Antibodies Raised Against the Second Extracellular Loop of the Human Muscarinic M3 Receptor Mimic Functional Autoantibodies in Sjogren's Syndrome

Disease mechanisms in Sjögren's syndrome: what do we know?

Why should we explore and study disease mechanisms? This is particularly important when we are dealing with complex pathogenesis without a direct causal agent e.g. syndromes with multiple organ involvements. Sjögren's syndrome is definitely such an entity. Also, there are a number of reasons for such studies such as disclosing the aetiology, to identify biomarkers for diagnosis and assessment of the disease process and monitor response to treatment, to determine targets for treatment, to define critical items in classification criteria, among others. Samples available for the study of disease mechanisms in Sjögren's syndrome have included serum (autoantibodies, cytokines), DNA (gene profiling, GWAS), cells (phenotypes/flow cytometry, proportion of cells/CyTOF), tissue (focal inflammation, germinal centres, mass cytometry), saliva (proteomics, biochemistry, mucosal immunity). An original explanatory concept for the pathogenesis of Sjögren's syndrome proposed a specific and self-perpetuating immune mediated loss of exocrine tissue as the principal cause of glandular hypofunction. This hypothesis however falls short of accommodating several Sjögren's syndrome-related phenomena and experimental findings. Today, the emergence of advanced bio-analytical platforms has further enabled the identification of central pathogenic processes and potential biomarkers. The purpose of this minor review is to highlight a selection of previous but also recent and novel aspects on the disease mechanisms in Sjögren's syndrome.

B7-H4 Inhibits the Development of Primary Sjögren's Syndrome by Regulating Treg Differentiation in NOD/Ltj Mice

Background

This study is aimed at exploring the role of B7-H4 in the pathogenesis of primary Sjögren's syndrome (pSS) in NOD/Ltj mouse.

Methods

B7-H4 expression in salivary glands was examined by IHC, and lymphocyte infiltration was showed by H&E. Next, anti-B7-H4 mAb or immunoglobulin isotype was injected into NOD/Ltj mice. Cytokine levels were measured by quantitative RT-PCR, and immunoglobulins were measured by ELISA. T cell subsets were analyzed by flow cytometry. Last, we treated NOD/Ltj mice with B7-H4Ig and control Ig. CD4+Foxp3+ T cells were assessed by immunohistochemistry. Two-tailed Student's t-tests were used to detect the statistical difference in various measures between the two groups.

Results

B7-H4 expression was remarkably reduced in salivary glands of NOD/Ltj mice at 15 weeks compared with the NOD/Ltj mice at 8 weeks. Anti-B7-H4 mAb treatment increased lymphocyte infiltration in salivary glands. Inflammatory cytokines including IL-12, IL-18, IL-1α, TNF-α, IFN-α, and BAFF were upregulated markedly in anti-B7-H4 mAb-treated mice compared to IgG isotype-treated mice. Flow cytometry analysis showed that anti-B7-H4 mAb-treated mice had lower levels of CD4+Foxp3+/CD4+ T cells in spleen. Moreover, Foxp3 mRNA levels of salivary glands were diminished in anti-B7-H4 mAb-treated mice. Flow cytometry analysis showed that anti-B7-H4 mAb inhibited CD4+Foxp3+/CD4+ T cell production, while B7-H4Ig would promote naïve CD4+ T into Treg differentiation. Administration with B7-H4Ig displayed significantly decreased lymphocyte infiltration in salivary glands and low levels of total IgM and IgG in serum. Analysis of inflammatory cytokines in salivary glands after B7-H4Ig treatment revealed that the mRNA levels of IL-12, IL-6, IL-18, IL-1α, TNF-α, and IFN-α were significantly downregulated in B7-H4Ig-treated mice compared to control Ig treatment. B7-H4Ig-treated mice had significantly higher levels of CD4+Foxp3+/CD4+ T cells in spleen. IHC in salivary gland revealed that CD4+Foxp3+ T cells of B7-H4Ig treatment mouse were more than control Ig treatment.

Conclusions

Our findings implicate that B7-H4 has a protective role for salivary gland epithelial cells (SGECs) and therapeutic potential in the treatment of pSS.

Antibodies to the Muscarinic Acetylcholine Receptor M3 in Primary Biliary Cholangitis Inhibit Receptor Function on Cholangiocytes

Background and Aims: In primary biliary cholangitis (PBC), antibodies to a peptide of the muscarinic acetylcholine receptor 3 (mAChR3) have been described. Since the mAChR3 is expressed on cholangiocytes and mAChR3-signaling is involved in the pathogenesis of chronic inflammatory biliary diseases, we wanted to investigate whether anti-mAChR3-antibodies influence the function of the receptor and the proliferative response of cholangiocytes. Methods: Immunoglobulins were isolated by ammonium sulfate precipitation using sera from patients with PBC (n = 63) and with other chronic liver disorders (n = 150). All immunoglobulins were analyzed by a luminometric assay using Chinese hamster ovary (CHO) cells overexpressing the mAChR3 and cholangiocytes (TFK-1-cells) expressing the receptor constitutively. Cell proliferation was measured by ³H-thymidine assay. PBC patients were also analyzed in the follow-up. Results: Antibodies inhibiting the mAChR3 were found in 49 and 79% of PBC patients using CHO-cells or TFK-1-cells, respectively, but only in up to 26% of controls (p < 0.01). Stimulatory antibodies were hardly detected. Antibody reactivity only marginally changed during the course of the disease, independently of the choice of treatment (ursodeoxycholic acid, immunosuppressive therapy, or no medication). There was no correlation with laboratory, clinical or histological parameters, but the antibodies were more frequently found in PBC patients with a benign course (96%) than in patients with active disease progressing to late stages within 10 years (57%; p < 0.01). Proliferation of cells was not influenced by immunoglobulins from PBC-patients. Conclusion: Sera from patients with PBC contain inhibitory antibodies to the mAChR3 on cholangiocytes (TFK-1 cells) without influencing TFK-1-cell proliferation. These antibodies were predominantly observed in patients with non-progressing PBC.

Agonistic antibodies in systemic sclerosis

Systemic sclerosis (SSc) is characterized by microangiopathy, excessive fibrosis, and the presence of circulating autoantibodies to several cellular and extracellular components. The role of autoimmunity in generating the clinical and pathologic phenotypes in SSc has been long debated and is still matter of controversy. Distinct specificities of antinuclear antibodies (ANAs) are selectively detected in SSc patients and are associated with unique disease manifestations, but do not have a proven pathogenic role. A new group of autoantibodies reactive with cell surface receptors have been identified in SSc patients. They have been shown to directly activate pathways that may contribute to tissue and vascular damage. As such, they are proposed to have a role as agonistic autoantibodies in SSc. According to Koch's third postulate, the autoantibodies in question should cause disease when introduced into a healthy subject. Therefore, our review will focus on those autoantibodies for which agonistic activity has already been demonstrated not only in vitro, but, at least partly, also in vivo. These include the antibodies anti-endothelial cells (AECA), anti-Platelet-Derived Growth Factor Receptor (PDGFR), anti-Angiotensin II type 1 receptor (AT1R) and anti-endothelin-1 type A receptor (ETaR). In this review, we will discuss also a class of antagonistic autoantibodies, the anti-muscarinic-3 receptor (M3R) antibodies, since they seem to fulfill the aforementioned requirements.

