Rapid activation of the complement system by cuprophane depends on complement component C4

Profiling of time-dependent human plasma protein adsorption on non-coated and heparin-coated oxygenator membranes

Patients with severe lung diseases are highly dependent on lung support systems. Despite many improvements, long-term use is not possible, mainly because of the strong body defence reactions (e.g. coagulation, complement system, inflammation and cell activation). The systematic characterization of adsorbed proteins on the gas exchange membrane of the lung system over time can provide insights into the course of various defence reactions and identify possible targets for surface modifications. Using comprehensive mass spectrometry analyses of desorbed proteins, we were able to identify for the first time binding profiles of over 500 proteins over a period of six hours on non-coated and heparin-coated PMP hollow fiber membranes. We observed a higher degree of remodeling of the protein layer on the non-coated membrane than on the coated membrane. In general, there was a higher protein binding on the coated membrane with exception of proteins with a heparin-binding site. Focusing on the most important pathways showed that almost all coagulation factors bound in higher amounts to the non-coated membranes. Furthermore, we could show that the initiator proteins of the complement system bound stronger to the heparinized membranes, but the subsequently activated proteins bound stronger to the non-coated membranes, thus complement activation on heparinized surfaces is mainly due to the alternative complement pathway. Our results provide a comprehensive insight into plasma protein adsorption on oxygenator membranes over time and point to new ways to better understand the processes on the membranes and to develop new specific surface modifications.

Plasma C4 level was associated with mortality, cardiovascular and cerebrovascular complications in hemodialysis patients

BACKGROUND

Patients on maintenance hemodialysis (HD) exhibit a high risk of death, cardiovascular and cerebrovascular diseases (CCDs). Previous studies indicated complement activation associated with the increased risk of cardiovascular diseases in HD patients. This study aimed to explore whether the critical complement factors were associated with the adverse outcomes in HD patients.

METHODS

A total of 108 HD patients were included and followed up for 52 months. The baseline clinical characteristics and plasma C3c, C1q, CFH, CFB, C4, MAC, C5a, C3a and MBL were measured. The three endpoints were death, cardiovascular and cerebrovascular events (CCEs) and the composition of them. Univariate and multivariate Cox regression identified factors associated with the three endpoints respectively. X-tile analyses determined the optimal cut-off values for high risks. Restricted cubic spline plots illustrated the dose-response relationships. Correlations between the complement factors and risk factors for CCDs were analyzed.

RESULTS

Baseline plasma C4 was finally selected by univariate and multivariate Cox regression analyses for three endpoints, including all-cause mortality, CCEs and the composition of them. When baseline plasma C4 exceeded 0.47 (P = 0.001) or 0.44 (P = 0.018) g/L respectively, the risks for death or achieving the composite endpoint enhanced significantly. The relationships of C4 and HR for the three endpoints showed a positive linear trend. Plasma C4 had prominent correlations with blood TG (r = 0.62, P < 0.001) and HDL (r = -0.38, P < 0.001).

CONCLUSIONS

A higher baseline plasma C4 level was significantly associated with the future incidence of decease, CCEs and either of them. Plasma C4 level correlated with blood TG and HDL.

Histomorphometry of Ossification in Functionalised Ceramics with Tripeptide Arg-Gly-Asp (RGD): An In Vivo Study

