Anti-{alpha}-fodrin autoantibodies are not useful diagnostic markers of primary Sjögren's syndrome

Current State of Knowledge on Primary Sjögren's Syndrome, an Autoimmune Exocrinopathy

Primary Sjögren's syndrome (pSS) is a chronic systemic autoimmune rheumatic disease characterized by lymphoplasmacytic infiltration of the salivary and lacrimal glands, whereby sicca syndrome and/or systemic manifestations are the clinical hallmarks, associated with a particular autoantibody profile. pSS is the most frequent connective tissue disease after rheumatoid arthritis, affecting 0.3-3% of the population. Women are more prone to develop pSS than men, with a sex ratio of 9:1. Considered in the past as innocent collateral passive victims of autoimmunity, the epithelial cells of the salivary glands are now known to play an active role in the pathogenesis of the disease. The aetiology of the "autoimmune epithelitis" still remains unknown, but certainly involves genetic, environmental and hormonal factors. Later during the disease evolution, the subsequent chronic activation of B cells can lead to the development of systemic manifestations or non-Hodgkin's lymphoma. The aim of the present comprehensive review is to provide the current state of knowledge on pSS. The review addresses the clinical manifestations and complications of the disease, the diagnostic workup, the pathogenic mechanisms and the therapeutic approaches.

Usefulness of IgA Anti-α-fodrin Antibodies in Combination with Rheumatoid Factor and/or Antinuclear Antibodies as Substitute Immunological Criterion in Sjögren Syndrome with Negative Anti-SSA/SSB Antibodies

OBJECTIVE

We aimed to evaluate the usefulness of anti-α-fodrin antibodies (AFA) in combination with rheumatoid factor (RF) and/or antinuclear antibodies (ANA) as an alternative immunological criterion for Sjögren syndrome (SS) among patients with negative anti-Ro/La serology.

METHODS

The study included 350 patients (100 with rheumatoid arthritis, systemic lupus erythematosus, and systemic sclerosis, and 50 with primary SS) randomly selected and assessed for SS. All patients were tested for ANA, RF, anti-SSA/SSB, and AFA antibodies. SS diagnosis was made on a clinical basis by 2 rheumatologists based on the 6-item screening questionnaire, Schirmer-I test, nonstimulated whole salivary flow rate, fluorescein staining test, autoantibodies, lip biopsy, and medical chart review. Non-SS was defined as lack of clinical diagnosis and not fulfilling the American-European Consensus Group classification criteria and the American College of Rheumatology (ACR) criteria. The ACR criteria were applied substituting the immunological criteria as follows: (1) RF plus ANA > 1:320, (2) RF plus AFA, (3) ANA > 1:320 plus AFA, (4) RF alone, and (5) 2 positive tests out of RF, ANA > 1:320, or AFA. We estimated the sensitivity, specificity, positive predictive value, negative predictive value, and likelihood ratio positivity with 95% CI for each criterion.

RESULTS

There were 236 patients (67%) who tested negative for anti-SSA/SSB antibodies, of whom 65 (27.5%) were clinically diagnosed as SS, and 149 (63%) with non-SS. RF + AFA and ANA + AFA performed similarly to RF + ANA > 1:320. The model 2 out of 3 of RF, ANA, or AFA improved the sensitivity from 56.9% to 70.7%, although the specificity decreased.

CONCLUSION

The combination AFA + RF, AFA + ANA > 1:320, or at least 2 out of 3, performed well as a proxy immunological test for patients with SS and negative Ro/La serology.

Diagnostic accuracy of anti-alpha-fodrin antibodies for primary Sjögren's syndrome

OBJECTIVES

To estimate the diagnostic accuracy of anti-alpha-fodrin antibodies for primary Sjögren's syndrome (pSS).

METHODS

Sixty-four pSS subjects and 108 non-pSS patients were prospectively enrolled in this study. Serum anti-alpha-fodrin IgA and IgG were detected by ELISA in a blind fashion. The diagnostic accuracy of anti-alpha-fodrin antibodies was assessed by receiver operating characteristic (ROC) curve analysis. Logistic regression was used to investigate whether anti-alpha-fodrin antibodies could improve the accuracy of pSS diagnosis if used in addition to anti-SSA and anti-SSB.

RESULTS

The areas under the ROC curves for anti-alpha-fodrin IgG and IgA were 0.69 (95% confidence interval (CI): 0.60-0.77) and 0.63 (95% CI: 0.54-0.72), respectively (P < 0.01 for both). The optimal diagnostic thresholds for anti-fodrin IgG and IgA were 11.75 U/ml and 9.75 U/ml, respectively, with a sensitivity of 0.59 and 0.55, and a specificity of 0.75 and 0.73, respectively. Anti-alpha-fodrin IgG and IgA antibodies were associated with pSS after adjustment for anti-SSA and anti-SSB.

CONCLUSIONS

Anti-alpha-fodrin IgG and IgA antibodies are useful diagnostic markers which may improve the accuracy of pSS diagnosis.

