Cockroach allergens: function, structure and allergenicity.

Cockroach allergy is a widespread health problem in the world, associated with the development of asthma. The German and American cockroach species are important producers of a wide variety of allergens. Knowledge of their structure and function contributes to understand their role in allergy and to design tools for diagnosis and immunotherapy.

Tissue localization and regulation by juvenile hormone of human allergen Bla g 4 from the German cockroach, Blattella germanica (L.).

The German cockroach, Blattella germanica (L.), produces several potent protein aeroallergens, including Bla g 4, a approximately 20 kDa lipocalin. RT-PCR, Northern analyses and in situ hybridization showed that Bla g 4 is expressed only in the adult male reproductive system. Western blotting and ELISA with rBla g 4 antiserum detected immunoreactivity in the utricles and the conglobate gland, but not in other tissues of the male reproductive system. The Bla g 4 protein content of males increased from adult emergence to day 14, but during copulation Bla g 4 was depleted in the male and transferred to the female within the spermatophore. Topical application of juvenile hormone III stimulated Bla g 4 production by both conglobate gland and utricles.

IgE and IgG antibody responses to recombinant Alt a 1 as a marker of sensitization to Alternaria in asthma and atopic dermatitis.

BACKGROUND: Sensitization to Alternaria alternata is a risk factor for the development of wheezing and asthma. Alt a 1 is the major Alternaria allergen causing sensitization in asthmatics. Some atopic dermatitis (AD) patients have very high immunoglobulin (Ig)E antibody (ab) to Alternaria as analysed by Pharmacia CAP, however, it is not clear whether these are specific responses or whether Alt a 1 is involved in disease symptoms. OBJECTIVE: The aim of this study was to analyse specific IgE and IgG ab responses to recombinant Alt a 1 in asthmatic and AD patients and to compare these results to IgE ab against Alternaria measured by CAP. METHODS: Sera from individuals who were IgE positive to Alternaria by CAP were obtained from 58 patients with asthma/rhinitis, 19 patients with AD, and 20 patients with cystic fibrosis (CF) who were included as specificity controls. IgE and IgG ab to recombinant Alt a 1 were measured by radioimmunoassay (RIA). RESULTS: Of 43 asthma/rhinitis patients having an Alternaria CAP score > 2, a high percentage (93%) had both IgE and IgG ab to Alt a 1, emphasizing its importance as a major allergen. Only, 47% of AD patients with CAP score greater than 2 had ab to Alt a 1, and their levels were low when compared to the asthmatics. For CF controls, 75% of these patients had no IgE ab to Alt a 1, and those which were positive to Alt a 1 by RIA were also positive by CAP. Overall, patients with a low CAP (1-2) had a low prevalence (20-30%) of IgE or IgG ab to Alt a 1. CONCLUSION: IgE and IgG ab to Alt a 1 in asthmatics are good markers for sensitization to Alternaria. Although AD patients gave high Alternaria CAP scores, they had low or undetectable levels of IgE to Alt a 1, suggesting that other Alternaria allergens may be important in AD or that the CAP results are non-specific. Recombinant allergens may provide more specific measures of sensitization to fungi.

Molecular cloning, expression and modelling of cat allergen, cystatin (Fel d 3), a cysteine protease inhibitor.

BACKGROUND: Cats are an important source of indoor allergens. However, only two cat allergens, Fel d 1 and albumin, have been cloned and sequenced. IgE antibodies to Fel d 1 and albumin do not fully account for IgE responses to cat and there is good immunochemical evidence that cats produce other allergens. OBJECTIVE: To identify and define the molecular structure of the other potential cat allergens. METHODS: A cat skin cDNA library was screened using pooled serum obtained from five asthmatic patients which contained high levels of IgE antibody to cat dander. Selected cDNA clones were screened by plaque immunoassay and one cDNA clone, encoding cystatin, was expressed in E. coli. The three dimensional structure of cat cystatin was modelled using the SWISS-MODEL computer program. RESULTS: Three positive cDNA clones (A, B and C) were identified, two of which were fully sequenced. Clones A and C encoded the same 98 amino acid residue sequence which showed 79% and 75% homology with bovine and human cystatin A, respectively. The cat cystatin sequence contained the conserved cysteine protease inhibitor signature and two of three lipocalin motifs. By plaque immunoassay, 60-90% of cat allergic sera had IgE ab to the expressed cystatin clones. The cysteine protease inhibitor motif was also partially conserved in dog allergen sequences, Can f 1 and Can f 2, which are lipocalins. The recombinant protein was expressed in E. coli as an 11-kDa protein, corresponding to the predicted MW of cat cystatin. The three-dimensional structure of cat cystatin was modelled on human cystatin structures. CONCLUSION: A newly identified allergen, cystatin (Fel d 3), has been cloned from cat skin and is a member of the cysteine protease inhibitor family.

