IL6 and major depressive disorder: Beside from neurophysiological findings, several studies support the notion of interconnections between MDD and the release of pro-inflammatory cytokines, especially of the chemotactic Interleukin-8 (IL-8) and Interleukin-6 (IL-6), but results are yet inconsistent (Himmerich et al., 2019; Köhler et al., 2017; Tsai, 2021).