Introduction
Hemophagocytic lymphohistiocytosis (HLH) is a systemic inflammatory disorder
characterized by uncontrolled histiocytic proliferation, hemophagocytosis,
macrophage activation, and up-regulation of inflammatory cytokines (Grom AA.,
Current opinion in rheumatology 2003; 15: 587–590). HLH is usually divided
into two types: primary (familial) HLH and secondary (reactive) HLH. Primary HLH is
associated with primary immune deficiencies in which specific gene mutations play an
important role, such as perforin defects.
