Accelerated neutrophil apoptosis in neutropenic patients with hepatosplenic schistosomiasis is induced by serum Fas ligand.

Abstract

Neutropenia in patients with hepatosplenic (HS) schistosomiasis may stem from enhanced neutrophil apoptosis. However, the molecular mechanism of neutrophil apoptosis has not been clearly defined. Neutrophils harvested from neutropenic patients with HS schistosomiasis (n = 25), non-neutropenic patients with hepatointestinal (HI) schistosomiasis (n = 10), and age- and sex-matched healthy control subjects (n = 10) were examined for the degree of apoptosis after incubation with autologous sera. Neutrophil apoptosis was quantified by flow cytometry through determination of propidium iodide nuclear staining and confirmed by DNA gel electrophoresis at 0 time (fresh neutrophil), 4 and 24 h culture. Neutrophils from healthy subjects were also incubated with either 10% heterologous normal or neutropenic serum, with and without anti-Fas ligand antibody. Serum Fas ligand levels were assessed in sera of patient groups and healthy controls by ELISA. Compared with normal controls and HI, HS group demonstrated greater neutrophil apoptosis in the presence of autologous serum (P < 0.01, < 0.05, respectively). Furthermore, compared with normal neutrophils exposed to heterologous normal serum, those exposed to heterologous neutropenic serum exhibited higher apoptosis rates (P < 0.01). The apoptotic effect of neutropenic sera is attenuated by anti-Fas ligand. Fas expression was significantly higher in HS group as compared to both HI and normal healthy controls (P < 0.05). Serum Fas ligand levels were significantly higher among HS group as compared to both HI and control groups (P < 0.01 for both). Neutrophil apoptosis was not correlated to the size of spleen in HS group. In conclusion, the rate of neutrophil apoptosis is accelerated in neutropenic HS schistosomiasis. These findings suggest that enhanced neutrophil apoptosis demonstrated in HS patients is triggered by soluble Fas ligand, which is mostly derived from spleen.