Unravelling the expression of interleukin-9 in chronic rhinosinusitis: A possible role for Staphylococcus aureus.

Chronic rhinosinusitis with nasal polyps (CRSwNP) is a Th2 biased inflammation, associated with nasal colonization of Staphylococcus (S.) aureus. Interleukin (IL)-9 is a pro-inflammatory Th2 cytokine with a pivotal role in asthma, allergy and chronic obstructive pulmonary disease (COPD), but is less studied in CRSwNP. We aimed to characterize the expression and cellular source of IL-9 and examined S. aureus as potential local trigger in CRSwNP. We showed increased numbers of interleukin-9 producing neutrophils and mononuclear cells in the tissue of CRSwNP patients. This interleukin-9 production was stimulated by S. aureus and its enterotoxin B in vitro. These findings underline the contribution of S. aureus and define IL-9 as another relevant cytokine in type 2 CRSwNP.