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BACKGROUND - Decreased red blood cell survival contributes to the anemia of chronic renal failure patients. Because patients on chronic dialysis therapy are frequently exposed to excessive complement activation, we investigated the susceptibility of this patient population to erythrocyte C5b-9 deposition, complement-mediated lysis, and ghost formation.
METHODS - We developed a flow cytometric assay using antibodies to both glycophorin and the C5b-9 complex to detect C5b-9 deposition on intact erythrocytes and erythrocyte ghosts. Serum C5b-9 levels and C5b-9 deposition on erythrocyte ghosts were measured by enzyme-linked immunosorbent assay.
RESULTS - A significant increase in C5b-9 deposition on intact erythrocytes was demonstrated in patients with advanced chronic renal failure (2.2 +/- 0.5%) and in patients on chronic maintenance hemodialysis (2.3 +/- 0.4%) compared with normal volunteers (0.9 +/- 0.1%, P = 0.005 vs. chronic renal failure, P < 0.001 vs. chronic hemodialysis patients). There was also a significantly higher percentage of C5b-9-positive erythrocyte ghosts in patients with advanced chronic renal failure (20.6 +/- 5%) and in chronic hemodialysis patients (15.5 +/- 3.1%) compared with normal controls (2.6 +/- 0.9%, P < or = 0.001 vs. advanced chronic renal failure and chronic hemodialysis patients). Treatment of erythrocyte preparations with cobra venom factor, which activates the complement cascade, resulted in dramatic increases in the percentages of C5b-9-positive erythrocyte ghosts in patients with chronic renal failure (49.9 +/- 6.9%) and in chronic hemodialysis patients (45.0 +/- 4.2%) compared with normal volunteers (22.3 +/- 2.7%, P < 0.001 vs. chronic renal failure and chronic hemodialysis patients). Erythrocyte membrane expression of the complement regulatory proteins CD59 and CD55 did not significantly differ between normal controls and hemodialysis patients. Plasma C5b-9 levels after cobra venom factor stimulation were higher in chronic renal failure patients (538 micrograms/ml) compared with normal controls (345 micrograms/ml, P < 0.001).
CONCLUSIONS - Patients with chronic renal failure and on hemodialysis therapy are susceptible to erythrocyte C5b-9 deposition with subsequent lysis and ghost formation. Susceptibility to complement-mediated erythrocyte injury may contribute to the anemia of chronic renal disease.
The generation from arachidonic acid and purification of large quantities of a series of monohydroxy-eicosatetraenoic acids (HETEs) which differed only in the position of the hydroxyl group permitted an in vitro analysis of the relative effects of the HETEs on a variety of human neutrophil functions. All of the HETEs elicited maximal neutrophil chemotactic responses of comparable magnitude, but the chemotactic potencies exhibited a distinct rank order with 5-HETE greater than 8-HETE:9-HETE (85:15, w:w) greater than 11-HETE=12-L-HETE. Peak chemotactic responses were achieved at concentrations of 1 microgram/ml for 5-HETE, 5 microgram/ml for 8-HETE:9-HETE and 10 microgram/ml for 11-HETE and 12-L-HETE. In the absence of a concentration gradient, the HETEs were similar in potency with respect to the stimulation of neutrophil chemokinesis and the enhancement of the expression of neutrophil C3b receptors. At optimally chemotactic and chemokinetic concentrations, none of the HETEs stimulated the generation of superoxide by neutrophils, altered the expression of neutrophil IgG-Fc receptors, or evoked the release of lysosomal enzymes. Methyl esterification of 5-HETE and 12-L-HETE reduced the chemotactic activity to less than 12% of that of the parent compound. The HETE methyl esters competitively inhibited the chemotactic activity of the homologous free acids by approximately 50% at equimolar concentrations, without inhibiting the chemotactic activity of formyl-methionyl peptides or of chemotactic fragments of the fifth component of complement (C5fr). The stimulus specificity of the competitive inhibition of chemotaxis by HETE methyl esters and the functional selectivity of the HETEs as compared to the formyl-methionyl peptides and C5fr, which stimulate neutrophil oxidative metabolism and lysosomal enzyme release, suggest that HETEs activate human neutrophils by a unique mechanism.
Activation of complement and the relative number of C3b receptors expressed by neutrophils was assessed in patients undergoing haemodialysis with new and reused cellulosic membranes, and with polymethylmethacrylate (PMMA) membranes. Activation of complement was assessed by radioimmunoassay of plasma C3adesArg, and neutrophil C3b receptors were measured by fluorescent flow cytometry of cells indirectly stained with F(ab')2 anti-C3b receptor. During first use of cellulosic dialysis membranes by four patients, the mean expression of C3b receptors by neutrophils in blood taken from the afferent line of the extra-corporeal system after 10, 20, 60 and 120 min of dialysis increased to 127, 189, 255 and 296%, respectively. The mean plasma C3adesArg concentrations in the corresponding samples of blood were 225, 320, 236 and 160% of the pre-dialysis levels. During third and fifth use of the same membranes by these patients, the mean C3b receptor expression by neutrophils did not exceed 150% of the predialysis determination, and correspondingly minimal increases in plasma C3adesArg were observed. Analysis of blood taken simultaneously from the afferent and efferent lines of the first use cellulosic dialysis system indicated that the increase in C3b receptor expression by neutrophils and generation of C3adesArg occurred when blood came in contact with the dialysis membrane. Haemodialysis of four additional patients with the non-complement activating PMMA membrane caused only modest or no increases in neutrophil C3b receptors. Thus, complement activation in vivo is associated with up-regulation of neutrophilic C3b receptors, indicating that this cellular response previously described only in model, in vitro systems, is a physiological mechanism by which this cell can augment its capacity for responding to C3b opsonized material.
Hemodialysis with new cellulosic membranes is associated with profound granulocytopenia, with a nadir 15 min after initiation, followed by a rebound leukocytosis seen 1 h after initiation and persisting up to the termination of dialysis. The rapid reversal of granulocytopenia during hemodialysis has previously been ascribed to down-regulation of granulocyte C5a receptors. In this report, a method of characterizing C5a receptors by using a novel probe consisting of C5a attached to biotin via a six-carbon spacer chain is described. Cellulose acetate electrophoresis and cation exchange HPLC demonstrated a biotin-to-C5a ratio of 1:1. Analysis of granulocyte cell surface C5a receptors were performed with the probe with a fluorescein-avidin conjugate and by using fluorescence flow cytometry. The maximum decrease in C5a receptors was measured at the 15-min sampling time, when the number of C5a receptor decreased from 189,240 +/- 24,500 predialysis to 160,740 +/- 19,380 receptors (P was not significant) at the nadir of granulocytopenia. However, during recovery from neutropenia, granulocyte cell surface C5a receptors increased to 172,140 +/- 19,380 at 30 min and 193,800 +/- 24,510 at the end of dialysis. Concentrations of C3a and C5a peaked at 15 min and declined rapidly thereafter, but both remained significantly above baseline at all times. These studies suggest that down-regulation of C5a receptors, which is seen maximally at 15 min after initiation of dialysis, does not sufficiently account for the reversal of granulocytopenia during hemodialysis.