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The presence of hydrocortisone in virus-infected cell cultures leads to enhancement of the syncytia forming ability of Newcastle disease virus and to production of vescicular stomatitis virus particles which loose their infectivity upon storage below 0 degrees C.
Cell cultures and chicken embryos were treated with maximum tolerant concentrations of different compounds and infected with Newcastle disease virus simultaneously or 24 hours after the compounds were introduced. The similar results were obtained in both cases. It was found that Reglone inhibited Carbaryl increased virus multiplication. The study on dynamics of virus multiplication indicates that only in the case of IPO and Carbaryl their stimulatory effect on virus at the final stage was preceded by its inhibition.
The sensitivity of enzyme linked immunoassay (ELISA) was compared to that of haemagglutination inhibition (HI) test in detection of humoral antibodies in birds vaccinated with Newcastle disease virus (NDV). The highest antibody titre at day 21 post-vaccination as detected by ELISA in the sera of vaccinated birds was 2560 by all strains in contrast to the HI titres of 640 to 1280. The antibody titre was higher in all pre- and post-vaccination sera as determined by ELISA than detected by HI test.
Two kinds of RNA capable of producing interferon in a heterologous cell system occur in the cells producing interferon in response to induction by Newcastle disease virus. One of them has messenger activity for interferon and is presented by a single-stranded structure with sedimentation constant of 10-22 S. This RNA appears to belong to cellular messenger RNA. The other is capable of inducing interferon production by heterogenous cells, resistant to treatment with RN-ase and has sedimentation constant greater than 35 S. In our opinion, this RNA is the primary replicative RNA of the virus-inducer.
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Chicks with no specific antibodies were initially y vaccinated against Newcastle disease at 21 days old with the live 'La Sota' strain or beta-propiolactone-killed virus emulsified in mineral oils. After a second vaccination 15 or 21 days later with the live "La Sota' strain, the interference produced by the first vaccination on the antibody production induced by the second vaccination was investigated. It was found that the live virus vaccine used for the second immunization was affected by the antibodies induced by the first vaccination, as shown in previous work utilizing 1-day-old chicks.
We have determined the sequences of the 5' ends of three strains of Newcastle disease virus, permitting the assembly of the entire genomic sequence, which amounts to 15,186 nucleotides. This length is in agreement with the rule of six, which has been shown to determine replication efficiency in similar viruses. Comparison of the extreme 5' end of the trailer sequence with that of the 3'-terminal leader sequence of the virus reveals a high degree of complementarity. Variation between the 5'-terminal sequences of the different strains reveals the presence of alternative L gene polyadenylation signals, leading to correspondingly different trailer lengths.
Two modifications of a haemofusion-inhibition test (HFI-1 and HFI-2) were applied for the titration of antibodies to Newcastle disease virus (NDV) in chicken sera. Statistical analysis revealed a positive correlation of the HFI-1 antibody titres with those measured by the standard haemagglutination-inhibition (HI), virus neutralization (VN) and haemolysis-inhibition (HLI) tests. The same appeared true when the HFI-2 antibody titres were compared with the HI, VN, and HLI tests. Except for the several sera collected from birds immunized with formalin-inactivated vaccine, the HFI-2 antibody titres of individual serum samples were usually lower than those determined by HFI-1. The interpretation of these differences as well as some advantages and disadvantages of the proposed test are discussed.
Investigations were carried out on the immunogenesis and the serum-protein profile in the treatment of broilers with the protein hydrolysate Hydroprot as well as with Newcastle disease vaccine. The treatment with Hydroprot led to a lower average geometric titer of antibodies--6.4 on the 14th, 6.9 on the 24th, and 6.6 on the 39th day following immunization. Characteristic changes in the serum-protein profile were established--decrease in the total serum-protein, increase in the globulins and particularly in the fractions the peak level of which corresponded to the period of most strongly expressed immunity. The results obtained were associated with the involvement of amino acid synthesis in the immunologic process. They showed that under the effect of the preparation applied there set in enhanced immunogenesis as an expression of changed immune responsiveness.
Chick embryo cell cultures were infected with Newcastle disease virus (strains Italia, Beaudette and B1), labelled with 14C-amino acids from 5 to 6 hr post infection (p.i.), incubated in chase conditions from 6 to 10 hr p.i. in the presence or absence of cycloheximide (100 microgram/ml) and analyzed by slab polyacrylamide gel electrophoresis and autoradiography. In chase experiments the HN protein was stable in all three strains. The haemagglutinating activity of cell homogenates was greatly reduced after the addition of cycloheximide in tests with Beaudette and B1 strains; treatment of the homogenates with neuraminidase from Vibrio cholerae did not influence this effect.
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