title: Targeting proteins to distinct subcellular compartments reveals unique requirements for MHC class I and II presentation.
abstract: Peptides derived from exogenous proteins are presented by both MHC class I and II. Despite extensive study, the features of the endocytic pathway that mediate cross-presentation of exogenous antigens on MHC class I are not entirely understood and difficult to generalize to all proteins. Here, we used dendritic cells and macrophages to examine MHC class I and II presentation of hen egg-white lysozyme (HEL) in different forms, soluble and liposome encapsulated. Soluble HEL or HEL targeted to a late endosomal compartment only allowed for MHC class II presentation, in a process that was blocked by chloroquine and a cathepsin S (CatS) inhibitor; brefeldin A (BFA) also blocked presentation, indicating a requirement for nascent MHC class II. In contrast, liposome-encapsulated HEL targeted to early endosomes entered the MHC class I and II presentation pathways. Cross-presentation of HEL in early endosomal liposomes had several unique features: it was markedly increased by BFA and by blockade of the proteasome or CatS activity, it occurred independently of the transporter associated with antigen processing but required an MHC class I surface-stabilizing peptide, and it was inhibited by chloroquine. Remarkably, chloroquine facilitated MHC class I cross-presentation of soluble HEL and HEL in late endosomal liposomes. Altogether, MHC class I and II presentation of HEL occurred through pathways having distinct molecular and proteolytic requirements. Moreover, MHC class I sampled antigenic peptides from various points along the endocytic route.
authors.affiliation: Department of Pathology and Immunology, Washington University School of Medicine, St. Louis, MO 63110, USA.
authors.forename: Roger
authors.initials: R
authors.lastname: Belizaire
authors.forename: Emil R
authors.initials: ER
authors.lastname: Unanue
mesh_terms: D000818:Animals; D020126:Brefeldin A / Q000494:pharmacology; D002645:Chickens; D002738:Chloroquine / Q000494:pharmacology; D003713:Dendritic Cells / Q000276:immunology; D004705:Endocytosis / Q000276:immunology; D015395:Histocompatibility Antigens Class I / Q000187:drug effects / Q000235:genetics*; D000949:Histocompatibility Antigens Class II / Q000187:drug effects / Q000235:genetics*; D006801:Humans; D008081:Liposomes / Q000737:chemistry; D008264:Macrophages / Q000276:immunology; D051379:Mice; D016688:Mice, Inbred NOD / Q000276:immunology; D009113:Muramidase / Q000737:chemistry / Q000235:genetics
chemical_list: D015395:Histocompatibility Antigens Class I; D000949:Histocompatibility Antigens Class II; D008081:Liposomes; D020126:Brefeldin A; D002738:Chloroquine; D009113:Muramidase