IFNG and infection: Considering that patients with milder severity had higher frequencies of epitope-specific CTLs during the acute phase of infection, we speculated that HTNV GP epitope-specific CTLs might have been generated at an early time point after HTNV infection and elicited effective protective IFN-γ-producing CTL responses against HTNV in patients with milder HFRS rather than in those with more severe infection.