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.

What can Sjögren's syndrome-like disease in mice contribute to human Sjögren's syndrome?

For decades, Sjögren's syndrome (SS) and Sjögren's syndrome-like (SS-like) disease in patients and mouse models, respectively, have been intensely investigated in attempts to identify the underlying etiologies, the pathophysiological changes defining disease phenotypes, the nature of the autoimmune responses, and the propensity for developing B cell lymphomas. An emerging question is whether the generation of a multitude of mouse models and the data obtained from their studies is actually important to the understanding of the human disease and potential interventional therapies. In this brief report, we comment on how and why mouse models can stimulate interest in specific lines of research that apparently parallel aspects of human SS. Focusing on two mouse models, NOD and B6·Il14α, we present the possible relevance of mouse models to human SS, highlighting a few selected disease-associated biological processes that have baffled both SS and SS-like investigations for decades.

Muscarinic type 3 receptor autoantibodies are associated with anti-SSA/Ro autoantibodies in Sjögren's syndrome

Anti-muscarinic type 3 receptor autoantibodies (anti-M3R) are reported as potential inhibitors of saliva secretion in Sjögren's syndrome (SjS). However, despite extensive efforts to establish an anti-M3R detection method, there is no clinical test available for these autoantibodies. The purpose of this study was to propose inclusion of anti-M3R testing for SjS diagnosis through investigation of their prevalence using a modified In-Cell Western (ICW) assay. A stable cell line expressing human M3R tagged with GFP (M3R-GFP) was established to screen unadsorbed and adsorbed plasma from primary SjS (n=24), rheumatoid arthritis (RA, n=18), systemic lupus erythematosus (SLE, n=18), and healthy controls (HC, n=23). Anti-M3R abundance was determined by screening for the intensity of human IgG interacting with M3R-GFP cells by ICW assay, as detected by an anti-human IgG IRDye800-conjugated secondary antibody and normalized to GFP. Method comparisons and receiver-operating-characteristic (ROC)-curve analyses were performed to evaluate the diagnostic value of our current approaches. Furthermore, clinical parameters of SjS were also analyzed in association with anti-M3R. Anti-M3R was significantly elevated in SjS plasma in comparison with HC, SLE, or RA (P<0.01). SjS anti-M3R intensities were greater than two-standard deviations above the HC mean for both unadsorbed (16/24, 66.67%) and adsorbed (18/24, 75%) plasma samples. Furthermore, anti-M3R was associated with anti-SjS-related-antigen A/Ro positivity (P=0.0353). Linear associations for anti-M3R intensity indicated positive associations with focus score (R(2)=0.7186, P<0.01) and negative associations with saliva flow rate (R(2)=0.3052, P<0.05). Our study strongly supports our rationale to propose inclusion of anti-M3R for further testing as a non-invasive serological marker for SjS diagnosis.

Mouse Models of Primary Sjogren's Syndrome

Sjogren's syndrome (SjS) is a chronic autoimmune disorder characterized by immune cell infiltration and progressive injury to the salivary and lacrimal glands. As a consequence, patients with SjS develop xerostomia (dry mouth) and keratoconjunctivitis sicca (dry eyes). SjS is the third most common rheumatic autoimmune disorder, affecting 4 million Americans with over 90% of patients being female. Current diagnostic criteria for SjS frequently utilize histological examinations of minor salivary glands for immune cell foci, serology for autoantibodies, and dry eye evaluation by corneal or conjunctival staining. SjS can be classified as primary or secondary SjS, depending on whether it occurs alone or in association with other systemic rheumatic conditions, respectively. Clinical manifestations typically become apparent when the disease is relatively advanced in SjS patients, which poses a challenge for early diagnosis and treatment of SjS. Therefore, SjS mouse models, because of their close resemblance to the human SjS, have been extremely valuable to identify early disease markers and to investigate underlying biological and immunological dysregulations. However, it is important to bear in mind that no single mouse model has duplicated all aspects of SjS pathogenesis and clinical features, mainly due to the multifactorial etiology of SjS that includes numerous susceptibility genes and environmental factors. As such, various mouse models have been developed in the field to try to recapitulate SjS. In this review, we focus on recent mouse models of primary SjS xerostomia and describe them under three categories of spontaneous, genetically engineered, and experimentally induced models. In addition, we discuss future perspectives highlighting pros and cons of utilizing mouse models and current demands for improved models.

Autoantibodies against the Second Extracellular Loop of M3R Do neither Induce nor Indicate Primary Sjögren's Syndrome

Objectives

Anti-muscarinic acetylcholine type-3 receptor (anti-M3R) autoantibodies have been suggested to be pathogenic for primary Sjögren’s syndrome (pSS), and the second extracellular loop of M3R is suspected to carry a disease-promoting epitope. In this study, we aimed to evaluate the pathogenicity of autoantibodies against peptides derived from the second extracellular loop of M3R in mice and to determine whether those autoantibodies could be used as biomarker for pSS.

Methods

BALB/c mice were immunized with modified linear or cyclic peptides of the second extracellular loop of M3R. The function of exocrine glands was evaluated by measuring the secretion of saliva and tears. The histological evaluations were performed by using H&E staining or direct immunofluorescence staining. Autoantibodies against linear or cyclic peptides of the second extracellular loop of M3R in human and mice were determined using ELISA.

Results

Immunization induced mice to produce autoantibodies against the linear or cyclic peptides of the second extracellular loop of M3R, and those autoantibodies could bind onto salivary glands. However, those mice showed neither impairment in the secretion of tears or saliva nor histological abnormality in the exocrine glands. Furthermore, passive transfer of the IgG isolated from the immunized mice into healthy mice did not induced the dysfunction of the exocrine glands. The prevalence of autoantibodies against the peptides of the second extracellular loop of M3R was low in pSS patients, and it did not differ significantly from that in healthy controls.

Conclusions

Our results suggest that the autoantibodies against peptides of the second extracellular loop of M3R are not pathogenic in vivo and they are not suitable as biomarkers for pSS diagnosis.

