Type 2 cytokines in the thymus activate Sirpa+ dendritic cells to promote clonal deletion

The thymus contains a diversity of dendritic cells (DC) that exist in defined locations and have different antigen processing and presenting features. This suggests that they play non-redundant roles in mediating thymocyte selection. In an effort to eliminate SIRP+ cDC2, we discovered that a substantial proportion expresses the surface lectin, CD301b, in the thymus. These cells resemble the CD301b+ type 2 immune response promoting DC that are present in the skin draining lymph nodes. Transcriptional and phenotypic comparison to other DC subsets in the thymus revealed that thymic CD301b+ cDC represent an activated state that exhibits enhanced antigen processing and presentation. Furthermore, CD301b+ cDC2 demonstrated a type 2 cytokine signature and required steady state IL-4 receptor signaling. Selective ablation of CD301b+ cDC2 impaired clonal deletion without affecting regulatory T cells. TCR alpha repertoire sequencing confirmed that cDC2 promote deletion of conventional T cells with minimal effect on regulatory T cell selection. Together, these findings suggest that cytokine-induced activation of DC in the thymus substantially enforces central tolerance. CD11c and CD11b expressing cells were sorted from the thymus of 7-week-old wildtype (WT) and Mgl2DTR_eGFP treated with diptheria toxin for 48 hours and cells were submitted for scRNA sequencing