ABSTRACT
Anúindirect ELISA to determine the fraction of anti diphtheria toxoid [DTd] antibody [Ab] reactive with fraction A [FA] and fraction B [FB] of the toxoid is described. In principle, the binding of [DTd] adsorbed onto ELI SA-plates to the corresponding antibodies [Abs] was specifically blocked with horse F [ab]2 to either FA or FB of diphtheria toxin [DT]. The unblocked antigenic determinants of the DTd were used for determination of the corresponding Abs in sera from immunized humans and guinea pigs. The results revealed a high correlation between the levels of Abs to the DTd, FA and FB of the toxoid in sera from immunized hosts. In addition, it demonstrates that the use of DT-based immunotoxin alters the ratio of anti-FA/anti-FB. The developed ELI SA is reliable for monitoring of the levels of Abs to the toxic entity of the DT-based immunotoxins