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 allergens present in various tree pollens, fruits, and vegetables represent a family of important cross-reactive allergens. Although the DNA, deduced amino-acid sequence, and structure of Bet v 1 have been determined, little is known regarding its biologic functions.

OBJECTIVE

Human monoclonal antibodies derived from an individual allergic to birch pollen were used for refined ultrastructural localization of Bet v 1 in birch pollen grains to gain information regarding the allergen distribution and its possible biologic function. These data were to be supplemented by sequence analyses.

METHODS

Ultrathin sections of anhydrously prepared birch pollen grains were incubated with human monoclonal antibodies (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, human monoclonal antibodies bound to ribosome-rich areas and to pollen nuclei. 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 proteins as nucleotide binding proteins and explains why this group of plant proteins represents highly cross-reactive plant allergens against which many type I patients are sensitized.