Cockroach allergens: environmental distribution and relationship to disease

Measurement of German cockroach allergens and their isoforms in allergen extracts with mass spectrometry

BACKGROUND

Allergen extracts are the primary tool for diagnosis and treatment of allergic diseases. In the United States, most allergen extracts are non-standardized. More sophisticated analytical approaches are needed to characterize these products and enable manufacturers and regulators to better determine potency.

OBJECTIVE

To expand the multiple reaction monitoring (MRM) assay for an in-depth characterization of German cockroach (GCr; Blattella germanica) allergen extracts.

METHODS

We applied advanced liquid chromatography (LC) and mass spectrometry (MS) techniques including MRM. The expanded LC/MRM-MS method was optimized to measure known GCr allergens and their isoforms/variants in commercial extracts and environmental samples. We performed isoform-specific allergen measurements in multiple extracts from four commercial sources and extracts prepared using environmental samples from urban homes. To investigate causes of heterogeneity, we examined over 30 extraction process variables.

RESULTS

Evaluation of the commercial extracts confirmed the variability of production lots and commercial sources. Commonly used defatting and extraction protocols yielded extracts with comparable allergen profiles and content. However, the identity and quality of source materials was a major contributor to variability. In comparing commercial GCr extracts to environmental samples, relative quantities of Bla g 1, Bla g 2, Bla g 3, Bla g 4 and Bla g 11 were similar, while Bla g 5, Bla g 6, Bla g 7 and Bla g 8 were present in the environmental samples but largely absent for the commercial extracts.

CONCLUSIONS AND CLINICAL RELEVANCE

LC/MRM-MS can be used to measure all known GCr allergens in commercial allergen extracts and environmental samples. Significant differences exist between allergen profiles of commercial extracts and the profiles of environmental samples from dwellings. This analytical platform can serve as a template to achieve better product characterization of similarly complex products.

Pest Cockroaches May Overcome Environmental Restriction Due to Anthropization

Our species have altered their surroundings since its early dispersion on Earth. Unfortunately, thanks to human-modified habitats, several pest organisms such as domiciliary insects have expanded their distributions. Moreover, pest-related microorganisms may also be aided by anthropization. Pest cockroaches are globally distributed and capable of carrying several diseases. We explored if urbanization may buffer environmental conditions allowing pest insects to expand their distribution. Specifically, we suggest that human settlements may generate suitable microhabitats for synanthropic cockroaches, helping them to survive and establish with disregard to overall climatic restrictions. To test this idea we studied the distribution of pest cockroaches spanning the length of Chilean territory. Chile, along its 4270 km length north to south extent, is a country offering a formidable sampling of Earth's climatic diversity accompanied by dense urbanizations. We studied entomological collections and spatially analyzed pest cockroach distribution found in Chile and discovered that synanthropic cockroach populations are consistently concentrated near most urban developed zones of the country and not limited by overall temperature. Furthermore, health-concern pest cockroach species were widely distributed in Chilean territory, found even in its most southern urban centers as well as Easter Island. Therefore, these disease vectors could exist even in isolated and extreme climatic zones as long as urbanization provides the adequate microhabitat. We discuss the need for further research in order to assess if these distributions can be extrapolated to the pathogenic strains these pest insects may be carrying as reported in other regions of the planet.

Particularities of allergy in the Tropics

Allergic diseases are distributed worldwide and their risk factors and triggers vary according to geographical and socioeconomic conditions. Allergies are frequent in the Tropics but aspects of their prevalence, natural history, risk factors, sensitizers and triggers are not well defined and some are expected to be different from those in temperate zone countries. The aim of this review is to investigate if allergic diseases in the Tropics have particularities that deserve special attention for research and clinical practice. Such information will help to form a better understanding of the pathogenesis, diagnosis and management of allergic diseases in the Tropics. As expected, we found particularities in the Tropics that merit further study because they strongly affect the natural history of common allergic diseases; most of them related to climate conditions that favor permanent exposure to mite allergens, helminth infections and stinging insects. In addition, we detected several unmet needs in important areas which should be investigated and solved by collaborative efforts led by the emergent research groups on allergy from tropical countries.

Cockroach allergy and allergen-specific immunotherapy in asthma: potential and pitfalls

PURPOSE OF REVIEW

To provide a summary and discussion of cockroach allergy and clinical trials of cockroach allergen immunotherapy.