A novel luminescence-based method for the detection of functionally active antibodies to muscarinic acetylcholine receptors of the M3 type (mAchR3) in patients' sera

In different bioassays, functional antibodies reacting with the human muscarinic acetylcholine receptor M3(mAchR3) have been detected in sera from patients with Sjögren's syndrome (SS), and there is strong evidence that those antibodies may have pathogenetic relevance. However, depending on the method of detection, their prevalence varied. Furthermore, those bioassays are difficult to standardize. We report on the development and optimization of a novel test system based on a luminometric method to determine downstream signalling of mAchR3 which produces specific and reproducible results. Chinese hamster ovarian (CHO) cells were transfected with plasmids encoding mAchR3 and a green fluorescence protein (GFP)/aequorin fusion protein. Incubation of cells with carbachol resulted in an increase in intracellular [Ca(2+)], which was detected by measuring light emission with a luminometer, and the effect of incubation with patients' immunoglobulins (Ig) was evaluated. Optimal cell density, Ig preparation and time of incubation with patients' sera were determined. Sera from patients with primary Sjögren's syndrome (pSS; n = 40), systemic sclerosis (SSc; n = 47), myasthenia gravis (MG; n = 133) and 50 blood donors were analysed. Optimal assay conditions were obtained with a cell density of 100 000 cells/ml, isolation of Ig by ammonium sulphate precipitation and short-term incubation. Based on this highly reliable assay, 50% of the pSS patients had antibodies which inhibited carbachol-induced activation of mAchR3; none of the SSc patients, 6% of the patients with MG and 12% of the blood donors had antibodies which reacted with the mAchR3. This method facilitates the determination of functional anti-mAchR3 antibodies in patients' sera, confirmed their high prevalence in pSS patients and may, therefore, help to analyse their pathogenetic and clinical relevance in more detail.

The role of M3 muscarinic acetylcholine receptor reactive T cells in Sjögren's syndrome: a critical review

CD4+ T cells constitute the majority of infiltrating cells in salivary glands and lachrymal glands of patients with Sjögren's syndrome (SS). The pathophysiology of SS involves T cell recognition of antigens through the T cell antigen receptor, which triggers cytokine production and chronic inflammation. The M3 muscarinic acetylcholine receptor (M3R) molecule is expressed in exocrine glands, such as salivary glands and lachrymal glands, and plays an important role in exocrine secretion. Previous studies indicated the presence of M3R reactive T cells in peripheral blood of 40% of patients with SS and autoantibodies against M3R in sera of 9-100% of the same patients. Thus, M3R is considered a candidate receptor for autoantigen recognition by T and B cells. The relationship between B cell epitopes and the function of anti-M3R antibodies has been reported, suggesting the pathogenic role of anti-M3R antibodies in xerostomia commonly seen in SS patients. We generated new experimental mouse model, M3R-induced sialadenitis (MIS), using Rag1(-/-) mice inoculated with splenocytes from M3R(-/-) mice immunized with M3R synthetic peptides. Mice with MIS developed severe SS-like sialadenitis. Cell transfer experiments using M3R(-/-)xIFNγ(-/-) mice and M3R(-/-)xIL-17(-/-) mice showed that IFNγ and IL-17 are key cytokines in the pathogenesis of sialadenitis. These findings indicate the crucial roles of M3R-reactive Th1 and Th17 cells in autoimmune sialadenitis, and suggest that these cells, in addition to anti-M3R antibodies, are potential targets in new treatments for SS.

Effects of muscarinic acetylcholine 3 receptor(208-227) peptide immunization on autoimmune response in nonobese diabetic mice

The second extracellular loop (LFWQYFVGKRTVPPGECFIQFLSEPTITFGTAI, aa 205-237) of muscarinic acetylcholine 3 receptor (M3R) has been reported to be an epitope for autoantibodies generated during certain autoimmune disorders, including Sjögren's syndrome (SS). Autoantibodies against M3R(228-237) have been shown to interfere with the function of M3R. However, few studies have been performed on the M3R(205-227) peptide of the second extracellular loop. In the current study, we sought to investigate the effect of M3R(208-227) peptide immunization on autoimmune response in NOD/LtJ mice. We synthesized the M3R(208-227) peptide and immunized NOD/LtJ mice to investigate whether peptide-specific antibodies could be generated and whether immunization would lead to changes in autoimmune response in NOD/LtJ mice. Our results demonstrate that the secretions of Th-1, Th-2, and Th-17 cytokines are downregulated and lymphocytic infiltration is improved in the salivary glands and lacrimal glands following immunization with M3R(208-227) peptide in NOD/LtJ mice, suggesting that peptide immunotherapy using the M3R(208-227) peptide may represent a potential therapeutic alternative.

Autoantibodies against muscarinic type 3 receptor in Sjögren's syndrome inhibit aquaporin 5 trafficking

Sjögren's syndrome (SjS) is a chronic autoimmune disease that mainly targets the salivary and lacrimal glands. It has been controversial whether anti-muscarinic type 3 receptor (α-M3R) autoantibodies in patients with SjS inhibit intracellular trafficking of aquaporin-5 (AQP5), water transport protein, leading to secretory dysfunction. To address this issue, GFP-tagged human AQP5 was overexpressed in human salivary gland cells (HSG-hAQP5) and monitored AQP5 trafficking to the plasma membrane following carbachol (CCh, M3R agonist) stimulation. AQP5 trafficking was indeed mediated by M3R stimulation, shown in partial blockage of trafficking by M3R-antagonist 4-DAMP. HSG-hAQP5 pre-incubated with SjS plasma for 24 hours significantly reduced AQP5 trafficking with CCh, compared with HSG-hAQP5 pre-incubated with healthy control (HC) plasma. This inhibition was confirmed by monoclonal α-M3R antibody and pre-absorbed plasma. Interestingly, HSG-hAQP5 pre-incubated with SjS plasma showed no change in cell volume, compared to the cells incubated with HC plasma showing shrinkage by twenty percent after CCh-stimulation. Our findings clearly indicate that binding of anti-M3R autoantibodies to the receptor, which was verified by immunoprecipitation, suppresses AQP5 trafficking to the membrane and contribute to impaired fluid secretion in SjS. Our current study urges further investigations of clinical associations between SjS symptoms, such as degree of secretory dysfunction, cognitive impairment, and/or bladder irritation, and different profiles (titers, isotypes, and/or specificity) of anti-M3R autoantibodies in individuals with SjS.

Urban legends series: Sjögren's syndrome

Sjögren's syndrome (SjS) is one of the most common autoimmune rheumatic diseases, clinically characterized by xerostomia and keratoconjunctivitis sicca. We investigated the following controversial topics: (i) Do we have reliable ways of assessing saliva production? (ii) How important are the quantity and quality of saliva? (iii) Are only anti-SSA/Ro and anti-SSB/La relevant for the diagnosis of SjS? (iv) Are the American-European Consensus criteria (AECC) the best way to diagnose SjS? Results from literature searches suggested the following: (i) Despite the fact that numerous tests are available to assess salivation rates, direct comparisons among them are scarce with little evidence to suggest one best test. (ii) Recent developments highlight the importance of investigating the composition of saliva. However, more research is needed to standardize the methods of analysis and collection and refine the quality of the accumulating data. (iii) In addition to anti-Ro/La autoantibodies, anti α-fodrin IgA and anti-MR3 autoantibodies seem to be promising diagnostic markers of SjS, but more studies are warranted to test their sensitivity and specificity. (iv) AECC are classification, not diagnostic criteria. Moreover, recent innovations have not been incorporated into these criteria. Consequently, treatment directed to patients diagnosed using the AECC might exclude a significant proportion of patients with SjS.

