Functional and phenotypic evidence for presentation of Eα52-68 structurally related self-peptide(s) in I-Eα-deficient mice

The Y-Ae mAb and the 1H3.1 TCR-alpha beta (V alpha 1/V beta 6) are two immune receptors specific for I-A(b) MHC class II molecules complexed to the 52-68 fragment of the alpha-chain of I-E class II molecules (the E alpha(52-68) peptide). A profound intrathymic negative selection occurs in 1H3.1 TCR transgenic mice in the presence of an I-E alpha transgene. The administration of mAbs to 1H3.1/I-E alpha double-transgenic newborn mice reveals that Y-Ae, but not the isotype-matched anti-I-E Y17 mAb, rescues a significant number of mature (V beta 6(high)CD4(+)CD8(-)) thymocytes and allows the detection of E alpha(52-68)-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-A(b)/I-E alpha(-)) mice constitutively express an E alpha-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-E alpha gene can assemble one or more self-peptide:I-A(b) complexes recognizable by the E alpha(52-68):I-A(b) complex-specific Y-Ae mAb.