Interleukin-22-producing innate immune cells: new players in mucosal immunity and tissue repair?

Recent studies have identified a new population of interleukin-22-producing cells in mucosal tissues that share features with both lymphoid-tissue inducer cells and natural killer cells. How are these three cell populations related and what might be the function of the new cell population? Mucosal tissues, lying at the interface with the external environment, are constantly challenged by microbial, physical and chemical assaults. To provide the necessary immune defence to such challenges, lymph nodes and Peyer's patches are formed in utero in response to inductive signals from lymphoid-tissue inducer (LTi) cells. As discussed in this Progress article, a series of recent reports has identified a population of interleukin-22-producing mucosal cells in the gut and tonsils that share features with both LTi cells (by expressing RORγt) and natural killer cells (by expressing NKp46) and that might be involved in immunity and homeostasis in mucosal tissues.