The percentages of six immunoglobulin isotypes in human antibodies to tetanus toxoid: Standardization of isotype-specific second antibodies in solid-phase assay

The solid-phase radioimmunoassay for human antibodies was improved so that it gave the total concentration as well as the concentrations of IgM, IgA, IgG1, IgG2, IgG3 and IgG4 antibodies, all seven in the same “L units”/ml. This was accomplished by standardization of monoclonal antibodies with monoisotypic antibodies rather than myelomas; myelomas were found unsatisfactory for this purpose. For the first time it was possible to determine the isotype composition of an antibody population in percent terms. The weight equivalent of the L-unit in one hyperimmune tetanus antitoxin preparation was approximately 7.4 ng. The new solid-phase radioimmunoassay was applied to tetanus toxoid antibodies of the booster response. Total concentrations varied from 1700–26000 L units/ml (13–200 μg/ml). Concentrations of IgG1 antibodies were 1600–25000 units/ml (average 91% of the total) and concentrations of IgG4 antibodies 12–6900 units/ml (average 6.9% of the total). Antibodies of the other four isotypes were not detected in all sera and together they never exceeded 3% of the total.