Under the control of specific transcription factors (such as Δdbl-GATA-1, PU.1, and C/EBP) and in response to IL-5 [11], mature eosinophils are released into the peripheral circulation and then transferred to target tissues, being the gastrointestinal tract their main destination with the only exception of the healthy esophagus where the presence of eosinophils is a histological hallmark of pathology such as in eosinophilic esophagitis (EoE) [12]. This evidence concerns the gene SPI1 and eosinophilic esophagitis.