Plasma levels of interleukin‐8 and response to paroxetine in patients with major depressive disorder

Immune dysregulation plays a key role in major depressive disorder (MDD). However, little is known about the complicated involvement of various interleukins in MDD. This study was performed to investigate the correlation between plasma interleukin-8 (IL-8) levels and treatment outcome of paroxetine (a selective serotonin reuptake inhibitor) in patients with MDD.A total of 115 hospitalized patients (36 males and 79 females), aged from 18 to 72 years, were enrolled. Plasma levels of IL-8 were measured before treatment initiation (baseline) and at 8 weeks after oral paroxetine treatment. Efficacy of paroxetine was evaluated by use of the Hamilton Depression Rating Scale (HAMD-17). Baseline IL-8 levels were compared between responders and non-responders to paroxetine treatment.Plasma IL-8 levels decreased significantly after an 8-week antidepressant treatment in responders, in association with a dramatic decrease in HAMD-17 scores. In non-responders, plasma IL-8 levels did not change significantly at 8 weeks after antidepressant treatment. Baseline plasma IL-8 levels were found to be significantly lower in responders than in non-responders, showing a correlation between IL-8 and antidepressant response to paroxetine.These results indicate that plasma IL-8 levels were related to treatment outcome of paroxetine, and therefore suggest that IL-8 could be a promising predicator of treatment response in individual patients with MDD.