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PubMed1997

MyD88: an adapter that recruits IRAK to the IL-1 receptor complex.

IL-1 is a proinflammatory cytokine that signals through a receptor complex of two different transmembrane chains to generate multiple cellular responses, including activation of the transcription factor NF-kappaB. Here we show that MyD88, a previously described protein of unknown function, is recruited to the IL-1 receptor complex following IL-1 stimulation. MyD88 binds to both IRAK (IL-1 receptor-associated kinase) and the heterocomplex (the signaling complex) of the two receptor chains and thereby mediates the association of IRAK with the receptor. Ectopic expression of MyD88 or its death domain-containing N-terminus activates NF-kappaB. The C-terminus of MyD88 interacts with the IL-1 receptor and blocks NF-kappaB activation induced by IL-1, but not by TNF. Thus, MyD88 plays the same role in IL-1 signaling as TRADD and Tube do in TNF and Toll pathways, respectively: it couples a serine/threonine protein kinase to the receptor complex.

Adaptor Proteins, Signal Transducing↗
PubMed2002

Functional genomic analysis of phagocytosis and identification of a Drosophila receptor for E. coli.

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.

Actins↗
PubMed2004

Fluorescence-activated cell sorting (FACS) of Drosophila hemocytes reveals important functional similarities to mammalian leukocytes.

Drosophila is a powerful model for molecular studies of hematopoiesis and innate immunity. However, its use for functional cellular studies remains hampered by the lack of single-cell assays for hemocytes (blood cells). Here we introduce a generic method combining fluorescence-activated cell sorting and nonantibody probes that enables the selective gating of live Drosophila hemocytes from the lymph glands (larval hematopoietic organ) or hemolymph (blood equivalent). Gated live hemocytes are analyzed and sorted at will based on precise quantitation of fluorescence levels originating from metabolic indicators, lectins, reporters (GFP and beta-galactosidase) and antibodies. With this approach, we discriminate and sort plasmatocytes, the major hemocyte subset, from lamellocytes, an activated subset present in gain-of-function mutants of the Janus kinase and Toll pathways. We also illustrate how important, evolutionarily conserved, blood-cell-regulatory molecules, such as calcium and glutathione, can be studied functionally within hemocytes. Finally, we report an in vivo transfer of sorted live hemocytes and their successful reanalysis on retrieval from single hosts. This generic and versatile fluorescence-activated cell sorting approach for hemocyte detection, analysis, and sorting, which is efficient down to one animal, should critically enhance in vivo and ex vivo hemocyte studies in Drosophila and other species, notably mosquitoes.

Animals↗
PubMed2001

A genome-wide analysis of immune responses in Drosophila.

Oligonucleotide DNA microarrays were used for a genome-wide analysis of immune-challenged Drosophila infected with Gram-positive or Gram-negative bacteria, or with fungi. Aside from the expression of an established set of immune defense genes, a significant number of previously unseen immune-induced genes were found. Genes of particular interest include corin- and Stubble-like genes, both of which have a type II transmembrane domain; easter- and snake-like genes, which may fulfil the roles of easter and snake in the Toll pathway; and a masquerade-like gene, potentially involved in enzyme regulation. The microarray data has also helped to greatly reduce the number of target genes in large gene groups, such as the proteases, helping to direct the choices for future mutant studies. Many of the up-regulated genes fit into the current conceptual framework of host defense, whereas others, including the substantial number of genes with unknown functions, offer new avenues for research.

Animals↗
PubMed1997

Drosophila host defense: differential induction of antimicrobial peptide genes after infection by various classes of microorganisms.

Insects respond to microbial infection by the rapid and transient expression of several genes encoding potent antimicrobial peptides. Herein we demonstrate that this antimicrobial response of Drosophila is not aspecific but can discriminate between various classes of microorganisms. We first observe that the genes encoding antibacterial and antifungal peptides are differentially expressed after injection of distinct microorganisms. More strikingly, Drosophila that are naturally infected by entomopathogenic fungi exhibit an adapted response by producing only peptides with antifungal activities. This response is mediated through the selective activation of the Toll pathway.

