title: ER-phagosome fusion defines an MHC class I cross-presentation compartment in dendritic cells.
abstract: Induction of cytotoxic T-cell immunity requires the phagocytosis of pathogens, virus-infected or dead tumour cells by dendritic cells. Peptides derived from phagocytosed antigens are then presented to CD8+ T lymphocytes on major histocompatibility complex (MHC) class I molecules, a process called "cross-presentation". After phagocytosis, antigens are exported into the cytosol and degraded by the proteasome. The resulting peptides are thought to be translocated into the lumen of the endoplasmic reticulum (ER) by specific transporters associated with antigen presentation (TAP), and loaded onto MHC class I molecules by a complex "loading machinery" (which includes tapasin, calreticulin and Erp57). Here we show that soon after or during formation, phagosomes fuse with the ER. After antigen export to the cytosol and degradation by the proteasome, peptides are translocated by TAP into the lumen of the same phagosomes, before loading on phagosomal MHC class I molecules. Therefore, cross-presentation in dendritic cells occurs in a specialized, self-sufficient, ER-phagosome mix compartment.
mesh_terms: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters / Q000235:genetics / Q000378:metabolism; D000818:Animals; D017951:Antigen Presentation; D000941:Antigens / Q000276:immunology / Q000378:metabolism; D018414:CD8-Positive T-Lymphocytes / Q000276:immunology; D003546:Cysteine Endopeptidases / Q000378:metabolism; D003600:Cytosol / Q000378:metabolism; D003713:Dendritic Cells / Q000166:cytology* / Q000276:immunology* / Q000378:metabolism / Q000648:ultrastructure; D004721:Endoplasmic Reticulum / Q000378:metabolism* / Q000648:ultrastructure; D015395:Histocompatibility Antigens Class I / Q000276:immunology* / Q000378:metabolism; D008561:Membrane Fusion; D051379:Mice; D009097:Multienzyme Complexes / Q000378:metabolism; D010047:Ovalbumin / Q000276:immunology / Q000378:metabolism; D010587:Phagocytosis; D010588:Phagosomes / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure; D046988:Proteasome Endopeptidase Complex; D021381:Protein Transport
chemical_list: D000071181:ATP Binding Cassette Transporter, Subfamily B, Member 2; D018528:ATP-Binding Cassette Transporters; D000941:Antigens; D015395:Histocompatibility Antigens Class I; D009097:Multienzyme Complexes; C073119:TAP1 protein, human; C486171:Tap1 protein, mouse; D010047:Ovalbumin; D003546:Cysteine Endopeptidases; D046988:Proteasome Endopeptidase Complex