High prevalence of sensitization to cat allergen among Japanese children with asthma, living without cats

BACKGROUND: Cat allergy is common among children with asthma. Many cat-allergic patients in Japan and elsewhere do not keep cats, but nonetheless become sensitized through environmental exposure to cat allergen. OBJECTIVE: To assess the frequency of cat allergy and cat-specific immunoglobulin E (IgE) and immunoglobulin G (IgG) antibody responses in young Japanese patients with asthma in relation to self-reported cat exposure and Fel d 1 levels in dust samples. METHODS: Cat dander-specific IgE antibody was measured in sera from asthma patients using the CAP system. IgE and IgG antibody to Fel d 1 was measured by antigen binding radioimmunoassay and by chimeric enzyme immunoassay. Fel d 1 levels in dust samples from a subset of patients' homes were measured by monoclonal antibody-based enzyme immunoassay. RESULTS: Cat-specific IgE (CAP class>/=2) was found in sera from 70% of 44 patients who kept cats and 34% of 394 patients who had never kept cats. The prevalence of sensitization increased progressively to age 6 years (40%: positive), and then increased gradually to age 16 years (approximately 60%: positive) in patients who had never kept cats. There was an excellent correlation between cat CAP values and IgE levels to Fel d 1. The absolute amount of IgE antibody to Fel d 1 ranged from 0.01 to 15.6% of total IgE. Most patients who did not keep cats were exposed to Fel d 1 levels ranging from 0.07-8 microg/g dust. CONCLUSIONS: Sensitization to cat allergen is common among young asthmatic patients in Japan, even among patients who do not keep cats. Use of CAP and the chimeric enzyme-linked immunosorbent assay allows accurate diagnosis of cat allergy and quantification of specific IgE antibody levels.     

Allergens of mammalian origin. V.

Eight commercial cat dander extracts and two pelt extracts derived from mongrel and Siamese cats were compared. Cat allergen 1 and cat albumin were measured by radial immunodiffusion. Allergenic activity was evaluated by prick test and a modified radioallergosorbent test. In the latter, the dilution of each extract that produced 50% inhibition of binding of IgE antibodies to insolubilized cat allergen 1 (RAST 1) and insolubilized cat serum (RAST 2) was determined. The total non-dialysable solid content of the extracts did not correlate with any other parameter. Cat allergen 1 content determined by radial immunodiffusion correlated with average prick test results in ten cat-sensitive subjects and with RAST 1 activity. Cat albumin content correlated weakly with RAST 2 activity but not with any other measure of allergenic activity. Absorption of each extract with the γ-globulin fraction of rabbit antiserum to cat allergen 1 significantly reduced prick test reactivity and RAST 1 activity, but not RAST 2 activity. These results indicate that cat allergen 1 is an important allergen in cat dander extracts and its measurement may be used to standardize the allergenic activity of such extracts.     

Fel d 4, a cat lipocalin allergen

BACKGROUND: Cat allergy is unique among allergy to mammals in that the major allergen Fel d 1 is a uteroglobin-like protein and not a lipocalin. The biochemical spectrum of the cat allergens is thus uncertain, particularly with regard to the role that a cat lipocalin protein may play in sensitization to cats in allergic individuals. OBJECTIVE: To analyse cDNA encoding a lipocalin allergen and the corresponding recombinant allergen at both the molecular and immunological levels. METHODS: A submandibular salivary gland cDNA expression library was constructed and screened for clones producing IgE-binding polypeptides. cDNA encoding a lipocalin allergen and its corresponding recombinant allergen were analysed. RESULTS: An IgE binding molecule with high sequence identity to the boar salivary lipocalin and the horse lipocalin Equ c 1 allergen was isolated and designated, Fel d 4. Serum from 62.96% of cat-allergic subjects examined had measurable IgE antibody to Fel d 4 but typically at low levels. Despite this in 47% of sera the anti-Fel d 4 IgE titres were higher than the anti-Fel d 1 titres. IgE binding to the lipocalin allergen could be blocked by an allergen extract from cow and to a lesser degree by extracts from horse and dog. CONCLUSION: Fel d 4 is a lipocalin allergen produced by the cat, which binds IgE at relatively high frequency in cat-sensitive individuals. The allergen provides not only a means for investigating differences in the immune response to lipocalin allergens from that found for other mammalian species but also an important reagent for the diagnosis of cat allergy.     

