Innate lymphoid cells: key players in tissue-specific immunity

Excerpt

The discovery of innate lymphoid cells (ILCs) as a separate lineage of leukocytes with specialized subsets has profoundly changed our view of the immune system in the last decade. Although NK cells, as the first known member of this family, were identified already in the late 1970s [1], it took more than 20 years until the next ILC subtype, the ROR-γt⁺ lymphoid tissue inducer cell, was discovered [2, 3]. In the next years, sporadic reports indicated that the family of innate lymphocytes might actually be more heterogeneous than previously thought [4‐6]. However, it was the observation (made in the late 2000s) that NK cell receptor-positive IL-22-producing innate lymphocytes were clearly distinct from conventional NK cells [7‐10], together with the description of type 2 cytokine-producing ILCs in 2010 [11‐14] and the identification of committed ILC progenitors [15, 16] that finally led to the definition of ILCs as a heterogeneous group of lymphocytes that represent an independent leukocyte lineage. During the last decade, extensive investigations into all aspects of ILC biology have provided us with a detailed understanding of development, activation, and effector functions of different ILC subtypes in various tissue locations. The current issue of Seminars in Immunopathology comprises a series of reviews that cover general principles and tissue-specific functions of ILCs in homeostasis and inflammatory diseases. …