The stability of house dust mite allergens in glycerinated extracts

Preparation of chemically stable allergen-specific sublingual immunotherapy from Egyptian allergens

BACKGROUND

The term "allergen extracts" refers to solutions of proteins or glycoproteins extracted from source raw materials.

OBJECTIVES

This study was planned to prepare chemically stable sublingual immunotherapy from different allergens in Egypt.

METHODS

Allergen extraction from raw materials. The concentrated aqueous extract of each allergen was mixed with an equal volume of glycerol. The protein content of the preparations was determined using the modified Lowry assay method. The prepared allergens were stored for 9 months at 2-4°C. Samples were analyzed periodically (0, 3, 6, and 9 months of intervals) adopting the Lowry Assay method. Levels of specific IgE to Chenopodium album antigens were measured in patients' sera by ELISA.

RESULTS

The concentration of all prepared allergens, as indicated by the concentration of the protein content, was found to decrease exponentially with time, implying first-order kinetics of degradation. From the values of the slopes of the log plot for each allergen, the half-life time (t_1/2 ) and (t_1/4 ) values were calculated. The expiration date was considered as the time after which the allergen loses 25% of its potency. The obtained values of t_1/4% vary according to the type of vaccine. The most stable one is that of Chenopodium album pollens (2.4 years) and the least stable is that of house dust Mites (9 months). The immunological characters of Chenopodium album extract were stable for at least 6 months.

CONCLUSION

Differences exist among allergen extracts made by multiple manufacturers. So, developments in studies on allergen preparation and characterization in a different locality are necessary.

Update: stability of allergen extracts to establish expiration dating

PURPOSE OF REVIEW

The article reviews studies pertaining to US manufactured allergen extract stability that contribute to guidance for expiration dating for bulk concentrates, diluted patient testing and treatment vials, and adjustments following elevated temperature excursions.

RECENT FINDINGS

Studies on allergen stability were completed to satisfy the Food and Drug Administration requirements supporting labeled expiration dating for standardized short ragweed, dust mites, cat, grass, and venom extracts and are not published. These studies demonstrated the stability enhancing parameters of 50% glycerin and support the Food and Drug Administration mandated expiration of nonstandardized extracts allowing glycerin extracts twice the dating of nonglycerin aqueous extracts. Patient vials are commonly given 6-12 months dating. There is adequate evidence that human serum albumin stabilizes low protein diluted vials. High protease allergens such as molds and insects compromised potency of pollens when mixed. Subsequent work continued to define the effects of diluents on extract dilutions, temperature excursions that occasionally occur with shipping or refrigerator malfunctions, and allergen compatibility.

SUMMARY

Potency has been determined for allergen dilutions with diluents typically used for allergen immunotherapy. These studies along with changes of potency under various storage conditions and mixing designed to improve our guidance on expiration dating of allergen extracts will be discussed.

Quality control of house dust mite extracts by broad-spectrum profiling of allergen-related enzymatic activities

BACKGROUND

Diagnosis and immunotherapy of allergy against mites is based on complex extracts from large-scale cultures. However, the analysis of their composition using specific antibodies is limited. By taking advantage of the prevailing enzymatic nature of mite allergens, we have developed a broad-spectrum biochemical method for the standardization of native mite products.

METHODS

Microplate-based assays have been implemented for thirteen Dermatophagoides pteronyssinus enzymatic activities, associated with Der p 1, 3, 4, 6, 8, 9, 15 and 20 allergens. The dynamics of these activities along culture growth, and their profile in purified fractions (bodies and faeces) and international reference standards (WHO/IUIS, two CBER/FDA), have been characterized. The stability of enzymatic activities and major allergens under stress conditions (40°C) has been assessed in the presence/absence of specific protease inhibitors.

RESULTS

The analysis of enzymatic activities revealed distinct profiles along culture growth and between fractions (bodies and faeces). Remarkable differences were found when comparing international reference standards, being consistent with their source material (purified bodies or whole cultures). After 72 h at 40°C, only trypsin and alpha-amylase maintained high activity. Notably, the prominent role of trypsins in the hydrolytic degradation of major allergens is demonstrated by the use of inhibitors.