Anti-M3 muscarinic acetylcholine receptor antibodies in patients with Sjögren's syndrome

Sjögren's syndrome (SS) is an autoimmune disease that affects exocrine glands including salivary and lacrimal glands. Recently, autoantibodies against muscarinic acetylcholine receptor M3 (M3R) have been detected in serum from 9 to 100 % of patients with SS in addition to anti-SS-A and anti-SS-B antibodies. These observations suggest the possibility that anti-M3R antibodies could serve as a new diagnostic test in patients with SS. Some anti-M3R antibodies are directly responsible for salivary underproduction in patients with SS. Thus, strategies designed to eliminate such pathogenic antibodies could help cure SS sufferers. In this review, we summarize the current state of knowledge of anti-M3R autoantibodies in patients with SS and the correlation between B cell epitopes and the function of anti-M3R antibodies.

Subgroups of Sjögren syndrome patients according to serological profiles

Sjögren Syndrome (SS) is a systemic, autoimmune disorder characterized by lymphocytic infiltration of the exocrine glands. Different clinical associations have been described for each of the diverse autoantibodies found in SS patients. Antibodies directed against the Ro/La ribonucleoprotein complexes have been correlated with younger age, more severe dysfunction of the exocrine glands and a higher prevalence of extraglandular manifestations. Anti-nuclear antibodies and rheumatoid factors have been associated to extraglandular manifestations and an active immunological profile, while cryoglobulins are markers of more severe disease and correlate to lymphoma development and death. Antibodies to cyclic citrullinated peptides are scarce in SS and have been linked in some cases to the development of non-erosive arthritis. Furthermore, the presence of anti-mitochondrial antibodies and anti-smooth muscle antibodies in the sera of primary SS patients is considered indicative of primary biliary cirrhosis and autoimmune hepatitis, respectively. In addition, anti-centromere antibodies have been associated with a clinical phenotype intermediate between primary SS and systemic sclerosis, while antibodies against carbonic anhydrase have been related to renal tubular acidosis. Finally, an association of anti-muscarinic antibodies with cytopenias and a higher disease activity has also been described in primary SS. In conclusion, although not all of the above mentioned antibodies are useful for predicting distinct patient subgroups in SS, knowledge of the clinical associations of the different autoantibody specificities encountered in SS can advance our understanding of the disease and improve patient management.

Vasculitis in Sjögren's Syndrome

Sjögren's syndrome is a chronic autoimmune disease that is commonly manifested by immune attack on the exocrine glands with resultant dry eyes and dry mouth. Sjögren's syndrome patients also have disease in other organs. One of the most common extraglandular manifestations is vasculitis. Skin vasculitis, with palpable purpura clinically and leukocytoclastic vasculitis on pathological examination, is common. Although half of those individuals with subcutaneous vasculitis have only a single episode, skin vasculitic involvement is associated with more severe disease. Necrotizing vasculitis of medium-sized vessels resembling polyarteritis nodosa can occur in Sjögren's syndrome patients. Experience in therapy for vasculitis is limited, but intravenous IgG may be effective. Recent data support a relationship between neuromyelitis optica (Devic disease) and Sjögren's syndrome. Sjögren's syndrome patients with optic neuritis or transverse myelitis have anti-aquaporin-4, which are characteristic of Devic disease. Devic disease patients have salivary lymphocytic infiltration similar to that found among Sjögren's syndrome patients.

Muscarinic receptor agonists and antagonists: effects on ocular function

Muscarinic agonists act mainly via muscarinic M₃ cholinoceptors to cause contraction of the iris sphincter, ciliary muscle and trabecular meshwork as well as increase outflow facility of aqueous humour. In the iris dilator, the effect of muscarinic agonists is species dependent but is predominantly relaxation via muscarinic M₃ receptors. In the conjunctiva, muscarinic agonists stimulate goblet cell secretion which contributes to the protective tear film. Muscarinic M₂ and M₃ receptors appear mainly involved. In the lens muscarinic agonists act via muscarinic M₁ receptors to produce depolarization and increase [Ca(2+)](i). All five subtypes of muscarinic receptor are present in the retina. In the developing retina, acetylcholine appears to limit purinergic stimulation of retinal development and decrease cell proliferation. In the adult retina acetylcholine and other muscarinic agonists may have complex effects, for example, enhancing light-evoked neuronal firing in transient ON retinal ganglion cells and inhibiting firing in OFF retinal ganglion cells. In the lacrimal gland, muscarinic agonists activate M₃ receptors on secretory globular acinar cells to stimulate tear secretion and also cause contraction of myoepithelial cells. In Sjögren's syndrome, antibodies to the muscarinic M₃ receptor disrupt normal gland function leading to xerophthalmia although the mechanism of action of the antibody is still not clear. Atropine and pirenzepine are useful in limiting the development of myopia in children probably by an action on muscarinic receptors in the sclera, although many other muscarinic receptor antagonists are not effective.

Generation and functional analysis of monoclonal antibodies against the second extracellular loop of human M3 muscarinic acetylcholine receptor

The M3 muscarinic acetylcholine receptor (M3R) plays a crucial role in the activation of salivary and lachrymal glands. The M3R contains four extracellular domains (the N-terminal, and the first, second, and third extracellular loops), and we recently detected antibodies against each of these four domains in a subgroup of patients with Sjögren's syndrome (SS). Functional analysis indicated that the influence of such anti-M3R antibodies on salivary secretion might differ based on the epitopes to which they bind. To clarify the relationship between B-cell epitopes on the M3R and its function, we generated two hybridomas producing anti-M3R monoclonal antibodies against the second extracellular loop of M3R (anti-M3R(2nd) mAbs) and analyzed their function by Ca(2+)-influx assays, using a human salivary gland (HSG) cell line. These two anti-M3R(2nd) mAbs suppressed Ca(2+)-influx in the HSG cells induced by cevimeline stimulation, suggesting that autoantibodies against the second extracellular loop of M3R could be involved in salivary dysfunction in patients with SS.

Diagnostic significance of measuring antibodies to cyclic type 3 muscarinic acetylcholine receptor peptides in primary Sjogren's syndrome

OBJECTIVE

SS is an autoimmune disease characterized by salivary and lacrimal gland dysfunction leading to dry mouth (xerostomia) and dry eyes (xerophthalmia). Anti-muscarinic acetylcholine type-3 receptor (anti-M3R) autoantibodies have been shown to be a good serum marker in primary SS (pSS). The aim of this study was to assess the clinical correlations of anti-M3R-derived peptide antibodies in patients with pSS.

METHODS

Sequences of the first to fourth cycle-M3R (c1M3R-c4M3R)-derived peptide was synthesized by a solid-phase technique on an Applied Biosytems Peptide Synthesizer. Synthesized cM3R peptide (cM3RP) was used as substrate in an ELISA to detect IgG anti-cM3RP antibodies in serum samples of patients and controls. The clinical and biological parameters of the diseases were also evaluated. The EULAR SS disease activity index (ESSDAI) score was used to measure disease activity in patients with primary SS.

