IL4 and major depressive disorder: In the current study, the amount of IL-1β, IL-2, IL-4, IL-5, IL-13 and IFN-γ in the serum of HDM-sensitized mice were significantly higher than PBS control mice, demonstrating that chronic nasal HDM administration leads to systemic increases in these pro-inflammatory and Th2-related cytokines that are potentially associated with depression.