Identification of a novel cat allergen--cystatin.

BACKGROUND: Cat allergen is an important cause of sensitization among children with asthma in Japan. Although there is good evidence that cats produce other allergens, only one major allergen, Fel d 1, has been studied in detail. AIMS: To identify and define the molecular structure of the other potential cat allergens. METHODS: A cat skin cDNA library was screened using IgE antibodies to cat dander and selected clones were sequenced and expressed. RESULTS: One cDNA clone contained an open reading frame encoding a 98-amino acid residue protein. Sequence homology searches revealed a high degree of identity with bovine and human cystatin A, 79 and 75%, respectively. This cat cystatin clone contained the conserved cysteine protease motif and two of three lipocalin motifs. By plaque immunoassay, 60-90% of cat allergic sera had IgE Ab to cat cystatin. This cysteine protease inhibitor motif was partially conserved in dog allergens, Can f 1 and Can f 2, which are lipocalins. Recombinant cystatin was produced in Escherichia coli cells and purified as an 11-kD protein, corresponding to the predicted MW of cystatin. The structure of cat cystatin was modeled on human cystatin B using the SWISS-MODEL. CONCLUSION: A newly identified allergen, cystatin, has been cloned from cat skin and is a member of the cysteine protease inhibitor family.

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.

Cockroach allergens: environmental distribution and relationship to disease.

Cockroach allergy has been recognized as an important cause of asthma. Exposure to high levels of cockroach allergens in the home is a major risk factor for symptoms in sensitized individuals. Previously identified allergens from Blatella germanica and Periplaneta americana include Bla g 2 (inactive aspartic proteinase), 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). The primary site of cockroach allergen accumulation is the kitchen. However, lower levels of allergen can be found in bedding, on the bedroom floor, and in sofa dust. Strategies for decreasing exposure to cockroach have been investigated. The results suggest that a sustained decrease in cockroach allergen levels is difficult to accomplish, even after successful extermination of cockroach populations. The use of recombinant cockroach allergens may lead to the development of new approaches to asthma treatment in the future.

Recombinant allergens for diagnosis and therapy of allergic disease.

Many of the problems associated with using natural allergenic products for allergy diagnosis and treatment can be overcome with use of genetically engineered recombinant allergens. Over the past 10 years, the most important allergens from mites, pollens, animal dander, insects, and foods have been cloned, sequenced, and expressed. In many cases the three-dimensional allergen structure has been determined and B-cell and T-cell epitopes have been mapped. These studies show that allergens have diverse biologic functions (they may be enzymes, enzyme inhibitors, lipocalins, or structural proteins) and that as a rule the allergen function is unrelated to its ability to cause IgE antibody responses. High-level expression systems have been developed to produce recombinant allergens in bacteria, yeast, or insect cells. Recombinant allergens show comparable IgE antibody binding to their natural counterparts (where available) and show excellent reactivity on skin testing and in in vitro diagnostic tests. Cocktails of recombinant allergens can be formulated with predetermined and uniform allergen levels, which could replace natural allergens and result in the development of innovative, patient-based tests for allergy diagnosis. Recombinant allergens also offer the exciting possibility of developing new forms of allergen immunotherapy, including the use of hypoallergens, allergens coupled to IgE suppressive adjuvants, and peptide-based therapies. The production of recombinant allergens as defined molecular entities makes it feasible to consider the possibility of developing prophylactic allergen vaccines. The introduction of recombinant allergens in research and in clinical trials should lead to significant improvements in allergy diagnosis and treatment.

Cockroach allergens and asthma in Brazil: identification of tropomyosin as a major allergen with potential cross-reactivity with mite and shrimp allergens.

