Histological changes of bile duct in experimental graft-versus-disease across minor histocompatibility barriers. III. Immunoelectron microscopic observations.

Graft-versus-host disease (GVHD) was produced by injecting lymphoid cells from B10.D2 mice into BALB/C mice. Both are H-2-identical but differ only at multiple minor H loci. The expression and localization of MHC class II antigens on the bile duct epithelium was examined using an immunoelectron microscopical method. All GVHD mice developed bile duct lesions of chronic nonsuppurative cholangitis and expressed MHC class II antigens on their bile duct epithelium, while none of the control mice, which injected with the same number of syngeneic lymphocytes, developed bile duct lesions or expressed the antigens. The antigenic expression was characteristically localized on the basolateral surface of the bile duct epithelium but not on the apical surface. Furthermore, the expression varied markedly in its intensity and distribution within the same liver and even within a single bile duct. The infiltration of Lyt-1-positive helper/inducer lymphocytes in the duct epithelial layer apparent by electron microscopy was predominant to a much degree than that of Lyt-2-positive cytotoxic/suppressor lymphocytes and non-lymphocytic cells. The immunological mechanisms involving helper/inducer T cells in association with MHC class II antigens on bile duct epithelium may be important in the induction and progression of the bile duct lesions apparent in the present GVHD model.