Functional changes of monocytes due to dialysis membranes

The functional effects directly induced by dialysis membranes on peripheral monocytes were analyzed in a plasma-free model of simulated dialysis using Cuprophan, cuprammonium rayon, polyacrylonitrile, polymethylmetacrilate and polysulphone membranes. A severe reduction of monocyte phagocytosis of IgG-coated erythrocytes was found by using Cuprophan and cuproammonium rayon. The cytofluorimetric analysis of several cell surface receptors, involved in the immune phagocytosis and recognizable by five quoted monoclonal antibodies, did not reveal any significant change. The defective phagocytosis of the IgG-coated erythrocytes by monocytes, due to the exposure to cellulose-derived membranes, was paralleled by an impaired interiorization of heat-aggregated human immunoglobulins, as analyzed by electron microscopy. The cell membrane binding of aggregated immunoglobulins was found to be unaffected. The defect was associated to a remarkably depressed generation of reactive oxygen species after Zymosan stimulation. Therefore, the defective immune phagocytosis induced by exposure of monocytes to cellulosic membranes was not due to a receptor rearrangement or an impaired binding of ingestible particles, but to a reduced internalization capacity probably related to an energy source exhaustion (as shown by the lack of response to stimuli able to induce oxidizing species production). These features are similar to those described in monocytes from acute systemic lupus erythematosus patients.