Analysis of the complement C3 fragments associated with hemodialysis membranes

Modulation of CD11b/CD18 on Monocytes and Granulocytes following Hemodialysis Membrane Interaction in vitro

We studied the generation of CD11b/CD18 mobilizing factors in serum after incubation with dialysis membrane fragments of different chemical composition. We also evaluated the relative importance of the alternative and classical pathways of the complement system in the generation of such factors. Monocytes and granulocytes from healthy blood donors were incubated in normal human serum (NHS) and in NHS that had been preincubated with Cuprophan (CU) membrane (NHS-CU), Hemophan (HE) (NHS-HE) or polysulfone (PS) (NHS-PS). NHS-CU caused the highest up-regulation of the CD11b/CD18 receptor on monocytes and granulocytes. The rank in capacity to mobilize CD11b/CD18 on granulocytes was CU>HE>PS (p<0.001), CU>HE (p<0.05) and HE>PS (p<0.001). The rank in capacity to mobilize CD11b/CD18 on monocytes was CU>HE>PS (p<0.001), CU>HE (p<0.05) and HE>PS (p<0.01). NHS-PS induced a lower up-regulation of CD11b/CD18 compared to NHS which indicates that serum factors with the ability to mobilize the CD11b/CD18 receptor on monocytes and granulocytes are deposited on or adsorbed by PS. In order to study the relative contribution of the alternative and classical pathways of the complement system in the generation of CD11b/CD18 mobilizing factors in serum, three different serum preparations (1. both pathways intact. 2. only the alternative intact and 3. only the classical pathway intact) were used. The CU membrane activated the classical pathway to a larger extent than the PS membrane (p<0.01). When only the alternative pathway was intact no difference in the generation of CD11b/CD18 mobilizing factors between the CU and PS membranes was observed. These studies show that CD11b/CD18 mobilizing serum factors are generated after incubation with CU membranes and that such factors are probably adsorbed by PS. The classical pathway of complement activation seems to contribute to the generation of CD11b/CD18 mobilizing factors in serum.

Complement as a diagnostic tool in immunopathology

The complement system is a complex and autoregulated multistep cascade at the interface of innate and adaptive immunity. It is activated by immune complexes or apoptotic cells (classical pathway), pathogen-associated glycoproteins (lectin pathway) or a variety of molecular and cellular surfaces (alternative pathway). Upon activation, complement triggers the generation of proteolytic fragments that allow the elimination of the activating surface by enhancing inflammation, opsonization, phagocytosis, and cellular lysis. Moreover, complement efficiently discriminates self from non-self surfaces by means of soluble and membrane-bound complement regulators which are critical for innate self-tolerance. Complement deficiency or dysfunction disturb complement homeostasis and give rise to diseases as diverse as bacterial infections, autoimmunity, or renal and neurological disorders. Research on complement-targeted therapies is an expanding field that has already improved the prognosis of severe diseases such as atypical Haemolytic Uremic syndrome or Paroxysmal Nocturnal Haemoglobinuria. Therefore, complement analysis and monitoring provides valuable information with deep implications for diagnosis and therapy. In addition to its important role as an extracellular defense system, it has now become evident that complement is also present intracellularly, and its activation has profound implications for leukocyte survival and function. In this review, we summarize the essential, up-to-date information on the use of complement as a diagnostic and therapeutic tool in the clinics.

Specific adsorption of some complement activation proteins to polysulfone dialysis membranes during hemodialysis

Dialyser bioincompatibility is an important factor contributing to complications of hemodialysis with well known systemic consequences. Here we studied the local processes that occur on dialysis membranes by eluting proteins adsorbed to the polysulfone dialyser membranes of 5 patients after 3 consecutive routine maintenance hemodialysis sessions. At the end of each procedure, a plasma sample was also collected. These eluates and their accompanying plasma samples were separated by 2-dimensional gel electrophoresis; all proteins that were present in all patients were analyzed by tandem mass spectrometry; and a ratio of the relative spot intensity of the eluate to plasma was calculated. Of 153 proteins detected, 84 were found in all patients, 57 of which were successfully identified by mass spectrometry as 38 components of 23 unique proteins. In 10 spots the relative eluate intensity differed significantly from that in the plasma, implying preferential adsorption. These proteins included ficolin-2, clusterin, complement C3c fragment, and apolipoprotein A1. Our finding of a selective binding of ficolin-2 to polysulfone membranes suggests a possible role of the lectin complement pathway in blood-dialyser interactions.

Use of a bovine model to study the role of adhesion molecule CD11/CD18 in hemodialysis-induced neutropenia