RESULTS

(i) Anti-c2M3RP antibodies were highly prevalent in pSS patients, and the titre is much higher than anti-c1,3,4M3RP antibodies. (ii) The prevalence of anti-c2M3RP antibodies in pSS, SLE, RA and healthy controls was 62.2, 7.1, 5.3 and 1.6%, respectively. The prevalence of anti-linear-2-M3RP antibodies in pSS, SLE and RA patients and healthy controls were 56.1, 20.0, 14.7 and 9.4%. (iii) The specificity of anti-c2M3RP antibodies was 95.1%, much higher than that of linear polypeptide (84.7%) for pSS diagnosis. (iv) In pSS patients, anti-c2M3RP positivity had significantly increased frequency in patients who were RF or ANA positive, and had several haematological abnormalities, such as leucopenia, anaemia and thrombocytopenia. Furthermore, the ESSDAI score was significantly higher in anti-c2M3RP-positive pSS patients (P <  0.05).

CONCLUSION

Anti-c2M3RP antibody was highly specific for patients with pSS. The presence of anti-c2M3RP antibody in pSS indicates that c2M3RP may act as an autoantigen that may play a role in the pathogenesis of pSS.

Current concepts: mouse models of Sjögren's syndrome

Sjögren's syndrome (SjS) is a complex chronic autoimmune disease of unknown etiology which primarily targets the exocrine glands, resulting in eventual loss of secretory function. The disease can present as either primary SjS or secondary SjS, the latter of which occurs concomitantly with another autoimmune disease such as rheumatoid arthritis, systemic lupus erythematosus, scleroderma, or primary biliary cirrhosis. Current advancements in therapeutic prevention and treatment for SjS are impeded by lack of understanding in the pathophysiological and clinical progression of the disease. Development of appropriate mouse models for both primary and secondary SjS is needed in order to advance knowledge of this disease. This paper details important features, advantages, and pitfalls of current animal models of SjS, including spontaneous, transgenic, knockout, immunization, and transplantation chimera mouse models, and emphasizes the need for a better model in representing the human SjS phenotype.

Autoantibodies to muscarinic acetylcholine receptors found in patients with primary biliary cirrhosis

Background

Autoantibodies to the human muscarinic acetylcholine receptor of the M3 type (hmAchR M3) have been suggested to play an etiopathogenic role in Sjögren's syndrome. Primary biliary cirrhosis (PBC) often is associated with this syndrome. Therefore, we studied the co-presence of hmAchR M3 autoantibodies in patients with PBC.

Methods

Frequency of hmAchR M3 autoantibodies was assessed by Western blotting analysis as well as by an ELISA using a 25-mer peptide of the 2^nd extracellular loop of hmAchR M3. Co-localization of hmAchR M3/PBC-specific autoantibodies was studied by confocal laser scanning microscopy. Finally, sera from patients with PBC as well as from healthy controls were tested.

Results

Western blotting analysis as well as results from ELISA testing revealed a significantly enhanced IgG reactivity in PBC patients in contrast to healthy controls. Co-localization of autoantibodies with the hmAchR M3 receptor-specific autoantibodies was observed in 10 out of 12 PBC-patients but none of the 5 healthy controls. Antibodies of the IgM type were not found to be affected.

Conclusions

For the first time, our data demonstrate the presence of autoantibodies to the hmAchR M3 in PBC patients. These findings might contribute to the understanding of the pathogenesis of this disease. Further studies have to focus on the functionality of hmAchR M3 autoantibodies in PBC patients.

New epitopes and function of anti-M3 muscarinic acetylcholine receptor antibodies in patients with Sjögren's syndrome

M3 muscarinic acetylcholine receptor (M3R) plays a crucial role in the secretion of saliva from salivary glands. It is reported that some patients with Sjögren's syndrome (SS) carried inhibitory autoantibodies against M3R. The purpose of this study is to clarify the epitopes and function of anti-M3R antibodies in SS. We synthesized peptides encoding the extracellular domains of human-M3R including the N-terminal region and the first, second and third extracellular loops. Antibodies against these regions were examined by enzyme-linked immunosorbent assay in sera from 42 SS and 42 healthy controls. For functional analysis, human salivary gland (HSG) cells were preincubated with immunoglobulin G (IgG) separated from sera of anti-M3R antibody-positive SS, -negative SS and controls for 12 h. After loading with Fluo-3, HSG cells were stimulated with cevimeline hydrochloride, and intracellular Ca(2+) concentrations [(Ca(2+) )i] were measured. Antibodies to the N-terminal, first, second and third loops were detected in 42·9% (18 of 42), 47·6% (20 of 42), 54·8% (23 of 42) and 45·2% (19 of 42) of SS, while in 4·8% (two of 42), 7·1% (three of 42), 2·4% (one of 42) and 2·4% (one of 42) of controls, respectively. Antibodies to the second loop positive SS-IgG inhibited the increase of (Ca(2+) )i induced by cevimeline hydrochloride. Antibodies to the N-terminal positive SS-IgG and antibodies to the first loop positive SS-IgG enhanced it, while antibodies to the third loop positive SS-IgG showed no effect on (Ca(2+) )i as well as anti-M3R antibody-negative SS-IgG. Our results indicated the presence of several B cell epitopes on M3R in SS. The influence of anti-M3R antibodies on salivary secretion might differ based on these epitopes.

Mechanisms involved in injury and repair of the murine lacrimal gland: role of programmed cell death and mesenchymal stem cells

The non-keratinized epithelia of the ocular surface are constantly challenged by environmental insults, such as smoke, dust, and airborne pathogens. Tears are the sole physical protective barrier for the ocular surface. Production of tears in inadequate quantity or of inadequate quality results in constant irritation of the ocular surface, leading to dry eye disease, also referred to as keratoconjunctivitis sicca (KCS). Inflammation of the lacrimal gland, such as occurs in Sjogren syndrome, sarcoidosis, chronic graft-versus-host disease, and other pathological conditions, results in inadequate secretion of the aqueous layer of the tear film and is a leading cause of dry eye disease. The hallmarks of lacrimal gland inflammation are the presence of immune cell infiltrates, loss of acinar epithelial cells (the secreting cells), and increased production of proinflammatory cytokines. To date, the mechanisms leading to acinar cell loss and the associated decline in lacrimal gland secretion are still poorly understood. It is also not understood why the remaining lacrimal gland cells are unable to proliferate in order to regenerate a functioning lacrimal gland. This article reviews recent advances in exocrine tissue injury and repair, with emphasis on the roles of programmed cell death and stem/progenitor cells.

