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Peptidoglycan molecular requirements allowing detection by the Drosophila immune deficiency pathway.
Stenbak, Carolyn R,Ryu, Ji-Hwan,Leulier, Franç,ois,Pili-Floury, Sebastien,Parquet, Claudine,Hervé,, Mireille,Chaput, Catherine,Boneca, Ivo G,Lee, Won-Jae,Lemaitre, Bruno,Mengin-Lecreulx, D Williams Wilkins 2004 JOURNAL OF IMMUNOLOGY Vol.173 No.12
<P>Innate immune recognition of microbes is a complex process that can be influenced by both the host and the microbe. Drosophila uses two distinct immune signaling pathways, the Toll and immune deficiency (Imd) pathways, to respond to different classes of microbes. The Toll pathway is predominantly activated by Gram-positive bacteria and fungi, while the Imd pathway is primarily activated by Gram-negative bacteria. Recent work has suggested that this differential activation is achieved through peptidoglycan recognition protein (PGRP)-mediated recognition of specific forms of peptidoglycan (PG). In this study, we have further analyzed the specific PG molecular requirements for Imd activation through the pattern recognition receptor PGRP-LC in both cultured cell line and in flies. We found that two signatures of Gram-negative PG, the presence of diaminopimelic acid in the peptide bridge and a 1,6-anhydro form of N-acetylmuramic acid in the glycan chain, allow discrimination between Gram-negative and Gram-positive bacteria. Our results also point to a role for PG oligomerization in Imd activation, and we demonstrate that elements of both the sugar backbone and the peptide bridge of PG are required for optimum recognition. Altogether, these results indicate multiple requirements for efficient PG-mediated activation of the Imd pathway and demonstrate that PG is a complex immune elicitor.</P>
The <i>Drosophila</i> Amidase PGRP-LB Modulates the Immune Response to Bacterial Infection
Zaidman-Ré,my, Anna,Hervé,, Mireille,Poidevin, Mickael,Pili-Floury, Sé,bastien,Kim, Min-Sung,Blanot, Didier,Oh, Byung-Ha,Ueda, Ryu,Mengin-Lecreulx, Dominique,Lemaitre, Bruno Elsevier 2006 Immunity Vol.24 No.4
<P><B>Summary</B></P><P>The <I>Drosophila</I> host defense against gram-negative bacteria is mediated by the Imd pathway upon sensing of peptidoglycan by the peptidoglycan recognition protein (PGRP)-LC. Here we report a functional analysis of PGRP-LB, a catalytic member of the PGRP family. We show that PGRP-LB is a secreted protein regulated by the Imd pathway. Biochemical studies demonstrate that PGRP-LB is an amidase that specifically degrades gram-negative bacteria peptidoglycan. In agreement with its amidase activity, PGRP-LB downregulates the Imd pathway. Hence, activation of PGRP-LB by the Imd pathway provides a negative feedback regulation to tightly adjust immune activation to infection. Our study also reveals that PGRP-LB controls the immune reactivity of flies to the presence of ingested bacteria in the gut. Our work highlights the key role of PGRPs that encode both sensors and scavengers of peptidoglycan, which modulate the level of the host immune response to the presence of infectious microorganisms.</P>