13 January 2000
Aims: To determine the intracytoplasmic expression of TNF-α, IL-2, IL-6 and IFN-γ, ex vivo and in vitro, in both monocytes and T lymphocytes by flow cytometry after appropriate stimulation using phorbol myristate acetate (PMA)/ionomycin or lipopolysaccharides (LPS) in the presence of monensin, in order to assess the bio(in)compatibility of different dialysis membranes. Methods: We examined monocytes and T lymphocytes taken from chronic hemodialysis patients (using either cuprophane (CUP), n = 6; polyacrylonitrile (AN 69), n = 6; or polysulfone (PS), n = 6 membranes), before and after a dialysis session. We compared the results with those obtained from end-stage chronic renal failure patients (n = 3) and healthy volunteers (n = 11). Results: Before any stimulation there was a statistically significant difference in the percentages of TNF-α, IL-6, and IFN-γ- expressing monocytes with respect to the dialysis membrane used. The highest percentages were observed for CUP and AN69 patients with figures of around 30% for each cytokine; the lowest percentages were found in PS patients and healthy volunteers. One hour after LPS stimulation the patterns remained unchanged for TNF-α and IFN-γ, whereas the percentages of IL-6-expressing cells in PS patients and in healthy volunteers reached the figures obtained in the other groups. When we examined the percentage of IFN-γ-, TNF-α- and IL-6-expressing monocytes in patients before and after a dialysis session, before any stimulation, we found that the results were significantly different for the three membranes (p = 0.01). Thus, a dialysis session with polysulfone membranes had no significant effect on the precentages of IFN-γ-, TNF-α-, and IL-6-expressing monocytes, whereas percentages were significantly lower after the dialysis session when using cuprophane or AN69 membranes, suggesting a release of these cytokines by the monocytes during dialysis. A significant number of IFN-γ- and IL-2-expressing T lymphocytes were only detected after 18 hours of PMA/ionomycin stimulation. The percentages of IFN-γ-expressing T cells recorded for the different membranes were not statistically different from those recorded for healthy subjects or pre-dialysis patients, i.e., they were between 11.5 and 20%. However, the percentages of IL-2-expressing T lymphocytes were significantly different between the 5 groups, i.e., 31.3, 30.5, 18.6, 13.9 and 7.6%, respectively, for CUP patients, pre-dialysis patients, healthy volunteers, PS and AN69 patients. This suggests that pre-dialysis and CUP patients have, at baseline, a stimulation of their T lymphocytes. Finally, a 4-hour dialysis session had no impact on the percentages of IL-2-expressing T lymphocytes, whereas it was associated with a significant decrease in the percentage of IFN-γ-expressing cells, but only when cuprophane membranes were used. Conclusion: Cytokine flow cytometry enables one to study, ex vivo, i.e., without any stimulation of the cells, and in vitro after appropriate stimulation, the bio(in)compatibility of dialysis membranes assessed by the intracytoplasmic cytokine profiles of TNF-α, IFN-γ, IL-6 and IL-2, evaluated at the single cell level.