title: Conformational variation of surface class II MHC proteins during myeloid dendritic cell differentiation accompanies structural changes in lysosomal MIIC.
abstract: Dendritic cells (DC), uniquely among APC, express an open/empty conformation of MHC class II (MHC-II) proteins (correctly folded molecules lacking bound peptides). Generation and trafficking of empty HLA-DR during DC differentiation are investigated here. HLA-DR did not fold as an empty molecule in the endoplasmic reticulum/trans-Golgi network, did not derived from MHC/Ii complexes trafficking to the cell surface, but was generated after invariant chain degradation within lysosomal-like MHC-II rich compartments (MIIC). In pre-DC, generated from monocytes cultured in the presence of GM-CSF, Lamp-1(+)MHC-II(+) compartments are predominantly electron dense and, in these cells, empty MHC-II molecules accounts for as much as 20% of total surface HLA-DR. In immature DC, generated in presence of GM-CSF and IL-4, empty HLA-DR reside in multilamellar MIIC, but are scarcely observed at the cell surface. Thus, the morphology/composition of lysosomal MIIC at different DC maturational stages appear important for surface egression or intracellular retention of empty HLA-DR. Ag loading can be achieved for the fraction of empty HLA-DR present in the "peptide-receptive" form. Finally, in vivo, APC-expressing surface empty HLA-DR were found in T cell areas of secondary lymphoid organs.
authors.affiliation: Department of Pathology Albert Einstein College of Medicine, New York, NY 10461, USA.
authors.forename: Ilaria
authors.initials: I
authors.lastname: Potolicchio
authors.forename: Sriram
authors.initials: S
authors.lastname: Chitta
authors.forename: Xiaonan
authors.initials: X
authors.lastname: Xu
authors.forename: Dora
authors.initials: D
authors.lastname: Fonseca
authors.forename: Giovanna
authors.initials: G
authors.lastname: Crisi
authors.forename: Vaclav
authors.initials: V
authors.lastname: Horejsi
authors.forename: Jack L
authors.initials: JL
authors.lastname: Strominger
authors.forename: Lawrence J
authors.initials: LJ
authors.lastname: Stern
authors.forename: Graca
authors.initials: G
authors.lastname: Raposo
authors.forename: Laura
authors.initials: L
authors.lastname: Santambrogio
mesh_terms: D000595:Amino Acid Sequence; D002454:Cell Differentiation / Q000502:physiology*; D002462:Cell Membrane / Q000378:metabolism*; D002478:Cells, Cultured; D003713:Dendritic Cells / Q000166:cytology* / Q000378:metabolism; D004721:Endoplasmic Reticulum / Q000648:ultrastructure; D016178:Granulocyte-Macrophage Colony-Stimulating Factor; D006684:HLA-DR Antigens / Q000378:metabolism; D000949:Histocompatibility Antigens Class II / Q000737:chemistry* / Q000378:metabolism; D006801:Humans; D015847:Interleukin-4 / Q000494:pharmacology; D008221:Lymphoid Tissue / Q000378:metabolism; D008247:Lysosomes / Q000378:metabolism*; D008969:Molecular Sequence Data; D009000:Monocytes / Q000648:ultrastructure; D022423:Myeloid Cells / Q000166:cytology* / Q000378:metabolism; D010455:Peptides / Q000378:metabolism; D011487:Protein Conformation; D021601:trans-Golgi Network / Q000648:ultrastructure
chemical_list: D006684:HLA-DR Antigens; D000949:Histocompatibility Antigens Class II; D010455:Peptides; D015847:Interleukin-4; D016178:Granulocyte-Macrophage Colony-Stimulating Factor