Diagnostic accuracy of salivary and serum-free light chain assays in primary Sjögren's syndrome: a pilot study

Diagnostic value of the saliva immunoglobulin free light chains concentrations measured in primary Sjцgren's syndrome

Proliferation and hyperactivation of B-lymphocytes in the salivary glands is a feature of primary Sjцgren's syndrome (pSS). Detection in saliva of proteins synthesized by B-lymphocytes may be important in the diagnosis of this disease.Objective: to evaluate the diagnostic value of measuring the concentration of immunoglobulin free light chains (FLC) in saliva in patients with pSS.Material and methods. The cross-sectional study included 24 patients with pSS over the age of 18 years. PSS was diagnosed according to the 2016 ACR/EULAR classification criteria. The control group consisted of 11 healthy volunteers. Blood-salivary glands histohematic barrier permeability ratio for albumin, FLC was measured. Quantitative determination of FLC and in blood and saliva was performed by enzyme immunoassay. An immunohistochemical study of biopsies of minor salivary glands (MSG) was carried out with a quantitative assessment of CD3+, CD4+, CD8+, CD20+, CD21+, CD68+, CD138+ cells. The Mann–Whitney U-test was used to compare quantitative traits. Identification of diagnostic thresholds for the concentration of FLC in saliva for the diagnosis of pSS was carried out using the ROC analysis method. An operating characteristic curve was plotted, the area under the curve, indicators of diagnostic specificity, diagnostic sensitivity, and diagnostic accuracy were calculated.Results and discussion. The obtained values corresponded to the low permeability of the histohematic barrier of the salivary glands for albumin and FLC in patients with pSS and healthy individuals. The median concentrations of FLC ê and ë in the saliva of patients with pSS and healthy volunteers were 1.08 [0.58; 1.91], 1.038 [0.55; 2.03] mg/l and 0.36 [0.32; 0.54], 0.35 [0.21; 0.52] mg/l, respectively. The concentration of FLC in the saliva of patients with pSS was statistically significantly higher than in the control group (p<0.01). The amount of FLC ê and ë in saliva correlated with the rate of unstimulated saliva flow: rs=-0.483 (p=0.02), rs=-0.491 (p=0.017), respectively.A relationship was found between the concentration of ê-chains in saliva and the specific number of CD138+ cells: rs=0.733 (p=0.025). Statistically significant correlations between the concentration of ë-chains and the number of mononuclear cells in the MSG have not been established.Based on the results of ROC analysis, diagnostic thresholds for FLC concentrations in the saliva of patients with pSS were determined. Concentrations of ê- and ë-type FLC in saliva of 0.56 and 0.68 mg/l correspond to area under the curve values of 0.84 (95% confidence interval, CI 0.69–0.98) and 0.83 (95% CI 0.71–0.97), sensitivity 79.2% (95% CI 59.5–90.8) and 75% (95% CI 55.1–88), specificity 81.8% (95% CI 52.3–96.8) and 90.9% (95% CI 62.3–99.5), respectively.Salivary FLC concentrations were compared in patients with pSS receiving and not receiving glucocorticoids (GC). The groups did not differ in a statistically significant way in terms of clinical and laboratory parameters. The median daily dose of GC was 10 [5; 10] mg in prednisolone equivalent. There were no significant differences between the concentrations of saliva FLC in patients of these groups.Conclusion. Salivary-fixed FLCs are most likely produced by cells localized in the stroma of the salivary glands. Determination of the concentration of FLC in saliva can be proposed as a diagnostic test for the pSS. The concentration of free ê-chains in saliva can be considered as a surrogate marker of benign B-cell proliferation in the MSG. Therapy with low and medium doses of GC in pSS does not affect the concentration of FLC in saliva.

Saliva Free Light Chains in Patients with Neuro-Sjögren

Background: Sjögren's syndrome (SS) is an autoimmune disease characterized by sicca symptoms and various extra-glandular manifestations. The diagnosis of SS requires sicca symptoms, anti-SSA(Ro)-antibody positivity, and/or pathological focus scores on a minor salivary gland biopsy. Previous studies have investigated different biomarkers in order to avoid invasive diagnostic procedures. It was found that kappa and lambda free light chains (KFLC and LFLC) in saliva are specific for SS. Methods: FLC concentrations in saliva and serum were determined in 130 patients-50 with SS and neurological involvement (Neuro-Sjögren) and 80 neurological controls. The EULAR SS disease activity index and patient reported index (ESSPRI) were determined in patients with SS. Results: Patients with SS revealed increased pain and decreased saliva production according to the ESSPRI and Saxon test, respectively, with increasing FLC concentrations in the saliva. No significant differences in serum and salivary protein concentrations were observed between patients with SS and controls. Conclusion: KFLC and LFLC concentrations in saliva are not suitable to distinguish patients with Neuro-Sjögren and neurological control subjects, thus a diagnostic biopsy is still required. The association of salivary KFLC and LFLC concentrations with saliva production and ESSPRI pain score suggests a complex relationship between dryness and pain in patients with SS.

