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The seroneutralization test based on the inhibition of syncytial effect (SN-ST) turned out to be very useful in the serological diagnostics of enzootic bovine leukaemia. The mean coefficient value of the SN-ST for positive sera (ELISA titer from 200 to 3200) was 0.1, for doubtful (ELISA = 100) - 0.52 and for negative sera 0.94. In case of negative serum the multinuclear cells (syncytium) were very large and numerous and with 85 to 100 nuclei; for doubtful sera they were small, scarce and with 25 to 30 nuclei. No syncytia were observed with the presence of negative sera. The time of incubation of BLV with positive sera played a very important role in the process of seroneutralization. The best results of SN-ST, which corresponded to the ELISA, were found after two hours of neutralization.
It has been found that CC81 cells cocultivated with the FLK-BLV or FLS-BLV cells from numerous syncytia within 17 hrs. Similar phenomenon, but less intensive, was observed in the culture of CC81 cells after treatment with the fluid from the 4-day culture of FLK-BLV cells. The culture of CC81 cells infected with particles of BLV separated from the culture fluid by ultracentrifugation showed also a cytopathogenic effect. The cells treated with large doses of the virus showed a marked dystrophy and break-up whereas smaller concentration of BLV caused formation of comparatively rare syncytia.
Serological studies were carried out using two kinds of antigens i.e. BLV and BLV plus parainfluenza virus (PI3) propagated in FLK cells. Out of 38 cattle sera sixteen (42.2 per cent) produced positive results with the BLV antigen and 31 (81.6 per cent) with the mixed antigen. The findings showed that with the mixed antigen the positive results rose by 39.4.
The usefulness of an imfnunoperoxidase test in the detection of bovine leukemia virus (BLV) was demonstrated. Positive results of the PLA test were observed in cell cultures permanently infected with BLV (FLK, HKR and a 50% mixture of FLK and non-infected cells). A brown- -red colour of the antibody-antigen immunological complex of the cytoplasm of BLV infected cells confirms possitive results of the PLA test after anti-BLV serum addition. The nucleus of these cells was not stained. Unstained cells showing indistinct morphological structure confirm negative results of the PLA test. All FLK and HKR cells in the PLA test showed possitive reaction but in the case a 50% mixture of uninfected and infected cells, only 30% of the cell population were positive. The results of the PLA test with BLV infected cells were consistent with a syncytial test. In the case of cells transfected with the DNA of env gene of BLV the results of the PLA test positive, whereas a syncytial assay was negative.
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