Elevation of the Serum Fas Ligand in Patients With Hemophagocytic Syndrome and Diamond-Blackfan Anemia

Fas ligand (FasL) is a membrane protein that is expressed in activated T cells and natural killer cells. FasL binds to Fas on target cells and induces apoptosis. There exists a soluble form of FasL (sFasL), and sFasL also induces apoptosis of Fas-bearing cells. The serum sFasL concentrations were reported to be elevated in patients with large granular lymphocytic leukemia and natural killer cell lymphoma. In this study, we have measured serum sFasL concentrations in other hematological disorders, including severe aplastic anemia (SAA), hemophagocytic lymphohistiocytosis (HLH), and Diamond-Blackfan anemia (DBA). The serum sFasL concentration of age-matched healthy controls was 0.16 ± 0.11 ng/mL (mean ± SD, n = 22). The serum sFasL levels in the patients with HLH and DBA were 3.75 ± 3.82 (n = 19;P < .0001, HLH v control) and 2.76 ± 2.43 ng/mL (n = 6; P = .012, DBA v control), respectively. Serum interferon-γ concentration was elevated in the patients with HLH (1.61 ± 2.62 ng/mL) but not in those with DBA (below the detectable level). These results suggest that the Fas-FasL system plays a role, at least in part, in the pathophysiology of HLH and DBA.