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Bluetongue virus (BTV) infection causes a haemorrhagic disease in sheep, whereas BTV infection typically is asymptomatic in cattle. Injury to the endothelium of small blood vessels is responsible for the manifestations of disease in BTV-infected sheep. The lungs are central to the pathogenesis of BTV infection of ruminants ; thus endothelial cells (ECs) cultured from the pulmonary artery and lung microvasculature of sheep and cattle were used to investigate the basis for the disparate expression of bluetongue disease in the two species. Ovine and bovine microvascular ECs infected at low multiplicity with partially purified BTV were equally susceptible to BTV-induced cell death, yet ovine microvascular ECs had a lower incidence of infection and produced significantly less virus than did bovine microvascular ECs. Importantly, the relative proportions of apoptotic and necrotic cells were significantly different in BTV-infected EC cultures depending on the species of EC origin and the presence of inflammatory mediators in the virus inoculum. Furthermore, BTV-infected ovine lung microvascular ECs released markedly less prostacyclin than the other types of ECs. Results of these in vitro studies are consistent with the marked pulmonary oedema and microvascular thrombosis that characterize bluetongue disease of sheep but which rarely, if ever, occur in BTV-infected cattle.

Bluetongue is an insect-transmitted disease of sheep and wild ruminants that is caused by bluetongue virus (BTV). Cattle are asymptomatic reservoir hosts of BTV. Infection of lung microvascular endothelial cells (ECs) is central to the pathogenesis of BTV infection of both sheep and cattle, but it is uncertain as to why sheep are highly susceptible to BTV-induced microvascular injury, whereas cattle are not. Thus, to better characterize the pathogenesis of bluetongue, the transcription of genes encoding a variety of vasoactive and inflammatory mediators was quantitated in primary ovine lung microvascular ECs (OLmVECs) exposed to BTV and/or inflammatory mediators. BTV infection of OLmVECs increased the transcription of genes encoding interleukin- (IL) 1 and IL-8, but less so IL-6, cyclooxygenase-2, and inducible nitric oxide synthase. In contrast, we previously have shown that transcription of genes encoding all of these same mediators is markedly increased in BTV-infected bovine lung microvascular ECs and that BTV-infected bovine ECs produce substantially greater quantities of prostacyclin than do sheep ECs. Thus, sheep and cattle were experimentally infected with BTV to further investigate the role of EC-derived vasoactive mediators in the pathogenesis of bluetongue. The ratio of thromboxane to prostacyclin increased during BTV infection of both sheep and cattle, but was significantly greater in sheep (P = 0.001). Increases in the ratio of thromboxane to prostacyclin, indicative of enhanced coagulation, coincided with the occurrence of clinical manifestations of bluetongue in BTV-infected sheep. The data suggest that inherent species-specific differences in the production and activities of EC-derived mediators contribute to the sensitivity of sheep to BTV-induced microvascular injury.

A panel of six neutralizing murine monoclonal antibodies (MAbs) to equine arteritis virus (EAV) was produced. The MAbs were characterized by Western immunoblotting assay and competitive ELISA. The six MAbs identify a single neutralization site on a 29K envelope glycoprotein. Deglycosylation of viral proteins prior to immunoblotting showed that the 29K protein is the glycosylated form of a 20K protein. Equine anti-EAV serum also strongly bound the 29K glycoprotein, as well as an unglycosylated protein of 17K. The equine autisera to EAV blocked the binding of a selected MAb to EAV, whereas normal equine serum did not. Two neutralization-resistant escape mutant (EM) variants of the EAV prototype were produced using MAb 6D10. The phenotypic properties of the EM viruses were characterized by neutralization and immunoblotting assays with two MAbs (6D10 and 5G11). The two MAbs failed to neutralize either EM virus, and they did not react in an immunoblot assay with any proteins of the EM viruses. In contrast, binding of the equine antiserum to viral proteins was equivalent with prototype and EM virus strains. These data clearly indicate that a 29K envelope glyeoprotein expresses at least one neutralization determinant of EAV.

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