Sensitive assay for measurement of antibodies to Clostridium botulinum neurotoxins A, B, and E: use of hapten-labeled-antibody elution to isolate specific complexes.

The measurement of chicken and human antibodies to Clostridium botulinum neurotoxins A, B, and E was accomplished by affinity isolation of complexes containing these antibodies. By this approach, a mixture of toxin with the test antibody, fluoresceinated antibody, and enzyme (Russell's viper venom factor X activator)-labeled antibody is allowed to form a complex in solution phase. This complex is then bound to a matrix containing antifluorescein antibody. All components not bound to the matrix are washed off, and the complex is isolated intact by elution with fluorescein, which competes with the complex for binding to the antifluorescein matrix. The eluted complex is then bound to a matrix which specifically binds the test antibody (anti-chicken immunoglobulin Y [IgY] or anti-human IgG), and the bound complex is measured by using the enzyme label. Using this approach, we were able to measure as little as 1 ng of specific antibody per ml from affinity-isolated, monospecific chicken antibody preparations and to measure antibody specifically from IgY fractions of monospecific chicken antibody preparations. Human antibodies from subjects immunized with pentavalent toxoid preparations were detectable at dilutions as great as 24,300-fold, and undiluted serum from most control subjects showed no measurable antibody. Antibody was also measured in 65 subjects who were receiving preparations of neurotoxin A (BOTOX) for the treatment of spastic disorders. Eighteen of them had toxin-specific antibody reactive with toxin B, and two of them had toxin-specific antibody reactive with toxin A. The two patients having antibody to toxin A were refractory to treatment with this toxin. This approach of isolation of hapten-labeled immune complexes under nondenaturing conditions with hapten is broadly applicable to the specific measurement of antibodies present at very low concentrations in serum.