In vitro complement-independent activation of human neutrophils by hemodialysis membranes: role of the net electric charge.

Polymethylmethacrylate (PMMA) membranes with different net electric charges and percentage water contents (anionic 71%, neutral 70%, cationic 75%) were evaluated for their ability to stimulate plasma-free human polymorphonuclear neutrophils (PMN), and compared for potency to cuprophan (Cu), already described as being a potent trigger of PMN. The release of lysozyme, beta-glucuronidase, lactic dehydrogenase (LDH), and the generation of a platelet aggregating activity were studied in the supernatants from plasma-free human PMN incubated with different membranes. The PMN intracellular content of neutrophil cationic proteins (NCP), elastase, and cathepsin G were also studied by immunofluorescence using specific antisera on smears of PMN before and after incubation with each membrane. Only cationic, but not anionic or neutral PMMA induced a marked release of lysozyme (range 20-25% of the sonicated control, assumed as 100%), and beta-glucuronidase (40-43%), and marked depletion of the intracellular content of NCP, elastase, and cathepsin G, suggesting a degranulation process. Platelet aggregating activity was generated and referred to the release of platelet activating factor (PAF) only in the supernatants from PMN incubated with cationic, but not with anionic, or neutral PMMA membranes. These results indicate that modification of the net electric charge can per se turn PMMA, commonly recognized as inert, into a material with marked PMN activating effects, comparable to those of Cu, a highly reactive polymer.