Increased serum β2-microglobulin is associated with clinical and immunological markers of disease activity in systemic lupus erythematosus patients.

The objective of this study was to explore the relationship between serum levels of β2-microglobulin (β2MG), which some studies suggest reflect disease activity in systemic lupus erythematosus (SLE), and various clinical and immunological markers of disease activity in SLE. Twenty-six SLE patients and 10 healthy controls were included. Disease activity was assessed by: SLEDAI, 24 hr-proteinuria, circulating levels of complement C3, anti-double-stranded DNA (anti-dsDNA), β2MG and various pro-inflammatory and anti-inflammatory cytokines (IL-6, IL-8, IL-10, IL-18) measured with a multiplex assay, IFN-α assessed with a reporter gene assay, and a combined expression score of 12 IFN-α inducible genes in peripheral blood mononuclear cells. Median serum levels of β2MG were significantly higher in SLE patients vs controls (2.8 mg/L, range: 1.1-21.6 and 1.2 mg/L, range: 0.9-1.7, respectively, p < 0.001). β2MG was correlated with SLEDAI score (R = 0.68, p < 0.001), 24 hr-proteinuria (R = 0.64, p < 0.001), and complement C3 (R = -0.52, p = 0.007). The cytokines were significantly correlated with β2MG: IL-6 (R = 0.45, p = 0.02), IL-8 (R = 0.75, p < 0.001), IL-10 (R = 0.67, p < 0.001) and IL-18 (R = 0.71, p < 0.001) as were serum IFN-α (R = 0.45, p = 0.02) and the IFN-α inducible gene-score (R = 0.51, p = 0.01). The results support that β2MG may serve as a marker of disease activity in SLE. The correlations with the measured cytokines indicate that increased β2MG in SLE reflects immunological activity.