The Inhibition Of IFN-β Expression By HP-PRRSV And Its Molecular Mechanism

Highly Pathogenetic Porcine Reproductive and Respiratory Syndrome Virus(HP-PRRSV) was developed from classic PRRSV, which could cause serious reproductive failure in pregnant sows and severe respiratory distress in piglets and growing pigs. Macrophages played an important role in the cell immune responses. In normal circumstance, pathogens could be phagocytosed by macrophages and form phagosome, and gradually change into phagolysosome and finally experience degradation in the immune cells. However, some pathogens are able to survive and replicate in the macrophages, such as HP-PRRSV infection could inhibit host innate immune response. As the type I IFN function as a critical role for the innate immune response, and it has been reported that classic PRRSV was able to inhibit the type I IFN expression, but the mechanism of the HP-PRRSV infection was still not well understood. This study investigated the disease risk of receptors, the expression tendency of type I IFN and IRF3, and the replication tendency of HP-PRRSV. The purpose of this study was to investigate the features of host immune response to HP-PRRSV infection and the mechanism of the HP-PRRSV infection. The results are:(1) HP-PRRSV could inhibit IFN-β expression. We detected IFN-β expression in the four groups of MARC-145 cells(-HP-PRRSV, +HP-PRRSV, Poly(I:C), Poly(I:C)+ HP-PRRSV). The expression in the cells treated with HP-PRRSV and without HP-PRRSV was extremely weak, and the expression of IFN-β could significantly increase with the treatment of Poly(I:C), whereas the stimulation was inhibited by the HP-PRRSV infection. As the type I IFN expression in the cells treated with HP-PRRSV and without HP-PRRSV was too weak to present the expression tendency, we chose the cells treated with Poly(I:C) as control group, and the cells treated with both Poly(I:C) and HP-PRRSV as test group.(2) HP-PRRSV could inhibit IFN-β protein expression of supernatant in MARC-145 cells. The expression of IFN-β protein and mRNA in test group and control group were consistent. The expression of IFN-β protein of supernatant of test group in MARC-145 was lower than that of control group.(3) HP-PRRSV could inhibit IFN-β mRNA expression in PAM cells. The expression of IFN-β mRNA of test group in PAM cells was lower than that of control group.(4) HP-PRRSV could inhibit IRF3 mRNA and protein expression. In MARC-145 and PAM cells, the expression of IRF3 mRNA and total protein was consistent with the IFN-β, and IRF3 expression of test group was lower than that of control group.(5) HP-PRRSV could inhibit IRF3 nuclear translocation. In MARC-145 and PAM cells, the expression of IRF3 protein of nucleus in test group was lower than that of control group.(6) HP-PRRSV could inhibit IRF3 phosphorylation. In MARC-145 and PAM cells, the expression of IRF3 phosphorylated protein in test group was lower than that of control group.(7) HP-PRRSV might inhibit Ser396 phosphorylation of IRF3 protein. Bioinformatic results indicated that Ser396 was located in the junction of helix and coil region, and the exposure of this site has been reported to play an important role in IRF3 phosphorylation, therefore, HP-PRRSV might inhibit the phosphorylation of IRF3 by interfering the exposure of this site.(8) HP-PRRSV has no effect on CBP expression. In MARC-145 and PAM cells, CBP mRNA expression not significantly changed after HP-PRRSV infection, which indicated that HP-PRRSV might not inhibit CBP expression.(9) The SNPs of the CD169 and CD163 might affect the infection risk related with phagocytosis. The detection of genotypes of 6 SNPs of 524 pigs and the analysis of the disease risk of different genotype showed that 3 genotypes might related with HP-PRRSV infection, which were AA genotype of CD169–C1654A、CT genotype of CD169–C4175T、AA genotype of CD163– A2552 G. Individuals with these genotypes might be resist to the HP-PRRSV infection.(10) The SNPs might affect the phagocytosis ability of CD169 and CD163. Three SNPs of CD169 could lead to amino acids change, and bioinformatic results showed that these 3 SNPs might located in the immunoglobulin region, thus amino acids change might affect the phagocytosis ability. Three SNPs of CD163 were all located in the adhesion region, and two SNPs of CD163 could not cause amino acids change, but might change the preferences of codons, which might further affect the number of translated proteins. The third SNP of CD163 could change animo acid, and might affect the phagocytosis ability.