A novel autoantibody reactive with carbonic anhydrase in sera from patients with systemic lupus erythematosus and Sjögren's syndrome

Systemic lupus erythematosus complicated with Fanconi syndrome: a case report and literature review

Background

Systemic lupus erythematosus is an autoimmune disease with diverse clinical manifestations. The symptoms of SLE in children are more atypical than adults. Childhood SLE complicated with Fanconi syndrome is extremely rare and even more difficult to diagnose.

Case presentation

This article reports a preschool boy with SLE who presented with renal tubular acidosis, accompanied by weakness in both lower limbs, delayed growth, and malnutrition. It was later found that the patient had the complication of Fanconi syndrome with renal tubular acidosis. Ultimately, renal biopsy confirmed lupus nephritis. The patient was treated with corticosteroid combined with mycophenolate mofetil, hydroxychloroquine, and belimumab. The symptoms of the child were relieved.

Conclusion

Here we report an extremely rare case of childhood SLE complicated with Fanconi syndrome. There has been no similar clinical report. It is necessary to be alert to the possibility of atypical SLE in children to avoid missed diagnosis and misdiagnosis.

Oxidative modification of carbonic anhydrase by peroxynitrite trigger immune response in mice and rheumatic disease patients

BACKGROUND

Carbonic anhydrases (CA) are metalloenzymes with wide tissue distribution, involved in many important physiological processes, and in some rheumatic diseases, autoantibodies are formed against these enzymes. Recent studies have suggested that oxidative stress triggers anti-CA antibody formation. In this study, we aimed to investigate the effects of modification with oxidative/nitrosative stress end products on CA antigenicity in mice and the relationship between the modified CA autoantibodies and oxidant-antioxidant status in patients with rheumatoid arthritis (RA) and Sjögren's syndrome (SjS).

METHODS

CA I and CA II isoenzymes were isolated from human erythrocytes and modified with 4-hydroxynonenal (4-HNE), malondialdehyde (MDA), and peroxynitrite (PN). Balb-c mice were immunized with these agents to determine the effects of modification on CA antigenicity. The autoantibody titers of modified CA isoenzymes were detected in patients. In addition MDA, 4-HNE, 3-nitrotyrosine (3-NT), superoxide dismutase (SOD), and glutathione peroxidase (GSH-Px) activities were measured to assess the oxidant-antioxidant status in patients.

RESULTS

Modifications of carbonic anhydrase with oxidative stress end products, HNE, MDA and PN, lead to alterations in the immune response to these enzymes in mice. It was found that HNE and MDA decreased the antigenicity while PN increased. In addition, PN-modified CA autoantibody levels were found to be significantly different in both RA and SjS patients compared to their controls (p<0.05).

CONCLUSIONS

PN modifications can also trigger an immune response against CA isoenzymes in mice, and PN-modified CA I and CA II autoantibody titers were found at a significantly high level in both RA and SjS patients.

Anti-carbonic anhydrase II antibody reflects urinary acidification defect especially in proximal renal tubules in patients with primary Sjögren syndrome

Primary Sjögren syndrome (pSS) is a systemic autoimmue disease featured by excessive autoantibody production. It has been demonstrated that anti-carbonic anhydrase II (anti-CA II) antibody is correlated with renal tubular acidosis in pSS; however, no further details about urinary acidification defect have been reported, and the antibody's relationship with other organ impairments remains unknown. This case-control study aimed to examine anti-CA II antibody levels in relation to various systemic complications in pSS, and evaluate its potential role as a organ-specific biomarker in a Chinese cohort. Serum anti-CA II antibody levels were determined using ELISA in 123 patients with pSS and 72 healthy controls. The medical records of the patients were collected, and the correlation between serum anti-CA II antibody and clinical/immunological parameters was investigated. Serum anti-CA II antibody level and its positive rate were significantly increased in pSS patients compared with controls, and ANA-positive patients presented even higher titers of the antibody. In anti-CA II positive group, remarkably higher urine pH and bicarbonate, as well as lower urine titratable acid and serum potassium were observed, which indicated renal tubular acidification dysfunction both involving bicarbonate reabsorption and acid secretion. In addition, platelet count and complement 3, complement 4 levels decreased, whereas serum IgG, IgA and γ-globulin levels increased notably in accord with a higher EULAR SS disease activity index score in these patients. Further analysis showed that anti-CA II antibody was most elevated in patients with defect in bicarbonate reabsorption, reflecting proximal renal tubular injury, rather than in patients with distal renal tubular acidosis as previously reported. In conclusion, anti-CA II antibody reflects renal (especially proximal renal tubular) and hematologic impairment as well as increased disease activity in pSS. It may act as a serum biomarker of systemic damage of pSS.