The present study investigated the osseointegration promoted by functionalised ceramics with peptide Arg-Gly-Asp (RGD) in a rabbit model in vivo. Histomorphometry of the RGD functionalised ceramic implants was conducted by a trained pathologist to quantify the amount of mature and immature ossification at the bone interface, and then compared to titanium alloy implants. The region of interest was the area surrounding the implant. The percentage of ROI covered by osteoid implant contact and mature bone implant contact were assessed. The presence of bone resorption, necrosis, and/or inflammation in the areas around the implant were quantitatively investigated. All 36 rabbits survived the experimental period of 6 and 12 weeks. All implants remained in situ. No necrosis, bone resorption, or inflammation were identified. At 12 weeks follow-up, the overall mean bone implant contact (p = 0.003) and immature osteoid contact (p = 0.03) were improved compared to the mean values evidenced at 6 weeks. At 6 weeks follow-up, the overall osteoid implant contact was greater in the RGD enhanced group compared to the titanium implant (p = 0.01). The other endpoints of interest were similar between the two implants at all follow-up points (p ≥ 0.05). Functionalised ceramics with peptide RGD promoted ossification in vivo. The overall osteoid and bone implant contact improved significantly from 6 to 12 weeks. Finally, RGD enhanced ceramic promoted faster osteoid implant contact in vivo than titanium implants. Overall, the amount of ossification at 12 weeks is comparable with the titanium implants. No necrosis, bone resorption, or inflammation were observed in any sample.

Immunologic reactions to bone and articular implants

BACKGROUND

In recent years the number on implantable devices that have been used in orthopedic surgeries has increased exponentially. As the number of people with orthopedic implants has grown, implant failure has become an increasingly important public health issue. While a significant percent of joint implants fails at between 15 and 20 years some authors suggest that one of the main causes is the interaction between the immune system of the host and the material of the implant METHODS: The search engines used for research comprised of PubMed, Google Scholar and Cochrane Library.

RESULTS

This review aims to summarize relevant and recent data on the immune reactions that are taking place at the juxtaposition between the implant and the patient's tissue, the time frame in which these immune reactions take place and some of the factors that can influence this reaction. The immune reactions can be divided into: hyperacute immune reactions (anaphylactic shock), acute reactions, the transition between the acute phase and the chronic phase and last but not least chronic immune reactions to such implants.

CONCLUSION

The research being done with regard to implant-related immunology strives to help in solving the problem of long-term implant failure.

The complement cascade at the Utah microelectrode-tissue interface

Devices implanted within the central nervous system (CNS) are subjected to tissue reactivity due to the lack of biocompatibility between implanted material and the cells' microenvironment. Studies have attributed blood-brain barrier disruption, inflammation, and oxidative stress as main contributing factors that lead to electrode recording failure. The complement cascade is a part of the innate immunity that focuses on recognizing and targeting foreign objects; however, its role in the context of neural implants is substantially unknown. In this study, we implanted a non-functional 4x4 Utah microelectrode array (UEA) into the somatosensory cortex and studied the complement cascade via combined gene and immunohistochemistry quantification at acute (48-h), sub-acute (1-week), and early chronic (4-weeks) time points. The results of this study demonstrate the activation and continuation of the complement cascade at the electrode-tissue interface, illustrating the therapeutic potential of modulating the foreign body response via the complement cascade.

Association of Glomerular Complement C4c Deposition With the Progression of Diabetic Kidney Disease in Patients With Type 2 Diabetes

Objectives: As accumulating data supporting the potential role of the complement system in the pathogenesis of diabetic kidney disease (DKD), the present study aimed to explore the association of glomerular complement C4c deposition with the baseline clinicopathological characteristics and the prognosis of DKD in type 2 diabetes (T2DM) patients.

Methods: A total of 79 T2DM patients with biopsy-proven DKD were enrolled. Clinicopathological features and renal outcomes were compared between groups divided by the glomerular C4c deposition patterns and median values of serum C4. Renal outcomes were defined by doubling of serum creatinine level or progression to end-stage renal disease (ESRD). A Cox proportional hazards model was employed to identify the risk factors associated with renal events.

