Cross-species analyses reveal RORγt-expressing dendritic cells are a lineage of antigen presenting cells conserved across tissues

Conventional dendritic cells (cDCs) are potent antigen presenting cells (APCs) that exhibit tissue and age-specific diversity allowing them to direct situation-adapted immunity. Thereby they harbor great potential for being targeted in vaccination and cancer. Here, we resolve conflicting data about expression of retinoic acid receptor-related orphan receptor-γt (RORψt) in cDCs. We show that RORψt+ DCs exist in murine lymphoid and non-lymphoid tissues across age. Fate mapping, functional assays and single cell multiomic profiling reveal these cells as ontogenetically and transcriptionally distinct from other well characterized cDC subtypes, as well as from RORψt+ type 3 innate lymphocytes (ILC3s). We show that RORψt+ DCs can migrate to lymph nodes and activate naïve CD4+ T cells in response to inflammatory triggers. Comparative and cross-species transcriptomics revealed homologous populations in human spleen, lymph nodes and intestines. Further, integrated meta-analyses aligned RORψt+ DCs identified here with other emerging populations of RORψt+APCs, including R-DC-like cells, Janus cells/extrathymic Aire expressing cells (eTACs) and subtypes of Thetis cells. While RORψt+APCs have primarily been linked to T cell tolerance, our work establishes RORψt+ DCs as unique lineage of immune sentinel cells conserved across tissues and species that expands the functional repertoire of RORψt+ APCs beyond promoting tolerance. One sentence summary RORγt+ DC exhibit versatile APC functions and are a distinct immune lineage conserved across age, tissues and species that entails Thetis cells, Janus cells/RORγt+ eTACs and R-DC-like cells. ### Competing Interest Statement The authors have declared no competing interest.