title: Identification and characterization of major histocompatibility complex class II compartments in cortical thymic epithelial cells.
abstract: Previous studies have concentrated on elucidating the subcellular localization of major histocompatibility (MHC) class II molecules mainly in B cells, macrophages, and dendritic cells. Despite very rich cell-surface expression of MHC class II molecules by cortical thymic epithelial cells (cTECs), little is known regarding the expression of these molecules by cTECs at the subcellular level. In the present study we focused on the identification and characterization of MHC class II compartments (MIICs) in cTECs in situ by immunogold electron microscopy (IEM). We found that MHC class II molecules were located exclusively in the cytoplasmic vacuoles, and we identified these MHC class II molecule-containing cytoplasmic vacuoles as MIICs in cTECs. These MIICs were immunopositive for early endosomal, late endosomal, and lysosomal markers. Moreover, in these MIICs, MHC class II molecules were colocalized with cathepsin L, H2-DM, class II-associated invariant chain (Ii), and class II-associated invariant chain peptide (CLIP). Similarly, Ii molecules were colocalized with endosomal and lysosomal markers, cathepsin L, and H2-DM in the vacuoles. Taken together, these results suggest that MIICs in cTECs represent conventional endocytic compartments. The colocalization of MHC class II molecule or Ii with cathepsin L and H2-DM in the MIICs suggests that MIICs in cTECs may be sites of Ii degradation and peptide loading.
authors.affiliation: Department of Oral and Maxillofacial Surgery, Yamaguchi University School of Medicine, Ube, Japan. myyamini@hotmail.com
authors.forename: Yamini
authors.initials: Y
authors.lastname: Arudchelvan
authors.forename: Yukio
authors.initials: Y
authors.lastname: Nishimura
authors.forename: Nobuko
authors.initials: N
authors.lastname: Tokuda
authors.forename: Tomoo
authors.initials: T
authors.lastname: Sawada
authors.forename: Yoshiya
authors.initials: Y
authors.lastname: Ueyama
authors.forename: Tetsuo
authors.initials: T
authors.lastname: Fukumoto
mesh_terms: D000818:Animals; D000944:Antigens, Differentiation, B-Lymphocyte / Q000378:metabolism; D015415:Biomarkers / Q000032:analysis; D056668:Cathepsin L; D002403:Cathepsins / Q000378:metabolism; D002451:Cell Compartmentation; D003546:Cysteine Endopeptidases; D011992:Endosomes / Q000378:metabolism; D004847:Epithelial Cells / Q000378:metabolism / Q000648:ultrastructure; D005260:Female; D000949:Histocompatibility Antigens Class II / Q000378:metabolism*; D008247:Lysosomes / Q000378:metabolism; D008854:Microscopy, Electron; D016253:Microscopy, Immunoelectron; D051381:Rats; D011919:Rats, Inbred Strains; D013950:Thymus Gland / Q000166:cytology / Q000378:metabolism* / Q000648:ultrastructure; D014018:Tissue Distribution
chemical_list: D000944:Antigens, Differentiation, B-Lymphocyte; D015415:Biomarkers; D000949:Histocompatibility Antigens Class II; C045084:invariant chain; D002403:Cathepsins; D003546:Cysteine Endopeptidases; D056668:Cathepsin L; C534280:Ctsl protein, rat