The early neutropenia that occurs with cellulose-based dialysis membranes is believed to result from a cascade of immune events: complement activation, engagement of leukocyte adhesion molecules, cytokine release, and leukocyte sequestration. The beta2 integrin CR3 (CD11b/CD18) is upregulated during hemodialysis, binds complement factor iC3b, and mediates leukocyte adhesion to endothelium and leukoaggregation. Despite being invoked in dialysis-induced neutropenia, there is no direct evidence of a role for CD11b/CD18 in the neutropenia. A unique animal model of beta2-integrin deficiency was discovered in calves experiencing recurrent infections and a paucity of leukocytes in infected tissue. We hypothesized that beta2 integrins mediate the neutropenia of dialysis and directly tested this hypothesis using beta2-integrin-deficient calves. Two 3-month old beta2-integrin-deficient and two age-matched Holstein calves were dialyzed using cuprophane dialyzers. Beta2-integrin-deficient calves had less than 2% of normal neutrophil CD18 expression by flow cytometry. Normal calves had a marked decrease in circulating neutrophils (P < 0.05) to 15% of normal 15 minutes into dialysis (total, four treatments), as well as a decrease in monocytes to 39% (P < 0.05) and lymphocytes to 58% (P < 0.05). CD18-deficient calves had an attenuated decrease in neutrophils (65%; P = not significant), monocytes (78%; P = not significant), and lymphocytes (105%; P = not significant) at 15 minutes. These data, although obtained in a small sample, show that a bovine model can be used to study the early neutropenia of dialysis. These data also suggest that a direct role of beta2 integrins may be occurring in this process.

On the binding of complement to solid artificial surfaces in vitro

Since the realization of a complement activation capacity by artificial surfaces upon contact with blood, a common belief has evolved that charged nucleophilic surface groups such as amine (-NH2) and hydroxyl (-OH) react with and eventually bind to the internal thioester in complement factor 3 (C3). A covalent amide or ester linkage is thereby supposed to form between C3b and the surface itself. In this report, we present complement surface binding data by null-ellipsometry for two nucleophilic surfaces (-NH2 and -OH), for surfaces with immunoglobulin G (IgG) covalently bound, and for IgG spontaneously pre-adsorbed to hydrophobic silicon. The results reveal that the plasma proteins that were deposited during complement activation became eluted by sodium dodecyl sulfate. Hence the direct covalent binding between C3 and solid nucleophilic surfaces seems to be only of moderate importance, at least during shorter serum incubations. This strongly suggests that the prevalent covalent linkage model between solid artificial surfaces and C3b is not accurate. Instead we suggest a more pronounced role for C3 associations to other adsorbed proteins and or electrostatic and hydrophobic protein-surface interactions.

Interaction of poly(2-acrylamido 2-methylpropane sulfonate)-grafted polystyrene beads with cationic complement proteins

Influence of various biomaterials on the complement system in serum has been intensively studied by many research groups, since activation of the complement pathway in vivo has been known to give rise to some pathological conditions, such as inflammation and anaphylaxis. Much effort has been devoted to develop new materials that do not activate or deteriorate the complement system. The present work is aimed at revealing the mode of reactions of anionic poly(2-acrylamido 2-methylpropane sulfonate) grafted on polystyrene bead (PAMPS-g-bead) with serum complement. Complement activity assay, determination of complement proteins levels, and immunoblot analysis were carried out for sera pretreated with PAMPS-g-beads. The results clearly showed that, when PAMPS-g-beads were incubated with serum, those beads adsorbed several complement proteins, i.e. C1q, factor D, factor P, C6, and C8, but the generation of activation fragments of complement components was not observed. Especially, factor D was most effectively removed from serum, resulting in potential inhibition of the alternative pathway. A larger amount of PAMPS-g-beads was needed to decrease the serum CH50 level. That may be caused by removal of C6. Although some polyanions, such as dextran sulfate, were reported to activate the complement system, the obtained results indicate that the PAMPS-g-bead is not an activator of the complement pathway, but acts as an adsorbent of complement components. One possible clinical application of the PAMPS-g-beads is adsorption of serum factor D by extracorporeal treatment of patients with renal failure with a high level of factor D, because the increased quantity of factor D in serum may cause consistent activation of the alternative pathway.

Occurrence of C-reactive protein in cryoglobulins

A previous case report described the formation of a complex between a monoclonal IgA with cryolabile properties and C-reactive protein (CRP). Our study provides the first evidence for the frequent occurrence of CRP in cryoglobulins (Cg) of all three types according to Brouet's classification. We performed a systematic immunochemical analysis of cryoglobulins from 18 patients by Western blotting and in 15 of 18 cryoprecipitates a single band (23 KD), immunoreactive with anti-CRP antibody, was demonstrable irrespective of the clonal composition of the cryoglobulins. This band was detectable in 4/5 of type I, in 6/8 of type II, and in 5/5 of type III cryoprecipitates, classified according to Brouet et al. In addition, the complement proteins C1q and C3 were present in nearly all CRP-containing cryoglobulins, presumably reflecting previous activation of the classical complement pathway at least. All three CRP-negative cryoprecipitates were derived from sera with low cryoglobulin content (1-2 g/l). Longitudinal investigation of 23 cryoprecipitates from seven patients confirmed that successful detection of CRP by Western blotting depends on the protein concentration of the cryoglobulins. Since complexed CRP was previously shown to be an effective activator of complement, via C1q binding, CRP may modulate pathophysiologic effects mediated by cryoglobulins in vivo.

Does surface chemistry affect thrombogenicity of surface modified polymers?