Animals↗
PubMed2005

Manduca sexta serpin-6 regulates immune serine proteinases PAP-3 and HP8. cDNA cloning, protein expression, inhibition kinetics, and function elucidation.

Analogous to blood coagulation and complement activation in mammals, some insect defense responses (e.g. prophenoloxidase (proPO) activation and Toll pathway initiation) are mediated by serine proteinase cascades and regulated by serpins in hemolymph. We recently isolated Manduca sexta serpin-6 from hemolymph of the bacteria-challenged larvae, which selectively inhibited proPO-activating proteinase-3 (PAP-3) (Wang, Y., and Jiang, H. (2004) Insect Biochem. Mol. Biol. 34, 387-395). To further characterize its structure and function, we cloned serpin-6 from an induced fat body cDNA library using a PCR-derived probe. M. sexta serpin-6 is 55% similar in amino acid sequence to Drosophila melanogaster serpin-5, an immune-responsive protein. We produced serpin-6 in an Escherichia coli expression system and purified the soluble protein by nickel affinity and hydrophobic interaction chromatography. The recombinant protein specifically inhibited PAP-3 and blocked proPO activation in vitro in a concentration-dependent manner. Matrix-assisted laser desorption ionization-time of flight mass spectrometry indicated that the cleavage site of serpin-6 is between Arg373 and Ser374. Serpin-6 is constitutively present in hemolymph of naive larvae, and its mRNA and protein levels significantly increase after a bacterial injection. The association rate constant of serpin-6 and PAP-3 is 2.6 x 10(4) m(-1) s(-1), indicating that serpin-6 may contribute to the inhibitory regulation of PAP-3 in the hemolymph. We also identified the covalent complex of serpin-6 and PAP-3 in induced hemolymph by immunoaffinity chromatography and mass spectrometry. Furthermore, immulectin-2, serine proteinase homologs, proPO, PO, attacin-2, and a complex of serpin-6 and hemolymph proteinase-8 were also detected in the proteins eluted from the immunoaffinity column using serpin-6 antibody. These results suggest that serpin-6 plays important roles in the regulation of immune proteinases in the hemolymph.

Amidohydrolases↗
PubMed2000

The Drosophila caspase Dredd is required to resist gram-negative bacterial infection.

The Drosophila innate immune system discriminates between pathogens and responds by inducing the expression of specific antimicrobial peptide-encoding genes through distinct signaling cascades. Fungal infection activates NF-kappaB-like transcription factors via the Toll pathway, which also regulates innate immune responses in mammals. The pathways that mediate antibacterial defenses, however, are less defined. We have isolated loss-of-function mutations in the caspase encoding gene dredd, which block the expression of all genes that code for peptides with antibacterial activity. These mutations also render flies highly susceptible to infection by gram-negative bacteria. Our results demonstrate that Dredd regulates antibacterial peptide gene expression, and we propose that Dredd, Immune Deficiency and the P105-like rel protein Relish define a pathway that is required to resist gram-negative bacterial infections.

Animals↗
PubMed2002

Regulation of larval hematopoiesis in Drosophila melanogaster: a role for the multi sex combs gene.

Drosophila larval hematopoietic organs produce circulating hemocytes that ensure the cellular host defense by recognizing and neutralizing non-self or noxious objects through phagocytosis or encapsulation and melanization. Hematopoietic lineage specification as well as blood cell proliferation and differentiation are tightly controlled. Mutations in genes that regulate lymph gland cell proliferation and hemocyte numbers in the body cavity cause hematopoietic organ overgrowth and hemocyte overproliferation. Occasionally, mutant hemocytes invade self-tissues, behaving like neoplastic malignant cells. Two alleles of the Polycomb group (PcG) gene multi sex combs (mxc) were previously isolated as such lethal malignant blood neoplasm mutations. PcG genes regulate Hox gene expression in vertebrates and invertebrates and participate in mammalian hematopoiesis control. Hence we investigated the need for mxc in Drosophila hematopoietic organs and circulating hemocytes. We show that mxc-induced hematopoietic hyperplasia is cell autonomous and that mxc mainly controls plasmatocyte lineage proliferation and differentiation in lymph glands and circulating hemocytes. Loss of the Toll pathway, which plays a similar role in hematopoiesis, counteracted mxc hemocyte proliferation but not mxc hemocyte differentiation. Several PcG genes tested in trans had no effects on mxc hematopoietic phenotypes, whereas the trithorax group gene brahma is important for normal and mutant hematopoiesis control. We propose that mxc provides one of the regulatory inputs in larval hematopoiesis that control normal rates of plasmatocyte and crystal lineage proliferation as well as normal rates and timing of hemocyte differentiation.

