AIM: To examine the expression of intercellular adhesion molecule-1 (ICAM-1) and lymphocyte function-associated antigen-1 (LFA-1) expression on canals of Hering (CoH)and bile ductules associated with the autoimmune process of bile duct destruction in primary biliary cirrhosis (PBC).METHODS: Ten wedged liver biopsies of PBC (five cases each of stages 2 and 3) were studied. The liver specimens were processed for transmission electron microscopy.Immunohistochemistry was performed using anti-ICAM-1 and anti-LFA-1 mouse mAbs. In situ hybridization was done to examine the messenger RNA expression of ICAM-1 in formalin-fixed, paraffin-embedded sections using peptide nucleic acid probes and the catalyzed signal amplification (CSA) technique. Immunogold-silver staining for electron microscopy was performed using anti-ICAM and anti-LFA-1 mouse mAbs. The immunogold particles on epithelial cells of bile ductules and cholangiocytes of CoH cells were counted and analyzed semi-quantitatively.Western blotting was performed to confirm ICAM-1 protein expression.RESULTS: In liver tissues of PBC patients, immunohistochemistry showed aberrant ICAM-1 expression on the plasma membrane of epithelial cells lining bile ductules,and also on mature cholangiocytes but not on hepatocytes in CoH. LFA-1-positive lymphocytes were closely associated with epithelial cells in bile ductules. ICAM-1 expression at protein level was confirmed by Western blot. In situ hybridization demonstrated ICAM-1 mRNA expression in bile ductules and LFA-1 mRNA in lymphocytes infiltrating the bile ductules. By immunoelectron microscopy, ICAM-1 was demonstrated on the basal surface of epithelial cells in bile ductules and on the luminal surfaces of cholangiocytes in damaged CoH. Cells with intermediate morphology resembling progenitor cells in CoH were not labeled with ICAM-1 and LFA-1.CONCLUSION: De novo expression of ICAM-1 both on mature cholangiocytes in CoH and epithelial cells in bile ductules in PBC implies that lymphocyte-induced destruction through adhesion by ICAM-1 and binding of LFA-1-expressing activated lymphocytes takes place not only in bile ductules but also in the CoH.