Differential effects of virulent and avirulent equine infectious anemia virus on macrophage cytokine expression

The pathogenic and vaccine strains of equine infectious anemia virus differentially induce cytokine and chemokine expression and apoptosis in macrophages

The attenuated equine infectious anemia virus (EIAV) vaccine was the first attenuated lentivirus vaccine to be used in a large-scale application and has been used to successfully control the spread of equine infectious anemia (EIA) in China. To better understand the potential role of cytokines in the pathogenesis of EIAV infection and resulting immune response, we used branched DNA technology to compare the mRNA expression levels of 12 cytokines and chemokines, including IL-1α, IL-1β, IL-4, IL-10, TNF-α, IFN-γ, IP-10, IL-8, MIP-1α, MIP-1β, MCP-1, and MCP-2, in equine monocyte-derived macrophages (eMDMs) infected with the EIAV(DLV121) vaccine strain or the parental EIAV(DLV34) pathogenic strain. Infection with EIAV(DLV34) and EIAV(DLV121) both caused changes in the mRNA levels of various cytokines and chemokines in eMDMs. In the early stage of infection with EIAV(DLV34) (0-24h), the expression of the pro-inflammatory cytokines TNF-α and IL-1β were significantly up-regulated, while with EIAV(DLV121), expression of the anti-inflammatory cytokine IL-4 was markedly up-regulated. The effects on the expression of other cytokines and chemokines were similar between these two strains of virus. During the first 4 days after infection, the expression level of IL-4 in cells infected with the pathogenic strain were significantly higher than that in cells infected with the vaccine strain, but the expression of IL-1α and IL-1β induced by the vaccine strain was significantly higher than that observed with the pathogenic strain. In addition, after 4 days of infection with the pathogenic strain, the expression levels of 5 chemokines, but not IP-10, were markedly increased in eMDMs. In contrast, the vaccine strain did not up-regulate these chemokines to this level. Contrary to our expectation, induced apoptosis in eMDMs infected with the vaccine strain was significantly higher than that infected with the pathogenic strain 4 days and 6 days after infection. Together, these results contribute to a greater understanding of the pathogenesis of EIAV and of the mechanisms by which the immune response is induced after EIAV infection.

EIAV S2 enhances pro-inflammatory cytokine and chemokine response in infected macrophages

Equine infectious anemia virus (EIAV) infection is distinctive in that it causes a rapid onset of clinical disease relative to other retroviruses. In order to understand the interaction dynamics between EIAV and the host immune response, we explored the effects of EIAV and its S2 protein in the regulation of the cytokine and chemokine response in macrophages. EIAV infection markedly altered the expression pattern of a variety of pro-inflammatory cytokines and chemokines monitored in the study. Comparative studies in the cytokine response between EIAV(17) and EIAV(17DeltaS2) infection revealed that S2 enhances the expression of IL-1alpha, IL-1beta, IL-8, MCP-2, MIP-1beta and IP-10. Moreover, S2 specifically induced the expression of the newly discovered cytokine, IL-34. Taken together, these results may help explain the effect of cytokine and chemokine dysregulation in EIAV pathogenesis and suggest a role of S2 in optimizing the host cell environment to promote viral dissemination and replication.

Validation of quantitative polymerase chain reaction assays for measuring cytokine expression in equine macrophages

The study of the equine immune system and inflammatory responses, by measuring cytokine expression, can provide important insight into disease pathogenesis in the horse. A set of quantitative real-time polymerase chain reaction (QPCR) assays for the equine cytokines IL-1alpha, IL-1beta, IL-6, IL-8 and TNF-alpha were validated using QPCR primers and probes which were generated for the equine IL-1alpha, IL-1beta, IL-6, IL-8, TNF-alpha and 18S genes. Amplification efficiency, intra-assay and inter-assay variation were determined using 10-fold dilutions of plasmid for each gene. Under these conditions the amplification efficiencies of the primers and probes ranged from 99% to 101%. The mean coefficient of variation (CV) across five sets of plasmid DNA for both intra-assay and inter-assay variation was 0.63% (range 0.2% to 1.8%). Amplification efficiency was also determined using 2-fold dilutions of cDNA and under these conditions amplification efficiency ranged from 83% to 95%. The specificity of amplification was confirmed by DNA sequencing of reaction products. The QPCR assays were also evaluated using three sets of cDNA from equine monocyte derived macrophages (EMDM) stimulated for 1 h with lipopolysaccharide (LPS). The general trend was the same for all three samples with IL-1alpha showing the greatest induction and IL-6 the lowest induction. The range of cytokine induction was greater than has previously been reported with values ranging from 12-fold to 30,000-fold. We present a set of QPCR primers and probes that are suitable for quantitation of expression of a set of equine cytokines. The primers and probes have been rigorously analyzed, and we demonstrate that they are specific for the desired genes, have a high amplification efficiency and the assays are highly reproducible.

SU proteins from virulent and avirulent EIAV demonstrate distinct biological properties

Biologic activity of equine infectious anemia virus (EIAV) surface (SU) glycoprotein was assayed in a mouse model. Recombinant SU from virulent EIAV17 (SU17), administered intraperitoneally to mouse pups, induced dose-dependent diarrheal responses similar to those reported for SIV SU (Virology 277 (2000) 250). SU17 caused fluid accumulation without histological lesions in mouse intestinal loops, induced chloride secretory currents in Ussing chambers and increased inositol 1,4,5 triphosphate (IP3) levels in HT29 cells. An SU17 peptide, SU17(299-330), provoked a dose-dependent diarrheal response akin to enterotoxic peptides from SIV. In contrast, SU from an avirulent EIAV strain failed to induce a dose response in mouse pups and produced lower levels of activity than SU17 in Ussing chambers and IP3 assays. These results demonstrate that a mouse pup model is useful to monitor EIAV SU biologic activity, showing clear differences between the activities of SU derived from virulent and avirulent viruses, and may provide a useful screen of EIAV virulence.