Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China.
Key Laboratory of Agricultural Environmental Microbiology, Ministry of Agriculture, College of Life Sciences, Nanjing Agricultural University, Nanjing, Jiangsu 210095, China.
Microb Pathog. 2017 Nov;112:279-287. doi: 10.1016/j.micpath.2017.10.006. Epub 2017 Oct 5.
Spiroplasma melliferum generally parasitizes honeybees and is one of main pathogens causing 'bee creeping disease' in China. Spiroplasma melliferum can be spread through honeybee pollination, which causes severe economic losses to apiculture. The design of this study was based on previous studies that utilized an in vitro bioassay to investigate the effects of S. melliferum CH-1 infection. We identified invasive S. melliferum CH-1 within Apis mellifera using transmission electron microscopy and investigated the immune response of honeybees infected with S. melliferum CH-1 by assaying the cellular immune response of the haemocytes, the plasma level of phenoloxidase activity and the transcript levels of 5 antimicrobial peptides, including the Abaecin, Apidaecin, Defensin 1, Defensin 2, and Hymenoptaecin gene products. The percentage of granulocytes in the haemolymph of infected honeybees was significantly higher than those of the controls during the early phase of infection, but the percentage of plasmatocytes was significantly higher than those of the controls at the fifth day post-infection. The phenoloxidase activity of the infected honeybees reached a maximum at the second day, and then decreased continuously. Moreover, the transcript levels of the 5 evaluated antimicrobial peptide genes were significantly increased during the early phase of infection and all 5 antimicrobial peptides were significantly decreased during the middle phase of infection. During the late phase of infection, only Defensin 2 and Hymenoptaecin showed significantly increased transcription. These results suggest that the honeybee immune responses could be activated by S. melliferum CH-1 during the early phase of infection and that S. melliferum CH-1 is also capable of circumventing the host defensive mechanisms to complete its life cycle within the honeybee during the middle phase of infection.
蜜环菌通常寄生在蜜蜂身上，是中国主要的“蜜蜂爬行动物病”病原体之一。蜜环菌可以通过蜜蜂授粉传播，这给养蜂业造成了严重的经济损失。本研究的设计基于之前的研究，该研究利用体外生物测定法研究了 S. melliferum CH-1 感染的影响。我们使用透射电子显微镜鉴定了感染 A. mellifera 的侵袭性 S. melliferum CH-1，并通过检测血细胞的细胞免疫反应、酚氧化酶活性的血浆水平以及 5 种抗菌肽的转录水平来研究感染 S. melliferum CH-1 的蜜蜂的免疫反应，这 5 种抗菌肽包括 Abaecin、Apidaecin、Defensin 1、Defensin 2 和 Hymenoptaecin 基因产物。感染蜜蜂血淋巴中的粒细胞百分比在感染早期显著高于对照组，但在感染后第 5 天，浆细胞的百分比显著高于对照组。感染蜜蜂的酚氧化酶活性在第 2 天达到最大值，然后持续下降。此外，在感染早期，5 种评估的抗菌肽基因的转录水平显著增加，在感染中期，所有 5 种抗菌肽的转录水平均显著下降。在感染后期，只有 Defensin 2 和 Hymenoptaecin 的转录明显增加。这些结果表明，蜜蜂的免疫反应可以被 S. melliferum CH-1 在感染早期激活，并且 S. melliferum CH-1 也能够绕过宿主防御机制，在感染中期完成其在蜜蜂体内的生命周期。
