Trial use of a polymethylmethacrylate membrane for the removal of free immunoglobulin light chains in dialysis patients

Background. Free immunoglobulin light chains (FLCs) accumulate at high levels in the blood of dialysis patients and are likely to cause immunodeficiency during periods of dialysis. Our group examined the blood FLC concentration, κ/λ ratio and rates of FLC removal in different dialysis modes using different dialysis membranes. Methods. Polymethylmethacrylate (PMMA) membrane (BG-PQ, Toray) under the haemodialysis (HD) condition was used for seven chronic maintenance dialysis patients who had been treated by hemodiafiltration (HDF) (five polyester-polymer alloy (PEPA) and two polysulphone) in a crossover fashion. FLCs in serum were measured with a FREELITE™ Human Kappa Free Kit and Lambda Free Kit prepared by Binding Site, UK (supplied by Medical & Biological Laboratories Co., Ltd, Japan). Each κ-type and λ-type FLC was quantitatively measured with a Dade Behring BNII™. Western blotting was conducted using a goat anti-human κFLC polyclonal antibody. Results. The κ and λ serum FLCs in HD patients (n = 7) were 157.4 ± 88.9 and 121.9 ± 56.3 mg/L, respectively, and were accumulated in concentrations 4- to 16-fold higher than the concentrations in healthy controls. The κ/λ ratio was included in the reference range (0.26–1.65). In the HD cases dialysed with PMMA membrane, the FLCs were removed mainly by adsorption, leaving only very small quantities in the whole dialysis waste fluid. The ratio between the total removed quantity and albumin leakage ((κ+λ)/Alb) was higher in the PMMA HD group than in the HDF group, and the rate of κFLC removal was higher than the rate of λFLC removal. The serum κFLC in dialysis patients had a multimer structure. In western blotting, the adsorbed κFLC (including multimer structure) detected in the PMMA membrane exceeded that detected in the dialysate with the polysulphone membrane. Conclusions. Although the FLCs were removed at high rates under the HDF condition, they were also effectively removed by adsorption with the PMMA membrane under the HD condition. It may be possible to effectively remove the FLC multimer with a PMMA membrane via adsorption. In future studies on FLC removal in patients with chronic renal failure, it will be necessary to assess not only the quantity of simple removal from the blood but also the qualitative properties, such as the degree to which accumulation and removal rates depend on the κ/λ ratio and multimer structures.