Molecular features determining lymphocyte reactivity in allergic contact dermatitis to chloramphenicol and azdiamphenicol

Background: We report on two cases of allergic contact dermatitis to chlora mphenicol and azidamphenicol respectively, with in vivo and in vitro lympho cyte reactivity were explored because chloramphenicol, azidamphenicol, and thiamphenicol exhibit almost identical chemical structures. Methods: With chloramphenicol, azidamphenicol, and the chemically related t hiamphenicol, we performed patch tests and lymphocyte transformation tests with both patients. Furthermore, the interleukin-5 and interferon-gamma con centrations in the cultures of peripheral blood mononuclear cells of one pa tient were determined. Results: Patch tests showed delayed hypersensitivity reactions to chloramph enicol and azidamphenicol, but not to thiamphenicol. These results were con firmed by lymphocyte transformation tests with peripheral blood mononuclear cells of the patients, showing a proliferative T-cell response to azidamph enicol and chloramphenicol. Moreover, lymphocytes from one patient secreted large amounts of interleukin-5, but not of interferon-gamma upon coculture with azidamphenicol. Conclusions: Since lymphocyte reactivity was observed to chloramphenicol an d azidamphenicol, but not to thiamphenicol, the epitope(s) recognized by th e allergen-reactive T cells may be formed by the nitro-group of the benzene ring shared by chloramphenicol and azidamphenicol.