Evidence has indicated elevated concentrations of pro-inflammatory cytokines are associated with major depressive disorder (MDD) and treatment response, but the nature of this association remains unclear.
A sample of 32 medication-free participants with a major depressive episode (age 38.5 years) and age, gender, ethnicity and IQ matched 24 healthy controls (age 40.6 years) were examined. MDD diagnosis was ascertained using the Diagnostic and Statistical Manual of Mental Disorders (4th ed.; DSM-IV; APA, 1994) and depressive symptoms by the Hamilton Rating Scale for Depression (HRSD-17; Hamilton, 1960). MDD participants were administered duloxetine at a daily dosage of 60mg for 12 weeks, with an optional dose increase to 120 mg daily after 8 weeks, while healthy controls were not administered any medication. Depressive and anxiety symptoms were measured at baseline week 0, weeks 1, 8 and 12 using the Hamilton Rating Scale for Depression (Hamilton, 1960) and Hamilton Anxiety Rating Scale (Hamilton, 1959), respectively.
MDD participants exhibited elevated depressive and anxiety symptoms at all assessment times compared to healthy controls. MDD participants also displayed different levels of IL-1 and of IL-6 at specific time points (i.e., week 1 and week 12, respectively) compared to healthy controls. Significantly different trajectories over time were observed for IL-6 (but not IL-1) which were associated with an increase in anxiety symptoms between baseline week 0 and week 8. IL-6 concentrations decreased over baseline weeks 0, 1 and 8 but increased at week 12 for MDD participants, whilst healthy control IL-6 concentrations increased during baseline weeks 0, 1 and 8 but decreased at week 12.
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