IFN-I signaling in type 2 conventional dendritic cells supports TH2 and T follicular helper differentiation after allergen immunization

Type 2 dendritic cells (DC2s) are essential for TH2 differentiation, but the signaling pathways involved in allergen sensing, DC activation and instruction of CD4+ T cell priming remain unclear. Previous transcriptomic analyses demonstrated a type-I interferon (IFN-I) signature in skin cDC2s following immunization with non-viable larvae of Nippostrongylus brasiliensis (Nb), house dust mite (HDM), and Schistosoma egg antigen (SEA). Blocking IFN-I signaling with anti-IFNAR1 (aIFNAR1) led to reduced TH2 cytokine responses to these antigens, however, the phenotype of cytokine-producing CD4+ T cells was not further defined. Here we show that conditional loss of IFNAR1 signaling in CD11c+ DCs significantly impaired effector TH2 and TFH CD4+ T cell responses to Nb. In vivo proliferation experiments demonstrated reduced numbers of highly divided CD4+ T cells in IFNAR1{Delta}CD11c mice compared to IFNAR1WT, with the highly divided population comprising both TH2 and TFH. Characterization of the cDC2 compartment by flow cytometry and bulk RNAseq demonstrated lower numbers of Nb+ cDC2s in the skin-draining LN and a reduced expression of Il15 and Il15Ra in IFNAR1{Delta}CD11c mice compared to IFNAR1WT, while expression of costimulatory molecules including CD80, CD86, Cd40 and Pdcd1lg2 (PD-L2) was not impaired. Therefore, IFN-I conditioning of skin cDC2s is necessary for their effective priming of CD4+ T cell responses to allergens, providing evidence for a role of tissue cytokines in driving cDC2 activation in a TH2 context.