Characterization of the 18-kDa apple allergen by two-dimensional immunoblotting and microsequencing.

A low-temperature extract taken from Golden Delicious apples was separated by two-dimensional polyacrylamide gel electrophoresis. By means of two-dimensional immunoblotting with patients' serum containing IgE specific to Bet v I, a rabbit polyclonal antiserum raised against Bet v I, and two Bet v I specific monoclonal antibodies, epitopes cross-reactive to Bet v I were identified on an apple allergen with a molecular mass of 18 kDa and pI 5.5. Furthermore, certain antibody reactivities with 4 isoproteins of a molecular mass of 16 kDa and pIs ranging from 4.9 to 5.5 were observed, which may indicate the presence of Bet v I related epitopes on these proteins. Based on 26 amino acid residues, N-terminal sequencing of the 18-kDa apple allergen revealed 62% sequence identity between Bet v I from birch pollen and the apple allergen. Our results therefore support the view that both proteins express common as well as non-related IgE-reactive epitopes.