The allergenic and antigenic properties of three "purified" fractions of ragweed pollen, pool C, fraction IV2, and Delta, prepared in separate laboratories by different techniques were investigated. Gel diffusion studies indicated that none of the fractions contain only one antigen. However, it appears that a number of antigens in whole ragweed extract have been reduced or eliminated in the preparation of these materials. Positive indirect hemagglutination reactions were produced in higher titers and with a greater number of sera from untreated ragweed-sensitive patients with each of the three fractions than with whole ragweed extract. The Delta fraction was most potent in eliciting hemagglutination. Pool C reacted in highest titer with most sera. Hemagglutination inhibition data suggest that all of the necessary hemagglutinating antigens are present in each fraction, but there are some quantitative differences. Each of the fractions was more skin reactive than whole ragweed extract. In vitro neutralization of reagin indicated that each of these fractions probably contained, in variable amounts, all of the allergens in whole ragweed extract. However, the in vivo neutralization studies suggested that only Delta contains most, if not all, of the allergens present in whole ragweed extract and that some of these allergens have been climinated or markedly diminished in the process of preparing pool C and fraction IV2.
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