Protective and other biological properties of Bacillus anthracis soluble antigens.

The soluble antigens were explored of the culture filtrate (CF) derived during static growth of B. anthracis vaccine strain 34F2 on a medium containing casein hydrolysate. Electrofocusing of CF preparations revealed that the protective activity was distributed over a wide range of pH 3-7. The most pronounced and stable protective activity was observed at pH 4.6-4.8. Following toxin factors were isolated and identified: protective antigen (87 kD), oedema factor (87 kD) and lethal factor (78-81 kD). The greatest protective activity was associated with antigens characterized by a molecular weight of 78-87 kD and toxic activity. Preparations of the oedema and lethal factors had the same protective activity as protective antigen (PA) preparations. Other CF soluble antigens protected about 30% of immunized guinea pigs. A protein was isolated with a molecular weight of 80 kD and isoelectric point at pH 5.3-5.7 which was not toxic and did not form toxic mixtures in association with other toxin factors; this protein featured a high immunogenic activity, however, it protected only 31% of immunized animals. Factors are analyzed which determine differences in the protective effects of live and chemical vaccines.