BACKGROUND: Cockroaches produce several proteins that induce IgE antibody responses. Although cockroaches are abundant in warm and humid areas, sensitization to cockroach allergens has not been investigated in Brazil. OBJECTIVE: The aims of this study were to investigate the frequency of cockroach allergy among patients with asthma, rhinitis, or both in Brazil and to identify American cockroach allergens. METHODS: Skin tests using cockroach extracts were performed on children and young adults with asthma, rhinitis, or both. A Periplaneta americana complementary (c)DNA library was screened by using IgE antibodies from Brazilian patients allergic to cockroaches. Reactivity of an mAb directed to Dermatophagoides pteronyssinus tropomyosin against cockroach tissue was examined by immunofluorescence. RESULTS: Cockroach allergy was present in 55% and 79% of the patients, as determined by using skin prick tests alone or combined prick and intradermal tests, respectively. Five cDNA clones reacted with IgE antibody and contained the same sequence. A representative clone (1300 bp), pa 12, coded for a protein that reacted with 50% of the sera from patients allergic to cockroaches on plaque immunoassay and showed a high degree of homology to tropomyosins, particularly those from invertebrates. P americana tropomyosin showed 80%, 81%, and 82% sequence identity to tropomyosins from D pteronyssinus, D farinae, and shrimp, respectively, which have been previously defined as important allergens. An mAb directed against D pteronyssinus tropomyosin, which also recognizes shrimp tropomyosin, showed binding to cockroach striated muscle. CONCLUSION: Our results support the recommendation that cockroach extracts should be routinely used for the evaluation of patients with asthma, rhinitis, or both in Brazil. The identification of P americana tropomyosin as an important allergen will make it possible to investigate cross-reactivity among cockroaches, mites, and food derived from invertebrates.

Molecular cloning of Per a 1 and definition of the cross-reactive Group 1 cockroach allergens.

BACKGROUND: Sensitization to allergens produced by German and American cockroaches is strongly associated with the cause of asthma. Most of the cockroach allergens identified to date have been species specific. OBJECTIVE: The aim of this study was to identify and sequence cross-reactive cockroach allergens. METHODS: A Periplaneta americana cDNA library was screened with IgE antibody from patients in the United States who were allergic to cockroach and who were sensitized to Blattella germanica. RESULTS: A cDNA clone was isolated that contained an 870-bp sequence with a 695-bp open reading frame, encoding a 231 amino acid protein, molecular weight 26.2 kd. Plaque immunoassays using anti-Bla g 1 and anti-Per a 1 mAbs and a panel of human IgE antibodies showed that the protein expressed by these clones was Per a 1. Sequence homology searches showed that Per a 1 was homologous to 5 previously reported, but unidentified, sequences from B germanica and P americana. These sequences encoded proteins with multiple molecular sizes containing approximately 100 amino acid repeats. The Per a 1 sequence also showed 31% identity to a mosquito precursor protein, ANG12, which may be involved in digestion. The Per a 1 cDNA was expressed in Pichia pastoris to produce purified recombinant allergen (yield, 14 mg/L). CONCLUSION: The results define the molecular structure and antigenic relationships between a new family of cross-reactive "Group 1" allergens produced by both P americana and B germanica. These recombinant allergens and specific mAbs will provide tools to improve the diagnosis and treatment of allergic diseases caused by cockroaches.

Novel allergen structures with tandem amino acid repeats derived from German and American cockroach.

Cockroaches produce potent allergens that are an important cause of asthma. The two principal domiciliary cockroach species, Blattella germanica and Periplaneta americana, secrete major allergens, Bla g 1 and Per a 1. Here, we report the molecular cloning of three Bla g 1 cDNA clones, which showed 70% amino acid sequence identity with Per a 1. Plaque immunoassays with human IgE antibodies or murine monoclonal antibodies showed that these allergens were antigenically cross-reactive. The Bla g 1 sequences also showed homology to five previously undefined cockroach allergen sequences. An unusual feature of all these sequences was that they contained multiple tandem amino acid repeats of approximately 100 amino acid residues. Between one and seven repeat units were identified by dot-plot matrix analysis. The sequences also showed homology to a mosquito protein involved in digestion (ANG12 precursor) and to mitochondrial energy transfer proteins. High levels of Bla g 1 were found in cockroach hindgut and proventriculus. Amino acid sequencing of natural Bla g 1 and Per a 1 suggested that these allergens are cleaved by trypsin-like enzymes following secretion into the digestive tract. The repeat sequences appear to have evolved by duplication of an ancestral amino acid domain, which may have arisen from the mitochondrial energy transfer proteins.

