ON THE SEROLOGICAL PROPERTIES OF NEWCASTLE DISEASE VIRUS

Abstract

It is well known that interest informations on the antigenic structure of viruses have been obtained with complement fixation. The serological properties of Newcastle disease virus, however, have been mainly studied by neutralization and hemagglutination and available references on its complement fixing properties are limited. For complement fixation many kinds of animals may be able to donate antibodies, but the natural host should be considered to be standard as source of antibodies. As chicken serum, which is of the most susceptible natural host for the virus, fails to fix complement when inactivated by heating at 56°C for 30 minutes, indirect complement fixation has been recommended as an available technique. Recently the possibility of direct complement fixation with chicken serum was suggested by Nitzschke (1956) and Brumfield (1957). The author tried to establish the direct complement fixation in the Newcastle disease virus-chicken serum system and to examine complement fixing properties of the virus and antigenic difference among several strains with the technique.
The Sato, Miyadera and W strains of Newcastle disease virus, different in origin and pathogenicity, were chiefly employed. The Sato strain was isolated from an affected bird in the outbreak of the acute type disease in 1930 and the Miyadera strain, of the mild type disease in 1951. The W strain, originating from American living vaccine, is an avirulent one in chickens.
Results are summarized as follows.
1. Direct complement fixation was successfully performed in the Newcastle disease virus-chicken serum system, using sera in the active phase and the incubation at 37°C for 60 minutes in a water bath.
2. Complement was specifically fixed with infected embryonic tissues under the presence of immune serum. The highest fixation was shown in the test with chorioallantoic membranes and no fixation was detected in the test with allantoic fluid.
3. Two kinds of antigens, soluble and viral, existed in infected embryonic tissues. The former was prepared by the complete elimination of hemagglutinin from the suspension of chorioallantoic membranes, using centrifugation and absorption with chicken red cells, and the latter, by centrifugal concentration of hemagglutinin from allantoic fluid.
Although hemagglutinability was approximately the same in titer, the amount of soluble antigen in chorioallantoic membranes seemed to be different among the strains.
4. Antibodies against soluble and viral antigens were produced in chickens hyperimmunized with inactivated virus or infected with active virus. Antibody against viral antigen was usually from 2 to 8 times higher than that against soluble antigen in titer.
5. Partial antigenic differences among the strains were revealed by cross hemagglutination inhibition with sera absorbed with heterologous antigens, particularly the Sato strain appeared to be different from the others. Cross complement fixation failed to detect the partial differences among them, even when viral antigen was used. The Miyadera and W antigens, both soluble and viral, showed stronger reaction with the Sato immune serum than that with the homologous. The Sato strain seemed to be more effective to produce antibodies in chickens.