IL21 and bacterial infectious disease: Although the IL-17 cytokine family is associated with cells of the adaptive arm of the immune system, in bacterial infections such as those caused by P. aeruginosa, innate immune cells are the first responders in secretion of IL-17, IL-21, IL-22, and IL-23 (Nieuwenhuis et al., 2002; Aujla et al., 2008; Coquet et al., 2008; Sutton et al., 2012).