Results: Patients with glomerular C4c deposition had worse renal insufficiency than those without C4c deposits, along with higher 24-h urinary protein, triglyceride, but lower serum albumin and higher interstitial inflammation score. Besides, serum C4 levels positively correlated with urinary protein and serum C3 levels. During 21.85 ± 16.32 months of follow-up, Kaplan-Meier curve analysis showed significantly faster deterioration of renal function for patients with positive glomerular C4c deposition as well as higher levels of serum C4. More specifically, more than 50% of the patients with glomerular C4c had co-deposition of C3c or C1q, and patients with glomerular complement complex of C4c and one or two of C3/C1q deposition had more severe proteinuria and a higher rate of DKD progression than those with negative C4c deposits. The univariate Cox regression indicated that factors of combined serum and glomerular C4, urinary protein, serum creatinine, serum C3, combined glomerular C4c and IgM and interstitial inflammation were associated with an increased risk of DKD, but only glomerular C4c intensity (HR 1.584, 95% CI [1.001, 2.508], p = 0.0497), as well as baseline age and diabetic neuropathy, were independent risk factors for renal survival by the multivariate Cox analysis.

Conclusions: Glomerular C4c deposition was associated with deteriorated renal function and outcomes in patients with T2DKD. Glomerular C4c deposition was an independent risk factor for DKD progression.

Assessment of the Role of C3(H2O) in the Alternative Pathway

In this study we investigate the hydrolysis of C3 to C3(H₂O) and its ability to initiate activation via the alternative pathway (AP) of the complement system. The internal thioester bond within C3 is hydrolyzed by water in plasma because of its inherent lability. This results in the formation of non-proteolytically activated C3(H₂O) which is believed have C3b-like properties and be able to form an active initial fluid phase C3 convertase together with Factor B (FB). The generation of C3(H₂O) occurs at a low but constant rate in blood, but the formation can be greatly accelerated by the interaction with various surfaces or nucleophilic and chaotropic agents. In order to more specifically elucidate the relevance of the C3(H₂O) for AP activation, formation was induced in solution by repeated freeze/thawing, methylamine or KCSN treatment and named C3(x) where the x can be any of the reactive nucleophilic or chaotropic agents. Isolation and characterization of C3(x) showed that it exists in several forms with varying attributes, where some have more C3b-like properties and can be cleaved by Factor I in the presence of Factor H. However, in common for all these variants is that they are less active partners in initial formation of the AP convertase compared with the corresponding activity of C3b. These observations support the idea that formation of C3(x) in the fluid phase is not a strong initiator of the AP. It is rather likely that the AP mainly acts as an amplification mechanism of complement activation that is triggered by deposition of target-bound C3b molecules generated by other means.

In Vivo Evaluation of the Biocompatibility of Biomaterial Device

Biomaterials are widely used to produce devices for regenerative medicine. After its implantation, an interaction between the host immune system and the implanted biomaterial occurs, leading to biomaterial-specific cellular and tissue responses. These responses may include inflammatory, wound healing responses, immunological and foreign-body reactions, and even fibrous encapsulation of the implanted biomaterial device. In fact, the cellular and molecular events that regulate the success of the implant and tissue regeneration are played at the interface between the foreign body and the host inflammation, determined by innate and adaptive immune responses. This chapter focuses on host responses that must be taken into consideration in determining the biocompatibility of biomaterial devices when implanted in vivo of animal models.

The lectin pathway in renal disease: old concept and new insights

The complement system is composed of a network of at least 40 proteins, which significantly contributes to health and disease. The lectin pathway (LP) is one of three pathways that can activate the complement system. Next to protection of the host against pathogens, the LP has been shown to play a crucial role in multiple renal diseases as well as during renal replacement therapy. Therefore, several complement-targeted drugs are currently being explored in clinical trials. Among these complement inhibitors, specific LP inhibitors are also being tested in renal abnormalities such as in immunoglobulin A nephropathy and lupus nephritis. Using various in vitro models, Yaseen et al. (Lectin pathway effector enzyme mannan-binding lectin-associated serine protease-2 can activate native complement component 3 (C3) in absence of C4 and/or C2. FASEB J 2017; 31: 2210-2219) showed that Mannan-associated serine protease2 can directly activate C3 thereby bypassing C2 and C4 in the activation of the LP. These new findings broaden our understanding of the mechanisms of complement activation and could potentially impact our strategies to inhibit the LP in renal diseases. In support of these findings, we present data of human renal biopsies, demonstrating the occurrence of the LP bypass mechanism in vivo. In conclusion, this review provides a detailed overview of the LP and clarifies the recently described bypass mechanism and its relevance. Finally, we speculate on the role of the C4 bypass mechanism in other renal diseases.

