ARG1 and allergic asthma: Previous studies, including our own, have demonstrated that M2 macrophages are one of the major cell types in the airway of allergic asthma patients and produce large amounts of inflammatory factors, such as IL-13, CCL17, CCL22, eotaxin, Ym1, found in inflammatory zone 1 (FIZZ1) and arginase 1(Arg 1), during the course of disease development and progression (7, 8).