ILC2: at home in the thymus.

The relevance of innate lymphoid cells (ILC) for anti-infectious immunity remains a matter of constant debate. At the same time, evidence for additional, non-immune related functions of ILC is steadily increasing. In the thymus, non-immune functions of ILC were shown for group 3 ILC (ILC3), which regulate differentiation and proliferation of thymic epithelial cells. In this issue of the European Journal of Immunology, Withers and colleagues [Eur. J. Immunol. 2018. 48: 1481-1491] now show that ILC2, a subset of ILCs specialized in tissue protection and regeneration, are the major ILC subset in the adult thymus, heavily outnumbering ILC3. These findings raise novel questions on the function of thymic ILC, and warrant re-evaluation of the importance of ILC2 and their cytokines during thymic function and repair.