Animals↗
PubMed1999

Constitutive activation of toll-mediated antifungal defense in serpin-deficient Drosophila.

The antifungal defense of Drosophila is controlled by the spaetzle/Toll/cactus gene cassette. Here, a loss-of-function mutation in the gene encoding a blood serine protease inhibitor, Spn43Ac, was shown to lead to constitutive expression of the antifungal peptide drosomycin, and this effect was mediated by the spaetzle and Toll gene products. Spaetzle was cleaved by proteolytic enzymes to its active ligand form shortly after immune challenge, and cleaved Spaetzle was constitutively present in Spn43Ac-deficient flies. Hence, Spn43Ac negatively regulates the Toll signaling pathway, and Toll does not function as a pattern recognition receptor in the Drosophila host defense.

Animals↗
PubMed2026

Insect immune systems: same same but different but still same.

Insects are the most diverse group of animals in nature, occupying nearly every ecological niche and playing central roles as pollinators, pests, and disease vectors. Despite this vast diversity, insects rely on a set of conserved yet evolutionarily adaptable immune pathways to defend against pathogens. Early studies in insect immunity have laid the foundation for human immunology, and recent advances in genomic and transgenic technologies have renewed interest in understanding how immune responses vary across insect orders. Insects are highly diverse in their immune systems; each species has unique immune responses that help fight infections from specific pathogens. Nevertheless, they share multiple aspects of recognition, regulation, and effector mechanisms. This review focuses on current knowledge of the immune systems of major insect lineages to highlight both shared signaling pathways, immune cells, and humoral factors, as well as lineage-specific responses that reflect distinct ecological pressures that have shaped the host-microbe interactions. Comparing different insect species and orders not only provides insights into the evolutionary divergences and convergences of immune system features but also offers complementary knowledge among species within the same order, helping fill existing gaps. Understanding these evolutionary patterns not only deepens our understanding of insect immunity but also informs the development of transgenic strategies to disrupt pathogen transmission in key vector species.

Animals↗
PubMed2006

Bovine peptidoglycan recognition protein-S: antimicrobial activity, localization, secretion, and binding properties.

Peptidoglycan (PGN) recognition proteins (PGRPs) are pattern recognition molecules of innate immunity that are conserved from insects to humans. Various PGRPs are reported to have diverse functions: they bind bacterial molecules, digest PGN, and are essential to the Toll pathway in Drosophila. One family member, bovine PGN recognition protein-S (bPGRP-S), has been found to bind and kill microorganisms in a PGN-independent manner, raising questions about the identity of the bPGRP-S ligand. Addressing this, we have determined the binding and microbicidal properties of bPGRP-S in a range of solutions approximating physiologic conditions. In this study we show that bPGRP-S interacts with other bacterial components, including LPS and lipoteichoic acid, with higher affinities than for PCP, as determined by their abilities to inhibit bPGRP-S-mediated killing of bacteria. Where and how PGRPs act in vivo is not yet clear. Using Immunogold electron microscopy, PGRP-S was localized to the dense/large granules of naive neutrophils, which contain the oxygen-independent bactericidal proteins of these cells, and to the neutrophil phagolysosome. In addition, Immunogold staining and secretion studies demonstrate that neutrophils secrete PGRP-S when exposed to bacteria. Bovine PGRP-S can mediate direct lysis of heat-killed bacteria; however, PGRP-S-mediated killing of bacteria is independent of this activity. Evidence that bPGRP-S has multiple activities and affinity to several bacterial molecules challenges the assumption that the PGRP family of proteins recapitulates the evolution of TLRs. Mammalian PGRPs do not have a single antimicrobial activity against a narrow range of target organisms; rather, they are generalists in their affinity and activity.

