Cloning and identification of MARC-145 cell proteins binding to 3'UTR and partial nucleoprotein gene of porcine reproductive and respiratory syndrome virus

Development and biological characterization of an infectious cDNA clone of NADC34-like PRRSV

Introduction

Porcine Reproductive and Respiratory Syndrome virus (PRRSV) causes high abortion rates in gestating sows and stillbirths, as well as high piglet mortality, seriously jeopardizing the pig industry in China and worldwide.

Methods

In this study, an infectious clone containing the full-length genome of NADC34-like PRRSV was constructed for the first time using reverse genetic techniques. The gene was amplified segmentally onto a plasmid, transfected into BHK-21 cells, and the transfected supernatant was harvested and transfected into PAM cells, which showed classical cytopathic effects (CPE).

Results

The virus rJS-KS/2021 was successfully rescued which could be demonstrated by Western Blot and indirect immunofluorescence assays. Its growth curve was similar to the original strain. Replace the 5'UTR and 3'UTR of rJS-KS/2021 with 5'UTR and 3'UTR of HP-PRRSV (strain SH1) also failed to propagate on MARC-145.

Discussion

In this study, an infectious clone of NADC34-like was constructed by reverse genetics, replacing the UTR and changing the cellular tropism of the virus. These findings provide a solid foundation for studying the recombination of different PRRSVs and the adaption of PRRSVs on MARC-145 in the future.

Comparison of Primary Virus Isolation in Pulmonary Alveolar Macrophages and Four Different Continuous Cell Lines for Type 1 and Type 2 Porcine Reproductive and Respiratory Syndrome Virus

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) has a highly restricted cellular tropism. In vivo, the virus primarily infects tissue-specific macrophages in the nose, lungs, tonsils, and pharyngeal lymphoid tissues. In vitro however, the MARC-145 cell line is one of the few PRRSV susceptible cell lines that are routinely used for in vitro propagation. Previously, several PRRSV non-permissive cell lines were shown to become susceptible to PRRSV infection upon expression of recombinant entry receptors (e.g., PK15^Sn-CD163, PK15^S10-CD163). In the present study, we examined the suitability of different cell lines as a possible replacement of primary pulmonary alveolar macrophages (PAM) cells for isolation and growth of PRRSV. The susceptibility of four different cell lines (PK15^Sn-CD163, PK15^S10-CD163, MARC-145, and MARC-145^Sn) for the primary isolation of PRRSV from PCR positive sera (both PRRSV1 and PRRSV2) was compared with that of PAM. To find possible correlations between the cell tropism and the viral genotype, 54 field samples were sequenced, and amino acid residues potentially associated with the cell tropism were identified. Regarding the virus titers obtained with the five different cell types, PAM gave the highest mean virus titers followed by PK15^Sn-CD163, PK15^S10-CD163, MARC-145^Sn, and MARC-145. The titers in PK15^Sn-CD163 and PK15^S10-CD163 cells were significantly correlated with virus titers in PAM for both PRRSV1 (p < 0.001) and PRRSV2 (p < 0.001) compared with MARC-145^Sn (PRRSV1: p = 0.22 and PRRSV2: p = 0.03) and MARC-145 (PRRSV1: p = 0.04 and PRRSV2: p = 0.12). Further, a possible correlation between cell tropism and viral genotype was assessed using PRRSV whole genome sequences in a Genome-Wide-Association Study (GWAS). The structural protein residues GP2:187L and N:28R within PRRSV2 sequences were associated with their growth in MARC-145. The GP5:78I residue for PRRSV2 and the Nsp11:155F residue for PRRSV1 was linked to a higher replication on PAM. In conclusion, PK15^Sn-CD163 and PK15^S10-CD163 cells are phenotypically closely related to the in vivo target macrophages and are more suitable for virus isolation and titration than MARC-145/MARC-145^Sn cells. The residues of PRRSV proteins that are potentially related with cell tropism will be further investigated in the future.

Innate immune responses to replication of porcine reproductive and respiratory syndrome virus in isolated Swine alveolar macrophages

Porcine reproductive and respiratory syndrome (PRRS) is an infectious disease caused by a positive RNA strand arterivirus. PRRS virus (PRRSV) interacts primarily with lung macrophages. Identifying the genetic components involved in host resistance/susceptibility would represent an important step forward in the design of disease control programs. In this study, alveolar macrophages derived from five commercial pig lines were used to study the innate immune response to PRRSV infection in vitro. Analysis by flow cytometry has demonstrated that bronchial alveolar lavage fluid (BALF) preparations were almost exclusively composed of alveolar macrophages and that the pigs tested were free from infection. Macrophages from the Landrace line showed significantly reduced virus replication and poor growth of PRRSV during 30 h of infection. By 72 h, PRRSV viral load was down to 2.5 log(10) TCID(50) compared with an average of 5 log(10) TCID(50) for the other breeds tested. These observations suggest that factors intrinsic to the Landrace breed may be responsible for this reduced or delayed response to PRRSV. Preliminary investigation suggests that the PRRSV coreceptor, sialoadhesin, may not be responsible for the Landrace macrophage phenotype as its abundance and localisation were comparable in all the breeds. Strikingly, we found that the reduced or delayed growth of PRRSV was temporally associated with high levels of tumor necrosis factor-alpha (TNF-alpha) and interleukin (IL)-8 mRNA accumulation and substantial reduction of secretion of IL-8, suggesting a key contributory role for cytokine synthesis and secretion during the innate immune response to PRRSV infection.

Defining the cellular target(s) of porcine reproductive and respiratory syndrome virus blocking monoclonal antibody 7G10

We produced a monoclonal antibody (MAb) (7G10) that has blocking activity against porcine reproductive and respiratory syndrome virus (PRRSV). In this study, we identified the components of the 7G10 MAb-bound complex as cytoskeletal filaments: vimentin, cytokeratin 8, cytokeratin 18, actin, and hair type II basic keratin. Vimentin bound to PRRSV nucleocapsid protein and anti-vimentin antibodies showed PRRSV-blocking activity. Vimentin was expressed on the surface of MARC-145, a PRRSV-susceptible cell line. Simian vimentin rendered BHK-21 and CRFK, nonsusceptible cell lines, susceptible to PRRSV infection. These results suggest that vimentin is part of the PRRSV receptor complex and that it plays an important role in PRRSV binding with the other cytoskeletal filaments that mediate transportation of the virus in the cytosol.