Gut-Busters: IL-17 Ain't Afraid of No IL-23.

Interleukin-23 (IL-23) is considered a critical regulator of IL-17 in lymphocytes. Whereas antibodies targeting IL-23 ameliorate colitis, IL-17 neutralization exacerbates disease. In this issue, Cua and colleagues and Maxwell and colleagues show that IL-17 maintains intestinal barrier integrity, helping explain this dichotomy (Lee et al., 2015; Maxwell et al., 2015).