Phagocytosis is an important defense mechanism against microbial pathogens, but many pathogens get the ability to subvert it. This research was aimed at discovering the potential mechanism of the gram posi-tive and negative bacteria to survive from phagocytosis. In this study, Drosophila melanogaster S2 cells were applied as the host, and active/heat-inactivated Escherichia coli and Staphylococcus aureus were applied as in-vaders. Cultured S2 cells were incubated with Escherichia coli (EC), Staphylococcus aureus (SA), heat-inacti-vated Escherichia coli (HIEC) or Staphylococcus aureus (HISA), separately. After incubation, S2 cells were collected for transmission electron microscopy (TEM) analysis, confocal laser scanning microscopy analysis, flow cytometry (FCM) analysis and real time quantitative PCR analysis. Results showed that S2 cells could phagocytose HIEC efficiently at 1 d post-inoculation, but they could not clear HISA. HISA could survive within S2 cells for at least 4 d, and peptidoglycan (PG) and lipopolysaccharide-activated S2 cells could not digest HISA efficiently either. Comparing S2 cells, intracellular HISA did not destroy the S2 cells even at 4 d post-inoculation. The pHrodo-labeled HIEC was observed in an acidified environment at 1 h post-inoculation, but HISA was not. In addition, the percentage of phagocytized pHrodo-labeled bacteria showed no great differences whether the bacteria were engulfed alive or heat-killed. Defensin and drosomycin were up-regulated in the HISA + PG treatment, but S2 cells could not digest HISA. Also, results confirmed that antiphagocytic proper-ties were located on the surface of heat-inactivated S. aureus but not on that of heat-inactivated E. coli. Thus, cellular immunity is important for Drosophila melanogaster S2 cells fighting gram-positive bacteria, and the role of phagocytosis shed light on clearing of the bacterial pathogens.%吞噬作用是一种对抗微生物病原体的重要机制,但许多细菌均有抗吞噬作用.利用透射电镜和激光共聚焦显微镜结合细胞生物学技术,对黑腹果蝇Drosophila melanogaster S2细胞吞噬热灭活大肠埃希菌(heat inactivated Escherichia coli,HIEC)和热灭活金黄葡萄球菌(heat inactivated Staphylococcus aureus,HISA)的作用进行了研究.结果表明:S2细胞能够在接种后1 d内有效清除HIEC,但不能清除HISA;经聚肽糖(PG)或脂多糖(LPS)激活的S2细胞同样不能有效地清除HISA,HISA能够在S2细胞内至少存活4 d.在接种细胞酸性指示剂(pHrodo)标记的细菌1 h后,HIEC处于酸化环境中,而HISA没有;检测S2细胞的吞噬百分率显示S2细胞吞入活细菌与灭活细菌的敏感度没有显著差异.PG处理后的S2细胞防御素(defensin)与抗真菌肽(drosomycin)均显著上调表达,但仍无法消化HISA.结果证实:灭活金黄葡萄球菌表面具有抑制吞噬作用中消化步骤的成分,而灭活大肠埃希菌没有.研究揭示了在S2细胞对抗革兰氏阳性菌时,吞噬作用在清除该类病原体时所起到的重要作用以及金黄葡萄球菌抑制消化过程从而抵御细胞吞噬的策略.
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