Judith A. Woodfolk

Sensitisation, asthma, and a modified Th2 response in children exposed to cat allergen: a population-based cross-sectional study

BACKGROUND Although asthma is strongly associated with immediate hypersensitivity to indoor allergens, several studies have suggested that a cat in the house can decrease the risk of asthma. We investigated the immune response to cat and mite allergens, and asthma among children with a wide range of allergen exposure. METHODS We did a population-based cross-sectional study of children (aged 12-14 years), some of whom had symptoms of asthma and bronchial hyper-reactivity. Antibodies to mite (Der f 1) and cat (Fel d 1) allergens measured by isotype (IgG and IgG4) specific radioimmunoprecipitation assays were compared with sensitisation and allergen concentrations in house dust. FINDINGS 226 children were recruited, 47 of whom had symptoms of asthma and bronchial hyper-reactivity. Increasing exposure to mite was associated with increased prevalence of sensitisation and IgG antibody to Der f 1. By contrast, the highest exposure to cat was associated with decreased sensitisation, but a higher prevalence of IgG antibody to Fel d 1. Thus, among children with high exposure, the odds of sensitisation to mite rather than cat was 4.0 (99% CI 1.49-10.00). Furthermore, 31 of 76 children with 23 microg Fel d 1 at home, who were not sensitised to cat allergen had >125 units of IgG antibody to Fel d 1. Antibodies to Fel d 1 of the IgG4 isotype were strongly correlated with IgG antibody in both allergic and non-allergic children (r=0.84 and r=0.66, respectively). Sensitisation to mite or cat allergens was the strongest independent risk factor for asthma (p<0.001). INTERPRETATION Exposure to cat allergen can produce an IgG and IgG4 antibody response without sensitisation or risk of asthma. This modified T-helper-2 cell response should be regarded as a form of tolerance and may be the correct objective of immunotherapy. The results may also explain the observation that animals in the house can decrease the risk of asthma.

Delayed anaphylaxis, angioedema, or urticaria after consumption of red meat in patients with IgE antibodies specific for galactose-α-1,3-galactose

BACKGROUND Carbohydrate moieties are frequently encountered in food and can elicit IgE responses, the clinical significance of which has been unclear. Recent work, however, has shown that IgE antibodies to galactose-alpha-1,3-galactose (alpha-gal), a carbohydrate commonly expressed on nonprimate mammalian proteins, are capable of eliciting serious, even fatal, reactions. OBJECTIVE We sought to determine whether IgE antibodies to alpha-gal are present in sera from patients who report anaphylaxis or urticaria after eating beef, pork, or lamb. METHODS Detailed histories were taken from patients presenting to the University of Virginia Allergy Clinic. Skin prick tests (SPTs), intradermal skin tests, and serum IgE antibody analysis were performed for common indoor, outdoor, and food allergens. RESULTS Twenty-four patients with IgE antibodies to alpha-gal were identified. These patients described a similar history of anaphylaxis or urticaria 3 to 6 hours after the ingestion of meat and reported fewer or no episodes when following an avoidance diet. SPTs to mammalian meat produced wheals of usually less than 4 mm, whereas intradermal or fresh-food SPTs provided larger and more consistent wheal responses. CAP-RAST testing revealed specific IgE antibodies to beef, pork, lamb, cows milk, cat, and dog but not turkey, chicken, or fish. Absorption experiments indicated that this pattern of sensitivity was explained by an IgE antibody specific for alpha-gal. CONCLUSION We report a novel and severe food allergy related to IgE antibodies to the carbohydrate epitope alpha-gal. These patients experience delayed symptoms of anaphylaxis, angioedema, or urticaria associated with eating beef, pork, or lamb.

Is the hygiene hypothesis still a viable explanation for the increased prevalence of asthma

The hygiene hypothesis states that a reduced exposure to allergens in early life is solely implicated in the growing propensity for allergy sensitization. Important elements of the hypothesis include helminth infection, exposure to endotoxins, exposure to pets and growing up on a farm. However, the hygiene hypothesis alone does not provide an adequate explanation for the observed increase in allergic disease. For example, in North American inner cities, asthma is increasing among children who live in very poor housing, which might be assumed to be somewhat dirty. In order to explain the increase in asthma, we need to take a broader view and also consider alterations related to the adoption of a western lifestyle. It has been suggested that lifestyle changes related to obesity (e.g. a change in diet) are associated with asthma. Other changes include a progressive decrease in physical activity. This lifestyle factor seems to correlate best with the recent increase in asthma. Clearly, the link between physical activity and asthma needs to be investigated in more detail.

A role for IL-10-mediated HLA-DR7-restricted T cell-dependent events in development of the modified Th2 response to cat allergen.

