MEETING REPORT

TOLLing away in Brazil

Jane A Mitchell, Katherine A Fitzgerald, Anthony Coyle, Neal Silverman & Neil Cartwright

Toll 2006, Recent Advances in Pattern Recognition, held in Salvador, Brazil, 4–7 March 2006, was both comprehensive and cutting edge, covering topics ranging from molecular recognition and signaling to new therapies in the clinic.

attern-recognition receptors of the sense pathogen-associated or danger-asso- Developments in fly innate immunity Pinnate immune system are critical for ciated molecular patterns extracellularly or In response to fungal or bacterial infection, host responses to both foreign products in endosomes (Fig. 1). However, one of the drosophila rapidly produce a battery of anti- http://www.nature.com/natureimmunology (pathogen-associated molecular patterns) most important aspects of this meeting was microbial peptides via the Toll and immune and danger signals from the host (danger- how basic research on pattern-recognition deficiency (Imd) pathways, respectively associated molecular patterns). The most receptor sensing and signaling in the innate (Fig. 1). These pathways lead to the activa- recent advances and exciting new discover- immune system has translated to a better tion of NF-κB homologs Dif and dorsal or ies in this field were presented at Toll 2006, understanding of disease processes and in Relish. Unlike some human TLRs, Toll does Recent Advances in Pattern Recognition, certain cases even to emerging successful not directly recognize pathogen-associated held in Salvador, Brazil, 4–7 March 2006. treatments. This rapidly expanding field all molecular patterns but instead functions This was the second international meeting began with the discovery of Toll in the fruit- as a receptor for the cytokine-like mol- on Toll-like receptors (TLRs) and in addi- fly Drosophila melanogaster. ecule spätzle. An inactive precursor form tion to TLRs included extensive discussion of spätzle is found in the hemolymph. After of the more recently recognized pattern- Toll and TLRs infection, this pro-spätzle is cleaved, gener- recognition receptors of the CATERPILLER A mutant drosophila was described in 1985 ating the active C-106 fragment. A family

Nature Publishing Group Group 200 6 Nature Publishing family (also known as NACHT–leucine-rich (ref. 1) and was named ‘Toll’ (meaning of C-terminal proteinase domain–contain-

© repeat (NLR) proteins), which includes both weird, mad or cool) because of its unusual ing serine proteases, many of which seem nucleotide-binding oligomerization domain appearance. This was caused by a mutation to function ‘upstream’ in the Toll pathway, (Nod) proteins and pyrin domain–contain- in the Toll gene, which encodes a single- between microbial recognition and spätzle ing (Nalp) proteins; the RNA helicases pass transmembrane receptor. Later, Toll cleavage, have been characterized (Jean- RIG-I, Mda5 and LGP2; and the peptido- was shown to be responsible for the control Marc Reichhart, Strasbourg, France). Most glycan-recognition proteins (PGRPs), most of fungal and Gram-positive bacterial infec- notably, several protease cascades, each critical for insect immunity but less well tions in the adult fly2. functioning ‘downstream’ of different rec- characterized in mammals. Both the NLR In the mid-1990s, several groups noticed ognition receptors, seem to converge on a proteins and RNA helicases are found in sequences in mammalian expressed sequence single spätzle processing protease known as the cytoplasm, and lack membrane-span- tag databases encoding proteins homolo- SPE9. ning regions. This is in contrast to the TLRs, gous to Toll3–5. Medzhitov and Janeway Gram-positive bacteria are recognized by which have a transmembrane region and made the critical discovery linking one two PGRPs, PGRP-SA and PGRP-SD, which of these TLRs with the activation of tran- recognize lysine-containing peptidoglycan. scription factor NF-κB and the induction Two other PGRPs, PGRP-LC and PGRP-LE, Jane A. Mitchell and Neil Cartwright are with of costimulatory molecules, suggesting that function in the Imd pathway. These receptors Cardiothoracic Pharmacology, Unit of Critical these receptors may link innate and adaptive ‘preferentially’ recognize diaminopimelic Care Medicine, National Heart and Lung Institute, immune responses3. Subsequently, Beutler acid–type peptidoglycan, found in Gram- Imperial College, Dovehouse Street, London SW3 and colleagues, through positional cloning negative bacteria. PGRP-LC is a cell surface 6LY, UK. Katherine A. Fitzgerald and of the lps mutation in mice, and Akira and receptor that recognizes both polymeric Neal Silverman are with the University of colleagues, using targeted deletion, clearly and monomeric forms of diaminopimelic Massachusetts Medical School, defined TLR4 as the signal-transducing acid–type peptidoglycan (Neal Silverman, Worcester, Massachusetts, 01605, USA. receptor for (LPS)6–8. Worcester, Massachusetts, USA). In con- Anthony Coyle is with MedImmune, Gaithersburg, Since then, ligands have been identified for trast, PGRP-LE seems to be located in the Maryland 20878, USA. nine of ten human TLRs as well as for many cytoplasm, where it recognizes monomeric e-mail: [email protected] of the murine-specific TLRs. fragments of diaminopimelic acid–type

