title: Processing and MHC class II presentation of exogenous soluble antigen involving a proteasome-dependent cytosolic pathway in CD40-activated B cells.
abstract: Activated B cells have the capacity to present antigen and induce immune responses as potent antigen-presenting cells (APCs). As in other APCs, antigen presentation by B cells involves antigen internalization, antigen processing, and peptide loading onto MHC molecules. However, while the mechanism of antigen processing has been studied extensively in other APCs, this pathway remains elusive in B cells. The aim of this study was to investigate the MHC class II processing pathway in CD40-activated B cells (CD40Bs), as a model for activated, antigen-presenting B cells. Using CMV pp65 as a model antigen, we evaluated processing and presentation of the CD4 + T-cell epitope 509-523 (K509) by human CD40Bs in ELISPOT assays. As expected, stimulation of specific CD4 + T-cell clones was attenuated after pretreatment of CD40Bs with inhibitors of classic class II pathway components. However, proteasome inhibitors such as epoxomicin limited antigen presentation as well. This suggests that the antigen is processed in a non-classical, cytosolic MHC class II pathway. Further experiments with truncated protein variants revealed involvement of the proteasome in processing of the N and C extensions of the epitope. Access to the cytosol was shown to be size dependent. Epoxomicin sensitivity exclusively in CD40B cells, but not in dendritic cells, suggests a novel processing mechanism unique to this APC. Our data suggest that B cells process antigen using a distinct, non-classical class II pathway.
authors.affiliation: Cologne Interventional Immunology, Cologne University Hospital, Cologne, Germany.
authors.forename: Hans Jiro
authors.initials: HJ
authors.lastname: Becker
authors.affiliation: Department of General Medicine, Okayama University Graduate School of Medicine, Dentistry and Pharmaceutical Sciences, Okayama, Japan.
authors.forename: Eisei
authors.initials: E
authors.lastname: Kondo
authors.affiliation: Cologne Interventional Immunology, Cologne University Hospital, Cologne, Germany.
authors.forename: Alexander
authors.initials: A
authors.lastname: Shimabukuro-Vornhagen
authors.affiliation: Cologne Interventional Immunology, Cologne University Hospital, Cologne, Germany.|Max Planck Institute for Metabolism Research, Cologne, Germany.
authors.forename: Sebastian
authors.initials: S
authors.lastname: Theurich
authors.affiliation: Cologne Interventional Immunology, Cologne University Hospital, Cologne, Germany.
authors.forename: Michael S
authors.initials: MS
authors.lastname: von Bergwelt-Baildon
mesh_terms: D017951:Antigen Presentation / Q000187:drug effects / Q000276:immunology*; D001402:B-Lymphocytes / Q000276:immunology* / Q000378:metabolism*; D019013:CD40 Antigens / Q000378:metabolism*; D002738:Chloroquine / Q000494:pharmacology; D003600:Cytosol / Q000378:metabolism; D003713:Dendritic Cells / Q000187:drug effects / Q000276:immunology / Q000378:metabolism; D000939:Epitopes / Q000276:immunology*; D000949:Histocompatibility Antigens Class II / Q000276:immunology* / Q000378:metabolism*; D006801:Humans; D008213:Lymphocyte Activation / Q000276:immunology*; D009842:Oligopeptides / Q000494:pharmacology; D046988:Proteasome Endopeptidase Complex / Q000378:metabolism*; D015398:Signal Transduction; D016176:T-Lymphocyte Subsets / Q000276:immunology / Q000378:metabolism
chemical_list: D019013:CD40 Antigens; D000939:Epitopes; D000949:Histocompatibility Antigens Class II; D009842:Oligopeptides; D002738:Chloroquine; D046988:Proteasome Endopeptidase Complex; C078846:epoxomicin
keywords: B cells; T cells; antigen Presentation/Processing; antigens/Peptides/Epitopes; dendritic cells; human; vaccination