Carrot allergy: double-blinded, placebo-controlled food challenge and identification of allergens

BACKGROUND: Allergic reactions to carrot affect up to 25% of food-allergic subjects. Clinical manifestations of carrot allergy and IgE responses to carrot proteins, however, have never been studied in subjects with carrot allergy confirmed by means of double-blinded, placebo-controlled food challenge (DBPCFC). OBJECTIVE: The purposes of this investigation were to confirm clinically relevant sensitizations to carrot by means of DBPCFC, to validate current diagnostic methods, and to identify IgE-reactive carrot proteins in patients with true allergy. METHODS: DBPCFCs were performed in 26 subjects with histories of allergic reactions to carrot. Patients underwent skin prick tests with carrot extract, fresh carrot, and various pollen extracts. Specific IgE to carrot, celery, birch, and mugwort pollen and to rBet v 1, rBet v 2, and rBet v 6 were measured through use of the CAP method. Carrot allergens were identified by means of immunoblotting and blotting inhibition. RESULTS: Twenty of 26 patients had positive DBPCFC results. The sensitivity of the determination of carrot-specific IgE antibodies through use of the CAP method (> or =0.7 kU/L) was 90%, the sensitivity for skin prick testing with commercial extracts was 26%, and the sensitivity for prick-to-prick tests with raw carrot was 100%. The Bet v 1--related major carrot allergen Dau c 1 was recognized by IgE from 85% of patients; 45% were sensitized to cross-reactive carbohydrate determinants and 20% to carrot profilin. In 1 subject, a Bet v 6--related carrot allergen was recognized. In 4 patients, IgE binding to Dau c 1 was not inhibited or was weakly inhibited by rBet v 1 or birch pollen extract. CONCLUSION: This study confirmed the allergenicity of carrot by means of DBPCFC. DBPCFC-positive patients had exclusively specific IgE antibodies to birch pollen--related carrot allergens, Dau c 1 being the major allergen. The lack of inhibition of IgE binding to Dau c 1 by birch allergens in a subgroup of patients might indicate an secondary immune response to new epitopes on the food allergen that are not cross-reactive with Bet v 1.     

Etiologic role of unapparent exposure in cat allergy

To determine the importance of unnoticed exposure to cat, we studied 20 patients with a history of respiratory allergy. All the patients had a positive prick test to cat dander extract, and none of them kept cats as pets. The prick test was carried out with a dander extract from cat at a concentration of 100 BU/ml. The specific IgE was determined by the commercially available Pharmacia CAP System. We carried out a conjunctival challenge test. The concentration of Fel d I was quantified in dust samples from the patients' homes by a commercially available method. The patients were reassessed in order to establish a relation between exposure and symptoms, and concealed allergen sources. Sixteen patients, showed significant levels of Fel d I in their homes (mean of 3.35 μg g of dust). The conjunctival challenge test was positive in 15 patients. These patients showed an exposure mean of 0.4 μg/g of dust. The mean levels of specific serum IgE were higher in those patients with a positive challenge than in those with a negative challenge ( P = 0.0145). In nine reassessed patients, a relation was established between natural exposure and the onset of the symptoms. A possible hidden allergen source was established in 11 patients. Hidden exposure to cat allergen may play a role in the symptomatology of many atopic patients, and investigation of sensitization to Fel d I should be included in the routine allergologic evaluation of all patients with asthma or perennial rhinitis.     

Detection of specific IgE antibodies towards cat flea (Ctenocephalides felis felis) in patients with suspected cat allergy

Cat flea sensitivity is considered one of the most important skin diseases in cats and dogs. Cat fleas, however, are also a growing allergen problem for humans. Cat flea-specific IgE antibodies were studied in serum samples from 70 patients with suspected cat allergy, using RAST-based techniques and the nitrocellulose immunoblotting method. Results from RAST studies, using cat and cat flea as allergosorbents, showed that 46% of the patients were RAST positive against both cat and cat flea. 9% of the patients were RAST positive only against the cat flea. The nitrocellulose immunoblotting experiments were in agreement with the RAST results showing specific IgE to cat flea. The results indicate that some cat-allergic patients have specific IgE both towards cat and cat flea but also that some of the patients with suspected cat allergy might have specific IgE towards the cat flea and not the cat. RAST-inhibition and immunoblotting experiments also indicate that the allergen composition of cat flea extract differs from that of cat extract, even if common allergens have been detected, leading to cross-reactivity in some sera.     

