While Th1 immunity, characterised by IFN-γ, has been linked with susceptibility to gastrointestinal nematodes [26], other studies indicate that Th1 immunity can be linked with resistance to H. contortus, for example, Caribbean hair sheep show higher IFN-γ production than susceptible sheep at 4 weeks post-infection [27]. The gene discussed is IFNG; the disease is infection.