The three Rs of innate immune recognition: Toll like receptors (TLRs), RIG-like receptors (RLRs) and Nod-like receptors (NLRs)

The function of the innate immune system is thought to be the recognition of invading pathogens, the activation of inflammation to control the pathogen, and the subsequent activation of the acquired immune response. The innate immune system utilises a set of germline-encoded receptors, called PRRs, in order to recognise specific molecular patterns or motifs called PAMPs (Pathogen-Associated Molecular Patterns) on invading pathogens (Medzhitov & Janeway 1998). There are three families of PRRs, the Toll-lke receptor (TLR) family, the RIG-like receptor (RLR) family and the NOD-like receptor family.  The TLR family of proteins is an integral part of the mammalian innate immune system. TLRs are ancient pattern recognition receptors highly conserved from Drosophila to humans, that are expressed on immune cells and are able to distinguish a great variety of microbial ligands (Takeda, Kaisho, & Akira 2003). To date there are at least ten different TLRs that can recognise a wide variety of microbial conserved patterns. Most TLRs (TLR1, TLR2, TLR4, TLR5, TLR6) seem to activate cells by engaging their ligands on the cell surface, whereas TLR3, TLR7, TLR8 and TLR9 seem to trigger signalling intracellularly. These TLRs have been shown to reside in the ER and to recognise their ligands once they have been endocytosed (Heil et al. 2004).  RLRs have been recently discovered and play a key role in sensing RNA virus invasion. They recognise viral RNA independently of TLRs and unlike TLRs, which are found either on the cell surface or endosomes RLRs are found in the cytoplasm where cellular RNA is also present (Takeuchi & Akira 2009). The two main RNA helicases are RIG-I (retinoic acid inducible protein I) and MDA5 (melanoma differentiation associated gene 5). It has been shown that RIG-I and MDA5 recognise different viruses and different viral RNAs (Kato H et al. 2006;Loo et al. 2008) (Fig. 1). RIG-I recognizes single-stranded RNA (ssRNA) containing a terminal 5 -triphosphate (ppp)(Pichlmair A et al. 2007), as well as linear dsRNA no longer than 23 nucleotides(Kato et al. 2008). MDA5 recognises long strands of dsRNA but the mechanism by which this occurs is less clear (Kato, Takeuchi, Mikamo-Satoh, Hirai, Kawai, Matsushita, Hiiragi, Dermody, Fujita, & Akira 2008). The nucleotide-binding domain, leucine rich containing (NLR) protein family is a recent addition to the members of innate immunity effector molecules. NLRs play key roles in the cytoplasmic recognition of whole bacteria or their products. NLR proteins comprise a diverse protein family (over 20 in humans), indicating that NLRs have evolved to acquire specificity to various pathogenic microorganisms, thereby controlling host-pathogen interactions.

The aim of this meeting is to provide an overview of these three families of receptors and provide the most recent advances in the area of innate immune pattern recognition

Meeting chairs:  :  Dr Martha Triantafilou/Professor Kathy Triantafilou, Cardiff University School of Medicine, UK

 This event  has CPD accreditation and will have a  troubleshooting panel session.

On registration you will be able to submit your questions to the panel that will be asked by the chair on the day of the event

8:45 – 9:15        Registration

9:15 – 9:30        Introduction by the Chairs:  Dr Martha Triantafilou/Professor Kathy Triantafilou,Cardiff University School of Medicine, UK

9:30  – 10:00     NLR activation - what we do and don't know 

Dr Tom Monie, University of Cambridge, UK

This talk will focus on the mechanisms of NLR activation, particularly in the NLRC subfamily. It will introduce our current understanding of how these receptors are activated; how they are regulated; and how they signal within a cell. Recent advances in the areas of ligand recognition and protein:protein interactions will be introduced

10:00– 10:30    Talk to be confirmed

Professor Dirk Werling, Royal Veterinary College¸UK

10:30 – 11:00   Intracellular DNA recognition by the innate immune system

                            Professor Veit Hornung, Universitätsklinikum Bonn¸Germany

                            A central function of our innate immune system is to sense microbial pathogens by the presence of their nucleic acid genomes or their transcriptional or replicative activity. In mammals, a receptor-based system is mainly responsible for the detection of these “non-self” nucleic acids. Tremendous progress has been made in the past years to identify host constituents that are required for this intricate task. With regard to the sensing of RNA genome based pathogens by our innate immune system, a picture is emerging that includes certain families of the toll-like receptor family and the RIG-I like helicases. At the same time, intracellular DNA can also trigger potent innate immune responses, yet the players in this field are less clear. In this talk an update is given on our latest progress on intracellular DNA sensing by the innate immune system.

11:00– 11:25   Mid-morning break,   Poster Viewing and  Trade Show

11:25 – 11:55   Talk to be confirmed

Dr Nicholas Gay, University of Cambridge, UK

11:55 – 12:25    Understanding innate immunity to rhinovirus infection in asthma

Dr Michael Edwards, National Heart Lung Institute, London, UK

Asthma exacerbations are frequently caused by rhinovirus infection. Asthmatic individuals suffer exaggerated inflammatory responses and deficient innate anti-viral responses. Both harmful, pro-inflammatory responses and beneficial anti--viral reponses are initiated by infection of the bronchial epithelium, naturally infected by rhinovirus in vivo. Understanding the signalling pathways involved in rhinovirus infection that evoke both pro-inflammatory cytokines and beneficial type I and type III intefreons may identify novel therapeutic targets that can alleviate inflammation or boost natural interferon production. This presentation will discuss the role of RLH and TLR signalling in inflammation and host defense in response to rhinovirus infection in asthma.

