Runx/Cbfβ complexes protect group 2 innate lymphoid cells from exhausted-like hyporesponsiveness during allergic airway inflammation

Regulating the development of pulmonary Group 2 innate lymphoid cells

Group 2 innate lymphoid cells (ILC2s) are members of the family of innate lymphoid cells and are innately committed to type 2 immune responses. In the lungs, ILC2s are the predominant population of innate lymphoid cells (ILCs) and their development is orchestrated by several different transcription factors ensuring lineage commitment by intrinsic regulation. ILC2s are present in the lungs from the foetal period onwards and are thus exposed to extrinsic regulation due to the airways' continuous morphological changes upon birth. In this review, we will briefly summarise the dependence of ILC2s on transcription factors and discuss recently described characteristics and function of early life ILC2s in the lungs.

RUNX transcription factors: orchestrators of development

RUNX transcription factors orchestrate many different aspects of biology, including basic cellular and developmental processes, stem cell biology and tumorigenesis. In this Primer, we introduce the molecular hallmarks of the three mammalian RUNX genes, RUNX1, RUNX2 and RUNX3, and discuss the regulation of their activities and their mechanisms of action. We then review their crucial roles in the specification and maintenance of a wide array of tissues during embryonic development and adult homeostasis.

KLRG1 and NKp46 discriminate subpopulations of human CD117+CRTH2- ILCs biased toward ILC2 or ILC3

Recently, human ILCs that express CD117 and CD127 but lack CRTH2 and NKp44 have been shown to contain precursors of ILC1, ILC2, and ILC3. However, these ILCs have not been extensively characterized. We performed an unbiased hierarchical stochastic neighbor embedding (HSNE) analysis of the phenotype of peripheral blood CD117⁺ ILCs, which revealed the presence of three major subsets: the first expressed NKp46, the second expressed both NKp46 and CD56, and the third expressed KLRG1, but not NKp46 or CD56. Analysis of their cytokine production profiles and transcriptome revealed that NKp46⁺ ILCs predominantly develop into ILC3s; some of them can differentiate into ILC1/NK-like cells, but they are unable to develop into ILC2s. In contrast, KLRG1⁺ ILCs predominantly differentiate into ILC2s. Single-cell cultures demonstrate that KLRG1⁺ ILCs can also differentiate into other ILC subsets depending on the signals they receive. Epigenetic profiling of KLRG1⁺ ILCs is consistent with the broad differentiation potential of these cells.

Transcription Factors in the Development and Function of Group 2 Innate Lymphoid Cells

Group 2 innate lymphoid cells (ILC2s) are tissue-resident cells and are a major source of innate T_H2 cytokine secretion upon allergen exposure or parasitic-worm infection. Accumulating studies have revealed that transcription factors, including GATA-3, Bcl11b, Gfi1, RORα, and Ets-1, play a role in ILC2 differentiation. Recent reports have further revealed that the characteristics and functions of ILC2 are influenced by the physiological state of the tissues. Specifically, the type of inflammation strongly affects the ILC2 phenotype in tissues. Inhibitory ILC2s, memory-like ILC2s, and ex-ILC2s with ILC1 features acquire their characteristic properties following exposure to their specific inflammatory environment. We have recently reported a new ILC2 population, designated as exhausted-like ILC2s, which emerges after a severe allergic inflammation. Exhausted-like ILC2s are featured with low reactivity and high expression of inhibitory receptors. Therefore, for a more comprehensive understanding of ILC2 function and differentiation, we review the recent knowledge of transcriptional regulation of ILC2 differentiation and discuss the roles of the Runx transcription factor in controlling the emergence of exhausted-like ILC2s. The concept of exhausted-like ILC2s sheds a light on a new aspect of ILC2 biology in allergic diseases.