Rämet Mika, Manfruelli Pascal, Pearson Alan, Mathey-Prevot Bernard, Ezekowitz R Alan B
Laboratory of Developmental Immunology, Massachusetts General Hospital for Children, and Department of Pediatrics, Harvard Medical School, 55 Fruit Street, Boston, Massachusetts 02114, USA.
Nature. 2002 Apr 11;416(6881):644-8. doi: 10.1038/nature735. Epub 2002 Mar 24.
The recognition and phagocytosis of microbes by macrophages is a principal aspect of innate immunity that is conserved from insects to humans. Drosophila melanogaster has circulating macrophages that phagocytose microbes similarly to mammalian macrophages, suggesting that insect macrophages can be used as a model to study cell-mediated innate immunity. We devised a double-stranded RNA interference-based screen in macrophage-like Drosophila S2 cells, and have defined 34 gene products involved in phagocytosis. These include proteins that participate in haemocyte development, vesicle transport, actin cytoskeleton regulation and a cell surface receptor. This receptor, Peptidoglycan recognition protein LC (PGRP-LC), is involved in phagocytosis of Gram-negative but not Gram-positive bacteria. Drosophila humoral immunity also distinguishes between Gram-negative and Gram-positive bacteria through the Imd and Toll pathways, respectively; however, a receptor for the Imd pathway has not been identified. Here we show that PGRP-LC is important for antibacterial peptide synthesis induced by Escherichia coli both in vitro and in vivo. Furthermore, totem mutants, which fail to express PGRP-LC, are susceptible to Gram-negative (E. coli), but not Gram-positive, bacterial infection. Our results demonstrate that PGRP-LC is an essential component for recognition and signalling of Gram-negative bacteria. Furthermore, this functional genomic approach is likely to have applications beyond phagocytosis.
巨噬细胞对微生物的识别和吞噬作用是先天性免疫的一个主要方面，从昆虫到人类都保守存在。黑腹果蝇具有循环巨噬细胞，其吞噬微生物的方式与哺乳动物巨噬细胞相似，这表明昆虫巨噬细胞可作为研究细胞介导的先天性免疫的模型。我们在果蝇类巨噬细胞S2细胞中设计了基于双链RNA干扰的筛选方法，并确定了34种参与吞噬作用的基因产物。这些产物包括参与血细胞发育、囊泡运输、肌动蛋白细胞骨架调节的蛋白质以及一种细胞表面受体。这种受体，肽聚糖识别蛋白LC（PGRP-LC），参与革兰氏阴性菌而非革兰氏阳性菌的吞噬作用。果蝇的体液免疫也分别通过Imd和Toll途径区分革兰氏阴性菌和革兰氏阳性菌；然而，尚未鉴定出Imd途径的受体。在这里，我们表明PGRP-LC对于体外和体内由大肠杆菌诱导的抗菌肽合成都很重要。此外，无法表达PGRP-LC的图腾突变体对革兰氏阴性菌（大肠杆菌）感染敏感，但对革兰氏阳性菌感染不敏感。我们的结果表明，PGRP-LC是革兰氏阴性菌识别和信号传导的重要组成部分。此外，这种功能基因组学方法可能在吞噬作用之外还有其他应用。