Mono/polyclonal free light chains as challenging biomarkers for immunological abnormalities

Free light chain (FLC) kappa (k) and lambda (λ) consist of low molecular weight proteins produced in excess during immunoglobulin synthesis and secreted into the circulation. In patients with normal renal function, over 99% of FLCs are filtered and reabsorbed. Thus, the presence of FLCs in the serum is directly related to plasma cell activity and the balance between production and renal clearance. FLCs are bioactive molecules that may exist as monoclonal (m) and polyclonal (p) FLCs. These have been detected in several body fluids and may be key indicators of ongoing damage and/or illness. International guidelines now recommend mFLC for screening, diagnosis and monitoring multiple myeloma and other plasma cell dyscrasias. In current clinical practice, FLCs in urine indicate cast nephropathy and other renal injury, whereas their presence in cerebrospinal fluid is important for identifying central nervous system inflammatory diseases such as multiple sclerosis. Increased pFLCs have also been detected in various conditions characterized by B cell activation, i.e., chronic inflammation, autoimmune disease and HCV infection. Monitoring the coronavirus (COVID-19) pandemic by analysis of salivary FLCs presents a significant opportunity in clinical immunology worthy of scientific pursuit.

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.

Go Ask Your Patients! PSS-QoL Reported Perception of Dryness Correlates With Lacrimal and Salivary Flow in Primary Sjögren's Syndrome

Introduction/Objectives: The patient perspective is an essential outcome parameter in the quest for effective therapy in primary Sjögren's Syndrome (PSS). The EULAR Sjögren's Syndrome Patient Reported Index (ESSPRI) is recommended by EULAR to quantify patient's symptom burden and has been used in several clinical trials. Surprisingly, the patient's perception of dryness quantified with ESSPRI does not correlate with objective measures of salivary or lacrimal flow. Thus, we evaluated a newly developed assessment tool-the Primary Sjögren's Syndrome Quality of Life Questionnaire (PSS-QoL)-for quantifying symptoms of dryness in comparison with the ESSPRI and objective measurements of salivary and lacrimal flow. Methods: Data of patients from the PSS registry of the Medical University of Graz fulfilling the 2016 ACR/EULAR classification criteria for PSS were analyzed. The patient perspective was analyzed by PSS-QoL, ESSPRI, Xerostomia Inventory (XI) and Ocular Surface Disease Index (OSDI). Sicca signs were measured with Schirmer's test, unstimulated salivary flow test (USF) and stimulated salivary flow test (SSF). ESSDAI (EULAR Sjögren's Syndrome Disease Activity Index) and EGA (Evaluator Global Assessment, numeric rating scale from 0 to 10) were obtained. In addition, free light chains (FLC) κ and λ, rheumatoid factor (RF) IgM and IgA were determined. Results: Data from 123 PSS patients were analyzed; 91.9% (n = 113) were female, with a mean disease duration of 6.2 (±5.3) years and mean age of 60.1 (±12.4) years. PSS-QoL-dryness revealed significant negative correlations with Schirmer's test (r = -0.31, p < 0.05) and SSF-test (r = -0.390, p < 0.01). In contrast, we found no significant correlation between ESSPRI-dryness and any objective dryness test. Lower perceived dryness was associated with higher immunological activity determined by increased levels of IgG, FLC and RF-IgA. Whereas patients with only subjective signs of dryness had lower immunological activity. Discussion: Patients' perception of dryness assessed by PSS-QoL correlates with objective measurements of salivary gland function while ESSPRI-dryness did not. Based on the PSS-QoL and objective measures of dryness two distinct groups of PSS patients could be distinguished, which may have implications in daily practice and future clinical studies.

Free light chains and autoimmunity

The study of free light chains (FLCs) has grown as area of enormous interest for many clinicians with the aim of disclosing the exact biological role and potential use of FLCs in the clinical routine. Moreover, the attention given to immunological functions of FLCs has sparked a new light into their pathogenic contribution in different chronic autoimmune-based inflammatory diseases. The release of intracellular antigens following cell death or ineffective clearance of apoptotic debris, modification of self-antigens, and molecular mimicry may trigger the production of immunoglobulins after activation and polyclonal expansion of B cells, by which FLCs are released. The discovery of polyclonal FLCs as potential biomarkers started with the observation of their increased concentrations in a variety of biological fluids related to patients with autoimmune diseases. This review deals with the use of polyclonal FLCs for identifying severity and monitoring outcome after treatment in some autoimmune diseases, namely systemic lupus erythematosus, myasthenia gravis, systemic sclerosis, rheumatoid arthritis and Sjögren's syndrome, as supported by the fact that levels of FLCs correlate with both B cell activation markers and other specific markers of disease activity. In a near future, following the evidence shown, FLCs might probably work as early prognostic markers of severity and also as indicators of response to treatment or early assessment of relapse in selected autoimmune diseases.