Infection of monocytes with European porcine reproductive and respiratory syndrome virus (PRRSV-1) strain Lena is significantly enhanced by dexamethasone and IL-10

Monocytes are considered refractory to porcine reproductive and respiratory syndrome virus type 1 (PRRSV-1) infection. However, monocytes are only short-lived in blood, being able to differentiate into macrophages and dendritic cells (DC). It was therefore merited to revisit PRRSV-1 interaction with monocytes, particularly those treated with cytokines influencing monocyte biology. Thus, several factors were screened, particularly those modulating monocyte differentiation and expression of putative PRRSV-1 receptors (CD169 and CD163). M-CSF, known to stimulate macrophage differentiation, did not increase their susceptibility to PRRSV-1. Nor did GM-CSF or IL-4, known drivers for monocyte-derived DC (MoDC) differentiation. In contrast, monocyte treatment with IL-10 or the corticosteroid, dexamethasone, known to be potent suppressors of monocyte differentiation, was correlated with increased susceptibility to PRRSV-1 infection. While this effect was strongly correlated to CD163 and CD169 expression, our data suggest that receptor expression is not the only factor driving successful infection of PPRSV-1 in monocytes.