NATURE VOLUME 7 NUMBER 7 JULY 2006 675 MEETING REPORT

peptidoglycan. Binding of monomeric pep- Gram-positive Fungi bacteria tidoglycan by either PGRP-LC or PGRP-LE Bereswinde causes the formation of receptor dimers or Gram-negative Yeast bacteria LYS-PGN oligomers, a process likely to be critical for persephone signal transduction. Both receptors contain a RHIM-like (receptor-interacting protein PGRP-SA SPE PGRP-SC1/2 PGRP-SD kinase homotypic interaction motif–like) Herrade pro-spz DAP-PGN domain that seems to be critical for signaling spz Virus but not for interactions between the recep- 10 DCV, FHV tors and the imd signaling protein . Finally, Toll PGRP-LC Bruno Lemaitre (Gif-sur-Yvette, France) and FHV B2 Julien Royet (Marseille, France), reporting dMyD88

on PGRP-LB and PGRP-SC1/2, respectively, PGRP-LE IFN- showed that these soluble PGRPs, found in RNAi ? like?

the gut, degrade peptidoglycan through their imd amidase action, downmodulating the Imd Jak-STAT pathway. In addition, PGRP-LB is present in serum and functions during systemic infec- tion. PGRP-SC1/2 has also been found to Dif dorsal downregulate systemic infection, although Relish Antiviral factors? Antiviral it is not yet known if it is also present in factors? 11,12 serum . PGRP-LB In the relatively new field of insect anti- http://www.nature.com/natureimmunology viral immunity, two mechanisms of RNA virus control in flies have been identified Figure 1 Recognition and signaling in D. melanogaster. Two pathways, Toll and Imd, respond (Joules Hoffman, Paris). Signaling by the to bacterial and fungal pathogens and activate NF-κB homologs (Dif, dorsal and Relish), driving Janus kinase–signal transducer and activator antimicrobial peptide gene expression. D. melanogaster Toll is activated by the cytokine spätzle of transcription pathway is activated after (spz). Pro-spätzle is found in the circulation and is cleaved after infection by the C-terminal proteinase domain protease spätzle processing enzyme (SPE). Alternative pathways respond viral infection, inducing the transcriptional to different pathogens and activate different C-terminal proteinase domain proteases (herrade, activation of genes, probably including those bereswinde and persephone), which all converge on the spätzle processing enzyme to activate encoding mediators of antiviral immunity. Toll. Gram-positive bacteria, with lysine-containing peptidoglycan (LYS-PGN), are recognized by However, this pathway does not directly the soluble receptors PGRP-SA and/or PGRP-SD. Gram-negative bacteria produce diaminopimelic recognize and respond to virus but instead acid–type peptidoglycan (DAP-PGN), which is recognized by either PGRP-LC on the cell surface is stimulated by an unidentified interferon- or by PGRP-LE inside the cell. Both of these receptors rely on a RHIM-like (receptor-interacting protein kinase homotypic interaction motif–like) motif for signal transduction (red bar). The like molecule that must be upregulated Imd pathway induces the expression of PGRP-LB, which is a catalytic PGRP that degrades 13 Nature Publishing Group Group 200 6 