MBP and Achalasia: Another study of 28 achalasia patients who had esophageal muscle biopsies taken during POEM found immunohistochemical staining for eosinophil major basic protein (MBP) and eosinophil-derived neurotoxin (EDN) in 24 cases (86%), and the authors speculated that achalasia with eosinophil infiltration of esophageal muscle might represent a subtype of EoE [62].