title: Alteration of a model antigen by Au(III) leads to T cell sensitization to cryptic peptides.
abstract: Certain metal ions are known to be potent sensitizers, but the self proteins modified by metal ions and the self peptides recognized by 'metal-specific' T cells are unknown. In humans and mice treatment with gold anti-rheumatic drugs, containing Au(I), may lead to allergic and autoimmune side effects. Human and murine T cells do not react to Au(I), however, but to the reactive metabolite Au(III). Here we show that alteration by Au(III) of a model antigen, bovine ribonuclease (RNase)A, results in T cell sensitization to cryptic peptides of this protein. Upon immunization of mice with Au(III)-pretreated RNase [RNase/Au(III)], CD4+ T cell hybridomas specific for RNase/Au(III) were obtained in addition to those recognizing the immunodominant peptide RNase 74-88; the latter also were obtained after immunization with native RNase. RNase/Au(III)-specific T cell hybridomas reacted against RNase/Au(III) and RNase denatured by S-sulfonation of cysteine residues, but not against native RNase, or RNase pretreated with Au(I), A1(III), Cu(II), Fe(II), Fe(III), Ni(II), Mn(II), or Zn(II). Using a panel of overlapping, synthetic RNase peptides which were devoid of gold or gold-induced modifications, epitope mapping revealed that RNase/Au(III)-specific T cell hybridomas recognized the cryptic peptides 7-21 and 94-108, respectively. Comparison of the proliferative response of bulk CD4+ T cells, prepared from splenocytes after immunization with either RNase/Au(III) or native RNase, revealed that Au(III) pretreatment of RNase led to a markedly enhanced response to the two cryptic peptides while it did not influence the response to the immunodominant peptide. The cryptic peptides were also presented after preincubation of bone marrow-derived macrophages with RNase and Au(I), but not with RNase alone, suggesting that oxidation of Au(I) to Au(III) and subsequent protein alteration by Au(III) can happen in mononuclear phagocytes. We conclude that Au(III) alteration of proteins alters antigen processing and, thus leads to presentation of cryptic peptides. This mechanism may shed light on the development of allergic and autoimmune side effects of Au(I) anti-rheumatic drugs. In addition, it might provide a general mechanism of how metal ions act as T cell sensitizers.
authors.affiliation: Division of Immunology, Medical Institute of Environmental Hygiene, Heinrich Heine University, Düsseldorf, Germany.
authors.forename: P
authors.initials: P
authors.lastname: Griem
authors.forename: K
authors.initials: K
authors.lastname: Panthel
authors.forename: H
authors.initials: H
authors.lastname: Kalbacher
authors.forename: E
authors.initials: E
authors.lastname: Gleichmann
mesh_terms: D000595:Amino Acid Sequence; D000818:Animals; D000918:Antibody Specificity; D017951:Antigen Presentation / Q000187:drug effects; D016525:Antigenic Modulation / Q000187:drug effects*; D001853:Bone Marrow; D000939:Epitopes / Q000276:immunology; D005260:Female; D006046:Gold / Q000276:immunology / Q000494:pharmacology*; D006052:Gold Sodium Thiomalate / Q000276:immunology / Q000378:metabolism* / Q000494:pharmacology; D006825:Hybridomas / Q000737:chemistry / Q000201:enzymology; D006863:Hydrogen-Ion Concentration; D007114:Immunization; D008213:Lymphocyte Activation / Q000187:drug effects*; D008264:Macrophages / Q000276:immunology; D051379:Mice; D008810:Mice, Inbred C57BL; D018448:Models, Immunological; D008969:Molecular Sequence Data; D010455:Peptides / Q000276:immunology* / Q000494:pharmacology*; D011487:Protein Conformation / Q000187:drug effects; D012260:Ribonucleases / Q000187:drug effects / Q000276:immunology; D013601:T-Lymphocytes / Q000187:drug effects* / Q000276:immunology
chemical_list: D000939:Epitopes; D010455:Peptides; D006052:Gold Sodium Thiomalate; D006046:Gold; D012260:Ribonucleases