IL-1β-induced production of IL-6 (Chen et al., 2005; Trompet et al., 2008) has not only been shown to increase age-associated cognitive decline (Trompet et al., 2008), but also lead to depression (Capuron et al., 2008; Raison and Miller, 2011; Lee and Giuliani, 2019). This evidence concerns the gene IL6 and major depressive disorder.