Although high dose exposure to inhaled cat allergen (Fel d 1) can cause a form of tolerance (modified Th2 response), the T cell mechanism for this phenomenon has not been studied. T cell responses to Fel d 1 were characterized in both allergic (IgEpos) and modified Th2 (IgEnegIgGpos) responders as well as serum Ab-negative controls (IgEnegIgGneg). Fel d 1 stimulated high levels of IL-10 in PBMC cultures from all individuals, with evidence of Th2 and Th1 cytokine skewing in allergic and control subjects, respectively. Using overlapping peptides, epitopes at the N terminus of Fel d 1 chain 2 were shown to stimulate strong T cell proliferation and to preferentially induce IL-10 (peptide 2:1 (P2:1)) or IFN-γ (P2:2) regardless of the allergic status of the donor. Injection of cat extract during conventional immunotherapy stimulated expansion of IL-10- and IFN-γ-producing chain 2 epitope-specific T cells along with increased Fel d 1-specific serum IgG and IgG4 Ab. Six of 12 modified responders expressed the major HLA-DRB1 allele, *0701, and both P2:1 and P2:2 were predicted ligands for this allele. Cultures from DR7-positive modified responders produced the highest levels of IL-10 to P2:1 in addition to other major and minor epitopes within chains 1 and 2. In the presence of anti-IL-10 mAb, both T cell proliferation and IFN-γ production were enhanced in a Fel d 1- and epitope-specific manner. We conclude that IL-10-producing T cells specific for chain 2 epitopes are relevant to tolerance induction, and that DR7-restricted recognition of these epitopes favors a modified Th2 response.

Allergy and Dermatophytes

SUMMARY Tinea pedis (athletes foot) and onychomycosis (infection of the toenails) caused by the dermatophyte fungus Trichophyton are highly prevalent in adults. Several Trichophyton allergens have been identified based on elicitation of immunoglobulin E antibody-mediated immediate-hypersensitivity (IH) responses. Evidence of an etiologic role for Trichophyton in asthma in some subjects with IH and chronic dermatophytosis is provided by bronchial reactivity to Trichophyton. Improvement of asthma after systemic antifungal treatment corroborates this link. A unique feature of Trichophyton allergens is the ability of the same antigen to elicit delayed-type hypersensitivity (DTH) in individuals who lack IH reactivity. Delayed responses appear to confer protection, while IH responses do not, based on the association with acute versus chronic skin infection. The amino acid sequence identity of Trichophyton allergens with diverse enzyme families supports a dual role for these proteins in fungal pathogenesis and allergic disease. Characterizing the immunologic properties of Trichophyton allergens and defining immune mechanisms which drive dichotomous responses are pivotal to understanding the dermatophyte-allergy relationship. Recent studies have identified DTH-associated major T-cell epitopes which could facilitate the development of peptide vaccines. Characterization of additional molecular targets by using new techniques may aid not only in the eradication of infection but also in the resolution of allergic symptoms.

Evaluation of different techniques for washing cats: quantitation of allergen removed from the cat and the effect on airborne Fel d 1.

BACKGROUND AND OBJECTIVE The purpose of this study was to examine the quantity and distribution of the major cat allergen, Fel d 1, on cats and to evaluate the efficacy of washing, both in removing allergen from the cat and reducing airborne allergen levels. METHODS Airborne samples were collected on four glass fiber filters in a 30 m3 room, before and 3 hours after serial washing of eight cats (45-minute sampling at 18 L/min for each filter). Aliquots of hair and bath water were also collected and assayed for Fel d 1 content. RESULTS Extracting cat hair with tap water or pet shampoo for 3 minutes removed mean levels of 191 and 245 microg of Fel d 1 per gram of hair, respectively; the quantity of allergen on samples of cat hair ranged from 1 microg/gm to more than 1770 microg/gm. The highest concentration of allergen was found on hair from the neck. Estimates of the total Fel d 1 on the cat, based on shaving the whole cat, ranged from 3 to 142 mg (mean = 67 mg). Washing cats reduced airborne allergen 3 hours later. Washing three cats at weekly intervals for 5 weeks in a veterinarians office produced a mean decrease of 44% in airborne Fel d 1 (n = 15, p < 0.02). Washing three cats by immersion for 3 minutes at weekly intervals for a 1-month period produced a mean decrease in airborne allergen of 79% (n = 12, p < 0.001). However, after repeated washing, the airborne levels before the next wash were not consistently decreased. The quantity of Fel d 1 removed by immersion varied from 1 to 35 mg. CONCLUSION Cats carry large quantities of Fel d 1, only a small proportion of which (approximately 0.002%/hr) becomes airborne. Washing cats by immersion will remove significant allergen from the cat and can reduce the quantity of Fel d 1 becoming airborne. However, the decrease is not maintained at 1 week.

Allergens and their role in the allergic immune response

Summary:  Allergens are recognized as the proteins that induce immunoglobulin E (IgE) responses in humans. The proteins come from a range of sources and, not surprisingly, have many different biological functions. However, the delivery of allergens to the nose is exclusively on particles, which carry a range of molecules in addition to the protein allergens. These molecules include pathogen‐associated molecular patterns (PAMPs) that can alter the response. Although the response to allergens is characterized by IgE antibodies, it also includes other isotypes (IgG, IgA, and IgG4), as well as T cells. The challenge is to identify the characteristics of these exposures that favor the production of this form of response. The primary features of the exposure appear to be the delivery in particles, such as pollen grains or mite feces, containing both proteins and PAMPs, but with overall low dose. Within this model, there is a simple direct relationship between the dose of exposure to mite or grass pollen and the prevalence of IgE responses. By contrast, the highest levels of exposure to cat allergen are associated with a lower prevalence of IgE responses. Although the detailed mechanisms for this phenomenon are not clear, it appears that enhanced production of interleukin‐10 in response to specific Fel d 1 peptides could influence the response. However, it is striking that the animal sources that are most clearly associated with decreased responses at high allergen dose are derived from animals from which humans evolved more recently (∼65 million years ago). Although the nose is still recognized as the primary route for sensitization to inhalant allergens, there is increasing evidence that the skin is also an important site for the generation of IgE antibody responses. By contrast, it is now evident that delivery of foreign proteins by the oral route or sublingually will favor the generation of tolerance.

