Cross-reactivity of plant and animal allergens

Cross-reactivity of pollen allergens: impact on allergen immunotherapy

OBJECTIVE

To provide guidelines for the rational formulation of allergen immunotherapy extracts based on knowledge of pollen allergen and epitope cross-reactivity.

DATA SOURCES

A PubMed search was performed for articles published from 1966 to 2007 using the keywords pollen, allergen, and cross-reactivity. Older literature was found through cross-referencing of older articles and older reviews on pollen cross-reactivity.

STUDY SELECTION

Articles that dealt with crude pollen extracts and characterized allergens that addressed cross-reactivity were selected for inclusion in this review.

RESULTS

In addition to unique allergens, several families of botanic proteins have similarities that allow them to act as pan-allergens. Although frequently these are minor allergens, in some circumstances they may also be major allergens. Recent studies have investigated nonspecific lipid transfer proteins, calcium-binding proteins, pathogenesis-related protein families, and profilins. Calcium-binding proteins and nonspecific lipid transfer proteins are responsible for pollen-fruit interactions and pollen cross-reactivity. Clarification of pollen allergen enzymatic activity helps explain the ubiquitous nature of these proteins.

CONCLUSION

Characterization of specific pollen allergens and their protein families has provided insight into cross-reactivity. Clarification of these relationships allows for consolidation or substitution in formulation of inhalant extracts.

Characterization of genes for a pollen allergen, Cry j 2, of Cryptomeria japonica

BACKGROUND

Cry j 2 is one of the major pollen allergens of Cryptomeria japonica. The polymorphism of Cry j 2 isoforms and the conservation of the structure of Cry j 2 in coniferous species remain to be analyzed.

METHODS

A cDNA library derived from the pollen of C. japonica was screened using a fragment of Cry j 2 cDNA. Restriction fragment length polymorphism analysis was performed to examine the diversity of Cry j 2 genes. The promoters of Cry j 2 genes were isolated with a commercially available cloning kit. Clonal variations in the expression of Cry j 2 in pollen were examined by RNA gel blot analysis, and the conservation of the structure of the Cry j 2 gene in coniferous species was evaluated by DNA gel blot analysis.

RESULTS

We isolated three cDNA clones encoding novel isoforms of Cry j 2. We also sequenced a total of 16 promoter regions from 10 specimens. The sequences of promoter regions of Cry j 2 genes were highly divergent. The amount of Cry j 2 mRNA also varied considerably. The Cry j 2 gene was found to be conserved among species belonging to Taxodiaceae and Cupressaceae but to vary between Taxodiaceae and Pinaceae.

CONCLUSIONS

The coding and promoter regions of Cry j 2 genes contain large numbers of polymorphisms. Our analysis revealed large variations in the expression of Cry j 2 at the transcriptional level, and we suggest that conserved homologs of Cry j 2 confer cross-allergenicity among Taxodiaceae and Cupressaceae.

Computational detection of allergenic proteins attains a new level of accuracy with in silico variable-length peptide extraction and machine learning

The placing of novel or new-in-the-context proteins on the market, appearing in genetically modified foods, certain bio-pharmaceuticals and some household products leads to human exposure to proteins that may elicit allergic responses. Accurate methods to detect allergens are therefore necessary to ensure consumer/patient safety. We demonstrate that it is possible to reach a new level of accuracy in computational detection of allergenic proteins by presenting a novel detector, Detection based on Filtered Length-adjusted Allergen Peptides (DFLAP). The DFLAP algorithm extracts variable length allergen sequence fragments and employs modern machine learning techniques in the form of a support vector machine. In particular, this new detector shows hitherto unmatched specificity when challenged to the Swiss-Prot repository without appreciable loss of sensitivity. DFLAP is also the first reported detector that successfully discriminates between allergens and non-allergens occurring in protein families known to hold both categories. Allergenicity assessment for specific protein sequences of interest using DFLAP is possible via ulfh@slv.se.

