Cell culture assays involving sophisticated techniques such as flow cytometry as readout to determine the virulence of CSFV are cumbersome and difficult to standardize for diagnostic applications. The ideal assay would use simple genetic readouts comprising nucleotide sequence information and quantitative RT-PCR. This implies knowledge of the viral and host determinants of virulence. An important finding of the project 1.10.13 is that highly virulent CSFV replicate more efficiently in IFN-γ-stimulated macrophages than lower virulent viruses. Thus, virulence may be related to the capacity of a virus to evade the antiviral state of the macrophages. The viral determinants for this phenotype are unknown.
The macrophage factors that are differentially activated after infection with CSFV of different virulence are also unknown. Very preliminary data in our laboratory indicate that the porcine reproductive and respiratory syndrome virus (PRRSV) does also differ in its capacity to infect activated macrophages, depending on the virulence of the isolate. This emphasizes the importance of understanding the macrophage factors that determine CSFV infection. These factors may be of general importance for virus infection. Their identification may prove useful to characterize the virulence of viruses with macrophage tropism in general, including PRRSV, porcine circovirus (PCV) and African swine fever (ASF).
According to the findings with IFN-γ-stimulated macrophages in project 1.10.13, the main goal of this follow-up project is to identify the viral genetic elements that determine evasion from the antiviral state of macrophages.
In addition, this project aims (i) to study the replication properties of CSFV isolates of different virulence in IFN-γ-stimulated macrophages and (ii) to identify the genes that are up-regulated in these macrophages in response to infection with the different viruses.