The Diagnostic Performance of Early Sjögren's Syndrome Autoantibodies in Juvenile Sjögren's Syndrome: The University of Florida Pediatric Cohort Study

Objectives

The aim of this study was to evaluate the clinical validity of early Sjögren's syndrome (SS) autoantibodies (eSjA), which were originally marketed for early diagnosis of SS, for juvenile SS (JSS) in a recently identified pediatric cohort.

Methods

A total of 105 symptomatic subjects with eSjA results available were evaluated at the Center for Orphaned Autoimmune Disorders at the University of Florida and enrolled for this study. JSS diagnosis was based on the 2016 ACR/EULAR SS criteria. Demographic/clinical/laboratory parameters were compared between JSS (n = 27) and non-JSS (n = 78) for % positivity, sensitivity, and specificity of eSjA (SP1, anti-salivary protein; CA6, anti-carbonic anhydrase VI; PSP, anti-parotid secretory protein) and classic SS-autoantibodies (cSjA; ANA, SSA/SSB, RF, and others) either alone or in combination. Associations between eSjA and diagnostic/glandular parameters were also determined by Fisher's exact test.

Results

Compared to non-JSS, JSS patients exhibited sicca symptoms demonstrating reduced unstimulated salivary flow rate (USFR) and abnormal glandular features revealed by salivary gland ultrasound (SGUS). Among cSjA, ANA demonstrated the highest sensitivity of 69.2%, while SSA, SSB, and RF showed around 95% specificities for JSS diagnosis. The % positive-SSA was notably higher in JSS than non-JSS (56% vs. 5%). Of eSjA, anti-CA6 IgG was the most prevalent without differentiating JSS (37%) from non-JSS (32%). Sensitivity and specificity of eSjA were 55.6 and 26.9%, respectively. Autoantibodies with potentially applicable specificity/sensitivity for JSS were seen only in cSjA without a single eSjA included. There were no associations detected between eSjA and focus score (FS), USFR, SSA, SGUS, and parotitis/glandular swelling analyzed in the entire cohort, JSS, and non-JSS. However, a negative association between anti-PSP and parotitis/glandular swelling was found in a small group of positive-SSA (n = 19, p = 0.02) whereas no such association was found between anti-PSP-positive compared to anti-PSP-negative. JSS and non-JSS groups differed in FS, USFR, and EULAR SS Patient Reported Index Dryness/Mean in CA6/PSP/ANA, SP1, and SSA-positive groups, respectively. Additionally, a higher FS was found in RF-positive than RF-negative individuals.

Conclusions

eSjA underperformed cSjS in differentiating JSS from non-JSS. The discovery of clinical impact of eSjA on early diagnosis of JSS necessitates a longitudinal study.

From Hypokalemic Crisis to Sjogren's Syndrome: A Case Report and Literature Review

Renal involvement occurs in approximately 5% of patients with Sjögren's syndrome (SS). We reported the case of a 20-year-old African woman who was received for paralysis of 4 limbs secondary to hypokalemia. The diagnosis of renal tubular acidosis type 1 complicated by hypokalemia was retained. In the etiologic research of renal tubular acidosis type 1, primary SS was retained. The patient received symptomatic treatment based on potassium chloride, sodium bicarbonate, hydration, and a low protein diet. In terms of etiological treatment, she was put on corticosteroid and hydroxychloroquine. The outcome was favorable with correction of acidosis and hypokalemia.

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

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

[Renal involvement in Sjögren's syndrome]

Primary Sjögren syndrome is an autoimmune disorder characterized by lymphoplasmacytic infiltration of the exocrine (salivary and lachrymal) glands resulting in sicca symptoms (dryness). Systemic complications can occur in primary Sjögren syndrome, but renal involvement is rare, affecting<10% patients. The most frequent form of nephropathy in primary Sjögren syndrome is tubulointerstitial nephritis, where infiltration of the kidney by plasma cells is a key feature and shows similarity to the lymphoplasmacytic infiltration of the salivary glands. Electrolyte disturbances may occur in primary Sjögren syndrome, such as renal distal tubular acidosis, diabetes insipidus, Gitelman syndrome, or Fanconi syndrome. Glomerular involvement is less frequently detected in patients with primary Sjögren syndrome, but can take the form of membranoproliferative glomerulonephritis secondary to cryoglobulinaemia. The renal prognosis in patients with primary Sjögren syndrome and TIN or glomerular disease is usually good, but the risk of chronic kidney disease remains significant for some patients. Appropriate screening must be performed at least once a year in patients with systemic primary Sjögren syndrome in order to facilitate the early detection of renal complications. In this Review, we discuss the epidemiology, pathophysiology, differential diagnosis, and treatment of renal disease in primary Sjögren syndrome.

