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

The objective of the study was to evaluate the contribution of reactive oxy gen intermediate formation for receptor modulation on neutrophils by the ce llulosic dialyzer membrane cuprophan (CU). In patients dialyzed with CU, CD 11b 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 wi th polysulfone did not bring about major changes in surface receptor expres sion. br vitro incubation of isolated neutrophils in the presence of serum with hollow fibers of CU or polysulfone showed similar results: Only CU res ulted 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%). Tn co ntrast to receptor alterations, generation of reactive oxygen intermediate by CU occurred in the absence of serum. Inhibition experiments with soluble complement receptor I, which produced only partial inhibition of receptor up-/down-regulation, indicated the existence of also other than alternate c omplement-dependent mechanisms fur neutrophil activation By using C5-deplet ed serum instead of normal human serum, up-/down-regulation of CD11b, CD62L , and CD66b by CU was dramatically reduced, whereas C3-depleted serum did n ot produce that effect. CS-deficient serum repleted with purified C5, as we ll as purified C5 alone, was able to induce receptor modulation by CU compa rable to normal human serum. Methionine, a specific inhibitor for the oxida tive activation of C5, blocked the modulatory effect of CU in assays with p urified C5 as well as with serum. As a result, in addition to the alternati ve pathway of complement, a C5-dependent mechanism probably activated by ne utrophil-derived reactive oxygen intermediate lends to receptor modulation and subsequent generation of the well known side effects of bioincompatible dialyzer membranes.