Innate lymphoid cells (ILCs) are identified as novel population of hematopoietic cells which protect the body by coordinating the innate immune response against a wide range of threats including infections, tissue damages and homeostatic disturbances. ILCs, particularly ILC2 cells, are found throughout the body including the brain. ILCs are morphologically similar to lymphocytes, express and release high levels of T-helper (Th)1, Th2 and Th17 cytokines but do not express classical cell-surface markers that are associated with other immune cell lineages. Three types of ILCs (ILC1, 2 & 3) have been reported depending upon the cytokines produced. ILC1 cells encompass natural killer (NK) cells and interferon (IFN)-g releasing cells; ILC2 cells release the Th2 cytokines, IL-5, IL-9 and IL-13 in response to IL-25 and IL-33; and ILC3 cells which release IL-17 and IL-22. ILC2 cells have been implicated inmucosal reactions occurring in animal models of allergic asthma and virus-induced lung disorders resulting in the regulation of airway remodeling and tissue homeostasis. There is evidence for increased ILC2 cell numbers in allergic responses in man but little is known about the role of ILCs in chronic obstructive pulmonary disease (COPD). Further understanding of the characteristics of ILCs such as their origin, location and phenotypes and function would help to clarify the role of these cells in the pathogenesis of various lung diseases. In this review we will focus on the role of ILC2 cells and consider their origin, function,location and possible role in the pathogenesis of the chronic inflammatory disorders such as asthma and COPD.
Keywords: Cytokines; IL-17; IL-22; ILCs; Respiratory tract.