The Cellular and Molecular Bases of Allergy, Inflammation and Tissue Fibrosis in Patients with IgG4-related Disease

IgG4-related disease (IgG4-RD) is a spectrum of complex fibroinflammatory disorder with protean manifestations mimicking malignant neoplasms, infectious or non-infectious inflammatory process. The histopathologic features of IgG4-RD include lymphoplasmacytic infiltration, storiform fibrosis and obliterative phlebitis together with increased in situ infiltration of IgG4 bearing-plasma cells which account for more than 40% of all IgG-producing B cells. IgG4-RD can also be diagnosed based on an elevated serum IgG4 level of more than 110 mg/dL (normal < 86.5 mg/mL in adult) in conjunction with protean clinical manifestations in various organs such as pancreato–hepatobiliary inflammation with/without salivary/lacrimal gland enlargement. In the present review, we briefly discuss the role of genetic predisposition, environmental factors and candidate autoantibodies in the pathogenesis of IgG4-RD. Then, we discuss in detail the immunological paradox of IgG4 antibody, the mechanism of modified Th2 response for IgG4 rather than IgE antibody production and the controversial issues in the allergic reactions of IgG4-RD. Finally, we extensively review the implications of different immune-related cells, cytokines/chemokines/growth factors and Toll-like as well as NOD-like receptors in the pathogenesis of tissue fibro-inflammatory reactions. Our proposals for the future investigations and prospective therapeutic strategies for IgG4-RD are shown in the last part.

Recent Advances in Mouse Models of Sjögren's Syndrome

Sjögren's syndrome (SS) is a complex rheumatoid disease that mainly affects exocrine glands, resulting in xerostomia (dry mouth) and xerophthalmia (dry eye). SS is characterized by autoantibodies, infiltration into exocrine glands, and ectopic expression of MHC II molecules on glandular epithelial cells. In contrast to the well-characterized clinical and immunological features, the etiology and pathogenesis of SS remain largely unknown. Animal models are powerful research tools for elucidating the pathogenesis of human diseases. To date, many mouse models of SS, including induced models, in which disease is induced in mice, and genetic models, in which mice spontaneously develop SS-like disease, have been established. These mouse models have provided new insight into the pathogenesis of SS. In this review, we aim to provide a comprehensive overview of recent advances in the field of experimental SS.

Triosephosphate isomerase, carbonic anhydrase, and creatinine kinase-brain isoform are possible antigen targets in patients with achalasia

BACKGROUND

Idiopathic achalasia is an uncommon esophageal motor disorder. The disease involves interaction between inflammatory and autoimmune responses. However, the antigens related to the disease are still unknown.

AIM

To identify the possible antigen targets in muscle biopsies from lower esophageal sphincter (LES) of achalasia patients.

METHODS

Esophageal biopsies of patients with type I and type II achalasia and esophagogastric junction outflow obstruction (EGJOO) were analyzed. Lower esophageal sphincter muscle biopsy from a Healthy organ Donor (HD) was included as control for two-dimensional gel electrophoresis. Immunoblotting of muscle from LES lysate with sera of type I, type II achalasia, or type III achalasia, sera of EGJOO and sera of healthy subjects (HS) was performed. The target proteins of the serum were identified by mass spectrometry Matrix-assited laser desorption/ionization time-of-flight (MALDI-TOF).

KEY RESULTS

The proteomic map of muscle from LES tissue lysates of type I, and type II achalasia, EGJOO, and HD were analyzed and divided into three important regions. We found a difference in the concentration of certain spots. Further, we observed the serum reactivity of type I achalasia and type II achalasia against 45 and 25 kDa bands of type I achalasia tissue. Serum of type III achalasia and EGJOO mainly recognized 25 kDa band. Bands correspond to triosephosphate isomerase (TPI) (25 kDa), carbonic anhydrase (CA) (25 kDa) and creatinine kinase-brain (CKB) isoform (45 kDa).

CONCLUSIONS AND INFERENCES

We identify three antigen targets, TPI, CA, and CKB isoform, which are recognized by sera from patients with achalasia.

The Human Carbonic Anhydrase II in Platelets: An Underestimated Field of Its Activity

Carbonic anhydrases constitute a group of enzymes that catalyse reversible hydration of carbon dioxide leading to the formation of bicarbonate and proton. The platelet carbonic anhydrase II (CAII) was described for the first time in the '80s of the last century. Nevertheless, its direct role in platelet physiology and pathology still remains poorly understood. The modulation of platelet CAII action as a therapeutic approach holds promise as a novel strategy to reduce the impact of cardiovascular diseases. This short review paper summarises the current knowledge regarding the role of human CAII in regulating platelet function. The potential future directions considering this enzyme as a potential drug target and important pathophysiological chain in platelet-related disorders are described.

