IL17A and psoriatic arthritis: Quite surprisingly, besides the high efficacy of blocking IL-17 in other chronic inflammatory conditions, such as psoriasis, psoriatic arthritis, and ankylosing spondylitis, as well as the relevant role of IL-17 in CD pathogenesis and severity (Jiang et al., 2014), the IL-17 blockers, secukinumab and brodalumab, further worsened disease activity in CD patients in RCT trials (Hueber et al., 2012; Targan et al., 2016).