Studies showed that there is a bidirectional relationship between depression and inflammation, so that depression can cause up-regulation of inflammatory mediators and thereafter the inflammatory cytokines can cause depression behaviours.30 Recent studies have indicated that increased serum pro-inflammatory cytokines such as IL-6, IL-1, TNF-α, IL-2, IFN-α and other inflammatory cytokine are associated with depression.15,31,32. Here, IL2 is linked to major depressive disorder.