Update on innate lymphoid cells in atopic and non-atopic inflammation in the airways and skin.

Innate lymphoid cells (ILC) is the collective term for a group of related innate lymphocytes, including NK cells and the more recently appreciated non-NK ILC (ILC1, ILC2 and ILC3). ILC all depend on the common γ-chain of the IL-2 receptor and the transcription factor Id2. Furthermore, ILC lack rearranged antigen-receptors such as those expressed by T and B cells. Recent data indicate that non-NK ILC contribute to a wide range of homeostatic and pathophysiological processes primarily by virtue of cytokine production. A lot of effort has been put into understanding the role for the non-NK ILC in mucosal homeostasis, including in the gut and lungs. Recent reports also point towards a role for ILC in skin inflammation. In the lung, ILC may propagate stromal-derived danger signals, with subsequent induction of mainly type 2 cytokine production. This might represent an early trigger of type 2-mediated pathology, which subsequently also engages the adaptive immune system. Similarly, in the skin, ILC are well placed to sense keratinocyte-derived danger signals in an antigen-independent manner. Recent findings link ILC2 to atopic dermatitis and ILC3 to psoriasis. In this review, we provide an updated perspective on the role for non-NK ILC in atopic and non-atopic inflammation in the airways as well as in the skin.