Haemolytic 'efficiency' of C5b-9 complexes in drug-induced immune haemolysis: role of cellular C5b-9 distribution

Drug-induced immune hemolytic anemia

BACKGROUND

Drug-induced immune hemolytic anemia is frequently associated with serious complications.

OBJECTIVE

To identify which drugs are implicated in drug-induced immune hemolytic anemia, how they stimulate the production of antibodies and how they could be identified.

METHODS

Individual studies were selected from Pubmed and Scholar databases without any time restrictions placed on the studies. All English language reports including those from the cross-references (approximately 560) were carefully studied. The results of the most relevant clinical and serological studies in this field are summarized and discussed in this review.

RESULTS

Drugs may lead to the production of two types of antibodies. One type reacts with red blood cells (RBCs) only in the presence of the drug and/or its metabolites, and predominantly causes complement-mediated intravascular hemolysis. The second type reacts with RBCs, also in the absence of the drug, belongs to the IgG class, does not activate complement and causes Fc-mediated extravascular hemolysis. Some drugs may stimulate the production of both types of antibodies. Meanwhile, > 130 drugs have been reported to be the cause of immune hemolytic anemia (IHA) but the data are frequently incomplete or implausible.

CONCLUSION

The number of drugs involved in inducing IHA is increasing. However, the vast majority of these drugs seem to cause IHA only in isolated cases. Based on the number of reports in the literature, new drugs that most frequently cause IHA are the new generation of cephalosporins, diclofenac, oxaliplatin and fludarabin.

Cold target competition analysis of the classical activation pathway of complement-mediated cytotoxicity: a non-interaction model for competing lysis

A mathematical analysis of cold target competition experiments of complement-mediated lysis is presented, aimed at developing a minimal model of lysis where no interaction between the competing populations of sensitized blood group A and B erythrocytes is presumed. The model is able to predict the extent of lysis from the input values with remarkable accuracy suggesting that under the conditions used no stimulation and/or inhibition of the lysis of the sensitized erythrocytes occurs. The distribution of complement between the competing A and B erythrocyte populations is approximated by the model and found to be proportional to the 5th and 4th power of the ratios of the antibody and target cell concentrations, respectively. In accordance with earlier observations, suggesting that the interaction between the antibody and the C1q molecules is based on polar electrostatic charges, we propose that the sensitizing antibody provides an electrostatic field around the erythrocytes which attracts C1q molecules towards their membranes.

Functions and relevance of the terminal complement sequence

The terminal complement sequence is initiated upon cleavage of C5 with liberation of C5a anaphylatoxin, and involves the assembly of macromolecular C5b-9 complexes either on cell surfaces or in plasma. Cell-bound C5b-9 complexes generate transmembrane pores that can cause cell death, or they can elicit secondary cellular reactions triggered, for example, by passive flux of calcium ions into the cells. In vivo functions of the fluid-phase SC5b-9 complex have not yet been defined, but the identity of S-protein with vitronectin (serum spreading factor) provokes the anticipation that significant biological functions of this complex do exist. The terminal complement sequence may fulfil protective functions when it is triggered on alien cells that are marked for destruction. Dysregulation in the complement sequence may, however, result in detrimental attack by C5b-9 on autologous cells. Examples include not only autoimmune disease states, but also the activation of complement on dead or dying cells, and bystander attack on blood cells during cardiopulmonary bypass. Methods for detecting and quantifying C5b-9 are outlined, and the potential usefulness of such assays in clinical research is discussed.

Donath-Landsteiner autoimmune hemolytic anemia in children. A study of 22 cases

During the last 4 years, we have studied a total of 531 adults and 68 children with clinically and serologically well-defined forms of immune hemolytic anemias. Among these, Donath-Landsteiner (DL) hemolysis was the underlying disease in 22 of the 68 children (32.4%), but was not observed in adults. All children with DL hemolysis suffered from acute infections presumably of viral origin. In none of the cases was the DL hemolysis suspected clinically. Boys were more often affected than girls. The hemolytic episodes were severe, but resolved within few weeks. Serologically, all patients had a strongly positive direct antiglobulin test (DAT) using anti-C3d reagents, but a weak (n = 6) or negative (n = 16) IgG-DAT. DL hemolysins were always weak and transient, detectable with enzyme-treated red blood cells (RBC) in all, with untreated RBC in 12 of 22 sera. To explore the reason why these weak antibodies can cause extensive hemolysis in vivo, we compared the action of DL antibodies and of cold agglutinins (anti-I) on RBC by several reincubations at 4 and at 37 degrees C. The data obtained from this experiment demonstrate a stronger aggravation of hemolysis by DL than by anti-I antibodies, presumably due to low-affinity interaction between the cells and DL antibodies.