Tubulointerstitial nephritis-induced hypophosphatemic osteomalacia in Sjögren's syndrome: a case report and review of the literature

Sjögren's syndrome (SS) is a chronic autoimmune inflammatory disease that typically affects the salivary and lacrimal glands. Renal involvement is relatively uncommon and may precede other complaints. Tubulointestitial nephritis (TIN) is the most common renal involvement in SS. Osteomalacia occurring as the first manifestation of renal tubular disorder due to SS is very rare. We report a 39-year-old male who presented with polydipsia, polyuria, and multiple bone pain. Bone density test showed severe osteoporosis, and laboratory findings suggested hypokalemia, hypophosphatemia, and vitamin D deficiency, which supported the diagnosis of hypophosphatemic osteomalacia. He had nephrogenic loss of phosphate and potassium, tubular acidification, and concentration dysfunction. And, the diagnosis of chronic TIN was subsequently confirmed by renal biopsy. The patient reported dry mouth and physical examination showed multiple dental caries. Xerophthalmia, abnormal morphology, and function of the salivary glands by sonography and scintigraphy, together with positive anti-SSA and anti-SSB, confirmed the diagnosis of SS. The TIN indicated SS as the underlying cause of osteomalacia. After taking supplements of potassium, phosphate, vitamin D, and sodium bicarbonate for 1 month, bone pain was alleviated and serological potassium and phosphorus were also back to normal. In conclusion, renal involvement in SS may be latent and precede the typical sicca symptoms. Osteomalacia can be the first manifestation of renal disorder due to SS. Therefore, autoantibody investigations as well as the lacrimal and salivary gland examinations for SS should be considered and performed for suspected patients.

Antibodies reacting to carbonic anhydrase isozymes (I and II) and albumin in sera from dogs

IgGs to carbonic anhydrase isozymes (CA-I and CA-II) and albumin were identified in dog serum. IgG titers were determined in the sera of asymptomatic dogs, and in dogs with atopic dermatitis, diarrhea and/or vomiting, diabetes and/or pancreatitis, kidney disease, hepatic disease, and thyroid gland disease, using ELISA. Low titres of IgG-reactive CA-I, CA-II, BSA, and CSA were found in the sera of healthy beagles. Compared with healthy beagles, there was a significant difference in the titers of antibodies against CA-I in asymptomatic dogs, dogs with diabetes and/or pancreatitis, or thyroid gland disease, or hepatic disease. Compared with healthy beagles, there was a significant difference in the antibody titer of anti-CA-II IgG in asymptomatic dogs and in those with hepatic disease. There was a significant difference in the antibody titer of anti-BSA IgG between healthy beagles and dogs with hepatic disease.

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.

Renal involvement in primary Sjögren syndrome

Primary Sjögren syndrome (pSS) is an autoimmune disorder characterized by lymphoplasmacytic infiltration of the exocrine (salivary and lachrymal) glands that results in sicca symptoms (dryness of the eyes and mouth). Systemic complications can occur in pSS, but renal involvement is rare, affecting <10% patients. The most frequent form of nephropathy in pSS is tubulointerstitial nephritis (TIN), in which infiltration of the kidney by plasma cells is a key feature and shows similarity to the lymphoplasmacytic infiltration of the salivary glands. Electrolyte disturbances may occur in pSS, such as renal distal tubular acidosis, diabetes insipidus, Gitelman syndrome or Fanconi syndrome. Glomerular involvement is less frequently detected in patients with pSS, but usually takes the form of membranoproliferative glomerulonephritis secondary to cryoglobulinaemia. The renal prognosis in patients with pSS and TIN or glomerular disease is usually favourable, but the risk of chronic kidney disease remains high in patients with TIN. Appropriate screening must be performed at least once a year in patients with systemic pSS in order to facilitate the early detection of renal complications. In this Review we discuss the epidemiology, pathophysiology, differential diagnosis and treatment of renal disease in pSS.

The value of animal models to study immunopathology of primary human Sjögren's syndrome symptoms

Sjögren's syndrome (SjS) is a complex chronic autoimmune disease of multifactorial etiology that results in eventual loss of secretory function in the exocrine glands. The challenges towards finding a therapeutic prevention or treatment for SjS are due primarily to a lack of understanding in the pathophysiological and clinical progression of the disease. In order to circumnavigate this problem, there is a need for appropriate animal models that resemble the major phenotypes of human SjS and deliver a clear underlying biological or molecular mechanism capable of defining various aspects for the disease. Here, we present an overview of SjS mouse models that are providing insight into the autoimmune process of SjS and advance our focus on potential diagnostic and therapeutic targets.

Autoimmune pancreatitis as an initial manifestation of systemic lupus erythematosus

Abstract We report a case of systemic lupus erythematosus that concomitantly occurred with autoimmune pancreatitis. The clinical manifestations of pancreatitis improved in response to steroid therapy. Although the pathogenesis of autoimmune pancreatitis is still controversial, as is that of systemic lupus erythematosus, the observations in the present case suggest the presence of an autoimmune mechanism underlying autoimmune pancreatitis.

