Since MxA is archetypic of Mx1 proteins in general, we reasoned that the L4 loop also functions as a recognition platform for influenza viruses in the Mx1 proteins of other species that had been exposed to the virus for ever.
Mouse MX1 interacts with the influenza ribonucleoprotein complexes (vRNPs) and can prevent the interaction between polymerase basic 2 (PB2) and the nucleoprotein (NP) of influenza A viruses.
Here, we show that, very unexpectedly, congenic D2-Mx1(r/r) mice carrying the wild-type Mx1 gene from the A2G strain are not fully protected against lethal influenza virus infections.
Finally, human MX1 (also known as MXA), a closely related protein that has long been recognized as a broadly acting inhibitor of RNA and DNA viruses, including the orthomyxovirus influenza A virus, does not affect HIV-1, whereas MX2 is ineffective against influenza virus.
These results demonstrate for the first time that uncontrolled influenza A virus replication actively suppresses MxA gene expression and emphasize the critical role of innate immunity in controlling influenza virus replication in vivo.
MxA protein confers resistance to influenza viruses, and we have previously shown that MxA protein is strongly expressed in lesional anagen hair bulbs from patients with AA but not in normal follicles.