Definition

1. Noun:
   • A delayed hypersensitivity reaction mediated by cells of the immune system (specifically T-cells), rather than by antibodies. It is an allergic reaction that becomes apparent only hours after contact with the allergen.

Usage

• This term is used in medical and immunological contexts to classify and describe a specific mechanism of allergic response.
• It is often contrasted with immediate hypersensitivity reactions (Type I, II, and III).

Examples

• Noun:
  • Poison ivy rash is a classic example of a type IV allergic reaction.
  • The positive result for the tuberculin skin test indicates a type IV allergic reaction to the antigens.
  • Contact dermatitis from nickel in jewelry is caused by a type IV allergic reaction.

Advanced Usage

• "Delayed-type hypersensitivity (DTH)": This is a synonymous term frequently used in medical literature.
  • The immunologist explained that the granuloma formation was due to a delayed-type hypersensitivity response.

Variants and Related Words

• Cell-mediated hypersensitivity: Another technical term for this type of reaction.
• Contact dermatitis: A common clinical manifestation of a type IV allergic reaction.
• Hypersensitivity: The broader category of exaggerated immune responses, of which type IV is one kind.

Synonyms

• Delayed hypersensitivity reaction
• Cell-mediated immune reaction (in this specific allergic context)
• Delayed-type hypersensitivity (DTH)

Related Phrases

• T-cell mediated response: Describes the primary immune cells responsible for this reaction.
  • The pathology was consistent with a T-cell mediated response to the drug.

Noun

1. an allergic reaction that becomes apparent only hours after contact