Characterization of the isoforms of the group I allergen of Cynodon dactylon

Background: The group I allergen of Cynodon dactylon , Cyn d I, was found to consist of four to 10 isoforms. Methods: We studied the isoforms with the use of two-dimensional gel electrophoresis. The antigenic difference of the isoforms was evaluated by radioimmunoprecipitation with monoclonal antibodies (MAbs). The acidic isoforms and the basic and neutral isoforms were further isolated by MAb-affinity chromatography for RAST and competitive RAST. In addition, the N-terminal sequence was evaluated by microsequencing. Results: A total of 11 isoforms were found in Cyn d I in extracts prepared from different sources of Bermuda grass pollen (BGP). They were either acidic ( Cyn d I-A, I-B, I-C, I-D, I-E, I-F, I-G, I-H, and I-I), neutral ( Cyn d I-X), or basic ( Cyn d I-J). Cyn d I-G, with an isoelectric point of approximately 6.4, was constantly present in all the pollen preparations, whereas the content of the basic Cyn d I-J varied from less than 5% to greater than 20%. The molecular weight of the basic and neutral isoforms were slightly lower than those of the acidic isoforms. All isoforms shared a common antigenic determinant(s) recognizable by MAb 4-37, and the basic and neutral isoforms possessed a unique antigenic determinant(s) recognizable by MAb 1-61. RAST showed that both the acidic Cyn d I and the basic and neutral Cyn d I were recognized by human IgE in the pooled sera of persons allergic to BGP. Competitive RAST showed a high crossreactivity between the acidic and the basic and neutral isoforms. A 95% sequence identity also existed between the N-terminal 20 amino acid residues of basic Cyn d I-J and the dominant acidic isoform Cyn d I-G. Conclusions: The present study disclosed that basic Cyn d I-J is an important allergen and that the content of this isoform varies in different lots of BGP. (J ALLERGY CLIN IMMUNOL 1995;95:1206-14.)