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Updated: Jan 4, 2026
Opsono-Adherence Assay to Evaluate Functional Antibodies in Vaccine Development Against Bacillus anthracis and Other Encapsulated Pathogens
Published on: May 19, 2020
Different mechanisms of two anti-anthrax protective antigen antibodies and function comparison between them
Siping Xiong1,2,3, Tingting Zhou1, Feng Zheng1
1Epidemiological Department, Huadong Medical Institute of Biotechniques, Nanjing, 210002, China.
Background:
Bacillus anthracis causes a highly lethal infectious disease primarily due to toxin-mediated injury. Antibiotics are no longer effective to treat the accumulation of anthrax toxin, thereby new strategies of antibody treatment are essential. Two anti- anthrax protective antigen (PA) antibodies, hmPA6 and PA21, have been reported by our lab previously.
Methods:
The mechanisms of the two antibodies were elucidated by Electrophoresis, Competitive Enzyme-linked immune sorbent assay, Western blot analysis and immunoprecipitation test, and in vitro, in vivo (F344 rats) treatment test. The epitopes of the two antibodies were proved by Western blot and Enzyme-linked immune sorbent assay with different domains of PA.
Results:
In this study, we compared affinity and neutralization of these two antibodies. PA21 was better in protecting cells and rats, whereas hmPA6 had higher affinity. Furthermore, the neutralization mechanisms of the two antibodies and their recognition domains of PA were studied. The results showed that hmPA6 recognized domain IV, thus PA could not bind to cell receptors. Conversely, PA21 recognized domain II, thereby limiting heptamer oligomerization of PA63 in cells.
Conclusions:
Our studies elucidated the mechanisms and epitopes of hmPA6 and PA21. The present investigation can advance future use of the two antibodies in anthrax treatment or prophylaxis, and potentially as a combination treatment as the antibodies target different epitopes.
Insights
Two anthrax antibodies, hmPA6 and PA21, were studied for their effectiveness against Bacillus anthracis toxin. PA21 demonstrated superior protection in cells and rats, while hmPA6 showed higher affinity, offering potential for combination anthrax treatment.
Area of Science:
- Immunology
- Microbiology
- Infectious Diseases
Background:
- Bacillus anthracis toxin causes lethal disease.
- Antibiotics are ineffective against anthrax toxin.
- Novel antibody therapies are crucial for anthrax treatment.
Purpose of the Study:
- Compare the efficacy and mechanisms of two anti-anthrax protective antigen (PA) antibodies, hmPA6 and PA21.
- Elucidate the epitope recognition and neutralization strategies of these antibodies.
- Assess their potential for anthrax treatment and prophylaxis.
Main Methods:
- Electrophoresis, competitive ELISA, Western blot, and immunoprecipitation assays.
- In vitro and in vivo (F344 rats) treatment studies.
- Epitope mapping using PA domains.
Main Results:
- PA21 exhibited superior protection in cellular and rat models compared to hmPA6.
- hmPA6 demonstrated higher binding affinity for protective antigen (PA).
- hmPA6 targets PA domain IV, blocking PA-receptor binding; PA21 targets PA domain II, inhibiting PA63 oligomerization.
Conclusions:
- The study elucidated the distinct neutralization mechanisms and epitope specificities of hmPA6 and PA21.
- These antibodies offer promising therapeutic strategies for anthrax.
- Combination therapy using both antibodies targeting different epitopes may enhance anthrax treatment outcomes.
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