Is generation of C3(H2O) necessary for activation of the alternative pathway in real life?

In the alternative pathway (AP) an amplification loop is formed, which is strictly controlled by various fluid-phase and cell-bound regulators resulting in a state of homeostasis. Generation of the "C3b-like" C3(H₂O) has been described as essential for AP activation, since it conveniently explains how the initial fluid-phase AP convertase of the amplification loop is generated. Also, the AP has a status of being an unspecific pathway despite thorough regulation at different surfaces. During complement attack in pathological conditions and inflammation, large amounts of C3b are formed by the classical/lectin pathway (CP/LP) convertases. After the discovery of LP´s recognition molecules and its tight interaction with the AP, it is increasingly likely that the AP acts in vivo mainly as a powerful amplification mechanism of complement activation that is triggered by previously generated C3b molecules initiated by the binding of specific recognition molecules. Also in many pathological conditions caused by a dysregulated AP amplification loop such as paroxysmal nocturnal hemoglobulinuria (PNH) and atypical hemolytic uremic syndrome (aHUS), C3b is available due to minute LP and CP activation and/or generated by non-complement proteases. Therefore, C3(H₂O) generation in vivo may be less important for AP activation during specific attack or dysregulated homeostasis, but may be an important ligand for C3 receptors in cell-cell interactions and a source of C3 for the intracellular complement reservoir.

Immune responses towards bioengineered tissues and strategies to control them

PURPOSE OF REVIEW

Research into development of artificial tissues and bioengineered organs to replace physiological functions of injured counterparts has highlighted a previously underestimated challenge for its clinical translatability: the immune response against biomaterials. Herein, we will provide an update and review current knowledge regarding this important barrier to regenerative medicine.

RECENT FINDINGS

Although a clear understanding of the immune reactivity against biomaterials remains elusive, accumulating evidence indicates that innate immune cells, primarily neutrophils and macrophages, play a key role in the initial phases of the immune response. More recently, data have shown that in later phases, T and B cells are also involved. The use of physicochemical modifications of biomaterials and cell-based strategies to modulate the host inflammatory response is being actively investigated for effective biomaterial integration.

SUMMARY

The immune response towards biomaterials and bioengineered organs plays a crucial role in determining their utility as transplantable grafts. Expanding our understanding of these responses is necessary for developing protolerogenic strategies and delivering on the ultimate promise of regenerative medicine.

Taming hemodialysis-induced inflammation: Are complement C3 inhibitors a viable option?

Owing to an increasing shortage of donor organs, the majority of patients with end-stage kidney disease remains reliant on extracorporeal hemodialysis (HD) in order to counter the lifelong complications of a failing kidney. While HD remains a life-saving option for these patients, mounting evidence suggests that it also fuels a vicious cycle of thromboinflammation that can increase the risk of cardiovascular disease. During HD, blood-borne innate immune systems become inappropriately activated on the biomaterial surface, instigating proinflammatory reactions that can alter endothelial and vascular homeostasis. Complement activation, early during the HD process, has been shown to fuel a multitude of detrimental thromboinflammatory reactions that collectively contribute to patient morbidity. Here we discuss emerging aspects of complement's involvement in HD-induced inflammation and put forth the concept that targeted intervention at the level of C3 might constitute a promising therapeutic approach in HD patients.