CONCLUSIONS

Our method offers a robust approach to assess the complexity of mite extracts and highlights the critical importance of source materials for the composition and stability of finished products. The implementation of this approach in industry-based quality control procedures would contribute to the standardization of allergenic extracts used for diagnosis and immunotherapy.

Food-specific sublingual immunotherapy is well tolerated and safe in healthy dogs: a blind, randomized, placebo-controlled study

BACKGROUND

Food allergies are increasing in prevalence but no treatment strategies are currently available to cure dogs with food allergy. Over the past decade, experimental food allergen-specific sublingual immunotherapy (FA-SLIT) has emerged as a potential treatment for food allergies in human medicine. However, FA-SLIT has not been investigated in dogs. Therefore, the objective of this study was to prospectively evaluate the safety, tolerability and dispenser sterility of FA-SLIT in healthy dogs before testing it in food allergic dogs. Eight experimental healthy beagle dogs, never orally exposed to peanut, were randomized in two groups to receive SLIT with peanut or placebo for 4 months. Subjects were monitored daily for local and systemic adverse effects. Blood samples for complete blood count and serum biochemistry, and urine for urinalysis were collected and the dogs' body weight was recorded at day 0, 35 and 119 of the SLIT treatment. Sera for the determination of peanut-specific IgG and IgE were collected at day 0, 35, 49, 70, 91, 105 and 119. Intradermal tests were performed before (day 0) and after (day 119) the experiment. The content of each dispenser used to administer treatment or placebo was tested for sterility after usage. In order to assess the presence or absence of sensitization, dogs were challenged 6 months after the end of the study with 2000 μg of peanut extract daily for 7 to 14 days.

RESULTS

All dogs completed the study. The treatment did not provoke either local or systemic side-effects. Peanut-specific IgG significantly increased in treatment group. Even though a significant increase in peanut-specific IgE was also seen, intradermal tests were negative in all dogs before and after the experiment, and the challenge test did not trigger any adverse reactions in the treated dogs, which shows the protocol did not cause sensitization to peanut, but nevertheless primed the immune system as indicated by the humoral immune response. All dispenser solutions were sterile.

CONCLUSIONS

Our results demonstrate that the used peanut-SLIT protocol is well tolerated and safe in healthy dogs. Further studies should evaluate tolerability, safety and efficacy in dogs with food allergy.

Multiplex Assay for Protein Profiling and Potency Measurement of German Cockroach Allergen Extracts

Background

German cockroach (GCr) allergens induce IgE responses and may cause asthma. Commercial GCr allergen extracts are variable and existing assays may not be appropriate for determining extract composition and potency.

Objective

Our aim was to develop a multiplex antibody/bead-based assay for assessment of GCr allergen extracts.

Methods

Single chain fragment variable (scFv) antibodies against GCr were obtained by screening libraries derived from naïve human lymphocytes and hyperimmunized chicken splenocytes and bone marrow. Selected clones were sequenced and characterized by immunoblotting. Eighteen scFv antibodies (17 chicken, 1 human) coupled to polystyrene beads were used in this suspension assay; binding of targeted GCr allergens to antibody-coated beads was detected using rabbit antisera against GCr, and against specific allergens rBla g 1, rBla g 2, and rBla g 4. The assay was tested for specificity, accuracy, and precision. Extracts were also compared by IgE competition ELISA.

Results

Chicken scFv’s generated eight different binding patterns to GCr proteins from 14 to 150 kDa molecular weight. Human scFv’s recognized a 100 kDa GCr protein. The multiplex assay was found to be specific and reproducible with intra-assay coefficient of variation (CV) of 2.64% and inter-assay CV of 10.0%. Overall potencies of various GCr extracts were calculated using mean logEC50s for eight selected scFvs. Overall potency measures were also analyzed by assessing the contributions to potency of each target.

Conclusions

An scFv antibody-based multiplex assay has been developed capable of simultaneously measuring different proteins in a complex mixture, and to determine the potencies and compositions of allergen extracts.

