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

The thymus contains a diversity of dendritic cells (DCs) that exist in defined locations and have different antigen-processing and -presenting features. This suggests that they play nonredundant roles in mediating thymocyte selection. In an effort to eliminate SIRPα⁺ classic DC2 subsets, we discovered that a substantial proportion expresses the surface lectin, CD301b, in the thymus. These cells resemble the CD301b⁺ type 2 immune response promoting DCs that are present in the skin-draining lymph nodes. Transcriptional and phenotypic comparison to other DC subsets in the thymus revealed that thymic CD301b⁺ cDCs represent an activated state that exhibits enhanced antigen processing and presentation. Furthermore, a CD301b⁺ cDC2 subset demonstrated a type 2 cytokine signature and required steady-state interleukin-4 receptor signaling. Selective ablation of CD301b⁺ cDC2 subsets impaired clonal deletion without affecting regulatory T cells (T_reg cells). The T cell receptor α repertoire sequencing confirmed that a cDC2 subset promotes deletion of conventional T cells with minimal effect on T_reg cell selection. Together, these findings suggest that cytokine-induced activation of DCs in the thymus substantially enforces central tolerance.