It has been suggested that self major histocompatibility complex (MHC) peptides bound to self MHC molecules may be involved in the intrathymic induction of self tolerance. We studied the antigenicity of synthetic peptides derived from the first domain of DR beta 1*0101 chain in a DR beta 1*0101 responder. We found that a peptide corresponding to residues 21-42 of the beta chain could elicit the proliferation of autoreactive T cells. A T cell line (TCL-SUN) and 7 of 9 T cell clones (TCC) derived from TCL-SUN specifically recognized peptide 21-42 in the presence of APCs carrying the DR beta 1*0101 allele. DR beta 1*0101 positive APCs stimulated the TCCs in the absence of peptide, although the magnitude of the response was much lower than in cultures with peptide. This suggests that self DR1 molecules are continuously processed into peptides that are presented by the DR1 molecules on the surface of the cells. The data indicate that some T cells whose TCR binds to self MHC peptides presented by self MHC molecules are not deleted, although their ligand is continuously present. TCCs specific for peptide 21-42 presented in the context of DR1 were also stimulated by cells heterozygous for DR beta 1*0301 and 1601, indicating that some DR peptide-specific autoreactive T cells participate in alloreactivity.

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