IL4 and major depressive disorder: Similarly, one study reported higher blood levels of IFN-γ and IFN-γ/IL-4 ratio, with no difference in IL-4 levels alone, in adolescents with MDD compared with healthy participants (Gabbay et al., 2009), whilst two other studies showed no difference in IFN-γ between two groups (Pallavi et al., 2015), or even lower IFN-γ and IL-4 levels in MDD versus healthy controls (trend for significance) (Byrne et al., 2013).