IgG transcytosis is accelerated but its pathway is not disrupted by Brefeldin-A

To see the action of Brefeldin-A (Bref-A) to transcytosis of the immunoglobulin G (IgG), we have examined the early stage of endocytosis and intracellular transport of IgG and transferrin (Tf) in epithelial cells of the rat yolk sac in culture with and without Bref-A. In the absence of Bref-A, the endocytosed IgG and Tf appeared in large apical endosomes during the first 5-15 min. At 15 min Tf-recycling endosomes and IgG-transferring vesicles also appeared in the apical or basolateral cytoplasm, respectively. At 15 min in the presence of Bref-A, clouds of Tf-recycling endosomes accumulated in the apical cytoplasm, while distinct IgG-transferring vesicles were distributed further to the basolateral cytoplasm. This differential action of Bref-A to IgG-transferring vesicles and Tf-recycling vesicles suggested an unexplored mechanism of sorting and basolateral transport of IgG.