IL-23, which shares in common with IL-12 the p40 subunit, IL-12Rβ1, and components of signal transduction [5], is associated with Th17 responses, yet the role of IL-17 in parasite-induced ileitis is unclear; severe intestinal immunopathology was found in IL-17A-/- mice following oral infection with 100 ME-49 cysts [6], whereas IL-17RA-/- and IL-17R-/- mice presented decreased ileitis when orally infected with 30 and 15 cysts of the 76K strain, respectively [7,8]. This evidence concerns the gene IL12RB1 and Crohn ileitis.