Egg allergy, influenza vaccine, and immunoglobulin E antibody.

In a study of 70 patients with asthma, rhinitis, and eczema, those giving a definite history of allergic reactions to egg more frequently showed positive skin tests to egg extracts (p = less than 0.003), the wheal diameters of which were significantly larger (p = less than 0.01) than in patients with only a possible or no such history. Patients with a definite history of egg allergy had significantly higher levels of specific IgE antibody against egg yolk, egg white, and allantoic fluid than patients in the other two groups (p = less than 0.005). Seven patients, all of whom had given a definite history of allergy to egg, were found to have positive skin prick tests to influenza vaccine, at the concentration used in medical practice. Two of these patients had previously been given influenza vaccine and both had developed adverse reactions. Of the 22 patients giving a definite history of allergy to egg, the 7 (35 per cent) with positive skin tests to influenza vaccine had significantly larger skin tests and higher levels of specific IgE antibody to the egg extracts than the group as a whole (p = less than 0.001). Allergic reactions to influenza vaccine are likely to occur in patients who have a definite history of allergy to egg and large skin prick test reactions or high levels of specific IgE antibody to egg extracts. Those at risk can best be identified by skin prick testing with egg extracts and undiluted influenza vaccine.     

Skin reactivity and specific IgE antibody to two nonbiting midges in Korean respiratory allergy patients.

To evaluate the significance of chironomid as a respiratory allergen, we performed skin prick tests with Chironomus plumosus (CP) and Tokunagayusurika akamusi (TA) extracts on 475 respiratory allergy patients, and their specific IgE antibodies were detected by enzyme-linked immunosorbent assay (ELISA) in 106 positive reactors to skin prick test and 30 negative controls. Ninety-seven (20.4%) showed more than 2+ of allergen to histamine ratio to CP and 98 (20.6%) to TA on skin prick test. Seventy-one (73.2%) of 97 positive reactors had increased specific IgE to CP, and 34 (34.7%) of 98 positive reactors, to TA. CP-specific IgE was detected in 14 (14.4%) non-atopic asthmatics and 6 (6.2%) non-allergic rhinitis patients. TA-specific IgE was detected in 17 (17.4%) non-atopic asthmatics and 6 (6.1%) non-allergic rhinitis patients. No association was noted between skin reactivity to Dermatophagoides farinae and the prevalence of specific IgE to CP or TA (p > 0.05). The correlation between total IgE level and specific IgE level to CP and TA was poor (r = 0.07, 0.04). ELISA inhibition test suggested specificity of IgE binding and cross-allergenicity between CP and TA. It is suggested that CP and TA can induce IgE-mediated reaction in exposed patients and should be considered as important causative allergens in respiratory allergy patients in Korea.     

A comparative study of the allergens of cat urine, serum, saliva, and pelt

In direct RAST analyses of sera from 43 individuals with a history of cat allergy, 39.5% were positive to cat pelt, 37.5% to cat saliva, and 12% each to cat urine and serum. The cat pelt and saliva extracts contained allergen 1, but cat serum and cat urine collected by bladder puncture had no detectable levels of this allergen. A crossed immunoelectrophoresis/crossed radioimmunoelectrophoresis analysis failed to reveal any allergen in urine or serum that was not also present in the saliva or pelt preparations, although urine had two allergens not present in serum. When serum from a patient who was direct RAST positive to cat pelt, serum, saliva, and urine was tested by crossed radioimmunoelectrophoresis, it was determined that a total of six allergens were detectable in cat pelt, three in cat urine, and six in cat serum. Since cat serum contains no detectable cat allergen 1, it may be concluded that at least seven allergens derived from the cat are capable of binding to IgE antibody in humans.     