Curvature-dependent effects of nanotopography on classical immune complement activation

The aim of this study was to investigate how the size of nanosized surface features affect classical immune complement activation through adsorption of IgG and the following binding of C1q. By using model surfaces with immobilized SiO₂ nanoparticles of different sizes (8, 32 and 68 nm in diameter), three different curvatures with the same chemistry was systematically studied and analyzed using the acoustic sensing technique; Quartz Crystal Microbalance with Dissipation Monitoring (QCM-D). Circular Dichroism (CD) was employed to study any changes in the secondary structure of IgG using a methodology with stacked functionalized substrates. Our results show that the amount of IgG adsorption increased slightly with nanoparticle size, but also showed a strong size/curvature-dependent effect on the following C1q binding, with the highest binding to IgG adsorbed on the largest nanoparticles and a smooth control surface, indicating that classical immune complement activation possibly increase with decreasing curvature. We conclude that the difference in C1q binding was not due to changes in the secondary structure of IgG, suggesting that geometrical arrangement of adsorbed IgG is the determining factor.

STATEMENT OF SIGNIFICANCE

We have shown that small changes at the topographical nanoscale can give large effects on the initiation of the classical immune complement cascade, an important immunological reaction that take place when a foreign material is inserted in the body. By developing a methodology using silicon dioxide nanoparticles with three different sizes, to systematically study their impact on the secondary structure and binding of human immunoglobulin G (IgG) to the initiator protein C1q of the classical complement cascade, we have shown that the initiation of the classical immune complement is hampered by the sharp curvature of the smaller nanoparticles. We conclude that this is not mediated by changes in the secondary structure of the adsorbed proteins, but rather an effect of curvature-induced spatial mismatch. The results provide a possible mechanistic explanation on how nanotopography may effect protein adsorption and protein cascade events.

Granulocyte and monocyte CD11b expression during plasma separation is dependent on complement factor 5 (C5) - an ex vivo study with blood from a C5-deficient individual

The aim of the study was to investigate the role of complement factor 5 (C5) in reactions elicited by plasma separation using blood from a C5-deficient (C5D) individual, comparing it to C5-deficient blood reconstituted with C5 (C5DR) and blood from healthy donors. Blood was circulated through an ex vivo plasma separation model. Leukocyte CD11b expression and leukocyte-platelet conjugates were measured by flow cytometry during a 30-min period. Other markers were assessed during a 240-min period. Granulocyte and monocyte CD11b expression did not increase in C5D blood during plasma separation. In C5DR samples granulocytes CD11b expression, measured by mean fluorescence intensity (MFI), increased from 10481 ± 6022 (SD) to 62703 ± 4936, and monocytes CD11b expression changed from 13837 ± 7047 to 40063 ± 713. Granulocyte-platelet conjugates showed a 2.5-fold increase in the C5DR sample compared to the C5D sample. Monocyte-platelet conjugates increased independently of C5. In the C5D samples, platelet count decreased from 210 × 10⁹ /L (201-219) (median and range) to 51 × 10⁹ /L (50-51), and C3bc increased from 14 CAU/mL (21-7) to 198 CAU/mL (127-269), whereas TCC formation was blocked during plasma separation. In conclusion, up-regulation of granulocyte and monocyte CD11b during plasma separation was C5-dependent. The results also indicate C5 dependency in granulocyte-platelet conjugates formation.

The Complement System in Dialysis: A Forgotten Story?

Significant advances have lead to a greater understanding of the role of the complement system within nephrology. The success of the first clinically approved complement inhibitor has created renewed appreciation of complement-targeting therapeutics. Several clinical trials are currently underway to evaluate the therapeutic potential of complement inhibition in renal diseases and kidney transplantation. Although, complement has been known to be activated during dialysis for over four decades, this area of research has been neglected in recent years. Despite significant progress in biocompatibility of hemodialysis (HD) membranes and peritoneal dialysis (PD) fluids, complement activation remains an undesired effect and relevant issue. Short-term effects of complement activation include promoting inflammation and coagulation. In addition, long-term complications of dialysis, such as infection, fibrosis and cardiovascular events, are linked to the complement system. These results suggest that interventions targeting the complement system in dialysis could improve biocompatibility, dialysis efficacy, and long-term outcome. Combined with the clinical availability to safely target complement in patients, the question is not if we should inhibit complement in dialysis, but when and how. The purpose of this review is to summarize previous findings and provide a comprehensive overview of the role of the complement system in both HD and PD.

