The activation of the IFN beta induction/signaling pathway in porcine alveolar macrophages by porcine reproductive and respiratory syndrome virus is variable

Background It has been recognized that the expression of type I interferon (IFN alpha/beta) may be suppressed during infection with porcine reproductive, respiratory syndrome virus (PRRSV). This causes profound negative effects on both the innate and adaptive immunity of the host resulting in persistence of infection. Objective Test the effects of PRRSV infection of porcine alveolar macrophages (PAMs), the main target cell, on the expression of interferon beta (IFN beta) and downstream signaling events. Methods In order to examine those effects, PAMs harvested from lungs of healthy PRRSV-free animals were infected with virulent, attenuated, infectious clone-derived chimeric viruses, or field PRRS virus strains. Culture supernatants from the infected PAMs were tested for IFN beta protein expression by means of indirect ELISA and for bioactivity by a vesicular stomatitis virus plaque reduction assay. The expression of the Mx protein was assayed to ascertain signaling events. Results These experiments demonstrated that PRRSV does induce variably, the expression of bioactive IFN beta protein in the natural host cell. To further elucidate the effects of PRRSV infection on IFN beta signaling, Mx-1 an interferon stimulated gene (ISG), was also tested for expression. Interestingly, Mx-1 expression by infected PAMs generally correlated with IFN beta production. Conclusion The results of this study demonstrate that the induction of IFN beta and signaling in PAMs after PRRSV infection is variable.