TNF and major depressive disorder: According to the cytokine hypothesis depressive disorders are related to increased production of cytokines, including interleukins, tumour necrosis factor alpha (TNF-α) and interferon-α and -γ.[1] Higher blood levels of C-reactive protein, interleukin-6 (IL-6) and TNF-α are found in depressive patients compared to healthy subjects.[2] A meta-analysis of cytokines in major depression shows higher concentrations of the pro-inflammatory cytokines IL-6 and TNF-α in depressed patients compared with control subjects.[3]