The contribution of Th17 cells to the development of colitis is well described. 
The effector cytokines IL-17A and IL-17F have been proposed as potential 
therapeutic targets for the treatment of patients with inflammatory bowel 
disease. In a proof-of-concept study for the treatment of patients with Crohn's 
disease, secukinumab, a monoclonal antibody directed against IL-17A, was 
ineffective and associated with more adverse events than placebo. Wedebye 
Schmidt et al. propose that blockade of both IL-17A and IL-17F, rather than 
either cytokine alone, attenuates the development of colitis in a T-cell 
transfer model of experimental colitis. These findings suggest that combined 
blockade of IL-17A and IL-17F may be an effective strategy for the treatment of 
patients with inflammatory bowel disease.