Pathogenesis of post-transplant HPS may involve (1) the activation of T helper-1 (Th-1) cells and the overproduction of cytokines, tumor necrosis factor-alpha (TNF-α) and interferon-gamma (IFN-γ) caused by severe infection, and (2) abnormalities of CD8 + T lymphocyte and natural killer-cell (NK-cell) cytotoxicity caused by immunosuppression. The gene discussed is TNF; the disease is infection.