Neoplastic human colon cells in studies on the translocation of dimeric IgA

The translocation of dimeric IgA across epithelial cells was studied by immunoelectron microscopy in an in vitro system with cultured neoplastic human colon cells (HT-29). Ultrastructurally, the cells were found to be well-polarized epithelial cells connected by intercellular junctions. Secretory component (SC) was localized to the basolateral plasma membranes. Dimeric human IgA, when reacted with the cells at 0 C, bound selectively to SC. When incubated at 37 C, the bound dimeric IgA was internalized by pinocytosis and transported apically through the cytoplasm in vesicles. The vesicles were opened to the lumen at the apical surfaces or discharged into the lumen. We conclude that the translocation of dimeric IgA across intestinal epithelial cells has been defined at the ultrastructural level in cultured neoplastic colon cells in vitro.