,88 However, in more severe allergic disease, when it is paired with overexpression of other enzymes metabolizing Phe, it leads to a decrease of intracellular Phe levels in Th2 cells, which cannot then block OXPHOS, activate IL4I1, or inhibit proliferation, which results in unleashed expansion of pathogenic Th2a cells. The gene discussed is IL4I1; the disease is allergic disease.