Identification of Neutralizing and Nonneutralizing Epitopes in the Porcine Reproductive and Respiratory Syndrome Virus GP5 Ectodomain

Abstract

After infection of swine with porcine reproductive and respiratory syndrome virus (PRRSV), there is a rapid rise of PRRSV-specific nonneutralizing antibodies (NNA), while neutralizing antibodies (NA) are detectable not sooner than 3 weeks later. To characterize neutralizing epitopes, we selected phages from a 12-mer phage display library using anti-PRRSV neutralizing monoclonal antibody (MAb) ISU25-C1. In addition, phages carrying peptides recognized by swine antibodies with high seroneutralizing titer were isolated after subtracting from the library those clones binding to swine anti-PRRSV serum with no neutralizing activity. Two epitopes located in the ectodomain of PRRSV GP5 were identified. One of these epitopes, which we named epitope B, was recognized both by neutralizing MAb ISU25-C1 and swine neutralizing serum (NS) but not by swine nonneutralizing serum (NNS), indicating that it is a neutralizing epitope. Epitope B is sequential, conserved among isolates, and not immunodominant. Antibodies directed against it are detected in serum late after infection. In contrast, the other epitope, which we named epitope A, is hypervariable and immunodominant. Antibodies against it appear early after infection with PRRSV. This epitope is recognized by swine NNA but is not recognized by either neutralizing MAb ISU25-C1 or swine NA, indicating that it is not involved in PRRSV neutralization. During infection with PRRSV, epitope A may act as a decoy, eliciting most of the antibodies directed to GP5 and delaying the induction of NA against epitope B for at least 3 weeks. These results are relevant to the design of vaccines against PRRSV.

Accelerated evolution of PRRSV during recent outbreaks in China

“…Gp5, especially in the ectodomain, possesses many N-glycosylation sites, and it has been shown that both neutralizing and nonneutralizing epitopes exist in this major structural protein with some of these functional sites already identified [41][42][43]. Our results showed that viral ORF5 of recent outbreaks in China had undergone accelerated evolution, and this result accorded with previous studies that evolution of PRRSV was driven by positive selection [25,44] .…”

Arteriviruses, Pegiviruses, and Lentiviruses Are Common among Wild African Monkeys

“…As expected, we found hotspots of nonsynonymous variation in the regions of the SIV ver envelope gene that correspond to the "highly variable loops" that are preferentially targeted by host antibodies (23,46). We found a similar pattern of adaptive changes in the DMVV-1 genome, with signatures of nonsynonymous diversity found primarily in genes that code for envelope glycoproteins and/or regions corresponding to antibody epitopes that have been extensively mapped in other arteriviruses (47)(48)(49)(50)(51). This observation suggests that vervet monkeys infected with DMVV-1 produce antibodies that target DMVV-1 glycoproteins but that these antibodies may not be effective in clearing DMVV-1 infection, a scenario that may be akin to immune escape observed during SIV infection.…”

A Single Amino Acid Deletion in the Matrix Protein of Porcine Reproductive and Respiratory Syndrome Virus Confers Resistance to a Polyclonal Swine Antibody with Broadly Neutralizing Activity

“…In this study, reverse genetics of an infectious cDNA clone was used to confirm that a single amino acid deletion at position 10 in M of KS62 resulted in escape from broadly neutralizing sera, 16-45 and 15-4, while retaining sensitivity to serum with homologous neutralizing activity. The results suggest that epitopes recognized by sera with different neutralization properties are distinct, which can explain the large number of neutralizing epitopes previously described in the literature (12)(13)(14)(15)(16)(17). The results also point to the importance of thoroughly characterizing the neutralization properties of polyclonal and monoclonal antibodies used for epitope mapping experiments.…”

“…S1C in the supplemental material). Ostrowski et al (16) and Plagemann et al (17) described an epitope in GP5 in a type 2 genotype virus located in the vicinity of two conserved glycosylation sites in the ectodomain region (epitopes a and b in Fig. S1F in the supplemental material).…”