Protective immunity in anthrax — Antibodies targeting which Bacillus anthracis antigen are considered protective in humans and animals?

Introduction / Context:
Protective immunity against anthrax centers on neutralizing the key virulence factors. Vaccines and antitoxin therapies are designed to elicit or provide antibodies that block toxin function, preventing systemic damage even if exposure occurs.

Given Data / Assumptions:

• Bacillus anthracis virulence depends on a tripartite toxin (protective antigen, edema factor, lethal factor) and a poly-D-glutamate capsule.
• Vaccines commonly focus on protective antigen (PA) to elicit neutralizing antibodies.
• Capsule is poorly immunogenic and does not confer strong protection by itself.

Concept / Approach:
Neutralizing antibodies against the anthrax toxin, particularly the protective antigen component (PA), prevent toxin entry into host cells. This mechanism underpins the efficacy of anthrax vaccines that are PA-based. Antibodies to the capsular polypeptide are not reliably protective, and somatic polysaccharide antigens are not the principal protective targets in anthrax.

Step-by-Step Solution:

Verification / Alternative check:
Licensed human and veterinary vaccines rely on PA to induce protective immunity; monoclonal antitoxins also target toxin components, confirming the protective role.

Why Other Options Are Wrong:

• Capsular polypeptide: limited protective value; not the primary vaccine target.
• Somatic polysaccharide: not central to anthrax protective immunity.
• None of these: incorrect because antitoxin antibodies are protective.

Common Pitfalls:
Assuming all surface antigens are equally protective; for anthrax, toxin neutralization is key.

Final Answer:
Anthrax toxin