High-level expression of cockroach allergen, Bla g 4, in Pichia pastoris.

Exposure to cockroach allergens is a risk factor for allergic disease and has been linked to an increase in asthma morbidity among cockroach-sensitive inner-city children. Bla g 4 is a ligand-binding protein (or calycin) that causes IgE antibody responses in 40% to 60% of patients allergic to cockroaches. Recombinant Bla g 4 was expressed in Escherichia coli as an 18 kd protein but provided poor yields (only 0.25 mg/L culture). To improve yields, Bla g 4 was expressed in the Pichia pastoris yeast system as a 23 kd secreted protein at concentrations of 50 mg allergen/L. By cross-inhibition radioimmunoassay, Bla g 4 expressed in E. coli or P. pastoris provided overlapping inhibition curves. Both allergen preparations bound comparable levels of serum IgE antibody and showed similar skin test reactivity in individuals allergic to cockroaches (10[-1] to 10[-3] microg/ml). Deglycosylation of Pichia-expressed Bla g 4 with endoglycosidase F resulted in an 18 to 20 kd doublet, and liquid chromatography-mass spectrometry results suggested that the 20 kd band contained residual sugar residues. Both glycosylated and deglycosylated Pichia Bla g 4 showed comparable inhibition of IgE antibody binding in radioimmunoassay. Pichia-produced Bla g 4 had the same antigenic reactivity as that produced in E. coli, and glycosylation had no effect on IgE antibody binding. The high yield of Bla g 4 obtained in the Pichia system will facilitate studies on the structure and function of calycin allergens and on the immune response of asthma patients to cockroach allergens.

Induction of IgE antibody responses by glutathione S-transferase from the German cockroach (Blattella germanica).

We report that a major 23-kDa allergen from German cockroach (Blattella germanica) is a glutathione S-transferase (EC 2.5.1.18; GST). Natural B. germanica GST, purified from cockroach body extracts by glutathione affinity chromatography, and recombinant protein expressed in Escherichia coli using the pET21a vector, showed excellent IgE antibody binding activity. B. germanica GST caused positive immediate skin tests in cockroach-allergic patients using as little as 3 pg of recombinant protein. The NH2-terminal sequence of the natural protein and the deduced amino acid sequence from cDNA were identical except for one substitution (Phe9 --> Cys). Assignment of this protein to the GST superfamily was based on binding to glutathione and sequence identity (42-51%) to the GST-2 subfamily from insects, including Anopheles gambiae and Drosophila melanogaster. B. germanica GST contained 18 of the 26 invariable residues identified in mammalian GST by x-ray crystallography and exhibited enzymic activity against a GST substrate. Our results show that cockroach GST causes IgE antibody responses and is associated with asthma. The data strongly support the view that the immune response to GST plays an important role in allergic diseases.

Defined epitopes: in vivo and in vitro studies using recombinant allergens.

BACKGROUND: The aim of the studies was to investigate the biologic activity of recombinant cockroach and mite allergens and their potential for use in diagnosis and treatment of allergic disease. METHODS: Cockroach allergens Bla g 2, Bla g 4 and Bla g 5 and mite group 5 allergens were produced in bacterial expression vectors and used for immediate skin and serum IgE antibody tests. RESULTS: The cockroach allergens showed very good skin test reactivity in allergic patients, giving positive reactions at 10(-2)-10(-5) microg/ml; controls were negative at 10(0) microg/ml. These reactions correlated with serum IgE antibody results. The prevalence of reactivity to group 5 mite allergens varied with exposure. There was a high prevalence (70%) of sensitization to Blomia tropicalis allergen, Blo t 5, among patients from Brazil and Singapore, whereas < 20% of patients from Charlottesville, US and Manchester, UK gave positive skin tests to Blo t 5 (p < 0.001). CONCLUSIONS: The results show that recombinant allergens retain biologic activity and suggest that cocktails of two to four recombinant allergens could be used for diagnostic or therapeutic purposes. The phased introduction of recombinant allergens should improve the management of allergic disease.

