IL17A and major depressive disorder: They showed that (1) levels of Th17 cells were higher in brains of rodents that exhibited learned helplessness; (2) infusion of Th17 cells was associated with depression-like behaviors at sub-threshold stimulation; (3) infusion of anti-IL-17 antibody or administration of SR1001, an inhibitor of retinoid-related orphan receptor- γT (RORγT, a transcription factor essential for differentiation of naïve CD4+ T cells to Th17 cells) mitigated the effects of Th17 cell infusion; and (4) RORγT knockout mice exhibited marked resistance to learned helplessness paradigm [58].