Immunoglobulins from scleroderma patients inhibit the muscarinic receptor activation in internal anal sphincter smooth muscle cells

Systemic sclerosis (SSc) IgGs affecting the M(3)-muscarinic receptor (M(3)-R) have been proposed to be responsible for the gastrointestinal (GI) dysmotility in this disease. However, the effect of SSc IgGs on smooth muscle cell (SMC) function has not been studied. We determined the effect of SSc IgGs on the muscarinic receptor activation by bethanechol (BeCh; methyl derivate of carbachol) in SMC and smooth muscle strips from rat internal anal sphincter. IgGs were purified from GI-symptomatic SSc patients and normal volunteers, with protein G-Sepharose columns. SMC lengths were determined via computerized digital micrometry. The presence of M(3)-R and IgG-M(3)-R complex was determined by Western blot. IgGs from SSc patients but not from normal volunteers caused significant and concentration-dependent inhibition of BeCh response (P < 0.05). The maximal shortening of 22.2 +/- 1.2% caused by 10(-4) M BeCh was significantly attenuated to 8.3 +/- 1.2% by 1 mg/ml of SSc IgGs (P < 0.05). Experiments performed in smooth muscle strips revealed a similar effect of SSc IgG that was fully reversible. In contrast to the effect on BeCh, the SSc IgGs caused no significant effect (P > 0.05) on K(+) depolarization and alpha(1)-adrenoceptor activation by phenylephrine. Western blot studies revealed the specific presence of SSc IgG-M(3)-R complex. SSc IgGs attenuated M(3)-R activation, which was reversible with antibody removal. These data suggest that SSc GI dysmotility may be caused by autoantibodies that inhibit the muscarinic neurotransmission. Future treatment of SSc patients may be directed at the removal or neutralization of these antibodies.

Oral manifestations of Sjögren's syndrome

Sjögren's syndrome is a common autoimmune rheumatic disease. The most common symptoms of Sjögren's syndrome are extreme tiredness, along with dry eyes (keratoconjunctivitis sicca) and dry mouth (xerostomia). Saliva plays an essential role in numerous functions of the mouth. Xerostomia can be caused by medications, chronic diseases like Sjögren's syndrome, and medical treatments, such as radiation therapy and bone marrow transplant. Xerostomia can eventually lead to difficulty in swallowing, severe and progressive tooth decay, or oral infections. Despite having excellent oral hygiene, individuals with Sjögren's syndrome have elevated levels of dental caries, along with the loss of many teeth, early in the disease. Sjögren's syndrome alters the protein profile and brings about a change in the composition of saliva. There is an increase in the levels of lactoferrin, beta(2)-microglobulin, sodium, lysozyme C, and cystatin C, and a decrease in salivary amylase and carbonic anhydrase. Up to 90% of individuals with Sjögren's syndrome have antibodies targeting the Ro 60 and La autoantigens. Natural aging, regardless of Sjögren's syndrome, is also another factor that brings about a significant change in the composition of saliva. The most prevailing cause of xerostomia in elderly persons is the use of anticholinergic medications. Currently, there is no cure for Sjögren's syndrome, and treatment is mainly palliative.

Evidence that anti-muscarinic antibodies in Sjögren's syndrome recognise both M3R and M1R

Inhibitory anti-muscarinic receptor type 3 (M3R) antibodies may contribute to the pathogenesis of Sjögren's syndrome (SS), and putative anti-M3R blocking antibodies in intravenous immunoglobulin (IVIg) have been suggested as a rationale for treatment with IVIg. We investigated the presence of subtype-specific anti-MR autoantibodies in healthy donor and SS sera using MR-transfected whole-cell binding assays as well as M1R and M3R peptide ELISAs. Control antibodies against the second extracellular loop of the M3R, a suggested target epitope, were induced in rabbits and found to be cross-reactive on the peptides M3R and M1R. The rabbit antibodies had neither an agonistic nor an antagonistic effect on M3R-dependent ERK1/2 signalling. Only one primary SS (out of 5 primary SS, 2 secondary SS and 5 control sera) reacted strongly with M3R transfected cells. The same SS serum also reacted strongly with M1R and M2R transfectants, as well as M1R and two different M3R peptides. Strong binding to M1R and low-level activities against M3R peptides were observed both in SS and control sera. IVIg showed a strong reactivity against all three peptides, especially M1R. Our results indicate that certain SS individuals may have antibodies against M1R, M2R and M3R. Our results also suggest that neither the linear M3R peptide nor M3R transfectants represent suitable tools for discrimination of pathogenic from natural autoantibodies in SS.

Mechanisms of autoantibody production and the relationship between autoantibodies and the clinical manifestations in Sjögren's syndrome

The major target organs of Sjögren's syndrome (SS) are lacrimal glands and salivary glands where prominent lymphocytic infiltration occurs, which may induce varying levels of autoantibody production. Multiple factors, including environmental stress, viral infection, hormonal imbalance, and apoptosis, are thought to be involved in the pathogenesis of SS. Production of anti-SS-A/Ro and anti-SS-B/La antibodies is thought to be regulated by the presentation of autoantigens in context with an aberrant expression pattern of human leukocyte antigen (HLA) in situ. Molecular mimicry with some viral sequences is also hypothesized. The apoptosis-resistance phenotype of B cells in labial salivary glands (LSGs) of SS is important in autoantibody production. CD40/CD40L (CD40 ligand) and Bcl-2 family proteins, in tandem with B cell-activating factor (BAFF), are supposed to protect infiltrating lymphocytes from apoptosis. Anti-muscarinic3 receptor antibody plays an important role in cholinergic hyperresponsiveness in SS. Fragmentation of autoantigens such as SS-B/La or alfa-fodrin during the process of apoptosis causes the redistribution of these autoantigens, leading to the production of autoantibodies in SS. In this review, the role of autoantibodies found in SS, corresponding to clinical aspects of each antibody as well as the mechanisms of production, is discussed.

Early pathogenic events associated with Sjögren's syndrome (SjS)-like disease of the NOD mouse using microarray analysis

Recently, we reported development of the C57BL/6.NOD-Aec1Aec2 mouse carrying two genetic intervals derived from the NOD mouse. These two genetic regions confer full Sjögren's syndrome (SjS)-like disease in SjS-non-susceptible C57BL/6 mice. The current study was undertaken to apply microarray technology to define the molecular basis underlying onset of SjS-disease in C57BL/6.NOD-Aec1Aec2 mice. Using oligonucleotide microarrays, gene expression profiles of submandibular glands derived from 8- to 12-week-old C57BL/6.NOD-Aec1Aec2 mice and 8-week-old C57BL/6 mice were performed for comparison. Significant differential expressions were determined using the Mann-Whitney U test. Hybridizations using submandibular cDNA probes revealed 75 differentially expressed genes at 8 weeks and 105 differentially expressed genes at 12 weeks of age in C57BL/6.NOD-Aec1Aec2 mice compared to 8-week-old C57BL/6 mice. These genes were related generally to basic cellular activities such as transcription, translation, DNA replication, and protein folding. During the predisease phase, genes upregulated encode proteins associated with the IFN-gamma signal-transduction-pathway (Jak/Stat1), TLR-3 (Irf3 and Traf6) and apoptosis (casp11 and casp3), indicative of chronic proinflammatory stimuli, especially IL-1. Between 8 and 12 weeks of age, sets of clustered genes were upregulated that are associated with adaptive immune responses, especially B cell activation, proliferation and differentiation (Baffr, Taci, Bcma, Blys, April, CD70, CD40L, Traf1, Traf3, Pax5, c-Jun, Elk1 and Nf-kB), and neural receptors (Taj/Troy). Altered gene expressions of TLR3 and TNF-superfamily-receptors and ligands during this early phase of SjS suggest a possible viral etiology in the altered glandular homeostasis with an upregulated, possibly overstimulated, B-lymphocyte activation in the early autoimmune response present in the submandibular glands. The importance of NF-kappaB as a critical signal transduction pathway is also suggested but its link is not yet clear.

