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

In peripheral blood the majority of circulating monocytes present a CD14(hi gh)CD16(-) (CD14(++)) phenotype, while a subpopulation shows a CD14(low)CD1 6(+) (CD14(+)CD16(+)) surface expression. During haemodialysis (HD) using c ellulosic membranes transient leukopenia occurs. In contrast, synthetic bio compatible membranes do not induce this effect. We compared the sequestrati on kinetics for the CD14(+)CD16(+) and CD14(++) monocyte subsets during hae modialysis using biocompatible dialysers. Significant monocytopenia, as mea sured by the leucocyte count, occurred only during the first 30 min. Howeve r, remarkable differences were observed between the different monocyte subs ets. CD14(++) monocyte numbers dropped to 77 +/- 13% of the predialysis lev el after 15 min, increasing to greater than or equal to 93% after 60 min. I n 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). Ap proximately 6 h after the end of HD the CD14(+)CD16(+) cells returned to ba sal levels. Interestingly, the CD14(+)CD16(+) monocytes did not show reboun d monocytosis while a slight monocytosis of CD14(++) monocytes was occasion ally observed during HD. A decline in CD11c surface density paralleled the sequestration of CD14(+)CD16(+) monocytes. Basal surface densities of impor tant adhesion receptors differed significantly between the CD14(+)CD16(+) a nd CD14(++) subsets. In conclusion, during HD the CD14(+)CD16(+) subset rev ealed different sequestration kinetics, with a more pronounced and longer d isappearance 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 l eucocyte-endothelial, interactions.