With some exceptions, surface chemistry had little effect on platelet and leukocyte activation, and cell deposition, by scanning electron microscopy after blood exposure and clotting times among a group of 12 unmodified and plasma modified tubings. All materials activated platelets and leukocytes to detectable levels, although some materials increased the value of one activation parameter but not another. Unmodified materials [polyethylene (PE), Pellethane (PEU), latex, nylon, and Silastic] and modified materials (H(2)O plasma treated PE and PEU, CF(4) plasma treated PE, fluorinated PEU, NH(4) plasma treated PEU, polyethylene imine treated PEU, and heparin treated PEU) were characterised by XPS and contact angle. The objective of this project was to define a series of assays for the evaluation of hemocompatibility of cardiovascular devices with a view to clarify the specific requirements of ISO-10993-4, and to define an appropriate screening program for new blood contacting biomaterials. PE, PE--CF(4), PE--H(2)0, PEU--F, latex, and PEU-heparin were the exceptions to the general observations, although each behaved differently. PE proved to be least reactive, whereas PE-CF(4) was most reactive by several assays. Platelet microparticle formation (determined by flow cytometry), PTT, postblood exposure SEM, total SC5b-9, C3a, and platelet and leukocyte loss (cell counts) were able to distinguish differences among these materials, and often, but not always, showed expected correlations.

Complement activation by PVA as measured by ELIFA (enzyme-linked immunoflow assay) for SC5b-9

Polyvinyl alcohol (PVA) coated onto polyethylene (PE) tubes exposed to human serum for 1 hour at 37 degrees C resulted in the production of 1.03 +/- 0.04 microg/cm2 of the soluble form of the terminal membrane attack complex, SC5b-9. This was approximately 20 x that produced by the polyethylene. About one quarter of this total was found associated with the surface of PVA. SC5b-9 concentrations were determined by enzyme-linked immunoflow assay (ELIFA) a variant on ELISA that involved drawing the test sample, the antibodies and the chromogenic reagent through a nitrocellulose membrane filter. ELIFA enabled analysis of protein concentrations in the presence of SDS, so that SDS (0.05%) was used to desorb adsorbed SC5b-9 prior to analysis together with SC5b-9 in the bulk to get a more complete picture of PVA-associated complement activation.

Dissociation between complement activation, integrin expression and neutropenia during hemodialysis

Complement activation, neutrophil stimulation, increased cellular adhesiveness, transient leukocyte margination and pulmonary leukostasis take place during hemodialysis with cellulosic dialysis membranes. Several investigators have hypothesized that complement activation is primarily responsible for the acute neutropenia occurring during the early phase of bio-incompatible hemodialysis. We have investigated the relationship between complement activation, levels of expression of CD11b and CD61 integrins on neutrophils and platelets, neutrophil counts and blood gas measurements in patients dialyzed with three types of membranes, known to activate the complement system to a different extent. Polysulfone, cellulose acetate and cuprophane membranes were used subsequently in six patients in a prospective cross-over trial design to reduce inter-individual variability. Increased levels of CD61 and CD11b, as well as neutropenia, were detected regardless of the type of membrane used. We observed a high inter-individual variation with regard to complement activation suggesting varying susceptibility to dialysis membranes. We also report that the kinetics of anaphylatoxin generation were dissociated from those of the upregulation of adhesion molecules, early neutrophil margination and decrease in PaO2 during the first 30 min of hemodialysis. Similar results were obtained with all three types of dialysis membranes. The data strengthen the hypothesis that factors other than complement are involved in the induction of dialysis-related neutropenia and hypoxemia.

Flow cytometric study of in vitro neutrophil activation by biomaterials

Neutrophil activation for adherent and nonadherent cells, as measured by flow cytometry, was not strongly dependent on material surface chemistry. We had hypothesized that material-induced neutrophil activation was an important parameter associated with material failure. All materials tested [cellophane, an acrylonitrile copolymer (AN69), Pellethane, nylon, polyethylene terephthalate, low density polyethylene, and polydimethylsiloxane] activated isolated human neutrophils, which were resuspended in plasma or serum, to similar extents based on L-selectin shedding, CD11b upregulation, and stimulation of the oxidative burst after 30-min exposure. Inhibition of complement activation by sCR1 unexpectedly had little effect if any on nonadherent neutrophils. However, neutrophil adhesion, but not the level of activation of the adherent cells, was strongly dependent on complement activation. Pretreatment with albumin did not inhibit adhesion or reduce neutrophil activation, but plasma pretreatment resulted in increased activation for nonadherent and adherent cells. More adhesion and a higher level of activation of adherent cells was observed following pretreatment with fibrinogen, a ligand of CD11b. Taken together these results suggest that upon contact with a material, neutrophil activation may occur though mechanisms that are not mediated by complement. For example, the presence of plasma proteins such as fibrinogen at the interface may trigger activation and the release of other activating agents. Although the material differences are small, the extent of activation may be significant and warrant further study of the mechanism and consequences of that activation.