An autoimmune response to odorant binding protein 1a is associated with dry eye in the Aire-deficient mouse

Sjögren's Syndrome (SS) is a human autoimmune disease characterized by immune-mediated destruction of the lacrimal and salivary glands. In this study, we show that the Aire-deficient mouse represents a new tool to investigate autoimmune dacryoadenitis and keratoconjunctivitis sicca, features of SS. Previous work in the Aire-deficient mouse suggested a role for alpha-fodrin, a ubiquitous Ag, in the disease process. Using an unbiased biochemical approach, however, we have identified a novel lacrimal gland autoantigen, odorant binding protein 1a, targeted by the autoimmune response. This novel autoantigen is expressed in the thymus in an Aire-dependent manner. The results from our study suggest that defects in central tolerance may contribute to SS and provide a new and clinically relevant model to investigate the pathogenic mechanisms in lacrimal gland autoimmunity and associated ocular surface sequelae.

Prevalence of alpha-fodrin antibodies in patients with chronic hepatitis C infection and Sjögren syndrome

OBJECTIVE

Hepatitis C virus infection (HCV) is associated with various extrahepatic manifestations. Antibodies against alpha-fodrin are associated with sicca symptoms and may valuable diagnostic markers in patients with primary Sjögren syndrome (SS) lacking Ro antibodies. The frequency and role of alpha-fodrin antibodies in patients with chronic HCV infection are unknown. The aim of this study was to investigate the prevalence of alpha-fodrin antibodies in HCV-infected patients with SS.

MATERIAL AND METHODS

Alpha-fodrin antibodies were detected more often in hepatitis C patients (25%; n=142) than in HBV-infected individuals (8%; n=49) and healthy controls (6%; n=174) (p<0.01). Based on these findings, we investigated the frequency of sicca symptoms in a second cohort and studied other antibodies associated with SS.

RESULTS

HCV-infected individuals showed sicca symptoms in 53% of cases as determined by the Saxon and Schirmer tests, which was more frequent than in healthy controls (1%, p<0.01) but not in patients with autoimmune liver disease (51%). Antibodies specific for Ro (SS-A) were significantly more common in patients with autoimmune liver disease than in HCV-infected patients and healthy controls (16% versus 1% and 0%, p<0.003). SS was found in 18% of patients with HCV, in 15% of patients with autoimmune liver disease and in 1% of healthy controls. However, we found no correlation between sicca symptoms and the presence of antibodies against alpha-fodrin, Ro and La.

CONCLUSIONS

Patients with chronic HCV infection show a high prevalence of sicca symptoms and antibodies against alpha-fodrin. However, neither the frequency nor the severity of symptoms correlated with the presence of alpha-fodrin antibodies.

Heterogeneous Nuclear Ribonucleoprotein H1, a Novel Nuclear Autoantigen

Background: Serum samples from patients with autoimmune connective tissue diseases that show a finely speckled antinuclear antibody (ANA) on indirect immune-fluorescence often have antibodies against unknown nuclear target antigens. To search for such autoantigens we applied a proteomic approach using sera from patients with a high ANA titer (≥640) and finely speckled fluorescence but in whom no antibodies to extractable nuclear antigens (ENA) could be identified.

Methods: Using an immunoproteomics approach we identified heterogeneous nuclear ribonucleoprotein H1 (hnRNP H1) as a novel nuclear target of autoantibody response.

Results: Recombinant rat hnRNP H1 reacted in Western blot analyses with 48% of 93 sera from patients with primary Sjögren syndrome and with 5.2% of 153 sera from patients with other connective tissue diseases (diseased controls). For comparison, the diagnostic sensitivity and specificity of anti–Sjögren syndrome A (SSA) antibodies for primary Sjögren syndrome in the same patient cohort were 88.2% and 76.3%, respectively. Interestingly, 5 of 11 primary Sjögren syndrome patients with no anti-SSA or anti-SSB antibodies had anti–hnRNP H1 antibodies. Anti–hnRNP H1 antibodies were preabsorbed by hnRNP H1, as demonstrated by indirect immunofluorescence. In an evaluation of the presence of anti–hnRNP H1 antibodies in 188 consecutive samples submitted to the clinical laboratory with positive ANA (titer ≥160), anti–hnRNP H1 antibodies were found in 3 of 7 (2 primary and 5 secondary) Sjögren syndrome patients and in 8.3% of the diseased controls.

Conclusions: HnRNP H1 is a newly discovered autoantigen that could become an additional diagnostic marker.

The role of interleukin-10 promoter polymorphisms in primary Sjogren's syndrome

OBJECTIVE

To determine the impact of a broad spectrum of different polymorphisms within the interleukin-10 (IL-10) promoter gene on disease susceptibility to primary Sjogren's syndrome (pSS), clinical manifestations, and autoantibody production.

METHODS

We genotyped 111 unrelated German Caucasian patients with pSS and 145 healthy controls for the single nucleotide polymorphisms (SNPs) at positions -2849, -2776, -2769, -2763, -1349, -1082, -851, -819, -657, and -592 and for the microsatellites IL10.R and IL10.G. Allele and haplotype distributions were compared between patients and controls and between subgroups of patients with different clinical and laboratory findings.

RESULTS

We found no significant differences in the allele or haplotype frequencies between pSS patients and healthy controls. After Bonferroni correction we found a significant association of the ACC haplotype (at the -1082, -819, and -592 loci) with immunoglobulin (Ig)A antibodies to anti-alpha-fodrin.

CONCLUSION

Overall we found no associations of IL-10 promoter polymorphisms with the susceptibility to pSS in our cohort. The finding that the production of IgA anti-alpha-fodrin antibodies is associated with polymorphisms within the IL-10 promoter region suggests a genetic contribution to the generation of these antibodies.