A delayed hypersensitivity reaction, such as erythema multiforme, is classified as what type?

A delayed hypersensitivity reaction, such as erythema multiforme, is classified as Type IV hypersensitivity. This type of hypersensitivity is mediated by T cells rather than antibodies and involves a delayed response, typically occurring 24 to 48 hours after exposure to an antigen.

In the case of erythema multiforme, the immune system responds to certain triggers, such as infections or medications, by activating T cells that lead to inflammation and tissue damage in the skin. This mechanism is distinct from other types of hypersensitivity reactions.

Type I reactions involve IgE-mediated responses, typically associated with allergies and anaphylaxis. Type II reactions are characterized by antibody-mediated destruction of cells, such as in hemolytic anemia. Type III hypersensitivity involves immune complex deposition and inflammation, often leading to conditions like systemic lupus erythematosus. Thus, recognizing the unique characteristics of delayed hypersensitivity is critical for understanding its classification and the immune mechanisms at play, which in this case is Type IV.