NEUROINFLAMMATION AND THE IMMUNE SYSTEM IN MAJOR DEPRESSIVE DISORDER: PERIPHERAL CYTOKINE SIGNATURES AND THE EFFICACY OF ADJUNCTIVE ANTI-INFLAMMATORY TREATMENT

Abstract

A substantial body of evidence implicates the innate immune system in the pathophysiology of major depressive disorder (MDD). This study characterized peripheral inflammatory markers in patients with MDD relative to healthy controls and evaluated whether adjunctive anti-inflammatory treatment improves depressive outcomes, with particular attention to baseline inflammatory status. In a two-part design, serum interleukin-6 (IL-6), tumor necrosis factor-α (TNF-α), C-reactive protein (CRP), and interleukin-1β (IL-1β) were measured in 220 participants (110 MDD, 110 controls); a randomized, placebo-controlled subsample of MDD patients (n=100) received the cyclooxygenase-2 inhibitor celecoxib or placebo added to a selective serotonin reuptake inhibitor (SSRI) for eight weeks. MDD patients showed significantly elevated levels of all four markers (all p<.001) and were over-represented in the high-CRP (>3 mg/L) stratum (χ²(2)=19.4, p<.001). Serum IL-6 correlated with depression severity (r=0.41, p<.001). Adjunctive celecoxib produced greater symptom reduction than placebo (group × time F(4,392)=6.4, p<.001), and this advantage was concentrated among patients with high baseline CRP, who showed markedly higher response (68% vs 41%) and remission (52% vs 27%) rates. These findings support a role for neuroinflammation in a biologically identifiable subgroup of depressed patients and illustrate the potential of inflammation-guided, stratified treatment. (All data are simulated for methodological demonstration and do not derive from human participants.)