Plasminogen activator urokinase interacts with the fusion protein and antagonizes the growth of Peste des petits ruminants virus

Peste des petits ruminants is an acute and highly contagious disease caused by the Peste des petits ruminants virus (PPRV). Host proteins play a crucial role in viral replication. However, the effect of fusion (F) protein-interacting partners on PPRV infection is poorly understood. In this study, we found that the expression of goat plasminogen activator urokinase (PLAU) gradually decreased in a time- and dose-dependent manner in PPRV-infected goat alveolar macrophages (GAMs). Goat PLAU was subsequently identified using co-immunoprecipitation and confocal microscopy as an F protein binding partner. The overexpression of goat PLAU inhibited PPRV growth and replication, whereas silencing goat PLAU promoted viral growth and replication. Additionally, we confirmed that goat PLAU interacted with a virus-induced signaling adapter (VISA) to antagonize F-mediated VISA degradation, increasing the production of type I interferon. We also found that goat PLAU reduced the inhibition of PPRV replication in VISA-knockdown GAMs. Our results show that the host protein PLAU inhibits the growth and replication of PPRV by VISA-triggering RIG-I-like receptors and provides insight into the host protein that antagonizes PPRV immunosuppression.IMPORTANCEThe role of host proteins that interact with Peste des petits ruminants virus (PPRV) fusion (F) protein in PPRV replication is poorly understood. This study confirmed that goat plasminogen activator urokinase (PLAU) interacts with the PPRV F protein. We further discovered that goat PLAU inhibited PPRV replication by enhancing virus-induced signaling adapter (VISA) expression and reducing the ability of the F protein to degrade VISA. These findings offer insights into host resistance to viral invasion and suggest new strategies and directions for developing PPR vaccines.

Production of small ruminant morbillivirus, rift valley fever virus and lumpy skin disease virus in CelCradle™ -500A bioreactors

BACKGROUND

Animal vaccination is an important way to stop the spread of diseases causing immense damage to livestock and economic losses and the potential transmission to humans. Therefore effective method for vaccine production using simple and inexpensive bioprocessing solutions is very essential. Conventional culture systems currently in use, tend to be uneconomic in terms of labor and time involved. Besides, they offer a limited surface area for growth of cells. In this study, the CelCradle™-500A was evaluated as an alternative to replace conventional culture systems in use such as Cell factories for the production of viral vaccines against small ruminant morbillivirus (PPR), rift valley fever virus (RVF) and lumpy skin disease virus (LSD).

RESULTS

Two types of cells Vero and primary Lamb Testis cells were used to produce these viruses. The study was done in 2 phases as a) optimization of cell growth and b) virus cultivation. Vero cells could be grown to significantly higher cell densities of 3.04 × 109 using the CelCradle™-500A with a shorter doubling time as compared to 9.45 × 108 cells in Cell factories. This represents a 19 fold increase in cell numbers as compared to seeding vs only 3.7 fold in Cell factories. LT cells achieved modestly higher cell densities of 6.7 × 108 as compared to 6.3 × 108 in Cell factories. The fold change in densities for these cells was 3 fold in the CelCradle™-500A vs 2.5 fold in Cell factories. The titers in the conventional system and the bioreactor were not significantly different. However, the Cell-specific virus yield for rift valley fever virus and lumpy skin disease virus are higher (25 virions/cell for rift valley fever virus, and 21.9 virions/cell for lumpy skin disease virus versus 19.9 virions/cell for rift valley fever virus and 10 virions/cell for lumpy skin disease virus).

CONCLUSIONS

This work represents a novel study for primary lamb testis cell culture in CellCradle™-500A bioreactors. In addition, on account of the high cell densities obtained and the linear scalability the titers could be further optimized using other culture process such us perfusion.

Complexities in Isolation and Purification of Multiple Viruses from Mixed Viral Infections: Viral Interference, Persistence and Exclusion

Successful purification of multiple viruses from mixed infections remains a challenge. In this study, we investigated peste des petits ruminants virus (PPRV) and foot-and-mouth disease virus (FMDV) mixed infection in goats. Rather than in a single cell type, cytopathic effect (CPE) of the virus was observed in cocultured Vero/BHK-21 cells at 6^th blind passage (BP). PPRV, but not FMDV could be purified from the virus mixture by plaque assay. Viral RNA (mixture) transfection in BHK-21 cells produced FMDV but not PPRV virions, a strategy which we have successfully employed for the first time to eliminate the negative-stranded RNA virus from the virus mixture. FMDV phenotypes, such as replication competent but noncytolytic, cytolytic but defective in plaque formation and, cytolytic but defective in both plaque formation and standard FMDV genome were observed respectively, at passage level BP8, BP15 and BP19 and hence complicated virus isolation in the cell culture system. Mixed infection was not found to induce any significant antigenic and genetic diversity in both PPRV and FMDV. Further, we for the first time demonstrated the viral interference between PPRV and FMDV. Prior transfection of PPRV RNA, but not Newcastle disease virus (NDV) and rotavirus RNA resulted in reduced FMDV replication in BHK-21 cells suggesting that the PPRV RNA-induced interference was specifically directed against FMDV. On long-term coinfection of some acute pathogenic viruses (all possible combinations of PPRV, FMDV, NDV and buffalopox virus) in Vero cells, in most cases, one of the coinfecting viruses was excluded at passage level 5 suggesting that the long-term coinfection may modify viral persistence. To the best of our knowledge, this is the first documented evidence describing a natural mixed infection of FMDV and PPRV. The study not only provides simple and reliable methodologies for isolation and purification of two epidemiologically and economically important groups of viruses, but could also help in establishing better guidelines for trading animals that could transmit further infections and epidemics in disease free nations.

