Novel C5-dependent mechanism of neutrophil stimulation by bioincompatible dialyzer membranes

The objective of the study was to evaluate the contribution of reactive oxygen intermediate formation for receptor modulation on neutrophils by the cellulosic dialyzer membrane cuprophan (CU). In patients dialyzed with CU, CD11b and CD66b upregulation on neutrophils (by 104.3 +/- 37.9% and 85.7 +/- 31.1%, respectively), and a downregulation of L-selectin (by 44.9 +/- 26.9%) was seen, whereas expression of CD11a remained unaltered. Hemodialysis with polysulfone did not bring about major changes in surface receptor expression. In vitro incubation of isolated neutrophils in the presence of serum with hollow fibers of CU or polysulfone showed similar results: Only CU resulted in upregulation of CD11b and CD66b expression (by 65.5 +/- 18.7% and 60.1 +/- 24%) and a decrease in CD62L expression (by 60.6 +/- 18.2%). In contrast to receptor alterations, generation of reactive oxygen intermediate by CU occurred in the absence of serum. Inhibition experiments with soluble complement receptor 1, which produced only partial inhibition of receptor up-/down-regulation, indicated the existence of also other than alternate complement-dependent mechanisms for neutrophil activation. By using C5-depleted serum instead of normal human serum, up-/down-regulation of CD11b, CD62L, and CD66b by CU was dramatically reduced, whereas C3-depleted serum did not produce that effect. C5-deficient serum repleted with purified C5, as well as purified C5 alone, was able to induce receptor modulation by CU comparable to normal human serum. L-Methionine, a specific inhibitor for the oxidative activation of C5, blocked the modulatory effect of CU in assays with purified C5 as well as with serum. As a result, in addition to the alternative pathway of complement, a C5-dependent mechanism probably activated by neutrophil-derived reactive oxygen intermediate leads to receptor modulation and subsequent generation of the well known side effects of bioincompatible dialyzer membranes.