Immunoautoradiographic and protein-A/gold labelling experiments for localization of pollen allergens using antisera...

Using serum from human atopic individuals with a sufficiently high titre of IgE and IgG antibodies to birch- or hazel-pollen allergens and antigens, the localization of IgE binding sites in birch- and hazel-pollen grains was determined by pre- and post-embedding electron microscopic immunoautoradiography with 125I-anti-IgE, whereas the IgG binding sites were localized in ultrathin sections of birch-pollen grains by the protein-A/gold technique. Concerning the distribution patterns of both IgE/IgG binding sites within the pollen grains, no difference could be observed in the dormant pollen grain: Labelling was found in the exine part of the pollen wall and throughout the highly condensed cytoplasm except for starch grains and lipid droplets. The intine part and the germination pores were almost completely unlabelled. In pollen grains which had been soaked in a hypotonic buffer for 15 min, however, IgE binding sites were predominantly localized within the intine and the germination pores. The specificity of the labelling reactions and the observed differences in the localization patterns are discussed.