Antibody profiles and self-reported symptoms to pollen-related food allergens in grass pollen-allergic patients from northern Europe

BACKGROUND: Most studies on pollen-related food allergy have so far focused on the association of birch/weed pollen allergens and plant food allergy. The aim of this study was to elucidate the allergen spectrum among a group of grass pollen-allergic patients from northern Europe and to relate the results to clinical histories of pollen-related food allergy. METHODS: Fifty-eight grass pollen-allergic patients answered a questionnaire regarding allergy to foods. Blood samples were taken to test IgE-reactivity to a large panel of pollen allergens and pollen- and nonpollen-related food allergens using crude allergen extracts and recombinant and native allergens. RESULTS: Three different groups of grass pollen-allergic patients were identified according to their IgE antibody profile: a grass pollen group only (19%), a grass and tree pollen group (29%) and a grass, tree and compositae (pan-) pollen group (48%). No sensitization to Bet v 1 as well as almost no IgE to plant food was observed in the grass pollen group. In contrast, nearly all patients in the two tree-related groups had IgE to Bet v 1, which reflected the high frequency of adverse reactions to typical birch-related food in these groups. Only four patients belonging to the pan-pollen group displayed IgE to profilin Phl p 12/Bet v 2. Patients in the pan-pollen group reported significantly more symptoms to food allergens compared with patients in the two other groups. The most frequently reported symptom was the oral allergy syndrome. CONCLUSIONS: Sensitization to grass pollen alone is rare among grass pollen-allergic patients from northern Europe. The majority of patients are in addition sensitized to birch (Bet v 1), which seems to be closely related to their pollen-derived food allergy. The study highlights the advantage of using well-defined allergen molecules for the diagnosis of cross-reactivity between pollen and food allergens.     

The safety and efficacy of ALLERVAX CAT in cat allergic patients

Conventional immunotherapy for cat allergy is effective in reducing cat allergy symptoms in many patients, but this type of immunotherapy can cause severe reactions, including anaphylaxis, and often requires years of injections for successful desensitization. To improve the efficacy of immunotherapy for cat allergic patients, synthetic cat allergen peptides (ALLERVAX CAT) were generated, based on analysis of the immunodominant T cell epitopes of cat allergen. These peptides lack the tertiary structure of native Fel d1 and possess a significantly reduced capacity to bind to Fel d1-specific IgE. Using these peptides, we performed a multicenter, randomized, double-blind, placebo-controlled study of 133 cat allergic patients chronically exposed to cats or who had failed previous conventional cat immunotherapy. We evaluated the safety of ALLERVAX CAT treatment and determined whether ALLERVAX CAT treatment improved tolerance to cat allergen, as measured by symptom analysis and pulmonary function testing. Three of the ALLERVAX CAT-treated patients required systemic epinephrine for adverse reactions, but the frequency of all adverse reactions in both groups was not statistically different from that of the placebo group. The majority of adverse events were "late" events, most commonly associated with respiratory symptoms, and these events declined with successive injections. ALLERVAX CAT given at a dose of 750 microg/dose improved pulmonary function in patients with reduced baseline FEV1, and global evaluation of the subjects' ability to tolerate cats improved significantly in the actively treated groups relative to placebo. Thus, although therapy with ALLERVAX CAT is associated with some adverse events in patients with severe cat sensitivity, such therapy is an effective approach for the management of cat allergy, since it improves tolerance to cats and improves pulmonary function in cat allergic patients with reduced FEV1.     

The relationship of respiratory allergy, skin test reactivity, and serum IgE in a community population sample.

The relationship between prick and intradermal skin test reactivity and serum levels of total and specific IgE was evaluated in 311 subjects selected from a general population. Test results were related to the historical allergy status of the subjects. Prick test reactivity to 14 common local allergens correlated with the presence of allergy symptoms. Similarly, mean total serum IgE (PRIST) levels were significantly higher (p < 0.02) in allergic (187.9 IU) than in nonallergic subjects (107 IU) and were found to be positively correlated with the degree of prick test reactivity. Conversely, intradermal reactions following a negative prick test for that allergen showed no correlation with either the clinical allergy status or the level of total serum IgE. Bermuda-specific IgE was found to correlate closely with prick reactivity to that allergen as an overall agreement of 89.2% was observed. In contrast, only 2 of 12 positive Bermuda intradermal tests ≥5 mm and none of 38 smaller reactions following a negative prick response were associated with positive RASTs. The results strongly suggest that prick test reactivity correlates with both total and specific IgE and allergic symptomatology, but intradermal reactions in the absence of prick reactivity do not correlate with either clinical or immunologic evidence of allergy.     

