Complement component C3 fixes selectively to the major outer membrane protein (MOMP) of Legionella pneumophila and mediates phagocytosis of liposome-MOMP complexes by human monocytes.
Complement component C3 fixes selectively to the major outer membrane protein (MOMP) of Legionella pneumophila and mediates phagocytosis of liposome-MOMP complexes by human monocytes.
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DOI：
10.1084/jem.172.4.1201
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发表时间：
1990-10-01
期刊：
影响因子：
--
通讯作者：
Horwitz MA
中科院分区：
文献类型：
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作者：
Bellinger-Kawahara C;Horwitz MA
嗜肺军团菌是一种兼性细胞内细菌病原体，寄生于人类单核细胞和肺泡巨噬细胞。本实验室前期研究表明，血清中单核细胞补体受体CR1、CR3和补体成分C3介导嗜肺乳杆菌的吞噬。在本研究中，我们探讨了C3对嗜肺乳杆菌的固定作用。我们开发了一种全细胞酶联免疫吸附试验（ELISA）来测量C3在细菌表面的固定。通过该实验，C3固定在新鲜非免疫血清中被调理的嗜肺乳杆菌上，C3固定通过补体激活的替代途径进行。免疫印迹分析显示C3选择性地固定在嗜肺乳杆菌的特定受体分子上。与此一致的是，当整个嗜肺乳杆菌或细菌成分的硝化纤维素斑点在新鲜的非免疫血清中孵育时，C3只固定在嗜肺乳杆菌的主要外膜蛋白（MOMP）上，这是一种孔蛋白；在这些印迹上，C3不固定在嗜肺乳杆菌LPS上。为了进一步探讨MOMP在C3固定和吞噬中的作用，我们将纯化的MOMP重组为脂质体。通过ELISA检测，MOMP-脂质体，而非缺乏MOMP的普通脂质体，能强烈地固定C3。与MOMP在C3固定中的主导作用一致，MOMP脂质体在非免疫血清中形成与整个嗜肺乳杆菌具有相同表观分子量的C3复合物。调理化的放射性碘化momp -脂质体强烈粘附在单核细胞上，其粘附程度取决于血清的剂量。通过电镜观察，调理后的momp -脂质体被人单核细胞有效地吞噬，吞噬以传统的吞噬形式发生。本研究表明C3选择性地固定在嗜肺乳杆菌的MOMP上，并且在非免疫血清存在的情况下，MOMP可以介导脂质体的吞噬，并可能介导人单核细胞对完整的嗜肺乳杆菌的吞噬。
Legionella pneumophila is a facultative intracellular bacterial pathogen that parasitizes human monocytes and alveolar macrophages. Previous studies from this laboratory have shown that monocyte complement receptors CR1 and CR3 and complement component C3 in serum mediate L. pneumophila phagocytosis. In this study, we have explored C3 fixation to L. pneumophila. We developed a whole-cell enzyme-linked immunosorbent assay (ELISA) to measure C3 fixation to the bacterial surface. By this assay, C3 fixes to L. pneumophila that are opsonized in fresh nonimmune serum, and C3 fixation takes place via the alternative pathway of complement activation. Immunoblot analysis of opsonized L. pneumophila indicated that C3 fixes selectively to specific acceptor molecules of L. pneumophila. Consistent with this, when nitrocellulose blots of whole L. pneumophila or bacterial components are incubated in fresh nonimmune serum, C3 fixes exclusively to the major outer membrane protein (MOMP) of L. pneumophila, a porin; C3 does not fix to L. pneumophila LPS on these blots. To further explore the role of MOMP in C3 fixation and phagocytosis, we reconstituted purified MOMP into liposomes. By the ELISA, MOMP- liposomes, but not plain liposomes lacking MOMP, avidly fix C3. Consistent with a dominant role for MOMP in C3 fixation, MOMP-liposomes form a C3 complex of the same apparent molecular weight as whole L. pneumophila in nonimmune serum. Opsonized radioiodinated MOMP-liposomes avidly adhere to monocytes, and adherence is dose dependent upon serum. By electron microscopy, opsonized MOMP-liposomes are efficiently phagocytized by human monocytes, and phagocytosis takes place by a conventional appearing form of phagocytosis. This study demonstrates that C3 fixes selectively to the MOMP of L. pneumophila, and that, in the presence of nonimmune serum, MOMP can mediate phagocytosis of liposomes and, potentially, phagocytosis of intact L. pneumophila by human monocytes.