Anti-carbonic anhydrase II antibodies in end-stage renal disease patients

OBJECTIVE

The aim of this study was to investigate the presence of anti-carbonic anhydrase (CA II) autoantibodies in patients with end-stage renal disease (ESRD) and relationships between the autoantibody titers and ghrelin, glucose, blood urea nitrogen (BUN) and creatinine.

SUBJECTS AND METHODS

Serum CA II autoantibody titers, malondialdehyde (MDA), BUN, creatinine and ghrelin levels were measured in 45 ESRD patients and 45 healthy subjects.

RESULTS

The CA II autoantibody titers in the ESRD group (0.170 ± 0.237) were significantly higher than those in the control group (0.079 ± 0.032; p = 0.035). MDA and ghrelin levels were also significantly higher in the ESRD group (p < 0.001). A weak positive correlation was determined between anti-CA II antibody titers and MDA, and a negative correlation was observed between ghrelin levels and anti-CA II antibody titers (r = 0.287, p = 0.028 and r = -0.278, p = 0.032, respectively).

CONCLUSIONS

In ESRD patients, the results showed the development of an autoimmune response against CA II. This suggests that anti-CA II antibodies could be involved in the pathogenesis of ESRD.

Serum anti-carbonic anhydrase antibodies and oxidant-antioxidant balance in patients with acute anterior uveitis

PURPOSE

To study the existence of anti-carbonic anhydrase antibodies (anti-CA-I&II) in acute anterior uveitis (AAU) patients and to analyze the relationship between the levels of these antibodies and the total antioxidant capacity (TAC), total oxidant capacity (TOC), oxidative stress index (OSI), and malondialdehyde (MDA) level.

METHODS

Forty-five AAU cases and 43 healthy controls were enrolled in this prospective study.

RESULTS

The average anti-CA I and II antibody levels were 0.433 ± 0.306 and 0.358 ± 0.261 IU/mL, respectively, in the AAU group and 0.275 ± 0.147 and 0.268 ± 0.108 IU/mL, respectively, in the control group (p = 0.004 and p = 0.036, respectively). In addition, it was found that the TOC, OSI, and MDA levels in the AAU subjects were statistically significantly higher than those of the control subjects.

CONCLUSIONS

These results suggest that autoimmune responses against CA I and CA II and an altered serum oxidant-antioxidant balance may be involved in the pathogenesis of AAU.

Antibodies against carbonic anhydrase in patients with aplastic anemia

BACKGROUND/AIMS

Antibodies against carbonic anhydrase (CA) have been detected in patients with an aplastic anemia (AA)-like syndrome after autologous stem cell transplantation.

METHODS

We analyzed sera of 53 bona fide AA patients before and after treatment with anti-thymocyte globulin (ATG) or bone marrow transplantation for the presence of anti-CA antibodies.

RESULTS

Anti-CA antibodies were detected in 20 patients (38%) and were associated with older age at diagnosis of AA. Antibody-positive patients showed poor response to ATG treatment (complete response 14%) and inferior long-term survival (36% at 10 years), when compared to antibody-negative patients (complete response and 10-year survival both 64%). Two thirds of patients with antibodies at diagnosis of AA became antibody negative after treatment with ATG. Clearance of the antibody did not appear to be associated with hematological improvement.

CONCLUSION

Antibodies against CA are detected frequently at diagnosis of AA, and their presence identifies a subset of patients with poor response to immunosuppressive treatment.

Sjögren's syndrome: studying the disease in mice

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

Novel carbonic anhydrase autoantibodies and renal manifestations in patients with primary Sjogren's syndrome

OBJECTIVE

Anti-carbonic anhydrase II (anti-CA II) antibodies have been related to renal manifestations of primary SS (pSS), and animal studies have even suggested a pathogenic role for them. However, not all pSS patients with renal tubular acidosis (RTA) present with anti-CA II antibodies. Recently, several novel CA isoenzymes have been recognized and we aimed to investigate whether antibodies to these are associated with renal manifestations of pSS.

METHODS

We examined anti-CA II antibodies as well as anti-CA I, VI, VII and XIII antibodies by ELISA tests in 74 pSS patients on whom detailed nephrological examinations had been performed and, as controls, in 56 subjects with sicca symptoms, but no pSS.

RESULTS

The levels of anti-CA I, II, VI and VII antibodies were significantly higher in patients with pSS compared with subjects with sicca symptoms but no pSS. None of the anti-CA antibodies was associated with the presence of complete or incomplete RTA or proteinuria or urinary α₁m excretion in patients with pSS. However, levels of anti-CA II, VI and XIII antibodies correlated significantly with urinary pH, and inversely with serum sodium concentrations. The degree of 24-h urinary protein excretion correlated weakly with levels of anti-CA VII antibodies.

CONCLUSION

Not only antibodies to CA II, but also anti-CA VI and XIII antibodies seem to be associated with renal acidification capacity in patients with 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.

