Department of Pathology, University of California, San Diego, San Diego, California, USA.
Infect Immun. 2013 Jul;81(7):2592-7. doi: 10.1128/IAI.00108-13. Epub 2013 May 6.
Our previous studies showed that Histophilus somni and bovine respiratory syncytial virus (BRSV) act synergistically in vivo to cause more severe bovine respiratory disease than either agent alone causes. Since H. somni surface and secreted immunoglobulin binding protein A (IbpA) causes retraction of bovine alveolar type 2 (BAT2) cells and invasion between BAT2 cells in vitro, we investigated mechanisms of BRSV-plus-H. somni infection at the alveolar barrier. BRSV treatment of BAT2 cells prior to treatment with IbpA-rich H. somni concentrated culture supernatant (CCS) resulted in increased BAT2 cell rounding and retraction compared to those with either treatment alone. This mimicked the increased alveolar cell thickening in calves experimentally infected with BRSV followed by H. somni compared to that in calves infected with BRSV or H. somni alone. BRSV-plus-H. somni CCS treatment of BAT2 cells also enhanced paracellular migration. The effect of matrix metalloproteinases (MMPs) was investigated as well because microarray analysis revealed that treatment with BRSV plus H. somni synergistically upregulated BAT2 cell expression of mmp1 and mmp3 compared to that in cells treated with either agent alone. Enzyme-linked immunosorbent assay (ELISA) confirmed that MMP1 and MMP3 protein levels were similarly upregulated. In collagen I and collagen IV (targets for MMP1 and MMP3, respectively) substrate zymography, digestion was increased with supernatants from dually treated BAT2 cells compared with those from singly treated cells. Enhanced breakdown of collagen IV in the basal lamina and of fibrillar collagen I in the adjacent interstitium in the dual infection may facilitate dissemination of H. somni infection.
我们之前的研究表明，豪氏胸膜肺炎放线杆菌和牛呼吸道合胞病毒（BRSV）在体内协同作用，导致比单独使用任何一种病原体更严重的牛呼吸道疾病。由于豪氏胸膜肺炎放线杆菌表面和分泌的免疫球蛋白结合蛋白 A（IbpA）导致体外牛肺泡型 2（BAT2）细胞回缩和细胞间侵入，我们研究了 BRSV-豪氏胸膜肺炎放线杆菌感染肺泡屏障的机制。在用富含 IbpA 的豪氏胸膜肺炎放线杆菌浓缩培养上清液（CCS）处理 BAT2 细胞之前，用 BRSV 处理 BAT2 细胞会导致细胞圆缩和回缩增加，与单独用任何一种处理相比。这与在实验性感染 BRSV 后再感染豪氏胸膜肺炎放线杆菌的小牛相比，与单独感染 BRSV 或豪氏胸膜肺炎放线杆菌的小牛相比，肺泡细胞增厚增加相似。BRSV-豪氏胸膜肺炎放线杆菌 CCS 处理 BAT2 细胞也增强了细胞旁迁移。还研究了基质金属蛋白酶（MMPs）的作用，因为微阵列分析显示，与单独用任何一种处理剂处理的细胞相比，BRSV 加豪氏胸膜肺炎放线杆菌协同上调 BAT2 细胞中 mmp1 和 mmp3 的表达。酶联免疫吸附试验（ELISA）证实 MMP1 和 MMP3 蛋白水平也上调。在胶原 I 和胶原 IV（分别为 MMP1 和 MMP3 的靶标）底物酶谱中，与单独处理的细胞相比，来自双重处理的 BAT2 细胞的上清液中消化增加。在双重感染中，基底膜中胶原 IV 的分解和相邻间质中纤维状胶原 I 的分解增强可能有助于豪氏胸膜肺炎放线杆菌感染的传播。