RECENT FINDINGS

Cockroach allergen exposure among sensitized children is increasingly recognized as a key factor contributing to asthma morbidity. Recent trials suggest that cockroach immunotherapy holds promise as a treatment strategy with studies demonstrating immunomodulatory and clinical effects. However, a few obstacles need to be overcome to realize the full potential of this treatment modality as cockroach-allergic patients often exhibit complex sensitization patterns to multiple cockroach-associated proteins, and an immunodominant allergen has not been identified. These factors have made it difficult to produce standardized cockroach allergen extracts that are potent and provide the broad allergen profiles needed for optimal treatment. There have been important advances in the identification and cloning of cockroach allergens, and several strategies are being developed to provide therapeutic cockroach allergen products with enhanced clinical efficacy.

SUMMARY

Allergen immunotherapy has the capability of modulating the immune response to cockroach allergen and has potential as a valuable treatment modality. Further studies of the clinical efficacy, along with the development of improved therapeutic products, are needed to advance our knowledge and realize the full potential of this promising therapy.

Bla g 3: a novel allergen of German cockroach identified using cockroach-specific avian single-chain variable fragment antibody

BACKGROUND

The IgE response to cockroach allergens is thought to be associated with asthma. German cockroach (GCr) allergen extract is a complex mixture of allergens, and the identification and characterization of immunodominant allergens is important for the effective diagnosis and treatment of GCr-induced asthma.

OBJECTIVE

To characterize a novel GCr allergen homologous to the American cockroach allergen Per a 3.

METHODS

GCr-specific avian monoclonal antibodies were used for direct immunoprecipitation of specific targets from whole-body GCr extract. Precipitated protein was identified by mass spectrometry and sequence analysis. Putative recombinant protein also was expressed, purified, and used for determination of allergenicity, determined by IgE enzyme-linked immunosorbent assay with serum from 61 GCr-allergic patients. The identified target also was analyzed for heat stability using a bead-based assay.

RESULTS

The immunoprecipitated target of monoclonal antibody 2A1 was identified as a novel allergen of GCr homologous to American cockroach allergen Per a 3. This homolog, designated Bla g 3, has an apparent mass of 78 kDa, can be measured in GCr extract using antibody 2A1, and is a heat-stable protein. Screening of 61 serum samples from GCr-allergic patients showed a 22% prevalence of Bla g 3-specific IgE.

CONCLUSION

Bla g 3 is a GCr allergen with structural homology to American cockroach allergen Per a 3.

Achieving and maintaining asthma control in inner-city children

BACKGROUND

Despite guidelines-defined care, inner-city children of low socioeconomic status have poor asthma control.

OBJECTIVE

This study evaluated time to achieve control, maintenance of control, and factors associated with well controlled asthma for pediatric patients receiving specialty-based asthma care in mobile asthma clinics designed to reduce barriers to delivering effective asthma care (the Breathmobile Program).

METHODS

Existing clinical data collected from January 1998 to June 2008 for 7822 pediatric patients with asthma (34,339 visits) enrolled in similarly structured mobile asthma programs across the United States evaluated the effect of asthma control on the reduction of asthma-related morbidity, time to achieve asthma control, maintenance of asthma control, and factors associated with well controlled asthma.

RESULTS

Comparison of pre and post year data for subjects enrolled in the program for at least 1 year revealed reductions in the percentage of patients reporting emergency department visits (mean, 66%), hospitalizations (mean, 84%), and missed school days ≥5/year (mean, 78%). Well controlled asthma was achieved by visit 3 for an estimated 80% of patients. Factors contributing to well controlled asthma include non-African American race, visit interval <90 days, and adherence to prescribed therapy.

CONCLUSION

This study demonstrates the ability to achieve and maintain asthma control in high-risk populations in association with intensive, accessible, guidelines-defined care with close follow-up.

Prevalence of allergic rhinitis in 3-6-year-old children in Wuhan of China

BACKGROUND

Only a few prevalence studies of allergic rhinitis (AR) have been reported in China. This study aimed to evaluate the prevalence of AR in a population of 3-6-year-old children in Wuhan, China.