Nature Publishing by viral infection . In addition, the RNA peptidoglycan. PGRP-LB and PGRP-SC1/2 function in the serum and gut to degrade peptidoglycan © interference machinery is able to directly and thereby dampen the immune response. The response to the picorna-like drosophila C virus disrupt viral replication and infection. An (DCV) is independent of these pathways. Instead, virus infection activates an unidentified signaling elegant series of experiments using a trans- pathway that leads to production of antiviral factors in the infected cells as well as in neighboring genic Flock House virus system showed that cells via a putative interferon-like (IFN-like) factor and Janus kinase–signal transducer and the viral B2 gene product inhibits the RNA activator of transcription (Jak-STAT) signaling. RNA interference (RNAi) is another highly conserved antiviral mechanism that is often inhibited by viral products, including the B2 protein from Flock interference–mediated antiviral response, House virus (FHV). dMyD88, drosophila MyD88. whereas Dicer-2 mutant flies have increased susceptibility to viral infection14. An over- view of pattern recognition and signaling in changes in both the receptor ectodomain brane of TRAM. O’Neill also showed that the fly is presented in Figure 1. and cytoplasmic TLR–interleukin 1 recep- Mal is phosphorylated by Bruton’s tyrosine tor (TIR) domains, and the TIR domains kinase, leading to ‘downstream’ phosphory- TLR recognition and signaling seem to act as high-affinity, symmetrical lation and activation of the NF-κB subunit Understanding how ligands interact with surfaces to which adaptors can bind (Nick p65. Mal phosphorylation also results in TLRs is still an area of intense research, and Gay, Cambridge). polyubiquitination of itself by suppressor at the meeting some important advances The function of the adaptor proteins of cytokine signaling 1 and leads to its sub- were reported and definitive proofs were TRAM and Mal was also discussed (Luke sequent degradation, thereby limiting Mal provided. For example, direct binding O’Neill, Dublin). The kinase PKCε phos- signaling15. of ligand to TLR2 was shown for the first phorylates TRAM, a TLR4 complex–spe- The adaptor MyD88 may engage indi- time (Douglas Golenbock, Worcester, cific adaptor, at Ser16. This phosphorylation vidual TLRs differently, perhaps allowing Massachusetts, USA), whereas the MD-2- event is crucial for signaling, as cells defi- for separate gene pathways to be induced by LPS complex, and not LPS alone, was shown cient in PKCε have impaired activation a common adaptor protein. New mutated to be the true ligand for TLR4 (Jerrold of interferon-regulatory factor 3 (IRF3) alleles of the gene encoding MyD88, called Weiss, Iowa City, Iowa, USA). After ligand and impaired release of the chemokine ‘Pococurnate’ and ‘lackadaisical’, associ- binding, the formation of TLR dimers is RANTES (CCL5). However, such phos- ated with specific defects in signaling were associated with complex conformational phorylation also depletes the plasma mem- described (Bruce Beutler, La Jolla, California,

