Mosquito allergy: Immunological aspects and clinical management.

Mosquito allergy has been conceived as the cutaneous reactions that appears during and after mosquito biting process; a perception that is supported by several scientific research. Additional data have led to conceive that other manifestations of allergic responses may occur as a cause of the exposure to somatic mosquito allergens. Two main phenotypes of mosquito allergy are identifiable: the cutaneous allergic reactions, induced by salivary allergens, and other manifestations of the allergic responses such as asthma and allergic rhino conjunctivitis that are caused by somatic allergens. The cutaneous reactions have kept the focus of attention of the scientific community. It appears as skin lesions that resembles the phenotype of papular urticaria with a defined natural history of the disease. Although these two phenotypes of mosquito allergy seem to be well differentiated in terms of the allergens that are involved and the routes of exposures, other factors such as geographical distribution, may participate. Mosquitoes have adapted to the host immune response against bites, producing immunomodulatory molecules that counteract such defensive response. The role that the immunomodulatory molecules have on the allergic immune response has not been studied yet and it is still not known if affects all mosquito allergy phenotypes. Only a few studies of allergen specific immunotherapy for cutaneous allergic reactions induced by mosquito bites have been done, and none for respiratory allergic responses. The clinical practice focuses on symptom management and avoiding mosquito bites as much as possible. Avoiding mosquitoes, using different well described methods, is still the best option to limit contact with these insects. The lack of knowledge of mosquito allergy have raised several questions that affects the clinical management of this allergic disease, from its diagnosis, prevention and immunotherapy.

Nasal Provocation Challenges with Aedes aegypti Whole-Body Extract Induces Allergic Rhinitis.

BACKGROUND: Exposure to mosquitoes in the Tropics is perennial, and their somatic and saliva antigens have shown IgE binding capacity, although it is not clear whether this is due to cross-reactivity or primary sensitization. Inhalation of these allergens could trigger an allergic response. OBJECTIVE: The aim of the study was to evaluate the clinical relevance of sensitization to Aedes aegypti in a group of patients with allergic rhinitis. METHODS: A cross-sectional study with allergic rhinitis subjects and healthy controls sensitized to mosquito extract was performed. Sensitization to mosquito and house dust mites was evaluated using skin prick test (SPT) and antibody determination by ELISA. Nasal provocation test (NPT) with whole-body extract was used to determine clinical relevance. RESULTS: Allergic rhinitis patients were more sensitized to mosquito extract than controls with (+) SPT (66.6% vs. 7.6%). From these (+) SPT patients, 44.5% had (+) NPT, and just two (11%) presented mono-sensitization to mosquito. Antibody reactivity was similar between patients and controls; however, (+) NPT patients showed a tendency to had higher levels of IgE and IgG4. DISCUSSION: Mosquitoes are perennial in most tropical areas, and their body allergens could be associated with respiratory allergies.

Efficacy and safety of subcutaneous immunotherapy with a mixture of glutaraldehyde-modified extracts of Dermatophagoides pteronyssinus, Dermatophagoides farinae , and Blomia tropicalis.

Background: Allergen Immunotherapy (AIT) is an effective treatment of allergic respiratory diseases induced by the inhalation of house dust mite allergens. Objectives: To evaluate the efficacy and safety of glutaraldehyde polymerized allergen extracts using a mixture of Dermatophagoides pteronyssinus, D. farinae and Blomia tropicalis in mite allergic individuals residing in Colombia. Methods: Two hundred and fifty (250) patients with allergic rhinoconjunctivitis with, or without asthma and sensitized to D. pteronyssinus, D. farinae and B. tropicalis were included. A glutaraldehyde-modified extract containing a mixture of D. pteronyssinus, D. farinae and B. tropicalis was employed, using a cluster up-dosing schedule followed by a monthly maintenance dose. The primary endpoints to evaluate the clinical impact were the Combined Symptom and Medication Scores (CSMS) for allergic rhinitis, the Asthma Control Test (ACT) and the reduction in medication consumption. Results: Significant improvement was found after 3 months of treatment regarding CSMS (p < 0.0001) and ACT (p < 0.0001). Additionally, a significant decrease in medication consumption was found after 3 months of treatment (p < 0.0001). Adverse reactions, either local or systemic were mild and no severe reactions related to the vaccines were observed. Conclusion: After 12 months of allergen immunotherapy, glutaraldehyde-modified mixture of D. pteronyssinus, D. farinae and B. tropicalis proved to be safe and effective in the treatment of patients with rhinoconjunctivitis with or without asthma due to allergy to mites.