Evaluation of German cockroach (Orthoptera:Blattellidae) allergen and seasonal variation in low-income housing.

Six apartments in a low-income housing project were evaluated for German cockroach. Blattella germanica (L.), infestation and concentration of an allergen derived from these cockroaches (Bla g II). Kitchen and living room samples were collected monthly for 1 yr. In addition, airborne sampling was carried out in 5 kitchens. The kitchen had the highest allergen concentration in 65% of visits and the highest number of cockroaches trapped in 69% of visits. In the kitchen, the highest cockroach levels were seen in June, whereas the values for Bla g II peaked in August. In keeping with this, the closest correlation was between Bla g II (microgram/g dust) and the number of cockroaches found 2 mo earlier. Airborne samples were assayed for 2 separate allergens. Bla g II and Bla g I. No allergen was detectable in the absence of disturbance. By contrast, during disturbance with a vacuum cleaner both Bla g II and Bla g I were detectable in the air of each apartment. Results suggest that immunochemical assay of a major allergen in dust samples from the kitchen floor may be used to monitor exposure to German cockroaches, also that cockroach levels may be used as an indicator or predictor of allergen in dust.

Recombinant mite allergens. New technologies for the management of patients with asthma.

The introduction of molecular cloning techniques has led to advances in allergen identification and sequencing, production of recombinant allergens, identification of B-cell and T-cell epitopes, and tertiary structural analysis of allergen molecules. Over 10 groups of mite allergens have been cloned from Dermatophagoides spp., as well as several homologous allergens from Euroglyphus maynei, Lepidoglyphus destructor, and Blomia tropicalis. The availability of these allergens has made it feasible to consider their use for both diagnostic and therapeutic purposes. Several recombinant Dermatophagoides allergens show comparable reactivity on skin testing and in serologic assays to natural allergens, and cocktails of the recombinant proteins could be used as diagnostic reagents. New technologies have been developed for detection of allergen-specific IgE and for environmental allergen detection using rapid diagnostic tests. Novel approaches to immunotherapy are also being investigated, including T-cell-peptide based vaccines, allergen variants which lack IgE reactivity, and naked DNA vaccines. The application of allergen biotechnology should lead to improvements in the management of mite-allergic patients with asthma and represents a logical step toward reducing asthma mortality and morbidity.

Sensitization to Blomia tropicalis in patients with asthma and identification of allergen Blo t 5.

In tropical and subtropical regions of the world, allergens produced by Blomia tropicalis are an important cause of IgE-mediated sensitization among patients with asthma. We compared the relative importance of sensitization to the two mite species among asthma patients from Florida, Puerto Rico, and Brazil (n = 83), who were concurrently exposed to B. tropicalis and D. pteronyssinus, with patients from the United States and from the United Kingdom (n = 56) exposed to D. pteronyssinus. In addition, molecular cloning techniques were used to clone and express a major B. tropicalis allergen. There were significant differences between IgE antibody responses to B. tropicalis and D. pteronyssinus that were related to exposure: only 22% of patients exposed to both species had a high ratio (> 10) of IgE D. pteronyssinus:B. tropicalis, whereas 68% of patients exposed only to D. pteronyssinus had a ratio of > 10 (p < 0.001). A major 14-kD allergen (Blo t 5), cloned from a B. tropicalis cDNA library, showed 43% sequence homology to D. pteronyssinus Der p 5. Recombinant Blo t 5 produced in E. coli reacted with 45 to 69% of sera from B. tropicalis-allergic asthmatics and induced positive immediate skin tests at 10(-3) to 1 microg/ml. In vivo and in vitro comparisons of IgE responses to B. tropicalis, D. pteronyssinus, rBlo t 5, and rDer p 5, showed that B. tropicalis has unique allergens that cause specific IgE responses. The results suggest that B. tropicalis is an independent cause of sensitization and that use of recombinant Blo t 5 should lead to a better understanding of the role of B. tropicalis in causing asthma in tropical environments.