Abstract
One of the cornerstones of mucosal immunology has been the study of the selective secretion of polymeric IgA at the mucosal epithelium. We have focussed on the structural features which govern the association of polymeric immunoglobulin and its receptor. We have also described some of the features which distinguish the transcytotic pathway in the rat liver from the well known degradative pathway taken typically by asialoglycoproteins (1).