound changes to LG structure. In this study, we used DNA microarrays to examine the regulation of the gene expression of the genes for secretory function and organization of the LG. Long-Evans rats anesthetized with a mixture of ketamine/xylazine (80:10 mg/kg) underwent unilateral sectioning of the greater superficial petrosal nerve, the input to the pterygopalatine ganglion. After 7 days, tear secretion was measured, the animals were killed, and structural changes in the LG were examined by light microscopy. Total RNA from control and experimental LGs (n = 5) was used for DNA microarray analysis employing the U34A GeneChip. Three statistical algorithms (detection, change call, and signal log ratio) were used to determine differential gene expression using the Microarray Suite (5.0) and Data Mining Tools (3.0). Tear secretion was significantly reduced and corneal ulcers developed in all experimental eyes. Light microscopy showed breakdown of the acinar structure of the LG. DNA microarray analysis showed downregulation of genes associated with the endoplasmic reticulum and Golgi, including genes involved in protein folding and processing. Conversely, transcripts for cytoskeleton and extracellular matrix components, inflammation, and apoptosis were upregulated. The number of significantly upregulated genes (116) was substantially greater than the number of downregulated genes (49). Removal of the main secretory input to the rat LG resulted in clinical symptoms associated with severe dry eye. Components of the secretory pathway were negatively affected, and the increase in cell proliferation and inflammation may lead to loss of organization in the parasympathectomized lacrimal gland.

Autoantigens and Sjögren syndrome

PURPOSE

To review recent experimental evidence on the involvement of autoantigens and autoantibodies in the pathogenesis of organ-specific autoimmunity in Sjögren syndrome (SS).

METHODS

Among candidate autoantigens in SS, we investigated the role of alpha-fodrin in the lacrimal gland using a mouse model and a lacrimal gland cell line established in p53 knockout mice. We also tried to identify a novel organ-specific autoantigen by screening the human salivary gland cell line (HSG) against sera from SS patients. The specificity and sensitivity of this autoantigen to SS patient sera, its cellular localization, and the gene encoding the protein were analyzed.

RESULTS

In addition to the previously identified 120-kd alpha-fodrin in the salivary gland, a shorter fragment was detected, indicating that there may be a distinct apoptosis-related protease that cleaves alpha-fodrin in the lacrimal gland. A novel salivary gland-specific autoantibody was detected in 50.9% of sera from SS patients. The antigen recognized by this antibody may be a 45-kd nucleus protein not recognized in its native form.

CONCLUSION

The precise roles of autoantigens in organ-specific autoimmunity are still unclear, although accumulated evidence suggests that they may be associated with disease progression. Further studies of alpha-fodrin and the 45-kd antigen may contribute to the understanding of the pathogenesis of SS and may provide a new strategy for organ-specific therapy, such as vaccination with analogue peptides.

Lack of evidence for an increased microchimerism in the circulation of patients with Sjögren's syndrome

OBJECTIVE

To examine the hypothesis that fetal microchimerism plays a part in the pathogenic process of Sjögren's syndrome (SS).

METHODS

Genomic DNA samples were extracted from peripheral blood whole nucleated cells and the CD34+ cell enriched fraction of patients with SS and healthy women who had male offspring as well as nulliparous women. A Y chromosome-specific sequence was detected as a marker for fetal cells by a nested polymerase chain reaction (PCR) and by DNA hybridisation combined with PCR using specific primers and probes. All procedures were performed with great care to avoid the contamination of male DNA.

RESULTS

A nested PCR and DNA hybridisation combined with PCR was established that can detect a single male cell out of 1.67x10(5) female cells. It was not possible to increase the sensitivity further because the amount of template DNA held in the PCR was limited. When these methods were used, no fetal cells were detected in any samples from patients with SS, though they were detected in whole nucleated cells from two healthy women who had delivered sons previously.

CONCLUSIONS

The findings indicate that circulating fetal cells in patients with SS are uncommon (<1 in 1.67x10(5)), if they exist. With the conventional PCR based methods that were used, it is difficult to evaluate the quantitative difference in circulating fetal cells between patients with SS and healthy women.

An investigation of interactions between the immune system and stimulus-secretion coupling in mouse submandibular acinar cells. A possible mechanism to account for reduced salivary flow rates associated with the onset of Sjögren's syndrome

OBJECTIVES

To determine whether chronic exposure to lymphocyte-derived cytokines could inhibit the fluid secretory mechanism in salivary gland acinar cells and so account for the loss of gland function seen in the early stages of Sjögren's syndrome.

METHODS

Mouse submandibular acinar cells maintained in primary culture were exposed to a profile of cytokines produced by concanavalin A-activated splenic lymphocytes in vitro for periods up to 72 h. Agonist-evoked changes in intracellular Ca(2+) were determined microfluorimetrically in both control and cytokine-treated cells.

