ANALYSIS OF THE 3-DIMENSIONAL ANTIGENIC STRUCTURE OF GIANT RAGWEED ALLERGEN, AMB-T-5

The ragweed allergens Amb t 5 and Amb a 5 are among the smallest inhal ed protein allergens known, containing a single, immunodominant T-cell epitope. In this study we analyzed the B-cell epitope structure of Am b t 5. The three-dimensional structures of Amb t 5 and Amb a 5 have be en determined by NMR spectroscopy, providing a rare opportunity to ana lyze three-dimensional antigenic sites. Amb t 5 residues likely to be important for antigenicity were identified by examining the surface ar ea of Amb t 5 accessible to a probe of the size of an antibody molecul e. After changing these residues to the corresponding Amb a 5 residues , recombinant proteins were purified and tested for loss of antigenic activity. Inhibition radio-immunoassays, using sera from 8 individuals who had received immunotherapy with giant ragweed extract, allowed th e mutations to be divided into three groups: (1) mutations that had li ttle or no effect on antibody binding, (2) mutations that caused a los s of antigenic activity to a different degree in different sera and (3 ) mutations that drastically reduced antigenic activity in all sera te sted. This last set of mutations clustered in the third loop of Amb t 5, suggesting that antibody recognition of Amb t 5, like T-cell recogn ition, is primarily directed towards a single, immunodominant site. (C ) 1998 Elsevier Science Ltd. All rights reserved.