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Infectious pancreatic necrosis virus of fish, infectious bursal disease virus of chickens, Tellina virus and oyster virus of bivalve molluscs, and drosophila X virus of Drosophila melanogaster are naked icosahedral viruses with an electron microscopic diameter of 58 to 60 nm. The genome of each of these viruses consists of two segments of double-stranded RNA (molecular weight range between 2.6 x 10(6) and 2.2 x 10(6), and the virion, capsid proteins fall into three size class categories (large, medium, and small; ranging from 100,000 to 27,000) as determined by polyacrylamide slab gel electrophoresis. The hydrodynamic properties of the five viruses are similar as determined by analytical ultracentrifugation and laser quasi-elastic, light-scattering spectroscopy. The calculated particle weights range between 55 x 10(6) and 81 x 10(6). Tryptic peptide comparisons of 125I-labeled virion proteins showed that five viruses are different from each other, although there was considerable overlap in the peptide maps of the three aquatic viruses, indicting a degree of relatedness. Cross-neutralization tests indicated that drosophila X, infectious pancreatic necrosis, and infectious bursal disease viruses were different from each other and from oyster and Tellina viruses. The same test showed oyster and Tellina viruses to be related. The biochemical and biophysical properties of the five viruses cannt be included in the family Reoviridae or in any of the present virus genera.

SUMMARYThe electrophoretic mobilities of the two genome segments and the structural polypeptides of the chicken strain Cu-1 (serotype I) and the turkey isolate 23/82 (serotype II) of infectious bursal disease virus were compared. There is a close antigenic relationship between the smaller of the two major structural proteins (32K) of both strains. Neutralizing monoclonal antibodies are induced by the larger protein (40K in Cu-1) which differentiates between the two serotypes. The 40K structural protein also has epitopes which do not induce neutralizing antibodies and which are common to both strains. There is evidence that the antigenic region responsible for the production of neutralizing antibodies is highly conformation-dependent. Passively administered neutralizing antibodies directed against the 40K structural polypeptide of Cu-1 confer protective immunity to susceptible chickens, whereas antibodies directed against the 32K structural protein do not have any protective effect. INTRODUCTIONThe basic structure of the infectious bursal disease virus (IBDV), the aetiological agent of a disease of chickens which results in the destruction of the bursa of Fabricius, has been elucidated (Nick et al., 1976; M/iller et al., 1979) and has been shown to exhibit the structural characteristics of the Birnaviridae (Dobos et al., 1979;Brown, 1986). During the past few years isolates of IBDV from turkeys have been reported to be essentially identical to the chicken strains, but the turkey isolates were not pathogenic and could be distinguished by neutralization (McNulty et al., 1979;Jackwood et al., 1982); a second serotype was therefore established (McFerran et al., 1980). In order to localize the antigenic determinants on the structural proteins of IBDV which are responsible for the induction of neutralizing antibodies, a more detailed comparative analysis of the two types of viruses was necessary. Attempts were therefore made to obtain more precise information about the size of the two genomic segments ofdsRNA and the structural proteins of the turkey strain in relation to the known elements of the chicken virus. The antigenic sites which both types of viruses have in common and those which permit their distinction were traced with monoclonal antibodies. The need for a more precise analysis of the antigenic structure of IBDV was underlined by the attempts of other authors to describe antigenic regions which would lend themselves to the production of a vaccine in Escherichia coli or by peptide synthesis (Fahey et al., 1985a,b;Azad et al., 1986;Hudson et al., 1986).

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SUMMARYA virus-specific antigen was extracted from brains of rats and from MDCK cells infected with Borna disease (BD) virus and purified to homogeneity by immunoaffinity chromatography and HPLC. The antigen consists of two components which are almost equal in size (38000 tool. wt.), and it forms aggregates in its native form. The virus specificity of the two antigenic entities was confirmed by immunoblots with convalescent serum and monoclonal antibodies. Immunofluorescent staining with monoclonal antibodies and a hyperimmune serum prepared against the purified antigen showed the intranuclear fluorescence typical for BD virus-infected cells.

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(Canada). It was serially passed at a multiplicity of infection of 0.01 to 0.001 in a rainbow trout gonad cell line (RTG-2, obtained from G. Wizigmann, Grub, W. Germany), which was grown in plastic petri dishes. Extensive cytopathic effect was observed after 2 to 3 days of incubation at 20°C.

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