Single cell RNA sequencing of thymic dendritic cells reveals molecular determinants of antigen transfer in the thymus

The presentation of self-antigens in the thymus by medullary thymic epithelial cells (mTECs) and dendritic cells (DCs) is crucial for the establishment of central tolerance. While mTECs produce and present self-antigens in an autonomous manner, DCs acquire them from mTECs by Cooperative Antigen Transfer (CAT). Although CAT represents a key process of central tolerance, molecular determinants which drive CAT are largely unknown. To reveal these determinants, we compared the transcriptomes of CAT-experienced and CAT-inexperienced DCs via scRNAseq. Specifically, we sequenced TdTOMATO+ and TdTOMATO– CD11c+ and CD11b+ cells from the thymus of Foxn1CreR26TdTOMATO mice. In this model, fluorescent TdTOMATO protein is exclusively produced by thymic epithelium, thus TdTOMATO expression in DCs (CD11c+ and CD11b+ cells) mark their previous experience of CAT. Using this approach we unraveled several candidate determinants of CAT. We focused on the gene determinant, Cldn1, encoding the tight junction protein Claudin 1, that was found to be highly expressed among the CAT-experienced type 1 lineage DCs. We performed further experiments that confirmed its role in driving CAT. In addition, this scRNAseq approach allowed us to redefine the heterogeneity and maturation states of thymic DCs.