Fast form alpha-2-macroglobulin - A marker for protease activation in plasma exposed to artificial surfaces

OBJECTIVES

Investigation of the blood compatibility requires a number of sensitive assays to quantify the activation of the blood protein cascades and cells induced by biomaterials. A global assay measuring the blood compatibility of biomaterials could be a valuable tool in such regard. In this study, we investigated whether an enzyme-linked immunosorbent assay (ELISA), that specifically measures the electrophoretic "fast form" of α₂-macroglobulin (F-α₂M), could be a sensitive and global marker for activation of calcium dependent and in-dependent proteases in plasma exposed to biomaterials in vitro.

METHODS

A F-α₂M specific monoclonal antibody was generated and applied in an ELISA setup. Using the F-α₂M ELISA, we investigated activation of calcium dependent and in-dependent proteases by polyvinylchloride (n=10), polytetrafluoroethylene (n=10) and silicone (n=10) tubings as well as glass tubes (n=10).

RESULTS

We found that F-α₂M is a sensitive marker for activation of both calcium dependent and in-dependent proteases. A significant difference between F-α₂M concentrations in the control sample and plasma exposed to the artificial surfaces was found (p>0.001). This was observed both in the presence and absence of calcium. Furthermore, the highest F-α₂M concentration was in both cases found in plasma incubated with glass.

CONCLUSIONS

Our findings demonstrate that F-α₂M is a sensitive marker for detection of protease activation in plasma by artificial surfaces. Potentially, levels of F-α₂M could be a global marker of the blood compatibility of biomaterials.

Cardiovascular disease in haemodialysis: role of the intravascular innate immune system

Haemodialysis is a life-saving renal replacement modality for end-stage renal disease, but this therapy also represents a major challenge to the intravascular innate immune system, which is comprised of the complement, contact and coagulation systems. Chronic inflammation is strongly associated with cardiovascular disease (CVD) in patients on haemodialysis. Biomaterial-induced contact activation of proteins within the plasma cascade systems occurs during haemodialysis and initially leads to local generation of inflammatory mediators on the biomaterial surface. The inflammation is spread by soluble activation products and mediators that are generated during haemodialysis and transported in the extracorporeal circuit back into the patient together with activated leukocytes and platelets. The combined effect is activation of the endothelium of the cardiovascular system, which loses its anti-thrombotic and anti-inflammatory properties, leading to atherogenesis and arteriosclerosis. This concept suggests that maximum suppression of the intravascular innate immune system is needed to minimize the risk of CVD in patients on haemodialysis. A potential approach to achieve this goal is to treat patients with broad-specificity systemic drugs that target more than one of the intravascular cascade systems. Alternatively, 'stealth' biomaterials that cause minimal cascade system activation could be used in haemodialysis circuits.

Iron-induced necrotic brain cell death in rats with different aerobic capacity

Brain iron overload has a key role in brain injury after intracerebral hemorrhage (ICH). Our recent study demonstrated that ICH-induced brain injury was greater in low capacity runner (LCR) than in high capacity runner (HCR) rats. The present study examines whether iron-induced brain injury differs between LCRs and HCRs. Adult male LCR and HCR rats had an intracaudate injection of iron or saline. Rats were euthanized at 2 and at 24 h after T2 magnetic resonance imaging, and the brains were used for immunostaining and Western blotting. LCRs had more hemispheric swelling, T2 lesion volumes, blood-brain barrier disruption, and neuronal death at 24 h after iron injection (p < 0.05). Many propidium iodide (PI)-positive cells, indicative of necrotic cell death, were observed in the ipsilateral basal ganglia of both HCRs and LCRs at 2 h after iron injection. PI fluorescence intensity was higher in LCRs than in HCRs. In addition, membrane attack complex (MAC) expression was increased at 2 h after iron injection and was higher in LCRs than in HCRs. The PI-positive cells co-localized with MAC-positive cells in the ipsilateral basal ganglia. Iron induces more severe necrotic brain cell death, brain swelling, and blood-brain barrier disruption in LCR rats, which may be related with complement activation and MAC formation.

