ICOS is related to the CD28 superfamily and is highly expressed on activated T cells as well as regulatory T cells and is crucial for the survival and function of T cells, Th2 cell differentiation and for lung inflammatory responses. Binding ICOS to ICOS-Ligand activates a cascade of intracellular signaling molecules that prevent apoptosis and lead to the production of cytokines such as IL-4 and IL-13 . To date, ICOS Ligand has been reported to be expressed by B cells, non-lymphoid and lung epithelial cells but not by T cells or innate lymphoid cells and is down-regulated upon binding to ICOS as an immunoregulatory mechanism. The functional requirement of ICOS for the function and survival of ILC2 remains to be elucidated.
Maazi H, Patel N, Sankaranarayanan I, et al. ICOS:ICOS-Ligand interaction is required for type 2 innate lymphoid cell function, homeostasis and induction of airway hyperreactivity. Immunity. 2015;42(3):538-551.