Whereas increased IL-8 concentrations were observed in depressive participants (Simon et al., 2008) and in patients with acute or remitted MDD (Birur et al., 2017; Vogelzangs et al., 2016), reduced IL-8 concentrations and a negative correlation between the severity of depression and concentrations of IL-8 (with a higher severity of depression associated to lower IL-8 levels) were reported by Zou et al. (2018). This evidence concerns the gene CXCL8 and major depressive disorder.