BDNF and major depressive disorder: Moreover, a recent study showed that decreasing Arg1+ microglia in the hippocampus by knocking down the microglial IL4R suppressed hippocampal neurogenesis and enhanced vulnerability to CUMS, whereas increasing Arg1+ microglia in the hippocampus by enhancing IL4 signaling restored hippocampal neurogenesis and the resilience to stress-induced depression via brain-derived neurotropic factor (BDNF) (Zhang et al., 2021).