Animals↗
PubMed2005

Mycobacterium tuberculosis heat shock proteins use diverse Toll-like receptor pathways to activate pro-inflammatory signals.

Although the Toll-like receptors used by Mycobacterium tuberculosis membrane and secreted factors are known, the pathways activated by M. tuberculosis heat shock proteins are not. An efficient immune response against the intracellular pathogen M. tuberculosis is critically dependent on rapid detection of the invading pathogen by the innate immune system and coordinated activation of the adaptive immune response. Macrophage phagocytosis of M. tuberculosis is accompanied by activation of the transcription factor NF-kappaB and secretion of inflammatory mediators that play an important role in granuloma formation and immune protection during M. tuberculosis infection. The interaction between M. tuberculosis and the various Toll-like receptors is complex, and it appears that distinct mycobacterial components may interact with different members of the Toll-like receptor family. Here we show that recombinant, purified, mycobacterial heat shock proteins 65 and 70 induce NF-kappaB activity in a dose-dependent manner in human endothelial cells. Furthermore, we show that whereas mycobacterial heat shock protein 65 signals exclusively through Toll-like receptor 4, heat shock protein 70 also signals through Toll-like receptor 2. Mycobacterial heat shock protein 65-induced NF-kappaB activation was MyD88-, TIRAP-, TRIF-, and TRAM-dependent and required the presence of MD-2. A better understanding of the recognition of mycobacterial heat shock proteins and their role in the host immune response to the pathogen may open the way to a better understanding of the immunological processes induced by this important human pathogen and the host-pathogen interactions and may help in the rational design of more effective vaccines or vaccine adjuvants.

Animals↗
PubMed2004

Peptidoglycan molecular requirements allowing detection by the Drosophila immune deficiency pathway.

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.

Animals↗
PubMed2005

Hyper-IgE syndrome is not associated with defects in several candidate toll-like receptor pathway genes.

The genetic basis of hyper-IgE syndrome (HIES), also known as Job syndrome, a primary immunodeficiency associated with recurrent skin and pulmonary infections, is unknown. We hypothesized that HIES is due to a defect in the Toll-like receptor signaling pathway. We used a whole blood cytokine assay to compare inflammatory responses to stimulation with specific Toll-like receptor (TLR) pathway agonists in four individuals with HIES and nine healthy controls. Production of tumor necrosis factor-alpha, interleukin (IL)-1beta, IL-6, and IL-12 was not impaired in response to stimulation with lipopolysaccharide, peptidoglycan, zymosan, lipoteichoic acid, Staphylococcus aureus, Escherichia coli, or Streptococcus pneumoniae. Interferon (IFN)-gamma was reduced in HIES subjects in response to each of these stimuli. We sequenced several candidate genes from the TLR pathway in HIES individuals to determine whether any mutations were associated with this syndrome. No novel mutations or polymorphisms were found in the coding regions of TLR1, TLR2, TLR6, MyD88, or TRAF6. In summary, although HIES individuals had an IFN-gamma secretion defect, they also produced normal levels of several TLR-regulated proinflammatory cytokines. No unique mutations or polymorphisms were observed in several candidate genes from the TLR pathway. Our studies do not support a role for a defective TLR response in HIES individuals.

Adaptor Proteins, Signal Transducing↗
PubMed2002

The Drosophila immune response against Gram-negative bacteria is mediated by a peptidoglycan recognition protein.

The antimicrobial defence of Drosophila relies largely on the challenge-induced synthesis of an array of potent antimicrobial peptides by the fat body. The defence against Gram-positive bacteria and natural fungal infections is mediated by the Toll signalling pathway, whereas defence against Gram-negative bacteria is dependent on the Immune deficiency (IMD) pathway. Loss-of-function mutations in either pathway reduce the resistance to corresponding infections. The link between microbial infections and activation of these two pathways has remained elusive. The Toll pathway is activated by Gram-positive bacteria through a circulating Peptidoglycan recognition protein (PGRP-SA). PGRPs appear to be highly conserved from insects to mammals, and the Drosophila genome contains 13 members. Here we report a mutation in a gene coding for a putative transmembrane protein, PGRP-LC, which reduces survival to Gram-negative sepsis but has no effect on the response to Gram-positive bacteria or natural fungal infections. By genetic epistasis, we demonstrate that PGRP-LC acts upstream of the imd gene. The data on PGRP-SA with respect to the response to Gram-positive infections, together with the present report, indicate that the PGRP family has a principal role in sensing microbial infections in Drosophila.

