What is the pathogenesis of hemophagocytic lymphohistiocytosis (HLH)?

Caused by congenital or acquired immune dysregulation involving defects (inherited or acquired) in cytotoxic pathways of natural killer (NK) cells and/or cytotoxic T lymphocytes, leading to hypercytokinemia and an accumulation of activated lymphocytes and macrophages (termed histiocytes) in organs and tissues.