Previous studies have suggested that several growth factors or chemokines (eotaxins, IL-2/3/5/8, GM-CSF, and PGD2) could prime eosinophils,[8], [24], [25], [26], [27] but it is still unclear which factor dominates the priming effect of eosinophils in asthma and if priming is reversible. Here, IL2 is linked to asthma.