To assess the association between CD15+ Treg cells and asthma, we compared the proportion of sialyl LeX positive FOXP3+ Treg cells among CD4+ T cells between intermittent-to-mild (n = 20) and moderate-to-severe (n = 11) asthma and healthy controls (n = 19) (Fig. 5c). Here, FUT4 is linked to asthma.