Recombinant allergens for diagnosis and therapy of allergic disease

Mutational analysis of the IgE epitopes in the latex allergen Hev b 5

BACKGROUND

Hev b 5 is a major latex allergen and potential candidate for an immunotherapy reagent.

OBJECTIVE

The purpose of this study was to produce a hypoallergenic form of Hev b 5.

METHODS

We used SPOTs analysis with alanine substitution to identify amino acids (AAs) critical for IgE binding and used site-directed mutagenesis to produce recombinant proteins with altered IgE-binding activity.

RESULTS

Eleven epitopes were identified (5.1-5.11) in Hev b 5. Individual patients demonstrated variable epitope recognition, with the most intense reactivity to epitopes 5.4 and 5.7. IgE inhibition assays with synthetic peptides indicated that mutating a single epitope would not reduce IgE binding, but rather a combination of epitopes was required. After alanine substitutions to identify the important AAs, site-directed mutagenesis was used to replace the crucial AAs with alanine. Twenty clones with different combinations of altered epitopes were evaluated by means of IgE inhibition assays. Clones with mutations in single epitopes failed to reduce IgE binding, but changes to 8 epitopes (14 AAs) resulted in a 4500-fold reduction in IgE binding. Epitopes 5.7 and 5.9 were found to be cross-reactive, making Hev b 5 a multivalent allergen.

CONCLUSIONS

We produced a recombinant Hev b 5 protein with significantly reduced IgE-binding activity. Changing a minimum of 3 immunodominant epitopes was required to cause a 100-fold reduction in IgE binding. Changes in 8 epitopes, particularly the cross-reactive epitopes 5.7 and 5.9, were needed to maximize the reduction in IgE binding. Mutants with reduced IgE-binding activity may prove to be valuable reagents for immunotherapy.

The role and remediation of animal allergens in allergic diseases

Animal allergens are common causes of both acute and chronic allergic disease. The most important animal allergens are derived from mammals, principally cats, dogs, rats, mice, horses, and cows, which secrete or excrete allergens into the environment. Allergic sensitization may occur at home or in the workplace. Cat and dog allergens commonly cause allergies in the home and affect the general population. Laboratory animal handlers often have allergic reactions to rats and mice. Cow dander allergy is usually caused by occupational exposure and occurs in farmers and farm workers. Horse allergy occurs among people who regularly handle horses, either professionally or for recreational purposes. Over the past 20 years, the major animal allergens have been defined and characterized with regard to their molecular structure, immunogenicity, and environmental distribution. One remarkable finding has been the fact that most of the mammalian allergens that have thus far been cloned belong to a single family of proteins called the lipocalins. In addition to these molecular similarities, it has also been shown that most of the animal allergens are quite similar with regard to their aerodynamic properties. Although much is yet to be learned, progress is being made in our knowledge regarding the steps that may be necessary to control exposure to these allergens through environmental modifications in both homes and occupational settings. These measures include source control, air filtration devices, barrier devices, removal of carpeting and other reservoirs, and, in some cases, washing of the animal.

Novel drugs for treating asthma

The health burden of asthma is increasing globally at an alarming rate, providing a strong impetus for the development of new therapeutics, particularly drugs that may prevent development of the disease. Currently available inhaled bronchodilators and anti-inflammatory drugs are effective in most asthmatic patients, but this palliative therapy requires long-term daily administration. Despite considerable efforts by the pharmaceutical industry, it has been difficult to develop novel therapeutic agents, the leukotriene antagonists being the only new class of asthma treatments to be licensed in the past 30 years. It is clearly important to understand more about the underlying mechanisms of asthma and about how currently used drugs work before rational improvements in therapy can be expected. There are numerous therapies in clinical development that combat the inflammation found in asthma, specifically targeting eosinophils, IgE, adhesion molecules, cytokines (interleukin-4, -5, -13) and chemokines, inflammatory mediators, and cell signaling (kinase inhibitors). In particular, there is the obvious need for new therapy for severe asthma that is poorly controlled by high-dose corticosteroids as well as agents to counter acute emergency asthma. A long-term goal is to develop disease-modifying immunotherapy that could be introduced in childhood to alter the natural history of asthma. Thanks to the extensive efforts of the pharmaceutical industry, we can expect the introduction of a range of novel therapies for asthma in the near future.

Cockroach allergens and asthma

Asthma and allergy are the most common diseases associated with cockroach infestation of houses in the United States and other parts of the world. Sensitization and exposure to cockroach allergens is associated with increased asthma morbidity in the United States, especially among lower socioeconomic groups, including African American and Hispanic populations. Exposure to cockroach allergens in the first 3 months of life has been associated with repeated wheezing and asthma. The principal domestic cockroach species are Blattella germanica and Periplaneta americana. Both species produce several potent allergens, including Bla g 2 (inactive aspartic proteinase), Bla g 4 (calycin), Bla g 5 (glutathione-S-transferase), the group 1 cross-reactive allergens Bla g 1 and Per a 1, and tropomyosin. Structural homology between tropomyosins from cockroaches, mites, and shrimp may explain clinical cases of the oral allergy syndrome. The 3-dimensional structures of several cockroach allergens are known, and biologically active recombinant allergens have been produced in high-level expression vectors. The use of recombinant cockroach allergens should allow mechanisms of cockroach-induced asthma to be investigated and may lead to the development of new approaches to asthma treatment. Environmental allergen measurements of Bla g 1 and Bla g 2 have allowed exposure levels that cause allergic sensitization to be established. Abatement studies have shown that a sustained decrease in cockroach allergen levels is difficult but can be accomplished by professional application of insecticides, together with rigorous household cleaning. Cockroach asthma is an important public health problem that affects patients who are the least likely to be compliant with treatment with asthma medications or environmental control. Patient education, improvements in the housing stock, and improvements in environmental and immunologic treatment strategies are likely to be the most successful approaches to reduce the prevalence of cockroach-induced asthma.

The role of cockroach allergens in asthma

Cockroach allergy has been recognized as an important cause of asthma. Cockroach asthma has been described as a more severe disease, associated with perennial symptoms and high levels of total IgE. Cockroaches produce several allergens that induce sensitization, and exposure to high levels of cockroach allergens in the home is a major risk factor for symptoms in sensitized individuals. Previously identified allergens from Blattella germanica and Periplaneta americana, the most important domiciliary species, include Bla g 2 (inactive aspartic protease), Bla g 4 (calycin), Bla g 5 (glutathione-S-transferase), Bla g 6 (troponin), the Group 1 cross-reactive allergens Bla g 1 and Per a 1, Per a 3 (arylphorin), and Per a 7 (tropomyosin). Strategies for decreasing environmental exposure to cockroach have been recently investigated. The results suggest that a sustained decrease in cockroach allergen levels is difficult to accomplish, even after successful extermination of cockroach populations. Cockroach allergens have been cloned and produced as recombinant proteins in high-level expression vectors. The use of recombinant cockroach allergens should allow mechanisms of cockroach-induced asthma to be investigated and may lead to the development of new approaches to asthma treatment in the future.