Propagation of field highly pathogenic porcine reproductive and respiratory syndrome virus in MARC-145 cells is promoted by cell apoptosis

•Propagation of field HP-PRRSV in MARC-145 is cell-density dependent and the propagation is more effective in overgrown cells.•Apoptosis triggered automatically in the overgrown MARC-145 cells promotes the propagation of field virus in these cells.•Induction of apoptosis in MARC-145 cells mimics the promotion and further increased viral production.•A vigorous viral RNA replication and fast virus release in early life cycle of viral infection were detected in the apoptosis induced cells.•Propagation of wild type PRRSV in apoptosis induced cells may provide a way to replicate the virus for clinical diagnosis and vaccine development.

Infection of porcine reproductive and respiratory syndrome virus (PRRSV) induces cell apoptosis both in vivo and in vitro. However, the correlation between host cell apoptosis and PRRSV replication is unclear. Here, the promotion of PRRSV propagation by cell apoptosis in MARC-145 cells was reported. The observation on propagation of field highly pathogenic PRRSV (HP-PRRSV) in MARC-145 cells showed that infection of overgrown MARC-145 cells obviously elevated virus production and cell apoptosis was triggered in these cells before virus inoculation. The investigation on propagation of field HP-PRRSV in apoptosis induced MARC-145 cells displayed that induction of apoptosis further increased the virus production and a vigorous viral RNA replication accompanied by fast virus release in these cells was detected in the initial 24 h post infection. In addition, when field HP-PRRSV was serially passed in drug-treated MARC-145 cells, the progeny viruses kept a stable viral titer and infectivity to its native target cells in the tested generations. In summary, these findings demonstrated that apoptotic MARC-145 cells were more susceptible to field HP-PRRSV and propagation of the virus was promoted by effective replication and cell-to-cell transmission of the virus in these cells.