Abstract
Secondary bacterial pneumonia is a significant complication of severe influenza infection and Staphylococcus aureus and Streptococcus pneumoniae are the primary pathogens of interest. IL-22 promotes S. aureus and S. pneumoniae host defense in the lung through epithelial integrity and induction of antimicrobial peptides and is inhibited by the soluble decoy receptor IL-22-binding protein (IL-22BP). Little is known about the effect of the IL-22/IL-22BP regulatory pathway on lung infection, and it has not been studied in the setting of super-infection. We exposed wild-type and IL-22BP(-/-) mice to influenza A/PR/8/34 for 6 days prior to infection with S. aureus (USA300) S. pneumoniae. Super-infected IL-22BP(-/-) mice had decreased bacterial burden and improved survival compared to controls. IL-22BP(-/-) mice exhibited decreased inflammation, increased lipocalin 2 expression, and deletion of IL-22BP was associated with preserved epithelial barrier function with evidence of improved tight junction stability. Human bronchial epithelial cells treated with IL-22Fc showed evidence of improved tight junctions compared to untreated cells. This study revealed that IL-22BP(-/-) mice are protected during influenza, bacterial super-infection, suggesting that IL-22BP has a pro-inflammatory role and impairs epithelial barrier function likely through interaction with IL-22.