IFNAR1 and infection: However, since MyD88-deficient mice harbor only a mild increase in susceptibility to MCMV infection as compared to IFNAR-deficient mice, these types of systemic IFN-I responses might be rather required to prevent concomitant heterologous infections or for defense against viruses able to cause chronic infections, by allowing a systemic state of pathogen alert with induction of protective responses in all tissues.