title: Downmodulation of antigen presentation by H2-O in B cell lines and primary B lymphocytes.
abstract: Peptide loading onto MHC class II molecules takes place in endosomal compartments along the endocytic pathway. There, loading is facilitated by the catalytic function of the accessory molecule H2-M, which helps to exchange the invariant chain-derived CLIP peptide in the groove of class II molecules for antigenic peptide. H2-O is another accessory molecule specific to the class II pathway, which is found tightly associated with H2-M and selectively expressed in B cells. Using stable H2-O ribozyme-antisense transfectants, H2-O overexpressing murine B cell lines, and H2-O-transgenic mice, we investigated the effects of H2-O on antigen presentation. The results show that presentation of a variety of exogenous protein antigens to a panel of T cell hybridomas depended on the levels of H2-O in the antigen-presenting B cells. Thus, increased H2-O expression downmodulated, whereas reduced H2-O levels, enhanced presentation. Presentation of endogenous antigen was also diminished by H2-O. Despite the pronounced effects on antigen presentation, the mass spectrometric profiles of peptides eluted from Ab molecules were very similar in cells expressing different H2-O levels. The intracellular location of H2-O inhibitory activity was investigated with the drug chloroquine, which prevents acidification of the endocytic pathway. The observations indicate that H2-O predominantly inhibits antigen presentation in early endosomal compartments. Thus, H2-O appears to skew peptide loading to late endosomal/lysosomal compartments. This may favor presentation of antigens taken up by the B cell receptor.
authors.affiliation: German Cancer Research Center, DKFZ, Heidelberg, Germany.
authors.forename: Pascale
authors.initials: P
authors.lastname: Brocke
authors.forename: Elena
authors.initials: E
authors.lastname: Armandola
authors.forename: Natalio
authors.initials: N
authors.lastname: Garbi
authors.forename: Günter J
authors.initials: GJ
authors.lastname: Hämmerling
mesh_terms: D000818:Animals; D017951:Antigen Presentation / Q000276:immunology*; D000944:Antigens, Differentiation, B-Lymphocyte / Q000276:immunology; D001402:B-Lymphocytes / Q000276:immunology*; D002460:Cell Line / Q000276:immunology; D002738:Chloroquine / Q000494:pharmacology; D011992:Endosomes / Q000276:immunology; D000949:Histocompatibility Antigens Class II / Q000235:genetics / Q000276:immunology*; D006825:Hybridomas / Q000276:immunology; D016393:Lymphoma, B-Cell / Q000276:immunology / Q000473:pathology; D008247:Lysosomes / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D010446:Peptide Fragments / Q000032:analysis / Q000276:immunology; D016337:RNA, Catalytic / Q000235:genetics; D011947:Receptors, Antigen, B-Cell / Q000276:immunology; D011993:Recombinant Fusion Proteins / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology; D014162:Transfection; D014407:Tumor Cells, Cultured / Q000276:immunology
chemical_list: D000944:Antigens, Differentiation, B-Lymphocyte; C416186:H-2O antigen; D000949:Histocompatibility Antigens Class II; C111389:I-Ad antigen; D010446:Peptide Fragments; D016337:RNA, Catalytic; D011947:Receptors, Antigen, B-Cell; D011993:Recombinant Fusion Proteins; C045084:invariant chain; D002738:Chloroquine