title: A defective viral superantigen-presenting phenotype in HLA-DR transfectants is corrected by CIITA.
abstract: Activation of T lymphocytes by mouse mammary tumor virus superantigen (vSAg) requires binding to MHC class II molecules. The subcellular location where functional interactions occur between MHC class II molecules and vSAgs is still a matter of debate. To gain further insight into this issue, we have used human epithelial HeLa cells expressing HLA-DR1. Surprisingly, the human cells were unable to present transfected vSAg7 or vSAg9 to a series of murine T cell hybridomas. The defect is not related to a lack of vSAg processing, because these cells can indirectly activate T cells after coculture in the presence of B lymphocytes. However, after IFN-gamma treatment, the HeLa DR1(+) cells became apt at directly presenting the vSAg. Furthermore, transfection of CIITA was sufficient to restore presentation. Reconstitution experiments demonstrated the necessity of coexpressing HLA-DM and invariant chain (Ii) for efficient vSAg presentation. Interestingly, inclusion of a dileucine motif in the DRbeta cytoplasmic tail bypassed the need for HLA-DM expression and allowed the efficient presentation of vSAg7 in the presence of Ii. A similar trafficking signal was included in vSAg7 by replacing its cytoplasmic tail with the one of Ii. However, sorting of this chimeric Ii/vSAg molecule to the endocytic pathway completely abolished both its indirect and direct presentation. Together, our results suggest that functional vSAgs-DR complexes form after the very late stages of class II maturation, most probably at the cell surface.
authors.affiliation: Laboratoire d'Immunologie Moléculaire, Département de Microbiologie et Immunologie, Faculté de Médecine, Université de Montréal, Hôpital St.-Luc, Montréal, Canada.
authors.forename: Georges A
authors.initials: GA
authors.lastname: Azar
authors.forename: Rafick-Pierre
authors.initials: RP
authors.lastname: Sékaly
authors.forename: Jacques
authors.initials: J
authors.lastname: Thibodeau
mesh_terms: D020816:Amino Acid Motifs / Q000235:genetics / Q000276:immunology; D000818:Animals; D017951:Antigen Presentation / Q000235:genetics*; D000944:Antigens, Differentiation, B-Lymphocyte / Q000096:biosynthesis / Q000235:genetics; D000956:Antigens, Viral / Q000276:immunology / Q000378:metabolism*; D002460:Cell Line; D045744:Cell Line, Tumor; D004705:Endocytosis / Q000235:genetics / Q000276:immunology; D011992:Endosomes / Q000737:chemistry / Q000276:immunology / Q000378:metabolism; D004847:Epithelial Cells / Q000276:immunology / Q000378:metabolism; D006681:HLA-D Antigens / Q000096:biosynthesis / Q000235:genetics; D015798:HLA-DR1 Antigen / Q000096:biosynthesis / Q000235:genetics*; D006367:HeLa Cells; D000949:Histocompatibility Antigens Class II / Q000096:biosynthesis / Q000235:genetics; D006801:Humans; D016130:Immunophenotyping; D007371:Interferon-gamma / Q000502:physiology; D008324:Mammary Tumor Virus, Mouse / Q000235:genetics / Q000276:immunology*; D051379:Mice; D009687:Nuclear Proteins / Q000235:genetics* / Q000502:physiology; D021381:Protein Transport / Q000235:genetics / Q000276:immunology; D015398:Signal Transduction / Q000235:genetics / Q000276:immunology; D018089:Superantigens / Q000276:immunology / Q000378:metabolism*; D015534:Trans-Activators / Q000235:genetics* / Q000502:physiology; D014162:Transfection / Q000379:methods
chemical_list: D000944:Antigens, Differentiation, B-Lymphocyte; D000956:Antigens, Viral; D006681:HLA-D Antigens; C084245:HLA-DM antigens; D015798:HLA-DR1 Antigen; D000949:Histocompatibility Antigens Class II; C083728:MHC class II transactivator protein; D009687:Nuclear Proteins; D018089:Superantigens; D015534:Trans-Activators; C045084:invariant chain; D007371:Interferon-gamma