IL6 and major depressive disorder: A multitude of studies and meta-analyses show that patients with major depressive disorder (MDD) have, on average, increased serum levels of pro-inflammatory cytokines, like interleukin 1 beta (IL-1-beta), IL-6 and tumour necrosis factor alpha (TNF-alpha), and of the acute phase protein, C-reactive protein (CRP)1,2,4,5.