Molecular mechanisms of innate immune signal tranduction by the Toll-like receptor 4

Humans have evolved complex and effective ways of fighting infections caused by microbes such as bacteria and viruses, the immune system. Sometimes the immune system goes wrong and this can cause serious diseases such as rheumatoid arthritis and diabetes. Our research aims to understand at a molecular level how the cells of the immune system are able to recognise microbes and the ways in which these cells respond to cause the familiar symptoms of an infection such as fever and tiredness, and to generate specific antibodies that fight the invading microbes. In this programme we will study the way in which immune system cells respond to a powerful toxins and allergens, such as endotoxin or LPS, released by certain types of bacteria during an infection. Although normal responses to endotoxin are an important part of the fight against infection, it can cause a highly dangerous condition called endotoxic shock in patients with severe septicaemia and this pathological response frequently causes organ failure and death. In fact endotoxin shock is responsible for about 135000 deaths every year in Europe alone. The proposed studies should shed light on why endotoxin can produce a beneficial reaction in some conditions and a damaging response in others.

The discovery of pattern recogniion receptors (PRRs) is one of the most important advances in immunology of the last 20 years. One class of PRRs, the Toll-like receptors (TLRs) are now understood to play critical roles in the initiation of inflammatory responses to infection by viruses, bacteria and other microbial pathogens. TLR4, the receptor for Gram- lipopolysaccharides, is of of particular importance in this regard and recent studies have also implicated it as a key mediator of the sterile and allergic inflammatory responses charcteristic of chronic diseases such as rheumatoid arthritis and asthma.

This Programme Grant has three objectives all of which aim to understand the molecular mechanisms of signal transduction by TLR4 and to use this information to develop novel therapies for sepsis, allergic asthma and sterile inflammation. Firstly we will use structural biology and the emerging technique of single molecule imaging to study the signal transduction process in living cells. This approach will allow us to visualise the formation of transient signalling complexes in real time and define the molecular basis of signalling specificity, the stoichiometry of the constituent subunits and the cooperativity of the signalling process. In the second part of the programme we will use biophysical, biochemical and cell based techniques to determine the mode of action of lipid bearing aeroallergens and the endogenous ligands fibronectin and tenascin C all of which activate or enhance signalling by TLR4. Finally, in collaboration with Pfizer Inc we will determine how at the structural level antagonistic antibodies directed against TLR4 are able to inhibit signalling and use structure based design to develop novel inhibitors of TLR4 for use in the treatment of endotoxic shock and other inflammatory diseases mediated by TLR4.