Mx1, also known as myxovirus resistance 1, encodes a GTPase that is an interferon-induced protein. It plays a crucial role in the innate antiviral immune response, restricting the replication of a variety of viruses, especially RNA viruses such as influenza A virus, Thogoto virus, and zoonotic avian influenza A virus [2,3,1]. Mx1 is considered an important part of the host's defense mechanism against viral infections, and its activity is independent of other interferon-induced genes in some cases [2].

In gene knockout studies, Mx1-/-mice were susceptible to influenza A virus challenge infection, indicating that Mx1 expression in the non-hematopoietic cellular compartment is required for protection against influenza virus [2]. Also, in the context of zoonotic H7N9 influenza virus, rare, heterozygous single-nucleotide variants in the MX1 gene were associated with increased human susceptibility, as most of the MxA variants identified lost the ability to inhibit H7N9, and nearly all of the inactive MxA variants exerted a dominant-negative effect on the antiviral function of wild-type MxA [1].

In conclusion, Mx1 is a key component of the innate antiviral immune response, protecting against various viral infections. Gene knockout mouse models have been instrumental in revealing its role in influenza virus and zoonotic H7N9 influenza virus infections, highlighting its importance in understanding the host-pathogen interaction and potential for developing antiviral strategies.