Objective: The dysfunction of monocytes in uremic patients has been demonstrated to be associated with monocyte accelerated apoptosis. The study was conducted toelucidate the mechanisms by which monocyte apoptosis was induced.
Methods: Seven non-dialyzed chronic uremic patients and 18 hemodialysis (HD) patients were enrolled in the study. Fifteen healthy volunteers were selected as controls. The expression of Fas and Fas ligand (FasL) was examined by immunofluorescent staining and flow cytometer analysis. The levels of soluble FasL (sFasL) in plasma were analyzed by enzyme-linked immunosorbent assay (ELISA). The percentage of apoptotic cells in monocytes cultured in vitro with recombinant human FasL (rHu-FasL) was quantitated by DNA content analysis after extraction of the degraded DNA. Monocyte survival rate was analyzed by 5-diphenyl tetrazolium bromide (MTT) staining.
Results: Expression of Fas on monocytes was significantly higher in uremic and HD patients than that in healthy subjects. Higher levels of Fas expression were demonstrated on monocytes from HD as patients compared with those from non-dialyzed patients. There was no difference in monocyte Fas expression between pre- and post-dialysis session and between patients using polysulfone and cellulose dialyzer. There was no detectable FasL expression on monocytes from both uremic patients and healthy controls. Plasma sFasL could be detected in uremic and HD patients, but not in healthy controls. There was no significant difference in levels of plasma sFasL between non-dialyzed and HD patients, pre- and post-dialysis session, and patients treated with polysulfone and cellulose dialyzer. When monocytes were cultured in vitro with rHu-FasL for 2 hours, higher levels of apoptosis and lower survival rate were found in monocytes from HD patients as compared with those from healthy controls.
Conclusion: The up-regulated expression of functional Fas on monocytes and the presence of sFasL in plasma may contribute to the accelerated apoptosis of monocytes seen in uremic patients.