We studied distribution patterns of type IV collagen α chains in the subepithelial basement membrane (SBM) of the human gastrointestinal tract - the esophagus through the anal canal - by immunofluorescent microscopy using α(IV) chain-specific monoclonal antibodies. The α1(IV), α2(IV), α5(IV), and α6(IV) chains were found in the SBM throughout the tract, indicating the localization of [α1(IV)]2 α2(IV) and [α5(IV)]2 α6(IV) heterotrimeric molecules. The [α1(IV)]2 α2(IV) molecule was continuously stained, while the [α5(IV)]2 α6(IV) molecule was weakly stained in gastric glands and small intestinal crypts. In addition, the SBM at the luminal surface epithelium of the stomach and large intestine contained small amounts of α3(IV) and α4(IV) chains which combined to form the α3(IV) α4(IV) α5(IV) heterotrimeric molecule with α5(IV) chain. The SBM beneath the villous epithelium of the small intestine was also demonstrated to have an α3(IV) chain and α4(IV) chain. Considering the specific locations of the type IV collagen trimers throughout the gastrointestinal SBM, the supramolecular network containing the α3(IV) α4(IV) α5(IV) molecule appears to function as a selective permeability barrier and /or as a protection against chemical stress from the luminal digestive enzymes.
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