Mechanism Of Bone Marrow Lesions And Infection Of Piglets Infected With HP-PRRSV HuN4Strains

Porcine reproductive and respiratory syndrome (PRRS) is characteristics of fever, anorexia, reproductive disorders, severe acute respiratory disorder as well as other symptoms of infection diseases, which was caused by PRRS virus (PRRSV). PRRS was first appeared in1987in the United States. Since2006, highly pathogenic PRRS (HP-PRRS) is widely prevalent in our country, with high fever, high morbidity and mortality, which has caused seriously economic losses to the pig industry in our country. PRRSV belongs to the family of Arteriviridae, a single positive strand (+) RNA virus. It is well documented that PRRSV can cause severe immunosuppression in host, which is one of the important pathogens that causing swine immune disorders. Host interaction mechanism which is not yet clear, little research especially on PRRS virus (PRRSV) infection of the bone injury mechanism of piglets. Therefore, the study was used the bone marrow as the research object, the depth of the impact of PRRSV host central immune organ has important scientific significance.Our previous studies demonstrated that HP-PRRSV HuN4strain caused the infected weaned pigs severe clinical symptoms and severe lesions in central immune organs-thymus. The purpose of this study is to further investigate the infection and lesions in bone marrow of piglets infected with HP-PRRSV HuN4strain, as well as the changes in subpopulations of lymphocytes in blood and bone marrow. In this study, the injury of bone marrow was evaluated by the following aspects:the virus and apoptotic cells in bone marrow, the cell type of bone marrow cells infected by the virus, as well as the co-localization between apoptotic cells and infection. Results:PRRSV were discovered in bone marrow cells of all piglets infected by HP-PRRSV HuN4strain from3d.p.i. During HP-PRRSV HuN4infection, the viral load in the bone marrow was10copies/107events at3d.p.i, since then, the virus load was increasing; the viral load reached107.5±1.1copies/107events at7d.p.i. and the viral load was slightly decreased with106.1±0.4/107events at10d.p.i. The viral load in bone marrow cells from the HP-PRRSV HuN4F112group showed a low level during the virus infection, it was only only103.2±0.4copies/107events at7d.p.i.. Cell apoptosis in bone marrow was analyzed by flow cytometry assay:in the HP-PRRSV HuN4group, the apoptosis rate of bone marrow cells rised up to26.9±3.9%at3d.p.i.; it was significantly increased from7d.p.i. and10d.p.i, with40.1±4.7%and45.7±5.9%, respectively. While in the HP-PRRSV HuN4F112group, apoptotic cells were also observed in bone marrow cells with slightly higher than that in control, the apoptosis rate in bone marrow cells started to rise45.7±5.9%at3d.p.i, and which showed a slightly increasing trend at7and10d.p.i, with26.2±2.5%and26.7±2.9%, respectively, which was significantly higher than that in control group (p<0.05). To further confirm the apoptosis in bone marrow, the TUNEL assay was used to detect apoptosis in bone marrow, the results in both HP-PRRSV HuN4and HuN4F112were able to cause apoptosis in bone marrow cells, In addition, bone marrow from HP-PRRSV HuN4strain infected piglets showed more serious injuries, including myeloid precursor cells and granulocytes in bone marrow were shown a large number of cell apoptosis, and the apoptosis rate was shown an increasing with the viral infection trend at7and10d.p.i. By laser scanning confocal analysis, the PRRSV was replicated in SWC3+SWC8+/-cells. In addition, a large number of bone marrow SWC3+SWC8+occurred apoptosis. To identify the cell type in apoptosis and virus infected cells, PRRSV-infected target cells underwent apoptosis, and in the late stage of infection a large number of infected bone marrow precursor cells and granulocytes were observed underwent apoptosis. In addition to apoptosis of infected cells, a large number of uninfected cells also occurred in bone marrow cells. In HP-PRRSV HuN4group, During the experiment, CD3+cells within the bone marrow increases the proportion was significantly higher, bone marrow CD4’CD8+and CD4+CD8+cells was significantly increased (p<0.05), the proportion of CD4-CD8+subpopulations of CD4+CD8and CD4-CD8-cells was significantly decreased (p<0.05), while in peripheral blood, CD3+cells decreased, a momentary reduction phenomenon, which further detects the proportion of cells CD4CD8found that these cells showed a similar trend in the proportion of cells within the bone marrow and showed a similar trend; It was detected that CD4-CD8+and CD4+CD8+cells in the bone marrow from HP-PRRSV HuN4strain infected piglets was significantly increased (p<0.05), CD4+CD8-and CD4-CD8-cells was significantly reduced (p<0.05); within PRRSV HuN4F112group, the proportion of T lymphocytes were showed similar changes compared to control group. Furthermore, CD4-CD8+cells in PBLs was significantly increased (p<0.05) and the proportion of CD4-CD8+subpopulations was significantly reduced only at7d.p.i (p<0.05).