Leukocyte C5a receptor modulation during hemodialysis

Exposure of blood to hemodialysis (HD) membranes results in the activation of the complement system. In this study, flow cytometry was used to analyze the binding of fluoresceinated chemotactic factors (C5a, f-Met-Leu-Phe-Lys [fMLPL], and casein) and aggregated IgG to PMN and monocytes isolated from normal whole blood following passage through a hemodialyzer. Analysis of ligand binding by these PMN and monocytes showed no difference in the binding of casein. fMLPL, or aggregated IgG throughout the 45 minute procedure. In contrast, a progressive decrease in the binding of C5a by PMN and monocytes occurred. By 45 minutes, the average percentage of PMN binding C5a had dropped from 95 to 61% and monocytes from 73 to 40%. In additional studies, blood samples were obtained from chronic renal failure patients undergoing hemodialysis at four different time intervals during dialysis. Total white blood cell (WBC) counts showed that the mean WBC count at 30 minutes dropped to 60.9% of the predialysis WBC count, and rebounded to 133.8% by two hours and 128.2% by four hours. Analysis of the binding of C5a, casein, fMLPL, or aggregated IgG by PMN or monocytes from HD patients indicated that were no significant differences at the four time intervals studied. When blood samples from normal subjects or chronic hemodialysis patients were incubated in vitro with dialysis membrane fibers, a loss of identifiable C5a receptors was observed on PMN from normal blood, while PMN from HD patients showed no significant change in the percentage of C5a-receptor-positive cells. When normal PMN were isolated and resuspended in either normal or patient plasma and then exposed to HD membrane fibers, only cells in normal plasma showed a significant drop in C5a binding. These studies indicate that C5a receptors on PMN and monocytes obtained from normal donor blood exposed to dialysis membranes are specifically blocked or internalized. In contrast, even though PMN and monocytes from HD patients are continuously exposed to C5a generated during the dialysis procedure, they do not show a decrease in the binding of C5a. These findings suggest that adaptive mechanisms function in chronically hemodialyzed patients to modulate the effects of excessive C5a generation during HD.