The transport by hepatocytes of immunoglobulin A from blood to bile visualized by autoradiography and electron microscopy.

Polymeric myeloma IgA, labelled with 125I, was injected intravenously into rats that were killed 5, 30, or 60 min later and the livers removed, fixed and sectioned. Autoradiographs of ultra-thin sections examined in the electron microscope showed that the IgA first became bound to the plasma membrane of the hepatocytes but after 30 min much of it was transported across their cytoplasm and became localized around the bile canaliculi. At this time, autoradiographs of 1 micrometer sections examined in the light microscope showed the contents of the bile ducts in the portal tracts to be labelled heavily. These results confirm the previous finding of rapid transport of IgA across the liver and show directly that the hepatocytes are the cells that carry it out. No intracellular organelle or vesicular structure, discernible within the resolving power of the techniques used, could be implicated in the transport mechanism.