Human studies of Allergic inflammation

Professor (Emeritus) Barry Kay, Group Leader

An understanding of the role of infiltrating inflammatory leukocytes and fixed tissue cells at mucosal surfaces is central to unravelling the complexities of allergy and asthma processes. Using clinical material Professor Kay and colleagues have had a long-term interest in the mechanisms of eosinophil and Th2 cell-mediated tissue damage and consequent repair and remodelling events. Models of provoked asthma and allergy, in the clinical laboratory under controlled conditions, are well established and involve tissue sampling from allergic volunteers. For example, research bronchoscopies are performed on asthmatics and normal control subjects to obtain bronchial biopsies and bronchoalveolar lavage fluid. This has enabled us to dissect the relationship between late-phase allergic reactions, bronchial hyperrresponsiveness and airway inflammation. From these studies the eosinophil has emerged as a major cell in regulating the deposition of extracellular matrix proteins in the airways. More recent work points to crucial interactions between T cells, epithelial cells and neuropeptides in causing the oedematous erythema of late-phase (chronic) allergic reactions. The ability of T-cell peptide epitopes, on the one hand to provoke late reactions when given by inhalation, but on the other to induce anergy or tolerance when administered intradermally, is also the subject of on-going work.

Inflammation and remodelling

Eosinophils, repair and remodelling

Several in vitro and animal studies have suggested that eosinophils play a role in fibrosis, remodelling and repair processes associated with IgE-mediated hypersensitivity. Using the allergen-induced cutaneous late-phase reaction as a model of allergic inflammation we showed that eosinophil-derived TGFß1 and IL-13 are temporarily associated with myofibroblast formation and deposition of tenascin and procollagen-1. Infusions of anti-IL-5 to human atopic subjects inhibited eosinophil infiltration and downregulated allergen-induced tenascin deposition in the skin. After allergen inhalational challenge there was a significant increase in the numbers of HSP47 (a chaperone of collagen synthesis) positive airway fibroblasts and in the thickness of tenascin in the reticular basement membrane (RBM) of asthmatics. There were also increases in the number of phospho-Smad2+ epithelial cells and nuclear phospho-Smad2+ fibroblasts as well as phospho-STAT6+ epithelial cells post-allergen challenge. Thus, allergen challenge in mild asthmatics induces activation of epithelial cells and fibroblasts as well as increased tenascin deposition within the RBM. Airway remodelling in asthma may, in part, result from repeated stimulation of the bronchial mucosa by allergen exposure. We are currently studying the role of TGFß and the related bone morphogenic proteins (BMPs) and activins. This family of mediators are activated by enzymatic cleavage and act on a shared receptor/signalling system in tissue development and remodelling in chronic inflammation. We are also studying the expression patterns of Type I (ALK1-7) and Type II receptors and activated phosphorylated R-Smads and inhibitory Smad -7 in human airway tissue in response to allergen challenge.

Collaborators: Dr Harsha Kariyawasam, Professor Douglas Robinson, Dr Sun Ying (KGT)

Eosinophil depletion and lumican expression

Late phase allergic reactions

Pathways Leading to Acute and Chronic Allergic Reactions

When the skin, nose or airways of atopic subjects are provoked with a single dose of allergen this produces, respectively, and within minutes, an immediate cutaneous weal-and-flare reaction, sneezing and runny nose, or wheezing. In about half of the subjects these immediate-type hypersensitivity responses are followed by a late-phase reaction (LPR) which is slow to peak (6-9 hours) and slow to resolve. In the skin, LPRs are characterized by an oedematous, red and slightly indurated swelling, in the nose by sustained blockage and, in the airways by further wheezing. Allergic tissue reactions in the skin and nose serve as a surrogate for events in the airways and have the advantage over lung studies of greater accessibility and multiple sampling for time-course studies. The LPR serves as a model for several allergic diseases including asthma, rhinitis, atopic dermatitis and urticaria. By taking biopsies and using the skin blister technique at the site of LPRs we have been able to track the crucial cells and mediators associated with allergic tissue reactions. We have also studied the role of IgE on these processes by performing biopsies before and after administration of omulizumab (a monoclonal anti-IgE).

T-cell peptide induced late phase reactions

We have also developed an asthma provocation model which provides information on the T cell component of allergic airway inflammation, independently of initial mast cell activation. It involves the administration of allergen-derived T-cell peptide epitopes, either intradermal injection or by inhalation. This produces an isolated late-phase asthmatic reaction which has a similar time-course of onset and resolution to that produced with whole allergen. They are termed “isolated” late reactions since there was no early (immediate) asthmatic reaction, presumably because the peptides were too short to cross-link IgE on mast cells and basophils. Our present research suggests that in peptide-induced late reaction there is a cascade of events involving IL-13, neuropeptides and epithelial cells. The contribution of the vasculature and airway wall oedema is also of great current interest.

Early and late-phase skin reaction

Collaborators: Dr Mark Larché, Dr Liam Heaney (Belfast), Dr Trevor Hansel, Professor Tak Lee (KGT), Dr Stuart Hirst (KGT), Dr Sun Ying (KGT), Dr Mina Gaga (Athens), Dr Yee-Ean Ong (St George's Hospital)

T cell peptide allergy vaccine

When allergen-derived peptides are given repeatedly via the intradermal route this induces a state of “tolerance” or “anergy”. Professor (Emeritus) Kay and Dr Mark Larché have exploited this as a novel therapy for allergic disease. The approach, which is termed Peptide Antigen Desensitisation ("PAD") involves the selection of Major Histocompatibilty Complex class II (MHC II)-matched short synthetic peptide therapeutics for potential treatment of a range of high prevalence allergic diseases.

An Imperial College spin-out company (Circassia Limited) has been established with the aim of developing this platform technology to a wide range of allergens.

Collaborators: Dr Mark Larché, Dr Adrienne Verhoef