GP4 of porcine reproductive and respiratory syndrome virus contains a neutralizing epitope that is susceptible to immunoselection in vitro

Glycoprotein 4 (GP4) of porcine reproductive and respiratory syndrome virus (PRRSV) contains a highly variable neutralizing epitope. The present study aimed to investigate whether this epitope is susceptible to immunoselection by antibodies in vitro. Cultivation of PRRSV in vitro in the continuous presence of neutralizing monoclonal antibodies (mAbs) directed against this epitope resulted in the selection of mAb-resistant PRRSV strains within five passages. Comparison of the GP4 amino acid (aa) sequence of the original PRRSV strain with the GP4 aa sequences of the mAb-resistant PRRSV strains revealed aa substitutions within this epitope. In conclusion, this study shows that the neutralizing epitope on GP4 is susceptible to immunoselection by antibodies in vitro.