Abstract
The rapid evolution of porcine reproductive and respiratory syndrome viruses (PRRSV) poses a major challenge to effective disease control since available vaccines show variable efficacy against divergent strains. Knowledge of the antigenic targets of virus-neutralizing antibodies that confer protection against heterologous PRRSV strains would be a catalyst for the development of next-generation vaccines. Key to discovering these epitopes is the isolation of neutralizing monoclonal antibodies (mAbs) from immune pigs. To address this need, we sought to establish systems to enable the isolation of PRRSV neutralizing porcine mAbs. We experimentally produced a cohort of immune pigs by sequential challenge infection with four heterologous PRRSV strains spanning PRRSV-1 subtypes and PRRSV species. Whilst priming with PRRSV-1 subtype 1 did not confer full protection against a subsequent infection with a PRRSV-1 subtype 3 strain, animals were protected against a subsequent PRRSV-2 infection. The infection protocol resulted in high serum neutralizing antibody titers against PRRSV-1 Olot/91 and significant neutralization of heterologous PRRSV-1/-2 strains. Enriched memory B cells isolated at the termination of the study were genetically programmed by transduction with a retroviral vector expressing the Bcl-6 transcription factor and the anti-apoptotic Bcl-xL protein, a technology we demonstrated efficiently converts porcine memory B cells into proliferating antibody-secreting cells. Pools of transduced memory B cells were cultured and supernatants containing PRRSV-specific antibodies identified by flow cytometric staining of infected MARC-145 cells and in vitro neutralization of PRRSV-1. Collectively, these data suggest that this experimental system may be further exploited to produce a panel of PRRSV-specific mAbs, which will contribute both to our understanding of the antibody response to PRRSV and allow epitopes to be resolved that may ultimately guide the design of immunogens to induce cross-protective immunity.
Highlights
Porcine reproductive and respiratory syndrome (PRRS) is the most important infectious disease affecting the global pig industry
The highest Neutralizing antibodies (nAbs) titers were against the heterologous porcine reproductive and respiratory syndrome viruses (PRRSV)-1 Porcillis and PRRSV-2 VR2332 strains (p < 0.05) and lowest titers were seen against PRRSV-2 KS06-7210 and KS62
The first step toward this goal was the sequential infection of naïve pigs with heterologous PRRSV strains, to promote the maturation and expansion of B cells recognizing conserved neutralizing epitopes
Summary
Porcine reproductive and respiratory syndrome (PRRS) is the most important infectious disease affecting the global pig industry. PRRS viruses (PRRSV) are a major threat to both animal welfare and food security, as demonstrated by the pig high fever disease outbreak that rapidly spread across Southeast Asia with devastating consequences [1]. PRRSV exists as two genetically and antigenically distinct species, PRRSV-1 and -2, which are both rapidly evolving. The emergence of highly pathogenic strains from both species [1, 4, 5] and the failure of current live attenuated vaccines to provide broad protection against an everexpanding diversity of viral strains pose significant challenges to effective disease control world-wide. Neutralizing antibodies (nAbs) confer protection against PRRSV [6] and recent studies have shown antibody responses can neutralize a wide diversity of PRRSV strains [7,8,9,10,11]. An improved understanding of conserved antigenic targets of nAbs would enable the design of novel vaccines
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