Plasma cytokine profiles in depressed patients who fail to respond to selective serotonin reuptake inhibitor therapy

Objective: Approximately 30% of patients with depression fail to respond to a selective serotonin reuptake inhibitor (SSRI). Few studies have attempted to define these patients from a biological perspective. Studies suggest that overall patients with depression show increased production of proinflammatory cytokines. We examined pro- and anti-inflammatory cytokine levels in patients who were SSRI resistant. Methods: Plasma concentrations of IL-6, IL-8, IL-10, TNF-α and sIL-6R were measured with enzyme linked immunosorbent assays (ELISA) in DSM-1V major depressives who were SSRI resistant, in formerly SSRI resistant patients currently euthymic and in healthy controls. Results: Patients with SSRI-resistant depression had significantly higher production of the pro-inflammatory cytokines IL-6 (p = 0.01) and TNF-α (p = 0.004) compared to normal controls. Euthymic patients who were formerly SSRI resistant had proinflammatory cytokine levels which were similar to the healthy subject group. Anti-inflammatory cytokine levels did not differ across the 3 groups. Conclusion: Suppression of proinflammatory cytokines does not occur in depressed patients who fail to respond to SSRIs and is necessary for clinical recovery.