Introduction
When bitten by an arbovirus-infected mosquito, peripheral blood mononuclear cells (PBMCs) are amongst the first cells to encounter the virus and may be vital for the development of antiviral activity. Ross River virus (RRV) infection in horses and humans is often subclinical, however, some individuals experience chronic debilitating arthritogenic signs. Some studies suggest that monocytes may contribute to the chronicity of the disease. However, little is known regarding the interactions between RRV and PBMCs in acute infection.
Methods
EDTA-stabilised blood samples were collected from nine RRV seronegative horses and PBMCs isolated using Ficoll-Histopaque, and the cells challenged with RRV (MOI = 1). Cells were harvested at 6 and 24 hours, and RNA was purified, cDNA synthesised, and qPCR performed for selected inflammatory biomarkers to quantify gene-expression. Results were expressed as means of fold changes (compared to control) ± SEM.
Results
Toll-like receptor 7 (TLR-7) was slightly upregulated from 0.9 ± 0.1 to 1.3 ± 0.2 over time. Interleukin (IL) 6 and 8 were both upregulated over time, from 1.4 ± 0.4 to 13.1 ± 11.7 and from 1.3 ± 0.1 to 2.5 ± 0.9, respectively. Interestingly, there was minimal change in interferon (IFN)-α gene expression, whereas, IFN-γ was markedly upregulated from 2.3 ± 0.6 to 12.9 ± 8.8. Monocyte chemoattractant protein (MCP) 1 was down-regulated from 1.4 ± 0.1 to 0.9 ± 0.2, while MCP-2 was unchanged.
Conclusion
Up-regulation of TLR-7 suggest that PBMCs are involved in early viral recognition and elicit an antiviral response via ILs and IFN-γ, when encountering RRV, to control viral replication and inflammation. The role of MCPs in the pathogenesis of RRV may be minimal. More studies are underway to elucidate the equine innate immune response to RRV.