Interleukin-1 family and serotonin transporter in first-episode, drug-naive major depressive disorder: A pilot study

Abnormalities of neuroinflammatory process and serotonergic system have been reported in major depressive disorder (MDD). However, most previous studies were performed in recurrent MDD and only a few studies explored the interaction of the two systems. This study examined both systems concurrently and their clinical relevance in first-episode drug-naive MDD. Thirty-four MDD patients and 34 age and gender matched healthy controls (HC) were recruited. Plasma concentrations of the cytokines of interleukin-1 (IL-1) family, including IL-1 alpha, IL-1 beta, IL-1 receptor antagonist (IL-1Ra) and IL-1 receptor type 2 (IL-1R2) were measured using enzyme-linked immune-sorbent assays. The serotonin transporter (SERT) availability in midbrain, thalamus, caudate, and putamen was examined by single-photon emission computed tomography with I-123-ADAM. There were significantly lower concentrations of pro-inflammatory IL-1 beta and its inhibitor, IL-1R2 in MDD than HC. The SERT availability was at the same level between groups. A negative association between IL-1Ra concentration and the SERT availability in midbrain was observed in MDD but not in HC. Both IL-1 beta concentration and the SERT availability in caudate negatively correlated with depression severity and the effect of IL-1 beta was not moderated or mediated by the SERT. In conclusion, this study demonstrated the involvement of IL-1 family in the early stage of MDD, especially for IL-1 beta. SERT was not the main central target of altered IL-1 beta and these two systems might contribute to MDD by different mechanisms. The pathophysiology might be varied between early and recurrent MDD and tuning treatment strategies at different clinical stages might be needed.