Contribution of the lymph antigens to the MHC II self-peptidome (APP2P.102)

Abstract

Abstract Thymic MHC class II peptide presentation shapes the CD4+ T cell repertoire. Conventional migratory dendritic cells (cDC) participate in this process by presenting peripheral self antigens to the developing thymocytes after migration to the thymus. To evaluate the contribution of cDC in central tolerance we analyzed their HLA-DR1 eluted peptidome. Over 3000 peptides with a prediction score above identity, were sequenced. Peptides derived from both intracellular and extracellular sources displayed a snap shot of the HLA-DR1-restricted self peptidome presented under physiological conditions. Processing enzymes responsible for generating these peptides were identified and included cathepsins, metalloproteases, calpains and caspases among others. Comparative analysis between the HLA-DR1 eluted peptidome and naturally processed peptides found in the human lymph identified peptides that shared common sequences, common N or C terminal cleavage site, and few peptides that completely overlapped, indicating that peptides found in biological fluids can contribute to the overall MHC-II peptidome presented by cDC. HLA-DR1 binding affinity and HLA-DM sensitivity was evaluated for several of the mapped peptides. Peripheral injection of the eluted peptides in HLA-DR1 mice identified their role in CD4+ thymocytes selection. Altogether our data indicate that peptides found in biological fluids can shape the thymic T cell repertoire and contribute to the generation of central tolerance.