Abstract
Dendritic cells (DC) are important modulators of the immune response with the ability to present antigen to naive T cells. DC can be generated in vitro from blood monocytes (MoDC), which represent an appropriate model to study DC biology. In addition, they are important targets for many viruses and this interaction is crucial for the establishment of an anti-viral immunity. Equine arteritis virus (EAV) and Equine encephalosis virus (EEV) cause infectious diseases in equids. Little is known of the effect both viruses have on host immune cells, particularly DC. An optimized system was established to generate equine MoDC (eqMoDC) in vitro. Purified recombinant equine cytokines (GM-CSF and IL-4) were used for the differentiation of Mo to immature MoDC (iMoDC) and a cocktail of stimuli was used for DC maturation. The phenotype of DC, studied using flow cytometry and microarray analysis, and functional assays, such as endocytosis/phagocytosis, mixed leukocyte reactions, antigen presentation and cross presentation, were applied to characterise immature and mature MoDC (mMoDC). To study the interaction with EAV and EEV, MoDC were infected with strains of different genotypes and pathogenicity and virus replication was determined through titration and real-time quantitative PCR (qPCR). Both viruses were able to infect Mo and MoDC but showed differences in their replication pattern. EAV demonstrated a productive replication leading to lysis of cells whereas EEV displayed a possible restricted or restricted-persistent replication. Mature MoDC were the most susceptible to these viruses, unlike iMoDC which were the least susceptible cells thereby preserving their phenotypic and functional characteristics. The replication of EAV resulted in an apoptosis mediated cell death, which inevitably inhibited the differentiation and function of DC. On the other hand, EEV drove the differentiation of Mo. Both viruses inhibited the ability of mMoDC to activate T cells, which is a mechanism used to evade host anti-viral immunity.