The effect of the protective antigen of Bacillus anthracis on the formation of immunity under the action of live anthrax vaccines

: The preparation of low-molecular protective antigen (PA) isolated from strain 34F2 (Sterne) and having a molecular weight of 34 and 51 kD, unlike the preparation of high-molecular PA with a molecular weight of 87 kD, suppressed the formation of acquired resistance to anthrax when introduced into guinea pigs in mixture with live spores of strains of STI, 34F2 and new vaccine strain 228/8; this phenomenon was mainly accompanied by a decrease in the level of antibodies to lethal factor (LF) nad in the antitoxic activity of blood serum. The immunosuppressing action of low-molecular PA depended on the kind of vaccine strain introduced together with this antigen, which suggested the existence of differences in the ligand determinants of strains 34F2 and STI. In contrast to high-molecular PA, low-molecular PA blocked the action of the lethal mixture of PA and LF on the culture of peritoneal mononuclear phagocytes of CBA mice. The competitive relationships between low-molecular PA and high-molecular PA are discussed.