Abstract
BACKGROUND: The association between inflammation and major depressive disorder (MDD) remains poorly understood, given the heterogeneity of patients with MDD. AIMS: We investigated inflammatory markers, such as interleukin (IL)-6, high-sensitivity C reactive protein (hsCRP) and tumour necrosis factor-α (TNF-α) in melancholic, atypical and anxious depression and explored whether baseline inflammatory protein levels could indicate prognosis. METHODS: The sample consisted of participants (aged 18-55 years) from a previously reported multicentre randomised controlled trial with a parallel-group design registered with ClinicalTrials.gov, including melancholic (n=44), atypical (n=37) and anxious (n=44) patients with depression and healthy controls (HCs) (n=33). Subtypes of MDD were classified according to the 30-item Inventory of Depressive Symptomatology, Self-Rated Version and the 17-item Hamilton Depression Rating Scale. Blood levels of TNF-α, IL-6 and hsCRP were assessed using antibody array analysis. RESULTS: Patients with MDD, classified according to melancholic, atypical and anxious depression subtypes, and HCs did not differ significantly in baseline TNF-α, IL-6 and hsCRP levels after adjustment. In patients with anxious depression, hsCRP levels increased significantly if they experienced no pain (adjusted (adj.) p=0.010) or mild to moderate pain (adj. p=0.038) compared with those with severe pain. However, the patients with anxious depression and severe pain showed a lower trend in hsCRP levels than patients with atypical depression who experienced severe pain (p=0.022; adj. p=0.155). Baseline TNF-α (adj. p=0.038) and IL-6 (adj. p=0.006) levels in patients in remission were significantly lower than those in patients with no remission among the participants with the atypical depression subtype at the eighth-week follow-up. CONCLUSIONS: This study provides evidence of differences in inflammatory proteins in patients with varied symptoms among melancholic, atypical and anxious depression subtypes. Further studies on the immunoinflammatory mechanism underlying different subtypes of depression are expected for improved individualised therapy. TRIAL REGISTRATION NUMBER: NCT03219008.