ALTERATION OF A MODEL ANTIGEN BY AU(III) LEADS TO T-CELL SENSITIZATION TO CRYPTIC PEPTIDES

Certain metal ions are known to be potent sensitizers, but the self pr oteins modified by metal ions and the self peptides recognized by 'met al-specific' T cells are unknown. In human and mice treatment with gol d anti-rheumatic drugs, containing Au(I), may lead to allergic and aut oimmune 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 alt eration by Au(III) of a model antigen, bovine ribonuclease (RNase) A. results in T cell sensitization to cryptic peptides of this protein. U pon 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, 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), Al(III), Cu(II), Fe(II) , FE(III), Ni(II), Mn(II), or Zn(II). Using a panel of overlapping, sy nthetic RNase peptides which were devoid of gold or gold-induced modif ications, epitope mapping revealed that RNase/Au(III)-specific T cell hybridomas recognized the cryptic peptides 7-21 and 94-108, respective ly. Comparison of the proliferative response of bulk CD4+ T cells, pre pared from splenocytes after immunization with either RNase/Au(III) or native RNase, revealed that Au(III) pretreatment of RNase led to a ma rkedly enhanced response to the two cryptic peptides while it did not influence the response to the immunodominant peptide. The cryptic pept ides were also presented after preincubation of bone marrow-derived ma crophages with RNase and Au(I), but not with RNase alone, suggesting t hat 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 th e development of allergic and autoimmune side effects of Au(I) anti-rh eumatic drugs. In addition, it might provide a general mechanism of ho w metal ions act as T cell sensitizers.