title: Native IgG2a(b) is barely antigenic to major histocompatibility complex class II-restricted T cells owing to inefficient internalization by professional antigen-presenting cells.
abstract: Peptide epitopes derived from immunoglobulin variable regions represent tumour-specific antigens on B-cell neoplasms and can be recognized by syngeneic, major histocompatibility complex (MHC) class II-restricted T cells. Immunoglobulin peptide/MHC class II complexes may also be involved in autoimmunity and CD4+ T-cell-mediated B-cell regulation. Thus, the IgG2a(b) H-chain allopeptide gamma2a(b) 435-451 presented on I-Ad mimics the epitope implicated in herpes simplex virus-induced autoimmune stromal keratitis and is the target of T helper 1 (Th1) clones that suppress IgG2a(b) production in vivo. We here report that spleen and thymus cells constitutively present the autologous gamma2a(b) epitope to a gamma2a(b) 435-451/I-A(d) reactive T-cell hybridoma as a function of the animal housing conditions (specific pathogen-free or not) and the serum levels of IgG2a(b). Constitutive presentation in the spleen was predominantly performed by dendritic cells. Whereas spleen cells poorly presented native IgG2a(b) to a gamma2a(b) 435-451/I-A(d) reactive T-cell hybridoma, IgG2a(b) in the form of immune complexes were presented > 200-fold more efficiently owing to internalization via low-affinity FcgammaR on macrophages. The antigenicity could also be improved by homotypic aggregation and by targeting IgG2a(b) to complement receptors on the A20 B-cell lymphoma. Mice without detectable IgG2a(b)-containing immune complexes typically exhibited minimal constitutive presentation. Nevertheless, native IgG2a(b) can sensitize antigen-presenting cells in vivo, as mice that were devoid of immune complexes and carried an IgG2a(b)-producing tumour did present constitutively, even at physiological IgG2a(b) serum levels. Whereas the amounts of IgG released from most B-cell lymphomas may be too low to allow spontaneous priming of tumour-specific MHC class II-restricted T cells, administration of tumour immunoglobulin in aggregated form might improve the efficacy of idiotype vaccination.
authors.affiliation: Department of Immunology, Institute of Medical Biology, University of Tromsø, School of Medicine, Tromsø, Norway.
authors.forename: K
authors.initials: K
authors.lastname: Bartnes
authors.forename: K
authors.initials: K
authors.lastname: Hannestad
mesh_terms: D000818:Animals; D017951:Antigen Presentation; D000936:Antigen-Antibody Complex / Q000276:immunology; D000951:Antigens, Neoplasm / Q000097:blood / Q000276:immunology*; D000939:Epitopes / Q000097:blood / Q000276:immunology*; D000949:Histocompatibility Antigens Class II / Q000276:immunology*; D006825:Hybridomas / Q000276:immunology; D007074:Immunoglobulin G / Q000097:blood / Q000276:immunology*; D016393:Lymphoma, B-Cell / Q000276:immunology; D051379:Mice; D008807:Mice, Inbred BALB C; D008810:Mice, Inbred C57BL; D008815:Mice, Inbred Strains; D009374:Neoplasms, Experimental / Q000276:immunology; D013154:Spleen / Q000276:immunology; D013601:T-Lymphocytes / Q000276:immunology*; D013950:Thymus Gland / Q000276:immunology
chemical_list: D000936:Antigen-Antibody Complex; D000951:Antigens, Neoplasm; D000939:Epitopes; D000949:Histocompatibility Antigens Class II; D007074:Immunoglobulin G