Type four hypersensitivity reaction is a cell-mediated reaction that can occur in response to contact with certain allergens resulting in what is called contact dermatitis or in response to some diagnostic procedures as in the tuberculin skin test. Certain allergens must be avoided to treat this condition.

What is an example of type 4 hypersensitivity?

Ocular examples of type IV hypersensitivity include phlyctenular keratoconjunctivitis, corneal allograft rejection, contact dermatitis, and drug allergies, although drug sensitivities can lead to all four types of hypersensitivity reaction.

How is Type 4 hypersensitivity diagnosed?

The prototypical type IV hypersensitivity reaction is the tuberculin test, but similar reactions can occur after contact with sensitizing antigens (e.g., poison ivy, certain metals) and lead to epidermal reactions characterized by erythema, cellular infiltration, and vesicles.