Three sera from ragweed-sensitive patients were fractionated by chromatography on DEAE cellulose columns and gel filtration. It was confirmed that the reaginic activity in the chromatographic fractions did not parallel γA-globulin concentration. The γA-globulin fractions from the same sera contained reaginic activity. When the γA-globulin preparations were further fractionated by chromatography on DEAE cellulosc columns, the reaginic activity was concentrated into one of the three subfractions. The precipitation of γA-globulin in the subfraction and the original γA-globulin preparation with rabbit anti-γA-globulin antibody was not accompanied by any detectable decrease of reaginic activity. The results indicated that the reaginic activity in the fractions was not associated with γA-globulin, but with impurities which were not detected by immunodiffusion methods. The subfractions of the γA-globulin preparation from a ragweed-sensitive patient blocked passive sensitization of normal human skin with reaginic antibody of a heterologous system. The blocking activity of the fractions paralleled the sensitizing activity against ragweed-pollen extract. It was also found that a fraction containing reagin but no detectable γA-globulin had a definite blocking activity, whereas γA-myeloma proteins did not. These findings suggest that both the blocking activity and reaginic activity are associated with the same protein other than γA-globulin.
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