Porcine reproductive and respiratory syndrome virus (PRRSV) plays a key role in porcine respiratory disease complex modulating the host immune response and favouring secondary bacterial infections. Pulmonary alveolar macrophages (PAMs) are the main cells supporting PRRSV replication, with CD163 as the essential receptor for viral infection. Although interstitial pneumonia is by far the representative lung lesion, suppurative bronchopneumonia is described for PRRSV virulent strains. This research explores the role of several immune markers potentially involved in the regulation of the inflammatory response and sensitisation of lung to secondary bacterial infections by PRRSV-1 strains of different virulence. Conventional pigs were intranasally inoculated with the virulent subtype 3 Lena strain or the low virulent subtype 1 3249 strain and euthanised at 1, 3, 6 and 8 dpi. Lena-infected pigs exhibited more severe clinical signs, macroscopic lung score and viraemia associated with an increase of IL-6 and IFN-γ in sera compared to 3249-infected pigs. Extensive areas of lung consolidation corresponding with suppurative bronchopneumonia were observed in Lena-infected pigs. Lung viral load and PRRSV-N-protein⁺ cells were always higher in Lena-infected animals. PRRSV-N-protein⁺ cells were linked to a marked drop of CD163⁺ macrophages. The number of CD14⁺ and iNOS⁺ cells gradually increased along PRRSV-1 infection, being more evident in Lena-infected pigs. The frequency of CD200R1⁺ and FoxP3⁺ cells peaked late in both PRRSV-1 strains, with a strong correlation between CD200R1⁺ cells and lung injury in Lena-infected pigs. These results highlight the role of molecules involved in the earlier and higher extent of lung lesions in piglets infected with the virulent Lena strain, pointing out the activation of routes potentially involved in the restraint of the local inflammatory response.

猪繁殖与呼吸综合征病毒（PRRSV）在猪呼吸道疾病复合物调节宿主的免疫反应并促进继发性细菌感染中起关键作用。肺泡巨噬细胞（PAM）是支持PRRSV复制的主要细胞，其中CD163是病毒感染的必需受体。尽管到目前为止，间质性肺炎是代表性的肺部病变，但描述了PRRSV强毒株的化脓性支气管肺炎。这项研究探索了几种免疫标记物的潜在作用，这些标记物可能通过不同毒力的PRRSV-1株对炎症反应的调节和肺部对继发性细菌感染的敏感性调节。常规猪鼻内接种有毒力的亚型3 Lena株或低毒力的亚型1 3249株，并在1、3、6、8 dpi下安乐死。与感染3249头猪的猪相比，感染了莉娜的猪表现出更严重的临床体征，宏观肺脏评分和病毒血症与血清中IL-6和IFN-γ的升高有关。在莉娜感染的猪中观察到广泛的肺固结区域，与化脓性支气管肺炎相对应。肺病毒载量和PRRSV在莉娜感染的动物中-N-蛋白⁺细胞始终较高。PRRSV -N-蛋白⁺细胞与CD163 ⁺巨噬细胞明显下降相关。CD14 ⁺和iNOS ⁺细胞的数量随着PRRSV-1感染而逐渐增加，在莉娜感染的猪中更为明显。在两个PRRSV-1菌株中，CD200R1 ⁺和FoxP3 ⁺细胞的频率均达到峰值，与CD200R1 ⁺之间的相关性强感染了莉娜的猪的肺细胞和肺损伤。这些结果突显了在感染力力Lena菌株的仔猪中，参与早期和更高程度肺部病变的分子的作用，指出了可能抑制局部炎症反应的途径的激活。