Interferon-α response to swine arterivirus (PoAV), the porcine reproductive and respiratory syndrome virus

We studied the interferon-alpha (IFN-alpha) system in relation to the porcine arterivirus (PoAV), porcine reproductive and respiratory syndrome virus (PRRSV). Recombinant porcine IFN-alpha inhibited the growth of this virus in alveolar macrophage cultures, When pigs were challenged intranasally with PoAV, their serum contained IFN-alpha in relatively low concentrations on the second day after challenge and up to 5 days at the latest. Most animals had no IFN-alpha in their lung secretions, even though PoAV replicates in the respiratory tract. In vitro, PoAV replicates in alveolar macrophages, but neither these nor peripheral blood mononuclear cells (PBMC) produced IFN-alpha in response to infection. This may be because PoAV suppresses IFN-alpha production. When macrophages treated with PoAV were superinfected with swine transmissible gastroenteritis virus (TGEV), a known good inducer of IFN, no IFN-alpha was detected. This suppressive effect was lost when the virus was inactivated by UV light. Our results suggest that downregulation of IFN-alpha production may play an important part in enabling PoAV to replicate in cell cultures and in pigs.