Exhausted-like Group 2 Innate Lymphoid Cells in Chronic Allergic Inflammation

Mammalian group 2 innate lymphoid cells (ILC2s) are responsible for the early production of type 2 cytokines at mucosal barriers upon exposure to allergen. Inflammatory tissue environmental cues can influence ILC2 activity, and this cellular population can be further categorized into subtypes with additional or alternative functions. Subtypes can include trained (or 'memory-like') ILC2s, which recall previous allergic inflammation, inflammatory ILC2s, which acquire the ability to produce IL-17, and ex-ILC2s, which produce ILC1 cytokines. However, the functional states of ILC2s at sites of chronic or severe inflammation are not well characterized. Here, we discuss the emergence of ILC2s with 'exhausted'-like signatures, and argue that their hyporesponsiveness to stimulation and expression of inhibitory receptors is relevant in mammalian chronic allergic inflammation.