title: The role of tetraspanin CD63 in antigen presentation via MHC class II.
abstract: Interactions between MHC class II (MHC II)-positive APCs and CD4(+)  T cells are central to adaptive immune responses. Using an Epstein-Barr virus (EBV)-transformed B lymphoblastoid cell line (LCL) as MHC II-positive APCs and CD4(+)  T-cell clones specific for two endogenously expressed EBV antigens, we found that shRNA knockdown of the tetraspanin protein CD63 in LCL cells consistently led to increased CD4(+)  T-cell recognition. This effect was not due to enhanced antigen processing nor to changes in MHC II expression since CD63 knockdown did not influence the amount or dimerization of MHC II in LCL cells. We therefore investigated the possible involvement of exosomes, small MHC II- and tetraspanin-abundant vesicles which are secreted by LCL cells and which we found could themselves activate the CD4(+)  T-cell clones in an MHC II-dependent manner. While equal loadings of exosomes purified from the control and CD63(low)  LCLs stimulated T cells to a comparable degree, we found that exosome production significantly increased following CD63-knockdown, suggesting that this may underlie the greater T-cell stimulatory capacity of the CD63(low)  LCLs. Taken together, our data reveal a new insight into the mechanisms by which tetraspanins are involved in the regulation of MHC II-dependent T-cell stimulation.
authors.affiliation: School of Cancer Sciences, University of Birmingham, Edgbaston, Birmingham, UK.
authors.forename: Sven H
authors.initials: SH
authors.lastname: Petersen
authors.forename: Elena
authors.initials: E
authors.lastname: Odintsova
authors.forename: Tracey A
authors.initials: TA
authors.lastname: Haigh
authors.forename: Alan B
authors.initials: AB
authors.lastname: Rickinson
authors.forename: Graham S
authors.initials: GS
authors.lastname: Taylor
authors.forename: Fedor
authors.initials: F
authors.lastname: Berditchevski
mesh_terms: D056704:Adaptive Immunity; D017951:Antigen Presentation / Q000235:genetics; D000956:Antigens, Viral / Q000276:immunology / Q000378:metabolism; D001402:B-Lymphocytes / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure / Q000821:virology; D015496:CD4-Positive T-Lymphocytes / Q000276:immunology / Q000378:metabolism* / Q000473:pathology / Q000821:virology; D002461:Cell Line, Transformed; D002999:Clone Cells; D055354:Exosomes / Q000276:immunology / Q000378:metabolism* / Q000648:ultrastructure; D004854:Herpesvirus 4, Human / Q000276:immunology*; D000949:Histocompatibility Antigens Class II / Q000276:immunology / Q000378:metabolism; D006801:Humans; D008213:Lymphocyte Activation / Q000235:genetics; D008854:Microscopy, Electron; D034741:RNA, Small Interfering / Q000235:genetics; D060149:Tetraspanin 30 / Q000235:genetics / Q000276:immunology / Q000378:metabolism*
chemical_list: D000956:Antigens, Viral; D000949:Histocompatibility Antigens Class II; D034741:RNA, Small Interfering; D060149:Tetraspanin 30