Induction of xanthine oxidase by virus infections in newborn mice

In the liver tissue of newborn mice, xanthine oxidase activity is very low during the first 7 to 14 days of life. Infection of mice with several different viruses prematurely induced xanthine oxidase activity 2- to 10-fold in the liver tissue. Generally, overt signs of illness appeared after xanthine oxidase induction; however, some viruses induced the enzyme activity without causing morbidity or deaths. The elevated enzyme activity could not be correlated with alteration of either lactate dehydrogenase or glutamate-pyruvate transaminase. Likewise, there were no histological changes in the livers of infected animals when xanthine oxidase levels were abnormally elevated. These observations suggest that measurement of xanthine oxidase may be an effective method for the detection of subclinical or inapparent viral infections in either naturally infected newborn mice or in newborn mice inoculated with suspected virus-containing materials.