The role of pulmonary intravascular macrophages in porcine reproductive and respiratory syndrome virus infection

Abstract

AbstractThe objective of this article is to summarize the current state of knowledge of the complex interaction of porcine reproductive and respiratory syndrome virus (PRRSV) and porcine pulmonary intravascular macrophages (PIMs). PIMs play an important role in pulmonary surveillance, and in the past few years we have investigated their role in PRRSV infection. PRRSV antigens and nucleic acids have been demonstrated in PIMs bothin vitroandin vivo. Examination of cultured PIMs infected with PRRSV revealed the accumulation of viral particles in the smooth-walled vesicles. PRRSV-infected PIMsin vitroyielded a virus titer similar to pulmonary alveolar macrophages. PRRSV infection induces either apoptosis or cell lysis of PIMs. Thein vitrobactericidal activity of PRRSV-infected PIMs is significantly decreased. Phagocytic activity of PIMs, as measured by pulmonary copper clearance, is significantly decreased in PRRSV-infected pigs. This evidence supports the hypothesis that PRRSV-induced damage to PIMs results in increased susceptibility to bacteremic diseases. Recent studies with PRRSV andStreptococcus suiscoinfection confirmed that PRRSV predisposes pigs toS. suisinfection and bacteremia. These results could explain the increase in bacterial respiratory diseases and septicemias observed in PRRSV-infected pigs.