Mosquitoes: Important Sources of Allergens in the Tropics.

There are more than 3,000 mosquito species. Aedes aegypti, Ae. communis, and C. quinquefasciatus are, among others, three of the most important mosquito allergen sources in the tropics, western, and industrialized countries. Several individuals are sensitized to mosquito allergens, but the epidemiological data indicates that the frequency of sensitization markedly differs depending on the geographical region. Additionally, the geographical localization of mosquito species has been affected by global warming and some mosquito species have invaded areas where they were not previously found, at the same time as other species have been displaced. This phenomenon has repercussions in the pathogenesis and the accuracy of the diagnosis of mosquito allergy. Allergic individuals are sensitized to mosquito allergens from two origins: saliva and body allergens. Exposure to saliva allergens occurs during mosquito bite and induces cutaneous allergic reactions. Experimental and clinical data suggest that body allergens mediate different manifestations of allergic reactions such as asthma and rhinitis. The most studied mosquito species is Ae. aegypti, from which four and five allergens of the saliva and body, respectively, have been reported. Many characterized allergens are homologs to arthropod-derived allergens, which cause strong cross-reactivity at the humoral and cellular level. The generalized use of whole body Ae. communis or C. quinquefasciatus extracts complicates the diagnosis of mosquito allergy because they have low concentration of saliva allergens and may result in poor diagnosis of the affected population when other species are the primary sensitizer. This review article discusses the current knowledge about mosquito allergy, allergens, cross-reactivity, and proposals of component resolved approaches based on mixtures of purified recombinant allergens to replace saliva-based or whole-body extracts, in order to perform an accurate diagnosis of allergy induced by mosquito allergen exposure.

An Engineered Hybrid Protein from Dermatophagoides pteronyssinus Allergens Shows Hypoallergenicity.

The house dust mite (HDM) Dermatophagoides pteronyssinus is an important risk factor for asthma and rhinitis. Allergen specific immunotherapy that is based on recombinant proteins has been proposed for the safer and more efficient treatment of allergic diseases. The aim of this study was to design and obtain a hybrid protein (DPx4) containing antigenic regions of allergens Der p 1, Der p 2, Der p 7, and Der p 10 from this mite. DPx4 was produced in Escherichia coli and its folding was determined by circular dichroism. Non-denaturing dot-blot, ELISA, basophil activation test, dot blot with monoclonal antibodies, ELISA inhibition, and cysteine protease activity assays were performed. Mice that were immunized with DPx4 were also analyzed. We found that DPx4 had no cysteine protease activity and it showed significantly lower IgE reactivity than Der p 1, Der p 2, and D. pteronyssinus extract. DPx4 induced lower basophil activation than Der p 2 and the allergen extract. Immunized mice produced IgG antibodies that inhibited the binding of allergic patient's IgE to the allergen extract and induced comparatively higher levels of IL-10 than the extract in peripheral blood mononuclear cells (PBMC) culture. These results suggest that DPx4 has immunological properties that are useful for the development of a mite allergy vaccine.

Cellular and Humoral Responses to Cte f 2, a Cat Flea Allergen, in Children with Papular Urticaria.

BACKGROUND: Papular urticaria (PU) is a common insect bite skin hypersensitivity in tropical countries. In order to gain insight into its causal allergens, we aimed to evaluate cellular and humoral immune responses to the recombinant salivary antigen Cte f 2 from the cat flea Ctenocephalides felis. METHOD: Sixty patients with PU and 27 healthy controls were included in this study. Specific IgE, IgG, IgG1, and IgG4 against Cte f 2 and C. felis extract were determined by ELISA. The T-cell response was analyzed using a carboxyfluorescein succinimidyl ester (CFSE)-based dilution assay and Th1/Th2/Th17 cytokine measurements. In addition, a proteomic analysis of IgG and IgE reactive spots of C. felis extract was performed. RESULTS: The frequency of IgE sensitization to Cte f 2 was similar between patients (36.7%) and controls (40.7%). The specific IgE, IgG1, and IgG4 responses to Cte f 2 and C. felis extract were not significantly different between patients and controls. Among the 3 conditions (i.e., Cte f 2, C. felis extract, and only medium) Cte f 2 was the strongest inducer of CD3+CD4+ proliferation in the patients; however, the mean response was not significantly different from those in controls (Cte f 2: 4.5 vs. 2.5%; p = 0.46). No salivary proteins were identified in C. felis, and most of the spots were identified as muscle-skeletal components (tropomyosin, actin, myosin, and ankirin). CONCLUSIONS: Cte f 2 induces IgE and IgG production as well as T-cell proliferation in children living in a geographical area where PU induced by a flea bite is common. The use of C. felis extract is not recommended for the study of bite-induced hypersensitivity disease since salivary antigens are not well represented.

