Ly6G+Nur77+ macrophages initiate the type-2 immune response to allergens in the lung

The mechanisms of allergen sensing and type 2 immune response initiation remain unclear. Using a house dust mite (HDM)-induced allergic airway model, we demonstrated that host detection of protease activity in HDM was crucial for initiating T helper type 2 (Th2) responses. This process was driven by the major allergen Der p 1, a cysteine protease, which was sensed by protease-activated receptor 2 (PAR2) on a novel population of perivascular lung macrophages expressing Ly6G and nuclear receptor Nur77. These macrophages required PAR2 and Nur77 for activation and accumulation and regulated conventional dendritic cell (mDC) migration to draining mediastinal lymph nodes (mLN) via cysteinyl leukotriene (CysLTs) production. CysLTs enhanced CCR7-driven migration of mDCs toward its ligand, CCL21, facilitating arrival to mLNs for T cell priming and expansion. Inhibiting CysLTs biosynthesis reduced mDC migration and dampened Th2 allergic responses, highlighting new therapeutic paths and mechanisms in type 2 immunity. Overall design: This study aims to compare allergen-activated Ly6G? macrophages (Ly6G? MF) and non-classical monocytes in the lung using single-cell RNA sequencing (scRNA-seq). Eight-week-old C57BL/6J mice (Mus musculus) were treated intranasally with 10 µg of the cysteine protease papain in a 100 µL volume. After 24 hours, lungs were processed into a single-cell suspension, and two distinct cell populations were isolated by fluorescence-activated cell sorting (FACS): Ly6G?Ly6C?CX3CR1?CD11b^hi SIGLEC-F? macrophages (Ly6G? MF) and Ly6G?Ly6C?CX3CR1?CD11b?SIGLEC-F?CD16.2^hi non-classical monocytes. The sorted cells were subjected to scRNA-seq to characterize their transcriptional profiles. This dataset provides insights into the relationship and functional differences between these allergen-responsive myeloid subsets in the lung.