676 VOLUME 7 NUMBER 7 JULY 2006 NATURE IMMUNOLOGY MEETING REPORT

USA). The lackadaisical mutant impaired results. That observation leads us to specu- mediate interaction with ligands similar to signaling by TLR7 and TLR9 only. Notably, late that differential sensing of pathogens by TLRs. Nod1 and Nod2 contain one or two the Pococurnate mutant, which has altera- specific tissues or cells is a crucial aspect of -recruitment domains (CARDs), tions in the BB loop of the TIR domain, lacks pattern-recognition receptor biology. respectively, which interacts with a CARD all MyD88-dependent signaling except that That point was also made by Caetano Reis in the adaptor RIP2-RICK. The idea that initiated by the TLR2-TLR6 heterodimer. e Sousa (London), who used chimeric mice peptidoglycan is sensed by Nod proteins This opens the possibility of complex regu- with TLR4-deficient bone marrow–derived and not TLR2 was firmly established by lation at the level of MyD88 through as-yet- cells and TLR4-sufficient stromal cells to Koichi Fukase (Osaka, Japan). In experi- unknown mechanisms. Finally, in addition identify tissue-specific signaling required ments using chemically synthesized pepti- to MyD88 and the adaptor TRIF, the adaptor for the maturation of dendritic cells. When doglycan fragments and cell-based assays, protein ASC seems to be important in pat- these mice were challenged with LPS, robust muramyl dipeptide (as found in all bacterial tern-recognition receptor signaling; ASC is production of inflammatory cytokines from peptidoglycan) was shown to be sensed by a ‘downstream’ adaptor of cryopyrin (also the stromal tissues was noted. The idea that Nod2, whereas diaminopimelic acid–con- called Nalp3), which forms a large multipro- TLRs on stromal cells can mediate disease taining peptidoglycan fragments (found in tein complex, the ‘’, which is (atherosclerosis) was also elegantly shown Gram-negative and certain Gram-positive essential for interleukin 1β release and the using Tlr2−/− chimeras (Peter Tobias, La peptidoglycan) was found to be sensed by consequent immune response (Vishva Dixit, Jolla, California, USA). In this system, Nod1. No function for TLR2 was noted for San Francisco). TLR2-specific danger-associated molecular sensing either muramyl dipeptide or diami- patterns exacerbated atherosclerotic lesion nopimelic acid–containing peptidoglycan. Agonists and receptor specificities development through non–bone marrow– This helps to explain published work show- The effect on host defense of structural dif- derived cells. However, exogenously admin- ing that purified peptidoglycan lacking con- ferences in LPS from different bacteria was istered TLR2 ligands exacerbated lesion taminating lipopeptide or lipoteichoic acid discussed. LPS from various bacteria, such development through TLR2 expressed on does not signal through TLR2 proteins16. http://www.nature.com/natureimmunology as Yersinia pestis, which causes plague, and bone marrow–derived cells. That is consis- Nod1-mediated detection of peptidogly- from the Gram-negative intracellular bac- tent with data showing that isolated blood can was also demonstrated using live infec- terium Francisella tularensis, which causes vessels in vitro can sense TLR2-specific tion of epithelial or endothelial cells with tularemia, induce low or absent TLR4 acti- pathogen-associated molecular patterns Listeria monocytogenes (Stefan Hippenstiel, vation. When Y. pestis is grown at human differently from macrophages, using TLR6 Berlin). body core temperature (37 °C), a tetra- and not TLR1 (Jane Mitchell and Neil acylated lipid A–containing LPS is present, Cartwright, London). Those findings chal- Viral recognition which is a poor TLR4 agonist. However, this lenge the present idea of immunologically Viral recognition in the mammalian system form of LPS can antagonize the effects of a privileged sites and suggest a more sophis- was a chief theme of this meeting. In addi- hexa-acylated LPS synthesized by the same ticated model of tissue-specific immune tion to the sensing of viruses by TLRs, the bacteria grown at flea (vector) temperature responses in which stromal cells of the car- sensing of viruses by the RNA helicases RIG- (26 °C). The ability to switch LPS structure diovascular system sense pathogens without 1, Mda5 and LGP2 in antiviral responses is

Nature Publishing Group Group 200 6 Nature Publishing at mammalian body temperature represents the necessary requirement of ‘professional’ also important. Shizuo Akira (Osaka, Japan)

