RT Journal Article SR Electronic T1 Visualizing the Site and Dynamics of IgG Salvage by the MHC Class I-Related Receptor, FcRn JF The Journal of Immunology JO J. Immunol. FD American Association of Immunologists SP 2021 OP 2029 DO 10.4049/jimmunol.172.4.2021 VO 172 IS 4 A1 Ober, Raimund J. A1 Martinez, Cruz A1 Vaccaro, Carlos A1 Zhou, Jinchun A1 Ward, E. Sally YR 2004 UL http://www.jimmunol.org/content/172/4/2021.abstract AB The MHC class I-related receptor, FcRn, plays a central role in regulating the serum levels of IgG. FcRn is expressed in endothelial cells, suggesting that these cells may be involved in maintaining IgG levels. We have used live cell imaging of FcRn-green fluorescent protein transfected human endothelial cells to analyze the intracellular events that control IgG homeostasis. We show that segregation of FcRn-IgG complexes from unbound IgG occurs in the sorting endosome. FcRn or FcRn-IgG complexes are gradually depleted from sorting endosomes to ultimately generate multivesicular bodies whose contents are destined for lysosomal degradation. In addition, the pathways taken by FcRn and the transferrin receptor overlap, despite distinct mechanisms of ligand uptake. The studies provide a dynamic view of the trafficking of FcRn and its ligand and have relevance to understanding how FcRn functions to maintain IgG homeostasis.