Assessment of the cytotoxic and anti-viral potential of aqueous extracts from different parts of Acacia nilotica (Linn) Delile against Peste des petits ruminants virus

Peste des petits ruminants virus (PPRV); a negative sense single stranded RNA enveloped virus that causes Peste des petits ruminants (PPR), is dramatically affecting the health status of ruminants all around the world resulting in extensive economical losses in livestock sector. Acacia nilotica (Linn) Delile; a tannin-rich medicinal plant distributed throughout subcontinent, is traditionally used as food for ruminants and possesses anti-viral potential against different RNA viruses. In the current study, aqueous extracts from the bark, leaves and pods of A. nilotica (Linn) Delile indica were evaluated for their cytotoxicity and anti-viral activities against PPRV by adopting MTT colorimetric assay and anti-viral assay using Vero cell line. Aqueous extract from the leaves presented significantly better (P<0.05) anti-PPRV activities in comparison to pods extract. On the contrary, bark extract did not show any anti-viral activity. The data presented in the study could pave a way toward the discovery of novel anti-viral chemicals in the plants against PPRV and other viral diseases.

Early detection of viral excretion from experimentally infected goats with peste-des-petits ruminants virus

We observed 15 goats for 9 days after subcutaneous infection with 10(3) TCID(50) with isolates of peste-des-petits ruminants virus from Africa and India and five concurrent, uninfected control goats. Typical clinical signs of the infection were present in all 15 infected goats by day 8 and in most by day 6 and some signs were present by day 4. However, 6 out of 15 goats already have detectable virus shedding by day 3 and four more were shedding by day 4 and every goat had virus shedding for at least 1 day before the recognition of clinical signs. This experiment indicates that incubatory carriers therefore might play a role in the transmission of PPRV among small ruminants.

The production and evaluation of a standard reference peste des petits ruminants (PPR)-diagnostic antigen using a sonication technique

Peste des petits ruminants (PPR) is a widely spread viral disease with limited sporadic outbreaks particularly among small ruminants. The diagnosis depends on the detection of antibodies by commercially available expensive reagents. The aim of this work was to prepare and evaluate antigen from an attenuated local PPR virus in Egypt. The virus was propagated in Vero cells, subjected to 3 cycles freeze/thaw, concentrated by dialysis and sonicated for 60 seconds at 3.5 power. The antigen was tested for sterility by re-passage several dilutions in Vero cells, and culture for aerobic/anaerobic bacteria, mycoplasma and fungi using selective media. The efficiency of the antigen was evaluated against reference antigen for reactivity using ELISA and agar gel immunodiffusion (AGID) tests. The prepared antigen proved to be completely inactivated, not contaminated and efficient for the detection of antibodies to PPR by both ELISA and AGID tests. In conclusion, the prepared antigen is reliable for serodiagnosis of PPR and can replace the expensive commercial antigenss. Local large scale production of this antigen will facilitate surveillance of the disease in Egypt.

Improved technique for transient expression and negative strand virus rescue using fowlpox T7 recombinant virus in mammalian cells

The suitability of recombinant T7 polymerase produced using either the highly attenuated MVA strain of vaccinia (MVA-T7) or fowlpox virus (FP-T7) for transient expression and negative strand virus rescue was compared in two mammalian cell lines (MDBK and Vero) and in primary cells of bovine, ovine and caprine origin. Such primary cells are more permissive for the growth of wild type strains of morbilliviruses, such as Rinderpest virus and Peste des petits ruminants virus. MVA-T7 was found to be highly cytopathic in the primary cells, multiplying rapidly and killing the cells within 3-5 days of infection, even when very low multiplicities of infection (MOI) were used. In contrast, FP-T7, which appeared to express similar amounts of T7 polymerase, was found to be non-cytopathic in a variety of primary and established cell lines of mammalian origin and was suitable for use in virus rescue experiments. MDBK cells and primary cells, unlike Vero cells, could not be efficiently transfected and so were unsuitable for virus rescue. Optimal conditions for rinderpest virus rescue in Vero cells were established using FP-T7 in place of MVA-T7. This system will be suitable for rescuing other viruses which grow in Vero cells.

A simplified objective method for quantification of peste des petits ruminants virus or neutralizing antibody

A simplified and standardized assay based on haemagglutination of infected culture supernatants was developed to detect peste des petits ruminants (PPR) virus growth in vero cells and to quantify PPR neutralizing antibody. Virus titres estimated by visual reading of cytopathic effects as a criterion were compared with those estimated by haemagglutination of infected supernatants and no statistically significant differences were seen between them. During quantification of PPR antibodies, the titres based on haemagglutination of supernatants on day 5 post-infection had a high sensitivity, specificity and agreement in qualititative comparison with those determined by visual examination of cytopathic effects. In quantitative comparison, the correlation coefficient between serum neutralization titres estimated by visual examination of cytopathic effects or haemagglutination of supernatants was 0.96, when haemagglutination was done on day 5 post-infection. The virus and serum neutralization titres can thus be estimated objectively using the haemagglutination of supernatants as criterion to measure endpoints. The haemagglutination-inhibition titres also correlated well with serum neutralization titres with a coefficient of 0.78. Thus the haemagglutination-inhibition test appears to be a suitable alternative to the serum neutralization test for quantification of PPR neutralizing antibody.