IL17A and inflammatory bowel disease: It should be pointed out that besides the high efficacy of blocking IL-23 (e.g., by ustekinumab) as well as the important role of the IL-23/IL-17 axis in IBD pathogenesis and severity [4, 49–51, 68], the IL-17 neutralizing agent, secukinumab, is ineffective in CD patients in RCT [69].