Schlesinger L S, Hull S R, Kaufman T M
Department of Medicine, Department of Veterans Affairs Medical Center, Iowa City, IA.
J Immunol. 1994 Apr 15;152(8):4070-9.
Recent studies from this laboratory have demonstrated that macrophage phagocytosis of virulent strains (Erdman and H37Rv), but not the attenuated H37Ra strain of Mycobacterium tuberculosis, is mediated by phagocyte mannose receptors (MR) in addition to complement receptors (CR1 and the leukocyte integrins CR3 and CR4). Lipoarabinomannan (LAM) is a major surface lipoglycan of M. tuberculosis. LAM from the Erdman strain (Man-LAM) contains mannose oligosaccharides at the terminal portions of the molecule. This study investigated the ability of ManLAM to serve as a microbial ligand in adherence to human monocyte-derived macrophages (MDM). Polystyrene microspheres were coated with known amounts of purified ManLAM, LAM without the terminal mannosyl units from an avirulent mycobacterium (AraLAM), lipomannan (LM), or buffer and incubated with MDM monolayers in the absence of serum. The presence of LAM on microspheres was confirmed by indirect immunofluorescence studies. Microspheres coated with ManLAM demonstrated a more than threefold increase in adherence to MDM when compared with microspheres coated with AraLAM, LM, or buffer and the low levels of adherence of microspheres in the latter three groups were comparable. Compared with control monolayers, selective down-modulation of MDM MR on a mannan substrate abrogated the enhanced adherence of microspheres mediated by ManLAM. Adherence of microspheres coated with AraLAM, LM, or buffer was not influenced by MR modulation. To confirm the importance of the terminal mannosyl units of ManLAM in the enhanced adherence of ManLAM microspheres to MDM, these units were selectively removed by exomannosidase treatment. The structure of LAM products before and after enzyme treatment was confirmed by high performance anion exchange chromatography with pulsed amperometric detection. Removal of the terminal mannosyl units abolished the capacity of ManLAM to mediate enhanced adherence of microspheres to MDM. Finally, preincubation of Erdman M. tuberculosis with CS-40, a mAb directed against LAM, resulted in a consistent inhibition of adherence of the bacteria to MDM (up to 49% inhibition), confirming a role for ManLAM on intact bacteria in adherence to MDM. Thus, we provide evidence for a novel receptor-ligand pathway in phagocytosis of M. tuberculosis that consists of MR on macrophages and mannosyl units at the terminal end of ManLAM, a major microbial surface lipoglycan.
该实验室最近的研究表明，巨噬细胞对结核分枝杆菌的强毒株（埃尔德曼株和H37Rv株）而非减毒株H37Ra株的吞噬作用，除了补体受体（CR1以及白细胞整合素CR3和CR4）外，还由吞噬细胞甘露糖受体（MR）介导。脂阿拉伯甘露聚糖（LAM）是结核分枝杆菌的一种主要表面脂多糖。来自埃尔德曼株的LAM（甘露糖-LAM）在分子末端含有甘露糖寡糖。本研究调查了甘露糖-LAM作为微生物配体黏附于人类单核细胞衍生巨噬细胞（MDM）的能力。用已知量的纯化甘露糖-LAM、来自无毒力分枝杆菌的不含末端甘露糖基单元的LAM（阿拉伯糖-LAM）、脂甘露聚糖（LM）或缓冲液包被聚苯乙烯微球，并在无血清条件下与MDM单层培养物一起孵育。通过间接免疫荧光研究证实微球上存在LAM。与用阿拉伯糖-LAM、LM或缓冲液包被的微球相比，用甘露糖-LAM包被的微球对MDM的黏附增加了三倍多，而后三组微球的低水平黏附相当。与对照单层相比，在甘露聚糖底物上对MDM的MR进行选择性下调消除了甘露糖-LAM介导的微球增强黏附。用阿拉伯糖-LAM、LM或缓冲液包被的微球的黏附不受MR调节的影响。为了证实甘露糖-LAM末端甘露糖基单元在甘露糖-LAM微球对MDM增强黏附中的重要性，通过外切甘露糖苷酶处理选择性去除这些单元。酶处理前后LAM产物的结构通过高效阴离子交换色谱-脉冲安培检测进行了确认。去除末端甘露糖基单元消除了甘露糖-LAM介导微球对MDM增强黏附的能力。最后，用针对LAM的单克隆抗体CS-40对埃尔德曼结核分枝杆菌进行预孵育，导致细菌对MDM的黏附受到一致抑制（高达49%的抑制），证实完整细菌上的甘露糖-LAM在黏附于MDM中起作用。因此，我们为结核分枝杆菌吞噬作用中的一种新型受体-配体途径提供了证据，该途径由巨噬细胞上的MR和主要微生物表面脂多糖甘露糖-LAM末端的甘露糖基单元组成。
