Replication characteristics of porcine reproductive and respiratory syndrome virus (PRRSV) European subtype 1 (Lelystad) and subtype 3 (Lena) strains in nasal mucosa and cells of the monocytic lineage: indications for the use of new receptors of PRRSV (Lena)

Abstract

Recently, it has been demonstrated that subtype 3 strains of European type porcine reproductive and respiratory syndrome virus (PRRSV) are more virulent/pathogenic than subtype 1 strains. This points to differences in the pathogenesis. In the present study, a new polarized nasal mucosa explant system was used to study the invasion of the low virulent subtype 1 PRRSV strain Lelystad (LV) and the highly virulent subtype 3 PRRSV strain Lena at the portal of entry. Different cell types of the monocytic lineage (alveolar macrophages (PAM), cultured blood monocytes and monocyte-derived dendritic cells (moDC)) were enclosed to examine replication kinetics of both strains in their putative target cells. At 0, 12, 24, 48 and 72 hours post inoculation (hpi), virus production was analyzed and the infected cells were quantified and identified. Lena replicated much more efficiently than LV in the nasal mucosa explants and to a lesser extent in PAM. Differences in replication were not found in monocytes and moDC. Confocal microscopy demonstrated that for LV, almost all viral antigen positive cells were CD163+Sialoadhesin (Sn)+, which were mainly located in the lamina propria of the respiratory mucosa. In Lena-infected nasal mucosa, CD163+Sn+, CD163+Sn- and to a lesser extent CD163-Sn- monocytic subtypes were involved in infection. CD163+Sn- cells were mostly located within or in the proximity of the epithelium. Our results show that, whereas LV replicates in a restricted subpopulation of CD163+Sn+ monocytic cells in the upper respiratory tract, Lena hijacks a broader range of subpopulations to spread within the mucosa. Replication in CD163+Sn- cells suggests that an alternative entry receptor may contribute to the wider tropism of Lena.

RNA-Sequence Analysis of Primary Alveolar Macrophages after In Vitro Infection with Porcine Reproductive and Respiratory Syndrome Virus Strains of Differing Virulence

“…This differs from results of in vivo studies, in which a higher replication rate was reported for Lena compared to other PRRSV subtype 1 strains [6]. Frydas et al [53] have shown that, while LV can replicate in a restricted subpopulation of monocytic cells, Lena appears to target an ample range of cell subpopulations to disseminate within the mucosa. This finding might explain the high replication rate of the Lena strain in vivo, as airway mucosal surface is a common entry site for the virus [53].…”

Host–pathogen interactions during porcine reproductive and respiratory syndrome virus 1 infection of piglets

“…The virus can persist for long periods of time in lymphoid tissues (Wills et al, 2003) and whilst virus had been cleared from blood we still detected PRRSV antigen at 35 dpi in lungs, local lymph nodes and the thymus. It has been reported recently that the virulent PRRSV-1 Lena strain may replicate in CD163 − sialoadhesin − cells (Frydas et al, 2013). Since we observed a higher number of infected cells in tissues in pigs infected with virulent subtype 3 strain SU1-Bel, we speculate that this may be attributable to other highly pathogenic strains of PRRSV-1 subtype 3.…”

Review on the transmission porcine reproductive and respiratory syndrome virus between pigs and farms and impact on vaccination

“…No RT-PCR positive nasal swabs were detected after 49 dpi [37]. Further work done at the University of Ghent has shown that the ability of a given isolate for infecting different subsets of potentially susceptible cells in the nasal mucosa is the critical factor for nasal shedding [53, 54] (see also Sect. 4.2).…”

“…Increased replication efficiency and higher viral titres in serum were also observed for the highly pathogenic HuN4 [57] and Lena [52] strains, although in these cases the viral shedding was not assessed. Moreover, in several studies by Frydas et al [53, 54, 58] it was shown, at least for genotype 1, that different isolates replicate to a different extent in the nasal mucosa, and this may have an influence on the formation of aerosols. Collectively, these data suggest that pigs infected with highly virulent strains could shed higher amounts of virus than pigs infected with low virulent strains, and that the replication in nasal mucosa varies between isolates.…”