Allergen stability of testing/treatment boards and immunotherapy vials with various diluents

BACKGROUND

Otolaryngologists commonly use glycerin and normal saline with phenol (NSP) in diluting solutions to help preserve allergenicity in immunotherapy vials. Studies have shown that diluting with human serum albumin (HSA) may provide better allergen stability. The purpose of this study was to assess the ability of various diluents to preserve allergen content in testing/treatment boards (TTBs) and immunotherapy treatment vials (ITVs) at multiple time points.

METHODS

TTBs with 4 allergens were prepared with HSA, NSP, 10% glycerin, and 50% glycerin. The major allergen content of the TTBs was measured at creation (time 0), 3 days, 8 weeks, and 18 weeks. Multiallergen ITVs containing the 4 allergens were prepared from the NSP board (diluted to 10% glycerin) and the HSA board (diluted in HSA) at the time of making the freshly prepared TTBs and again 8 weeks later, simulating the creation of ITVs from a "new" and an "old" TTB. The major allergen content of these ITVs was determined at creation and at interval time points thereafter.

RESULTS

TTBs and ITVs showed a substantial loss of allergen at day 3. The loss of allergen was more pronounced in the more dilute (#4, #5, and #6) vials. HSA and 50% glycerin showed superior allergen preservation compared to NSP and 10% glycerin in TTBs. HSA showed superior allergen preservation compared to 10% glycerin-NSP in ITVs.

CONCLUSION

The use of HSA as a diluent in TTBs and ITVs showed superior allergen preservation compared to NSP and 10% glycerin, particularly for more dilute vials.

The effects of storage conditions on the stability of house dust mite extracts

Purpose

Allergen extracts from the house dust mite (HDM, Dermatophagoides pteronyssinus) are widely utilized for diagnosis and treatment of allergic diseases. It is known that allergen extracts degrade and lose potency when stored over time.

Methods

This study aimed to determine the optimal conditions for stability of allergen extracts. This study was undertaken to investigate the optimal storage conditions for HDM extracts, the effects of adding 0.03% human serum albumin (HSA) and 50% glycerol were evaluated at -20℃, 4℃, and room temperature (RT). Changes in protein and group 1 major allergen (Der p 1) concentration, as well as allergenicity were measured over a 1 year period using the Bradford assay, two-site ELISA, and ELISA inhibition.

Results

Protein concentrations decreased by 86%, 51%, and 6% at RT, 4℃, and -20℃, respectively, when stored in distilled water. Overall allergenicity remained high (89.9%) when the extracts was reconstituted in 50% glycerol solution, and was 93.1% when reconstituted in 50% glycerol and 0.03% HSA at RT. Allergenicity was decreased to 36.6% and 33.3%, however, reconstitution in DW or 0.03% HSA solution at RT, respectively. Allergenicity was remained high as 92.0%-97.0% when stored at 4℃ regardless of the buffer conditions.

Conclusions

Storage temperature is the most important factor in preserving allergenicity of HDM extracts, which is ideal at 4℃. The addition of 50% glycerol to the storage buffer was also found to play an important role in increasing the shelf-life of HDM extracts at RT.

Multiplex microbead measurements for the characterization of cat and ragweed allergen extracts

BACKGROUND

Current assays for allergen extracts can measure either overall potency or the levels of individual allergens.

OBJECTIVE

To develop a multiplex allergen extract potency assay (MAEPA) for allergen extracts that can concurrently measure individual allergens and characterize the overall allergen levels in the mixture.

METHODS

Six anti-Fel d 1 and 6 anti-Amb a 1 recombinant antibodies were generated and were covalently bound to carboxy-labeled beads. Antibody-bound beads were then used to measure Fel d 1 and Amb a 1 levels in commercial cat hair and short ragweed pollen (SRP) extracts, respectively, using bead-based flow cytometry. These major allergen levels were compared with those obtained using a conventional antibody-based method. Allergen levels were calculated by comparing the half-maximal effective concentrations of dose-response curves analyzed using 4-parameter fits. Bead-antibody pairs were tested to determine whether the presence of additional bead-antibody pairs affected the apparent potency of the extract.

