TNF and major depressive disorder: Indeed, higher IL-13 levels are associated with more severe depression and a higher number of suicide attempts (Vai et al., 2021), and elevated levels of IL-2 (Suhee et al., 2023), TNF-a (Tuglu et al., 2003), and IL-8 (Kuzior et al., 2020) are associated with depressive symptoms in clinical studies.