Low concentrations of citrate reduce complement and granulocyte activation in vitro in human blood

Background

The use of acetate in haemodialysis fluids may induce negative effects in patients including nausea and increased inflammation. Therefore, haemodialysis fluids where acetate is substituted with citrate have recently been developed. In this study, we investigated the biocompatibility of citrate employing concentrations used in haemodialysis.

Methods

The effects of citrate and acetate were investigated in human whole blood in vitro under conditions promoting biomaterial-induced activation. Complement activation was measured as generation of C3a, C5a and the sC5b-9 complex, and granulocyte activation as up-regulation of CD11b expression. For the experimental set-up, a mathematical model was created to calculate the concentrations of acetate and citrate attained during haemodialysis.

Results

Citrate reduced granulocyte activation and did not induce higher complement activation compared with acetate at concentrations attained during haemodialysis. Investigating different citrate concentrations clearly showed that citrate is a potent complement inhibitor already at low concentrations, i.e. 0.25 mM, which is comparable with concentrations detected in the blood of patients during dialysis with citrate-containing fluids. Increased citrate concentration up to 6 mM further reduced the activation of C3a, C5a and sC5b-9, as well as the expression of CD11b.

Conclusions

Our results suggest that citrate is a promising substitute for acetate for a more biocompatible dialysis, most likely resulting in less adverse effects for the patients.

Inhibition of biomaterial-induced complement activation attenuates the inflammatory host response to implantation

Although complement is a known contributor to biomaterial-induced complications, pathological implications and therapeutic options remain to be explored. Here we investigated the involvement of complement in the inflammatory response to polypropylene meshes commonly used for hernia repair. In vitro assays revealed deposition of complement activation fragments on the mesh after incubation in plasma. Moreover, significant mesh-induced complement and granulocyte activation was observed in plasma and leukocyte preparations, respectively. Pretreatment of plasma with the complement inhibitor compstatin reduced opsonization >2-fold, and compstatin and a C5a receptor antagonist (C5aRa) impaired granulocyte activation by 50 and 67%, respectively. We established a clinically relevant mouse model of implantation and could confirm deposition of C3 activation fragments on mesh implants in vivo using immunofluorescence. In meshes extracted after subcutaneous or peritoneal implantation, the amount of immune cell infiltrate in mice deficient in key complement components (C3, C5aR), or treated with C5aRa, was approximately half of that observed in wild-type littermates or mice treated with inactive C5aRa, respectively. Our data suggest that implantation of a widely used surgical mesh triggers the formation of an inflammatory cell microenvironment at the implant site through complement activation, and indicates a path for the therapeutic modulation of implant-related complications.

Targeted complement inhibition as a promising strategy for preventing inflammatory complications in hemodialysis

Hemodialysis is the most common method used to remove waste and hazardous products of metabolism in patients suffering from renal failure. Hundreds of thousands of people with end-stage renal disease undergo hemodialysis treatment in the United States each year. Strikingly, the 5-year survival rate for all dialysis patients is only 35%. Most of the patients succumb to cardiovascular disease that is exacerbated by the chronic induction of inflammation caused by contact of the blood with the dialysis membrane. The complement system, a strong mediator of pro-inflammatory networks, is a key contributor to such biomaterial-induced inflammation. Though only evaluated in experimental ex vivo settings, specific targeting of complement activation during hemodialysis has uncovered valuable information that points toward the therapeutic use of complement inhibitors as a means to control the unwelcomed inflammatory responses and consequent pathologies in hemodialysis patients.

