IL6 and major depressive disorder: In fact, significantly higher serum levels of the IL-6 and TGFB1 cytokines have been reported in patients with schizophrenia compared to healthy controls (Ergün et al., 2017) and mutations in TGFB1 have been associated with the susceptibility and treatment response of schizophrenia (Frydecka et al., 2013) and major depressive disorder (Bialek et al., 2020).