IL17A and inflammatory bowel disease: Increasingly evidence has prompted that plasticity of interleukin (IL)-17 secreting T helper (Th17) cells plays a crucial role in both conditions of IBD, of which the flexibility allow this subset to embrace pro-inflammatory and protective roles in mucosal immunity by secreting a spectrum of cytokines without requiring de novo differentiation of naïve T cells (Koenen et al., 2008; Harbour et al., 2015; Ueno et al., 2015).