Molecular mechanisms based on the identification of genetic defects associated with the clinical picture of familial hemophagocytic lymphohistiocytosis (FHLH), Griscelli syndrome (GS-2) and Chédiak-Higashi syndrome (CHS). Perforin is secreted via cytotoxic granules and leads to disruption of the target cell. Cytotoxic granule processing occurs by means of a complex that contains at least a Rab27α/Munc13-4 complex and several other unknown proteins. The exact functions of LYST and syntaxin 11 are not known. In case of syntaxin 11, monocytes or macrophages/dendritic cells may interact with cytotoxic cells by an unknown mechanism.