RESULTS

Allergen contents of cat hair and SRP extracts determined using the MAEPA and anti-Fel d 1 and anti-Amb a 1 antibodies were comparable with potencies determined using conventional methods. Cross-interference from the concurrent use of multiple beads was minimal. Six lots of cat hair extract and 6 lots of SRP extract were tested.

CONCLUSIONS

The MAEPA, a bead-based assay using recombinant antibodies, accurately determined Fel d 1 levels in cat hair allergenic extracts and Amb a 1 levels in SRP extracts. The results of this assay are reproducible and are consistent with data obtained using conventional methods.

Effects of summer mailing on in vivo and in vitro relative potencies of standardized timothy grass extract

BACKGROUND

Allergen extracts can degrade when exposed to temperatures significantly beyond the optimum storage recommendation of 4 degrees C. Many allergen extracts are mailed to their final destinations throughout the year with exposure to varied environmental conditions.

OBJECTIVE

To evaluate the effect of summer mailing on the in vitro and in vivo potency of timothy grass extract.

METHODS

Standardized timothy grass extracts, 10,000 and 100,000 BAU/mL, were mailed round-trip between San Antonio, Texas, and Phoenix, Arizona, during August 2007. In-transit temperatures were recorded using a portable temperature logger. After mailing of the extracts, we performed quantitative in vitro enzyme-linked immunosorbent assay inhibition and in vivo ID50 EAL (Intradermal Dilution for 50-mm Sum of Erythema Determines Bioequivalent Allergy Units) analysis.

RESULTS

Measured extract exposure temperatures were greater than 20 degrees C for 11 days and 30 degrees C for 6 hours during standard mailing in weather temperatures exceeding 38 degrees C. Enzyme-linked immunosorbent assay inhibition results for the 100,000- and 10,000-BAU/mL control samples were 97,900 and 10,580 BAU/mL, respectively, and for the mailed extracts were 96,800 and 7830 BAU/mL, respectively. These measurements fell within the current Food and Drug Administration lot release limits (67%-149%) and stability limits (50%-200%) relative to the standardized reference. The ID50EAL determinations of the control vs mailed extracts were 12.98 vs. 12.28, 12.66 vs. 12.32, and 11.97 vs 11.70 for the 3 patients. These differences were not statistically significant.

CONCLUSIONS

Mailing of timothy grass extract produced no significant reductions in in vitro relative potencies or in vivo skin test reactivity in 3 sensitive patients.

Stability evaluation of house dust mite vaccines for sublingual immunotherapy

Allergen-specific immunotherapy with house dust mite (HDM) allergen extracts can effectively alleviate the symptoms of allergic rhinitis and asthma. The efficacy of the immunotherapeutic treatment is highly dependent on the quality of house dust mite vaccines. This study was performed to assess the stability of house dust mite allergen vaccines prepared for sublingual immunotherapy. Lyophilized Dermatophagoides pteronyssinus (Dpt) mite bodies were the starting material for the production of sublingual vaccines in four therapeutic concentrations. The stability of the extract for vaccine production, which was stored below 4 ?C for one month, showed consistence in the protein profile in SDS PAGE. ELISA-inhibition showed that the potencies of Dpt vaccines during a 12 month period were to 65-80 % preserved at all analyzed therapeutic concentrations. This study showed that glycerinated Dpt vaccines stored at 4?C preserved their IgE-binding potential during a 12 month period, implying their suitability for sublingual immunotherapeutic treatment of HDM allergy.

Stability of allergen extracts used in skin testing and immunotherapy

PURPOSE OF REVIEW

The present article reviews allergen extract stability applied to US manufactured products. Methods used to measure potency of extract concentrates, patient prescription dilute extracts, and mixes containing degrading enzymes will be discussed.

