Intriguingly, pretreatment of D2-Mx1r/r mice with interferon [11] or with defective interfering particles protects D2-Mx1r/r from severe IAV disease [12, 13] and death, most likely because functional MX1 protein is produced before infection, thus inhibiting the rapid spread of virus in the early infection phase. The gene discussed is MX1; the disease is infection.