Assessing the role of PRRSV minor glycoproteins in the induction of a protective immune response

The role of PRRSV minor glycoproteins in the induction of a protective immune response is an area of PRRSV research that may have an impact on vaccine development. GP2, GP3, and GP4 form a trimer on the surface of the virion and it has been demonstrated that GP2 and GP4 interact with the CD163 receptor on host cells, and because of the trimer formation, GP3 may be interacting with the receptor as well. Previous work by many laboratories has shown minimal cross-protection between Type I and Type II PRRSV. With this knowledge, GP2, GP3, and GP4 of a Type II infectious clone were cloned into a Type I infectious clone, which serves as a vector for the proteins. The chimeric virus is being used to elucidate the contribution of the minor glycoproteins to a protective immune response in swine.

The GP2, GP3, and GP4 of a Type II infectious clone (FL12) were PCR amplified and then cloned into a Type I infectious clone (SD0108) in place of the corresponding Type I proteins. Infectious chimeric virus (SDFL24) was recovered and serum-virus neutralization assays were performed in MARC-145 cells to evaluate the sensitivity of the SDFL24 to FL12-infected, convalescent sera. An animal study to evaluate protection in vivo is currently ongoing.

The SD0108 construct containing GP2, GP3, and GP4 of FL12 is fully infectious. The chimeric virus SDFL24 grew well in MARC-145 cells to a titer of 10^5.75 TCID₅₀/ml. While the parental strain SD0108 is not sensitive to neutralization by FL12 convalescent sera (mean antibody titer of > 1:4), the chimeric SDFL24 is sensitive to neutralization by FL12 convalescent sera with a mean titer of 1:32. However, SDFL24 is less sensitive to neutralization when compared to FL12, which has a mean titer of 1:200. An animal experiment to evaluate the role of the proteins in a protective immune response is ongoing. Sera from infected animals will be used to characterize the neutralizing antibody response against parental and heterologous PRRSV strains. PBMCs will also be harvested and the cellular immune response will be evaluated. Protection after challenge will be measured by viremia and viral load in tissue.

Swapping the minor glycoproteins of Type II into a Type I backbone did not alter the replication of the virus. The chimeric virus containing only GP2, GP3, and GP4 of Type II is sensitive to neutralization by Type II convalescent sera, indicating that GP2, GP3, and GP4 are important for neutralization. This study allows us to weigh the relative contribution of GP2, GP3, and GP4 to overall neutralization. The protective capabilities of the chimeric virus are being evaluated in an animal experiment.

Disclosure of Interest: None Declared.