Exploring, Understanding and Intervening in IgE-dependent Mechanisms in Allergic Disease and Asthma

The incidence of allergic disease, and asthma in particular, has increased alarmingly in the UK and there is an urgent need for new therapies. Antibodies of a type known as immunoglobulin E (IgE) are crucially involved in the allergic response, and individuals susceptible to allergies have high IgE levels. These IgE antibodies recognise allergens that enter the airways (e.g. grass pollen), the gut (food allergens) or the skin (contact allergies), and then trigger allergic reactions. We know, from the success of an anti-IgE treatment, that removal of IgE relieves allergic symptoms. But anti-IgE, itself an antibody, is very expensive, requires administration in the clinic, and is licensed only for severe asthma. By understanding how the body produces IgE, and the way IgE activates allergic reactions, we expect to discover new ways to inhibit IgE, and develop compounds that are cheaper, more widely applicable to different allergic conditions, and easier to administer.

The cells in the body that make antibodies, B-cells, switch in response to certain signals from producing beneficial, protective antibodies to producing IgE; our aim is to understand and prevent this switch. We have discovered that switching can occur in the nose rather than, as previously thought, only in lymph nodes, and now, using nasal tissue available from a surgical procedure (to clear nasal passages) developed at Guy?s Hospital, we can study the process in detail. We shall use an ultra-high resolution microscope (the first of its kind in the UK) to study events within the B-cell nucleus as the genes for IgE are switched on, and then study the survival and proliferation of these IgE-producing cells. This work will undoubtedly identify new targets for intervention.

We have also discovered that ?superantigens?, bacterial molecules that trigger antibody production, are present in asthmatic patients? airways. We believe that these superantigens may promote IgE production, in the lung or nose, and will study how they interact with IgE ? opening up a new approach to allergy treatment. We will also investigate the claim that certain IgE molecules are more active than others in triggering allergy. We have already determined the molecular structure of IgE and found that it changes its shape when it triggers an allergic reaction. We can now test compounds that prevent this change in shape, collaborating with the pharmaceutical industry to develop small-molecule inhibitors that overcome the limitations of anti-IgE.

The IgE antibody is a central element in the allergic response and the aetiology of asthma. Our proposed research is predicated on the existing evidence that IgE is an effective therapeutic target. The options include suppression of IgE synthesis and the interactions of IgE with its receptors, with allergens and with superantigens. We plan to address the following questions:
1. Since we know that heavy-chain chain switching to IgE occurs locally in the target organs of allergy, we need next to complement our biochemical studies on regulation of switching to IgE by imaging of the genes and associated proteins. Cell biological investigations of this kind have been limited by the resolution of commercial confocal microscopes, but a new instrument constructed here gives an unprecedented improvement in resolution, thus bringing it into the required range.
2. Thanks to a new surgical technique of turbinectomy developed at Guy?s Hospital by our collaborator, we can now explore the mechanisms by which the B-cells in the nasal mucosa are driven to synthesise and secrete IgE. We will also isolate single plasma cells secreting IgE antibodies directed against aeroallergens and S. aureus superantigens, clone and express their light-chain and epsilon heavy-chain genes and prepare recombinant IgE antibodies for structural studies.
3. We have discovered that bacterial superantigens are involved in the pathogenesis of allergic disease. We will explore the details of allergen- and superantigen-IgE interactions by X-ray crystallography (cf. our earlier X-ray structures of IgE and superantigen-antibody complexes).
4. We wish to uncover the structural basis for mast cell signalling triggered by monomeric murine IgE in the absence of antigen (with the collaboration of two groups in the US), and to survey our recombinant human IgEs for similar activity. The outcome will throw light on the relevance of ?highly cytokinergic? IgE to the pathogenesis of allergy.
5. We plan to develop a new generation of inhibitors to target the conformational change that the IgE molecule undergoes upon interaction with its high-affinity receptor, FceRI. We shall investigate the mechanism of action of peptide and other inhibitors, and anti-IgE Fabs, by structural and biophysical methods to ascertain whether they affect the conformational change. These results will provide a basis for design of inhibitors through collaboration with the pharmaceutical industry.