Two reaginic sera from atopic patients were fractionated by chromatography on DEAE cellulose columns, and by gel filtration through Sephadex G-200 columns. The skin-sensitizing activity in the chromatographic fractions did not parallel the concentration of γD-globulin (IgD). Gamma-D globulin in the reagin-containing fractions and one of the original sera were precipitated with rabbit antibody specific for γD-globulin. Essentially all reaginic activity in the fractions and in the serum remained in the supernatants, indicating that the reaginic antibody is not γD-globulin. Comparisons were made between the reaginic antibody and human γA anti-A isoagglutinins. When anti-γA-globulin antibody was added to the mixture of the reagin-containing fraction and γA anti-A isoagglutinin, the isoagglutinin was completely precipitated, whereas all reaginic activity remained in the supernatant. In sucrose density-gradient ultracentrifugation, the reaginic antibody sedimented intermediate between polymer and monomer forms of γA-globulin antibodies. The average sedimentation coefficient of the reaginic antibody was estimated to be 8 S. The electrophoretic mobility of the reaginic antibody is slower than γA isoagglutinin in Sephadex G-25 zone electrophoresis. These findings together with our previous report1 indicate that the reaginic antibody is associated with none of the known four immunoglobulins, i.e., γG-, γM-, γA-, and γD-globulins, and suggest the presence of a fifth immunoglobulin as a carrier of reaginic activity.
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