© a principal virulence factor for Y. pestis and immune cells such as macrophages. presented data obtained with both RIG-I- correlates with the lack of LpxL, a late acyl- Group B streptococci signal in macro- and Mda5-deficient mice. In contrast to RIG- transferase in the LPS biosynthetic pathway phages in a MyD88-dependant way via two 1-knockout mice, Mda5-knockout mice are found in many other Gram-negative bacte- known, distinct mitogen-activated pro- fully viable. Although most RIG-1-knockout ria. Forcing Y. pestis to express LpxL and syn- tein kinase pathways, p38 and Jnk (Philipp mice die at an embryonic stage of develop- thesize hexa-acylated LPS at 37 °C creates an Henneke, Worcester, Massachusetts, USA). ment, RIG-1-knockout embryonic fibro- avirulent strain in Tlr4+/+ but not in Tlr4−/− Although both pathways lead to cyto- blasts and dentritic cells can be collected. mice (Egil Lien, Worcester, Massachusetts, kine expression by macrophages, only p38 Type I interferon production by RIG-I-defi- USA). mediates phagocytosis and the formation cient fibroblasts and conventional dentritic F. tularensis has potential as an air- of reactive oxygen species. Selective inhibi- cells are severely impaired in response to borne ‘bioterror’ agent. F. tularensis has tion of Jnk in an in vivo mouse model of the RNA virus Newcastle disease virus. In an ‘unusual’ LPS, which when purified is a group B streptococcal improved sur- contrast, RIG-I-deficient plasmacytoid den- weak TLR4 agonist but is not an antagonist vival by reducing but tritic cells, the main type I interferon–pro- of Escherichia coli LPS. Notably, this purified preserving bacterial clearance. This obser- ducing cells in the blood, have normal type F. tularensis LPS, when given 2 days before vation shows the potential for developing I interferon responses to Newcastle disease challenge with a median lethal dose of live drugs that selectively block virus, although this response is dependent bacteria, both blunts the inflammatory in sepsis while leaving immune function on MyD88 and TLR7. Experiments using response and primes the adaptive immune unhindered. cells from both RIG-1-deficient and Mda5- response, resulting in host protection when deficient mice showed that many other injected intradermally (Stephanie Vogel, NLR proteins single-stranded RNA viruses, including Baltimore). It seems that the route of bac- The NLR proteins (Nod1 and Nod2) are part Sendai virus, vesicular stomatitis virus and terial administration is vital in mediating of a large family of cytosolic proteins with Japanese encephalitis virus, are sensed via this adaptive response. When injected intra- structural homology to the acti- RIG-1, whereas Mda5 senses only picor- peritoneally, a greater bacterial burden and vator Apaf-1. It is thought that the leucine- naviruses such as encephalomyocarditis increased proinflammatory gene expression rich repeat domains found in NLR proteins virus. Moreover, Mda5 can contribute to

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TLR1 Bacteria poly(I)·poly(C) responses in vivo, unlike Virus TLR2 RIG-1, which senses in vitro–transcribed TLR4 17 TLR5 synthetic double-stranded RNA . TLR6 RIG-1 has an N-terminal CARD and MyD88MyD88 (±Mal)(±Mal) a C-terminal helicase domain (DExD/H box helicase). RIG-I helicase is a double- Cytosolic EndosomeEndosome dsRNA, influenza bacteria stranded RNA–dependent ATPase that can ssRNA paramyxovirus, JEV CpG DNA dsRNA Flu, VSV RIG-I unwind double-stranded RNA in vitro. RIG- HSV PolyIC, picornavirus I signaling after ligand binding requires the TLR7 Mda5 TLR3 adaptor mitochondrial antiviral signaling TLR8 TLR9 (MAVS), which interacts with RIG-I through Nod1 MAVS Mitochondria Nod2 Nalps proteins CARD-CARD interactions. Localization to Ipaf the mitochondrial membrane is essential MyD88 TRIF for RIG-I signaling, a fact that is exploited ASC by hepatitis C virus, which produces a pro- Caspase-1 P Inflammasome tease to cleave MAVS and release it from 18 IRFs the mitochondrial membrane (Takashi RIP2 Fujita, Fukushima, Japan). MAVS-deficient macrophages are defective in type I inter- MAP kinases feron signaling after infection with Sendai virus or treatment with poly(I)·poly(C) and

