Classical swine fever virus induces proinflammatory cytokines and tissue factor expression and inhibits apoptosis and interferon synthesis during the establishment of long-term infection of porcine vascular endothelial cells

Abstract

Infection with virulent strains of classical swine fever virus (CSFV) results in an acute haemorrhagic disease of pigs, characterized by disseminated intravascular coagulation, thrombocytopenia and immunosuppression, whereas for less virulent isolates infection can become chronic. In view of the haemorrhagic pathology of the disease, the effects of the virus on vascular endothelial cells was studied by using relative quantitative PCR and ELISA. Following infection, there was an initial and short-lived increase in the transcript levels of the proinflammatory cytokines interleukins 1, 6 and 8 at 3 h followed by a second more sustained increase 24 h post-infection. Transcription levels for the coagulation factor, tissue factor and vascular endothelial cell growth factor involved in endothelial cell permeability were also increased. Increases in these factors correlated with activation of the transcription factor NF-kB. Interestingly, the virus produced a chronic infection of endothelial cells and infected cells were unable to produce type I interferon. Infected cells were also protected from apoptosis induced by synthetic ouble-stranded RNA. These results demonstrate that, in common with the related pestivirus bovine viral diarrhoea virus, CSFV can actively block anti-viral and apoptotic responses and this may contribute to virus persistence. They also point to a central role for infection of vascular endothelial cells during the pathogenesis of the disease, where a proinflammatory and procoagulant endothelium induced by the virus may disrupt the haemostatic balance and lead to the coagulation and thrombosis seen in acute disease.

Classical swine fever virus induces activation of plasmacytoid and conventional dendritic cells in tonsil, blood, and spleen of infected pigs

“…Other in vitro investigations showed that CSFV also disrupted secretion of IFN-α and proinflammatory cytokines in porcine aortic and kidney endothelial cell lines [7,11]. It is to emphasize that CSFV-infected mo-DC were able to mature only when TNF-α and IFN-α were added into culture medium [13].…”

Classical swine fever virus infection protects aortic endothelial cells from pIpC-mediated apoptosis

“…The presence of an apoptosis-resistant, infected cell population, such as endothelial cells, is consistent with the high viral loads detected in acutely infected animals. Endothelial cells are important immune modulators (Bensaude et al, 2004;Campos et al, 2004) and so infection of these cells is likely to play a key role in the immunosuppressant and haemorrhagic effects of CSFV.…”

“…Previously, it was found that CSFV infection of primary porcine endothelial cells could counteract the pro-apoptotic effects of the dsRNA mimic pIpC (Bensaude et al, 2004). However, little was known concerning the mechanistic aspects of this process.…”

“…A well-described mechanism of cellular recognition of dsRNA is that mediated by PKR, which results in the inhibition of translation followed by apoptosis due to lack of protein expression (Garcia et al, 2007). Studies have also suggested a direct role for PKR in inducing apoptosis through caspase-8 and -9 (Iordanov et al, 2005a, b Previously, it was found that CSFV infection of primary porcine endothelial cells could counteract the pro-apoptotic effects of the dsRNA mimic pIpC (Bensaude et al, 2004). However, little was known concerning the mechanistic aspects of this process.…”

“…These observations suggest a complex interplay between the virus and the host immune system. CSFV infection is accompanied by depression of cellular immune defences (Ganges et al, 2008) and particularly innate responses mediated by interferon (Bensaude et al, 2004;La Rocca et al, 2005;Ruggli et al, 2005;Seago et al, 2007). In vivo, elevated levels of cell death by apoptosis are thought to account for the characteristic depletion of circulating leukocytes (Sanchez-Cordon et al, 2002;Summerfield et al, 2000Summerfield et al, , 2001.…”