To investigate the effects of classical swine fever virus (CSFV) virulent strain Shimen (SM) infection on piglets peripheral blood leucocytes, the 60-days weanling piglets were infected with the shinen strain and the peripheral blood samples of the piglets were collected to analyze the kinetics of the CSEV nucleic acid, the peripheral blood leucocytes subpopulation and SLA molecule expression on the peripheral blood leukocytes. The results showed that the piglets rectal temperature increased 48 hours after intramuscular injection of CSFV SM strain, the CSFV nucleic acid was detected in the peripheral blood at 2DPI, the content of CSFV nucleic acid increased and up-regulated to a peak at 6DPI as 10 (4.84 +/- 0.98 times as 2DPI. The amount of WBC, LYM and PLT significantly decreased, where in the amount of WBC decreased to 65.87% at 1DPI and 50% at 2DPI respectively; the amount of LYM decreased to 70.68%, 47.88% and 23.29% at 1DPI, 2DPI, and 3DPI, respectively; the amount of PLT decreased day by day and to 34.59% at 6DPI; the amount of NK, gammadeltaT, Tc, Th, CD3+ CD4+ CD8+ and CD3- CD4- CD8- cells decreased after infection; 78.49% of NK cells decreased at 1DPI and then there was no significant change from 2DPI to 6DPI. The amount of gammadeltaT, Tc, CD4- CD8- CD3-,CD4+ CD8+ CD3+ cells decreased to 41.74%, 43.83%, 15.87%, and 32.96% at 3DPI, respectively, However, the amount of T helper cells decreased continually to 42.95% at 6DPI; the amount of SLA I positive lymphocytes decreased significantly and the amount of SLA I positive CD3 cells decreased to 23.07% and 15.38% at 1DPI and 2DPI respectively; the SLA I positive granulocytes increased continually from 92.20% at 1DPI to 98.30% at 3DPI; the amount of CD3 SLA II + cells in lymphocytes decreased from 1.38% at 1DPI to 0.22% at 2DPI, while the SLA II + granulocytes increased continually to a peak at 3DPI and 53.76% of granulocytes expressed the SLA II molecule, but the percentage of the granulocytes expressing SLA II molecules decreased to 12.54% and 4.06% at 4DPI and 5DPI respectively. The study indicated that the CSFV SM strain infection could escape the immune surveillance and cause immunosuppression through inhibiting the host's innate antiviral immunity and the SLA molecule expression to affect the antigen presentation.
Animals ; Cells, Cultured ; Classical Swine Fever ; genetics ; immunology ; virology ; Classical swine fever virus ; pathogenicity ; physiology ; Gene Expression ; Histocompatibility Antigens Class I ; genetics ; immunology ; Histocompatibility Antigens Class II ; Leukocyte Count ; Leukocytes ; immunology ; virology ; Random Allocation ; Swine ; Virulence

Classical swine fever virus (CSFV) causes a highly contagious disease among swine that has an important economic impact worldwide. CSFV strain LOM is an attenuated virus of low virulent strain of Miyagi isolated from Japan in 1956. Eight DNA fragments representing the genome of the CSFV strain LOM were obtained by RT-PCR. These were used to determine the complete nucleotide sequence and construct a full-length cDNA clone which was called Flc-LOM. Sequence analysis of the recombinant clone (Flc-LOM) revealed the presence of eight mutations, resulting in two amino acid substitutions, when compared to the parental sequence. RNA transcripts of both LOM and Flc-LOM were directly infectious in PK-15 cells. The rescued Flc-LOM virus grew more slowly than the parental virus, LOM, in the cells. Intramuscular immunization with Flc-LOM was safe and highly immunogenic in pigs; no clinical signs or virus transmission to sentinel animals were observed after 35 days. CSFV-specific neutralizing antibodies were detected 14 days post-infection. After challenge with the virulent CSFV strain SW03, pigs immunized with Flc-LOM were shown to be fully protected. Thus, our newly established infectious clone of CSFV, Flc-LOM, could serve as a vaccine candidate.
Animals ; Antibodies, Viral/blood ; Base Sequence ; Cell Line ; Classical Swine Fever/immunology/*virology ; Classical swine fever virus/*genetics/immunology/pathogenicity ; Cloning, Molecular ; DNA, Complementary/genetics/immunology ; Immunization/methods/standards/veterinary ; Molecular Sequence Data ; Neutralization Tests/veterinary ; RNA, Viral/chemistry/genetics ; Recombinant Proteins/immunology ; Reverse Transcriptase Polymerase Chain Reaction/veterinary ; Sequence Analysis, DNA ; Specific Pathogen-Free Organisms ; Swine ; Virulence