Differential impact of porcine reproductive and respiratory virus and swine Influenza A virus infections on respiratory Lymph Nodes B cells and macrophages.

Porcine Reproductive and Respiratory Syndrome Virus (PRRSV) has a profound impact on the swine industry due to its ability to persist in infected animals. The PRRSV family exhibits considerable genetic variability, with PRRSV-1 and PRRSV-2 now classified as two distinct species (Betaarterivirus suid 1 and 2). Interestingly, both species - and their corresponding attenuated vaccine strains - can persist for months, in part by delaying the appearance of neutralizing antibodies. Leveraging recently developed tools for in-depth analysis of the previously poorly characterized porcine inverted lymph node (LN), we investigated early events in LN B cell maturation during PRRSV-1 infection and compared them to those induced by acute swine influenza A virus infection. We highlighted PRRSV-specific mechanisms, including PD-L1 upregulation in efferent macrophages, the presence of extrafollicular centrocytes, and the influx of inflammatory monocytes/macrophages. These findings are consistent with previous observations in PRRSV-2 infections and may therefore reflect conserved immune evasion mechanisms across PRRSV strains.