The Pathogenicity Study On Coinfection Of Classical Swine Fever Virus And Foot-and-mouth Disease Virus In PK-15 Cells

Classical swine fever(CSF)and Foot-and-mouth disease(FMD)are two important infectious diseases in pigs,these two kinds of pig diseases have caused great economic loss to the swine industry in China.Both CSFV and FMDV are typical immunosuppressive viruses,which can induce the apoptosis of host lymphocytes after infection,directly or indirectly participate in the natural immune signaling pathway and inhibit the production of interferon,causing the suppression of immune function in the body.More and more researchers have found that,with the development of intensive animal production technology and the convenience of transportation brings the chances of pathogen transmission are increased,pigs are prone to two or more mixed pathogens once infected.After coinfection of CSFV and FMDV in pigs,we found that the clinical manifestations are intensified.However,interaction of CSFV-FMDV mixed infection on each other and the mechanism of effect on the host is still unavailable.The purpose of this study was to investigate effects of CSFV and FMDV viral multiplication and on the interferon pathway during coinfection of CSFV and FMDV,hoping to provide basic data for further revealing the molecular mechanism of changed pathogenicity of co-infection of CSFV and FMDV.In this study,we established an in vitro model of mixed infection in PK-15 cells.Differences in levels of replication between the two viruses and interferon expression levels of CSFV-FMDV mixed infection were detected by CPE,Real-time fluorescence quantification(RT-qPCR),Western blotting,indirect immunofluorescence and ELISA.The CSFV virus protein expression plasmid was constructed and co-infected with FMDV in PK-15 cells.These proteins were screened and identified by RT-qPCR and Western blotting.Then overexpressed of screened proteins in coinfected with FMDV,and the expression levels of FMDV and interferon were detected by RT-qPCR.The results showed that the mixed infection of CSFV strain C and FMDV enhanced the CPE of PK-15 cells.Mixed infection of CSFV and FMDV promoted the replication of CSFV,and inhibited the replication of FMDV.The mixed infection of Shimen strain CSFV and FMDV did not affect CPE,but inhibited the replication of CSFV and promoted the replication of FMDV,it was completely opposite to that of C strain CSFV;Coinfection of C strain CSFV and FMDV,leading to type Ⅰ interferon expression level did not change,butⅡ type interferon expression level down;CSFV C protein was screened to inhibit FMDV replication,and the inhibitory effect was exactly the same as the above results.Above results showed that CSFV-FMDV mixed infection by CSFV C protein to inhibite replication of FMDV,and by influencing the type Ⅱ interferon signaling pathways to suppressed.