rPhl p 11
Phl p 11 is an 18 kD allergen with structural similarity to the soybean trypsin inhibitor (STI) family of proteins. This class of grass pollen allergen was first described from Lolium perenne by van Ree et al. (1), who found significant levels of IgE antibodies binding to the purified native protein in 179 of 270 (66%) of grass pollen sensitized subjects. Determinants for IgE binding were found to exist on both the polypeptide chain and the carbohydrate structures of the glycoprotein. Phl p 11 shows 94% sequence identity to the homologous L. perenne protein (Lol p 11) and 33%-47% to described pollen proteins from a wider range of different plant species, including Oryza sativa, Zea mays, Betula pendula, Olea europea (Ole e 1), Syringa vulgaris (Syr v 1) and Ligustrum vulgare (Lig v 1).

 

Recombinant Phl p 11 lacks carbohydrate modification and has a calculated molecular weight of 15.8 kD. van Ree et al. (2) reported an 8% carbohydrate content of the homologous L. perenne protein. The recombinant P. pratense allergen, which represents the polypeptide chain of the natural allergen, appears to bind IgE from approximately one-quarter of grass pollen allergics.

Single components from timothy grass, Phleum pratense, are available for specific IgE testing, produced either with recombinant technique or as purified native proteins. As an alternative the next generation of immunotherapy may be based on recombinant allergen components, possibly modified to reduce the risk of anaphylaxis. If the sensitization profile to e.g. timothy is known, only those components to which the patient is actually sensitized should be relevant for therapy. This would eliminate the risk that the therapeutic reagent induces IgE antibodies to additional components. The single components of timothy in specific IgE tests may also be used for monitoring immunotherapy with the natural extract.

rPhl p 7,  a two-EF-hand Ca2+-binding protein is likely to cross-react with pollen proteins from most plants, in particular with other grass species, trees of the Fagales order, olive and weeds. rPhl p 12;  profilin from timothy is a so-called pan-allergen that may be involved in cross-reactivities seen between many different plants, including plant-derived foods (examples of other profilins: Hev b 8 = profilin in Latex (Hevea braziliensis), Bet v 2 = profilin in Birch (Betula verrucosa)). However, both rPhl p 7 and rPhl p 12 have shown to be minor allergens and the clinical consequence of the speculated cross-reactivity with other plants is probably not of major importance, but cannot be excluded.