RESULTS

Acinar cells maintained in primary culture in the presence of cytokines for up to 72 h were able to mobilize intracellular calcium in response to stimulus by acetylcholine in an identical fashion to those maintained in primary culture in the absence of cytokines. Acute application of the conditioned medium produced by the activated lymphocytes had an antisecretory effect on acetylcholine-evoked Ca(2+) mobilization, which was found to be mediated by cholinesterase rather than by cytokines.

CONCLUSION

Neither chronic nor acute exposure to the profile of cytokines released by concanavalin A-activated splenic lymphocytes interfered in any way with the second messenger cascade and fluid and electrolyte secretion in acinar cells. Our data suggest an alternative hypothesis, in which elevated levels of cholinesterase can metabolize acetylcholine released within the salivary glands and thus prevent fluid secretion.

Androgens and dry eye in Sjögren's syndrome

Sjögren's syndrome is an extremely complex and currently incurable autoimmune disorder, which occurs primarily in females, and is associated with lacrimal gland inflammation, meibomian gland dysfunction, and severe dry eye. We hypothesize that androgen deficiency, which reportedly occurs in primary and secondary Sjögren's syndrome (e.g., systemic lupus erythematosus, rheumatoid arthritis), is a critical etiologic factor in the pathogenesis of dry eye syndromes. We further hypothesize that androgen treatment to the ocular surface will promote both lacrimal and meibomian gland function and alleviate both "aqueous-deficient" and "evaporative" dry eye. Our results demonstrate that androgens regulate both lacrimal and meibomian gland function, and suggest that topical androgen administration may serve as a safe and effective therapy for the treatment of dry eye in Sjögren's syndrome.

Gender and androgen treatment influence the expression of proto-oncogenes and apoptotic factors in lacrimal and salivary tissues of MRL/lpr mice

The objectives of this study were to (1) determine whether Fas antigen, Fas ligand, p53, and proto-oncogene mRNAs may be detected in lacrimal and submandibular glands of the MRL/lpr mouse model of Sjögren's syndrome, and (2) examine whether gender and androgen or cyclophosphamide therapy influence the mRNA expression of these apoptotic factors. Tissues were obtained from treated or untreated MRL/lpr mice after the onset of disease and processed for the analysis of mRNAs by RT-PCR and Southern blot hybridization. Our results demonstrated that (1) Fas antigen (exons 1-->2 or 3-->7+), Fas ligand, c-myb, c-myc, bcl-2, Bax, p53, and androgen receptor (AR) mRNAs are present in exocrine tissues of MRL/lpr mice; (2) the amounts of c-myb, c-myc, bcl-2, p53, and AR mRNA are higher (P < 0.05) and the level of Fas antigen (exons 1-->2) mRNA is lower (P < 0.05) in lacrimal glands of female compared to male mice. In contrast, the content of c-myb and p53 mRNA is greater (P < 0.05) in submandibular tissues of female relative to those of male mice; and (3) testosterone or cyclophosphamide treatment led to a significant (P < 0.05) decline in the mRNA levels of c-myb, bcl-2, and/or AR, but an increase (P < 0.05) in the mRNA amount of Bax, in lacrimal, but not in salivary, glands of female mice. These findings demonstrate that gender-associated differences exist in the expression of apoptotic factor mRNAs in exocrine tissues of autoimmune mice and that some of these differences appear to be due to the influence of androgens.

Effect of sialodacryoadenitis virus exposure on acinar epithelial cells from the rat lacrimal gland

Sialodacryoadenitis virus (SDAV), a RNA coronavirus, induces degenerative, necrotic and atrophic alterations in acinar epithelial cells of the rat lacrimal gland. To begin to explore the underlying mechanism(s) of this viral effect, we sought in the present study to: (1) determine whether SDAV invades and replicates in lacrimal gland acinar cells in vitro and (2) assess whether short-term SDAV challenge interferes with the viability or function of acinar cells in vitro. For comparison we also evaluated the relative infectivity of SDAV in acinar epithelial cells from lacrimal, submandibular and parotid glands, given that salivary tissues are known to be highly susceptible to SDAV infection in vivo. Acinar epithelial cells from lacrimal, submandibular or parotid glands were isolated from male rats, exposed briefly to SDAV or control cell antigen and then cultured for four, eight or twelve days. At experimental termination, SDAV titers in both media and sonicated cell extracts were evaluated by plaque assay titration on mouse L2 cell monolayers. To evaluate functional aspects of lacrimal gland acinar cells, SDAV-infected cells were incubated in the presence or absence of dihydrotestosterone and culture media were analyzed by RIA to measure the extent of the androgen-induced increase in secretory component (SC) production. Our results showed that: (1) SDAV invades and replicates in lacrimal gland acinar cells, Viral challenge resulted in a significant, time-dependent increase in SDAV titers, that were primarily cell-associated and greatly exceeded amounts contained in the original inoculum; (2) SDAV infection did not compromise lacrimal acinar cell viability or prevent the cellular SC response to androgens. Viral presence, though, did often attenuate the magnitude of this hormone action; and (3) SDAV infects salivary acinar cells, but the kinetics and magnitude or viral replication in lacrimal, submandibular and parotid cells showed considerable variations. These findings demonstrate that SDAV invades and replicates in acinar epithelial cells from lacrimal and salivary glands. The resulting release of infectious progeny may play a role in the SDAV-induced pathology of exocrine tissues in vivo.

