Investigation Of Resistance To Superinfection Induced By The Attenuated Equine Infectious Anemia Virus Vaccine Strain

Aims: The Chinese attenuated equine infectious anemia virus (EIAV) vaccine is a unique model for vaccines of lentiviruses. Decoding the mechanism on inducing solid immune protection by the vaccine will provide valuable information to the development of other lentiviral vaccines, such as vaccines against HIV-1. Previous studies have revealed that multiple mechanisms including specific immunity contribute to the protection. Viral interference is an important phenomenon of non-specific restriction to certain viral infections. In this study, the viral interference conducted by the EIAV vaccine to the supperinfection of the pathogenic strains is investigated to identify its impact to the immune protection evoked by the vaccine.Methods: The Chinese attenuated EIAV vaccine strain EIAVFDDV and a heterologous virulent strain EIAVUK-3 was used to investigate supperinfection and interference of EIAV in this study. Techniques of ViewRNA and real-time PCR were employed to qualitatively and quantitatively analysis the presence of co-infection, supperinfection or resistance to supperinfection between the EIAV vaccine and virulent strains in cultured donkey dermal cells, which are target cells of EIAV. In addition, the real-time PCR was also applied to detect the expression of ELR1, the sole receptor of EIAV, on the mRNA level during these infections.Results: The pre-infection of the attenuated vaccine strain EIAVFDDV resulted in the interference to the subsequent infection of the virulent strain EIAVUK-3. Exhibited by using ViewRNA hybridization, the RNA copy numbers of EIAVUK-3 in cells pre-infected with EIAVFDDV for 24 hr were significantly lower than that the cells infected with EIAVUK-3 alone. Moreover, the copy numbers of EIAVUK-3 were further declined when the cells were pre-infected by the vaccine strain for 36 hr, and the EIAVUK-3 infection was barely observed in cases that the pre-infections were performed for 48 and 72 hr. Quantitatively analyzed by real-time PCR, the EIAVUK-3 copy numbers in unpre-infected cells was 9-fold and 29-fold higher when compared with viral copies in cells pre-infected with EIAVFDDV for 0 and 12 hr, respectively. A 170-fold decrease in EIAVUK-3 RNA copy number was measured in cells pre-infected with the vaccines strain for 24 hr. A maximum of 960-fold reduction in viral RNA copy was detected in samples pre-infected with EIAVFDDV for 48 hr. These quantitative data are consistent with the observations using ViewRNA. Additionally, no reduction in the ELR1 mRNA was observed in cells that pre-infected with EIAVFDDV.Conclusions: The pre-infection of EIAV vaccine strain EIAVFDDV resulted in significant interference in the subsequent infection of heterologous virulent strain EIAVUK-3. This resistance of cells to the superinfection is not correlated with the expression levels of the EIAV receptor ELR-1. These results implicate that the viral interference, a part of non-specific resistance to viral infection, possibility plays certain roles in the immune protection induced by the attenuated EIAV vaccine.