In BD depression, IL-6 is the predominant cytokine, in euthymic state it is IL-4, and in manic episode it is IL-2, IL-4, IL-6, while patients with unipolar depression have mainly elevated TNF-α, IL-6 and soluble IL-2 receptor (sIL-2R) [65]. This evidence concerns the gene IL2 and major depressive disorder.