Relationship between Immunity and Interferon Production in Macrophages

When Newcastle disease virus (NDV) was inoculated into macrophage cultures, interferon (IF) of various molecular weights appeared in the culture fluid. The molecular weight of IF produced in the macrophages derived from normal mice in at least 6 hr post‐inoculation of inducer was different from that produced in the macrophages from immunized mice. The IF with a molecular weight as high as 100 000 was unstable against pH 2 treatment and heat treatment, while that of 70 000 or less was stable.