Complement-dependent acceleration of apoptosis in neutrophils by dialyzer membranes

Recently, we have shown that cuprophan (CU) causes receptor modulation by a C5-dependent mechanism, which is activated by neutrophil-derived reactive oxygen intermediates. The objective of our study was to evaluate the contribution of dialyzer membranes to the induction of apoptosis in human neutrophils [polymorphonuclear cells (PMNs)]. PMNs harvested from healthy donors were incubated with hollow fibers from a biocompatible membrane polysulfone (PS) and a bioincompatible membrane CU, all in the presence of 25% human serum. After 4, 8, and 12 hours of incubation at 37 degrees C, apoptosis was quantitated by counting the numbers of cells showing features of apoptosis on cytospins by light microscopy and also by flow cytometry using propidium iodide nuclear staining. Compared with PMNs incubated with serum alone, cells cultured with fibers of PS demonstrated a higher percentage of apoptosis. Fibers from CU dialyzers led to a more pronounced induction of apoptosis in PMNs, which was significantly higher compared with PS. This effect was partly mediated by heat-sensitive serum products and depended on the presence of divalent cations. In contrast to the recently described C5-dependent pathway in PMN receptor modulation by CU, this effect seemed to depend on the presence of the complement factor C3. In conclusion, our results indicate that besides the well-known accelerated apoptosis of PMNs in uremia, both biocompatible and bioincompatible dialyzer material itself can accelerate apoptosis in human PMNs.