Description
RORt+ innate lymphoid cells (ILC) are crucial players of innate immune responses and represent a major source of IL-22, which has an important role in mucosal homeostasis. The signals required by RORt+ ILC to express IL-22 and other cytokines, including TNF, have only partially been elucidated. Here we show that RORt+ ILC can directly sense the environment by the engagement of the activating receptor NKp44. NKp44 triggering in RORt+ ILC selectively activates a coordinated pro-inflammatory program, including TNF, while cytokine stimulation induces preferentially IL-22 expression. However, combined engagement of NKp44 and cytokine receptors results in a strong synergistic effect. These data support the concept that NKp44+ RORt+ ILC can be activated without cytokines and are able to switch between IL-22 or TNF production, depending on the triggering stimulus.