IL1B and major depressive disorder: Indeed, proinflammatory cytokines, including IL-1beta, interleukin-6 (IL-6), and tumor necrosis factor-alpha (TNF-alpha), have been implicated in the etiology of depression, contributing to cellular damage, impaired neuronal plasticity, and neurotransmission in the prefrontal cortex and hippocampus (Felger and Lotrich 2013).