Identification of the strain-specifically truncated nonstructural protein 10 of porcine reproductive and respiratory syndrome virus in infected cells.

The nonstructural protein 10 (nsp10) of porcine reproductive and respiratory syndrome virus (PRRSV) encodes for helicase which plays a vital role in viral replication. In the present study, a truncated form of nsp10, termed nsp10a, was found in PRRSV-infected cells and the production of nsp10a was strain-specific. Mass spectrometric analysis and deletion mutagenesis indicated that nsp10a may be short of about 70 amino acids in the N terminus of nsp10. Further studies by rescuing recombinant viruses showed that the Glu-69 in nsp10 was the key amino acid for nsp10a production. Finally, we demonstrated that nsp10a exerted little influence on the growth kinetics of PRRSV in vitro.

Critical role of cytochrome c1 and its cleavage in porcine reproductive and respiratory syndrome virus nonstructural protein 4-induced cell apoptosis via interaction with nsp4.

Porcine reproductive and respiratory syndrome virus (PRRSV) actively induces cell apoptosis both in vitro and in vivo, which can contribute critically to viral pathogenesis. Previous studies have shown that the PRRSV nonstructural protein 4 (nsp4) is an important mediator of this process, but the underlying molecular details remain poorly understood. In this study, we found that the PRRSV nsp4 interacted with the mitochondrial inner membrane protein cytochrome c1 (cyto.c1) and induced its proteolytic cleavage. Interestingly, the cleaved N-terminal fragment of cyto.c1 was found to exert apoptotic activity, which could cause mitochondrial fragmentation, resulting in apoptotic cell death. And RNA interference (RNAi) silencing experiments further confirmed the crucial role which cyto.c1 played in nsp4- and PRRSV-induced cell apoptosis. Thus, our data provide an important piece of mechanistic clues for PRRSV-induced cell apoptosis and also elucidate a novel mechanism for the 3C-like proteases in this finding.

Cytokine mRNA expression profiles in peripheral blood mononuclear cells from piglets experimentally co-infected with porcine reproductive and respiratory syndrome virus and porcine circovirus type 2.

Porcine reproductive and respiratory syndrome virus (PRRSV) and porcine circovirus type 2 (PCV2) significantly impact the swine industry worldwide. Co-infections with these viruses are common and several lines of evidence suggest that both PRRSV and PCV2 modify host immune responses that facilitate infection. This study examined cytokine mRNA expression profiles of peripheral blood mononuclear cells (PBMCs) from piglets experimentally co-infected with PRRSV and PCV2 to define the influence of co-infection on host immunity. PBMCs from infected and control piglets were stimulated with concanavalin A and the IL-2, IL-4, IL-6, IL-10, IL-12p40, IFN-gamma and TNF-alpha mRNA levels were determined by quantitative reverse transcription-polymerase chain reaction (RT-PCR). PBMCs from PRRSV/PCV2 co-infected piglets had significantly reduced IL-2, IL-4, IL-6, IL-12p40 and IFN-gamma and significantly increased TNF-alpha mRNA levels compared to those of the piglets infected with either PRRSV or PCV2 alone. The IL-10 mRNA levels in all virus-infected groups were significantly up-regulated early during infection. These results suggested that co-infection synergistically suppresses T helper 1 (Th1)-type and Th2-type cytokine production by PBMCs, indicating that co-infection likely compromises cell-mediated and humoral immune responses resulting in increased severity of the diseases in piglets.