Unipolar depressed inpatients without comorbid personality disorder exhibit elevated IL-6 levels at admission and a decrease after discharge: A longitudinal study.

BACKGROUND: One-third of patients with unipolar depression (UD) do not achieve remission after treatment. There is a growing interest in the role of inflammation in the pathogenesis of UD; however, no study has evaluated differences in cytokine levels between patients with UD with and without comorbid personality disorders (PD). We compared cytokine levels (IFN-γ, TNF-α, IL-2, IL-4, IL-6, IL-10, and IL-17) among inpatients with and without comorbid PD, and healthy controls (HC).

METHODS: Longitudinal study with three groups: UD (n = 53), UD+PD (n = 31), and HC (n = 100). Cytokine levels were compared at admission and discharge using one-way ANOVA and Bonferroni post hoc tests. Multiple linear regressions adjusted for potential confounders were conducted. Cytokine levels within each clinical group at admission and discharge were compared using a paired t-test.

RESULTS: At admission, IL-6 and IL-17 levels were higher in both UD and UD+PD groups compared to the HC (p < 0.001), while IL-10 levels were higher in the UD group compared to the HC (0.043). IL-6 levels were higher in the UD group than in the UD+PD group (p = 0.039). At discharge, levels of IL-6 (p = 0.002) and IL-17 (p < 0.001) were higher in both clinical groups compared to the HC, with no differences between the UD and UD+PD groups. IL-6 levels were reduced in the UD group at discharge. Depressive symptoms improved in both clinical groups.

CONCLUSION: Both clinical groups showed elevated cytokines compared to HC. Patients with UD without comorbid PD had higher IL-6 levels than those with the comorbidity at admission. These findings may have clinical implications for the therapeutic management of these patients, especially in the development of biologically based treatments targeting inflammatory mechanisms.