What type of hypersensitivity reaction is characterized by delayed cell-mediated drug reactions such as erythema multiforme?

The correct answer is Type IV hypersensitivity reaction. This type of hypersensitivity is characterized by delayed immune responses primarily mediated by T lymphocytes rather than antibodies. In cases such as erythema multiforme, which is often triggered by drugs, the immune response involves T cells recognizing specific antigens presented by skin cells. When these T cells become activated, they release cytokines that recruit and activate other immune cells, leading to inflammation and tissue damage.

Type IV hypersensitivity typically manifests 24 to 72 hours after exposure to the offending agent, consistent with the delayed nature of the reaction seen in conditions like erythema multiforme. This contrasts with the other types of hypersensitivity reactions, which are immediate or mediated by antibodies rather than cell-mediated responses. Understanding the mechanisms behind these different types of hypersensitivity helps in diagnosing and managing allergic reactions effectively.