IL17A and major depressive disorder: Under the influence of IFN I type (IFN-α and IFN-β), an increase in which can induce the development of depression [57,58], neutrophils show a significant chemotactic effect on Th17 lymphocytes [46], with Th17 lymphocytes beginning to express higher levels of IL-23R and IL-17 mRNA [59,60], characteristic of pathogenic Th17 lymphocytes.