Expression of the putative ORF1 capsid protein of Torque teno sus virus 2 (TTSuV2) and development of Western blot and ELISA serodiagnostic assays: correlation between TTSuV2 viral load and IgG antibody level in pigs

Porcine Torque teno virus (TTV) has a single-stranded circular DNA genome and is currently classified into a new genus Iotatorquevirus with two species in a newly established family Anelloviridae. Viral DNA of both porcine TTV species (TTSuV1 and TTSuV2) has a high prevalence in both healthy and diseased pigs worldwide and multiple infections of TTSuV with distinct genotypes or subtypes of the same species has been documented in the United States and in Europe. However, the prevalence of specific TTSuV antibodies in pigs remains unknown. In this study, the putative ORF1 capsid protein from TTSuV2 isolate PTTV2c-VA was expressed in Escherichia coli. The purified recombinant ORF1 protein was used as the antigen for the development of Western blot and indirect ELISA to detect TTSuV2-specific IgG antibodies in pig sera. The results revealed a relatively high rate of seropositivity to TTSuV2 in conventional pigs from different sources but not in gnotobiotic pigs. Overall, pigs with undetectable TTSuV2 viral load were more likely to have a lower anti-TTSuV2 antibody level. An analysis of 10 conventional pigs during a 2-month period showed that decreased viral loads or presumed virus clearance were associated with elevated anti-ORF1 IgG antibody levels. Interestingly, porcine circovirus associated disease (PCVAD)-affected pigs had a significantly lower level of TTSuV2 antibody than PCVAD-unaffected pigs (p<0.01). This is the first study to establish essential serodiagnostic tools for investigation of TTSuV seroprevalence and infection dynamics, which will help elucidate the potential pathogenicity of TTSuV infection in pigs.

Pathogenicity of three isolates of porcine respiratory coronavirus in the USA

The pathogenicity of three isolates of porcine respiratory coronavirus (AR310, LEPP and 1894) from the USA was assessed in specific pathogen-free pigs. Pigs inoculated with 1894 developed mild respiratory disease and pigs inoculated with AR310 and LEPP developed moderate respiratory disease from four to 10 days after they were inoculated, but all the pigs recovered fully by 14 days after inoculation. Gross and microscopic examination revealed mild (1894) to moderate (AR310 and LEPP) multifocal bronchointerstitial pneumonia from four to 10 days after inoculation. The lesions were characterised by necrotising bronchiolitis, septal infiltration with mononuclear cells, and a mixed alveolar exudate. No clinical signs or microscopic lesions were observed in control pigs that had not been inoculated.

Antigenic and genetic stability of bovine immunodeficiency virus during long-term persistence in cattle experimentally infected with the BIV(R29) isolate

Experimental infection of cattle with bovine immunodeficiency virus (BIV) is characterized by persistent, low levels of virus replication in the absence of clinical disease. A virus neutralization (VN) assay was developed to examine the role of VN antibodies in controlling virus replication in cattle experimentally infected with the BIV(R29) isolate of BIV. All animals developed VN antibody, but there was no correlation between VN titres and restriction of virus replication in vivo. BIV infection did not induce high-titred, cross-neutralizing antibody and there was no evidence for antigenic variation through more than 4 years in vivo. Genetic comparisons among the BIV(R29) inoculum virus and viruses isolated from infected animals identified only limited genetic variation during 4 years in vivo. Moreover, there was no evidence that the observed variation was due to selection. Analyses of genetic diversity in the virus stock used for inoculation indicated a fairly homogeneous population. In the absence of high levels of virus replication and overt clinical disease, there appeared to be little selection of virus variants, resulting in antigenic and genetic stability of BIV(R29) during long-term, persistent infection.

Characterization of primary cell cultures as potential target cells for analysis of bovine cytotoxic T lymphocytes

In domestic animal species, assessment of cell-mediated immune responses to virus infection is hampered by the requirement for class I MHC compatibility between target and effector cells. Additional complicating factors can include an inability to infect target cells in vitro, or virus-induced lysis of infected target cells. One way to circumvent these problems is to use virus-mediated gene transfer to deliver individual viral genes to autologous primary target cells. Several primary bovine cell cultures were assessed as potential target cells for cytotoxic T lymphocyte (CTL) assays by measuring their levels of class I MHC expression and susceptibilities to retroviral gene delivery. High levels in both class I MHC expression and susceptibility to gene delivery were seen in adherent cell cultures isolated from peripheral blood (PBAC). PBAC, which arose as an outgrowth of adherent peripheral blood mononuclear cell cultures, had morphology, protein expression patterns, and response to functional assays characteristic of high endothelial cells. Expression of viral vector-delivered genes in PBAC cells was confirmed with a recombinant retrovirus carrying the green fluorescent protein (GFP) gene. The use of vector-mediated delivery of viral genes to bovine high endothelial cells is a promising method for assessment of cell-mediated immunity in cattle.

