Type IV hypersensitivity reactions & Diagnostic tests and treatments

What induces Type IV hypersensitivity reactions?

Type IV hypersensitivity reactions are induced by intracellular bacteria, viruses, and fungi.

Prolonged macrophage activation and cellular destruction may lead to the formation of granulomas.

How can chemicals induce delayed hypersensitivity in Type IV reactions?

Chemicals like poison oak or poison ivy can modify skin proteins, which are then processed and presented to T cells.

This activation of antigen-specific T cells induces localized inflammation, such as in contact dermatitis.

How can Type IV hypersensitivity be diagnosed?

Type IV hypersensitivity can be diagnosed using skin tests that require monitoring for 48-72 hours.

What is the tuberculin test and how is it used in diagnosing delayed-type hypersensitivity?

The tuberculin test is used to observe prior exposure to M. tuberculosis antigen.

A small amount of the antigen is applied subcutaneously, and the site is monitored for an inflammatory reaction.

A reaction that arises in 48-72 hours suggests prior exposure and sensitization to the antigen.