Clinical studies demonstrate elevated levels of various immune cells (e.g., CD8+ T cells, natural killer [NK] cells, monocytes, macrophages) and soluble mediators (e.g., TNF-α, IFN-γ, IL-6, IL-1, IL-10, perforin, granzyme) in both serum and blister fluid of SJS/TEN patients (3, 12). The gene discussed is PRF1; the disease is toxic epidermal necrolysis.