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The reproducibility of laboratory methods, recommended by WHO and used by manufacturing and control institutions of most countries for the evaluation of the immunogenic potency of the pertussis, diphtheria and tetanus components of adsorbed DPT vaccine in the process of its production, was studied. This immunogenic potency was experimentally studied in comparison with the immunogenic potency of national standard samples from Bulgaria, Czechoslovakia, Hungary, Poland and Russia. The results of this study indicated that the coded commercial lots of adsorbed DPT vaccine corresponded to WHO requirements with respect to the immunogenic potency of all their components. At the same time, according to data provided by different laboratories, the indices of their immunogenic potency varied within rather wide limits. Taking into account the necessity of dosing all components of adsorbed DPT vaccine by immunizing (protective) units, the reliability of the recommended control methods should be enhanced by the maximum standardization of all testing conditions and the organization of periodic workshops on the basis of the leading WHO laboratory with a view to improving the qualification of specialists carrying out the quality control of commercial lots of adsorbed DPT vaccine.

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To decrease the antigenic load in booster immunizations of children against diphtheria and tetanus, the immunological effectiveness and reactogenicity of different doses of both antigens (i. e 1 Lf and 1 BU; 2.5 Lf and 2.5 BU; 5 Lf and 5 BU) were studied. The study revealed that all these doses of the preparation were practically nonreactogenic: the total of systemic reactions was 0.9%. The study of the immunological effectiveness of adsorbed DT toxoid with reduced antigen content revealed the advantage of the commercial dose of the preparation (5 Lf of diphtheria antigen and 5 BU of tetanus antigen) over such doses of diphtheria and tetanus antigens as, respectively, 1 Lf and 1 BU; 2.5 Lf and 2.5 BU. Still, this advantage disappeared as early as 6 months after booster immunization. The results of these investigations indicate that booster immunization of children aged 6 years and over may be made with lower doses of adsorbed DT toxoid with reduced antigen content.

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On the basis of the experimentally established dependence of the degree of binding of diphtheria toxoid with standard diphtheria antitoxin on the duration of their joint incubation with the maximum binding occurring in 3-4 hours of incubation at 37 degrees C, the method of the in vitro determination of the antigenic activity of diphtheria toxoid in liquid and adsorbed preparations is proposed. The method is based on the principle of double binding with the use of diphtheria antigenic (toxoid) erythrocyte diagnosticum. The antigenic activity of diphtheria toxoid, evaluated by the degree of its maximum binding with diphtheria antitoxin, correlated with its antitoxin-binding activity in animal experiments and did not correlate with its flocculating activity. The antigenic activity of diphtheria toxoid in adsorbed preparations, evaluated by their maximum binding with standard diphtheria antitoxin, was shown to be closely related to the immunogenic potency of these vaccines in animals.

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The immunological effectiveness of two batches of adsorbed DPT vaccine, the batch with the normal content of antigens (control) and the batch with the content of diphtheria and tetanus toxoids reduced to 20 Lf/ml and 5 BU/ml respectively (test batch), has been studied under the conditions of controlled trial. As a result, the reduction of the antigenic content of adsorbed DPT vaccine has been found to exert no negative influence on the immunological effectiveness of the diphtheria, tetanus, and pertussis components of this preparation under the conditions of the new immunization schedule.

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Different batches of the same preparation manufactured at the same enterprise, or at different enterprises, in accordance with the same manufacturing regulations have been found to be capable of producing a damaging effect of different intensity on the continuous cell culture L132. The titers vary, according to their cytotoxic effect, from 1 : 32 to 1 :2048. The components of B. pertussis antigens and thimerosal solutions have been found to produce the most pronounced cytotoxic effect on the cells. The comparison of the results of the titration of adsorbed DPT vaccine in cell cultures with clinical manifestations has shown correlation between a greater degree of cell damage in vitro and severe local reaction. Therefore, in the process of the quality control of preparations cell cultures provide more sensitive tests than laboratory animals, which is confirmed by our data obtained in revealing the toxic properties of adsorbed DPT vaccine and its components.

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Continuous cell cultures are sensitive test systems used not only for the determination of the toxicity of diphtheria exotoxin, but also for revealing the toxic properties of adsorbed DPT vaccine. Morphological changes induced by the action of diphtheria exotoxin and adsorbed DPT vaccine in the cultures of L929, HeLa, FL, L132 and monkey tonsil cells are similar in character. The effect produced by the diphtheria exotoxin and adsorbed DPT vaccine on cell cultures may be characterized as toxic, subtoxic and minimal. Nevertheless, even in the cultures treated with minimal concentrations the pathological state of the cells can be detected in the next 2 or 3 serial subcultures.

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