STAT1 and viral infectious disease: While an interferon-resistant cell line with entire STAT1 induction has been reported (Yang et al, 1998), STAT1 seems to be an essential component of interferon signalling as STAT1 deficient mice do not respond to interferons and are highly sensitive toward viral infections (Durbin et al, 1996; Meraz et al, 1996); in addition complementation of the IFN-unresponsive mutant cell line U3 interferon with STAT1, cDNA constructs reportedly restores ISGF3 formation and transcriptional response to interferon (Müller et al, 1993).