Immunoelectron-microscopic localization of diffusible birch-pollen antigens in ultrathin sections using the protein-A/gold technique.

Pollen grains from Betula pendula were fixed in a mixture of p-formaldehyde and cetylpyridinium chloride (CPC) for the precipitation of soluble pollen glycoproteins. After dehydration and embedding at low temperatures in the water-soluble resin, Lowicryl K4M, ultrathin sections of the pollen grains were incubated using specific antibodies against birch-pollen extract and protein-A/gold complexes. Antigen activity was found in the CPC-precipitated surface material and within the exine (bacular cavities) and the cytoplasm (except for starch grains and lipidic droplets). There was no labelling within the intine. The region of the germinal aperture also showed a very low degree of antigen activity. The control sections were almost completely free of background staining.