Tetanus toxoid vaccine triggers antigen presentation for immunity

Steps:

• Identify the toxoid as a harmless antigen mimicking the tetanus toxin.
• Recall that injected antigens are phagocytosed by immune cells like neutrophils.
• Understand antigen processing: engulfed material is degraded into peptides.
• Note presentation: peptides bind MHC molecules and display on cell surfaces to activate T cells.

Why A is correct:

• Neutrophils act as phagocytes that ingest and process antigens for MHC class II presentation on cell surfaces, initiating adaptive immunity (definition of antigen presentation pathway).

Why the others are wrong:

• B: Toxoids are protein antigens that elicit immune responses, regardless of lacking whole pathogen cells.
• C: Antibodies are produced but levels decline over time; long-term immunity relies on memory cells, not persistent blood antibodies.
• D: Formaldehyde chemically modifies the toxin (e.g., cross-links amino groups) to inactivate it while preserving immunogenic epitopes, without fully denaturing shape.

Final answer: A