National Kidney Foundation report on dialyzer reuse. Task Force on Reuse of Dialyzers, Council on Dialysis, National Kidney Foundation

The Council on Dialysis of the National Kidney Foundation convened an expert panel to evaluate the current practice and literature related to the reuse of hemodialyzers. The panel reviewed and evaluated literature related to reuse since the last report of the National Kidney Foundation recommendations on reuse was published in 1988. The group sought to develop a consensus concerning the effect of reuse of hemodialyzers on mortality; the efficiency of delivered hemodialysis when reused hemodialyzers are used in the clinical setting; the clinical effects of reused dialyzers as compared with dialyzers not reused on intradialytic symptoms; infections in patients using reused dialyzers; and the effect of reused dialyzers on complement activation, cytokine production, and beta2-microglobulin metabolism and clearance. In addition, the panel reviewed the literature on the potential toxicity of germicides used in the processing of dialyzers for reuse as well as recent changes in federally mandated regulations concerning labeling of dialyzers for reuse, the monitoring of the reuse process, and the effectiveness of reused dialyzers to achieve a prescribed delivered clearance as estimated by urea kinetic modeling or by percent urea reduction. The National Kidney Foundation takes no position for or against dialyzer reuse. The principal reason for the practice of reuse is economical. In view of the uncertainties related to the safety and biological impact of reuse procedures, the task force recommends that a full discussion of the issue of reuse and its potential beneficial and detrimental effects be undertaken with each patient. There is no conclusive evidence to substantiate the notion that either morbidity or mortality associated with single use or reuse is different. Microbial contamination of the water used for dialyzer reprocessing increases patient morbidity. The chemical quality of water used for dialyzer reprocessing should, at least, fall within the same standards as those recommended for product water intended for hemodialysis. Dialyzers should not be reprocessed from patients who have tested positive for hepatitis B surface antigen. The effects of reprocessing high-flux dialyzers on beta2-microglobulin clearance are dependent on the reprocessing technique, the number of reuses, and the nature of the dialyzer membrane used. There are insufficient data on the effects of reuse on beta2-microglobulin behavior to make uniform recommendations. Untoward effects of reused dialyzers may still occur in spite of rigorous adherence to the AAMI guidelines. For example, use of the total cell volume method for assessing changes in small molecule clearances will not show the loss of performance attributable to dialysate shunting. For this reason, the measurement of Kt/V for urea as recommended by the AAMI or the determination of the urea reduction ratio (URR) is strongly recommended at least monthly to gauge the adequacy of the dialysis procedure. Given the significant fall in dialyzer efficiency for urea removal that can occur after repeated uses of a dialyzer, dialysis prescriptions in units practicing reuse should be designed to deliver a Kt/V or URR value that exceeds the dose used for patients treated with single-use dialyzers to make allowance for any possible reuse-induced reduction in dialyzer efficiency. Technicians and other personnel responsible for the reprocessing of dialyzers should receive proper training. These health care providers should be certified in reprocessing by an examining body so that professional competency can be assured.

Biocompatibility of membranes used in the treatment of renal failure

Haemodialysis membranes with a wide range of solute and hydraulic permeabilities are used clinically. Such membranes are manufactured from either cellulose or synthetic co-polymers and their biocompatibility is commonly characterized by the complement activation and white cell changes observed during their use. The cellobiosic unit may be modified by the partial or total replacement of the hydroxyl groups by diethylaminoethyl (Hemophan), acetate (cellulose acetate), triacetate (cellulose triacetate) or 2,5-acetate (Diaphan). We have undertaken a prospective study in which such renal membranes have been studied in terms of the complement activation and neutropenia produced with the aim of investigating the relationship between modification of the cellobiosic unit and the magnitude of neutropenia and complement activation, and the extent to which membrane base material influences these parameters, by comparing the changes observed in modified cellulose membranes with that for a synthetic membrane (polysulphone). Our findings show that, while the degree of substitution varies between < 1% and total substitution, there is no correlation between the numbers of hydroxyl groups replaced and alteration of complement activation and neutropenia. However, by modification of the cellobiosic unit it is possible to produce a membrane whose biocompatibility is similar to that of a membrane manufactured from a synthetic co-polymer such as polysulphone.

Possible clinical effects of the interaction of hemodialysis membranes with adhesion proteins

In this study data obtained in an in vitro hemodialysis model are related to various parameters measured in patients' plasma during hemodialysis in a clinical crossover study. In vitro, blood from healthy volunteers was dialyzed under standardized conditions using the capillaries Fresenius MTS C (Cuprophane) and Hospal AN 69 (Polyacrylonitrile). Following dialysis, surface bound proteins were eluted with saline, 1 M Tris and 2% SDS, and analyzed by immunoblotting. Depending on the capillary, different protein patterns could be identified in the eluates. Intact forms of adhesion proteins were predominantly (fibrinogen) or exclusively (vitronectin) found in PA eluates. In contrast, low molecular weight products of fibrinogen as well as high molecular weight components containing antithrombin III (AT III) were present in CP eluates. Their presence may reflect fibrinolytic and procoagulatory activity during dialysis with CP capillaries. A microscopic investigation of CP membranes demonstrated fibrin lined platelet conglomerates. In the plasmas of patients dialyzed with CP capillaries high D-Dimer concentrations were found. We also noticed that during dialysis with PA membranes less heparin was consumed than during dialysis with CP membranes. Our study showed a good correlation of the observations in the vitro system and the measurements in patient samples.

Role of bioincompatibility in dialysis morbidity and mortality

This review examines the mechanisms by which bioincompatibility in dialysis systems may have an effect on morbidity and mortality in the dialysis population. Direct toxic effects of membrane materials and various chemical substances have been well demonstrated in the chronic dialysis population. Activation of the complement cascade and stimulation of cytokine production may have autocrine effects on leukocyte function with sequelae such as enhanced rates of infection and the development of B2-microglobulin amyloidosis. The variable effect of different membrane materials on each of these effector systems is examined. Bioincompatibility may effect the incidence of infection, malignancy, cardiopulmonary disease, and malnutrition as well as induce novel disease processes. All these confounding variables must be considered when evaluating the effect of dialysis on mortality and morbidity.