Rescue of anaemia and autoimmune responses in SOD1-deficient mice by transgenic expression of human SOD1 in erythrocytes

Oxidative stress has been implicated as a cause of various diseases such as anaemia. We found that the SOD1 [Cu,Zn-SOD (superoxide dismutase)] gene deficiency causes anaemia, the production of autoantibodies against RBCs (red blood cells) and renal damage. In the present study, to further understand the role of oxidative stress in the autoimmune response triggered by SOD1 deficiency, we generated mice that had the hSOD1 (human SOD1) transgene under regulation of the GATA-1 promoter, and bred the transgene onto the SOD1(-/-) background (SOD1(-/-);hSOD1(tg/+)). The lifespan of RBCs, levels of intracellular reactive oxygen species, and RBC content in SOD1(-/-);hSOD1(tg/+) mice, were approximately equivalent to those of SOD1(+/+) mice. The production of antibodies against lipid peroxidation products, 4-hydroxy-2-nonenal and acrolein, as well as autoantibodies against RBCs and carbonic anhydrase II were elevated in the SOD1(-/-) mice, but were suppressed in the SOD1(-/-);hSOD1(tg/+) mice. Renal function, as judged by blood urea nitrogen, was improved in the transgenic mice. These results rule out the involvement of a defective immune system in the autoimmune response of SOD1-deficient mice, because SOD1(-/-);hSOD1(tg/+) mice carry the hSOD1 protein only in RBCs. Metabolomic analysis indicated a shift in glucose metabolism to the pentose phosphate pathway and a decrease in the energy charge potential of RBCs in SOD1-deficient mice. We conclude that the increase in reactive oxygen species due to SOD1 deficiency accelerates RBC destruction by affecting carbon metabolism and increasing oxidative modification of lipids and proteins. The resulting oxidation products are antigenic and, consequently, trigger autoantibody production, leading to autoimmune responses.

Potential for differential diagnosis of autoimmune pancreatitis and pancreatic cancer using carbonic anhydrase II antibody

OBJECTIVES

Pancreatic ductal epithelia contain an abundance of carbonic anhydrase (CA), and the presence of antibodies to this enzyme has been described in autoimmune disorders. We previously found a small amount of an immunoglobulin G-like material in purchased CAII reagents, which led to pseudopositive reactions.

METHODS

We determined the optimum measurement conditions for detecting anti-CAII antibody using an enzyme-linked immunosorbent assay and sera from 140 patients with pancreatic diseases.

RESULTS

Compared with the prevalence of anti-CAII antibody in healthy subjects, a significantly higher seroprevalence of the antibody was detected in patients with autoimmune pancreatitis (AIP) (88.9%, P < 0.02), Sjögren syndrome (67.6%, P < 0.01), and alcoholic chronic pancreatitis (45.8%, P < 0.01). No positive results were obtained among patients with pancreatic cancer. Moreover, the antibody value obtained in the pancreatic cancer patients was actually lower than that obtained in healthy subjects.

CONCLUSIONS

The anti-CAII antibody is probably not a specific marker of AIP because it was present at a higher frequency in the sera of patients with other pancreatic diseases. Nevertheless, the anti-CAII antibody may be a useful tool for the differential diagnosis of AIP and pancreatic cancer.

Animal models of Sjögren's syndrome

Sjögren's syndrome is an autoimmune, chronic inflammatory disease characterized by focal mononuclear cell infiltration of exocrine tissues, accompanied by loss of secretory function. The pathogenesis of autoimmune diseases is complex and, therefore, difficult to study in vitro. As of today, the role of initiating factors remains obscure, clinical symptoms develop late, and there are no tests for early diagnosis of SS. Hence, the disease is difficult to detect and treat. Animal models may provide insights into the identification of target antigens, narrowing the relevant pathological immune mechanisms, and to study the evolution of tissue pathology. This review summarizes current knowledge on murine strains, both spontaneous and induced models, used to study Sjögren's syndrome. Special attention is paid to the characteristics of different strains regarding their properties to mimic specific aspects or stages of the disease.

Usefulness of mouse models to study the pathogenesis of Sjögren's syndrome

Sjögren's syndrome (SS) is an autoimmune disorder characterized by ocular and oral dryness as well as systemic manifestations. The immunopathogenesis of SS is complex with different intricate factors. Because of the delay in the appearance of symptoms and due to ethical issues it is very difficult to study the wide array of factors intervening in the pathogenesis of SS in human patients. To circumvent this problem, different animal models have been elaborated for studying the different subsets of the aspects of the physiopathology of this disease. In this review, we focus on the mouse models that have been established to deepen our insight into the immunopathogenesis of SS.

