Th17 cells increased in preclinical depression animal models (learned helplessness and chronic restraint stress paradigms) and blockage of Th17 cell differentiation by a deficiency in retinoic acid receptor-related orphan receptor (ROR)γT transcription factor and inhibition of RORγT transcription factor pharmacologically or using IL17-A antibody rendered the animal resistant to learned helplessness42. Here, IL17A is linked to major depressive disorder.