Apical to basolateral transcytosis and apical recycling of immunoglobulin G in trophoblast-derived BeWo cells: Effects of low temperature, nocodazole, and cytochalasin D

The murine neonatal Fc receptor, FcRn, carries out two functions: materno-f etal IgG delivery and maintenance of serum IgG homeostasis. During human pr egnancy maternal IgG is transferred across placental syncytiotrophoblasts p resumably by the human homolog of FcRn, hFcRn. Trophoblast-derived BeWo cel ls express hFcRn endogenously and can be considered as a model system to in vestigate IgG transport in syncytiotrophoblasts. Using a pulse-chase protoc ol, we here demonstrate that polarized BeWo cells exhibit not only apical t o basolateral transcytosis but also apical IgG recycling. Thus, for the fir st time we demonstrate that epithelial cells can be involved in both matern o-fetal IgG transmission and regulation of serum IgG levels. Lowering the t emperature from 37 to 16 degreesC reduced, but did not block, IgG recycling and transcytosis. Microtubule-disruption by nocodazole did not influence t ranscytosis or apical recycling. Disassembly of filamentous actin by cytoch alasin D stimulated apical endocytosis and recycling, while transcytosis re mained unaffected. In summary, in BeWo cells apically internalized IgG ente rs both a transcytotic and recycling pathway. While the transcytotic route is temperature-sensitive but independent from microtubules and actin filame nts, the apical recycling pathway is temperature-influenced and stimulated by actin disassembly, suggestive for the involvement of distinct endosome s ubcompartments in transcytosis and recycling. (C) 2001 Academic Press.