Antibodies to alpha-fodrin derived peptide in Sjögren's syndrome

Characteristics of primary Sjögren's syndrome-associated peripheral nervous system lesions

OBJECTIVE

The aim of this study is to investigate potential risk factors associated with peripheral nervous system lesions in primary Sjögren's syndrome (pSS) through a retrospective analysis of clinical manifestations, examination characteristics, and clinical electrophysiological features.

MATERIALS AND METHODS

A retrospective case-control study was conducted at Nanfang Hospital, including 108 patients diagnosed with pSS following the criteria revised by the American College of Rheumatology in 2016. The study spanned from January 2015 to October 2020. The patient cohort was divided into two groups, an experimental group (N = 27) consisting of patients with primary Sjögren's syndrome-peripheral nervous system lesions (pSS-PNS), and a control group (N = 81) comprising patients without peripheral neurological impairment, i.e., primary Sjögren's syndrome-non peripheral nervous system lesions (pSS-nPNS).

RESULTS

The results showed a significant correlation between immunoglobulin G (IgG), α-Fodrin immunoglobulin G (α-FIgG), platelet counts (PLT), dry mouth and peripheral neuropathy of Sjogren's syndrome (p < 0.01). The research also revealed that α-FIgG (OR 2.03; 95% CI 1.14-3.64), IgG (OR 1.23; 95% CI 1.06-1.42), and PLT (OR 1.01; 95% CI 1.00-1.01) were identified as risk factors for the onset of peripheral neuropathy of Sjogren's syndrome, while dry mouth had a negative correlation (OR 0.08; 95% CI 0.02-0.40). Remarkably, the total risk assessment of the independent variables demonstrated a high AUC (95%CI) of 0.923 (0.861-0.986; p < 0.001), indicating an excellent prediction of pSS-PNS occurrence through the ROC analysis. Additionally, high platelet counts and strong positive anti-SSB antibody titer were found to be risk factors for dual motor and sensory nerve damages among pSS-PNS patients.

CONCLUSION

IgG, α-FIgG, and PLT were identified as independent risk factors for patients with pSS-PNS. The likelihood of peripheral neuropathy appeared to increase in tandem with the elevated levels of above three factors. Interestingly, we found that dry mouth might play a protective role in this context. Our study further noted that both high platelet counts and strong positive anti-SSB antibody titer may be associated with increased risk of both motor and sensory nerve involvement in pSS-PNS patients. These findings have significant implications for both the etiologies and therapeutics of pSS-PNS.

Autoimmune diseases in China

Autoimmune diseases, such as rheumatoid arthritis, systematic lupus erythematosus and Sjögren's syndrome, are a group of diseases characterized by the activation of immune cells and excessive production of autoantibodies. Although the pathogenesis of these diseases is still not completely understood, studies have shown that multiple factors including genetics, environment and immune responses play important roles in the development and progression of the diseases. In China, there are great achievements in the mechanisms of autoimmune diseases during the last decades. These studies provide new insight to understand the diseases and also shed light on the development of novel therapy.

Tissue-Specific Autoantibodies Improve Diagnosis of Primary Sjögren's Syndrome in the Early Stage and Indicate Localized Salivary Injury

Primary Sjögren's syndrome (pSS) is a chronic autoimmune disease characterized by lymphocytic infiltration of exocrine glands. Due to the absence of specific clinical manifestations and biomarkers in the early stage, pSS is generally underrecognized. To elucidate the role of the tissue-specific autoantibodies (TSAs), i.e., anti-CA6, anti-SP1, and anti-PSP antibodies, we enrolled 137 pSS patients, 32 secondary Sjögren's syndrome (sSS) patients, and 127 healthy controls (HCs), whose serum and saliva samples were collected. TSA levels were detected by ELISA, and the clinical and laboratory data was reviewed from the medical records. The analysis results showed the following: (1) Compared to HCs, the serum IgA levels of anti-CA6, anti-SP1 and anti-PSP were significantly higher in pSS as well as in sSS patients, and anti-CA6 IgG was also notably higher in pSS patients. (2) The positivity of anti-CA6, anti-PSP and all the three antibodies together were significantly increased in anti-SSA-negative pSS patients. (3) The average IgM levels of anti-CA6 and anti-SP1 decreased as the disease duration extended. (4) The anti-CA6-positive patients have significantly higher levels of serum IgA, while the anti-PSP-positive group has a notably higher serum IgM level. (5) Another autoantibody specific to the salivary glands, anti-α-fodrin antibody, was elevated in TSA-positive patients, especially in the anti-CA6-positive group. (6) Preliminary detection of saliva TSAs showed that all the IgG levels of these three antibodies increased significantly in pSS patients. In conclusion, TSAs improve diagnosis of pSS in the early stage, especially in anti-SSA-negative patients, and their tissue-specific nature indicates localized salivary injury, which deserves further studies to clarify the mechanism.

Characteristics of germinal center-like structures in patients with Sjögren's syndrome

AIM

To analyze the relationship between ectopic germinal centers (GCs) in the salivary glands and the clinical/laboratory characteristics of patients with Sjögren's syndrome (SS).

METHODS

Retrospectively, 126 patients with primary SS (pSS) and 16 patients with secondary SS (sSS) were analyzed. Minor salivary gland biopsies were evaluated for the presence of GC-like morphology by hematoxylin and eosin (H&E) and immunohistochemical (IHC) staining for CD21. Clinical and serological data were obtained from medical records.

