| Equine infectious anemia virus (EIAV) is a member of Lentivirus Genus and infects only equids.The Chinese attenuated EIAV vaccine has been proven being able to induce effective immune protectionagainst the infection of homologous and heterologous EIAV pathogenic strains. This vaccine is the onlylentiviral vaccine that was successfully applied to control the spread of a disease in a country. Themechanism of how the EIAV vaccine reduced the virulence and obtained the ability to induce solidprotective immunity should provide valuable information for the development of other lentiviralvaccines. In this study, the fetal donkey dermal (FDD) cell-adapted vaccine strain (EIAVFDDV13) ofEIAV vaccine was used to intensively investigate the relationship between the super-infection resistance(SIR) induced by EIAVFDDV13and the activation of innate immunity, which in turn regulates adaptiveimmunities.SIR is the phenomenon that is established after primary infection of viruses, preventing theinfected cell from being superinfected by a similar type of virus. Lentiviruses, including HIV andEIAV, are known to induce SIR in various host cells. To better understand the contribution of SIR to theprotective immunity induced by attenuated lentiviral vaccines, the SIR induced between the ChineseEIAV attenuated vaccine strain EIAVFDDV13and an infectious molecular clone strain EIAVUK3from awild type EIAV pathogenic strain EIAVwyomingin primary equine monocyte-derived macrophages(eMFM) were studied.The real-time quantitative PCR and ViewRNA, a novel RNA in situ hybridization technique, wereapplied in this study to specifically measure the replication patterns of these two EIAV strains for theanalysis of SIR. Results revealed that EIAVFDDV13induced a predominant SIR against EIAVUK3ineMDM in vitro, and the intensity of SIR was significantly stronger than the SIR induced by EIAVUK3toagainst EIAVFDDV13. In addition, the mRNA expression levels of several innate immunity-related factors,including TLR3, IFNβ, Trim5α and Tetherin, induced by these viruses were analyzed by theBranched-DNA technique to investigate the potential mechanism of above differences in induced SIR.These innate immunity-related factors are presumed directly or indirectly responsible for the inducedSIR, as they are known playing important roles in suppressing the entrance or replication of lentivirusesin host cells. Results showed that the expression levels of these factors in eMDM were up regulatedmore significantly by the attenuated EIAVFDDV13than by the pathogenic EIAVUK3.Further experiments revealed that a similar panel of enhanced mRNA expression of these fourfactors in eMDM was induced by treating the cells with Poly I: C, a synthetic analog of dsRNA and anactivator of TLR3. Moreover, the eMDM treated with Poly I: C appeared strong resistance to theinfection of EIAV. When the expression of TLR3in eMDM was knocked down by a specific type ofsiRNA, the effect of Poly I: C-induced up-regulation of TLR3expression was greatly reduced as well.Consequently, the resistance of these TLR3-silenced cells to EIAV was distinctly declined comparedwith eMDM stimulated with Poly I:C, but not TLR3-silenced. Based on these results, the activation of TLR3pathway is presumed playing an important role in the SIR induced by the attenuated vaccinestrain EIAVFDDV13, which is significantly stronger than that induced by a pathogenic strain.In conclusion, experimental data obtained in this study facilitate better understanding of thebiological characteristics of the Chinese attenuated EIAV vaccine and provide additional information forthe study on protective immunities induced by the vaccine, which will be a valuable reference for thedevelopment of other lentiviral vaccines. |
