Human Diphtheria Antitoxin in Immunoglobulin Classes IgG and IgA

Abstract

Diphtheria antitoxin that could be attributed to each immunoglobulin class (γG, γA and γM) in human sera was measured using radioiodinated diphtheria toxoid. Soluble toxoid-antitoxin complexes were formed, following which each immunoglobulin was precipitated with rabbit antisera specific for that class. Comparisons of the antigen-binding activity with toxin-neutralizing and hemagglutinating activities of the same samples indicated that the antitoxin associated with γG- and γA-globulins can quantitatively be measured by the technique. The kinetics of the response to immunization were studied by measuring antigen-binding activity of γG and γA antitoxins. In general, γG and γA antitoxins appeared in circulation at the same time after the immunization but there was no correlation between the concentration of the immunoglobulins and antitoxin belonging to the proteins. In addition, γA antitoxin was fractionated into polymer and monomer fractions; results of studies on these fractions suggested a preponderance of antitoxin activity associated with the polymer form of γA-globulin.