Improved ELISA for determination of anti-diphtheria and/or anti-tetanus antitoxin antibodies in sera.

Double-antigen ELISAs for detection and quantification of anti-tetanus or anti-diphtheria antibodies in serum have been developed. The assays showed good correlations with established toxin neutralizing assays and were functionally specific for IgG antibodies. The double-antigen set-up allows specific antibodies to bind to antigen-coated microtitre wells with one arm and the free arm to bind to biotin-labelled antigen. The amount of antibodies able to bind labelled antigen was assessed by adding enzyme-conjugated streptavidin and colour substrate followed by measurement of the colour using an ELISA reader. The double-antigen principle makes it possible to compare samples of different species on the same plate, permitting the direct use of existing international references of animal or human origin. The double-antigen ELISAs showed a detection limit of 0.00002 IU/ml for both antibodies and were suitable for quantifying antibodies in blood samples collected on filter paper as well as in serum. The assays required no special equipment compared to traditional ELISA.