EXTRAORDINARY STABILITY OF IGE-BINDING PARIETARIA POLLEN ALLERGENS INRELATION TO CHEMICALLY BOUND FLAVONOIDS

It is known that the skin-active and IgE-binding components in Parieta ria pollen extracts are not restricted to the predominant protein alle rgens of M-r 12 000-15 000, but are present as well among the naturall y occurring constituents of M-r < 10 000. Indeed, the IgE-binding Pari etaria pollen components are quite heterogeneous, ranging from high- t o low-molecular mass, whereby the IgE-binding epitopes display an unus ual chemical stability. Furthermore, the pollen of Parietaria species demonstrably contain a high proportion of flavonoid pigments. Since th ese pollen grains cannot be collected entirely free from non-pollen pl ant parts, the usual allergenic extracts of Parietaria encompass both the polyphenolic substrate molecules and the enzyme polyphenoloxidase as ingredients for the oxidative generation of flavonol-protein conjug ates during the extraction process. In the present work this is illust rated by spectroscopic analyses of the free and bound flavonoids in Pa rietaria pollen extracts, as well as of the peptide fragments produced from the allergenic proteins by enzymatic or chemical hydrolysis. Non e of these relatively harsh treatments had a significant effect on the IgE-binding properties of the allergenic (sub-)components, even thoug h detectable proteins in isoelectric focusing and immunoblotting were lost. It is proposed that the extraordinary stability of IgE-binding P arietaria components over a wide molecular range may be attributed to chromophoric flavonoid side-chains as (parts of) the corresponding B-c ell epitopes. (C) 1997 Elsevier Science Ltd.