Clinical relapse in systemic lupus erythematosus: Correlation with antecedent elevation of urinary free light-chain immunoglobulin

Abstract

This paper reports preliminary evidence suggesting that measurements of free light-chain Ig (FLIg) in urine may represent quantitative markers ofin vivo polyclonal B-cell activation. Thus, longitudinal levels of urinary FLIg in patients with systemic lupus erythematosus (SLE) may be used to track or monitor thein vivo immunopathologic B-cell activity of SLE and be helpful in predicting a disease relapse. Our findings showed that dramatic rises in urinary FLIg occurred during asymptomatic intervals that preceded by 4–8 weeks the first symptomatic signs of acute SLE relapse. These results suggest that a sizable lead time may exist between the occurrence of immunopathologic B-cell stimulation and the resultant symptoms and tissue damage of immune complex-induced acute inflammation. In these studies the measurement of urinary FLIg was accomplished by an indirect method using ng-sensitive radioimmunoassays (RIAs) that measured isotypic IgG, IgA, IgM, total κ-Ig, and total λ-Ig. As a control for the assessment of renal tubular function and the excretion of low molecular weight proteins in SLE patients, longitudinal measurements of beta-2-microglobulin (B2M) and lysozyme were made using a novel solid-phase³H-biotin RIA technique.