Abstract
BackgroundPorcine reproductive and respiratory syndrome virus (PRRSV) continues to be an important problem for the swine industry. Inactivated vaccines and modified-live virus vaccines are widely used in the field; however, the efficacy of these PRRSV vaccines is suboptimal due to poor immunogenicity. Granulocyte–macrophage colony stimulating factor (GM-CSF) has been extensively used as an effective genetic and protein adjuvant to enhance the efficiencies vaccines expressing tumor or pathogen antigens. The purpose of this study was to determine if GM-CSF could increase the efficiency of PRRSV vaccine.MethodsThe GM-CSF gene was inserted in the HuN4-F112 vaccine strain by overlap PCR. The expression of GM-CSF by the recombinant virus was confirmed with methods of indirect immunofluorescent assay (IFA) and Western blotting. The stability of recombinant virus was assessed by cDNA sequence and IFA after 20 passages. To detect the biological activity of GM-CSF expressed by the recombinant virus, bone marrow-derived dendritic cells (BMDCs) were isolated and co-cultured with the recombinant virus or parental virus and the surface phenotypes of BMDCs were examined by flow cytometric analysis. The cytokines secreted by BMDCs infected with PRRSV, or treated with LPS, GM-CSF or medium alone were evaluated by ProcartaPlexTM Multiplex Immunoassays and qRT-PCR.ResultsA novel modified-live PRRSV vaccine strain expressing GM-CSF (rHuN4-GM-CSF) was successfully constructed and rescued. The GM-CSF protein was stable expressed in recombinant virus-infected cells after 20 passages. Analysis of virus replication kinetics showed that the novel vaccine strain expressing GM-CSF had a similar replication rate as the parental virus. In vitro studies showed that infection of porcine BMDCs with rHuN4-GM-CSF resulted in increased surface expression of MHCI+, MHCII + and CD80/86+ that was dependent on virus expressed GM-CSF. The expression of representative cytokines was significantly up-regulated when BMDCs were incubated with the recombinant GM-CSF expressing virus.ConclusionsOur results indicated that the expression of GM-CSF during infection with a vaccine strain could enhance the activation of BMDCs and increase cytokine response, which is expected to result in higher immune responses and may improve vaccine efficacy against PRRSV infection.
Highlights
Porcine reproductive and respiratory syndrome virus (PRRSV) continues to be an important problem for the swine industry
Construction and rescue of the recombinant PRRSV Pei et al [26] and Lawson SR et al [15] showed that the position between ORF1b and ORF2 of PRRSV is a suitable site for foreign gene insertion [15,26]
The Granulocyte–macrophage colony stimulating factor (GM-CSF) gene and the synthesized transcription-regulating sequence 6 (TRS6) sequence were inserted between the stop codon of ORF1b and the start codon of ORF2 of the infectious molecular clone of HuN4-F112 vaccine strain by overlap PCR (Figure 1)
Summary
Porcine reproductive and respiratory syndrome virus (PRRSV) continues to be an important problem for the swine industry. Inactivated vaccines and modified-live virus vaccines are widely used in the field; the efficacy of these PRRSV vaccines is suboptimal due to poor immunogenicity. In 2006, a highly virulent strain of PRRSV (HP-PRRSV), which caused significant morbidity can be characterized by high fever, was first detected in China and rapidly spread to most provinces of China [4,5,6]. Under these circumstances, vaccination against PRRSV provides invaluable support to increase host resistance, reduce environmental contamination, and reduce the chance of regional outbreaks. To respond to the recently emerged HP-PRRSV, new live attenuated vaccines were developed by passaging HP-PRRSV isolates in MARC-145 cell lines [7,8,9]
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