| La Sola strain and V4 strain of Newcastle disease (ND) virus (NDV) has been widely used in many countries. There were many differences between immunogenicity of the two vaccine strains when they were used. In order to clarify the differences of immune responses mechanism of the two vaccine strains to chicken, and to improve vaccines immunity effectively, effect of La Sota and V4 strain on chicken T cell subpopulations and immunodominance epitopes of their F protein have been compared. Firstly CD4+T and CD8+T subpopulations changes in chickens vaccinated with Newscastle disease virus strains La Sota and V4 were compared by flow cytometry. The result showed that there was a relatively higher percentage of CD4+ and CD8+ T lymphocytes in PBLs and spleens of chickens vaccinated with the V4 strain as compared to La Sota strain in general. This indicated that CD4+, CD8+T lymphocytes proliferate response to V4 strain was higher than to La Sota strain. Besides it was showed that the percentage of CD4+ T cells in PBLs of chickens vaccinated with La Sota or V4 strain was significantly increased at 1 day PI. This indicated that the T lymphocytes had proliferated by that time. A cell-mediated immune response occurred at 1 days P*! following NDV La Sota or V4 strain vaccination, and made crucial effect that vaccinated birds were resistant to virulent virus challenge prior to the appearance of neutralizing antibodies.According the differences of immune response of chickens vaccinated with the two vaccine strains respectively, we identified and compared the antigen epitopes of La Sota and V4 strain. B cell-epitopes on F protein of NDV La Sota and V4 strain were predicted by Hydrophilicity, Flexibility, Accessibility, Antigenicity and Secondary structure index. T cell-epitopes on F protein of NDV La Sota and V4 strain were predicted by AMPHI rule, Tcell Motif of Rothbard-Taylor and Sette MHC Motifs------I-A Regions rule. It was showed thatthere are 19 B cell-epitopes and 24 T cell-epitopes on F protein of NDV La Sota and V4 strain respectively. And there are 9 different B cell-epitopes and 11 different T cell-epitopes between them.Based on the above result, we identified these epitopes and compared them. Firstlyfull-length cDNA of F gene from NDV La Sola strain were obtained by using RT-PCR and the cDNA was cloned into pMD18-T vector. The result of sequencing showed that the cDNA contains whole open reading frame of F gene (1662bp), and the cDNA had 4 nucleotide differences and 99.8% of homology in comparison with the sequence of La Sota strain F gene from GENEBANK.The predicted epitopes genes were divided into 6 segments. The 12 segments of La Sota and V4 strains F gene were subcloned and were constructed into transfer vector, and 10 recombinants were expressed. 5%-20%T Tris-Tricine gels electrophoresis was used to analyse the expressed proteins and the expressed proteins were purified with Ni-NTA agarose.Antigenicity of expressed pepetides was identified by Western Blot with anti-La Sota and anti-V4 strain serum. The results showed that positive response occurred with peptide PI, P4, P5 and P6 and neutralized epitopes known were not in four segments. The four segments are located in l-48aa, 201-274aa, 377-458aa, 469-530aa. While peptide P2 can not react with antiserum. The comparison of antigenicity showed that B cell-epitopes on F protein of NDV strain La Sota and V4 were different in peptide Pland P4 that were in coiled-coil adjacent fusion peptide. It indicated that immunogenicity of strain La Sota and V4 was different possibly.After SPF chickens being vaccinated with La Sota P5 , V4 P5 peptide and inactived La Sota, V4 vaccine , antibody liters were detected by ELISA. The result showed that chickens vaccinated with inactived La Sota or V4 vaccine have high antibody liter and there is no significant differences between chickens were vaccinated La Sota P5 , V4 P5 peptide and control. The level of IFN-y mRNA was delected by RT-PCR, and the result showed that the level of IFN-y mRNA was lower in vaccina...
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