Mechanisms of intra-dialyser granulocyte activation: A sequential dialyser elution study

Introduction. During haemodialysis (HD), an early and transient white blood cell (WBC) reduction is noted in the peripheral blood, which has been attributed mainly to the sequestration of polymorphonuclear cells (PMN) in the pulmonary vasculature. However, WBC also adhere to the dialyser, as demonstrated before in an elution study performed after HD. In the present study, we investigated if intradialyser WBC sequestration contributes to the WBC nadir in the blood shortly after the start of HD and whether or not different mechanisms underlie PMN adherence in dialyser and lung. In addition, PMN degranulation was analysed not only in peripheral blood but also in dialyser eluates (DE). Subjects and methods. Dialysers were eluted after 71/2 (DE-71/2) and 180 (DE-180) min of HD in eight patients. Blood samples were taken before HD (tO), and at t71/2 and t180. Besides WBC count and differentiation, PMN adhesion (CDllb and CD62L) and degranulation markers (CD63 and CD66b) were assessed by flow cytometry. Results. In the blood, a WBC fall was noted at t71/2 (from 5.8 to 4.8 x 10(9)/l; absolute about 5 x 10(9) cells). DE contained 3.0 x 10(6) cells at t71/2, and 57.2 x 10(6) at t180 (P=0.015). As for CDllb, at t71/2 both in the blood and DE an increased expression was observed, as compared to tO (P=0.01); CDllb expression in DE-71/2 was higher than in DE-180 (P=0.025). In contrast, CD62L showed downregulation only in DE both at t71/2 (mean fluorescence intensity (MFI) PB 4172 and DE-71/2 2353, P=0.01), and at t180 (MFI 794, P=0.03 versus DE-71/2), when compared to blood at tO. As for degranulation markers, an increase was observed in blood at t71/2 (MFI CD63 from 357 to 506, P=0.02; CD66b from 507 to 794, P=0.001), in comparison with tO. fluted PMN at t71/2 showed a higher expression of CD63 than PMN in blood at t71/2 and DE-180 (MFI in DE-71/2 1280 and blood 506, P=0.003). The expression of CD66b was increased in DE-7% (MFI 1803 versus blood 794, P=0.01), and even more in DE-180 (MFI 2763, P=0.002), when compared to blood. Conclusions. From these data it is concluded first, that intradialyser PMN sequestration does not contribute markedly to the WBC nadir in the circulation. Second, intradialyser PMN trapping appears to result primarily from non-adhesion-molecule-mediated factors, as indicated by an increased expression of CDllb at t71/2 on eluted PMN associated with low cell numbers in DE, and normalized CDllb expression at t180 associated with considerably higher cell numbers in DE. Third, HD-induced degranulation seems to be a complex phenomenon. After a rapid transient onset, characterized by an early upregulation of CD63 and CD66b on PMN leaving the dialyser, degranulation continues within the device as indicated by an additional rise in the expression of CD66b on PMN in DE-180.