IMMUNOLOGY

Detailed explanation-1: -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.

Detailed explanation-2: -Type IV hypersensitivity, often called delayed-type hypersensitivity, is a type of hypersensitivity reaction that can take a day or more to develop. Unlike the other types, it is not humoral (not antibody-mediated) but rather is a type of cell-mediated response.

Detailed explanation-3: -Delayed hypersensitivity (also known as a Type-IV hypersensitivity reaction) is an immunologic reaction that is mediated primarily by T cells and monocytes and presents hours to days after the antigen crosses into the skin.