The requirement for pro-inflammatory cytokine production in clearing R. equi was further illustrated by Darrah and colleagues, who showed that IFN-γ deficient (Ifng-/-) mice infected with low dose R. equi were hypersusceptible to infection (died 13 days post-infection), and mice with impaired nitric oxide (Nos2-/-) or superoxide (Gp91phox-/-) production were even more susceptible and died by days 7.5 and 9.5 post infection, respectively [23]. The gene discussed is IFNG; the disease is infection.