Biliary transport of IgA: role of secretory component.

Abstract

Biliary transport of rat immunoglobulin (Ig) was studied by perfusion of isolated rat liver with blood containing radiolabeled Ig. Transport to bile was selective for polymeric IgA. Between 15 and 27% of polymeric IgA was transported from blood to bile during a 210 min perfusion period and approximately 60% of the IgA transported to bile bore a secretory component. Small quantities of IgM (0.12%) were transported; transport of IgG2a, IgE or monomeric IgA was not detected. Purification of radiolabeled polymeric IgA by affinity chromatography on human secretory component-Sepharose yielded a fraction that was transported more efficiently (i.e., up to 40% transported). Secretory IgA (colostral or biliary) was transported 1/25th-1/12th as well as polymeric IgA myeloma protein. Complexes of 125I-labeled secretory component and polymeric IgA formed in vitro were transported poorly (0.1%) compared to polymeric IgA (26%). Biliary transport of polymeric IgA may require a combination of it with secretory component in the liver. Rabbit IgG anti-rat secretory component antibodies were transported to bile but normal rabbit IgG was not.