Studies on the Local Immune Mechanism in the Hepatobiliary Tract of the Rat : Immunological Analysis of the Liver and Bile after Retrograde Injection of HRP into the Common Bile Duct

A new experimental model was developed in rats to investigate the local immune mechanism in the hepatobiliary tract. Animals were initially sensitized with subcutaneous injection of horseradish peroxidase(HRP) in the hind foot pads followed by retrograde boosting with the same antigen through the common bile duct 8 weeks after the initial sensitization(ID-rat). Rats which were boosted intravenously with HRP (IV-rat), which recieved HRP into the common bile duct without initial sensitization(S-rat), and normal rats served as control. The number of anti-HRP antibody forming cells increasd significantly in the portal triad of the liver in the ID-rats. These cells were shown to be positive for lgA by double immunohistochemistry for HRP and lgA. The amount of lgA in the bile also increased in the ID-rats. Immunoblotting after PAGE of the bile revealed the presence of anti-HRP antibody activity. The specific anti-HRP antibody activity in the bile corresponded with secretory lgA. These results indicated that the hepatobiliary system responds to antigenic stimulus by producing specific lgA antibody, and the lymphoid cells localized in the portal triad might serve as the hepatobiliary tract-associated lymphoid tissue, the same as GALT and BALT