Induction and inhibition of apoptosis by pseudorabies virus in the trigeminal ganglion during acute infection of swine

We examined the ability of pseudorabies virus (PRV) to induce and suppress apoptosis in the trigeminal ganglion during acute infection of its natural host. Eight pigs were intranasally inoculated with a virulent field strain of PRV, and at various early times after inoculation, the trigeminal gangli a were assessed histologically. PRV-infected cells were detected by use of immunohistochemistry and in situ hybridization, and apoptosis was identifie d by in situ terminal deoxynucleotidyltransferase-mediated dUTP nick end la beling. Light and electron microscopy was also used for morphological studi es. Apoptosis was readily detected among infiltrating immune cells that wer e located surrounding PRV-infected neurons. The majority of PRV-infected ne urons did not show morphological or histochemical evidence of apoptosis, ev en including those neurons that were surrounded by numerous inflammatory ce lls and exhibited profound pathological changes. However, neuronal virus-in duced apoptosis also occurred but at a sporadic low level. These findings s uggest that PRV is able to block apoptosis of infected trigeminal ganglioni c neurons during acute infection of swine. Furthermore, our results also su ggest that apoptosis of infiltrating inflammatory cells may represent an im portant viral mechanism of immune evasion.