Immunization of Balb/c mice with modified auto-antigens for induction of autoimmune sialoadenitis

Sjögren's syndrome is an autoimmune disease characterized by sialoadenitis and elevated titers of autoantibodies. To assess whether it is possible to induce inflammatory changes in salivary gland tissues, a series of immunizations in Balb/c mice have been undertaken, using salivary gland extract, modified or not, added to several adjuvants. Mice's humoral immune response to salivary gland antigens was monitored by ELISA. Inflammatory cells infiltrating gland tissue were seen 3 months after immunization with salivary gland extract modified with pepsin (AgGp) and metaperiodate (AgGMp). Although pathological progression was not observed, the histopathological picture was similar to the initial phase of Sjögren's syndrome. In addition, a monoclonal antibody reactive with 3 gland polypeptides and anhydrase carbonic II was rescued among B cells from immunized mice. Thus, immunizations with modified autoantigens were able to initiate pathological damage to glandular tissue and stimulate the proliferation of auto-reactive B cells.

Induction of Anti-Carbonic-Anhydrase-II Antibody Causes Renal Tubular Acidosis in a Mouse Model of Sjögren’s Syndrome

BACKGROUND/AIM

We recently reported that renal tubular acidosis (RTA) in Sjogren's syndrome (SjS) is associated with high titers of an autoantibody against carbonic anhydrase (CA) II, an important enzyme in renal acid-base regulation. The purpose of this study was to determine whether a CA-II antibody could cause RTA in a mouse model of SjS.

METHODS

PL/J mice were immunized with human CA II to induce CA II antibody formation, whereas controls were injected with phosphate-buffered saline and adjuvant. After 6 weeks, anti-CA-II antibody titers were measured, then ammonium chloride was administered orally for 1 week to detect any acidification defect.

RESULTS

CA-II-immunized mice showed higher anti-CA-II antibody titers than control mice. Pathologically, lymphocytic and plasma cell infiltration was seen in the salivary glands and kidneys of CA-II-immunized mice, but not in controls. On acid loading, blood pH and urine pH decreased in both groups of mice, but the slope of urine pH versus blood pH was less steep in the CA-II-immunized mice, suggesting that these mice had an impaired ability to reduce their urine pH in the face of metabolic acidosis.

CONCLUSION

CA-II-immunized mice had a urinary acidification defect, which may be similar to that seen in patients with SjS.

Elevated oxidative stress in erythrocytes due to a SOD1 deficiency causes anaemia and triggers autoantibody production

Reactive oxygen species are involved in the aging process and diseases. Despite the important role of Cu/Zn SOD (superoxide dismutase) encoded by SOD1, SOD1-/- mice appear to grow normally under conventional breeding conditions. In the present paper we report on a novel finding showing a distinct connection between oxidative stress in erythrocytes and the production of autoantibodies against erythrocytes in SOD1-/- mice. Evidence is presented to show that SOD1 is primarily required for maintaining erythrocyte lifespan by suppressing oxidative stress. A SOD1 deficiency led to an increased erythrocyte vulnerability by the oxidative modification of proteins and lipids, resulting in anaemia and compensatory activation of erythropoiesis. The continuous destruction of oxidized erythrocytes appears to induce the formation of autoantibodies against certain erythrocyte components, e.g. carbonic anhydrase II, and the immune complex is deposited in the glomeruli. The administration of an antioxidant, N-acetylcysteine, suppressed erythrocyte oxidation, ameliorated the anaemia, and inhibited the production of autoantibodies. These data imply that a high level of oxidative stress in erythrocytes increases the production of autoantibodies, possibly leading to an autoimmune response, and that the intake of antioxidants would prevent certain autoimmune responses by maintaining an appropriate redox balance in erythrocytes.

Detection of autoantibody against carbonic anhydrase II in various liver diseases by enzyme-linked immunosorbent assay using appropriate conditions

BACKGROUND

Immunoglobulin G autoantibody against carbonic anhydrase (CA) II has been detected in the sera of patients with a variety of autoimmune diseases. Antibody against CAII has also been described as a serological marker for distinguishing between cases of autoimmune cholangitis (AIC) and those of primary biliary cirrhosis (PBC). However, the optimal antibody measurement conditions (enzyme-linked immunosorbent assay: ELISA) have not yet been established. Moreover, we also found that a small amount of an IgG-like material exists in purchased CAII reagents, which causes pseudopositive reactions.

METHODS

The sera of 96 patients with liver disease were examined for the presence of anti-CAII antibody using antigen (CAII) not containing the IgG-like material as the most suitable measurement conditions. Compared with the anti-CAII antibody prevalence of 3.8% found in normal subjects, a significantly higher seroprevalence of the antibody was detected in patients with PBC (31.0%, P<0.02), autoimmune hepatitis (AIH) (50.0%, P<0.01) and chronic viral hepatitis (27.5%, P<0.01). But, in cases of PBC, no significant correlation was noted between the level of anti-CAII antibody and the presence of anti-mitochondrial antibodies (AMA).