[Antireceptor and antichannel autoantibodies]

This review of literature concerns the different autoantibodies directed against membrane receptors and ion channels. The target antigens, the associated pathologies, the pathogenesis and the methods of detection of these autoantibodies will be addressed. Some of these autoantibodies are thought to be closely related to the autoimmune disease whereas for some others their pathogenesis role is still unclear. Overall, the roles of antibodies are different between diseases, but the presence of such autoantibodies support the basis of intervening immunotherapy, antibody titers predicted the activity of the diseases and some of them are very specific and become the useful markers for the diagnosis. Some autoantibodies are detected routinely as the antiacetylcholine receptor, voltage-gated potassium and calcium channels autoantibodies whereas most of them are detected very rarely and only by specialized laboratories. This review will be divided in three parts with the following classification: the first group of autoantibodies directed against membrane receptors included receptors with an enzymatic activity (mostly tyrosine kinase) with one transmembrane domain, receptors associated to G protein with seven transmembrane domains, ion channels and receptors associated to the membrane by the glycosyl phosphatidyl inositol and the second group of intracellular receptor autoantibodies directed to the estrogens, androgens, lamin and kinesin receptors.

Antimuscarinic antibodies in primary Sjögren's syndrome reversibly inhibit the mechanism of fluid secretion by human submandibular salivary acinar cells

OBJECTIVE

Sjögren's syndrome (SS) is an autoimmune condition affecting salivary glands, for which a clearly defined pathogenic autoantibody has yet to be identified. Autoantibodies that bind to the muscarinic M3 receptors (M3R), which regulate fluid secretion in salivary glands, have been proposed in this context. However, there are no previous data that directly show antisecretory activity. This study was undertaken to investigate and characterize the antisecretory activity of anti-M3R.

METHODS

Microfluorimetric Ca2+ imaging and patch clamp electrophysiologic techniques were used to measure the secretagogue-evoked increase in [Ca2+]i and consequent activation of Ca2+-dependent ion channels in individual mouse and human submandibular acinar cells. Together, these techniques form a sensitive bioassay that was used to determine whether IgG isolated from patients with primary SS and from control subjects has antisecretory activity.

RESULTS

IgG (2 mg/ml) from patients with primary SS reduced the carbachol-evoked increase in [Ca2+]i in both mouse and human acinar cells by approximately 50%. IgG from control subjects had no effect on the Ca2+ signal. Furthermore, the inhibitory action of primary SS patient IgG on the Ca2+ signal was acutely reversible. We repeated our observations using rabbit serum containing antibodies raised against the second extracellular loop of M3R and found an identical pattern of acutely reversible inhibition. Anti-M3R-positive serum had no effect on Ca2+-dependent ion channel activation evoked by the direct intracellular infusion of inositol 1,4,5-triphosphate.

CONCLUSION

These observations show for the first time that IgG from patients with primary SS contains autoantibodies capable of damaging saliva production and contributing to xerostomia. The unusual but not unprecedented acute reversibility of the effects of anti-M3 autoantibodies is the subject of further research.

Molecular mimicry: anti-DNA antibodies bind microbial and nonnucleic acid self-antigens

Although cells of the innate immune response have a variety of pattern recognition receptors that are triggered by blood classes of markers, a critical feature of the adaptive immune response is antigenic specificity. Yet it is becoming increasingly clear that the specificity of lymphocyte receptors admits of some laxity. Cross-reactivity may, in fact, be necessary for lymphocyte survival as antigen receptor signaling maintains cellular viability in the absence of antigen activation. Studies of molecular mimicry have revealed many instances in which antibodies to microbial antigens bind also to self-antigens; in some cases, this cross-reactivity has pathogenic potential. In this chapter, we describe cross-reactivity between two self-antigens, DNA and NMDA receptors, and how antibodies with specificity for DNA in patients with splenic lupus may cause central nervous system damage by virtue of binding also to neuronal receptors. This example serves as a reminder that cross-reactivity may exist among self-antigens as well as between foreign and self-antigens.

Salivary production rates fall with age in subjects having anti-centromere, anti-Ro, and/or anti-La antibodies

OBJECTIVES

To clarify the relationship between a subject's sicca-associated autoantibodies type and changes in salivary production rate (SPR) with age in subjects having any of these antibodies.

METHODS

One hundred and eighty-five subjects (female:male = 178:7), who had at least one of the three autoantibodies, anti-centromere (ACA), anti-Ro (SSA), and/or anti-La (SSB), and 65 healthy females were enrolled. The Saxon test was used to measure SPR.

RESULTS

SPRs in the seven male subjects were significantly higher than those in the 178 females tested. Therefore, only female subjects were used for the following analyses. Subjects were classified into substantially four groups according to their seropositivities for ACA, anti-Ro, and/or anti-La: group A, subjects having ACA alone; group B, subjects having anti-Ro alone; group E, subjects having anti-Ro and anti-La; group DFG, subjects having ACA with anti-Ro and/or anti-La. The frequency of Sjögren's syndrome (SS) was 74.0-94.1% in these groups. SPR did not decrease with age in normal female controls. By contrast, SPR decreased significantly with age in the groups having sicca-associated antibodies. The degree of SPR decrease compared between groups was: group A group [symbol: see text] B > group E [symbol: see text] group DFG. In the analysis of the subgroup having any of the sicca-associated antibodies but not fulfilling the classification criteria of SS, SPR also decreased with age.

CONCLUSION

SPR in subjects having any of the sicca-associated antibodies (ACA, anti-Ro, or anti-La) decreased with age.

