The S32 amino acid deletion in the GP5 protein modulates the infectivity of porcine reproductive and respiratory syndrome virus

The high genetic diversity of porcine reproductive and respiratory syndrome virus (PRRSV) poses a significant challenge to effective vaccination and infection prevention. Recently, NADC30-like PRRSV has become dominant in China. In this study, we characterized a PRRSV isolate XJ2020 from a vaccinated pig. The isolate exhibited moderate pathogenicity in piglets and clustered within the same sub-lineage as NADC30. Sequence analysis identified a unique deletion of the serine residue at position 32 (S32) in the GP5 protein. This deletion was introduced into a highly pathogenic PRRSV (HP-PRRSV) strain, JX2015, to generate the mutant JX2015-ΔS32 using a reverse genetic approach. We found that JX2015-△S32 showed reduced propagation in Marc-145 cells and decreased sensitivity to neutralization by MLV-derived anti-PRRSV positive serum, but exhibited enhance replication in primary porcine alveolar macrophages (PAMs) compared to its parental strain JX2015. Interestingly, the viral load in lung and ileum samples from JX2015-△S32-infected piglets was higher, but the lung injury was milder than in JX2015-infected piglets. Overall, this study highlights the S32 site in the PRRSV GP5 protein as an important factor influencing virus propagation, neutralization, cell tropism and pathogenicity in piglets, and suggests that targeting this residue could lead to the development of more effective PRRSV vaccines.