In the superior frontal gyrus medial segment, IL-4 was higher in AD + MDD group (0.028 ± 0.011) compared to AD only (0.022 ± 0.008) (F1,34 = 4.186, p = 0.049, Fig. 1C), suggesting that the co-morbidity depression in AD may induce an anti-inflammatory environment. This evidence concerns the gene IL4 and major depressive disorder.