Haynes J S, Halbur P G, Sirinarumitr T, Paul P S, Meng X J, Huffman E L
Department of Veterinary Pathology, College of Veterinary Medicine, Iowa State University, Ames, USA.
Vet Pathol. 1997 Jan;34(1):39-43. doi: 10.1177/030098589703400106.
Three groups of 5-week-old cesarian-derived, colostrum-deprived pigs were inoculated intranasally with either a high-virulence isolate (VR2385) or a low-virulence isolate (VR2431) of porcine reproductive and respiratory syndrome virus (PRRSV) or with uninfected cell culture and media. Formalin-fixed, paraffin-embedded tissues from pigs euthanatized at 10, 21, and 28 days post-inoculation were examined by in situ hybridization for PRRSV nucleic acid using a digoxigenin-labeled antisense RNA probe approximately 1,000 nucleotides in length. Alveolar macrophages were positive in the lungs of 9/9, 2/2, and 0/2 VR2385-inoculated pigs and 7/9, 1/2, and 2/3 VR2431-inoculated pigs at 10, 21, and 28 days post-inoculation, respectively. More positive cells were detected in lungs from VR2385-inoculated pigs compared to VR2431-inoculated pigs at 10 and 21 days post-inoculation. Positive cells within lymph nodes were tingible body macrophages in germinal centers and macrophages or interdigitating dendritic cells within the paracortical area. VR2385 was detected in the tracheobronchial lymph node (TBLN) and mediastinal lymph node (MLN) of 7/9 and 9/9 pigs at 10 days post-inoculation, but was only detected in the TBLN of 1/2 and 0/2 pigs and in the MLN of 0/2 and 1/2 pigs at 21 and 28 days post-inoculation, respectively. In contrast, VR2431 was detected in teh TBLN and MLN of 5/9 and 2/9 pigs at 10 days post-inoculation and in the TBLN of 0/2 and 1/3 pigs and in the MLN of 0/2 and 0/3 pigs at 21 and 28 days post-inoculation, respectively. There were more positive cells in TBLN and MLN in pigs inoculated with VR2385 at 10 days post-inoculation. Macrophages located at the epithelial-lymphoid interface of tonsilar crypts and within the paracortical areas were positive in tonsils of 9/9, 2/2, and 1/2 VR2385-inoculated pigs and 7/9, 1/2, and 1/3 VR2431-inoculated pigs at 10, 21, and 28 days post-inoculation, respectively. Positive cells in the thymic medulla were multinucleate and were only detected at 10 days post-inoculation in 2/9 VR2385-inoculated pigs and 4/9 VR2431-inoculated pigs. Positive cells within the spleen were few, spindle-shaped, located within smooth muscle trabecula, and only present at 10 days post-inoculation in 3/9 VR2385-inoculated pigs. We conclude that the tissue tropism and distribution of positive cells within tissues is similar for VR2385 and VR2431. However, tissues from more pigs and more cells within tissues were positive in pigs inoculated with VR2385 than VR2431 at 10 and 21 days post-inoculation. These findings indicate that the more virulent isolate VR2385 may replicate better in vivo than the less virulent isolate VR2431. This supports the hypothesis that an increased ability to replicate in vivo contributes to increased virulence of PRRSV.
将三组5周龄剖腹产、未摄入初乳的仔猪经鼻接种猪繁殖与呼吸综合征病毒（PRRSV）的高毒力分离株（VR2385）或低毒力分离株（VR2431），或接种未感染的细胞培养物和培养基。在接种后第10、21和28天对安乐死的猪的福尔马林固定、石蜡包埋组织进行原位杂交，使用长度约为1000个核苷酸的地高辛标记反义RNA探针检测PRRSV核酸。接种VR2385的猪在接种后第10、21和28天，肺中的肺泡巨噬细胞阳性率分别为9/9、2/2和0/2，接种VR2431的猪分别为7/9、1/2和2/3。与接种VR2431的猪相比，接种VR2385的猪在接种后第10和21天肺中检测到更多阳性细胞。淋巴结内的阳性细胞为生发中心的含铁血黄素巨噬细胞和副皮质区内的巨噬细胞或交错突细胞。接种VR2385的猪在接种后第10天，7/9的猪气管支气管淋巴结（TBLN）和9/9的猪纵隔淋巴结（MLN）中检测到VR2385，但在接种后第21天和28天，分别仅在1/2和0/2的猪的TBLN以及0/2和1/2的猪的MLN中检测到。相比之下，接种VR2431的猪在接种后第10天，5/9的猪TBLN和2/9的猪MLN中检测到VR2431，在接种后第21天和28天，分别仅在0/2和1/3的猪的TBLN以及0/2和0/3的猪的MLN中检测到。接种VR2385的猪在接种后第10天，TBLN和MLN中有更多阳性细胞。接种VR2385的猪在接种后第10、21和28天，扁桃体隐窝上皮-淋巴界面和副皮质区内的巨噬细胞阳性率分别为9/9、2/2和1/2，接种VR2431的猪分别为7/9、1/2和1/3。胸腺髓质中的阳性细胞为多核，仅在接种后第10天在2/9接种VR2385的猪和4/9接种VR2431的猪中检测到。脾脏内的阳性细胞很少，呈纺锤形，位于平滑肌小梁内，仅在接种后第10天在3/9接种VR2385的猪中出现。我们得出结论，VR2385和VR2431在组织嗜性和组织内阳性细胞分布方面相似。然而，在接种后第10和21天，接种VR2385的猪比接种VR2431的猪有更多猪的组织和组织内更多细胞呈阳性。这些发现表明，高毒力分离株VR2385在体内的复制可能比低毒力分离株VR2431更好。这支持了在体内复制能力增强有助于PRRSV毒力增加的假设。