High‐dose exposure to cat is associated with clinical tolerance – a modified Th2 immune response?

BACKGROUND: Allergen-specific IgG4 antibodies, it is suggested, may be protecting against allergy development by blocking responses. Levels are proposed as a marker of modified Th2 response. OBJECTIVES: To assess the levels of IgE, IgG1 and IgG4 antibodies to cat in relation to cat exposure, asthma and allergic diseases. METHODS: We studied a population-based sample of 412 schoolchildren of 12-13 years of age. Parents of 402 children completed a questionnaire covering their child's medical history, the keeping of cats and other background data. Skin prick tests (SPTs) to common aeroallergens were performed in 371 of the children. Blood samples for the analyses of IgE, IgG1 and IgG4 antibodies were obtained from 309 of them. RESULTS: All children had an immune response to cat, predominantly of the IgG1 subclass. The levels of cat-specific IgG1 and IgG4, but not IgE, were high in children currently keeping a cat. Children with asthma had increased levels of cat-specific IgE and IgG1, and children with a positive SPT to cat also had increased IgG4. The presence of IgG4 was not associated with asthma or sensitization, unless there was a simultaneous production of IgE. Twenty-five percent of the children had an immune response with only IgG4, and no IgE antibodies to cat. This group of children had the highest frequency of cat-keeping, but a similar prevalence of asthma and allergy as those with neither IgE nor IgG4 antibodies to cat. CONCLUSION: Cat-keeping was associated with a modified Th2 response, producing IgG4 but not IgE antibodies. This immune response was not associated with an increased risk of asthma or allergy. However, the IgG4 antibodies did not directly mediate any protective effect.     

The importance of nasal provocation test in the diagnosis of natural rubber latex allergy

Background:  Most studies regarding natural rubber latex (NRL) allergy have concentrated on the prevalance using skin prick test (SPT) and specific IgE assay. The objective of this study is to examine the target organ (skin, nasal mucosa) responses in patients with positive SPT to NRL using the nasal provacation test (NPT) and glove use test (GUT).
Methods:  Four thousand four hundred and twenty patients presented to our polyclinic between July 2003 and January 2007 were evaluated. One thousand six hundred and ninety-nine patients had positive SPT to one or more allergens (NRL and other inhaler allergens). Twenty-nine patients with positive SPT to NRL comprised the NRL sensitive group (group 1). Thirty-five randomized patients with positive SPT to an inhaler allergen other than NRL and negative NRL-specific IgE comprised atopic control group (group 2). Thirty healthy individuals who had no allergic diseases and had negative SPT and NRL-specific IgE comprised the healthy control group (group 3).
Results:  The lowest NRL allergen concentration leading to NPT positiveness was 0.05 μg/mL. NPT was negative in groups 2 and 3. NPT was found to have a sensitivity of 96%, specificity of 100%, negative predictive value of 98% and positive predictive value of 100%. GUT was found to have a sensitivity of 81%, specificity of 90%, negative predictive value of 75% and positive predictive value of 93%.
Conclusions:  Nasal provocation test was successfully used for the first time in the diagnosis of NRL allergy. NPT is a more sensitive method as compared to GUT.     

Sensitization to cat allergens in non-cat owner patients with respiratory allergy.