Soluble complement receptor type 1 inhibits complement activation induced by hemodialysis membranes in vitro

A variety of bioincompatible events that occur during hemodialysis have been attributed to complement activation. However, cause-effect relationships have been based primarily on indirect evidence and the results of in vitro studies, because an acceptable method for inhibiting complement activation during clinical hemodialysis has been unavailable. Methods for inactivating complement in vitro are available, but the most commonly used of these techniques (heat inactivation and chelation of divalent cations) lack specificity. A recombinant, soluble form of human complement receptor type 1 (sCR1) has been developed recently and shown to inhibit complement activation in vivo. Here, we report studies aimed at determining the effects of sCR1 on dialysis-induced complement activation and neutrophil degranulation. In a concentration dependent fashion, sCR1 inhibited plasma complement activation by cuprophan membrane in vitro. Using a maximally inhibitory concentration (30 micrograms/ml), sCR1 blocked generation of C3a(desArg) by cuprophan, cellulose acetate, and polymethylmethacrylate membranes by 90%, 84%, and 84%, respectively. In contrast, elastase release (a measure of neutrophil degranulation) was inhibited by 70%, 70%, and 44%, respectively, suggesting that dialysis-induced neutrophil activation is mediated in part by noncomplement dependent mechanisms. Both heat- and EDTA-treatment of plasma abolished dialysis membrane-induced complement activation, but these treatments also affected noncomplement dependent components of the degranulation process. These observations show that, compared with other commonly used methods for inhibiting dialysis induced complement activation, sCR1 is more specific. An additional advantage of sCR1 is its potential for use in the clinical setting.

Complement activation by cellulosic dialysis membranes

AIMS

To assess the effect of cellulosic dialysis membranes on the production of complement degradation products to determine to the role of the classical pathway.

METHOD

Complement activation was studied in 33 patients during a single haemodialysis session using cellulosic membranes. Pre- and post-dialysis plasma EDTA valves of C3, C4, C3dg, C4d and C reactive protein (CRP) were measured. Statistical analysis was done using the Wilcoxon signed rank test.

RESULTS

Post-dialysis C4 (p = 0.0003), C3dg (p < 0.0001), and C4d (p = 0.003) concentrations were increased compared with pre-dialysis values. There was no significant change in C3 (p = 0.095) and CRP (p = 0.13) values. Post-dialysis C3dg and C4d concentrations correlated significantly (p = 0.007). IgG, an undialysed molecule, was quantified and post-dialysis valves were significantly higher than those before dialysis (p = 0.0002), indicating a degree of haemoconcentration. To remove this effect, the C3:IgG, C4:IgG, C3dg:IgG, C4d:IgG and CRP:IgG ratios were calculated. Compared with pre-dialysis values, post-dialysis C3dg:IgG and C4d:IgG ratios were increased and C3:IgG decreased significantly. No change was observed in C4:IgG and CRP:IgG ratios.

CONCLUSION

This study confirms that significant complement activation takes place following dialysis with cellulosic membranes. This is denoted by an increase in C3dg. This was paralleled by a rise in C4d, implying a contributory role for the classical pathway. Concomitant post-dialysis increases in IgG and C4 indicate a degree of haemoconcentration; but removal of this effect shows that C3dg and C4d are increased following dialysis--suggesting classical, in addition to alternative, pathway activation.

Plasma protein adsorption to hemodialysis membranes: studies in an in vitro model

Upon interaction of whole blood with foreign materials, heterogeneous protein films are deposited onto the artificial surface (eg, hemodialysis membranes). The composition of these protein films subsequently affects various processes, eg, thrombogenesis or activation of the complement system. We developed an in vitro model with which we can identify and study proteins interacting with capillaries during hemodialysis. Using this model we studied the cuprophane dialyzer GFS 120 (CP) and the polymethylmetacrylate membrane Filtryzer B2-1.2 (PMMA). Heparinized whole blood from healthy young volunteers was dialyzed on an extracorporeal dialysis machine. After the dialysis procedure the adsorbed material was eluted from the hemodialysis membranes by different eluants and subsequently analyzed by sodium dodecyl sulfate-polyacrylamide gel electrophoresis (SDS-PAGE) and immunoblotting. A number of proteins could be identified in the eluates of both membrane types. Interestingly, platelet glycoproteins could only be found in PMMA eluates. Albumin, IgG, and antithrombin III were mainly present in the cuprophane eluates. Fibrinogen was demonstrable in all eluates, but in relatively low amounts, and the protein was significantly degraded. Degradation products of antithrombin III and complement factor 3 could also be identified. The process causing the degradation has not yet been identified, but may be due to proteases released from damaged cells.

