Radioimmunoassay for detection of antigen and antibodies to Newcastle disease virus

When Newcastle disease virus (NDV) is treated with NP 40 and ether a membrane fraction of 150,000 m.w. is obtained. This fraction, which is composed of two polypeptides with m.w. of 56,000 and 76,000, was used in a radioimmunoassay (RIA). The assay was developed for both antigen and antibody and was found to be reproducible, specific, and highly sensitive. Titers of 1:51,200 were determined by RIA as compared to 1:4 by agar gel diffusion and 1:200 by hemagglutination inhibition (HI). As little as 5 ng of viral protein were detected by RIA inhibition technique. Labeled antigen could be stored in the presence of serum, KCl and Titon X 100 at -20°C for as long as 6 weeks and retained similar reactivity as fresh reagent.