By detecting cytotoxic mediators such as granzyme B (which is also suitable for the detection of exanthematous beta-lactam reactions) or Fas ligand, the ELISpot assay also offers the option to identify a possible trigger, even in severe bullous drug reactions such as erythema multiforme (EM), Stevens-Johnson syndrome (SJS), and toxic epidermal necrolysis (TEN) [106, 107]. This evidence concerns the gene GZMB and Stevens-Johnson syndrome.