Activation of cell-mediated immunity in depression: association with inflammation, melancholia, clinical staging and the fatigue and somatic symptom cluster of depression.

Observed Findings

• Serum neopterin was significantly elevated in depressed patients compared to healthy controls, with the highest levels in patients with melancholia.
• Positive correlations existed between serum neopterin, pro-inflammatory cytokines (IL-1 and TNFα), and the number of previous depressive episodes.
• Both IL-1 and TNFα were associated with chronic fatigue symptoms measured by the FF Rating Scale.
• Neopterin and TNFα were predictive of melancholic features, while age, FF score, and TNFα predicted chronic fatigue group membership.
• Inflammatory markers were higher in patients with more recurrent depressive episodes.

Inferred Conclusions

• Cell-mediated immune activation and pro-inflammatory cytokine responses are pathophysiologically linked to depression and its melancholic and fatigue subtypes.
• Neopterin may contribute to depression through activation of oxidative and nitrosative stress pathways, suggesting immune activation as a mechanism underlying depressive symptoms.
• Recurrent depressive episodes may amplify both immune and inflammatory responses, potentially creating a cycle that increases vulnerability to future episodes and chronic symptoms.
• CMI activation and inflammation may represent a distinct biological subtype of depression characterized by fatigue and somatic symptoms.

Remaining Questions