Animals↗
PubMed2026

Alternative splicing of toll-like receptor pathway mRNAs in lung immune cells from patients with ARDS.

Acute respiratory distress syndrome (ARDS) is characterized by robust inflammation in the lungs and systemic circulation. In this context, the toll-like receptor (TLR) signaling pathway plays a major role, driving inflammation that promotes host defense but also causing pathological tissue damage. To limit excessive inflammation, TLR signaling must be tightly controlled. One mechanism that modulates TLR signaling is alternative splicing of TLR pathway pre-mRNAs, which balances production of positively acting inflammatory mediators with alternative splice forms that terminate inflammation. To determine whether altered TLR pathway splicing contributes to pathological inflammation in ARDS, we evaluated two central mediators of the TLR signaling pathway, the MyD88 signaling adapter and the IRAK1 signaling kinase, in leukocytes isolated from bronchoalveolar lavage (BAL) of patients with ARDS. We found that MyD88 gene expression was decreased in BAL immune cells, whereas IRAK1 gene expression was increased. In parallel, we monitored long proinflammatory (MyD88-L and IRAK1) and shorter anti-inflammatory (MyD88-S and IRAK1c) splice forms and determined that IRAK1 splicing was shifted in a proinflammatory direction in patients with ARDS. Finally, we evaluated relationships between MyD88 isoform levels in BAL leukocytes and clinical outcomes. We conclude that pre-mRNA splicing of TLR pathway genes is altered in lung immune cells in patients with ARDS, that monitoring splicing of these genes may provide important prognostic information, and that manipulating splicing of these genes may be a useful novel therapeutic approach that needs further investigation.NEW & NOTEWORTHY We found that MyD88 expression is decreased, that IRAK1 expression is increased, and that IRAK1 splicing is shifted in a proinflammatory direction, in lung immune cells in patients with ARDS. We also find that MyD88 expression levels may correlate with survival in patients with ARDS. Thus, changes in expression and splicing of these two genes offer potential novel prognostic and therapeutic targets for ARDS.

Humans↗
PubMed2003

Toll-like receptor signaling pathways.

Members of the Toll-like receptor (TLR) family recognize conserved microbial structures, such as bacterial lipopolysaccharide and viral double-stranded RNA, and activate signaling pathways that result in immune responses against microbial infections. All TLRs activate MyD88-dependent pathways to induce a core set of stereotyped responses, such as inflammation. However, individual TLRs can also induce immune responses that are tailored to a given microbial infection. Thus, these receptors are involved in both innate and adaptive immune responses. The mechanisms and components of these varied responses are only partly understood. Given the importance of TLRs in host defense, dissection of the pathways they activate has become an important emerging research focus. TLRs and their pathways are numerous; Science's Signal Transduction Knowledge Environment's TLR Connections Map provides an immediate, clear overview of the known components and relations of this complex system.

Adaptor Proteins, Signal Transducing↗
PubMed2006

Adenoviral infection induces a multi-faceted innate cellular immune response that is mediated by the toll-like receptor pathway in A549 cells.

Adenovirus vectors are known to induce certain genes and impact innate response networks, but a broad understanding of this process and its mechanisms is currently lacking. For this reason, we chose to investigate and characterize Ad innate immunity using homogeneous, primary MEF cells replete with all the elements of the pathogen-sensing Toll-Like Receptor (TLR) pathway. By using an array-based approach to maximally define transcriptome changes induced upon Ad vector infection, we discovered that Ad infection induces a potent gene and transcription factor network response. This response is characterized by significant changes in the expression of genes involved in focal adhesion, tight junction, and RNA regulation, in addition to TLR pathway and other innate sensing genes. Further investigation using human A549 cells knocked down for various TLR pathway adaptors, revealed significant impacts on the Ad initiation of NF-kB and interferon responses, thus confirming TLR involvement in Ad-mediated immunity across diverse species.

Adenoviridae↗