Functional and Phenotypic Evidence for Presentation of Eα52–68 Structurally Related Self-Peptide(s) in I-Eα-Deficient Mice

Abstract

The Y-Ae mAb and the 1H3.1 TCR-αβ (Vα1/Vβ6) are two immune receptors specific for I-Ab MHC class II molecules complexed to the 52–68 fragment of the α-chain of I-E class II molecules (the Eα52–68 peptide). A profound intrathymic negative selection occurs in 1H3.1 TCR transgenic mice in the presence of an I-Eα transgene. The administration of mAbs to 1H3.1/I-Eα double-transgenic newborn mice reveals that Y-Ae, but not the isotype-matched anti-I-E Y17 mAb, rescues a significant number of mature (Vβ6highCD4+CD8−) thymocytes and allows the detection of Eα52–68-reactive T cells in the periphery. These observations indicate that deletion of autoreactive T cells can be specifically inhibited in vivo by an mAb specific for the deleting self-peptide:self-MHC class II complex. Similar inhibition experiments indicate that C57BL/6 (I-Ab+/I-Eα−) mice constitutively express an Eα-independent, Y-Ae-recognizable epitope(s). This finding is confirmed by the phenotypic analysis of mature (MHC class II high) C57BL/6 bone marrow-derived dendritic cells. Collectively, these observations further illustrate the peptide specificity of negative selection and demonstrate that MHC class II-positive cells from unmanipulated C57BL/6 mice that lack a functional I-Eα gene can assemble one or more self-peptide:I-Ab complexes recognizable by the Eα52–68:I-Ab complex-specific Y-Ae mAb.