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

Christopher C. Overend, Junru Cui, Marvin J. Grubman, Antonio E. Garmendia

It has been recognized that the expression of type I interferon (IFNα/β) 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. Test the effects of PRRSV infection of porcine alveolar macrophages (PAMs), the main target cell, on the expression of interferon beta (IFNβ) and downstream signaling events. 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 IFNβ 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. These experiments demonstrated that PRRSV does induce variably, the expression of bioactive IFNβ protein in the natural host cell. To further elucidate the effects of PRRSV infection on IFNβ signaling, Mx-1 an interferon stimulated gene (ISG), was also tested for expression. Interestingly, Mx-1 expression by infected PAMs generally correlated with IFNβ production. The results of this study demonstrate that the induction of IFNβ and signaling in PAMs after PRRSV infection is variable.