Characterization of a hybrid protein designed with segments of allergens from Blomia tropicalis and Dermatophagoides pteronyssinus.

BACKGROUND: Sensitization to allergens of the house dust mites Dermatophagoides pteronyssinnus and Blomia tropicalis is an important risk factor for asthma and allergic diseases. Allergen-specific immunotherapy is currently based on natural allergen extracts, however, in the last years recombinant allergens with different modifications have shown promising immunological properties that may be advantageously applied for developing novel allergy vaccines. METHODS: A hybrid molecule (MAVAC-BD-2) containing epitopes of B. tropicalis (Blo t 5, Blo t 8 and Blo t 10) and D. pteronyssinus (Der p 1, Der p 2, Der p 7 and Der p 8) allergens was constructed, expressed in Escherichia coli and purified by affinity chromatography. Its folding was analyzed by circular dichroism. Antibody reactivities were evaluated by ELISA and non-denaturing dot blot assays using a battery of sera from mite allergic patients and non-allergic subjects. ELISA inhibition and dot blot assays with monoclonal antibodies were used to detect B-cell epitopes. Human basophil activation and induction of IgG-blocking antibodies in mice immunized with the hybrid protein were also evaluated. RESULTS: MAVAC-BD-2, expressed as a 22.8 kDa protein, showed a lower frequency and strength of IgE reactivity compared to Blo t 5, Der p 1, Der p 2 and the extracts of B. tropicalis and D. pteronyssinus. MAVAC-BD-2 inhibited 26% of IgE reactivity to Der p 2 and Blo t 5, reacted with anti-Der p 1 and anti-Der p 2 monoclonal antibodies and did not induce relevant basophil activation. MAVAC-BD-2 immunized mice produced specific antibodies that reacted against mite extracts and the purified allergens, as well as IgG antibodies that blocked the human IgE reactivity to mite extracts. CONCLUSION: MAVAC-BD-2 has hypoallergenic characteristics and in mice induces IgG antibodies that block the human IgE reactivity to mite extracts.

Mammalian raw materials used to produce allergen extracts.

OBJECTIVE: To provide information about the complexity of skin-derived mammalian allergen extracts and recent advances made in their characterization and production. DATA SOURCES: Original and review articles (involving nonfood allergy to mammals) published in indexed journals were searched in the PubMed database. STUDY SELECTIONS: Studies were selected with the following criteria: novelty, species of the study, and date of publication. RESULTS: The information provided will help in the understanding and the selection of the appropriate allergen source materials for the preparation of extracts for the diagnosis and treatment of allergic respiratory diseases induced by the inhalation of skin-derived mammalian allergens. The data presented herein suggest the presence of cross-reactive and species-specific allergens in extracts prepared from different mammalian dander. Dander should be strongly considered in the preparation of allergenic extracts not only of cats and dogs but also of other mammalian species. CONCLUSION: New methods should be developed to estimate the relative quantities of specific allergens in the extracts. The current knowledge illustrates the complexity of these extracts, and more efforts should be undertaken to fully understand the wide spectrum of mammalian allergens.

Allergens involved in the cross-reactivity of Aedes aegypti with other arthropods.

