An increase of two well-known pro-inflammatory cytokines, called interleukin (IL)-1β and tumor necrosis factor-α (TNF-α), as well as a decrease of anti-inflammatory cytokines (e.g., IL-10, IL-4, and TGF-β1) have been observed in hippocampus and cortex of animal models of depression (You et al., 2011) and MDD patients (Farooq et al., 2017; Caruso et al., 2019). This evidence concerns the gene IL4 and major depressive disorder.