In this respect, both NKT cells and γδ-T cells have been identified as major sources of IL-17 production at mucosal surfaces, providing protection against P. aeruginosa (Nieuwenhuis et al., 2002; Coquet et al., 2008; Sutton et al., 2012), and NK cells have been shown to secrete IL-22 following Gram-negative pneumonia (Aujla et al., 2008). Here, IL17A is linked to bacterial pneumonia.