IGHE and allergic disease: PGD2 is the major lipid mediator released by mast cells following crosslinking of allergen‐specific IgE molecules displayed on their surface in sensitized individuals as part of the early allergic reaction.10, 11 Furthermore, eosinophils, dendritic cells, macrophages, and endothelial cells12 produce PGD2 and substantial amounts have been detected in tissues affected by allergic reactions, such as lung,13 skin,14, 15 and esophagus.