IL2 and major depressive disorder: Recent research on depression biomarkers has revealed numerous associations with biomolecules involved in immune responses, such as inflammation [10]. Meta-analyses and systematic reviews have demonstrated significant alterations in the levels of IL-1β, IL-2, IL-4, IL-8, soluble IL-6 receptor (sIL-6R), IL-5, CCL3, IL-17A, and TGF-β1 in individuals with depression [10].