RESULTS

GC-like structures were observed in 36/126 (28.6%) pSS patients and 4/16 (25.0%) sSS patients. The mean inflammatory focus score of the gland was significantly higher in GC-positive samples than in GC-negative ones in both pSS and sSS patients (P = 0.007 and 0.024, respectively). In pSS, significantly elevated titers of rheumatoid factor (RF)-IgM (P = 0.023) and antinuclear antibodies (ANA) (P = 0.036), increased levels of IgA (P = 0.012) and IgG (P = 0.017) were encountered in GC-positive patients. The GC-positive group also presented higher prevalence of anti-SSA antibodies, lower levels of white blood cells, higher levels of erythrocyte sedimentation rate and γ-globulin, although not statistically significant. In sSS patients with ectopic GC formation, ANA titers were remarkably elevated. The anticyclic citrullinated peptide (anti-CCP)-IgG titers and the prevalence of antikeratin antibody (AKA)-IgG, antiperinuclear factor (APF)-IgG were also increased, yet not significantly. GCs were found to be associated with antibody and immunoglobulin production.

CONCLUSION

This study indicates that SS patients with ectopic GCs have distinct features. Ectopic GC structures were particularly noted in patients with higher focus scores, and might play an essential role in sustaining antibody production as well as B cell activation.

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.

Mucosal administration of alpha-fodrin inhibits experimental Sjögren's syndrome autoimmunity

Introduction

α-Fodrin is an autoantigen in Sjögren's syndrome. We hypothesized that mucosal administration of α-fodrin might prevent the disease.

Methods

Four-week-old NOD mice were immunized (intranasal) with a 1 μg or 10 μg dose of α-fodrin every other day. PBS 10 μl/dose and Glutathione transferase (GST 10 μg/dose (control mice) were intranasally administrated by the same procedure. The salivary flow was maintained in immunized animals. The animals were analyzed for the presence of anti-Sjögren's syndrome A, anti-Sjögren's syndrome B, rheumatoid factor and antinuclear, anti-α-fodrin, and anti-type 3 muscarinic acetylcholine receptor polypeptide (anti-M3RP) by immunofluorescence or ELISA. The cytokines IFNγ and IL-10 were measured by ELISA. Salivary glands were examined by H&E staining and immunohistochemical analysis. The water-volume intake was calculated for each group. The induction of regulatory T cells was assessed by fluorescence-activated cell sorting analysis for the frequency of Foxp3⁺ cells among peripheral CD4⁺CD25⁺ T cells.

Results

The appearance of anti-α-fodrin and anti-M3RP antibodies was delayed in mice immunized with α-fodrin. The titers of anti-α-fodrin and anti-M3RP antibodies were lower in immunized mice (P < 0.05), but there was no significant difference between the low-dose or high-dose immunization groups. Five out of eight mice in the GST group, five of eight mice in the PBS group, two of eight mice in the α-fodrin 1 μg/dose group, and three out of eight mice in the α-fodrin 10 μg/dose were positive for antinuclear antibodies. The levels of serum IFNγ in mice immunized with 1 μg/dose or 10 μg/dose α-fodrin, with PBS, and with GST were 41.9 ± 16.2 pg/ml, 37.1 ± 15.4 pg/ml, 86.8 ± 17.8 pg/ml and 71.6 ± 11.1 pg/ml, respectively, while we found no difference in the levels of serum IL-10 among the groups. The number of Foxp3⁺ CD4⁺CD25⁺ regulatory T cells was higher in the α-fodrin groups compared with the PBS and GST control groups (P < 0.05). Lymphocytic infiltration and expression of α-fodrin in the salivary glands was decreased in α-fodrin-treated groups. The fluid intake of mice in the 1 μg/dose α-fodrin, 10 μg/dose α-fodrin, PBS, and GST groups was 39.2 ± 2.1 ml, 40.4 ± 2.5 ml, 49.3 ± 3.1 ml and 51.6 ± 2.8 ml, respectively.

Conclusion

Mucosal administration of α-fodrin effectively inhibited the progression of experimental Sjögren's syndrome autoimmunity.

The epitope study of alpha-fodrin autoantibody in primary Sjögren's syndrome

Alpha-fodrin, an intracellular organ-specific cytoskeleton protein, was identified recently as an autoantigen associated with Sicca- and Sjögren's syndrome (SS). Identification of the antigenic determinants of alpha-fodrin is a prerequisite to developing highly sensitive and specific anti-alpha-fodrin antibodies, which provides potential means for the diagnosis of primary Sjögren's syndrome (pSS) in patients. Based on the structure and predicted antigenic sites of alpha-fodrin protein with 560 amino acids (alpha-fodrin 560), we prepared a set of overlapping recombinant protein fragments covering antigenic epitopes and synthesized a set of peptides derived from the alpha-fodrin protein. These recombinant proteins and synthesized peptides were subjected to screening with pSS patients sera, respectively. The peptide with the strongest immunoreactivity was used as antigenic peptide to define further the role of anti-alpha-fodrin-peptide antibodies in the sera of 135 patients with pSS, 48 patients with systemic lupus erythematosus (SLE), 88 patients with rheumatoid arthritis (RA) and 83 normal controls. Our data showed that the N-terminal peptide of amino acids 46-59 (N46) of alpha-fodrin 560 was the epitope with strongest antigenicity. The prevalences of anti-N46 peptide antibodies (alpha-N46PA) in patients with pSS, SLE, RA and normal controls were 78.5%, 10.4%, 21.6% and 6.0%, respectively. The sensitivity and specificity of the autoantibodies in pSS were 78.5% and 86.8%, respectively. These results suggest the alpha-N46PA which shows highest sensitivity and specificity is of significance to develop an effective diagnostic approach for pSS.