Zonulin (haptoglobin 2 precursor)[1] is a protein that increases the permeability of tight junctions between cells of the wall of the digestive tract.
[2] It was discovered in 2000 by Alessio Fasano and his team at the University of Maryland School of Medicine.
[4] Gliadin (a glycoprotein present in gluten) activates zonulin signaling irrespective of the genetic expression of autoimmunity, leading to increased intestinal permeability of macromolecules.
[3][5] Zonula occludens toxin is being studied as an adjuvant to improve absorption of drugs and vaccines.
[6] In 2014 a zonulin receptor antagonist, larazotide acetate (formerly known as AT-1001), completed a phase 2b clinical trial.