CONCLUSIONS

While CAII may be a target antigen in autoimmune diseases, the anti-CAII antibody is not likely to be a specific marker of AIC. The optimum measurement conditions for the ELISA for anti-CAII antibody would provide us with valuable information to elucidate the underlying immunological abnormalities in liver diseases.

Primary biliary cirrhosis and autoimmune cholangiopathy

AMA are detected in the serum of 92% to 95% of patients with PBC using indirect immunofluorescent methods. AIC is the term used to describe the 5% to 8% of AMA-negative PBC patients who uniformly have ANA and SMA. Recent applications of more sensitive and specific tests to detect serum AMA have shown that most, if not all, patients with AIC actually do have AMA. Emerging evidence that AMA and mitochondrial autoantigens play important roles in the immunopathogenesis of NSDC also suggests that AIC and PBC are likely to be a single disease, exhibiting variation in the types of autoantibodies and in both the concentrations and immunoglobulin isotypes of AMA.

High prevalence of autoantibodies against carbonic anhydrase II and lactoferrin in type 1 diabetes: concept of autoimmune exocrinopathy and endocrinopathy of the pancreas

INTRODUCTION

Dysfunction of the exocrine as well as the endocrine pancreas has been reported in type 1 diabetes. Lymphocytic infiltration of the exocrine pancreas is observed in approximately half of Japanese type 1 diabetic patients.

AIMS

To investigate the involvement of autoimmunity against the exocrine pancreas in type 1 diabetes.

METHODOLOGY

We examined autoantibodies against human carbonic anhydrase II (ACA) and lactoferrin (ALF), antigens in the pancreatic duct cells and the pancreatic acinus, respectively, in 43 type 1 diabetic patients and 20 type 2 diabetic patients using the enzyme-linked immunosorbent assay method.

RESULTS

Of 43 type 1 diabetic patients, ACA was detected in 28 patients (65%) and ALF was detected in 29 patients (67%). One or both of the antibodies were detected in 33 type 1 diabetic patients (77%). In contrast, neither ACA nor ALF were detected in type 2 diabetic patients.

CONCLUSIONS

The high prevalence of both ACA and ALF strongly suggests the involvement of autoimmunity against the exocrine pancreas as well as the endocrine pancreas in some type 1 diabetic patients. We propose that these conditions be referred to as autoimmune exocrinopathy and endocrinopathy of the pancreas.

Autoantibodies in primary Sjögren's syndrome: new insights into mechanisms of autoantibody diversification and disease pathogenesis

Characterisation of autoantibodies and their target autoantigens in primary Sjögren's syndrome (SS) is an important entry point for studying this common systemic autoimmune disease. Diversification of anti-Ro/La responses is believed to occur by a process of determinant spreading following initiation of an autoimmune response to one component, possibly 52-kD Ro (Ro52). Recent evidence supports the ER-resident chaperone Grp78 as a potential candidate in the initiation of an autoimmune response against Ro52, by binding to a Grp78 binding motif in the COOH-terminal region of Ro52. The subsequent diversification of the anti-Ro/La response is influenced by distinct HLA class II alleles. Anti-salivary duct autoantibodies have been revisited and shown to be mimicked by cross-reactive isoantibodies to AB blood group antigens. Identification of autoantibodies that act as antagonists at M3-muscarinic receptors represents an important advance. As well as contributing to the sicca symptoms, the functional effects of these autoantibodies may explain associated features of autonomic dysfunction in patients with SS. Anti-M3 receptor autoantibodies occur in both primary and secondary SS and allow Sjögren's syndrome to be viewed as a disorder of anti-receptor autoimmunity.

Clinical relevance of autoimmune-related pancreatitis

Recently, a concept of 'autoimmune pancreatitis' (AIP) was proposed. Computed tomography, magnetic resonance imaging or ultrasonography show a diffusely enlarged pancreas with a so-called 'sausage-like' appearance. Hypergammaglobulinaemia, increased serum levels of total IgG or IgG4, positive autoantibodies such as antinuclear antibody, anti-lactoferrin antibody, anti-CA-II antibody, rheumatoid factor and anti-smooth muscle antibody, were often observed in patients with AIP. Microscopic findings showed fibrotic changes with infiltration of lymphocytes, plasmacytes and sometimes eosinophils in the pancreas. Major subgroups of lymphocytes infiltrating areas around pancreatic ducts were CD4(+) T-cells producing IFN-gamma. HLA-DR was expressed on pancreatic duct cells as well as CD4(+) cells. The diagnosis is made by a combination of clinical, laboratory and morphological findings. Laboratory data, pancreas images and diabetes mellitus in most patients do respond to steroid treatment. In conclusion, autoimmune-related pancreatitis appears to be a unique clinical entity. However, its importance in clinical practice needs further characterization.