Abstract
Abstract Background and Aims Anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitis is a systemic disease characterized by an immune-mediated process where inflammation plays a central role. The widely available serum biomarkers of inflammation are not always able to detect ongoing disease activity in ANCA-associated vasculitis (AAV) patients. Free light chains (FLCs) expression levels have been proposed as new promising biomarker in some immune-mediated and inflammatory diseases. The aim of this study is to evaluate the expression levels of FLCs in patients affected by AAV and investigate the potential effect of rituximab treatment on FLCs levels. Method We conducted a retrospective multicenter study enrolling AAV patients in complete remission of AAV (defined as BVAS/GPA = 0); those with clinical suspicion of underlying hematologic malignancy were excluded. We analyzed κ and λ FLCs serum concentrations and evaluated their correlation with biomarkers of immune system activation, such as erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), serum immunoglobulin (Ig) levels, serum C3 and C4 complement and albumin levels (which has a negative correlation with acute inflammatory phase). We assessed impact of rituximab (RTX) therapy within the last 6 months on the same laboratory parameters. Results A total of 137 patients with AAV were recruited, who were gender balanced, had an average age of 68 years and an estimated glomerular filtration rate of 68 (43-89) mL/min/1.73 m2. Fifty-one patients received rituximab treatment (RTX group), while 86 patients were on other immunosuppressive maintenance therapies (non-RTX group). In comparison to non-RTX group, patients treated with RTX experienced higher complement C3 levels, lower ESR levels and lower FLCs κ (p = 0.063) and λ (p = 0.013) levels. The differences between RTX and non-RTX groups in terms of FLCs were even more prominent after correction to total Ig concentration (p = 0.004 for κ /Ig and p = 0.003 for λ /Ig, respectively). Both, serum free κ and λ levels were found to correlate significantly with ESR (R = 0.55 and p < 0.001 for κ; R = 0.53 and p < 0.001 for λ) and albumin (R = ‒0.38 and p < 0.001 for κ; R = ‒0.33 and p < 0.001 for λ). Additionally, serum free κ levels showed an inverse association with C3 (R = ‒0.18 and p = 0.041). Conclusion In subjects with AAV, FLC levels were found to be associated with markers of inflammation and complement activation; hence FLCs levels may represent a promising biomarker for detection of subclinical inflammation in AAV patients on maintenance therapy. Rituximab therapy showed a potential to reduce the levels of markers of subclinical inflammation, including FLCs.
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