Lacrimal and salivary immunoglobulins in Sjögren's syndrome

Biomarkers of B cell activation in autoimmune connective tissue diseases: More than markers of disease activity

B cells play a central role in the pathogenesis of many autoimmune diseases, acting as antigen-presenting cells, producing inflammatory cytokines, and acting as a source of autoantibodies after differentiating into plasma cells. In this review, we aim to summarize and synthesize the literature for the utility of biomarkers of B cell activation (plasma immunoglobulins (Ig), free light chains (FLCs), and beta-2 microglobulin (β2M)) in monitoring inflammatory rheumatic connective tissue diseases, such as Sjogren's syndrome (SS), systemic lupus erythematosus (SLE), dermatomyositis (DM), and systemic sclerosis (SSc). Clinically, it is quite difficult to gauge prognosis in these conditions as there, historically, have not been many quantitative markers of disease activity available. From our extensive literature review, Ig, FLC, and β2M may function as invaluable prognostic markers of ongoing disease activity, and potentially as biomarkers for response to therapy or disease relapse. They are inexpensive and unsophisticated tests that are vastly underused in the setting of autoimmune disease. However, clinicians still need to be aware of the potential of false positives in times of infection or plasma cell dyscrasia, as these disease states can artificially increase these biomarkers. Ultimately, the utility of serum Ig, FLCs, and β2M is clearly delineated in SS and SLE, and least investigated in DM, and additional prospective studies utilizing these biomarkers, and specific B cell targeted therapies are still needed.

Salivary free light chains and salivary immunoglobulins as potential non-invasive biomarkers in primary Sjögren's syndrome

BACKGROUND

B cells contribute significantly to the pathogenesis of primary Sjögren's syndrome (pSS). Free light chains (FLCs) are generated during the production of immunoglobulins (Igs) and are surrogates of B cell activity. We hypothesized that salivary FLCs and salivary Igs could represent salivary gland inflammation and therefore, serve as biomarkers in pSS.

METHODS

Patients >18 years old fulfilling the American College of Rheumatology / European League Against Rheumatism (EULAR) 2016 criteria for pSS and age-matched healthy and disease controls (sicca non-pSS, rheumatoid arthritis, systemic lupus erythematosus) were recruited for this cross-sectional study. FLCs in saliva and serum were measured by immunoturbidimetry. Serum and salivary Igs were measured by nephelometry and enzyme-linked immunosorbent assay, respectively. Area under the receiver operator characteristic curve was determined. The factors influencing the serum and salivary FLCs in pSS were determined using backward linear regression.

RESULTS

A total of 78 patients with pSS, 76 healthy controls and 62 disease controls were recruited. Median EULAR SS disease activity index (interquartile range) was 1 (3.75). Serum FLCκ and FLCλ, salivary FLCλ, serum and salivary IgG, salivary IgM was significantly higher in the pSS group compared to the controls. Areas under the curve for salivary FLCλ, serum FLCκ, serum and salivary IgG were 0.75, 0.72, 0.78 and 0.77, respectively. Regression analysis showed that salivary FLCκ, salivary FLCλ and salivary IgG were associated with positive salivary gland histopathology. Use of immunosuppressants and glucocorticoids was associated with lower values of salivary parameters.

CONCLUSION

Salivary FLCλ and salivary IgG were significantly different between pSS and control groups and could be potential non-invasive biomarkers in pSS. These findings should be confirmed in larger longitudinal studies.

