Serum Levels of Beta2-Microglobulin and Free Light Chains of Immunoglobulins Are Associated with Systemic Disease Activity in Primary Sjögren’s Syndrome. Data at Enrollment in the Prospective ASSESS Cohort

OBJECTIVES To analyze the clinical and immunological characteristics at enrollment in a large prospective cohort of patients with primary Sjögren's syndrome (pSS) and to investigate the association between serum BAFF, beta2-microglobulin and free light chains of immunoglobulins and systemic disease activity at enrollment. METHODS Three hundred and ninety five patients with pSS according to American-European Consensus Criteria were included from fifteen centers of Rheumatology and Internal Medicine in the "Assessment of Systemic Signs and Evolution of Sjögren's Syndrome" (ASSESS) 5-year prospective cohort. At enrollment, serum markers were assessed as well as activity of the disease measured with the EULAR Sjögren's Syndrome Disease Activity Index (ESSDAI). RESULTS Patient median age was 58 (25(th)-75(th): 51-67) and median disease duration was 5 (2-9) years. Median ESSDAI at enrollment was 2 (0-7) with 30.9% of patients having features of systemic involvement. Patients with elevated BAFF, beta2-microglobulin and kappa, lambda FLCS had higher ESSDAI scores at enrollment (4 [2]-[11] vs 2 [0-7], P = 0.03; 4 [1]-[11] vs 2 [0-7], P< 0.0001); 4 [2]-[10] vs 2 [0-6.6], P< 0.0001 and 4 [2-8.2] vs 2 [0-7.0], P = 0.02, respectively). In multivariate analysis, increased beta2-microglobulin, kappa and lambda FLCs were associated with a higher ESSDAI score. Median BAFF and beta2-microglobulin were higher in the 16 patients with history of lymphoma (1173.3(873.1-3665.5) vs 898.9 (715.9-1187.2) pg/ml, P = 0.01 and 2.6 (2.2-2.9) vs 2.1 (1.8-2.6) mg/l, P = 0.04, respectively). CONCLUSION In pSS, higher levels of beta2-microglobulin and free light chains of immunoglobulins are associated with increased systemic disease activity.