Single-cell transcriptomics reveals heterogenous thymic dendritic cell subsets with distinct functions and requirements for thymocyte-regulated crosstalk

Dendritic cells (DCs) are essential for establishing central tolerance in the thymus; however, mechanisms supporting their homeostasis and activation remain unresolved. Through single-cell transcriptomics and functional assays, we identify seven thymic conventional DC (cDC) subsets and discriminate their abilities to present self-antigens and induce regulatory T cells (Tregs). Mice blocked at different stages of T-cell development reveal that CD4+ single-positive (SP) and CD8SP thymocytes differentially support homeostasis and activation of cDC1s versus cDC2s/ plasmacytoid DCs (pDCs), respectively. CD8SP regulate cDCs via interferon signaling, while CD4SP promote NF- kB activation. CD40, which activates non-canonical NF-kB signaling, is required for both activation and homeostasis of cDC1s, although only activation is driven by cognate interactions with CD4SPs. Surprisingly, some DCs display an activated signature in the absence of mature thymocytes. Altogether, this study comprehensively identifies functionally distinct thymic DC subsets and elucidates requirements for crosstalk with thymocyte subsets that support their homeostasis and activation. ### Competing Interest Statement The authors have declared no competing interest.