Tetanus and diphtheria vaccines used in the DTP combination are toxoid vaccines. Which of the following correctly describes the process by which a toxoid is produced?
- A The exotoxin gene is cloned into a non-pathogenic vector to express an attenuated toxin
- B The exotoxin is heat-inactivated at 100°C to denature the toxic domain
- C The exotoxin is treated with formaldehyde to destroy toxicity while preserving immunogenicity ✓
- D The exotoxin is chemically conjugated to a carrier protein to enhance T-cell recognition
Correct answer: C. The exotoxin is treated with formaldehyde to destroy toxicity while preserving immunogenicity
Explanation
Toxoids are produced by treating bacterial exotoxins with formaldehyde (formalin) under controlled conditions. This process, called toxoiding, cross-links amino acid residues and destroys the toxin's enzymatic (toxic) activity while preserving the conformational epitopes needed for neutralizing antibody production. Heat inactivation would denature epitopes needed for protection. Conjugation describes a different vaccine platform entirely.
Reference: Plotkin's Vaccines, 7th ed.
High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP
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