IL9 and major depressive disorder: In addition, postmortem brain studies have also demonstrated that the expression of inflammatory cytokines, such as IFN-γ, IL-1α, IL-2, IL-3, IL-5, IL-8, IL-9, IL-12A, IL-13, IL-15 and TNF, is significantly changed in patients with depression and/or associated with the subsequent development of depression [177].