Pathogenicity and sequence analysis studies suggest potential role of gene 3 in virulence of swine enteric and respiratory coronaviruses

Coronaviruses have been commonly associated with enteric and respiratory diseases. Two of the swine coronaviruses, namely transmissible gastroenteritis virus (TGEV) and porcine respiratory coronavirus (PRCV), have been extensively studied. TGEV replicates in both the enteric and respiratory tracts and causes enteric disease, whereas, PRCV replicates in the respiratory tract with limited to no replication in the enteric tract. We have isolated PRCV from swine herds with respiratory disease and have reproduced moderate pneumonia in gnotobiotic and conventionally reared pigs with two of the PRCV isolates. We have also identified two PRCV isolates with low virulence. One consistent difference that we have observed between PRCV isolates of different pathogenicities is in gene 3. The gene 3 is intact in the two virulent PRCV isolates, whereas gene 3 is altered in the two low virulence isolates. A similar observation has been reported for TGEV as a nonpathogenic TGEV mutant with a small plaque morphology had a deletion in gene 3. We have also observed that one of the low virulence PRCV isolates, IA 1894, which has a deletion in gene 3, replicates poorly in cell cultures. Collectively these studies suggest that gene 3 may be an important determinant for in vivo virulence and in vitro replication of coronaviruses.

Sequence comparison of porcine respiratory coronavirus isolates reveals heterogeneity in the S, 3, and 3-1 genes

Four new porcine respiratory coronavirus (PRCV) isolates were genetically characterized. Subgenomic mRNA patterns and the nucleotide sequences of the 5' ends of the S genes, the open reading frame (ORF) 3/3a genes, and the ORF 3-1/3b genes of these PRCV isolates were determined and compared with those of other PRCV and transmissible gastroenteritis virus (TGEV) isolates. The S, ORF 3/3a, and ORF 3-1/3b genes are under intense study because of their possible roles in determining tissue tropism and virulence. Northern (RNA) blot analysis of subgenomic mRNAs revealed that mRNA 2, which encodes for the S gene, of the PRCV isolates migrated faster than the mRNA 2 of TGEV. The PRCV isolates AR310 and LEPP produced eight subgenomic mRNA species, the same number as produced by the virulent Miller strain of TGEV. However, the PRCV isolates IA1894 and ISU-1 produced only seven subgenomic mRNA species. All four of the PRCV isolates were found to have a large in-frame deletion in the 5' end of the S gene; however, the size and location of the deletion varied. Analysis of the ORF 3/3a gene nucleotide sequences from the four PRCV isolates also showed a high degree of variability in this area. The ORF 3 gene of the PRCV isolates AR310 and LEPP was preceded by a CTAAAC leader RNA-binding site, and the ORF 3 gene was predicted to yield a protein of 72 amino acids, the same size as that of the virulent Miller strain of TGEV. The PRCV isolates AR310 and LEPP are the first PRCV isolates found to have an intact ORF 3 gene. The ORF 3a gene of the PRCV isolate IA1894 was preceded by a CTAAAC leader RNA-binding site and was predicted to yield a truncated protein of 54 amino acids due to a 23-nucleotide deletion. The CTAAAC leader RNA-binding site and ATG start codon of ORF 3 gene of the PRCV isolate ISU-1 were removed because of a 168-nucleotide deletion. Analysis of the ORF 3-1/3b gene nucleotide sequences from the four PRCV nucleotides isolates also showed variability.

Three new isolates of porcine respiratory coronavirus with various pathogenicities and spike (S) gene deletions

Three new isolates of porcine respiratory coronavirus (PRCV) were isolated and partially characterized. These PRCV isolates showed a selective tropism for respiratory tissue and were antigenically related to transmissible gastroenteritis virus. PCR amplification of the 5' half of the spike (S) genes of the three PRCV isolates indicated that a large deletion, characteristic of PRCV, was present. By using cDNA probes specific for the transmissible gastroenteritis virus S gene, the PCR products were shown to be specific in a Southern blot. The three new PRCV isolates were shown to vary in S gene deletion size. In a separate study, these isolates have also been shown to vary in pathogenicity. These new PRCV isolates should serve as important tools in gaining a better understanding of the pathogenesis of coronavirus infections.

