Innate lymphoid cells in the upper airways: importance of CD117 and IL-1RI expression

• Although type 1, 2 and 3 innate lymphoid cells (ILC1s, ILC2s and ILC3s, respectively) are emerging as important cell populations regulating tissue homeostasis, remodelling and inflammation, a vast majority of our knowledge stems from in vitro and murine experiments, and requires thorough confirmation in human diseases.Relative levels of ILCs were evaluated by means of flow cytometry in freshly resected human upper airways mucosa of patients with chronic rhinosinusitis without nasal polyps (CRSsNP) and with nasal polyps (CRSwNP), taking into account the patient's clinical parameters and disease comorbidities.We report that the CD117 and interleukin-receptor type I (IL-1RI) expression status of human ILC2s depends on the local tissue environment. Only CD117+ IL-1RI+ ILC2s, exclusively present in CRSwNP, possess an interrelationship with type 2 T-helper cell cytokine and eosinophil levels in human upper airway mucosa. In CRSsNP, mainly CD117−IL-1RI− ILC2s are increased, yielding lower eosinophilia in this disease despite the high levels of ILC2s.These data unveil that the CD117− and CD117+ fractions within the native human ILC2 population are not a random phenomenon, in contrast to what could be concluded from in vitro data, and that the IL-1RI expression is not ubiquitous in ILC2s in vivo in humans, which cannot be assessed via in vitro and murine experiments.

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