METHODS

Sixteen kindergartens in Wuhan City were randomly selected; for each kindergarten, there were three classes from three grades (top, middle and bottom grade, 3-6 years old, respectively). Questionnaires generated by the authors were distributed and filled out by parents of the selected children, with a telephone interview subsequently. Skin prick test (SPT) was carried out on the children after a written consent was signed by the parents.

RESULTS

A total of 1211 (89.5%) valid questionnaires were returned for evaluation. The adjusted current prevalence of AR in 3-6-year-old children was 10.8% with the diagnostic criterion of nasal symptoms(+) and SPTs(+). In the SPTs(+) children, the most common inhalant allergen was house dust mites (94.7%), followed by moulds (28.4%). The prevalence of AR was higher in males than that in females (13.0% vs. 7.7%, P < 0.05). 15.8% and 23.2% of AR children were sensitive to egg and milk, respectively. The percentage of children sensitive to both inhalant and food allergens was 27.4%.

CONCLUSIONS

We found an unexpectedly high prevalence of diagnosed AR in 3-6-year-old children within the investigated population. Dust mite was the most important allergen source for 3-6-year-old children in Wuhan.

Morphology and three-dimensional reconstruction of the digestive system of Periplaneta americana

A three-dimensional (3-D) model of the digestive system of Periplaneta americana was built for the first time based on hematoxylin and eosin (H&E) staining, the study of multiple cross-sections of the larval cockroach, and 3-D reconstruction technology. The digestive system of P. americana includes the foregut, midgut, and hindgut and takes up most of the celom. The foregut comprises almost one half of the digestive system (43.57%). The midgut, the critical region for digestion and absorption, has the second highest volume ratio (35.21%). The hindgut, with the lowest volume ratio (21.22%), includes the ileum, colon, and rectum. After the ileal valve is the colon. The 3-D model presented in this paper provides a stereoscopic view for studying the adjacent relationship and arrangement of different gut sections of P. americana.

Occupational health risks due to shipboard cockroaches

OBJECTIVES

In various investigated populations, sensitization to cockroaches was observed in 8% of screened subjects from temperate climatic zones and in 36% of those from tropical zones. Because of the numerous hiding places and food storages aboard a ship the crews can be highly exposed to cockroaches. The aim of this study is to assess the prevalence of sensitization to cockroaches and potentially associated health risks in seafarers.

METHODS

In July 2005, a total of 145 seamen sailing under the German flag were recruited from a medical surveillance program for a cross-sectional study (response 95.4%). A standardized interview and a skin prick test (SPT) with nine common inhalant allergens and a cockroach extract (Blatella germanica) were performed. In cockroach-sensitized seafarers total and cockroach-specific IgE was measured and lung function tests conducted.

RESULTS

In total, 39 seamen (26.9%) were cockroach-sensitized according to SPT results. Presence of cockroach sensitization in seamen from the tropical zone (37.3%) was significantly higher than in seamen from the temperate zone (21.3%) (odds ratio 2.20, 95% confidence interval 1.04-4.66). The prevalence of sensitization to any of the other nine common allergen mixtures tested was lower (between 2.1 and 12.4%). Neither current or past cockroach exposure on board nor cumulative cockroach exposure and time since last cockroach exposure were associated with cockroach sensitization. Among cockroach SPT-positive seamen, cockroach-specific IgE was detected in 52.8%. Five out of 37 (13.5%) SPT-positive seamen exhibited an obstructive ventilation pattern. The prevalence of work-related atopic symptoms was 9.0% (n = 13). These symptoms were not related to cockroach sensitization.

CONCLUSION

The high prevalence of sensitization to cockroaches among seamen in the presented study emphasizes the strong sensitization potency of these insects. Longitudinal studies and bronchial cockroach challenge tests are necessary to assess the clinical relevance of cockroach sensitization aboard a ship in more detail.

Structural biology of allergens

Major allergens may have special aerobiological properties and allergenic structures. It would also be instructive to consider the properties of nonallergens and nonallergenic responses. In some cases, nonallergenic responses appear to result from a lack of antigenicity and in others from regulation. Proteolytic activity has been proposed as an adjuvant for allergenicity, but lipid binding is far more common and is found for more than 50% of the major allergens. Such structures can enhance allergenicity via Toll-like receptor (TLR) or CD1 pathways. TLR signaling can enhance both Th1 and Th2 responses and be induced by peptides as well as nonproteinaceous ligands.

