Elevation of plasma osteopontin concentration is correlated with disease activity in patients with systemic lupus erythematosus

Background. Osteopontin (OPN) is an extracellular matrix cell adhesion phosphoprotein with immunological activities including stimulation of macrophage chemotaxis, T-helper type 1 lymphocyte response and B-cell antibody synthesis. Overexpression of OPN has been associated with the development of the autoimmune/lymphoproliferative syndrome. Methods. We measured the plasma concentration and ex vivo production of OPN, and the plasma proinflammatory IL-18 concentration in 54 SLE patients with or without renal impairment (RSLE group and SLE group, respectively) and 26 sex- and age-matched control (NC) subjects using an enzyme-linked immunoabsorbent assay. Results. Plasma OPN concentrations were significantly higher in RSLE and SLE patients than in the NC group (both P < 0.001). Increase in OPN concentration correlated positively and significantly with SLEDAI score in all SLE patients (r = 0.308, P = 0.023). The ex vivo production of OPN upon mitogen activation of peripheral blood mononuclear cells was significantly higher in the RSLE and SLE groups than in the NC group (both P < 0.001). In RSLE patients, plasma OPN concentration showed a significant positive correlation with proinflammatory cytokine IL-18 concentration (r = 0.404, P = 0.037). Conclusion. The above results suggest that the production of OPN is associated with the inflammatory process and SLE development, and may serve as a potential disease marker of SLE.