IFNG and drug hypersensitivity syndrome: Immunohistochemical study of skin biopsies from both the exanthema and the patch test revealed positive results for interleukin (IL)-5, perforin, granzyme B, fatty acid synthase ligand (FasL), and interferon (IFN)-γ, which supported the notion that DRESS syndrome belongs to type IVb/IVc hypersensitivity reaction [101].