Which of the following is an example of Type IV hypersensitivity?

Type IV hypersensitivity, also known as delayed-type hypersensitivity, is mediated by T cells rather than antibodies. This type of immune response can take several hours to days to develop after the initial exposure to the antigen.

Contact dermatitis serves as a classic example of Type IV hypersensitivity. In this condition, exposure to certain allergens, such as poison ivy or nickel, leads to an immune response characterized by the activation of T-helper 1 cells. These activated T cells secrete cytokines, which recruit and activate macrophages and other inflammatory cells, ultimately resulting in localized inflammation and tissue damage that appear one or two days after exposure.

Understanding the characteristics of Type IV hypersensitivity is crucial because it distinguishes it from other types of hypersensitivity reactions, such as those mediated by antibodies. Asthma is often associated with Type I hypersensitivity, which involves IgE-mediated responses. Graves' disease is primarily an autoimmune condition, typically classified under Type II hypersensitivity due to its antibody-mediated dysfunction of the thyroid. Serum sickness is an example of Type III hypersensitivity, which involves immune complexes and is characterized by a more immediate type reaction.

Recognizing these distinctions is important for understanding the underlying mechanisms and clinical manifestations of different hypersensitivity types.