BACKGROUND: Cross-reactivity between Aedes aegypti and mites, cockroaches, and shrimp has been previously suggested, but the involved molecular components have not been fully described. OBJECTIVE: To evaluate the cross-reactivity between A aegypti and other arthropods. METHODS: Thirty-four serum samples from patients with asthma and/or allergic rhinitis were selected, and specific IgE to A aegypti, Dermatophagoides pteronyssinus, Dermatophagoides farinae, Blomia tropicalis, Periplaneta americana. and Litopenaeus vannamei was measured by enzyme-linked immunosorbent assay. Cross-reactivity was investigated using pooled serum samples from allergic patients, allergenic extracts, and the recombinant tropomyosins (Aed a 10.0201, Der p 10, Blo t 10, Lit v 1, and Per a 7). Four IgE reactive bands were further characterized by matrix-assisted laser desorption/ionization tandem time of flight. RESULTS: Frequency of positive IgE reactivity was 82.35% to at least one mite species, 64.7% to A aegypti, 29.4% to P americana, and 23.5% to L vannamei. The highest IgE cross-reactivity was seen between A aegypti and D pteronyssinus (96.6%) followed by L vannamei (95.4%), B tropicalis (84.4%), and P americana (75.4%). Recombinant tropomyosins from mites, cockroach, or shrimp inhibited the IgE reactivity to the mosquito at a lower extent than the extracts from these arthropods. Several bands of A aegypti cross-reacted with arthropod extracts, and 4 of them were identified as odorant binding protein, mitochondrial cytochrome C, peptidyl-prolyl cis-trans isomerase, and protein with hypothetical magnesium ion binding function. CONCLUSION: We identified 4 novel cross-reactive allergens in A aegypti allergenic extract. These molecules could influence the manifestation of allergy to environmental allergens in the tropics.

Identification and Characterization of IgE-Binding Tropomyosins in Aedes aegypti.

BACKGROUND: The mosquito Aedes aegypti is a potential source of important clinically relevant allergens. However, the allergenicity and cross-reactivity of most of these has not been fully described. METHODS: Natural wild-type mosquito tropomyosin was purified by size exclusion and anionic-exchange chromatography from an A. aegypti extract. Further characterization was accomplished by MALDI-TOF/TOF. Two recombinant variants of tropomyosin were obtained by expression in Escherichia coli. Specific IgE measurement by ELISA and skin tests for mosquito extract were performed in 12 patients with asthma or allergy rhinitis residing on the Caribbean island of Martinique. Cross-reactivity between natural A. aegypti tropomyosin and recombinant tropomyosins from A. aegypti, house dust mite, shrimp and Ascaris lumbricoides was analyzed by ELISA competition. RESULTS: Four variants of natural tropomyosin were purified. A band of 32 kDa in SDS-PAGE representing 2 tropomyosin variants (Aed a 10.0101 and Aed a 10.0201) reacted with specific IgE of 4 of the 12 (33%) allergic patients and with rabbit polyclonal anti-shrimp tropomyosin. A high degree of cross-reactivity (60-70%) was detected between natural mosquito tropomyosin and Blo t 10, Der p 10 and Lit v 1, and a lower degree with Asc l 3 from A. lumbricoides (<30%). rAed a 10.0101 inhibited IgE binding to natural A. aegypti tropomyosin; however, rAed a 10.0201 showed a low inhibitory capacity. CONCLUSION: Tropomyosin is a new IgE-binding protein from A. aegypti. Two of the 4 variants identified showed different degree of cross-reactivity with tropomyosins from other arthropods. The potential allergenic role of each variant should be further investigated.

Immunological aspects of the immune response induced by mosquito allergens.

Allergies caused by mosquito bites may produce local or systemic reactions. The inhalation of mosquito allergens may also cause asthma and/or allergic rhinoconjunctivitis in sensitized individuals. The mechanisms implicated in the development of these immune responses involve IgE antibodies, different subtypes of IgG and proinflammatory cytokines as well as basophils, eosinophils and mast cells. Several allergenic components have been identified in the saliva and bodies of mosquitoes and some of these are present in different mosquito species. The most common species implicated in allergic reactions belong to the genera Aedes, Culex and Anopheles. Several Aedes aegypti allergens have been cloned and sequenced. The recombinant molecules show IgE reactivity similar to that of the native allergens, making them good candidates for the diagnosis of mosquito allergies. Allergen-specific immunotherapy with mosquito extracts induces a protective response characterized by a decreased production of IgE antibodies, increased IgG levels, a reduction in the severity of cutaneous and respiratory symptoms and the need for medication. The aims of this review are to summarize the progress made in the characterization of mosquito allergens and discuss the types of immune responses induced by mosquito bites and the inhalation of mosquito allergens in atopic individuals.

