MBP and esophagitis: Poly-l-arginine is a ligand for the extracellular calcium sensing receptor (CaSR),10 a G-protein coupled receptor, which is found on many cell types throughout the body.11 The CaSR has many known ligands, including calcium, other polyvalent cations, spermine and amyloid β-peptide.11 We have previously characterised the presence and functional activity of the CaSR in the human oesophageal epithelium and in the oesophageal epithelial cell line HET-1A.12 Since the actions of MBP mimic polyarginine, we hypothesise that MBP, released by eosinophils in oesophagitis, acts as a CaSR ligand.