Background: Mite group 2 allergens Der p 2, Der f 2, and Eur m 2 are 14-kDa proteins of unknown function that share 83% to 85% amino acid sequence identity. Isoforms of the allergens within each genus have been identified which differ by 3 or 4 amino acids, but little is known of the influence of group 2 polymorphisms on human IgE antibody binding.
Objective: The purpose of this study was to investigate the importance of interspecies and isoform substitutions on murine mAb and IgE antibody binding and on the molecular structure of the group 2 allergens.
Methods: Site-directed mutagenesis was used to incorporate the isoform amino acid substitutions onto the Der p 2.0101 sequence. Recombinant allergens were expressed and purified from Escherichia coli and used to evaluate antibody binding by enzyme-linked immunosorbent assay (ELISA). Molecular modeling of the tertiary structure was used to analyze structural differences between the various group 2 allergens.
Results: The substitution of asparagine for aspartic acid at position 114 restored mAb binding of rDer p 2.0101; the other Der p 2 isoforms and the 3 rDer f 2 isoforms also reacted in the 2-site ELISA. The correlation of IgE binding to the Der p 2 isoforms was excellent and tended to be higher in the isoforms with the asparagine 114 substitution (r (2) = 0.87 vs r (2) = 0.95). rEur m 2.0101 bound to all mAb except 7A1; when compared with rDer p 2 for IgE binding, rEur m 2.0101 gave a correlation coefficient of r (2) = 0.68. Molecular modeling revealed that Eur m 2 and the storage mite homologs Lep d 2 and Tyr p 2 retain the tertiary fold of Der p 2. Eur m 2 has a conserved surface, whereas Lep d 2 and Tyr p 2 present most of the amino acid substitutions on this surface. Lep d 2 and Tyr p 2 did not react with mAb or with sera from patients with IgE to Dermatophagoides species.
Conclusion: The isoform substitutions of rDer p 2 can be distinguished by mAb. The allergenic cross-reactivity between Der p 2, Der f 2, and Eur m 2 is a direct result of the conserved antigenic surface, whereas the lack of cross-reactivity with Lep d 2 and Tyr p 2 is a result of the multiple substitutions across this surface.