Recombinant beta interferon could clear the low-dose infected porcine reproductive and respiratory syndrome virus (PRRSV) in MARC-145 cells

Porcine reproductive and respiratory syndrome virus (PRRSV) causes one of the most economically devastating and pandemic porcine diseases. Previous study has shown that MARC-145 cells pretreated with recombinant IFN-beta (rIFN-beta) couldn't develop cytopathic effect (CPE) of PRRSV. However, up to date, it is not clear whether MARC-145 cells post-treated with rIFN-beta could develop CPE of PRRSV. The present work showed that the MARC-145 cells didn't develop the CPE at 120 hr post-infection (p.i.) with low-dose of PRRSV when the cells were pre-treated with rIFN-beta (Group 1), post-treated with rIFN-beta at 4 hr p.i. (Group 2), or post-treated with rIFN-beta at 8 hr p.i. (Group 3), while the MARC-145 cells could develop CPE when the cells were infected with high-dose PRRSV and then treated with rIFN-beta at 24 hr p.i.. Furthermore, the indirect immunofluorescence assay confirmed that there were a few N protein-positive cells in the high-dose infected cells in Group 1, Group 2 and Group 3, while there were no N protein-positive cells in the low-dose infected. cells in all rIFN-beta treatment groups. In addition, the numbers of N protein-positive cells in high-dose infected cells (MOI = 10) in Group 1 were lower than that in Group 2 and Group 3. The results above demonstrated that both pre-treatment with rIFN-beta and an earlier post-treatment with rIFN-beta could inhibit the PRRSV replication and could clear the low-dose infected PRRSV, which indicated that the rIFN-beta had efficient antiviral activities when the cells have been infected with PRRSV.