In vivo and in vitro interferon (IFN) studies with the porcine reproductive and respiratory syndrome virus (PRRSV).

Some of the interactions between the porcine reproductive and respiratory syndrome virus (PRRSV) and the porcine interferon-alpha (IFN-alpha) system were studied. In a first experiment, it was shown that pretreatment of primary porcine alveolar macrophages (AMs) with recombinant porcine (rPo) IFN-alpha 1 resulted in significant reductions of PRRSV yield and numbers of antigen expressing cells. In a second experiment, sensitivity of PRRSV to IFN-alpha was confirmed in vivo. In pigs inoculated with porcine respiratory coronavirus (PRCV)--a potent inducer of endogenous IFN-alpha in the lungs of pigs--followed 2 days later by PRRSV--lung PRRSV titers were 1.7 to 2.9 log10 TCID50 reduced compared to those in singly PRRSV inoculated pigs. It was concluded therefore that PRRSV has a fairly good sensitivity to the antiviral effects of IFN-alpha. A third experiment documented that in vivo PRRSV infection generally does not affect PRCV-induced IFN-alpha production in the lungs of pigs. In addition, it was shown that the IFN-inducing capacity of PRRSV is at least 159 times lower than that of PRCV. This finding suggests that cells other than AMs may be responsible for IFN production in the lungs of pigs.