TLR4 and major depressive disorder: Fundamental to the misbalanced differentiation of T cells, the cytokines responsible for the proliferation of Th1 and Th17 cells have been shown to be upregulated by GSK-3 via its regulation of inflammatory transcription factors, such as NF-κB, STAT3, and CREB, all of which have been implicated in rodent models of depression, as well as the activation of the TLR4 [43,50,66,133,134,135,136].