Effect of inflammation on lacrimal gland function

The lacrimal gland is the main contributor to the aqueous layer of the tear film. It secretes proteins, electrolytes and water, which helps to nourish and protect the ocular surface. Lacrimal gland secretion is primarily under neural control, which is achieved through a neural reflex arc. Stimuli to the ocular surface activate afferent sensory nerves in the cornea and conjunctiva. This in turn activates efferent parasympathetic and sympathetic nerves in the lacrimal gland to stimulate secretion. Sex steroid hormones are also important regulators of lacrimal gland functions. A decrease or lack of lacrimal gland secretion is the leading cause of aqueous tear deficient dry eye syndrome (DES). It has been suggested that DES is an inflammatory disorder that affects the ocular surface and the lacrimal gland. In several pathological instances, the lacrimal gland can become a target of the immune system and show signs of inflammation. This can result from autoimmune diseases (Sjögren's syndrome), organ transplantation (graft versus host disease), or simply as a result of aging. The hallmarks of lacrimal gland inflammation are the presence of focal lymphocytic infiltrates and increased production of proinflammatory cytokines. The mechanisms leading to lacrimal gland dysfunction are still poorly understood. Apoptosis, production of autoantibodies, hormonal imbalance, alterations in signaling molecules, neural dysfunction, and increased levels of proinflammatory cytokines have been proposed as possible mediators of lacrimal gland insufficiency in disease states.

Successful treatment of a patient with primary Sjögren's syndrome with Rituximab

We report the course of a 55-year-old woman, the first patient with primary Sjögren's syndrome and distal renal tubular acidosis but without lymphoma to be treated with B-cell depletion using Rituximab. Rapidly after B-cell depletion, remarkable improvement in xerostomia occurred, while serological findings and tubular acidosis have been unchanged. In labial salivary gland biopsy, lymphocyte infiltration and particularly CD20-positive cells decreased strikingly. Aquaporin 1 (AQP-1) expression in myoepithelial cells was very low before treatment and increased noticeably. Apical AQP-5 in acinus cells likewise increased following Rituximab. In contrast, basolateral NKCC1 was expressed at unchanged intensity before and following Rituximab. The improvement has been sustained and still is most gratifying 10 months after treatment. B-cell depletion may be effective treatment in Sjögren's syndrome. Likewise, it may now be possible to separate the immunologic phenomena in Sjögren's syndrome from the consequences of prolonged hyposalivation when studying the pathophysiology of xerostomia.

Clinical associations of autoantibodies to human muscarinic acetylcholine receptor 3213–228 in primary Sjögren's syndrome

OBJECTIVES

The authors have previously identified a peptide of the human muscarinic acetylcholine receptor-3 (m3AChR) as a suitable antigen for the immunodetection of antimuscarinic acetylcholine receptor autoantibodies in primary Sjögren's syndrome (pSS). The aim of this study was to assess the clinical correlations and disease specificity of these antibodies.

METHODS

Seventy-three pSS, 40 rheumatoid arthritis (RA), 19 systemic lupus erythematosus (SLE), 14 secondary Sjögren's syndrome (sSS) patients, 22 subjects in whom pSS was suspected but in whom the diagnosis not could eventually be established (suspSS) and 40 healthy subjects were investigated. An enzyme-linked immunosorbent assay system developed by the authors using a 16-mer peptide of the m3AChR (m3AChR(213-228)) in a recombinant fusion peptide form was used as the antigen.

RESULTS

Anti-m3AChR(213-228) antibody positivity was observed in 66 (90%) of the pSS patients. The antibody levels correlated positively with the number of extraglandular organ manifestations. Both the mean antibody levels and the occurrence of anti-m3AChR(213-228) positivity were significantly higher in pSS than in the comparison groups. The test discriminated the pSS patients from the various comparison groups with specificities of 65, 68, 71 and 50% for RA, SLE, sSS and suspSS, respectively.

CONCLUSIONS

The presence of m3AChR(213-228) antibodies is a common feature in pSS. Although it is significantly more common in pSS than in the comparison groups, anti-m3AChR(213-228) positivity is not exclusive to pSS.

A peptide of human muscarinic acetylcholine receptor 3 is antigenic in primary Sjogren's syndrome

To evaluate the antigenicity of a peptide representing a part of the second extracellular loop of the human muscarinic acetylcholine receptor 3 (m3AChR) with autoimmune sera from primary Sjogren's syndrome (pSS), enzyme-linked immunosorbent assays (ELISAs) were developed. On the basis of the computer-predicted data, a 16-mer synthetic peptide KRTVPPGECFIQFLSE (KRSE213-228) was produced by solid-phase peptide synthesis. cDNA coding for the KRSE peptide was chemically synthetized and utilized to express the recombinant glutathione S-transferase (GST)-KRSE fusion protein. The immunoreactivities of the two antigens were tested in ELISAs with the sera of 40 pSS patients and 40 healthy controls. The specificity of the reaction was confirmed by inhibition assays and immunoblottings. The pSS sera resulted in significantly higher mean optical densities than those of the healthy controls (KRSE: 0.4149 vs 0.1494, p<0.0001; GST-KRSE 0.4765 vs 0.1764, p<0.0001). The immunological recognition with the recombinant fusion antigen was significantly better than that for the free peptide (p=0.0068). The sensitivities of the assays were 77.5% (KRSE) and 97% (GST-KRSE). The results of the concentration-dependent inhibition assays by the two systems of peptide presentation indicated that the KRSE sequence is specific for pSS sera. This is the first demonstration of the antigenicity of a novel peptide fragment of the human m3AChR in pSS. The analysed peptide could be of diagnostic relevance.

Passive transfer of Sjögren's syndrome IgG produces the pathophysiology of overactive bladder

OBJECTIVE

The presence, in patients with primary and secondary Sjogren's syndrome (SS), of autoantibodies that acutely inhibit M(3) muscarinic receptor (M3R)-mediated bladder contractions is difficult to reconcile with the fact that symptoms of detrusor overactivity and other features of cholinergic hyperresponsiveness occur in this disease. This study was undertaken to examine the in vivo effects of these autoantibodies on bladder function by examining bladder responsiveness and compliance following passive transfer of patient IgG to mice.

METHODS

Contractile responses of isolated bladder strips both to the muscarinic agonist carbachol and to electrically evoked acetylcholine release were measured 48 hours after injection of mice with patient or control IgG. A whole bladder assay with intact neuronal pathways was developed to assess bladder wall compliance on filling cystometry. Expression of M3R in bladders from IgG-injected mice was assessed by immunohistochemistry.

RESULTS

Passive transfer of SS IgG with inhibitory anti-M3R activity produced a paradoxical increase in contractile responses of detrusor strips to cholinergic stimulation. Cystometry of whole bladders revealed a corresponding decrease in bladder wall compliance and phasic detrusor contractions upon filling, replicating the urodynamic features of an overactive bladder. The features of cholinergic hyperresponsiveness were associated with increased postsynaptic M3R expression and were reproduced by injecting mice with a rabbit antibody against the second extracellular loop of M3R.

CONCLUSION

These findings are consistent with the notion that there is initial inhibition of parasympathetic neurotransmission by antagonistic autoantibodies to M3R, which produces a compensatory increase in M3R expression in vivo. The enhanced cholinergic responses during bladder distention result in detrusor overactivity. We conclude that the overactive bladder associated with SS is an autoantibody-mediated disorder of the autonomic nervous system, which may be part of a wider spectrum of cholinergic hyperresponsiveness.