Type 2 innate lymphoid cells: new players in asthma and allergy.

Two years ago, T helper cells, including Th1, Th2 and Th17 cells, were considered to be the most significant sources of cytokine during the orchestration of immune responses in the lung. Following the discovery of innate lymphoid cells, we now know that these previously unappreciated cytokine-secreting cells, including ILC1 (IFN-γ-expressing NK cells), ILC2 (IL-5 and IL-13-expressing nuocytes) and RORγ ILC (IL-17 and IL-22-expressing 'ILC3') are important mediators in immune processes. Herein we review the role of ILC2 specifically in inflammatory lung responses with special attention to allergen-induced and viral-induced type 2 lung disease.