Proliferative Vasculopathy and Cutaneous Hemorrhages in Porcine Neonates Infected with the Porcine Reproductive and Respiratory Syndrome Virus

Susceptibility of perivenous macrophages to PRRSV-1 subtype 1 LV and PRRSV-1 subtype 3 Lena using a new vein explant model

Vessel pathology such as increased permeability and blue discoloration is frequently observed with highly pathogenic PRRSV strains. However, data concerning the viral replication in the environment of blood vessels are absent. In the present study, ex vivo models with swine ear and hind leg vein explants were established to study the interaction of PRRSV-1 subtype 1 reference strain LV and highly pathogenic subtype 3 strain Lena with perivenous macrophages. The replication characteristics of these two strains were compared in vein explants by immunofluorescence analysis. The explants maintained a good viability during 48 hours of in vitro culture. We found that CD163-positive macrophages were mainly present around the veins and their number gradually decreased with increasing distance from the veins and longer incubation time. More CD163+Sn- cells than CD163+Sn+ cells (6.6 times more) were observed in the vein explants. The Lena strain demonstrated a higher replication level than the LV strain, with approximately 1.4-fold more infected cells in the surrounding areas of the ear vein and 1.1-fold more infected cells in the leg vein explants at 48 hours post inoculation. In both LV and Lena inoculated vein explants, most infected cells were identified as CD163+Sn+ (> 94%). In this study, an ex vivo vein model was successfully established, and our findings will contribute to a better understanding of the vein pathology during viral infections (e.g., PRRS, classical and African swine fever).

Susceptibility of porcine pulmonary microvascular endothelial cells to porcine reproductive and respiratory syndrome virus

Microvascular endothelial cells possess versatile functions and their roles in a variety of viral infections have been documented. Porcine reproductive and respiratory syndrome virus (PRRSV) infection induces severe lung inflammatory lesions in piglets, which is manifested as pulmonary endothelial dysfunction. However, the underlying mechanism of PRRSV affecting porcine pulmonary microvascular endothelial cells (PMECs) remains unknown. This study aimed to evaluate the susceptibility of PMECs to PRRSV. Primary PMECs were isolated and purified from piglet lungs, and the expression of three PRRSV receptors was characterized using immunofluorescence. Overt cytopathic effects of the PRRSV strain HN in PMECs were observed at day five post-infection, and PRRSV antigens in PMECs were determined at both RNA and protein levels using immunofluorescence and quantitative RT-PCR assays. The viral antigen significantly increased at 96 hr post-infection, and infectious virus was recovered from the supernatant of the infected PMECs. The results show that PMECs can be infected with the PRRSV strain HN, and that their receptor expression pattern is different from that of alveolar macrophages. The results of this study shed light on the potential roles of PMECs in PRRSV infection and provide a comprehensive understanding of the pathogenesis underlying its severe manifestation.

The ever-expanding diversity of porcine reproductive and respiratory syndrome virus

Porcine reproductive and respiratory syndrome (PRRS) virus appeared 20 years ago as the cause of a new disease in swine. Today PRRS is the most significant swine disease worldwide in spite of intensive immunological interventions. The virus showed remarkable genetic variation with two geographically distinct genotypes at the time of its discovery, indicating the possibility of prolonged evolutionary divergence prior to its appearance as a swine pathogen. Since then, both type 1 and type 2 have spread geographically, radiated genetically, and acquired new phenotypic characteristics, especially increased virulence. Here, we explore various hypotheses that might account for rapid expansion and diversification of PRRSV, including mechanisms specific to PRRSV and other arteriviruses, cellular modification processes, and immunological selection. Phylogenetic analysis of PRRSV has provided a broadly applicable means to relate diverse isolates, but it does not explain biological variation in virulence or immunological cross-protection. We present other methods of classification and review their limitations. Major questions about PRRSV remain unanswered despite intensive investigation, suggesting that the interaction of PRRSV with pigs involves novel biological processes that may be relevant to other RNA virus and host interactions.