Toxoids are produced by detoxifying toxins, typically using chemical treatment that preserves antigenicity.

• A. Detoxification by heat inactivation
• B. Detoxification by chemical treatment with formaldehyde
• C. Detoxification by irradiation
• D. Detoxification by proteolytic digestion

Answer: (B)

Toxoids are inactivated toxins that keep their antigenic structures intact so the immune system can recognize them and generate protective antibodies. Detoxifying with formaldehyde chemically modifies the toxin, inactivating its toxic function while preserving the epitopes that antibodies target. This makes a safe, immunogenic vaccine component, as used for diphtheria and tetanus. Other methods would disrupt the protein's shape or break it apart: heat tends to denature and ruin conformational epitopes, irradiation can damage or alter antigenic sites, and proteolytic digestion would degrade the protein and eliminate the antigenic targets.