Department of Biomedical Sciences and Pathobiology, Virginia-Maryland College of Veterinary Medicine, Virginia Tech, Blacksburg, Virginia, USA.
Bacterial and Parasitic Disease Research Division, National Institute of Animal Health, National Agriculture and Food Research Organization, Tsukuba, Ibaraki, Japan.
Infect Immun. 2018 Nov 20;86(12). doi: 10.1128/IAI.00365-18. Print 2018 Dec.
is capable of intracellular survival within professional phagocytic cells, but the mechanism of survival is not understood. The Fic motif within the direct repeat (DR1)/DR2 domains of the IbpA fibrillary network protein of is cytotoxic to epithelial and phagocytic cells, which may interfere with the bactericidal activity of these cells. To determine the contribution of IbpA and Fic to resistance to host defenses, strains and mutants that lacked all or a region of (including the DR1/DR2 regions) were tested for survival in bovine monocytic cells and for serum susceptibility. An mutant lacking IbpA, but not the DR1/DR2 region within , was more susceptible to killing by antiserum than the parent, indicating that the entire protein was associated with serum resistance. strains expressing IbpA replicated in bovine monocytes for at least 72 h and were toxic for these cells. Virulent strain 2336 mutants lacking the entire gene or both DR1 and DR2 were not toxic to the monocytes but still survived within the monocytes for at least 72 h. Monitoring of intracellular trafficking of with monoclonal antibodies to phagosomal markers indicated that the early phagosomal marker early endosome antigen 1 colocalized with all isolates tested, but only strains that could survive intracellularly did not colocalize with the late lysosomal marker lysosome-associated membrane protein 2 and prevented the acidification of phagosomes. These results indicated that virulent isolates of were capable of surviving within phagocytic cells through interference in phagosome-lysosome maturation. Therefore, may be considered a permissive intracellular pathogen.
能够在专业吞噬细胞内进行细胞内生存，但生存机制尚不清楚。 的纤维蛋白网络蛋白 IbpA 的直接重复 (DR1)/DR2 结构域内的 Fic 基序对上皮细胞和吞噬细胞具有细胞毒性，这可能会干扰这些细胞的杀菌活性。为了确定 IbpA 和 Fic 对宿主防御的贡献，测试了缺乏 IbpA 和 的所有或部分缺失 （包括 DR1/DR2 区域）的 菌株和突变体在牛单核细胞中的存活能力和血清敏感性。与亲本相比，缺乏 IbpA 但不缺乏 的 DR1/DR2 区域的 突变体对抗血清的杀伤更为敏感，表明整个蛋白与血清抗性有关。表达 IbpA 的 株至少在牛单核细胞中复制 72 小时，并对这些细胞有毒。缺乏整个 基因或 DR1 和 DR2 的毒力菌株 2336 突变体对单核细胞无毒，但仍至少在单核细胞中存活 72 小时。用吞噬体标记物的单克隆抗体监测 的细胞内转运表明，早期吞噬体标记物早期内体抗原 1 与所有测试的分离株共定位，但只有能够在细胞内生存的菌株不能与晚期溶酶体标记物溶酶体相关膜蛋白 2 共定位，并阻止吞噬体酸化。这些结果表明，毒力分离株能够通过干扰吞噬体 - 溶酶体成熟在吞噬细胞内生存。因此， 可以被认为是一种允许的细胞内病原体。
