Oral Presentation International Veterinary Immunology Symposium 2016

Strong activation of plasmacytoid dendritic cells induced by tight contact with porcine reproductive and respiratory syndrome virus-infected macrophages (#64)

Obdulio García-Nicolás 1 , Gaël Auray 1 , Carmen A Sautter 1 , Julie Rappe 1 , Kenneth C McCullough 1 , Nicolas Ruggli 1 , Artur Summerfield 1
  1. IVI, Mittelhäusern, BERN, Switzerland

Plasmacytoid dendritic cells (pDC) are a subset of the DC family specialized in sensing nucleic acids, resulting in the production of high levels of IFN-α secretion. Classically, this is induced by triggering endosomal Toll-like receptor (TLR) 7 and TLR9 through exposure to ssRNA or DNA, respectively. Porcine reproductive and respiratory syndrome virus (PRRSV) represents a macrophage-tropic virus which is unable to induce interferon (IFN) type I in its target cells. We isolated CD172a positive PBMC for pDC enrichment and macrophage differentiation from monocytes. Macrophages were infected with different genotype 1 and 2 PRRSV strains and co-cultured with pDC, then IFN-α was measured from cells supernatants. Although pDC are able to produce IFN-α in response to most of the free PRRSV-strains virions, we demonstrate here that they are not responsive the highly pathogenic PRRSV genotype 1 strain Lena. This contrasted with a prominent systemic IFN alpha (IFN-α) response in PRRSV Lena-infected pigs. Nevertheless, when PRRSV infected macrophages were co-cultures with enriched pDC strong IFN-α responses were found with all genotype 1 and 2 PRRSV strains, including Lena were observed. IFN-α production was clearly higher when compared to direct stimulation of pDC by free virions. We demonstrate that stimulation was dependent on integrin-mediated intercellular contact, intact actin filaments and membrane ceramide content in the macrophages. Although infected macrophages-derived exosomes stimulated pDC, an efficient delivery of the stimulatory component was dependent on a tight contact between pDC and the infected cells. In conclusion, with this mechanism the immune system can efficiently sense PRRSV, resulting in production of considerable quantities of IFN-α. While the role of such responses for the host immune response and viral pathogenesis needs to be determined in vivo, our work is in line with several other reports pointing on the potency of this pathway of pDC activation by virus-infected cells.