A sensitive radioimmunoassay for circulating alpha-interferon in the plasma of healthy children and patients with measles virus infection.

The mean circulating alpha-interferon of healthy children aged 2 to 13.5 yrs as measured by a radioimmunoassay was 0.119 +/- 0.031 ng/ml, which was significantly lower than that of young adults. Circulating alpha-interferon of children with measles virus infection aged 1 to 11 yrs, on their first visit to the hospital when they were fully symptomatic, was 0.095 +/- 0.035 ng/ml (n = 39). It was 0.105 +/- 0.070 ng/ml (n = 21) on their second visit, 7 to 10 days after their first visit when the patients were convalescent. The difference was statistically insignificant. It is concluded that immunoreactive circulating alpha-interferon is low in children and reaches maximum level in young adults, subsequently declining gradually with age. Immunoreactive circulating alpha-interferon, a possible reflection of endogenous alpha-interferon, does not change significantly by the infection of measles virus.