BACKGROUND: Cats represent one of the most important sources of indoor allergens. The sensitization rate can reach up to 60% in western countries. Keeping cats indoors is uncommon in big cities in Turkey, but cats living in the streets are common. OBJECTIVE: To investigate the prevalence of sensitization to cats in patients with respiratory allergy from Izmir, Turkey, and its relationship to home cat allergen levels. METHODS: A total of 387 patients (70.8% female; mean age, 34.3 years) with respiratory allergic diseases (rhinitis and/or asthma) were included in this study. Skin prick test to cat was performed. House dust samples were collected from the living room of 25 patients and 14 healthy subjects. The major cat allergen (Fel d 1) levels were measured by Dustscreen. Fel d 1 levels given by the manufacturer were as follows: 0.05, 0.13, 0.40, 1.1, and 6.2 mU/mL. RESULTS: The prevalence of cat sensitivity was 44.7% (n = 173). Only 6 patients (1.6%) had a history of feeding a cat in their houses. Thirty-six (92%) of 39 houses had detectable levels of cat allergen (mean Fel d 1 level, 2.24 +/- 2.69 mU/mL). The mean Fel d 1 levels were 1.58 +/- 2.51 mU/mL in the healthy group, 1.91 +/- 2.61 mU/mL in the asthmatic group, and 3.26 +/- 2.85 mU/mL in the group with allergic rhinitis (P = 0.12). The prevalence of cat sensitivity in patients who had 1.1 mU/mL of Fel d 1 in their homes was 57.1%. This rate was five times lower (11.1%) in patients who had the highest Fel d 1 level (6.2 mU/mL) in their homes. CONCLUSIONS: The prevalence of cat sensitivity in Izmir, where cats are generally not kept within homes, is as high as in western countries. The sampled houses have measurable levels of Fel d 1 even in the absence of indoor cats. High prevalence of cat sensitivity in Izmir is probably due to indirect exposure.     

Possible induction of food allergy during mite immunotherapy

Sera of 17 patients receiving immunotherapy for house-dust mite allergy were tested for IgE antibodies against snail and shrimp. Serum samples were taken at the start of immunotherapy and 14—20 months later. While the average IgE response to mite, Der p 1, and Der p 2 did not alter significantly, the average response to snail showed a significant increase. This included two conversions from negative to strongly positive. These novel IgE antibodies against snail were shown to be cross-reactive with mite. Three patients had a positive RAST for shrimp. For one of them, a strong increase of IgE against shrimp (and snail) was observed. In 2/3 snail/shrimp-positive sera, IgE antibodies against the cross-reactive allergen tropomyosin from mite, snail, and shrimp were demonstrated. A clear IgE response to snail (> 10% binding in a snail RAST) was confirmed by a positive skin prick test (SPT) for 6/10 patients. The two patients with antitropomyosin IgE also had a positive SPT for shrimp, and demonstrated the oral allergy syndrome (OAS) after eating shrimp. The observations in this study indicate that house-dust mite immunotherapy is accompanied by the induction of IgE against foods, including tropomyosin-reactive IgE. Food allergy (OAS) was observed in patients that had IgE antibodies against this cross-reactive allergen. In conclusion, induction of IgE during mite immunotherapy might occasionally cause allergy to foods of invertebrate animal origin.     

Allergens of mammalian origin : IV. Evidence for common allergens in cat and dog serum

IgE antibodies present in serum from 3 patients clinically sensitive to cat and dog were shown to combine with whole cat and dog sera linked to cellulose particles. Employing a modified radioallergosorbent technique (RAST), it was shown that cat and dog sera inhibited the binding of IgE antibodies to insolubilized cat serum and to insolubilized dog serum. These findings suggest that cat and dog sera have common allergens. Other mammalian sera were also tested and found to have little inhibitory activity. Cat and dog sera did not inhibit the binding of IgE antiragweed antibodies to an insolubilized ragweed fraction. Following separation of cat serum by gel filtration on Sephadex G-200 or electrophoresis in acrylamide gel, several fractions were found to inhibit the binding of IgE antibodies to insolubilized cat and dog sera. Whether the heterogeneity observed reflects the presence of single allergens with diverse size and charge properties or multiple allergens remains to be determined.     

Cladosporium herbarum and Pityrosporum ovale allergen extracts share cross-reacting glycoproteins

