STAT1 and infection: STAT1-knockout (STAT1-/-) BALB/c mice, which are incapable of responding to type II IFN (IFN-β) or to type I IFN (IFN-α and β ), showed markedly increased levels of inflammation, compared with wild-type (WT) mice, after infection with RSV, despite similar virus titers in the lung and similar rates of viral clearance (Durbin et al., 2002).