TLR4 and major depressive disorder: Serum-derived EV miRNA expression profiles of negatively regulating Toll-like receptor 4 (TLR4) signaling, including let-7e, miR-21-5p, miR-145, miR-146a, and miR-155, may be useful for determining whether serum-derived EV miRNAs can be used to predict antidepressant response in MDD [39].