Comparison of the skin test and ImmunoCAP system in the evaluation of mold allergy

BACKGROUND

Mold is ubiquitous in our environment and is a common allergen in allergic diseases. The skin test and the Pharmacia ImmunoCAP system (CAP) for assay-specific immunoglobulin E (IgE) antibodies are both widely used. The goal of this study was to compare the performance of the skin test and CAP in the evaluation of mold allergy.

METHODS

Patients with allergic rhinitis were enrolled at our outpatient department. The diagnosis of allergic rhinitis was based on typical symptoms for more than 2 years. All patients were tested by both intradermal skin test and serum assay for specific IgE antibodies. The skin test included house dust, cotton, ragweed, and 5 fungal antigens (Candida, Alternaria, Aspergillus, Cladosporium, and Penicillium). The serum-specific IgE antibodies were quantified using the radioimmunoassay version of CAP.

RESULTS

Seventy-five patients (44 males and 31 females) with allergic rhinitis were enrolled in this study. Their ages ranged from 12 to 76 years old, with a mean of 31.9 years. The positive rates of skin test and CAP were 56.0% versus 9.3% for Candida, 22.7% versus 1.3% for Alternaria, 16% versus 9.3% for Aspergillus, 14.7% versus 1.3% for Cladosporium, and 32% versus 8% for Penicillium. There were statistically significant differences between the positive rates for Candida, Alternaria, Cladosporium, and Penicillium when analyzed by the McNemar test.

CONCLUSION

The positive rate of the skin test is higher than CAP when evaluating mold allergy. Clinicians should note that a discrepancy may exist between the results of in vitro and in vivo tests when evaluating mold allergy.

Lack of correlation between regional pollen counts and percutaneous reactivity to tree pollen extracts in patients with seasonal allergic rhinitis

BACKGROUND

Although seasonal patterns of tree pollination have been reported, it is unknown if aerobiologic data correlate with patterns of in vivo sensitization.

OBJECTIVE

To evaluate the relationship between regional tree pollen exposure and patterns of in vivo percutaneous reactivity to specific tree pollen extracts in a local patient population with seasonal allergic rhinitis.

METHODS

Patients with spring seasonal allergic rhinitis and percutaneous sensitivity to 1 or more regional tree pollens were studied. Tree pollen counts were collected at the same urban site from 1997 to 2002 and at a suburban site in 2002. Patients underwent skin prick testing with commercial extracts of 15 indigenous tree species. Serum specific IgE measurements were assayed in a subset of sensitized patients.

RESULTS

Of 127 patients who reported symptoms consistent with seasonal allergic rhinitis during the spring pollen season, 93 qualified based on demonstration of at least 1 positive skin prick test result. Mean 5-year pollen counts (1997-2001) and 2002 urban counts were highly correlated (Spearman r = 0.95, P < .001), indicating that year-to-year pollen counts were consistent. No significant correlation was found between mean seasonal pollen counts (urban site, 1997-2001) and frequencies of skin prick test reactivity to specific tree pollen allergens (Spearman r = -0.03, P = .93). No significant relationship was found between 5-year mean tree pollen counts and positive serum specific IgE tests for specific tree pollens (Spearman r = -0.42, P = .30). Eight of 15 species elicited percutaneous reactions in more than 50% of patients (ie, satisfying definition of a major in vivo allergen). However, 6 of the 8 major tree allergens each represented 5% or less of 5-year mean total tree pollen counts.

CONCLUSION

No correlation was found between overall frequencies of in vivo sensitization to tree pollen allergens in a local population and regional pollen exposure data.

Cross-reactivity of pollen allergens

Pollen cross-allergenicity has practical implications on the management of inhalant allergy, in both evaluation and therapy, especially with allergen vaccine immunotherapy. The study of cross-reactivity among pollen allergens has expanded beyond investigation of crude extracts to the characterization and cloning of numerous pollen proteins. In this review, the interrelationships between these pollen allergens in the context of botanical systematics are examined, to provide a framework for cross-reactivity understanding. Recommendations for choices in evaluation and therapy are given.