Effector/memory Tregs express high levels of ICOS, which contributes to the survival and expansion of Tregs.36 Moreover, ICOS+ Tregs, which likely derive from expansion of thymus‐derived Tregs, are potentially highly suppressive.37 We found that the percentages of ICOS+ Tregs are increased in the blood of AD patients, regardless of FLG mutation status, serum IgE level and EASI score (Figure 4A). This evidence concerns the gene ICOS and Alzheimer disease.