Development and heterogeneity of type 2 innate lymphoid cells in mouse lungs

Lung group 2 innate lymphoid cells (ILC2s) drive allergic inflammation and promote tissue repair. To investigate the early developmental pathways that leads to the generation of lung ILC2, I divided adult bone marrow lymphoid primed multipotent progenitor (LMPPs) into CD127⁻ (LMPP-s) and CD127⁺ (LMPP+s) subsets and compared them with Ly6D⁻ and Ly6D⁺ common lymphoid progenitors (CLPs). Although, all lymphocytes are thought to develop from CLPs, LMPP+s differentiated into T cells and ILCs more rapidly and efficiently than other progenitors in transplantation assays. These results suggested that some ILCs and T cells may develop from LMPP+s via CLP-independent pathways. To investigate whether distinct ILC2 subsets mediate the distinct ILC2 functions and elucidate their developmental relationship, we generated RORα lineage tracer mice and analyzed them by single cell RNA sequencing, flow cytometry and functional assays. Adult lung ILC2s were divided into IL-18Rα⁺ST2⁻ and IL-18Rα⁻ST2⁺ subsets. The former had an immature ILC phenotype, produced little cytokines and contained ILC progenitor like cells expressing Tcf7, whereas the latter was conventional ILC2s. Neonatal lung conventional ILC2s (IL-18Rα⁻ST2⁺) were divided into two distinct effector subsets and an IL-18Rα⁺ST2⁻Tcf7⁺ progenitor-like subset. The two effector subsets were defined by the expression of ICOS and KLRG1, and they differentially produced the growth-factor amphiregulin and type 2 cytokines. Therefore, effector ILC2s diverge into tissue-repairing and pro-inflammatory subsets, which differ in transcriptional and phenotypic properties. The IL-18Rα⁺ST2⁻Tcf7⁺ cells are likely IL-18 responsive lung ILC progenitors, which may contribute to ILC-poiesis in neonatal and inflamed lungs.Medicine, Faculty ofPathology and Laboratory Medicine, Department ofGraduat