Extrahepatic bile duct growth in mice repeatedly injected with human normal serum, IgA-deficient serum or purified secretory IgA.

Another group of researchers has reported that seven intraperitoneal injections into mice of purified human serum IgA or normal human serum--but not IgA-deficient serum, mouse serum or saline--induced considerable growth of the extrahepatic bile duct epithelium. They stated that heterologous IgA was principally responsible for this effect. We have quantitated this growth by another method: enumeration of total and radiolabeled nuclei of the lumenal and glandular epithelium in transverse duct sections after tritiated thymidine injection and autoradiography. Our data show maximal incorporation between 18 and 24 hr after the last injection, with the highest labeling index in the lumenal epithelium after only three injections and before any duct enlargement. After four to seven injections, thymidine incorporation continued in juxtalumenal glands, together with massive glandular proliferation into the thickening wall and obvious inflammation. These changes were more pronounced in the liver-proximal part of the duct without affecting intrahepatic duct and gallbladder epithelia. Subcutaneous serum injections were less active. We confirm the inactivity of buffered saline, but, unlike previous authors, demonstrate strong activity in purified human milk secretory IgA and in IgA-deficient serum. We suggest that this different approach of quantitating epithelial proliferation will allow comparison of the bile duct growth effects of different, well-characterized human and animal IgA preparations.