A preliminary study of porcine reproductive and respiratory syndrome virus promoting Streptococcus suis type 2 infection of porcine alveolar macrophages
To investigate the effect of porcine reproductive and respiratory syndrome virus(PRRSV)on macrophages infected with different virulence of Streptococcus suis type 2(SS2),a model of co-infection of immortalized porcine alveolar macrophages(iPAMs)with highly pathogenic PRRSV Li11 and either a strong virulent strain of SS2,HA,or an avirulent strain,T1/5,was established in this study.The experiment was divided into the following four groups:the HA group,the PRRSV-HA group,the T1/5 group and the PRRSV-T1/5 group.The model was used to detect the effect of PRRSV on the adhesion,invasion and viability of HA and T1/5 in iPAMs cells by adhesion assay,invasion assay and intracellular survival assay,and the transcript levels of cytokines(TNF-α,IL-6,IL-8,IFN-β)were further detected by fluorescence quantitative PCR in iPAMs model cells of each infection group.The results of the adhesion assay showed that the adhesion levels of bacteria in the PRRSV-HA group were highly significant higher than those in the HA group after 2 hours of HA infection(P<0.01 or P<0.001),and the adhesion levels of bacteria in the PRRSV-T1/5 group were highly significant higher than those in the T1/5 group after 6 hours of T1/5 infection(P<0.001),indicating that the co-infection of PRRSV with HA or T1/5 can promote the adhesion of HA and T1/5 to iPAMs model cells,and the adhesion level of HA to iPAMs cells was higher than that of T1/5.The results of the invasion assay showed that after 4 hours of infection,the number of bacterial invasion into iPAMs cells in the co-infected group was highly significantly increased compared with that of the infected group alone(P<0.01 or P<0.001).The results of the intracellular survival assay showed that the survival rate of bacteria in the co-infected group was extremely significantly higher than that in the alone-infected group 2 hours after infection(P<0.001).The results of fluorescence quantitative PCR assay showed that at 4 hours of infection,the transcript levels of cytokines(TNF-α,IL-6,IL-8,and IFN-β)in iPAMs cells in the co-infected group were extremely significantly higher than those in the separately infected group(P<0.001).In this study,a model of co-infection of iPAMs with highly pathogenic PRRSV Li11 and SS2 strong virulent strain HA or non-virulent strain T1/5 was established for the first time,based on which it was found for the first time that PRRSV infection not only promotes adhesion,invasion,and survival of different virulent SS to and within iPAMs cells,but also significantly increases cytokine transcription.This study provides a theoretical basis for further investigation of the mechanism of mixed PRRSV and SS infection.
porcine reproductive and respiratory syndrome virusStreptococcus suisimmortalized porcine alveolar macrophagesco-infection
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