RECENT FINDINGS

Information about the allergen extract active ingredient components contributing to potency is increasing. Pertinent stability issues include the type of diluent used for extraction and mixing. Fifty percent glycerin greatly extends the time over which extracts remain potent, including in mixes with fungal and insect extracts known to contain protein-degrading enzymes. Diluents that contain additional protein content such as human serum albumin increase stability of dilute solutions. Many of the most rigorous studies on allergen stability have been performed by allergenic extract manufacturers in support of Food and Drug Administration approved dating for standardized products and are not published.

SUMMARY

Studies addressing how antigens in extracts change under various storage conditions have provided general guidance for expiration dating, but the diversity of extracts and testing methods have been less than complete. Additional findings that are increasing our knowledge of extract shelf life will be discussed.

Stability of protease-rich periplaneta Americana allergen extract during storage: formulating preservatives to enhance shelf life

Allergenic proteins in extracts degrade rapidly and lose potency on storage. Hence, formulation of optimum conditions is required to enhance shelf life of extracts for proper allergy diagnosis and immunotherapy. In the present study, allergenic potency of P. americana proteins was evaluated after storage with epsilon-aminocaproic acid (EACA), sucrose, glycerol, pepstatin A, and aprotinin, individually for 1, 3, 6, and 12 months at 4, 25, and 37 degrees C. P. americana extract stored with EACA and sucrose individually retained potency comparable to proteins in standard extract (freeze-dried extract, stored at-70 degrees C) upto 6 months at 4 degrees C. The extracts without preservatives or with glycerol, pepstatin A, aprotinin, or stored at 37/25 degrees C were severely degraded and lost potency by 3 months. A formulation containing a combination of EACA and sucrose enhanced the shelf life of P. americana proteins upto 12 months at 4 degrees C. Hence, EACA and sucrose together show better potential for stabilization of protease-rich extracts.

Competition enzyme-linked immunosorbant assay (ELISA) can be a sensitive method for the specific detection of small quantities of allergen in a complex mixture

RATIONALE

The competition ELISA assay is used to determine the potency of US standardized allergen extracts. We have been concerned that the competition ELISA is not sensitive to changes in individual allergen levels. This study was designed to determine the sensitivity of the competition ELISA to detect the specific loss of Bla g 1 and Bla g 2 in cockroach extracts.

METHODS

German cockroach extract E3Cg was made from defatted German cockroaches. New Zealand White rabbits were immunized with rBla g 1 or rBla g 2. Optimal dilutions of anti-Bla g 1 and anti-Bla g 2 sera were established by ELISA. E3Cg was selectively depleted of Bla g 1 or Bla g 2 by immunoabsorption with anti-Bla g 1 or anti-Bla g 2 attached to Protein G agarose beads. Competition ELISA using pooled human sera, or mixed anti-Bla g 1 and anti-Bla g 2 serum, was performed on the depleted extracts, and on depleted extracts reconstituted with rBla g 1 or rBla g 2.

RESULTS

Unlike pooled human-allergic IgE sera, anti-Bla g 1 and anti-Bla g 2 IgG -- in dilutions as low as 10(-6), could be used in the competition ELISA to measure the loss of allergen in depleted E3Cg. As little as 0.001 microg/mL of added rBla g 1 and 0.1 microg/mL of added rBla g 2, could be detected.

CONCLUSION

The competition ELISA can be highly sensitive to compositional differences in complex allergen mixtures, even when the specific detecting antibody is present in relatively small amounts.

