Both Horatio and Polonius: Innate Lymphoid Cells in Tissue Homeostasis and Repair.

Innate lymphoid cells (ILCs) have emerged as critical tissue-resident lymphocytes that coordinate responses to environmental stress and injury. Traditionally, their function was thought to mirror adaptive lymphocytes that respond to specific pathogens. However, recent work has uncovered a more central role for ILCs in maintaining homeostasis even in the absence of infection. ILCs are now better conceptualized as an environmental rheostat that helps maintain the local tissue setpoint during environmental challenge by integrating sensory stimuli to direct homeostatic barrier and repair programs. In this article, we trace the developmental origins of ILCs, relate how ILCs sense danger signals, and describe their subsequent engagement of appropriate repair responses using a general paradigm of ILCs functioning as central controllers in tissue circuits. We propose that these interactions form the basis for how ILC subsets maintain organ function and organismal homeostasis, with important implications for human health.