Nuevos esquemas de inmunoterapia específicas con alérgenos: [revisión] / New approaches for allergen-specific immunotherapy: [review]

Las enfermedades alérgicas, como el asma y la rinitis, son un problema de salud de importancia en todos los países y con una tendencia global al aumento en su prevalencia. La inmunoterapia específica con extractos alergénicos naturales es el único tratamiento con antígenos dirigido a brindar una protección duradera y que beneficia a la mayoría de la población tratada. Sin embargo, este tratamiento presenta inconvenientes porque los extractos son preparaciones de difícil estandarización y gran complejidad en sus componentes, lo que aumenta los riesgos de que se presenten reacciones adversas y nuevas sensibilizaciones a otros antígenos presentes en el extracto. Por lo tanto, se ha planteado la necesidad de desarrollar nuevos esquemas de inmunoterapia específica con el alérgeno en los que se utilicen moléculas bien caracterizadas de fácil estandarización y manejo, con las que se puedan brindar tratamientos más seguros y eficaces. Con estos nuevos esquemas se han diseñado vacunas basadas en alérgenos recombinantes y variantes o péptidos derivados de éstos, para ser administrados solos o con adyuvantes en preparaciones que favorecen la captación y presentación antigénica por las células dendríticas o tienen como blanco las células efectoras, como mastocitos y basófilos. Los estudios in vitro, en modelos animales y algunos en fase clínica en humanos, indican que estas preparaciones pueden brindar protección frente a la exposición alergénica o mejorar la sintomatología, al inducir la producción de anticuerpos bloqueadores de la actividad de la IgE, de células T reguladoras y de citocinas del perfil Th1.

Rates of allergic diseases such as asthma and rhinitis are on the rise as important health problems in every country of the world. Allergen specific immunotherapy with natural allergenic extracts is a treatment directed to changing the natural course of these diseases, and is a treatment that has reported beneficial effects in a majority of allergic patients. However, this treatment is difficult because of the complex composition of the extracts. The composition is difficult to standardize and, consequently, the risk of anaphylactic shock is increased; furthermore, sensitization can occur to other antigens present in the extract. Therefore, new allergen specific immunotherapy approaches are needed. Chemically defined and standardized antigens are more easily managed and provide a safer and more efficient treatment. Vaccines for immunotherapy have already been designed, based on recombinant allergens, variants (or peptides derived from them), that can be administrated alone or in combination with adjutants. Some of these preparations are indicated for facilitating the uptake and antigenic presentation by dendritic cells, or by targeting the mast cells and basophiles. Studies in vitro, in animal models and clinical trials in allergic patients, indicate that these preparations may provide protection against the allergen exposure and improve the symptoms by inducing the production of blocking antibodies of the IgE mediated response, production of regulator T cells and cytokines of Th1 profile.

[New approaches for allergen-specific immunotherapy]. / Nuevos esquemas de inmunoterapia específicas con alérgenos.

Rates of allergic diseases such as asthma and rhinitis are on the rise as important health problems in every country of the world. Allergen specific immunotherapy with natural allergenic extracts is a treatment directed to changing the natural course of these diseases, and is a treatment that has reported beneficial effects in a majority of allergic patients. However, this treatment is difficult because of the complex composition of the extracts. The composition is difficult to standardize and, consequently, the risk of anaphylactic shock is increased; furthermore, sensitization can occur to other antigens present in the extract. Therefore, new allergen specific immunotherapy approaches are needed. Chemically defined and standardized antigens are more easily managed and provide a safer and more efficient treatment. Vaccines for immunotherapy have already been designed, based on recombinant allergens, variants (or peptides derived from them), that can be administrated alone or in combination with adjutants. Some of these preparations are indicated for facilitating the uptake and antigenic presentation by dendritic cells, or by targeting the mast cells and basophiles. Studies in vitro, in animal models and clinical trials in allergic patients, indicate that these preparations may provide protection against the allergen exposure and improve the symptoms by inducing the production of blocking antibodies of the IgE mediated response, production of regulator T cells and cytokines of Th1 profile.