Trichophyton Antigens Associated with IgE Antibodies and Delayed Type Hypersensitivity SEQUENCE HOMOLOGY TO TWO FAMILIES OF SERINE PROTEINASES

The dermatophyte fungus Trichophytonexhibits unique immunologic properties by its ability to cause both immediate and delayed type hypersensitivity. An 83-kDaTrichophyton tonsurans allergen (Tri t 4) was previously shown to elicit distinct T lymphocyte cytokine profiles in vitro. The homologous protein, Tri r 4, was cloned from aTrichophyton rubrum cDNA library, and the recombinant protein was expressed in Pichia pastoris. This 726-amino acid protein contained an arrangement of catalytic triad residues characteristic of the prolyl oligopeptidase family of serine proteinases (Ser-Asp-His). In addition, a novelTrichophyton allergen, encoding 412 amino acids, was identified by its human IgE antibody-binding activity. Sequence similarity searches showed that this allergen, designated Tri r 2, contained all of the conserved residues characteristic of the class D subtilase subfamily (41–58% overall sequence identity). Forty-two percent of subjects with immediate hypersensitivity skin test reactions to a Trichophyton extract exhibited IgE antibody binding to a recombinant glutathione S-transferase fusion protein containing the carboxyl-terminal 289 amino acids of Tri r 2. Furthermore, this antigen was capable of inducing delayed type hypersensitivity skin test reactions. Our results define two distinct antigens derived from the dermatophyte Trichophyton that serve as targets for diverse immune responses in humans.

Chemical treatment of carpets to reduce allergen: A detailed study of the effects of tannic acid on indoor allergens

Tannic acid (TA), a protein-denaturing agent, has been reported to reduce allergen levels in house dust and is marketed for that purpose as 1% and 3% solutions. We investigated the effects of TA on dust allergens by using monoclonal antibody-based ELISAs for mite (Der p I, Der f I, and group II) and cat (Fel d I) allergens. Initial studies confirmed that TA reduced allergen levels in carpet dust. However, when dust samples from treated carpets are extracted in saline solution, residual TA redissolves and may interfere with the assessment of allergens. In the laboratory, concentrations of TA as low as 0.1% inhibited the assays, but this effect may be prevented by addition of 5% bovine serum albumin (BSA). After treatment of dust samples in the laboratory with 3% TA, the apparent reductions in Der p I and Der f I levels were 89% and 96%, respectively, but when the samples were extracted in 5% BSA the reductions were 74% and 92%. Similar effects were seen with dust samples from carpets treated with TA. In an extreme case in which a carpet had been repeatedly treated with TA, the apparent concentration of Der p I was < 0.05 microgram/gm without BSA and 2.1 and 8.4 microgram/gm when extracted in the presence of 1% and 5% BSA, respectively. Our testing of the ability of TA to denature Fel d I demonstrated an 80% reduction in allergen, but only in samples with an initial concentration of less than 200 micrograms Fel d I/gm dust.(ABSTRACT TRUNCATED AT 250 WORDS)

Environmental exposure to Aspergillus fumigatus allergen (Asp f I)

Asp f I is a major allergen produced by the mycelia of Aspergillus fumigatus. It is not present in spores and can be used as a specific marker for the detection of germination of this fungus. We investigated the domestic and outdoor concentration of Asp f I in Poole, U.K. and Charlottesville, VA, U.S.A. Asp f I was undetectable in 95% (281/296) of house dust extracts and present at low levels (< 0.17 μg/g of sieved dust, mean 0.038 μg/g) in the remainder. In contrast, Asp f I could be detected in 65% (15/23) of cultures of house dust, suggesting the presence of viable, but ungerminated, A. fumigatus in the majority of homes. Asp f I was detectable in 80% (28/35) of extracts of leaves and compost, but present in these outdoor samples at low levels (<0.11 μg/g, mean 0.27 μg/g). Air sampling for Asp f I was undertaken before and after vigorous disturbances at indoor (n= 5) and outdoor (n= 6) sites. Airborne Asp f I was not detected in domestic samples or in undisturbed outdoor samples. Following disturbance it could be measured in outdoor samples (range 7.6–29 ng/m3). The results suggest that while exposure to A. fumigatus is common, exposure to Asp f I and germinating A. fumigatus is uncommon. It is probable that those individuals who develop antibody responses to Asp f I have been exposed to A. fumigatus which has germinated in their respiratory tract.