Sensitization to epithelial antigens in chronic mucosal inflammatory disease: immunochemical similarity of macromolecules in human colonic epithelium with murine intestinal epithelial cell-associated components (ECAC).

In order to explore whether human intestinal epithelium contains cell-associated components that are organ-specific and therefore potentially autoantigenic, macromolecules were isolated in aqueous-soluble form from histologically normal human colonic epithelial cells, partially purified under nondenaturing conditions, then characterized biochemically and immunologically. Preparative non-SDS-polyacrylamide gel electrophoresis followed by electro-elution into a Tris-glycine buffer separated five human colonic fractions (yield 86%), all of which possessed an acidic isoelectric point (4.0-4.8) and a modest carbohydrate content (0.9-15%), resembling fractions of corresponding Rf similarly prepared from murine colonic epithelial cells. Immunological characterization suggested that two of the gel-purified fractions (B1, B2) isolated from colonic epithelium contained organ-specific determinants: (i) reactivity of B1/B2-specific immunoglobulin was not diminished by prior absorption with proteins from other epithelial surfaces (tracheal mucosal components) nor from normal serum; (ii) epitopes on ECAC B1 and B2 fractions were shared across species lines, with reactivity for the cross-reactive determinant being as much as 20-fold that of control protein; and (iii) localization studies with specific antibody showed an organ- and cell-restricted immunofluorescence pattern on freshly fixed human and murine mucosal epithelial tissue, using B1-specific monoclonal antibody. Given the reported binding of inflammatory bowel disease serum immunoglobulin and lamina propria mononuclear cells for murine ECAC determinants, our studies suggest these same antigens are present in human colonic epithelium, and are available as potential binding sites for antibody or lymphocytes participating in an autoaggressive immune response.