Allergic rhinoconjunctivitis: epidemiology

Allergic rhinoconjunctivitis has been studied much less frequently than asthma using epidemiologic approaches. Population-based studies are difficult to conduct because of misclassification arising from the reliance on self-reported questionnaires that use terms such as allergic rhinitis or hay fever to establish the diagnosis. In addition, many epidemiologic studies focus on diagnostic skin testing or allergen-specific IgE antibodies (RASTs) as an objective outcome to assess for hay fever. These techniques are helpful but not perfect measures for predicting hay fever outcomes in epidemiologic studies. It is generally accepted, however, that allergic rhinoconjunctivitis is one of the most common of chronic diseases and is the most common atopic disorder. This article reviews the definition of allergic rhinoconjunctivitis, the epidemiology of this disorder from infancy into adulthood, and environmental risk factors for development of sensitization to certain allergens.

Specific IgE and IgG antibody-binding patterns to recombinant cockroach allergens

BACKGROUND

The specificity of serum antibody responses to different cockroach allergens has not been studied.

OBJECTIVE

We sought to quantitate serum IgE and IgG antibodies to a panel of purified cockroach allergens among cockroach-sensitized subjects.

METHODS

IgE antibodies to recombinant cockroach allergens (rBla g 1, rBla g 2, rBla g 4, rBla g 5, and rPer a 7) were measured in sera containing IgE antibodies to Blattella germanica extract (n = 118) by using a streptavidin CAP assay and a multiplex flow cytometric assay. Specific IgG antibodies were determined by using radioimmunoprecipitation techniques.

RESULTS

Specific IgE antibodies measured by means of CAP assay and multiplex assay were strongly correlated ( r = 0.8, P < .001). The sum of IgE antibodies (in international units per milliliter) against all 5 allergens equated to IgE antibodies to cockroach extract. Although the prevalence of IgE antibodies was highest for rBla g 2 (54.4%) and rBla g 5 (37.4%), patterns of IgE antibody binding were unique to each subject. Surprisingly, only 16% of cockroach-sensitized subjects with IgE antibodies to house dust mite exhibited IgE antibody binding to cockroach tropomyosin (rPer a 7). Specific IgE antibodies were associated with increased IgG antibody levels, although detection of IgG in the absence of IgE was not uncommon.

CONCLUSION

The techniques described offer a new approach for defining the hierarchy of purified allergens. IgE antibodies directed against 5 allergens constitute the majority of the IgE antibody repertoire for cockroach. Such distinct patterns of IgE-IgG responsiveness to different cockroach allergens highlight the complexity of B-cell responses to environmental allergens.

Addressing the prevalence of respiratory allergy in the home environment

Respiratory allergy prevalence has always depended both on genetic predisposition and specific environmental allergenic stimulation that leads to sensitization and eventual symptomatic disease. Changes brought about by modern technology that have afforded a higher quality of life have also accidentally increased the levels of many respirable and ingestible allergens in the environment. In many cases these higher levels of exposure have exceeded individual thresholds, resulting in the phenotypic expression of allergy in many individuals who were previously asymptomatic even though they were genotypically predisposed to developing allergies. Prevalence can be decreased only if susceptible populations are identified as early as possible through careful family history taking and appropriate testing for sensitivity and if exposure to selected allergens is controlled.

Indoor allergen exposure in the development of allergy and asthma

Research evidence supports a causative relationship between indoor allergen exposure and the development of asthma. Epidemiologic studies demonstrate that exposure to indoor allergens, particularly house-dust mites and cockroaches and, to a lesser extent, animal allergens and mold, is a risk factor for the development of sensitization and perhaps respiratory symptoms. Sensitization to indoor allergen is clearly a major risk factor for the development of asthma and allergy. There is also epidemiologic and experimental evidence that, in sensitized subjects, higher exposure to indoor allergen causes morbidity. Most, but not all, prospective studies support the causative link between allergen exposure and asthma. Additional evidence comes from the prevention studies, in which reduction in indoor allergen exposure may lead to improvement in symptoms, pulmonary function, and bronchial hyperresponsiveness, and, if practiced, in early years of life, perhaps the development of asthma and allergy.