Attenuated but not virulent pseudorabies virus activates porcine bone marrow-derived dendritic cells

Pseudorabies viruses (PrV), the causative agent of Aujeszky's disease, continues to cause economic losses to pig producers across Southeast Asia. PrV is controlled by vaccination with live attenuated vaccines, such as the Bartha K61 strain, which has also shown promise as a viral vector. Despite the success of live attenuated PrV vaccines and their utility to be engineered as vaccine vectors, studies to understand the basis of their immunogenicity are scarce. Here, porcine bone marrow-derived dendritic cells (BMDC) were differentiated by culture with FLT3-L, generating eight myeloid cell populations differing in CADM1, CD172a, CD14, CD163 and CD11c expression, and included CADM1^high conventional (c)DC and CD14⁺ DC. In vitro infection of BMDC with GFP-expressing PrV strains Bartha K61 and virulent Kaplan revealed a more rapid infection with Bartha K61. Compared to PrV Kaplan infection, there was also an increase in maturation marker expression (MHC class II and CD80/86) in both infected and bystander BMDC populations following Bartha K61 infection. This was accompanied by a concomitant increased cytokine response. IL-12 and TNF production associated with the cDC and CD14⁺ DC subsets, suggests that infection of these cells may be key to the potent immunogenicity associated with PrV Bartha K61 vaccination.