tight junctions
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The molecular mortar between gut wall cells — when it loosens, gluten slips through and the immune system sees it.
The intestinal epithelium is a single layer of cells (enterocytes) lined up side by side. Tight junctions are protein complexes that seal the gaps between adjacent cells, making the barrier nearly impermeable to large molecules. They are the gate between the gut's contents and the underlying immune tissue.
The Zonulin Connection
gliadin — the primary disease-causing prolamin in wheat — directly triggers the release of zonulin, a protein that regulates tight junction permeability. When zonulin is released, tight junctions loosen, creating gaps through which gluten peptides can slip into the lamina propria (the tissue beneath the epithelium), where immune cells are waiting. This is called the paracellular pathway of gluten uptake.
This matters because gluten peptides that cross this barrier encounter tissue-transglutaminase and antigen-presenting cells — triggering the full immune cascade. In healthy individuals without genetic predisposition, even if gluten crosses the barrier it doesn't provoke the same response.
A Chicken-and-Egg Problem
Active celiac disease worsens tight junction integrity — inflammation itself disrupts the barrier, allowing more gluten through, which drives more inflammation. This feedback loop is part of why untreated celiac tends to progress.
As a Drug Target
Blocking the zonulin pathway is the mechanism behind larazotide-acetate, one of the most studied non-dietary treatments for celiac disease. By tightening tight junctions, larazotide aims to reduce gluten uptake and symptom burden — even without eliminating gluten from the diet. Phase 3 trial results were mixed.
Related Concepts
zonulin | gliadin | enterocytes | intestinal-permeability | larazotide-acetate | tissue-transglutaminase | cd4-t-cells