title: Major histocompatibility complex class II compartments in human B lymphoblastoid cells are distinct from early endosomes.
abstract: In human B lymphoblastoid cell lines, the majority of major histocompatibility complex (MHC) class II heterodimers are located on the cell surface and in endocytic compartments, while invariant chain (Ii)-associated class II molecules represent biosynthetic intermediates which are present mostly in the endoplasmic reticulum and Golgi complex. To investigate the origin of the MHC class II-positive compartments and their relation to early endosomes, the intracellular distribution of MHC class II molecules and Ii in relation to endocytic tracers was studied in human lymphoblastoid B cells by immunoelectronmicroscopy on ultrathin cryosections. Cross-linking of surface immunoglobulins, followed by a brief period of internalization of the immune complexes, did not alter the intracellular distribution of MHC class II molecules. While early endosomes were abundantly labeled for the cross-linked immunoglobulins, < 1% of total MHC class II molecules were detectable in early endosomes. MHC class II- and Ii-positive structures associated with the trans-Golgi network can be reached by endocytosed bovine serum albumin (BSA)-gold conjugates after 30 min of internalization. Prolonged exposure to BSA-gold allowed visualization of later endocytic compartments, in which a progressive loss of Ii was observed: first the lumenal portion, and then the cytoplasmic portion of Ii escaped detection, culminating in the formation of MHC class II-positive compartments (MIIC) devoid of Ii. The loss of Ii also correlated with a transition from a multivesicular to a multilaminar, electron-dense MIIC. The intracellular compartments in which class II molecules reside (MIIC) are therefore a heterogeneous set of structures, part of the later aspects of the endocytic pathway.
authors.affiliation: Laboratory of Cell Biology, Medical School, University of Utrecht, The Netherlands.
authors.forename: P J
authors.initials: PJ
authors.lastname: Peters
authors.forename: G
authors.initials: G
authors.lastname: Raposo
authors.forename: J J
authors.initials: JJ
authors.lastname: Neefjes
authors.forename: V
authors.initials: V
authors.lastname: Oorschot
authors.forename: R L
authors.initials: RL
authors.lastname: Leijendekker
authors.forename: H J
authors.initials: HJ
authors.lastname: Geuze
authors.forename: H L
authors.initials: HL
authors.lastname: Ploegh
mesh_terms: D000938:Antigen-Presenting Cells / Q000378:metabolism / Q000648:ultrastructure; D000941:Antigens / Q000737:chemistry / Q000378:metabolism*; D000944:Antigens, Differentiation, B-Lymphocyte; D001402:B-Lymphocytes / Q000276:immunology* / Q000648:ultrastructure; D001692:Biological Transport; D002451:Cell Compartmentation; D002460:Cell Line; D004721:Endoplasmic Reticulum / Q000276:immunology; D011992:Endosomes / Q000276:immunology*; D006056:Golgi Apparatus / Q000276:immunology; D006681:HLA-D Antigens / Q000378:metabolism*; D000949:Histocompatibility Antigens Class II / Q000378:metabolism; D006801:Humans; D007150:Immunohistochemistry; D066298:In Vitro Techniques; D007425:Intracellular Membranes / Q000378:metabolism; D008854:Microscopy, Electron; D010455:Peptides / Q000276:immunology / Q000378:metabolism
chemical_list: D000941:Antigens; D000944:Antigens, Differentiation, B-Lymphocyte; D006681:HLA-D Antigens; D000949:Histocompatibility Antigens Class II; D010455:Peptides; C045084:invariant chain