一株猪圆环病毒2型感染野生型C57BL/6小鼠的致病性分析

Pathogenicity of a porcine circovirus type 2 isolate in wild-type C57BL/6 mice

摘要:

背景 猪圆环病毒2型(porcine circovirus type 2, PCV2)是引发猪群多种临床表现疾病的重要病原，对养猪业造成了重大经济损失。目的 建立更适合PCV2感染的动物模型，分析一株PCV2d型毒株对C57BL/6小鼠的致病性。方法 腹腔注射PCV2感染C57BL/6小鼠，观察小鼠的临床症状及组织病理变化；qPCR测定组织中的病毒载量；血常规分析外周血中白细胞、红细胞和血小板的变化，流式细胞术分析外周血淋巴细胞的变化；RT-qPCR测定脾脏中IL-10、IL-6、TNF-α和IFN-α mRNA的表达。结果 PCV2感染导致小鼠精神萎靡、体重下降，所有小鼠脾脏均出现肿大、坏死，部分肝脏色泽变浅、肺脏有出血；组织病理切片显示，脾脏均出现多核巨细胞浸润，感染第14天后含铁血黄素明显增多；脾脏中病毒载量约为(2.19±0.93)×10² copies/mg；PCV2感染诱导小鼠外周血中红细胞、血小板数量显著减少，流式细胞术分析表明，在感染后第3、7、14天，小鼠外周血均出现淋巴细胞数量减少，主要涉及CD₈⁺ T细胞和CD₄⁺ T细胞。PCV2感染促进了小鼠脾脏中IL-10、IL-6、TNF-α mRNA的表达，而IFN-α mRNA的表达只在感染后第3天和第21天显著降低。结论 本研究鉴定了一株PCV2d型毒株对C57BL/6小鼠的致病性，为PCV2小鼠模型建立及其致病性研究提供了参考。

Abstract:

Background Porcine circovirus type 2 (PCV2) is a major pathogen responsible for various clinical manifestations in swine populations, causing severe economic losses to the swine industry.Objective To establish an animal model suitable for PCV2 infection, we analyzed the pathogenicity of a PCV2d strain in C57BL/6 mice.Methods C57BL/6 mice were inoculated intraperitoneally with the PCV2 isolate, and the clinical signs and histopathologic changes of the mice were observed. The viral load in the tissue was determined by qPCR. The number and percent of leukocytes, erythrocytes, and platelets in the peripheral blood were analyzed by routine blood analysis, and those of lymphocytes in the peripheral blood were analyzed by flow cytometry. The mRNA levels of IL-10, IL-6, TNF-α, and IFN-α in the spleen were determined by RT-qPCR.Results PCV2 resulted in depression and weight losses in mice. All the infected mice presented splenomegaly and spleen necrosis, and some mice showcased lightening of the liver color and hemorrhages in the lungs. Histopathologic sections showed multinucleated giant cell infiltration in the spleen at various days post infection (dpi), with a significant increase in hemosiderin at 14 dpi. The highest viral load was found in the spleen, approximately (2.19±0.93)×10² copies/mg. PCV2 infection induced a significant reduction in the number of erythrocytes and platelets in the peripheral blood of mice. Flow cytometry results showed that PCV2 infection decreased the number of lymphocytes in the peripheral blood at 3, 7, and 14 dpi, primarily involving CD₈⁺ T cells and CD₄⁺ T cells. In addition, PCV2 up-regulated the mRNA levels of IL-10, IL-6, and TNF-α in the spleens of mice, while down-regulating the mRNA level of IFN-α at 3 dpi and 21 dpi.Conclusion We clarified the pathogenicity of a PCV2d strain in C57BL/6 mice, providing a reference for establishing the PCV2-infected mouse model and studying the pathogenicity of PCV2.