Nicolaas Visser

Porcine reproductive and respiratory syndrome virus (PRRSV): monoclonal antibodies detect common epitopes on two viral proteins of European and U.S. isolates.

Sixteen hybridoma cell lines secreting monoclonal antibodies (mAbs) directed against two dutch isolates of the causative virus of Porcine Reproductive and Respiratory Syndrome (PRRSV) were produced. The hybridoma cells resulted from fusions of SP2/0 myeloma cells with splenocytes of STU mice immunized with purified PRRSV after induction of immunotolerance against host cell constituents. Screening of supernatant fluids was performed by an indirect immunofluorescence assay on PRRSV-infected porcine alveolar macrophages. Immunoblotting studies revealed that the mAbs had different protein specificities. One mAb reacted with a viral 15 kD protein, eleven were directed against a 40-50 kD protein, and four against a 30-40 kD protein. The mAb against the 15 kD putative nucleocapsid protein as well as five mAbs against the 40-50 kD protein recognized epitopes on these proteins which are conserved in various European and U.S. isolates of PRRSV.

A mouse model for testing the pathogenicity of equine herpes virus-1 strains.

A mouse model was developed for testing the pathogenicity of equine herpes virus-1 (EHV-1) strains. The model was validated with EHV-1 strains that are known to be of a low or high pathogenicity in horses. From all parameters tested, the safety index, which was calculated from the body weights of the mice after infection, proved to be the best predictive parameter. When this parameter was used, good and reliable correlations were found with the pathogenicity of the EHV-1 strains in horses. This method enabled the differentiation between the two experimental EHV-1 strains whose genetic backgrounds were supposedly equal.

Cell culture-grown putative bovine respiratory torovirus identified as a coronavirus

A putative bovine respiratory torovirus (BRTV) was propagated in bovine fetal diploid lung and human colonic tumour cells, and fringed pleomorphic particles were detected in the culture supernatants by electron microscopy. Antisera directed against a bovine (Breda strain) and equine (Berne strain) torovirus failed to react with BRTV-infected cells in immunofluorescence assays and did not neutralise BRTV. No toroviral RNA was found in the supernatants of infected cells by means of a reverse transcriptase-polymerase chain reaction with torovirus-specific primers. On the other hand, bovine coronavirus-specific antisera and monoclonal antibodies did neutralise the cytopathic effects, and coronaviral antigen was detected in the cultures by immunofluorescence. Furthermore, bovine coronavirus RNA was detected in the supernatants of BRTV-infected cells after nucleic acid amplification. It is concluded that the cytopathic BRTV isolate is a coronavirus.