Innate Lymphoid Cells (ilcs) Generate Memory for Pathogen-Associated Molecular Patterns (pamps) of Allergens, Which Contributes to Asthma

ILCs do not express antigen-specific receptors. Whether they are capable of generating memory for allergens is unknown. Mouse model of asthma, single cell RNA-seq and flow cytometry Exposure of Rag1 KO mice intranasally to PAMP-containing (Alternaria, dust mite, papain) allergens 3 days/week for 3 weeks generated a form of memory, which elicited an asthma-like response (airway hyperreactivity, eosinophilic inflammation and IL5+IL13+ ILC2s in the lung) upon a recall challenge with a subthreshold dose of the allergen 3-9 weeks later. This memory was PAMP-dependent and PAMP-specific. Ovalbumin, which lacks a PAMP, was ineffective. Alternaria-induced memory was recalled by Aspergillus (both contain the PAMP serine protease) but not dust mite (contains cysteine protease) challenge. Conversely, papain (a cysteine protease)-induced memory could be recalled by dust mite challenge. Sensitization with Alternaria that was pretreated with the serine protease inhibitor AEBSF abrogated memory-induced asthma implicating a role for serine protease-PAR2 interaction. Antibody-mediated elimination of NK cells did not affect memory-driven asthma suggesting a primary role for ILCs. Single cell RNA-seq identified 297 differentially expressed genes in the memory model. We validated upregulation of select genes including ICOS, CD90 and FHL2 by flow cytometry. Adoptive transfer of Alternaria-sensitized mouse lung ICOS+ ILC2s and human lung FHL2+ ILC2s to Rag2-/-:γc-/- mice induced asthma upon Alternaria challenge. Genetic and antibody-mediated depletion of ICOS inhibited memory-driven asthma. Likewise, antibody-mediated depletion of CD90 abrogated asthma. ILCs generate memory for allergen-associated PAMPs, which is associated with upregulation of select genes. Interference with these memory-associated ILC expressed genes may benefit asthma.