Apolipoprotein localization in the human bile duct and gallbladder

Apolipoproteins AI, AII and B were identified in the normal and pathological human bile duct and the gallbladder epithelium using an avidin-biotin immunoperoxidase technique. Small intestine and stomach sections served as positive and negative controls respectively. Staining was focal for apolipoproteins AI and AII, and continuous for apolipoprotein B. In addition to homogenous and granular cytoplasmic staining, foamy cytoplasmic staining, particularly for apolipoproteins AI and AII, was observed around lipid droplets in cells containing much lipid. No correlation between a particular pathological condition of the gallbladder (acute cholecystitis, mucocele, chronic cholecystitis, cholesterolosis) and staining pattern or intensity of staining was found for any of the apolipoproteins, although both apolipoproteins AI and AII stained more intensely than apolipoprotein B in each group. Positive staining was also found for all apolipoproteins in epithelial cells which had invaded the underlying connective tissue (gallbladder carcinoma), suggesting that the epithelial cells are capable of synthesizing apolipoproteins de novo. In this latter case, apolipoprotein B stained more intensely than for either AI or AII, and significantly (p less than 0.05) more strongly than that found in the other pathological groups. The identification of apolipoproteins in the gallbladder epithelium raises the interesting question of their origin and functional role.