Expression and stability of the Mx protein in different tissues of mice, in response to interferon inducers or to influenza virus infection.

We have defined some characteristics of the mouse Mx protein as a marker of biological response to interferon (IFN) and to virus infection in A2G mice. The Mx protein has been detected and quantitated by Western immunoblot analysis. Upon induction by poly(I):poly(C) or with Newcastle disease virus, the Mx protein is expressed and accumulated in a variety of organs, such as liver, lungs, spleen, kidneys, heart, and brain. In some organs the expression of the Mx protein is detected readily, as soon as 4 h after treatment. The highest protein level is reached at 24 h, and it remains stable for several days declining slowly to return to preinduced levels 2-3 weeks after treatment. Infection with an hepatotropic or a pneumotropic strain of influenza virus resulted in a systemic induction of Mx protein, the highest levels being found in the target organ for virus replication. Our results indicate that the Mx protein is a sensitive, quantitative, and stable marker to follow IFN activity or virus infection in an animal model.