Beta2 integrins are required for neutrophil degranulation induced by hemodialysis membranes

An untoward consequence of hemodialysis is degranulation of peripheral blood neutrophils. The mechanisms that mediate this process, however, have not been conclusively identified. In the present study, the participation of complement activation and beta 2 integrins (CD11/CD18) in hemodialysis-induced neutrophil degranulation was investigated. Incubation of neutrophils with cuprophan membrane stimulated the release of very small amounts of the cytoplasmic granular protein, elastase. This release was markedly enhanced by the addition of plasma. Inactivation of complement reduced degranulation by approximately 60%, but the contribution of anaphylatoxins C3a and C5a to the degranulation process was modest. Treatment of plasma with EDTA completely abolished neutrophil degranulation in the presence of cuprophan membrane. Further, when incubated with plasma and cuprophan membrane, neutrophils that are deficient in beta 2 integrins released only 10% as much elastase as normal cells. Together, these observations strongly suggest that one or more members of the beta 2 integrin family of receptors is essential for cuprophan membrane-induced neutrophil degranulation and that both complement-related and noncomplement-related factors serve as receptor ligands.

Identification of proteins absorbed to hemodialyser membranes from heparinized plasma

The protein layers formed during contact of plasma with hemodialysis membranes were studied. Dialysers having membranes of cellulose acetate (CA), saponified cellulose ester (SCE), cuprophane (CUP), polymethylmethacrylate (PMMA), and polyacrylonitrile (PAN) were used. Heparinized human plasma was recirculated through the dialysers for four hours. They were then rinsed and the proteins adsorbed to the membranes were eluted with 2% SDS. The yields of protein from the different membranes increased in the order: PMMA < CA < SCE < CUP < PAN. This is the probable order of increasing hydrophilicity. SDS-PAGE and Western blots were performed on the dialyser eluates. The blots were positive for most of the twenty proteins tested for. There were some interesting differences in adsorption patterns among the different membrane materials, notably for high molecular weight kininogen (HMWK), plasminogen and the C3 component of complement. HMWK was intact in the eluates from CA, CUP and SCE, whereas on PMMA and PAN there was evidence of cleavage, suggesting that activation of the contact phase of coagulation was more extensive on the latter two materials. Intact plasminogen was visible on all the blots. However, low molecular weight fragments were visible in the PAN eluates, suggesting activation of the fibrinolytic pathway. Low molecular weight fibrinogen fragments eluted from PAN membranes support this conclusion. C3 was visible in the blots obtained for all membrane materials, and the data suggest that complement is activated by all the membranes. A C3 fragment at about 30 kD (possibly C3d) was seen in the blots for the cellulosic membranes but not for PMMA or PAN.

Complement activation and cytokine production as consequences of immunological bioincompatibility of extracorporeal circuits

The use of devices which result in exposure of blood to artificial surface has gained increasing importance in routine medical and surgical practice. In the field of biocompatibility, attention has long been directed at the mechanisms of thrombus formation of surfaces. In recent years however, a special interest has emerged for the study of the immunological consequences of blood-artificial surface interactions, thus broadening the concept of hemocompatibility. The contact of blood with artificial devices results in the activation of a number of humoral and cellular processes involved in natural and in specific immunological recognition of foreign surfaces by the host, and in the secondary occurrence of acute and chronic adverse reactions in patients undergoing extracorporeal circulation. The purpose of this review is to discuss the mechanisms involved in immunological bioincompatibility of extracorporeal circuits, with particular emphasis on the molecular basis of the activation of the complement system, the role of endotoxins, and the induction of cytokine production by activated monocytes.

Complement activation during low-density lipoprotein apheresis

Complement system activation was investigated in two girls with familial homozygous hypercholesterolemia undergoing two monthly sessions on LA15 or LA40 (Kaneka liposorber). We determined blood levels of C3c and C3a, leukocyte counts, and plasma levels of C3c and C3a in the extracorporeal circulation device at the start of the sessions and 15 and either 60 or 120 min into them. Sequential eluates were collected from LA40 at the end of the sessions (0.5M NaCl, 1M hydroxylamine). Anaphylatoxin C3a increased throughout, especially with LA40. As previously reported, C3a was trapped in the dextran column but was noticeably present in efferent plasma. Besides many proteins, nonnative complement fragments bearing C3a and C3d antigens were detected in almost all the eluates, suggesting possible in situ complement activation. Practically, complement activation induced by the first filter is a risk; long-term side effects may arise from this extracorporeal circulation device.

The use of spent renal dialysis membranes for the isolation of large numbers of human neutrophils for biochemical studies. Application to purification of the myeloid IgA receptor (Fc alpha R)

Human neutrophils (PMN) can be eluted from spent Cuprophan renal dialysis membranes in large numbers (10(9)-10(10) per dialyser cartridge) and in relatively high purity by washing the membranes with 0.35 M NaCl. This offers the possibility of isolating relatively large amounts (10(-4)-10(-3) g) of minor PMN proteins such as those expressed on the cell surface. Here the technique is applied to the purification of the neutrophil IgA receptor (Fc alpha R). Affinity chromatography on IgA-Sepharose of NP-40 extracts of 125I-labelled PMN isolated from fresh venous blood routinely gave a receptor preparation showing one diffuse band, Mr 50-70 kDa, upon analysis by SDS-PAGE and autoradiography. When the same method was used with larger numbers of unlabelled PMN from fresh venous blood or renal dialysis membranes a preparation was obtained which gave multiple bands upon analysis by SDS-PAGE silver stained gels due to contamination of the receptor with cytoplasmic proteins which bound non-specifically to the IgA-Sepharose. Most of these contaminants could be removed by chromatography of the IgA-Sepharose eluates on wheat germ agglutinin-Sepharose.

