Compelling evidence has demonstrated positive correlations between asthma severity and an elevated number of M2 macrophages (7), which could increase cell recruitment and mucus secretion by facilitating the production of CCL17, CLL22, Fizz1, Arg1 and TGM2, leading to airway hyperresponsiveness in allergic asthma (37–39). This evidence concerns the gene CCL17 and allergic asthma.