What type of delayed hypersensitivity reaction typically occurs with contact dermatitis?

The correct choice is D, as contact dermatitis is primarily mediated by a Type IV hypersensitivity reaction. This type of reaction is also known as delayed-type hypersensitivity because the response develops hours to days after exposure to the allergen. In the case of contact dermatitis, a person is usually sensitized to a specific substance (like poison ivy, latex, or certain metals) upon first exposure. Upon subsequent exposures, T cells and other immune components recognize the allergen and mount an inflammatory response. This response is characterized by the infiltration of immune cells to the site of contact, leading to the symptoms associated with dermatitis, such as redness, swelling, and itchiness.

Type IV hypersensitivity is unique because it does not involve antibodies; rather, it is mediated by T lymphocytes (T cells) and macrophages. This mechanism distinguishes it from the other types of hypersensitivity reactions, such as Type I (immediate allergic reactions mediated by IgE antibodies), Type II (antibody-mediated cytotoxic reactions), and Type III (immune complex-mediated reactions). Understanding this classification helps in diagnosing and managing conditions like contact dermatitis effectively.