T cell activation-triggered IL-2 and IL-4 expression is partly dependent on ROS generation and follows oxidative signaling via mitochondrial respiration chain complex I. Inhibition of complex I function will decrease mtROS generation, thus blocking activation-induced secretion of IL-4 in CD4+ T cells from patients with atopic dermatitis, a disease characterized by elevated IL-4 and IgE. Here, IL4 is linked to atopic eczema.