Detection of endotoxin-like interleukin-1-inducing activity during in vitro dialysis

Abstract

In order to study the integrity of dialysis membranes to pyrogens, the dialysate side of a closed loop hemodialysis (HD) circuit was challenged with E. coli microfiltrate containing 500 ng/ml endotoxin. Three solutions, a) tissue culture medium/saline, b) 5% human serum albumin, and c) 10% fresh human plasma, were circulated in the blood loop for five hours. Samples drawn from the blood side were assayed for interleukin-1 (IL-1)-inducing activity on human mononuclear cells (MNC) in vitro. No IL-1-inducing substances were detected when saline or culture medium was circulated in the blood loop. Circulating 5% human serum albumin revealed IL-1-inducing activity in the samples drawn only after five hours of HD. However, the addition of 10% fresh human plasma to the blood side resulted in the appearance of an IL-1-inducing substance(s) after 15 minutes of HD. After 30 minutes, maximum IL-1-inducing activity was observed (control stimulation index, 3.30 ± 0.67 SEM VS. 7.59 ± 1.50, P < 0.02). The IL-1-inducing activity of the samples was completely inhibited by polymyxin B, a cationic antibiotic which blocks the IL-1-inducing activity of endotoxin. Additional experiments demonstrated that in vitro MNC IL-1-production induced by the same E. coli microfiltrate is enhanced in the presence of 10% plasma. These studies demonstrate that: (a) in the presence of plasma, IL-1-inducing factors pass into the blood compartment of a dialysis system challenged with bacterial pyrogen; and (b) MNC production of IL-1 is enhanced in the presence of plasma. Since the Limulus test is influenced by plasma, in vitro MNC-IL-1-production provides a more reliable and relevant assay to determine dialysis membrane permeability for pyrogens.