Live anthrax vaccine containing spores from attenuated strains STI-1 of Bacillus anthracis is used in Russia and former CIS (Commonwealth of Independent States) to prevent anthrax. In this paper we studied the duration of circulation of antibodies specific to spore antigens, the protective antigen (PA), the lethal factor (LF) and their domains (D) in donors’ blood at different times after their immunization with live anthrax vaccine. The relationship between the toxin neutralization activity level and the level of antibodies to PA, LF and their domains was tested. The effect of age, gender and number of vaccinations on the level of adaptive post-vaccination immune response has been studied. It was shown that antibodies against PA-D1 circulate in the blood of donors for 1 year or more after immunization with live anthrax vaccine. Antibodies against all domains of LF and PA-D4 were detected in 11 months after vaccination. Antibodies against the spores were detected in 8 months after vaccination. A moderate positive correlation was found between the titers of antibodies to PA, LF, or their domains, and the TNA of the samples of blood serum from the donors.
Neutralization of the lethal toxin of Bacillus anthracis is an important topic of both fundamental medicine and practical health care, regarding the fight against highly dangerous infections. We have generated a neutralizing monoclonal antibody 1E10 against the lethal toxin of Bacillus anthracis and described the stages of receptor interaction between the protective antigen (PA) and the surface of eukaryotic cells, the formation of PA oligomers, assembly of the lethal toxin (LT), and its translocation by endocytosis into the eukaryotic cell, followed by the formation of a true pore and the release of LT into the cell cytosol. The antibody was shown to act selectively at the stage of interaction between Bacillus anthracis and the eukaryotic cell, and the mechanism of toxin-neutralizing activity of the 1E10 antibody was revealed. The interaction between the 1E10 monoclonal antibody and PA was found to lead to inhibition of the enzymatic activity of the lethal factor (LF), most likely due to a disruption of true pore formation by PA, which blocks the release of LF into the cytosol.
Currently, live anthrax vaccine has been used for vaccine prophylaxis in Russia and neighbor countries for seve ral decades, but precise mechanism of post-vaccination protection mechanism remains unclear. Here, we provide data on examining serum antibody level against protective antigen (PA) and lethal factor (LF) in repeatedly vaccinated volun teers at early stage (5–8 days) and 1 month after the performing pre-scheduled annual revaccination. Amount of peripheral blood antigen-specific memory T cells after previous vaccinations was analyzed. It was showed that frequency of CD3+CD45RO+CD62L– memory effector T cells was increased in the majority of volunteers on day 5-8 day after performing pre-scheduled annual revaccination that peaked at day 7 by elevating it by 2-fold compared with the control group. Percentage of anthrax-specific central memory T cells did not increase at early stage after vaccination, whereas amount of activated CD3+CD45RO+CD62L+HLA-DR+ subset within this memory T cell population was increased. Likewise, percentage of activated CD3+CD45RO+CD62L–HLA-DR+ effector memory T cell subset was also increased. Moreover, serum anti-PA IgG were detected on day 5–8 day after pre-scheduled annual revaccination in half of volunteers, whereas anti-LF IgG were found only in a single volunteer. Rapidly elevated amount of serum anthrax-specific IgG antibodies evidences about sustained memory B cell response in peripheral blood samples in volunteers after pre-scheduled annual revaccination. However, percentage of CD19+CD27+ memory B cells was not significantly elevated at early stage after revaccination that tended to increase. Both helper and cytotoxic T cell subsets were activated on day 5–8 after revaccination revealed by upregulated expression of CD69 and/or CD25 markers, with the latter predominantly found on helper T cells, thereby accounting for their high proliferative activity, whereas the former — on cytotoxic T cell subsets. Detection of anti-PA IgG antibodies correlates with protection against anthrax, which was confirmed in animal models. Unfortunately, the level of serum anti-PA IgG antibodies rapidly declines after vaccination. Ability of memory B cells to rapidly trigger production of anthrax-specific antibodies in response to revaccination suggests that anti-anthrax immunity may be evaluated by measuring frequency of peripheral blood anthrax-specific memory B and T cells.
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