lipofectamine, but not after infection with NF-κB IL-1β L. monocytogenes (Zhijian Chen, Dallas). IL-18 http://www.nature.com/natureimmunology Continuing that same theme, Genhong Cheng (Los Angeles, USA) discussed how Figure 2 Recognition and signaling in the mammalian system. Microbial products can be sensed the RIG-1–MAVS complex provides a plat- by plasma membrane–associated TLRs (TLR1, TLR2, TLR4, TLR5 and TLR6) or endosomal form for interaction with tumor necrosis nucleic acid–sensing TLRs (TLR3, TLR7, TLR8 and TLR9). All TLRs signal by recruiting one or factor–associated factor 3 and the IκB kinase more TIR domain–containing adapter molecules (MyD88, Mal-TIRAP, TRIF-TICAM1 or TRAM- ε TICAM2), leading to TLR-specific patterns of gene expression. Recruitment of MyD88 contributes (IKK)–related kinases IKK and TBK1, lead- to mitogen-activated protein (MAP) kinase and NF-κB signaling, leading to the transcriptional ing to phosphorylation of IRF3 and IRF7 regulation of inflammatory cytokines. Recruitment of TRIF drives IRF3 responses and interferon- and expression of type I interferon. β production. TLR7 and TLR9 also induce interferon via MyD88 and IRF7. Cytoplasmic RNA A unique function for IKKε in virus infec- helicases, including RIG-I and Mda5, discriminate between different RNA viruses and signal via tion was also described. IKKε-deficient mice N-terminal CARDs, which engage the ‘downstream’ CARD adapter MAVS (CARDif, IPS1 or VISA) β are more susceptible to infection with influ- to trigger IRF3-dependent interferon- responses. Cytosolic bacteria engage the NLR proteins to trigger NF-κB activation via RIP2, or Nalp proteins present in large multiprotein ‘inflammasome’ enza A virus than are wild-type mice, with complexes to activate caspase-1 and the processing of interleukin 1β (IL-1β). ±, with or without; Nature Publishing Group Group 200 6 Nature Publishing increased viral load and mortality (Tom ssRNA, single-stranded RNA; Flu, influenza; VSV, vesicular stomatitis virus; HSV, herpes simplex © Maniatis, Worcester, Massachusetts, USA). virus; dsRNA, double-stranded RNA; JEV, Japanese encephalitis virus; PolyIC, poly(I)·poly(C); Notably, serum concentrations of interferon- Ipaf, adaptor protein. β in these mice are normal, yet induction of a number of interferon-stimulated genes is impaired. Those data suggest that in addition Tomai’s group (St. Paul, Minnesota, USA) therapeutic benefit in viral infections or can- to having a function redundant with that of demonstrating that the TLR7 agonist imiqui- cer are not completely understood, but this is TBK1, IKKε accomplishes a unique function mod (an imidazoquinoline) cures genital probably due to an early ‘controlled’ proin- in response to virus infection. It is well docu- warts caused by infection with human pap- flammatory response leading to the induction mented that bacteria cause sepsis, and the illoma virus. Imiquimod is also an approved of mainly T helper type 1 cytokine profiles. function of TLRs in this process is now the treatment for the neoplastic skin lesion basal subject of investigation. However, viruses, cell carcinoma. Because of that success, a sys- Parasites and Toll which also activate TLRs, adaptor proteins temic TLR7 agonist is in phase II clinical trials Research into the immunity of both hosts and and cytokine production, do not normally for the treatment of metastatic melanoma and parasite vectors has provided new insights into cause sepsis. That is intriguing but may not other cancers, and early results regarding its the mechanisms of the disease process and be universal, as the hemorrhagic fever viruses effectiveness are very encouraging. Finally, the may eventually lead to new treatment and Marburg and Ebola can induce sepsis-like potential of TLR9 (B-class and C-class CpG) eradication strategies. MyD88 is essential for symptoms in patients, possibly through acti- ligands for treatment of non–small cell lung normal human proinflammatory responses, vation of TLRs (Robert Finberg, Worcester, carcinoma was discussed (Art Krieg, Worcester, and for murine resistance to infection with Massachusetts, USA). An overview of recog- Massachusetts, USA). Promising phase II clini- protozoan parasites that cause human disease, nition in innate immunity in the mammalian cal data were presented, and the first CpG is emphasizing the importance of TIR domain– system is presented in Figure 2. now in phase III trials. Encouraging clinical containing proteins in resistance and patho- data using C-class CpG as a monotherapy to genesis (Ricardo Gazzinelli, Belo Horizonte, New drugs with miraculous results reduce viral titers in chronic carriers of hepa- Brazil). Also, a human polymorphism in the One of the most notable aspects of Toll 2006 titis C were also presented. The mechanisms adaptor Mal, which limits signaling, has been was the breathtaking clinical data from Mark by which activators of TLR7 or TLR9 provide identified, and heterozygous carriers of this

