Mycoplasma hyopneumoniae, the agent of porcine enzootic pneumonia (EP), is able to persist in the lung tissue and evade destruction by the host for several weeks. To understand the mechanism of pathogen survival, phagocytic uptake of M. hyopneumoniae by primary porcine alveolar macrophages was investigated. Intracellular location and survival of the pathogen were explored using gentamicin survival assays, flow cytometry and confocal microscopy of M. hyopneumoniae 232 labelled with green fluorescent protein (GFP). Following 1 h and 16 h of co-incubation, few viable M. hyopneumoniae were recovered from inside macrophages. Flow cytometric analysis of macrophages incubated with M. hyopneumoniae expressing GFP indicated that the mycoplasmas became associated with macrophages, but were shown to be extracellular when actin-dependent phagocytosis was blocked with cytochalasin D. Confocal microscopy detected GFP-labelled M. hyopneumoniae inside macrophages and the numbers increased modestly with time of incubation. Neither the addition of porcine serum complement or convalescent serum from EP-recovered pigs was able to enhance engulfment of M. hyopneumoniae. This investigation suggests that M. hyopneumoniae evades significant uptake by porcine alveolar macrophages and this may be a mechanism of immune escape by M. hyopneumoniae in the porcine respiratory tract.

中文翻译：

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猪肺炎支原体逃避体外猪肺泡巨噬细胞的吞噬作用

猪肺炎支原体是猪地方性动物肺炎 (EP) 的病原体，能够在肺组织中持续存在并在数周内躲避宿主的破坏。为了了解病原体存活的机制，研究了原代猪肺泡巨噬细胞对猪肺炎支原体的吞噬作用。使用庆大霉素存活测定、流式细胞术和用绿色荧光蛋白 (GFP) 标记的猪肺炎支原体 232 的共聚焦显微镜来探索病原体的细胞内定位和存活。共孵育 1 小时和 16 小时后，从巨噬细胞内部回收到很少有存活的猪肺炎支原体。对与表达 GFP 的猪肺炎支原体孵育的巨噬细胞进行流式细胞术分析表明支原体与巨噬细胞相关，但当肌动蛋白依赖性吞噬作用被细胞松弛素 D 阻断时，显示是细胞外的。共聚焦显微镜检测到巨噬细胞内的 GFP 标记的猪肺炎支原体，并且数量随着孵育时间适度增加。添加猪血清补体或来自 EP 恢复猪的恢复期血清均不能增强猪肺炎支原体的吞噬。该研究表明，M. hyopneumoniae 逃避了猪肺泡巨噬细胞的大量摄取，这可能是 M. hyopneumoniae 在猪呼吸道中的免疫逃逸机制。添加猪血清补体或来自 EP 恢复猪的恢复期血清均不能增强猪肺炎支原体的吞噬。该研究表明，M. hyopneumoniae 逃避了猪肺泡巨噬细胞的大量摄取，这可能是 M. hyopneumoniae 在猪呼吸道中的免疫逃逸机制。添加猪血清补体或来自 EP 恢复猪的恢复期血清均不能增强猪肺炎支原体的吞噬。该研究表明，M. hyopneumoniae 逃避了猪肺泡巨噬细胞的大量摄取，这可能是 M. hyopneumoniae 在猪呼吸道中的免疫逃逸机制。