Biocompatibility issues in hemodialysis

Hemodialysis, as a life-saving treatment modality for uremic patients, implies a repeated and compulsory contact of blood with foreign materials. As a consequence, biocompatibility problems are unavoidable. The same applies for the material used for the creation of vascular access, and for the alternative dialysis method, CAPD (continuous ambulatory peritoneal dialysis), although each system might cause its own and specific problems. Although in early dialysis the focus has been on maintenance of life and elimination of toxins, later on the important morbid implications of this lack of biocompatibility have been recognized. Eight major problems will be discussed, especially in the perspective of recent new findings in this field: (1) coagulation and clotting; (2) complement and leukocyte activation; (3) susceptibility to infection; (4) leaching or spallation; (5) surface alterations of solid materials; (6) allergic reactions; (7) shear; (8) transfer of compounds from contaminated dialysate. After description of the major biochemical and clinical implications of these problems, ways to prevent morbid events and future perspectives will be described.

Adherence of neutrophils to hemodialysis membranes: role of complement receptors

Complement activation occurs during hemodialysis using cellulosic dialysis membranes with the consequent deposition of C3 activation and degradation products on the membrane surface. To determine if these complement fragments are functionally active, we examined their capacity to mediate leukocyte adherence to cuprophan membranes. Immunoblotting of proteins eluted from plasma-treated cuprophan membranes confirmed the presence of both C3b and iC3b. Incubation of cuprophan membranes with heparinized whole blood resulted in adherence of leukocytes but not erythrocytes. Neutrophils were the primary cell type bound, with monocytes comprising less than 5% of the adherent cells. Studies using indium-labeled neutrophils demonstrated that the binding was plasma dependent and increased with time up to two hours. Neutrophil binding was inhibited by preincubation of the plasma-treated cuprophan membrane with anti-C3 or preincubation of neutrophils with an antibody directed against the alpha chain of complement receptor type 3 (CR3). These observations indicate that iC3b deposited on cuprophan membrane surface as a result of complement activation mediates neutrophil adherence via interaction with CR3. They also support the hypothesis that, in addition to the anaphylatoxins released into the fluid phase, complement activation products that remained membrane bound during hemodialysis also stimulate pathophysiological responses.

Diagnostic significance of hypocomplementemia

Hypocomplementemia is an important marker for the presence of IC-mediated disease and can be used to assess disease activity. However, in interpreting the clinical significance of hypocomplementemia, the following must be kept in mind: 1) There are numerous non-immunologic conditions that also can cause hypocomplementemia. Furthermore, some of these conditions can cause a multisystem disease that, along with the hypocomplementemia, can closely resemble an IC-mediated systemic vasculitis. Furthermore, these nonimmunologic conditions that lower serum complement levels can complicate the course of patients with inactive IC-mediated disease, spuriously indicating that the disease is active. The most relevant of these differential diagnostic problems are listed in Table 2. 2) There are a few conditions (for example, pregnancy) that can raise serum complement levels, thereby possibly obscuring the presence of a disorder (such as, active SLE) that is lowering complement levels. 3) There are some conditions that might be expected to lower serum complement levels, because of their effect on protein metabolism, but do not. Nephrotic syndrome, and moderately poor nutrition are examples. All of these factors should be considered when interpreting results of serum complement levels in a given patient.

Analysis of proteins eluted from hemodialysis membranes

To further investigate the types of interactions occurring between blood and hemodialysis membranes, proteins were sequentially eluted from used dialysers. Four different membranes (cuprophan, hemophan, cellulose acetate and polyacrylonitrile) were successively treated with a hydrogen bond cleaving agent (10 M urea), an ionic detergent destabilizing the hydrophobic interactions between apolar groups (SDS solution), and a hydroxylamine solution at alkaline pH to release postulated covalently bound C3 fragments. The eluted proteins were analyzed by SDS-PAGE and immunological techniques. Total protein determinations demonstrate different behaviour of the membranes as regards the 'protein cake'. Electrophoretic analysis suggests that qualitative and quantitative differences in the binding of the blood proteins are related to the membrane material. Complement fragment studies indicate that the complement activating potential of the dialysis membrane may not be determined by the availability of potential binding sites for activated C3b. An attempt is made to correlate these results with the biocompatibility concept.