Biochemical changes contributing to functional quiescence in lacrimal gland acinar cells after chronic ex vivo exposure to a muscarinic agonist

Profound secretory dysfunction can be associated with relatively modest lymphocytic infiltration of the lacrimal and salivary glands of Sjögren's syndrome (SjS) patients. SjS patients' sera contain autoantibodies to M3 muscarinic acetylcholine receptors (MAChR) that have variously been reported to have agonistic and antagonistic effects. We sought to identify consequences of chronic agonist stimulation by maintaining acinar cells from rabbit lacrimal glands for 20 h in the presence or absence of 10 microM carbachol (CCh). Exposure to CCh diminished the cells' ability to elevate cytosolic Ca2+ and secrete beta-hexosaminidase in response to acute stimulation with 100 microM CCh, but it enhanced their secretory responses to phenylephrine and ionomycin. Secretory vesicles appeared normal by electron microscopy, but confocal fluorescence microscopy revealed depletion of the secretory vesicle membrane marker, rab3D, and decreased ability to recruit secretory transport vesicles in response to acute 100 microM CCh. Additionally, the apical cortical actin cytoskeleton was disrupted and diminished compared to the basal-lateral cortical network. Subcellular fractionation analyses revealed that total membrane phase protein content was increased. The contents of beta-hexosaminidase and MAChR relative to total protein were not significantly altered, and MAChR abundance in the plasma membrane fraction was increased as the result of redistribution from endomembrane pools. However, relative cellular contents of the heterotrimeric guanosine triphosphate (GTP)-binding proteins, Gq and G11, were decreased. Additional biochemical changes included decreased contents of 47 kDa Gs and Gi3, protein kinase Calpha and rab3D and polymeric immunoglobulin (Ig) receptors; internalization of Na,K-ATPase from the plasma membranes to endomembrane compartments and decreased content of beta-hexosaminidase in the lysosomes. The observations demonstrate that chronic exposure to a MAChR agonist induces refractoriness to optimal stimulation, without causing receptor downregulation, by downregulating postreceptor-signalling mediators and effectors. The cells' secretory mechanisms for IgA and electrolytes also appear to be impaired, as does their ability to properly sort proteins to the lysosomes.

Risk factors for positive minor salivary gland biopsy findings in Sjögren's syndrome and dry mouth patients

OBJECTIVE

To investigate risk factors for positive minor salivary gland biopsy results in Sjögren's syndrome (SS) and dry mouth patients.

METHODS

A total of 289 patients with dry mouth symptoms were evaluated. Potential risk factors for positive minor salivary gland biopsy results (>1 focus of lymphocytes) were studied in 2 phases. In phase 1, predictor variable candidates were identified for the test study (phase 2). Odds ratios were calculated for predictor variables.

RESULTS

IgG, IgA, keratoconjunctivitis sicca, and sex, identified as the best predictor variables from phase 1 data, were included in a logistic regression model using phase 2 data. Only IgG demonstrated association with biopsy results (chi(2) = 20.4, P = 0.0001). An elevated IgG level (>1,482 mg/dl) had a high specificity (97% and 97%), high positive predictive value (PPV) (97% and 97%), but poor sensitivity (40% and 45%) in predicting positive biopsy results and SS, respectively.

CONCLUSION

Elevated serum IgG levels best predicted a positive biopsy result and SS with high PPV and specificities.

Primary Sjögren's syndrome--clinical and laboratory markers of disease activity

Primary Sjögren's syndrome is a chronic autoimmune disorder of the lacrimal and salivary glands, reflecting general involvement of the exocrine tissues and leading to functional impairment. This polyglandular disease is often associated with systemic extraglandular manifestations, and laboratory tests usually indicate polyclonal B-lymphocyte hyperactivity. Clinical and laboratory markers monitoring the disease processes are needed for improved management of primary Sjögren's syndrome. However, incomplete knowledge of the long-term course of inflammation as well as of clinical manifestations makes precise and simple directions for monitoring disease activity in primary Sjögren's syndrome difficult. This review describes potential primary (eg, salivary gland histopathology, autoantibodies, soluble interleukin-2 receptors, and beta 2-microglobulin) and secondary disease activity markers (clinical and laboratory signs of glandular and extraglandular organ damage) and their known associations. The importance of genetic characteristics, patient age, and symptom duration for the disease activity markers is indicated. The systematic use of primary and secondary disease activity markers will improve our understanding of primary Sjögren's syndrome and help create better guidelines for monitoring the disease.