Influence of porcine circovirus type 2 on TLRs of piglet lymphocytes in vitro

Six commercial piglets free of porcine circovirus type 2(PCV2) and porcine reproductive and respiratory syndrome virus(PRRSV) were chosen as experiment animals.Lymphocytes isolated from spleen were randomly distributed into two groups: negative control group and PCV2-incubated group.The splenocytes of PCV2 group were incubated with PCV2 at 5×105TCID 50 ·mL-1,and those of control group were incubated with equal volume of RPMI-1640.The amount of PCV2 infected cells was observed by indirect immunofluorescence assay(IFA) at 0,6,12,24 and 48 hours post infection(hpi),and the mRNA expression of TLR2,TLR3,TLR4,TLR7,TLR8 and TLR9 and the protein level of TLR3 and TLR4 were detected by real-time PCR and Western blot,respectively.The results showed that the mRNA levels of TLR2 and TLR9 were higher at 12,24 and 48 h(hpi) than those of control group(P0.01),and those of TLR3 and TLR4 mRNA were elevated at 24 h(P0.01).TLR3 protein contents significant increased at 6 and 12 h,and TLR4 protein contents significantly increased at 6,12,24 and 48 h(P0.05).The results demonstrated that PCV2 significantly activate transcriptions of TLR2,TLR3,TLR4 and TLR9,and elevate the protein level of TLR3 and TLR4 in piglet lymphocytes in vitro,which mediated the production of correlative inflammatory cytokines.This may be associated with the disorder secretion of inflammatory cytokines caused by PCV2.