Update on allergy immunotherapy

This article summarizes and provides commentary regarding guidelines on the administration of immunotherapy (IT) for allergic airway disease. Recent investigations have provided important insights into the immunologic mechanism of IT and the prominent role of interleukin-10-producing regulatory T lymphocytes. The most important aspect of successful IT is the administration of an appropriate dose of an extract containing a sufficient concentration of the relevant allergen. This is largely possible now only with standardized extracts. When the major allergen content of successful IT extracts was quantified, efficacy was demonstrated across a surprisingly narrow concentration range (approximately 5-24 μg per injection), irrespective of the extract. This presumably reflects the concentration of an antigen that drives an immune response toward tolerance. It may be predicted that as major allergen content is quantified in currently nonstandardized extracts, effective IT will also be achieved by administering a dose in this range, in contrast to current practices involving fairly arbitrary dosing decisions. With the availability of nonsedating antihistamines, intranasal corticosteroids, and the leukotriene modifiers, inadequate pharmacologic response or intolerable side effects are less commonly the major indications for starting IT for allergic rhinitis (AR). However, with the recognition that a relatively short course (3-5 years) of IT can provide long-term immunomodulation and clinical benefit, a desire to avoid long-term pharmacotherapy and the associated high costs may be the primary indication for IT in AR cases. While evidence overwhelmingly supports the beneficial influences of IT in asthma cases, the positioning of IT for this disorder is not established. The observed prevention of asthma in children who have AR is intriguing, but further studies are required to assess the extent to which the prevalence and severity of chronic asthma will be reduced when these children reach adulthood. Similarly, safety issues overwhelmingly suggest that uncontrolled asthma is the greatest risk factor for mortality associated with IT and that IT therefore may be contraindicated for most patients who have inadequate pharmacologic responses or are unable to tolerate useful pharmacologic agents. Paradoxically, these are the patients for whom a response to IT may be most desirable.

Effect of various stabilizing agents on Imperata cylindrica grass pollen allergen extract

BACKGROUND

Allergen extracts are unstable, heat labile or susceptible to proteases. Stability of allergen extracts is important for proper diagnosis and therapy of allergic disorders.

OBJECTIVE

The present study was undertaken to determine the preservation and stabilization conditions of Imperata cylindrica (Ic) grass pollen extract.

METHODS

The Ic extract was kept with 0.1 mepsilon-aminocaproic acid (EACA), 0.75 m sucrose, 5% glycerol, 0.03% human serum albumin (HSA) or 0.4% phenol for different time periods. The extracts were stored for 3, 6 and 12 months each at 4 degrees C, 4 degrees C with daily exposure to room temperature (RT) for 1 h, and RT. The quality of extracts was analysed by SDS-PAGE, Western blot, ELISA, ELISA inhibition and skin test.

RESULTS

Extracts kept with EACA and sucrose retained most of the protein bands followed by glycerol as determined by SDS-PAGE and Western blot during all storage periods and conditions in comparison with standard extracts. The extracts kept with HSA, phenol and without preservative (WP) showed protein degradation below 33 kDa after 3 months storage at all conditions. However, a 67-kDa allergen was stable in these extracts. EACA extract required 75 to 120 ng of protein for 50% inhibition in IgE binding under different conditions, whereas standard extract required 70 ng for the same. ELISA also demonstrated high allergenic reactivity of EACA extract. ID test on allergy patients with EACA extract demonstrated same allergenic potency as that of standard extract.

CONCLUSION

EACA is the best preservative/stabilizing agent of Ic pollen extract, followed by sucrose and glycerol. Ic extract kept with phenol, HSA and without preservative showed degradation within 3 months. EACA preserved extract is equally potent as that of standard extract up to 1 year's storage.

Decay of house-dust mite allergen Der f 1 at indoor climatic conditions

BACKGROUND

The decay of house-dust mite allergens is important for the outcome of avoidance measures for house-dust mite-allergic patients.

OBJECTIVE

To quantify the stability of Der f 1 from mattress dust when exposed to domestic conditions.

METHODS

Three samples of mattress dust were individually homogenized and divided into 64 subsamples. Mites were killed by freezing for 48 hours at -30 degrees C. The subsamples were exposed in eight homes, three storerooms, and one greenhouse, where temperature and relative humidity were recorded. Der f 1 was determined in extracts of subsamples (enzyme-linked immunoadsorbent assay) at 0, 3, 12, and 24 months.

RESULTS

In the three samples of mattress dust, the initial concentrations of Der f 1 (mean +/- standard deviation; STD) were: 169 (12), 3.9 (0.4), and 31 (2.6) microg/g, respectively. Median half-life of Der f 1 in the mattress dust samples was 10 years in the exposure homes, 18 years in the store rooms, and 1.0 year in the greenhouse. No correlations among preserved Der f 1 and temperature, relative humidity, and absolute humidity in homes were found (Spearman rank correlation test).

