Mechanism Of Porcine Circovirus Type 2 Infection Influencing Immune Responses Of Classical Swine Fever Attenuated Vaccine

Porcine circovirus type 2 (PCV2) infection can cause infected piglets immunosuppression, reducing the immune effect of vaccine. Now our country, the main measure to prevent CSF is immunization, But clinically has always seen the classical swine fever (CSF) vaccine immune failure phenomenon, which become one of the key factors for preventing the CSF. In this study, By analyzing the changes of humoral and cellular immune response and NK cells, T-cell subpopulations and cytokines in peripheral blood of the piglets, that PCV2 infection before or after vaccination with CSF vaccine,to show the Mechanism of porcine circovirus type 2 infection influencing immune responses of classical swine fever attenuated vaccine.Twenty 28-day-old healthy weaning piglets were randomly divided into four groups which were V-I、I-V、V and C, five piglets per group. The piglets in Group V-I were intramuscularly injected with CSF vaccine two days before being inoculated with PCV2, Group I-V infected by PCV2 two days before being injected with CSF vaccine, Group V only vaccinated by CSF vaccine and Group C as the blank control without inoculating anything. Piglets were vaccinated twice at an interval of twenty-one days. The levels of the CSFV-specific serum antibody were measured by ELISA at 7 d、14 d、21 d after primary vaccination and 7 d、14 d、21 d、28 d after secondary vaccination. The results suggest that PCV2 infection, either before or after vaccination, decreased CSFV-specific serum antibody production, and the seroconversion. Especially the Group I-V (after secondary vaccination.). These results indicate that the inhibitory action of humoral anamnestic response stimulated by CSF vaccine in Group I-V were even more obvious.Proliferation activity of peripheral blood lymphocytes (PBLC) was detected by MTT, The results showed that CSF attenuated vaccine slightly suppressed the proliferation activity at the early days of the immunization, but return to normal quickly. However, PCV2 infection caused the proliferation activity lower than Group V, then return to normal. Which suggested that PCV2 infection made the proliferation activity of PBLC much lower in a short time.Changes in peripheral white blood cell (WBC), NK cell and T-cell subpopulations were measured by Boood routine test and flow cytometry (FCM). The results showed that the counts of WBC, NK cell, T-cell subpopulations (Th, Tc, Tm,γδT)in Group V-I and I-V were lower than Group V,especially in Group V-I.These date demonstrated PCV2 infection, either before or after CSF attenuated vaccine vaccination, decreased the counts of WBC and lymphocytes.The transcriptional levels of PBLC cytokines(IFN-γ、IL-2、IL-4、IL-10、IL-12p40、IL-18) mRNA was measured by Real-time FQ-PCR. The results showed that PCV2 infection can reduce the transcriptional levels of IL-2、IFN-γ、IL-4、IL-10、IL-12p40、IL-18 mRNA at the primary vaccination, but go up the transcriptional levels of IL-10, IFN-γ, IL-18 mRNA , reduce the transcriptional levels of IL-2, IL-4 mRNA. These results indicated that PCV2 infection, either before or after CSF attenuated vaccine vaccination, could lead to the transcriptional levels of cytokines serious lack or disorders.Take together, PCV2 infection can decrease the level of humoral and cellular immunity, that were induced by CSF vaccine, and lead to the transcriptional levels of cytokines serious lack or disorders, Which are the important reasons for swine fever vaccine immune failure.