Plasma levels of interleukin-6 and selective serotonin reuptake inhibitor response in patients with major depressive disorder

Objective We investigated the plasma levels of interleukin (IL)-6 and 5-HTT polymorphisms in patients with major depressive disorder (MDD). This is the first report, to our knowledge, of an investigation into the association between 5-HTT gene polymorphism, plasma IL-6 levels, and responses to selective serotonin reuptake inhibitors (SSRIs) in Japanese patients with MDD. Method One-hundred and eighteen patients (51 male, 67 female) who met the DSM-IV criteria for MDD were enrolled. Their ages ranged from 24 to 78 (mean ± SD = 44 ± 12) years. The patients were treated with SSRIs (paroxetine in 66 cases, sertraline in 42 cases) for 8 weeks. Results The plasma levels of IL-6 were significantly higher in the SSRI responders than in the nonresponders (p = 0.0328), and the changes in plasma IL-6 levels correlated significantly with the changes in severity of depressive state (p = .0.007). No difference was found in baseline and the changes in plasma IL-6 levels between the patients with a 5-HTT gene (5-HTTLPR) L-carrier and those with S/S. Conclusion These results suggest that the plasma levels of IL-6 reflect the severity of MDD and that plasma IL-6 levels might be another biological-state marker for the depressive state. In addition, the 5-HTTLPR polymorphism might be independent of plasma IL-6 levels. Copyright © 2013 John Wiley & Sons, Ltd.