Antigenic and biological diversity among transmissible gastroenteritis virus isolates of swine

Twenty-four field isolates of transmissible gastroenteritis virus (TGEV) were isolated and examined for antigenic and biological characteristics. Most TGEV isolates produced a typical cytopathic effect (CPE) in swine testis (ST) cell culture, which included a ballooning or lifting away of the infected cells from the cell monolayer with heavy granulation evident. Minor variations in CPE were observed with one isolate, IA-145. Protein profiles of the TGEV isolates as determined by SDS-PAGE were essentially identical, with the exception of the isolate IA-101. The TGEV isolate IA-101 presented a higher molecular mass M protein and lacked an N protein doublet that was present in all other TGEV isolates. The TGEV isolates were shown to be closely related antigenically by using hyperimmune sera in a virus neutralization (VN) test. Some antigenic diversity was detected by utilizing monoclonal antibodies (mAbs) in a VN test. Titers of the mAbs were highest with the homologous Miller TGEV, and one virus isolate, IA-156, was very poorly neutralized with the mAbs used in this study. Indirect immunofluorescence assay (IFA) results were similar to those obtained by the VN test. These studies show that some biologic and antigenic diversity exists among TGEV isolates.

Experimental reproduction of pneumonia in gnotobiotic pigs with porcine respiratory coronavirus isolate AR310

The pathogenicity of porcine respiratory coronavirus (PRCV) isolate AR310 was determined for gnotobiotic pigs. PRCV-AR310 was isolated from the intestines of a nursery pig from a herd with endemic transmissible gastroenteritis. The AR310 isolate was plaque purified and cell culture propagated, passed once in a gnotobiotic pig, then used as inoculum for a gnotobiotic pig pathogenicity study. Eight pigs were inoculated oronasally with 2 x 10(6) plaque-forming units of PRCV-AR310. Eight pigs served as controls and received cell culture medium. Two pigs from each group were necropsied at 3, 5, 10, and 15 days postinoculation (DPI). There was moderate multifocal to coalescing reddish tan consolidation of 60% of the lung by 10 DPI. Microscopic examination revealed a necrotizing and proliferative bronchointerstitial pneumonia characterized by necrosis, squamous metaplasia, dysplasia, proliferation of airway epithelium, mononuclear cell infiltration of alveolar septa, mild type II pneumocyte proliferation, and lymphohistiocytic alveolar exudation. The microscopic lesions were mild by 3 DPI, moderate by 5 DPI, severe by 10 DPI, and mostly resolved by 15 DPI. No lesions were observed in the intestines of these pigs. There was no clinical respiratory disease. Control pigs remained normal and had no lesions. PRCV was isolated from the lungs but not from the intestines of inoculated pigs. PRCV was not isolated from the lungs or intestines of control pigs. PRCV was also isolated from the nasal and rectal swabs of inoculated but not of control pigs.

Controlled trial of pulse methylprednisolone versus two regimens of pulse cyclophosphamide in severe lupus nephritis

Pulse cyclophosphamide is more effective than prednisone alone in preventing renal failure in lupus nephritis. We undertook a randomised, controlled trial to find out whether pulse methylprednisolone could equal pulse cyclophosphamide in preserving renal function in patients with lupus nephritis, and whether there was a difference between long and short courses of pulse cyclophosphamide in preventing exacerbations. 65 patients (60 female, 5 male; median [range] age 29 [10-48] years) with severe lupus nephritis were assigned randomly to monthly pulse methylprednisolone for 6 months (25 patients), monthly pulse cyclophosphamide for 6 months (20), or monthly cyclophosphamide for 6 months followed by quarterly pulse cyclophosphamide for 2 additional years (20). Patients treated with pulse methylprednisolone had a higher probability of doubling serum creatinine than those treated with long-course cyclophosphamide (p less than 0.04). Risk of doubling creatinine was not significantly different between short and long course cyclophosphamide. However, patients treated with short-course cyclophosphamide had a higher probability of exacerbations than those treated with long-course cyclophosphamide (p less than 0.01). An extended course of pulse cyclophosphamide is more effective than 6 months of pulse methylprednisolone in preserving renal function in patients with severe lupus nephritis. Addition of a quarterly maintenance regimen to monthly pulse cyclophosphamide reduces the rate of exacerbations.