Abstract
Swine beta interferon (swIFN-) produced in HEK 293 cells infected with a recombinant, replication-defective human adenovirus 5 (Ad5) encoding the swIFN- gene was tested for antiviral activity against Porcine reproductive and respiratory syndrome virus (PRRSV). MARC-145 cells were incubated overnight with dilutions of supernatant fluids from HEK 293 cells infected with Ad5-swIFN- or with an Ad5 control virus (Ad5-Blue). Treated cells were infected with PRRSV; MARC-145 cells incubated with Ad5-Blue supernatants developed cytopathic effects (CPE), whereas those incubated with swIFN- showed no CPE. To confirm the antiviral activity of swIFN-, culture fluids from Ad5-swIFN--infected cells were affinity-purified on a Sepharoseanti-swIFN- matrix, and the resulting fractions exhibited antiviral activity upon infection with PRRSV. The antiviral effects were specific, as they were blocked by mAbs against swIFN-. Additional cultures of MARC-145 cells treated with swIFN--containing supernatants or affinity-purified swIFN- were infected with PRRSV and tested by real-time RT-PCR for viral RNA in culture supernatants at various times post-inoculation. These experiments confirmed the protective effects of swIFN-. swIFN- was also tested for antiviral activity on porcine alveolar macrophages (PAMs) obtained by bronchoalveolar lavage from PRRSV-negative swine. PAMs were treated with dilutions of swIFN- or Ad5-Blue culture fluids, infected with PRRSV and tested for viral RNA by real-time RT-PCR. The viral load data showed a dose-dependent protection in swIFN--treated PAMs, whereas no protection was evident from Ad5-Blue culture fluids. The data demonstrate that swIFN- protects both MARC-145 cells and PAMs from PRRSV infection.