HUMAN MONOCLONAL IGG ANTIBODIES DERIVED FROM A PATIENT ALLERGIC TO BIRCH POLLEN AS TOOLS TO STUDY THE IN-SITU LOCALIZATION OF THE MAJOR BIRCH POLLEN ALLERGEN, BET-V-1, BY IMMUNOGOLD ELECTRON-MICROSCOPY

Background: Bet v 1, the major birch pollen allergen, and related alle rgens present in various tree pollens, fruits, and vegetables represen t a family of important cross-reactive allergens. Although the DNA, de duced amino-acid sequence, and structure of Bet v 1 have been determin ed, little is known regarding its biologic functions. Objective: Human monoclonal antibodies derived from an individual allergic to birch po llen were used for refined ultrastructural localization of Bet v 1 in birch pollen grains to gain information regarding the allergen distrib ution and its possible biologic function. These data were to be supple mented by sequence analyses. Methods: Ultrathin sections of anhydrousl y prepared birch pollen grains were incubated with human monoclonal an tibodies (BAB1, BAB2, and BAB4). The binding sites were visualized in the transmission electron microscope by gold-conjugated anti-human IgG antibodies. Results: In the cytoplasm of the birch pollen grain, huma n monoclonal antibodies bound to ribosome-rich areas and to pollen nuc lei. Sequence analysis of Bet v 1 and homologous allergens identified a highly conserved p-loop motif in these proteins, which is typically found in nucleotide-binding proteins. Conclusions: Immunolocalization of Bet v 1 to ribosome-rich areas and the nucleus would be consistent with a highly conserved biologic function of Bet v 1 and homologous pr oteins as nucleotide binding proteins and explains why this group of p lant proteins represents highly cross-reactive plant allergens against which many type I patients are sensitized.