Susceptibility to fatal anaphylactic shock in mice was equally enhanced when one injection of 1 mg of egg albumin (Ea) was mixed with Freund's adjuvant or with 2 billion Bordetella pertussis cells. When the amount of Ea was reduced, Ea in Freund's adjuvant was more effective in sensitizing mice to fatal anaphylaxis than were B. pertussis cells. Only a few mice receiving 1 to 4 mg of Ea alone were sensitized to fatal anaphylaxis. Two injections of Ea without adjuvant, however, were capable of sensitizing mice to fatal anaphylaxis.

Mice which received Ea in Freund's adjuvant produced 10 to 100 times more antibody than those which received an equivalent amount of Ea mixed with B. pertussis. Even 40 days after a single injection of Ea in Freund's adjuvant the peak titer was not reached. Ea given alone stimulated only very low titers of antibody which appeard 30 to 40 days after injection of antigen.

As antigen dose was increased, antibody appeared earlier whether Ea was given with Freund's adjuvant or B pertussis. With low doses of Ea (0.001 mg), antibody was not detected until 30 to 40 days later.

No direct correlation between antibody titer of individual mice and their susceptibility to fatal anaphylaxis was observed. This was true whether antigen was given alone, with Freund's adjuvant, or with B. pertussis. In groups of mice in which fatal anaphylactic susceptibility was observed, antibodies to Ea were eventually detected. Thus, when the antibody mechanism had been properly stimulated, anaphylactic sensitivity was also present.

When Ea was administered with Freund's adjuvant, there appeared to be a decrease in anaphylactic sensitivity at the higher doses of Ea. At this time (30 to 40 days after sensitization) the antibody concentration was extremely high and the amount of Ea used in shocking dose may have not been adequate to produce fatal shock.

Zymosan was found to stimulate antibody production and anaphylactic sensitivity but to a lesser extent than B. pertussis or Freund's adjuvant.

The main mechanism by which B. pertussis increases susceptibility of mice to actively induced anaphylaxis is apparently by stimulation of the antibody response to the sensitizing antigen.

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