HRH4 and eosinophilic esophagitis: Importantly, we demonstrate that H1R and H2R, but not H3R or H4R, are constitutively and inducibly expressed by human esophageal epithelial cell lines in vitro, suggesting that inducible esophageal H4R expression in vivo in the setting of active EoE may be of non-epithelial origin.