Virus interference. II. Some properties of interferon

Interferon could be titrated by the amount of interference induced in fragments of chorioallantoic membranes challenged with influenza A virus. Over a ten-fold range, inverse proportion between interferon concentration and haemagglutinin titre reached by the challenge virus was observed. Interferon proved stable at 2 degrees C for 2 weeks. Marked inactivation took place after 1 h at 60 degrees C. Interferon was not measurably sedimented by 100 000 g for $\frac{1}{2}$ $\text{h}$. It was held back by gradocol filters of a.p.d. $0.6\mu $. It was not dialyzable. Interferon was active against influenza A, Sendai, Newcastle disease and vaccinia viruses. It was not neutralized by anti-MEL rabbit serum and only slightly inhibited by pooled human serum rich in complement-fixing antibody to influenza A soluble antigen.