Adjuvant effect of pertussis toxin on the production of anti-ovalbumin IgE in mice and lack of direct correlation between PCA and ELISA.

In studies designed to optimize the production and detection of anti-ovalbumin (anti-Oa) IgE in Ham/ICR mice, a range of doses of both Oa and pertussis toxin as the IgE adjuvant was explored. As determined by 48-hour passive cutaneous anaphylaxis (PCA) tests, the highest titre of anti-Oa IgE was obtained in a three-injection protocol with 0.1 micrograms Oa and 1 microgram pertussis toxin for the priming dose, followed by two further doses of 0.1 microgram Oa alone. In single-dose immunizations, the highest PCA responses were obtained in sera from mice given 20 micrograms Oa and 1 microgram pertussis toxin. These data confirm that murine IgE production to Oa depends on particular combinations of immunization variables. There was no direct correlation between the PCA and anti-IgE enzyme-linked immunosorbent assay (ELISA) titres of the PCA-positive sera; indeed there was a significant negative correlation. This relationship was not due to interference by IgG1, as there was no correlation between the anti-Oa IgG1 and anti-Oa IgE ELISA titres of the sera. These results highlight the need for caution in assuming that serum IgE levels as measured by ELISA will necessarily correlate positively with IgE biological activity as measured by allergen challenge in vivo.