Male mice receiving an intraperitoneal injection of LPS during postnatal development display microglial upregulation of CX3CR1 which, in a TLR4-dependent manner, causes heightened synaptic engulfment in the ACC and results in MDD-like symptoms upon acute exposure to unpredictable stressors during adolescence (Cao et al., 2021). Here, TLR4 is linked to major depressive disorder.