Haemodialysis monocytopenia: differential sequestration kinetics of CD14+CD16+ and CD14++ blood monocyte subsets

Abstract

In peripheral blood the majority of circulating monocytes present a CD14highCD16- (CD14++) phenotype, while a subpopulation shows a CD14lowCD16+ (CD14+CD16+) surface expression. During haemodialysis (HD) using cellulosic membranes transient leukopenia occurs. In contrast, synthetic biocompatible membranes do not induce this effect. We compared the sequestration kinetics for the CD14+CD16+ and CD14++ monocyte subsets during haemodialysis using biocompatible dialysers. Significant monocytopenia, as measured by the leucocyte count, occurred only during the first 30 min. However, remarkable differences were observed between the different monocyte subsets. CD14++ monocyte numbers dropped to 77 +/- 13% of the predialysis level after 15 min, increasing to > or = 93% after 60 min. In contrast, the CD14+CD16+ subset decreased to 33 +/- 15% at 30 min and remained suppressed for the course of dialysis (67 +/- 11% at 240 min). Approximately 6 h after the end of HD the CD14+CD16+ cells returned to basal levels. Interestingly, the CD14+CD16+ monocytes did not show rebound monocytosis while a slight monocytosis of CD14++ monocytes was occasionally observed during HD. A decline in CD11c surface density paralleled the sequestration of CD14+CD16+ monocytes. Basal surface densities of important adhesion receptors differed significantly between the CD14+CD16+ and CD14++ subsets. In conclusion, during HD the CD14+CD16+ subset revealed different sequestration kinetics, with a more pronounced and longer disappearance from the blood circulation, compared with CD14++ monocytes. This sequestration kinetics may be due to a distinct surface expression of major adhesion receptors which facilitate leucocyte-leucocyte, as well as leucocyte-endothelial, interactions.

Fig. 1

Changes in peripheral blood neutrophil and CD14⁺⁺ and CD14⁺CD16⁺ monocyte subset numbers during haemodialysis. Data are from 11 patients dialysed with biocompatible polyamide or polysulphone membranes. Values are shown as the percentage of the level before dialysis. ▪, Neutrophils; ○, CD14⁺⁺ monocytes; •, CD14⁺CD16⁺ monocytes.

Fig. 2

Two-colour CD14/CD16 immunostaining of peripheral blood monocytes during haemodialysis (HD). Peripheral blood specimens were stained with an anti CD14–FITC and an anti-CD16–PE-labelled antibody. Cells were further analysed by flow cytometry as described (see PATIENTS and METHODS). Results of a representative patient before HD (a), after 30 min of HD (b), and at the end of HD (c) are shown. The percentage of CD14⁺CD16⁺ monocytes (upper right quadrant) is 23% (a), 9% (b) and 17% (c).

Fig. 3

Changes in the CD14⁺CD16⁺ monocyte subpopulations in two patients during and after haemodialysis. Numbers of the CD14⁺CD16⁺ blood monocytes were calculated before and during a 4-h dialysis session, as well as up to 18 h after the end of dialysis. One patient used a polyamide membrane (▪) and the other patient a polysulphone dialyser (○).

Fig. 4

Rebound monocytosis in two patients (A and B) during haemodialysis. Absolute cell numbers, as well as percentage changes compared with predialysis levels, are shown for CD14⁺⁺ (•) and CD14⁺CD16⁺ (○) monocytes.