Given that both eosinophils and mast cells play a role in EoE pathogenesis, in 2013, Otani et al. [54] investigated whether mepolizumab reduced esophageal mast cell accumulation in paediatric EoE biopsy specimens from a previous, randomized, anti-IL-5 trial. This evidence concerns the gene IL5 and eosinophilic esophagitis.