Fluid phase generation of terminal complement complex as a novel index of bioincompatibility

Blood membrane interactions in hemodialysis have been shown to trigger complement (C) activation. As indicators of C-activation the anaphylatoxins (C3a and C5a) are problematical because of methodological difficulties and their kinetic properties. We developed a sensitive and specific micro-ELISA using a monoclonal antibody against neoantigens on the terminal complement complex (TCC); highly purified human TCC served as standard. Concentrations of TCC were measured in single-path perfusion systems (in vitro) and in the blood lines (arterial inlet; venous outlet) of patients on hemodialysis using steam-sterilized or ETO-sterilized dialyzers with the following membranes: cuprophan (CU), hemophan (HE) and polysulfone F6 (PS), respectively. All dialyzers with identical geometry were run under identical conditions. All membranes tested caused continuously ongoing net generation of TCC. In vitro, contact of serum with CU minidialyzers resulted in fivefold higher net release of TCC compared with HE and PS. In vivo TCC concentration-time profiles differed significantly between membranes in the rank order CU much much greater than HE greater than PS (mean basal concentration 58 x 10(-11) M; peak increase over baseline with CU 40-fold, HE fourfold, PS threefold). In addition, more TCC was generated from the same dialyzers with ETO than steam sterilization. TCC differed from C3a and C5a in the following respects: (i) lower detection limit (4 x 10(-11) vs. less than 5 x 10(-9) M for both C-anaphylatoxins); (ii) higher relative increment (inlet) during CU dialysis (25-fold vs. eightfold and twofold, respectively); (iii) C-anaphylatoxins yielded the same ranking (CU much greater than HE greater than PS), but TCC concentrations were not a linear function of C3a or C5a concentrations, respectively. Kinetic analysis (Bateman function) showed significant differences of invasion constants between membranes, that is, CU 0.088 min-1, HE 0.09, PS 0.168. The net amount of TCC released from the dialyzer was calculated under certain assumptions. It was 75.5 mg/4 hr for CU, 7.3 for HE and 5.0 for PS. The elimination constant was also dependent on the type of membrane. Using flow cytofluorometry and immunohistochemical methods (APAAP), TCC was demonstrated on membranes of granulocytes obtained during dialysis; this is compatible with potential in vivo cell activation. Generation of PGE2 and TNF alpha by adherent monocytes induced by cuprophan was C8 dependent: levels were significantly increased by addition of C8 to C8 deficient human serum concomitantly with generation of TCC.(ABSTRACT TRUNCATED AT 250 WORDS)

In vitro fixation of C3d and C5b-9 on platelets by human platelet reactive antibodies

Most platelet-reactive autoantibodies and alloantibodies are not able to fix complement in vitro. However, exceptions have been found. These antibodies are usually characterized by the conventional platelet complement fixation test. A recently developed competitive enzyme immunoassay for quantitation of platelet-associated immunoglobulins and a modification thereof allowed the quantitative study of fixation of C3d and the membrane attack complex (C5b-9) on platelets by HLA antibodies, human platelet autoantibodies, and drug-dependent antibodies (ddab). The highest amounts of both complement products were fixed through ddabs, whereas autoantibodies only showed moderate complement fixation. This enzyme immunoassay is a valuable tool for the characterization of the complement-fixing properties of platelet-reactive antibodies.