Phenotypic characterization of mononuclear inflammatory cells in salivary glands of bio-breeding rats

The purpose of this study was to assess whether mononuclear cell abnormalities exist in salivary glands from autoimmune Bio-Breeding (BB) rats. Frozen sections of gland tissues were prepared from five diabetes-resistant BB rats (BB-DR), from five BB rats with diabetes (BB-DP) and from five Wistar rats. A panel of six monoclonal antibodies was used to identify membrane antigens associated primarily with monocytes (ED1), mature tissue macrophages (ED2), lymphoid macrophages (ED3), MHC class II (Ia) antigen (OX6), CD5+ T lymphocytes (OX19), and rat B lymphocytes (OX33). Normal submandibular, sublingual and parotid glands contained few ED1-positive cells, usually two or fewer per field. Tissue macrophages identified by clone ED2 comprised a major mononuclear cell subset in both Wistar and BB rats. However, the number of ED2-positive mononuclear cells was significantly depressed in the submandibular and parotid glands from BB-DR and BB-DP animals, being present in quantities 25-50% of those observed in glands from normal Wistar rats (p < 0.001). In contrast, 25- to 30-fold greater numbers of ED3-positive macrophages were observed in submandibular glands from BB rats (p < 0.001). MHC class II (Ia) antigen expression also was 4- to 6-fold greater in BB rat submandibular glands, compared to Wistar rats (p < 0.001). CD5+ T-lymphocytes were rare or entirely absent in BB sublingual glands (0 to 1 cell per 0.87 mm2 field), compared to 47 cells per field from Wistar sublingual glands. No B lymphocytes were identified with antibody OX33 in any of the rat strains. These findings indicate that BB rat salivary glands differ significantly from Wistar salivary glands. In BB rats there is a rich population of ED3-positive macrophages and T lymphocytes in submandibular gland, low quantities of T lymphocytes in sublingual gland, and fewer ED2-positive macrophages in all three major salivary glands. These differences in mononuclear cell subpopulations may also influence salivary gland function in mucosal immunity.

Neuroendocrine changes in systemic lupus erythematosus and Sjögren's syndrome

It has become clear that the neuroendocrine and immune systems are closely linked and interdependent. The exact mechanisms of this interaction are only beginning to be unravelled. The complexity of these connections may partly explain why the aetiopathogenesis of autoimmune diseases remains obscure and why genetic, hormonal, microbial, environmental, as well as a host of other factors, have all been put forward as explanations. What has become clear is that a number of neuroendocrine and hormonal factors have important immunomodulatory roles in health and disease.

Differential distribution of neuronal markers and neuropeptides in the human lacrimal gland

BACKGROUND

The present study was undertaken in an attempt to broaden the spectrum of known neuronal markers and neuropeptides in the main lacrimal gland of the human by light-microscopic immunohistochemistry.

METHODS

Using antisera against the neuronal markers protein gene product (PGP) and S-100 protein (S-100), the distribution of nerve fibers in the human main lacrimal gland was studied. Vasoactive intestinal polypeptide (VIP), calcitonin gene-related peptide (CGRP), neuropeptide Y (NPY) and tyrosine hydroxylase (TH) were identified by their specific antisera.

RESULTS

The nerve fibers are distributed throughout the interstice between the glandular tubules. Associations were also found between nerve fibers and both the interlobular ductal system and blood vessels (mainly arterioles). Within the glandular lobules isolated groups of secretory cells stained positive for S-100 protein. Nerve fibers situated in the glandular interstice between the tubules showed predominantly positive immunoreactions for the neuropeptide VIP, while only very few fibers stained positive for CGRP, NPY and the catecholamine marker TH. Nerve fibers associated with interlobular blood vessels were mainly CGRP and NPY positive and stained only very rarely for VIP. The epithelia of interlobular ducts and excretory ducts were associated with CGRP-immunoreactive nerve fibers.

CONCLUSION

The neuropeptides identified in the lacrimal gland indicate the complexity with which a variety of biologic signals regulate and modulate the lacrimal gland.

Vth International Symposium on Sjögren's syndrome. Clinical aspects and therapy

There is increasing awareness that sicca syndrome can lead to ocular, oral and systemic complications. However, a wide variety of pathogenetic processes may lead to the same end result of diminished glandular secretion. Recognition of these different etiologies will lead to improved therapies. On the one hand, an active inflammatory/autoimmune process may respond to immunomodulatory drugs. On the other hands, processes that predominantly involve "neuroendocrine" dysfunction (unrelated to immune activity) of the gland will require a different approach.