SIMULTANEOUS QUANTITATION OF DIPHTHERIA AND TETANUS ANTIBODIES BY DOUBLE ANTIGEN, TIME-RESOLVED FLUORESCENCE IMMUNOASSAY

A dual, double antigen, time-resolved fluorescence immunoassay (DELFIA ) for the simultaneous detection and quantitation of diphtheria (D) an d tetanus (T) antibodies in sera has been developed, In the double ant igen format one arm of the antibody binds to antigen coated microtitre wells and the other arm binds to labelled antigen to provide a fluore scent signal. This assay was found to be functionally specific for IgG antibodies and showed a good correlation with established toxin neutr alization assays, Furthermore, the double antigen set-up was species i ndependent, permitting the direct use of existing international refere nces of animal origin to measure protective antibody levels in humans in international units (IU/ml). The detection limit corresponded to 0. 0003 IU/ml with Eu3+-labelled toxoids and to 0.0035 IU/ml using Sm3+-l abelled toxoids. The assay was fast with a high capacity making it a s uitable method for serological surveillance studies.