Isolation and characterization of a complement-activating lipid extracted from human atherosclerotic lesions

The major characteristics of human atherosclerotic lesions are similar to those of a chronic inflammatory reaction, namely fibrosis, mesenchymal cell proliferation, the presence of resident macrophages, and cell necrosis. Atherosclerosis exhibits in addition the feature of lipid (mainly cholesterol) accumulation. The results of the present report demonstrate that a specific cholesterol-containing lipid particle present in human atherosclerotic lesions activates the complement system to completion. Thus, lipid could represent a stimulatory factor for the inflammatory reaction, whose underlying mechanistic basis may be, at least in part, complement activation. The complement-activating lipid was purified from saline extracts of aortic atherosclerotic lesions by sucrose density gradient centrifugation followed by molecular sieve chromatography on Sepharose 2B. It contained little protein other than albumin, was 100-500 nm in size, exhibited an unesterified to total cholesterol ratio of 0.58 and an unesterified cholesterol to phospholipid ratio of 1.2. The lipid, termed lesion lipid complement (LCA), activated the alternative pathway of complement in a dose-dependent manner. Lesion-extracted low density lipoprotein (LDL) obtained during the purification procedure failed to activate complement. Specific generation of C3a desArg and C5b-9 by LCA indicated C3/C5 convertase formation with activation proceeding to completion. Biochemical and electron microscopic evaluations revealed that much of the C5b-9 present in atherosclerotic lesions is membraneous, rather than fluid phase SC5b-9. The observations reported herein establish a link between lipid insudation and inflammation in atherosclerotic lesions via the mechanism of complement activation.

Lack of responsiveness to glucose of microencapsulated islets of Langerhans after three weeks' implantation in the rat--influence of the complement

Microencapsulated islets of Langerhans retrieved from peritoneal cavity of rats three weeks after implantation had a reduced hormonal secretion and were no longer responsive to alterations in glucose levels. Activation of complement could not completely account for the observed fibrosis which was thought to be responsible for the loss of responsiveness of the encapsulated cells.

Transcription, not synthesis, of interleukin-1 and tumor necrosis factor by complement

Stimulation of interleukin-1 beta (IL-1 beta) and tumor necrosis factor (TNF alpha) production was studied during in vitro hemodialysis (HD) of whole blood using cuprammonium (Cup) or polysulfone (PS) dialyzers. In the absence of LPS, circulation of whole blood for two hours through Cup or PS dialyzers was not sufficient to induce production of IL-1 beta or TNF alpha in peripheral blood mononuclear cells (PBMC) during subsequent 24 hour culture. However, compared to freshly isolated cells, post-HD PBMC were primed to produce more IL-1 beta and TNF alpha when subsequently stimulated with LPS. Despite the lack of spontaneous monokine synthesis after HD, we observed transcription of mRNA coding for IL-1 beta and TNF alpha after two hours of LPS-free HD. When compared to levels of mRNA induced by 5 ng/ml LPS (100%), Cup induced 27 +/- 6% whereas PS did not induce detectable transcription of IL-1 beta. In the case of TNF alpha mRNA, Cup induced 26 +/- 8% and PS 13 +/- 3%. Recombinant C5a induced mRNA for IL-1 beta in PBMC without detectable IL-1 beta protein synthesis. We conclude that transcription of mRNA for IL-1 beta and TNF alpha during HD is primarily caused by complement activation by Cup, but that LPS or other factors are required for translation of IL-1 beta and TNF alpha mRNA transcribed during HD.

Adsorption of unactivated complement proteins by hemodialysis membranes

Hemodialysis using polyacrylonitrile (PAN) membranes has been reported to be associated with depletion of complement in the plasma, yet the increase in plasma C3a antigen concentrations and the degree of leukopenia are modest. These observations suggest that PAN membranes may have a large propensity to adsorb native complement proteins; as a consequence, complement depletion can occur without activation. In the present study, we observed that incubation of human serum in the presence of PAN membrane resulted in a 50% loss of serum hemolytic activity of C3. When radiolabeled purified components were offered, PAN membranes were found to adsorb C3 and C5 in a dose-dependent manner. Adsorption of these proteins by PAN was more than 20 times greater than adsorption by cuprophan, cellulose acetate or Hemophan (Akzo, formerly Enka, Wuppertal, FRG) at all concentrations examined. These results suggest that depletion of complement when serum is exposed to hemodialysis membranes may result from adsorption of complement components onto the membrane surfaces and does not necessarily indicate complement activation.

Activation of the alternative pathway of complement by cellulosic hemodialysis membranes

Compared to cellulose acetate, hemodialysis with cuprophan membranes is associated with greater activation of the alternative pathway of complement. Previous studies have shown that this difference is not due to a greater number of potential covalent binding sites for activated C3 on cuprophan. To investigate further the factors that influence complement activation by hemodialysis membranes, proteins were eluted from serum-treated cuprophan and cellulose acetate membranes with hydroxylamine at alkaline pH and analyzed by SDS-PAGE and Western blot. Approximately 23 times more total protein was removed from cellulose acetate. Virtually all the C3 in the cellulose acetate eluate was in the form of inactive fragments C3c and C3dg. In contrast, the functionally active form of C3 (C3b) was a prominent constituent of the cuprophan eluate. The binding of factor B (precursor of the catalytic subunit of the C3 convertase) and factor H (regulatory protein of C3 activation) to serum-treated membranes was also analyzed. By Scatchard's method, the affinity constant at equilibrium for factor B binding (KB) to the two types of membranes was not significantly different; however, there were approximately four times more factor B binding sites on the cuprophan than on the cellulose acetate. For cuprophan, the number of factor B binding sites was 1.6 times greater than the number of factor H binding sites. These studies demonstrate that a portion of the C3b molecules that bind to cuprophan are protected from degradation, and suggest that the complement activating capacity of hemodialysis membranes is determined by biochemical properties that modulate both the binding of serum proteins to the membrane and the interactions of the endogenous regulatory proteins with membrane-associated C3b.