CONCLUSION

Natural decay of Der f 1, with an estimated half-life of 10 years at housing conditions, has no practical consequence in reducing allergen exposure. Therefore, avoidance measures should include an active removal of the allergens.

Unraveling the ecology of risks for early childhood asthma among ethnically diverse families in the southwest

OBJECTIVES

We describe the prevalence of asthma risk factors within racial/ethnic and language groups of infants participating in an intervention study for reducing chronic asthma.

METHODS

Low-income children aged 9 to 24 months with 3 or more episodes of wheezing illness were enrolled. Baseline information included family and medical histories, allergic status, environmental exposures, emotional environment, and caregiver psychosocial resources.

RESULTS

Racial/ethnic and language groups-European Americans, African Americans, high-acculturated Hispanics, and low-acculturated Hispanics-showed different patterns of risk factors for childhood asthma, with low-acculturated Hispanics showing the most distinctive pattern.

CONCLUSIONS

Patterns of covariation of biological and psychosocial risk factors for childhood asthma were associated with racial/ethnic and language status among urban, low-income children.

Commercial dry dog food in the north central United States is not contaminated by Dermatophagoides house dust mites

Contamination of home-stored cereal grain food products with Dermatophagoides spp. house dust mites (HDM) was reported recently, along with anaphylaxis after consumption of these foods by dust mite-allergic people. We hypothesized that commercial dry dog food could become similarly contaminated, particularly if stored improperly, and could eventually contribute to allergic signs in dogs. Newly purchased bags of dry dog food (n = 30), from a variety of sources and manufacturers, and client samples of dry dog food (n = 50), stored under a variety of conditions, were obtained. Food samples were extracted in aqueous buffer, and extracts were assayed using ELISA for Dermatophagoides group II (Der II) allergen, as a marker for the presence of HDM. Der II allergen was not detected in any of the 30 newly purchased or 50 stored samples tested. Positive control samples consisting of house dust or dog food mixed with house dust, similarly extracted, and Dermatophagoides commercial allergen extract were positive for Der II in the same assay. We could find no evidence of HDM contamination in newly purchased or stored commercial dry dog food in the north central United States.

Group 13 grass allergens: structural variability between different grass species and analysis of proteolytic stability

BACKGROUND

Determination of the allergen composition of an extract is essential for the improvement of hyposensitization therapy. Surprisingly, although grass pollen extracts have been studied intensively for 20 years, a further major allergen, Phl p 13, was detected recently in timothy grass pollen.

OBJECTIVES

We sought to determine the occurrence and importance of group 13 allergens in various grass species and to investigate their proteolytic stability.

METHODS

The group 13 allergens were determined by means of 2-dimensional PAGE blotting with patient sera and group 13-specific mAbs. The allergens were isolated chromatographically from several pollen extracts and analyzed by means of microsequencing. Cross-reactivity among various grass species was studied by using Western blots and immunoblot inhibition tests. The stability of the allergens was tested under defined extraction conditions.

RESULTS

Group 13 allergens are detectable in all common grasses and show IgE cross-reactivity among them. The allergenic components were identified in the neutral pH range with molecular masses of 50 to 60 kd, and in the case of Phl p 13, maximal binding of the isoforms was observed at 55 kd and at an isoelectric point of 6 to 7.5. Protein sequencing clearly confirms structural identities between different grass species, although individual variations are found. If low-molecular-mass components were depleted by means of gel filtration, a rapid degradation of group 13 allergens was observed. This is in contrast to other pollen allergens described thus far.

CONCLUSION

Group 13 allergens are widespread and are major allergens in the grasses. Predicted from their primary structures, these allergens are polygalacturonases. This class of enzymes is already known from microorganisms, and these enzymes are recognized as potential inducers of asthma. Our studies indicate that the group 13 allergens show a considerable microheterogeneity and degradation, especially after depletion of low-molecular-mass components. One has to be aware of this pivotal fact when soluble grass pollen extracts are prepared for diagnostics and hyposensitization therapy.