Differences in the reactivity of short and giant ragweed with immunoglobulin E antibodies

Currently, the allergens in extracts of SRW and GRW are regarded as equivalent in their ability to react with IgE antibodies. We investigated whether IgE antibodies might recognize differences between these allergens. First, sera from individuals with positive skin tests to both RWs showed higher reactivity with solid-phase SRW in the RAST. Second, immunosorption of 24 sera showed that more than 90% of the IgE antibodies were removed by either SRW or GRW Sepharose. However, all of the sera contained IgE antibodies specific for SRW and six sera contained antibodies specific for both SRW and GRW. Third, the presence of IgE antibodies preferentially reactive with SRW was tested by neutralization of the P-K test. Two individuals were passively sensitized with a serum pool containing IgE antibodies specific for SRW; skin sites were challenged repetitively with an extract of GRW until they no longer reacted with GRW. Challenge of these sites with SRW showed an immediate wheal-and-flare reaction, indicating that antibodies were present in the serum pool which could not be neutralized by GRW and, thus, were specific for SRW. These results indicate that the sera of all RW-sensitive individuals in this study contained IgE antibodies specifically reactive with SRW and many sera contained antibodies specific for GRW. Overall, however, most of the IgE anti-RW reactivity was removed by either GRW or SRW.