Submitted to: Veterinary Immunology and Immunopathology
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/28/2010
Publication Date: 10/7/2010
Citation: He, D., Overend, C., Ambrogio, J., Magant, R.J., Grubman, M.J., Garmendia, A.E. 2010. Marked differences between MARC-145 cells and swine alveolar macrophages in IFN beta-induced activation of antiviral state against PRRSV. Veterinary Immunology and Immunopathology. Available: www.elsevier.com/locate/vetimm.2010.07.023. Interpretive Summary: Porcine reproductive respiratory syndrome virus (PRRSV) is considered one of the most important pathogens of swine and adversely affects the industry as a result of direct and indirect losses. PRRSV has become widely distributed throughout the world and substantial efforts are ongoing to design rational and effective control strategies. The mechanisms of protective immunity against PRRSV are not completely understood although there appears to be a consensus that both neutralizing antibody and cellular immunity are required for protection. Despite a high variability between animals, a strong cellular immunity appears to correlate with protection from PRRSV. Innate immunity plays a crucial role as a first line of defense against viral infections, including PRRSV, and it is characterized by being rapidly induced upon infection. We have previously constructed a replication-defective human adenovirus type 5 (Ad5) vector containing the swine interferon beta (IFNbeta) gene (Ad5-swIFNbeta) and demonstrated high levels of expression of biologically active IFNbeta protein in swine cells. This virus also induced a rapid antiviral response after administration to swine. Recently we demonstrated that some PRRSV isolates are sensitive to swIFNbeta. The present study was conducted to expand our understanding of the effects of IFNbeta on infection with PRRSV and compare the growth characteristics of different PRRSV isolates and their sensitivity to IFNbeta. We examined the ability of swIFNbeta to inhibit replication of different PRRSV isolates in both swine alveolar macrophages and MARC-145 cells, a monkey cell line susceptible to PRRSV. Initial data on the mechanism(s) of IFNbeta induced inhibition of PRRSV is discussed.
Technical Abstract: The replication kinetics of field isolates and a vaccine virus of porcine reproductive and respiratory syndrome virus (PRRSV) were evaluated in MARC-145 cells and porcine alveolar macrophages (PAM). In MARC-145 cells, the eclipse period of the vaccine virus was about 10 hours and was shorter than that observed with the field isolates. Conversely, in PAMs the eclipse period was about 12 hours for isolates Mo25544 and PDV130-9301 while the vaccine virus was detected at a later time point. The sensitivity of PRRSV isolates to recombinant swine interferon beta (rswIFNbeta) was also examined. In MARC-145 cells, Mo25544 was sensitive while the vaccine strain and PDV130-9301 were resistant to different extents. The sensitivity of an additional isolate Mo1257 was intermediate between that of the vaccine virus and Mo25544. In contrast, all the isolates and the vaccine virus were sensitive to rswIFNbeta in PAMs. Treatment with 2-aminopurine (2-AP), an inhibitor of double-stranded RNA-dependent protein kinase, restored virus replication of Mo25544, vaccine virus and PDV130-9301 in MARC-145 cells primed with rswIFNbeta. In contrast, virus replication could not be rescued with 2-AP in rswIFNbeta-treated PAMs indicating that these cells may respond through different antiviral pathways. The data suggest that replication differences do not necessarily correlate with differences in sensitivity to rswIFNbeta. However, the rswIFNbeta-induced antiviral response in PAMs was stronger than that of MARC-145 cells. Therefore, comparative molecular analyses between IFNbeta-sensitive and resistant isolates and between cells may help elucidate the mechanism PRRSV utilizes to evade the host innate immune response.