Elevated plasma midkine and pleiotrophin levels in patients with systemic lupus erythematosus

Emerging evidence suggests that two heparin-binding growth factor, midkine and pleiotrophin are implicated in the pathogenesis of autoimmune diseases including SLE. To investigate the plasma midkine and pleiotrophin levels in SLE patients, as well as their correlation with major clinical parameters and interleukin-17 (IL-17) level in SLE, 83 SLE patients and 123 controls including 20 rheumatoid arthritis (RA) patients, 21 Sjögren's syndrome (SS) patients and 82 healthy controls (HCs) were recruited. Plasma midkine, pleiotrophin and IL-17 levels were detected by ELISA. Midkine and pleiotrophin levels were significantly higher in SLE, RA and SS patients compared with HCs (all P < 0.05). There were significantly lower midkine and pleiotrophin levels in SLE compared to SS (P < 0.05 and P < 0.01, respectively). No significant differences in midkine and pleiotrophin levels were found between SLE and RA (P = 0.240 and P = 0.074, respectively). Both plasma midkine and pleiotrophin levels were associated with rash and anti-SSA in SLE. In addition, both midkine and pleiotrophin levels were positively associated with IL-17 level in SLE (both P < 0.001). Area under curve (AUC) of the receiver operating characteristic (ROC) curve for midkine and pleiotrophin were 0.606 (0.527-0.681) and 0.605 (0.526-0.680) respectively. In conclusion, elevated plasma midkine and pleiotrophin levels and their associations with rash, anti-SSA and IL-17 in SLE patients suggest their involvement in this disease.