BACKGROUND: Patients sensitized to airborne fungi such as Alternaria alternata and Cladosporium herbarum often also show positive skin prick test results and specific serum IgE antibodies to a yeast, Pityrosporum ovale. We examined whether part of the IgE binding to these fungi is explained by cross-reacting mould and yeast allergens. METHODS: Serum samples from 36 patients with positive skin prick test to A. alternata or C. herbarum were analyzed for IgE antibodies to fungal extracts by ELISA and immunoblot analysis. Cross-reactivity between mould and yeast extracts was studied by ELISA and immunoblot inhibition assays. In further analysis, the mannan-containing glycoproteins were removed from the yeast extract by concanavalin A-Sepharose chromatography, and the IgE binding properties of the extracts were compared. RESULTS: Serum IgE reactivity to P. ovale was found in 40% of the mould-sensitized patients. The IgE antibody binding to A. alternata and C. herbarum moulds was partially inhibited by the yeast P. ovale in ELISA and immunoblot inhibition assays. When the glycoproteins were removed from the extract, cross-reactivity was markedly reduced. CONCLUSION: Part of the IgE binding to mould and yeast allergen extracts is due to cross-reacting glycoproteins. False-positive IgE and skin prick test results should be taken into account in the diagnosis of mould allergy.     

Allergenicity and cross-reactivity of cat and dog allergenic extracts

This study aims to confirm that cat allergen 1 (CAT-1) is a major allergenic determinant in cat-sensitive patients, and to further define the role of other determinants, as well as to identify the determinants responsible for the cross-reactivity between cat and dog extracts. Firstly, the allergenic determinant with an electrophore-tic mobility of 18 kD (corresponding to CAT-1) is indeed a major allergenic determinant being recognized by the majority (75%) of cat-sensitive subjects. Secondly, the cross-reactivity between the two species was confirmed by RAST inhibition. Cat and dog soluble allergens could inhibit, to variable degrees, the binding of serum IgE from cat- and dog-sensitive patients to insolubilized allergens. Binding of serum IgE from subjects sensitive only to cats was inhibited by cat extracts only. These observations suggest the presence of determinants common to the two sources of extracts, and others specific for each species. These data were confirmed by immunoblot analysis. Indeed, an allergenic determinant of 69 kD was found in both cat and dog extracts. Conversely the allergenic determinants with an electrophoretic mobility of 18 and 32 kD were found only in cat extracts, and those at 22 and 24 kD were dog specific. However, surprisingly, serum IgE antibodies from patients sensitive only to cats reacted on immunoblot differently from those of both cat- and dog-allergic subjects. Indeed, the 18 kD determinant was the only one recognized by serum IgE antibodies from subjects sensitive to cats only, as opposed to the patients allergic to both species: then, the 69 kD determinant was strongly recognized and the 18 kD only slightly recognized. If these observations confirmed that CAT-1 is a major allergen in cat-sensitive subjects, they also showed a different profile of reactivity in patients sensitive to cats only and those sensitive to both cats and dogs, which could have diagnostic and therapeutic implications.     

Molecular cloning, expression and immunological characterisation of Pas n 1, the major allergen of Bahia grass Paspalum notatum pollen

Bahia grass, Paspalum notatum, is a clinically important subtropical grass with a prolonged pollination season from spring to autumn. We aimed to clone and characterise the major Bahia grass pollen allergen, Pas n 1. Grass pollen-allergic patients presenting to a tertiary hospital allergy clinic were tested for IgE reactivity with Bahia grass pollen extract by skin prick testing, ImmunoCAP, ELISA and immunoblotting. Using primers deduced from the N-terminal peptide sequence of a group 1 allergen of Bahia grass pollen extract separated by two-dimensional gel electrophoresis, the complete Pas n 1 cDNA was obtained by rapid amplification of cDNA ends and cloned. Biological relevance of recombinant Pas n 1 expressed in Escherichia coli was assessed by serum IgE reactivity and basophil activation. Twenty-nine of 34 (85%) consecutive patients presenting with grass pollen allergy were skin prick test positive to Bahia grass pollen. The Pas n 1 cDNA has sequence homology with the beta-expansin 1 glycoprotein family and is more closely related to the maize pollen group 1 allergen (85% identity) than to ryegrass Lol p 1 or Timothy grass Phl p 1 (64 and 66% identity, respectively). rPas n 1 reacted with serum IgE in 47 of 55 (85%) Bahia grass pollen-allergic patients, activated basophils and inhibited serum IgE reactivity with the 29 kDa band of Bahia grass pollen extract. In conclusion the cDNA for the major group 1 allergen of the subtropical Bahia grass pollen, Pas n 1, was identified and cloned. rPas n 1 is immunologically active and is a valuable reagent for diagnosis and specific immunotherapy of grass pollen allergy.