zonulin

The protein that opens the gate — released by gliadin to loosen the gut's tight junctions and let gluten peptides through.

Zonulin is a protein produced by intestinal epithelial cells (enterocytes) and liver cells that regulates the permeability of tight-junctions in the gut lining. In the context of celiac disease, it functions as an unintended enabler: gliadin triggers zonulin release, which loosens the tight junctions between enterocytes, allowing gluten peptides to cross the epithelial barrier and reach the immune tissue below.

The Mechanism

1. Gliadin binds to a receptor on the apical (gut-facing) surface of enterocytes
2. This triggers zonulin secretion
3. Zonulin acts on tight junction proteins (particularly ZO-1 and occludin), loosening them
4. Paracellular gaps open — gluten peptides and other luminal contents leak through
5. Peptides encounter tissue-transglutaminase and antigen-presenting cells in the lamina propria → immune response initiated

This pathway is sometimes called the "leaky gut" mechanism, though that term is used imprecisely in popular media.

Relevance Beyond Celiac

Zonulin-mediated permeability is not unique to celiac disease — it's also studied in type 1 diabetes, inflammatory bowel disease, and multiple sclerosis, leading to a broader hypothesis that intestinal barrier dysfunction is a shared mechanism in autoimmune diseases. This research is largely associated with Alessio Fasano's group (Harvard).

As a Drug Target

larazotide-acetate (AT-1001) works by blocking zonulin's action on tight junctions — essentially preventing the gate from opening. Early trials showed symptom reduction even without full dietary gluten elimination, suggesting that keeping the barrier closed can reduce immunological exposure. Phase 3 results were mixed (see larazotide-acetate).

Related Concepts

tight-junctions | gliadin | enterocytes | larazotide-acetate | intestinal-permeability | tissue-transglutaminase

Referenced In

mechanism | research_plan | glossary