Sensitization to grass pollen allergen molecules in a birth cohort-natural Phl p 4 as an early indicator of grass pollen allergy.

BACKGROUND: Grass pollen allergy is one of the most common allergies worldwide. OBJECTIVE: The aim of this study was to evaluate the usefulness of grass pollen allergen molecules for prediction of grass pollen allergy during childhood and up to adolescence. METHOD: Questionnaire data and sera obtained from the study subjects at the ages of 4, 8, and 16 years from the population-based Barn/Children Allergy Milieu Stockholm Epidemiology birth cohort were used. Sera from 763 representative subjects with serum samples available at all 3 ages were analyzed for IgE reactivity to 8 Phleum pratense (Phl p) allergens (MeDALL [Mechanisms for the Development of Allergies] chip) and to timothy grass extract (ImmunoCAP). Allergic rhinitis to grass pollen (ARg) was defined as upper airway symptoms during grass pollen exposure. RESULTS: The prevalence of sensitization to any Phl p molecule was higher compared with that to timothy extract at all 3 ages: at the age of 4 years, 9.7% versus 6.8%; at the age of 8 years, 28.4% versus 15.3%; and at the age of 16 years, 37.1% versus 27.1%. General estimating equations analyses revealed that among children sensitized at the age of 4 years, the overall odds ratio (OR) of later ARg (up to 16 years) was increased only for IgE reactivity to Phl p 1 (OR = 4.9) and natural Phl p 4 (OR = 6.9). The likelihood of later symptoms increased with the number of allergen molecules; at the age of 4 years, 2 or more molecules predicted ARg to 78% and 3 or more molecules predicted ARg to 95%. A positive test result for timothy extract predicted ARg to 70%. CONCLUSIONS: Natural Phl p 4 is a hitherto unrecognized early indicator of grass pollen allergy, in addition to Phl p 1. To identify grass pollen sensitization and predict later ARg, allergen molecules are of added value to timothy extract alone and may help clinicians improve prediction of grass pollen allergy.

Crystal structure and immunologic characterization of the major grass pollen allergen Phl p 4.

BACKGROUND: Phl p 4 is a major pollen allergen but exhibits lower allergenicity than other major allergens. The natural protein is glycosylated and shows cross-reactivity with related and structurally unrelated allergens. OBJECTIVE: We sought to determine the high-resolution crystal structure of Phl p 4 and to evaluate the immunologic properties of the recombinant allergen in comparison with natural Phl p 4. METHODS: Different isoallergens of Phl p 4 were expressed, and the nonglycosylated mutant was crystallized. The specific role of protein and carbohydrate epitopes for allergenicity was studied by using IgE inhibition and basophil release assays. RESULTS: The 3-dimensional structure was determined by using x-ray crystallography at a resolution of 1.9 Å. The allergen is a glucose dehydrogenase with a bicovalently attached flavin adenine dinucleotide. Glycosylated and nonglycosylated recombinant Phl p 4 showed identical inhibition of IgE binding, but compared with natural Phl p 4, all recombinant isoforms displayed a reduced IgE-binding inhibition. However, the recombinant protein exhibited an approximately 10-fold higher potency in basophil release assays than the natural protein. CONCLUSION: The crystal structure reveals the compact globular nature of the protein, and the observed binding pocket implies the size of the natural substrate. Plant-derived cross-reactive carbohydrate determinants (CCDs) appear to reduce the allergenicity of the natural allergen, whereas the Pichia pastoris-derived glycosylation does not. Our results imply yet undescribed mechanism of how CCDs dampen the immune response, leading to a novel understanding of the role of CCDs.