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polymorphism are afforded a degree of protec- Concluding remarks (1998). 5. Taguchi, T., Mitcham, J.L., Dower, S.K., Sims, J.E. & tion to malaria and other diseases (O’Neill). Pathogen-sensing receptors and their path- Testa, J.R. Genomics 32, 486–488 (1996). Understanding the immune response of the ways are a newly identified, vital piece of the 6. Poltorak, A. et al. Science 282, 2085–2088 (1998). mosquito may provide new leads to the control immunological puzzle. Their importance 7. Qureshi, S.T. et al. J. Exp. Med. 189, 615–625 (1999). 8. Hoshino, K. et al. J. Immunol. 162, 3749–3752 of malaria. Mosquitoes have their own ‘Toll’ spans from flies to humans and back again. (1999). and REL2 (an ortholog of Relish in drosphila; Much was learned at Toll 2006, but partici- 9. Jang, I.H. et al. Dev. Cell 10, 45–55 (2006). George Christophides, Athens, Greece). REL2 pants were left with the unmistakable feeling 10. Kaneko, T. et al. Nat. Immunol. 7, 715–723 (2006). 11. Bischoff, V. et al. PLoS Pathog 2, e14 (2006). functions in the immune response to both that this is just the tip of the iceberg. More 12. Zaidman-Remy, A. et al. Immunity 24, 463–473 Gram-positive and Gram-negative bacteria caipirinhas, anyone? (2006). 13. Dostert, C. et al. Nat. Immunol. 6, 946–953 (2005). as well to as plasmodium parasites, which dif- 14. Galiana-Arnoux, D., Dostert, C., Schneemann, A., ferentiates it from the drosphila Relish, which 1. Anderson, K.V., Bokla, L. & Nusslein-Volhard, C. Cell 42, Hoffmann, J.A. & Imler, J.L. Nat. Immunol. 7, 590–597 791–798 (1985). functions mainly in responses to Gram-nega- (2006). 2. Lemaitre, B., Nicolas, E., Michaut, L., Reichhart, J.M. & 15. Mansell, A. et al. Nat. Immunol. 7, 148–155 (2006). tive bacteria. Finally REL1, a p65-like molecule, Hoffmann, J.A. Cell 86, 973–983 (1996). 16. Travassos, L.H. et al. EMBO Rep. 5, 1000–1006 although not physiologically active in malarial 3. Medzhitov, R., Preston-Hurlburt, P. & Janeway, C.A., Jr. (2004). Nature 388, 394–397 (1997). 17. Kato, H. et al. Nature 441, 101–105 (2006). infection, can efficiently block malarial infec- 4. Rock, F.L., Hardiman, G., Timans, J.C., Kastelein, R.A. 18. Seth, R.B., Sun, L. & Chen, Z.J. Cell Res. 16, 141–147 tion when stimulated. & Bazan, J.F. Proc. Natl. Acad. Sci. USA 95, 588–593 (2006). http://www.nature.com/natureimmunology Nature Publishing Group Group 200 6 Nature Publishing ©

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