Plasma Concentration of Osteopontin (OPN) in Children with Systemic Lupus Erythematosus: Relationship with Disease Activity

Background: Osteopontin (OPN) is an important bone matrix mediator found to have key roles in inflammation and immunity. OPN is a cytokine which can play a number of roles in promoting activation of T lymphocyte, regulating balance between T-helper 1 and T-helper 2, participating in cell-induced immunologic response and stimulating B lymphocyte to express multi-clone antibodies. Overexpression of OPN has been associated with the development of the autoimmune/ lymphoproliferative syndrome. Objective: The aim of our present study was to analyze the possible correlation between the plasma concentration of OPN and disease activity in children with systemic lupus erythematosus (SLE). We also investigated the correlation between plasma IL-18 and OPN concentrations to further confirm the association of OPN with disease activity. Methods: We measured the plasma concentration of OPN, and the plasma proinflammatory IL-18 concentration in 40 SLE patients with or without renal disease (RSLE group and SLE group, respectively) and in 30 sex- and age-matched controls using enzyme immunoassay. Results: Plasma OPN concentrations were significantly higher in RSLE and SLE patients than in the controls (p = 0.000 and p = 0.002). Plasma OPN concentrations were significantly higher in RSLE patients than in the SLE patients (p = 0.000). Plasma OPN concentration correlated positively and significantly with SLE disease activity index in combined SLE patient groups (r = 0.34; p = 0.04). In RSLE patients, plasma OPN concentration showed a significant positive correlation with proinflammatory cytokine IL-18 concentration (r = 0.48; p = 0.004). 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.