Type 2 innate lymphoid cells (ILC2) contribute to immune homeostasis, protective immunity and tissue repair. Here we demonstrate that functional ILC2 can arise in the embryonic thymus, from shared T cell precursors, preceding the emergence of CD4 + CD8 + (double-positive) T cells. Thymic ILC2 migrated to mucosal tissues with colonization of the intestinal lamina propria. RORα expression repressed T cell development, while promoting ILC2 in the thymus. From RNA-seq, ATAC-seq and ChIP-seq data we propose a revised transcriptional circuit to explain the co-development of T cells and ILC2 from common progenitors in the thymus. When Notch signaling is present, Bcl11b dampens Nfil3/Id2 expression, permitting E protein-directed T cell commitment. However, concomitant expression of RORα overrides the Nfil3/Id2 repression, allowing Id2 to repress E proteins and promote ILC2 differentiation. Thus, we demonstrate that RORα expression represents a critical checkpoint at the bifurcation of the T cell and ILC2 lineages in the embryonic thymus.

Naïve CD4 + T lymphocytes initially undergo antigen-specific activation to promote a broad-spectrum response before adopting bespoke cytokine expression profiles shaped by intercellular microenvironmental cues, resulting in pathogen-focussed modular cytokine responses. Interleukin (IL)-4-induced Gata3 upregulation is important for the T helper 2 (T H 2) cell polarisation associated with anti-helminth immunity and misdirected allergic inflammation. Whether additional microenvironmental factors participate is unclear. Using whole mouse-genome CRISPR-Cas9 screens we discovered a previously unappreciated role for αvβ3 integrin in T H 2 cell differentiation. Low-level αvβ3 expression by naïve CD4 + T cells contributed to pan-T cell activation by promoting T-T cell clustering and IL-2/CD25/STAT5-signalling. Subsequently, IL-4/Gata3-induced selective upregulation of αvβ3 licenced intercellular αvβ3-Thy1 interactions among T H 2 cells, enhanced mTOR signalling, supported differentiation and promoted IL-5/IL-13 production. In mice, αvβ3 was required for efficient allergen-driven antigen-specific lung T H 2 cell responses. Thus, αvβ3-expressing T H 2 cells form multicellular factories to propagate and amplify T H 2 responses.

Type-2 immunity is characterised by interleukin (IL)-4, IL-5 and IL-13, eosinophilia, mucus production, IgE, and alternatively activated macrophages (AAM). However, despite the lack of neutrophil chemoattractants such as CXCL1, neutrophils, a feature of type-1 immunity, are observed in type-2 responses. Consequently, alternative mechanisms must exist to ensure that neutrophils can contribute to type-2 immune reactions without escalation of deleterious inflammation. We now demonstrate that type-2 immuneassociated neutrophil infiltration is regulated by the mouse RNase A homologue, eosinophil-associated ribonuclease 11 (Ear11), which is secreted by AAM downstream of IL-25-stimulated ILC2. Transgenic overexpression of Ear11 resulted in tissue neutrophilia, whereas Ear11-deficient mice have fewer resting tissue neutrophils, whilst other type-2 immune responses are not impaired. Notably, administration of recombinant mouse Ear11 increases neutrophil motility and recruitment. Thus, Ear11 helps maintain tissue neutrophils at homoeostasis and during type-2 reactions when chemokine-producing classically activated macrophages are infrequently elicited.

The development of innate lymphoid cell (ILC) transcription factor reporter mice has shown a previously unexpected complexity in ILC hematopoiesis. Using novel polychromic mice to achieve higher phenotypic resolution, we have characterized bone marrow progenitors that are committed to the group 1 ILC lineage. These common ILC1/NK cell progenitors (ILC1/NKP), which we call "aceNKPs", are defined as lineage – Id2 + IL-7Rα + CD25 – α4β7 – NKG2A/C/E + Bcl11b – . In vitro, aceNKPs differentiate into group 1 ILCs, including NK-like cells that express Eomes without the requirement for IL-15, and produce IFN-γ and perforin upon IL-15 stimulation. Following reconstitution of Rag2 –/– Il2rg –/– hosts, aceNKPs give rise to a spectrum of mature ILC1/NK cells (regardless of their tissue location) that cannot be clearly segregated into the traditional ILC1 and NK subsets, suggesting that group 1 ILCs constitute a dynamic continuum of ILCs that can develop from a common progenitor. In addition, aceNKP-derived ILC1/NK cells effectively ameliorate tumor burden in a model of lung metastasis, where they acquired a cytotoxic NK cell phenotype. Our results identify the primary ILC1/NK progenitor that lacks ILC2 or ILC3 potential and is strictly committed to ILC1/NK cell production irrespective of tissue homing.