The porcine reproductive and respiratory syndrome virus (PRRSV) is one of the most important viral pathogens in the swine industry. Despite great efforts of pig holders, veterinarians, researchers and vaccine developers, the virus still causes major production losses. It is clear that efficient and correct monitoring and rational development of vaccines are crucial in the combat against this pathogen. PRRSV-specific monoclonal antibodies (mAbs) are essential tools for both diagnostic and research purposes. This study describes the production of PRRSV GP3-, GP5- and N-specific hybridomas and an extensive characterization of the mAbs. The N-specific mAbs generated in this study appear to be useful tools for diagnostics, as they were found to react with genetically very different PRRSV isolates and may serve to discriminate between European and American type PRRSV isolates. These mAbs also allowed detection of the PRRSV N protein in both formalin-fixed, paraffin-embedded tissue sections and frozen tissue sections of PRRSV-infected lungs, further illustrating their diagnostic value. Different neutralization assays pointed out that none of the GP3- and GP5-specific mAbs tested shows virus-neutralizing capacity. This is noteworthy, as these mAbs recognize epitopes in the predicted ectodomains of their target protein and since the GP5-specific antibodies specifically react with the antigenic region that corresponds to the "major neutralizing epitope" suggested for American type PRRSV. The current findings argue against an important role of the identified antigenic regions in direct antibody-mediated neutralization of European type PRRSV in vivo. However, it is also clear that findings concerning a specific PRRSV epitope cannot always be generalized, as the antigenic determinants and their biological properties may differ radically between different virus isolates.
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