,37,38 The involvement of T cells in delayed hypersensitivity reactions has been shown by isolating drug-reactive T cell clones,39 and cytotoxic CD8+ T cells have been shown to be relevant especially in allergic skin reactions.40, 41, 42 More than 20 years ago, CD8+ T cells reactive to penicillin were isolated from patients with delayed type of hypersensitivity to penicillin.43 Here, CD8A is linked to type IV hypersensitivity disease.