12:25 –13:20                                                                                            Lunch,  Poster Viewing 

Information about the chairs

Over the past few years the Triantafilou group has been focusing on unravelling the molecular mechanisms behind the innate recognition of bacterial as well as viral pathogens. In particular, we have focused on the involvement of the Toll-like receptor (TLR) family of proteins, a recently identified family of pattern recognition receptors (PRRs), in the innate immune sensing. We have the expertise and the research tools for investigating receptor interactions using bio-imaging techniques, such a Fluorescence Resonance Energy Transfer (FRET), Fluorescence Recovery after Photobleaching (FRAP), Single Particle Imaging (SPFI), Single Particle Tracking (SPT), Fluorescent Loss in Photobleaching (FLIP) as well as live cell imaging. Using combinations of these techniques, our group has discovered novel concepts in innate immune recognition of microbial ligands by TLRs and co-operating PRRs. We have been one of the first to demonstrate that the single-receptor concept of innate immune recognition is an oversimplified one and that different combinational associations of receptors determine the innate immune response to different microbial pathogens, using a range of non-invasive biophysical techniques. We performed several studies investigating associations of PRRs in response to bacterial products from Helicobacter pylori,Neisseria meningitidis, and bacterial lipopeptides. Furthermore, we demonstrated that membrane microdomains, or "lipid rafts" play an important role in this receptor cluster formation by providing a microenvironment for these interactions to take place. This was the first ever publication demonstrating that TLRs exist and signal within lipid rafts (making this paper one of the most cited papers in the field). We provided the first dynamic picture of TLR engagement by their ligand by determining the lateral diffusion of receptors involved in the innate immune response before and after stimulation by bacterial products . It has helped us understand the organisation, lateral mobility and confinement of PRRs involved in the innate immune response on the plasma membrane.  In addition, using fluorescent imaging, we have revealed that TLR2 exists as a heterodimer prior to ligand engagement, as well as its intracellular trafficking and targeting in response to Gram-positive bacterial products. More recently, we have demonstrated that CXCR4 acts as a negative regulator for TLR2 and its significance in the innate recognition of Porphyromonas gingivalis (Hajishengallis et al. 2008). This was the first study demonstrating that TLR2-CXCR4 association can impair innate immune responses. Finally, we have shown that TLR4, TLR7 and TLR8 are involved in sensing viral products. These were the first studies to reveal how enteroviruses are recognised by the innate immune system. 

About the Speakers

Tom Monie is a Wellcome Trust Career Development Fellow who initially began researching viruses in order to understand how they successfully take over cellular function. He moved into the innate immune field working on structural and functional studies of TLR4. In 2008 he started his own group studying the NLR proteins NOD1 and NOD2. He is particularly interested in investigating how these proteins recognise their ligands and how their interaction with other cellular proteins impacts on the response to infection and development of disease

Clare Bryant -1985 BSc (Hons) Biochemistry and Physiology, University of Southampton, 1989 BVetMed, University of London,1992 PhD, University of London. 1992-1995 Wellcome Trust Veterinary Research Training Fellowship, Royal Veterinary College, University of London, 1995-1996 Research Scientist, William Harvey Research Institute, London, 1996-2000 Wellcome Trust Research Career Development Fellow and 2000-2003 Wellcome Trust Research Advanced Fellow, Department of Clinical Veterinary Medicine, The University of Cambridge, 2003-University Lecturer and Senior Lecturer in Clinical Pharmacology, Department of Veterinary Medicine, The University of Cambridge. Research Interests: Role of Pattern Recognition Receptors (PRRs) in bacterial infection; species specificity in PRR activation.

Michael R. Edwards Professional Qualifications: BSc (Hons), 1995, PhD 2001. Joined the laboratory of S.L. Johnston in 2001, became an Asthma UK Research Fellow, 2007. Research Interests & Goals are to understand the molecular and cellular basis of virus-induced asthma exacerbations, focusing on innate host responses involved in inflammation and host defence. Ultimately, to identify novel therapeutic targets for virus-induced asthma exacerbations

Dr Sandra Sacre completed her PhD exmaining the role of annexins in cardiovasular disease  in 2000 at University College London (UCL). She then spent one year as a postdoc at the Royal Free Hospital (UCL) focusing on ApoE receptor signalling before moving to the Kennedy Institute of Rheumatology  (part of Imperial College London), to work on toll-like receptors in rheumatoid arthritis. In November 2009, Sandra moved to Brighton and Sussex Medical School at the University of Sussex to set up her own laboratory where she continues to work on TLRs in rheumatic diseases.

Veit Hornung received his M.D. from the University of Munich (Germany) in 2003, and his postdoctoral training from the University of Munich and the University of Massachusetts Medical School in Worcester (USA). In 2008 he then joined the University of Bonn (Germany), where he is currently a full professor in the Institute of Clinical Chemistry and Pharmacology. Veit Hornung's research focuses on the recognition of nucleic acids by the innate immune system.

Ian Sabroe is a practicing respiratory physician with interests in asthma, COPD and pulmonary hypertension, and is Professor of Inflammation Biology at the University of Sheffield. His work has focused on identifying expression of TLRs and their functions in innate immune cells, exploring how innate immune cells and tissue cells cooperate to mediate the inflammatory response, and how these responses regulate responses to bacteria and viruses. Recent work has examined new models of inflammation in the human to allow probing of TLR signalling.