Clinical & Experimental Allergy Reviews最新文献

Pooideae encompass both common wild and cultivated grasses, which are responsible for grass pollen exposure and sensitization in Europe. Across Europe, the pollination period of different members of this subfamily overlap and hayfever sufferers are therefore naturally exposed to a mixture of pollens from different grass species. Because of their morphological homology, Pooideae pollens are evaluated together in pollen counts and cannot be distinguished. Neither patients themselves, nor physicians can link the onset of hayfever symptoms to a specific grass species.

In Germany, specific pollen extracts are currently used for immunotherapy of rye (Secale cereale) allergy. Like most common grasses, S. cereale belongs to the Pooideae subfamily. Using sera from grass pollen-allergic patients, immunoblotting and ELISA inhibition studies demonstrate that a five-grass allergenic extract from Anthoxanthum odoratum, Dactylis glomerata, Lolium perenne, Poa pratensis and Phleum pratense inhibits over 90% of IgE binding to rye allergens. This result confirms the high degree of homology between allergens from S. cereale and common grass species. We conclude that a five-grass pollen mixture is appropriate for desensitization of patients who are allergic to rye pollen without the need for additional rye pollen extracts.

In Europe, one-third of desensitization treatments for grass pollen allergy are supplemented with a mixture of cereal pollen extracts (Triticum sativum, Avena sativa, Zea mais and Hordeum vulgare). We have re-evaluated this practice in light of the recent availability of a desensitization tablet prepared from a mixture of pollen from five common grass species (Anthoxanthum odoratum, Dactylis glomerata, Lolium perenne, Poa pratensis and Phleum pratense) from the Pooideae subfamily. Common grasses and cultivated cereals are very closely related phylogenetically, and as a consequence, their pollen exhibit a similar molecular composition. The latter is confirmed by ELISA inhibition and immunobloting experiments. Thus, immunotherapy based on a mixture of five grass pollen allows to treat patients sensitized with pollen allergens from cultivated cereals, without a need for additional cereal pollen extracts.

To date, eleven groups of grass pollen allergens eliciting a specific IgE response in atopic individuals have been identified. Groups 1 and 5 allergens are the most critical (major) pollen allergens leading to the sensitization of 90% and 65–85% allergic patients, respectively. Other allergens frequently involved in the IgE response include groups 2/3, 4, 6, 7, 10–13 allergens. Allergens found in various Pooideae exhibit high homology in terms of their amino acid sequence composition, which translates into significant cross-reactivity in terms of antibody (IgE and IgG) as well as T cell responses. Nevertheless, for a given allergen group, there is evidence of both interspecies (i.e. differences in amino acid sequences) and intraspecies (multigenes, post-translational modification, mRNA splicing or editing) molecular variability.

Grass pollen allergic patients are naturally exposed and sensitized to multiple pollens from various Pooideae species. The question arises as to whether such patients should be desensitized with extracts based on a single pollen or a pollen mixture. Neither conventional diagnosis based on IgE reactivity nor pollen counts enable the identification of which grass species are involved in patient sensitization. Significant cross-immunogenicity is observed between allergens from Pooideae pollens due to their conserved amino acid sequences (e.g. >90% for group 1, 55–80% for group 5, 30–60% for other allergens, including minor allergens). Nevertheless, pollen allergens also contain species-specific T or B cell epitopes, and there is evidence that at least 50% of allergic patients are sensitized to such distinct epitopes. In addition, substantial quantitative differences exist in the allergen (e.g. group 1, 2/3, 4, 5, 6, 10, 13) content of pollens obtained from distinct grass species. In this context, we recommend a vaccine consisting of a combination of pollens from five common and well characterized Pooideae including Anthoxanthum odoratum, Dactylis glomerata, Lolium perenne, Phleum pratense and Poa pratensis for desensitization purposes. This 5-grass mixture is recommended because, (i) it has been validated, in terms of safety and efficacy, by established clinical practice; (ii) it better reflects natural exposure and sensitization conditions at the molecular level than a single pollen; and (iii) it provides a consistent and well-balanced composition of critical allergens, while extending the repertoire of T and B cell epitopes.