Interleukin-6 (IL-6) has a complex spectrum of biological activities, for example, growth and differentiation of B cells and synthesis of acute-phase proteins by the liver. To evaluate the role of this cytokine in the inflammatory response induced by blood interaction with hemodialysis membranes, we have investigated the IL-6 synthesis and release in supernatant of 24-hour cultured peripheral blood mononuclear cells (PBMC) isolated from: (a) 10 hemodialyzed patients, (b) seven patients with advanced chronic renal failure (GFR less-than-or-equal-to 10 ml/min), and (c) eight healthy control subjects. In the same groups of subjects we evaluated the relationship between IL-6 synthesis and release and beta-2-microglobulin (beta(2)m) production. Before and after dialytic treatment hemodialysis patient blood samples were drawn using the following criteria: (1) after two months of dialysis with cuprophan membranes, (2) after one and two months of dialysis with polymethylmethacrylate (PMMA) membranes, and finally, (3) after one further month of dialysis with cuprophan membranes. IL-6 was determined after 72 hours of incubation of PBMC supernatant serial dilutions with IL-6-dependent hybridoma cell line, 7TD1. Compared to IL-6 synthesis in control subjects (6.0 +/- 5.6 U/3 x 10(6) PBMC/24 hr), hemodialyzed patients, when treated with cuprophan membranes, showed significantly higher value of IL-6 production both before (23 +/- 13 U/3 x 10(6) PBMC/24 hr) and after (26.2 +/- 11.3 U/3 x 10(6) PBMC/24 hr) the dialytic session. When patients were hemodialyzed with PMMA membranes, at the start of dialysis IL-6 levels were not significantly different from values observed in healthy controls (10.6 +/- 4 U/3 x 10(6) PBMC/24 hr, after 1 month of dialysis and 7.8 U/3 x 10(6) PBMC/24 hr, after 2 months, respectively). When the patients were switched back to cuprophan membranes, IL-6 production was greatly increased after one month of dialysis (CU2, 44.6 +/- 9.4 U/3 x 10(6) PBMC/24 hr, at the start of dialysis) reaching values significantly higher than those obtained in the first period with cuprophan membranes. No difference was observed between the values of IL-6 production obtained pre- and post-dialysis with cuprophan or PMMA membranes. IL-6 production values in uremic non-dialyzed patients were similar to values found in control subjects (8.6 +/- 6.4 U/3 x 10(6) PBMC/24 hr). Beta(2)m release showed a behavior quite similar to IL-6 throughout the study. In fact, a statistically significant linear relationship was obtained between beta(2)m and IL-6 values of production (r = 0.8296, P < 0.001). In conclusion, our results show higher levels of IL-6 production in hemodialyzed patients treated with cuprophan membranes, thereby suggesting a chronic stimulation. Beta(2)m production is highly related to IL-6 production; this relationship suggests a possible implication for this cytokine in the pathogenesis of dialysis amyloidosis.