Complement-independent lysis of human red blood cells by cold hemagglutinins

Hemolysis mediated by human antibodies is generally ascribed to the attack of red blood cells (RBC) by complement. We here extend earlier in vitro observations which indicate that potent cold agglutinins can directly cause lysis of RBC without the participation of complement. We have noted that EDTA plasma taken from patients with cold agglutinin disease is frequently reddish if the plasma is not immediately separated from the cells at 37 degrees C. Moreover, eluates prepared in such cases from plasma or heat-inactivated serum (30 min at 56 degrees C) by absorption (at 4-20 degrees C) and elution (at 37 degrees C) are usually contaminated with hemoglobin, and a large number of RBC used for absorption is lost during the procedure. To characterize this phenomenon further, we examined the effect of different hemagglutinating antibodies in vitro on normal RBC in the absence of complement. Hemolysis (5-17%) of RBC only occurred after treating the cells with potent antibodies at low temperatures (0-20 degrees C). This hemolysis increased 2- to 3-fold when the RBC were treated with an enzyme and decreased with rising temperature. Unlike cells hemolyzed by complement activation, no C5b-9 complexes could be detected on RBC damaged by this mechanism.

Deposition of terminal C5b-9 complement complexes on erythrocytes and leukocytes during cardiopulmonary bypass

Hemolysis, leukopenia, a hemostatic deficit, and nonspecific systemic reactions collectively known as the postperfusion syndrome develop in patients who undergo cardiopulmonary bypass. We now report that terminal C5b-9 complement complexes are deposited on erythrocytes and polymorphonuclear neutrophilic leukocytes during cardiopulmonary bypass. Plasma samples taken from 48 unselected patients during and at the end of cardiopulmonary bypass contained raised levels of fluid-phase SC5b-9 complement complexes, indicating that the complement sequence had been activated to completion. Various degrees of overt intravascular hemolysis were observed in all the patients, and lysed erythrocyte membranes were recovered from the blood samples. Immunoassays performed with use of antibodies to C5b-9 neoantigens demonstrated the presence of C5b-9 on red-cell ghosts but not on intact erythrocytes. The appearance of ghosts carrying C5b-9 always coincided with hemolysis. Furthermore, granulocytes isolated from 20 patients during bypass were all found to carry C5b-9 complexes, whereas cells isolated before or 24 hours after surgery carried no C5b-9. The neoantigen-positive material present in detergent extracts of granulocytes sedimented in a broad peak (25 to 40 sedimentation coefficient [S]) in sucrose-density gradients, exactly as did pore-forming C5b-9 complexes. Deposition of C5b-9 on blood cells during cardiopulmonary bypass may be partly responsible for the hemolysis and may augment granulocyte activation by the stimulation of arachidonate metabolism in those cells.

Complement inhibitor S protein is associated with membranes of red blood cells from patients with paroxysmal nocturnal haemoglobinuria

S protein is a plasma glycoprotein (Mr = 78,000) which binds to nascent C5b-7 complexes upon complement activation in the fluid phase in whole serum. It thereby protects innocent bystander cells from complement mediated lysis. It is unknown whether S protein also functions as complement inhibitor on cell surfaces. We here report that S protein is recognized on red blood cells (RBC) from patients with paroxysmal nocturnal haemoglobinuria (PNH), but not on normal RBC. RBC from eight PNH patients showed 12-48% haemolysis subsequent to complement activation in the fluid phase, while normal RBC did not respond. Preincubation of the PNH cells with affinity-purified antibodies against human S protein resulted in a three- to five-fold increase of haemolysis, while preincubation of these cells with S protein decreased haemolysis by 40%. In contrast, haemolysis remained unaffected by other unrelated antibodies, i.e. IgG anti-Rh(D) and anti-A. If PNH RBC, normal RBC pretreated with 2-amino-ethylisouronium bromide (AET), or untreated normal RBC, respectively, were incubated with purified S protein in vitro, the uptake of antibodies against S protein was significantly enhanced with PNH and with AET-treated, but not with untreated normal RBC. Additionally, while normal RBC did not respond to reactive lysis initiated by purified C5b-6 and C7, PNH as well as AET-RBC showed significant haemolysis that could be inhibited by S protein in a dose-dependent fashion. These findings strengthen the assumption that the increased sensitivity of PNH cells towards reactive complement lysis is either due to the lack of an inhibitor of the terminal complement sequence and/or enhanced insertion of the membrane attack complex. These defects of PNH RBC may partly be overcome by the fluid phase complement inhibitor S protein which binds to PNH RBC and may thereby suppress homologous cytolysis.