The seal between cells lining your gut, blood vessels, and other barriers—when tight junctions leak, things get through that shouldn’t.Tight junctions are multiprotein complexes (claudins, occludins, ZO proteins) that form paracellular barriers between epithelial and endothelial cells. They regulate permeability across mucosal surfaces, the blood-brain barrier, and blood-retinal barrier. Tight junction dysfunction (increased intestinal permeability, ‘leaky gut’) is implicated in celiac disease, IBD, and autoimmune conditions. Larazotide (AT-1001) specifically targets tight junction regulation by antagonizing zonulin-mediated tight junction opening in the intestinal epithelium.