IFN-α treatment also significantly increased the density of Iba1+ microglia in the hippocampus, including the DG and hilus (Figure 1D) and CA3 (Supplementary Figure 1A), but not in other brain regions implicated in the pathology of depression (Belzung et al., 2014; Figure 1D; Supplementary Figure 1A). Here, IFNA1 is linked to major depressive disorder.