TNF and major depressive disorder: We therefore examined the effects of Aβ1-42 oligomers i.c.v. injection on the mRNA levels of pro-inflammatory cytokines (IL-1β and TNF-α) and anti-inflammatory cytokines (IL-4 and TGF-β1) in the hippocampus (Figure 4), a brain area of primary relevance in the pathogenesis of depression (Villa et al., 2016).