Immune responses to implants - a review of the implications for the design of immunomodulatory biomaterials

A key for long-term survival and function of biomaterials is that they do not elicit a detrimental immune response. As biomaterials can have profound impacts on the host immune response the concept emerged to design biomaterials that are able to trigger desired immunological outcomes and thus support the healing process. However, engineering such biomaterials requires an in-depth understanding of the host inflammatory and wound healing response to implanted materials. One focus of this review is to outline the up-to-date knowledge on immune responses to biomaterials. Understanding the complex interactions of host response and material implants reveals the need for and also the potential of "immunomodulating" biomaterials. Based on this knowledge, we discuss strategies of triggering appropriate immune responses by functional biomaterials and highlight recent approaches of biomaterials that mimic the physiological extracellular matrix and modify cellular immune responses.

Protection of nonself surfaces from complement attack by factor H-binding peptides: implications for therapeutic medicine

Exposure of nonself surfaces such as those of biomaterials or transplanted cells and organs to host blood frequently triggers innate immune responses, thereby affecting both their functionality and tolerability. Activation of the alternative pathway of complement plays a decisive role in this unfavorable reaction. Whereas previous studies demonstrated that immobilization of physiological regulators of complement activation (RCA) can attenuate this foreign body-induced activation, simple and efficient approaches for coating artificial surfaces with intact RCA are still missing. The conjugation of small molecular entities that capture RCA with high affinity is an intriguing alternative, as this creates a surface with autoregulatory activity upon exposure to blood. We therefore screened two variable cysteine-constrained phage-displayed peptide libraries for factor H-binding peptides. We discovered three peptide classes that differed with respect to their main target binding areas. Peptides binding to the broad middle region of factor H (domains 5-18) were of particular interest, as they do not interfere with either regulatory or binding activities. One peptide in this group (5C6) was further characterized and showed high factor H-capturing activity while retaining its functional integrity. Most importantly, when 5C6 was coated to a model polystyrene surface and exposed to human lepirudin-anticoagulated plasma, the bound peptide captured factor H and substantially inhibited complement activation by the alternative pathway. Our study therefore provides a promising and novel approach to produce therapeutic materials with enhanced biocompatibility.

Proteomic profiling of blood-dialyzer interactome reveals involvement of lectin complement pathway in hemodialysis-induced inflammatory response

PURPOSE

dialysis-induced inflammatory response including leukocyte and complement activation is considered a significant cofactor of chronic morbidity in long-term hemodialysis (HD) patients. The aim of this study was to provide better insight into its molecular background.

EXPERIMENTAL DESIGN

in 16 patients, basic biocompatibility markers, i.e. leukocyte counts and C5a levels, were monitored during HD on a polysulfone membrane. Proteins adsorbed to dialyzers were eluted and separated by 2-DE. Selected proteins were identified by MS; ficolin-2 plasma levels were assessed. Data are given as medians (quartile ranges).

RESULTS

in total, 7.2 (34.7) mg proteins were retrieved from dialyzer eluates and were resolved into 217 protein spots. The proteins most enriched in eluates (and hence selectively adsorbed) were those involved in complement activation (C3c, ficolin-2, mannan-binding lectin serine proteases, properdin) and cell adhesion (actin, caldesmon, tropomyosin, vitronectin, vinculin). A significant decrease of plasma ficolin-2 (41% [4.7], p<0.001) was evidenced during one HD session, associated with leukopenia (r=0.73, p=0.001) and C5a production (r=-0.62, p=0.01) at 15 min.

CONCLUSIONS AND CLINICAL RELEVANCE

ficolin-2 adsorption to polysulfone dialyzer initiates the lectin pathway of complement activation, mediates dialysis-induced leukopenia, and results in a significant depletion of ficolin-2, an essential component of innate immunity.

Glycosaminoglycans enhance the fibrillation propensity of the β2-microglobulin cleavage variant--ΔK58-β2m

Dialysis related amyloidosis (DRA) is a serious complication to long-term hemodialysis treatment which causes clinical symptoms such as carpal tunnel syndrome and destructive arthropathies. The disease is characterized by the assembly and deposition of β2-microglobulin (β2m) predominantly in the musculoskeletal system, but the initiating events leading to β2m amyloidogenesis and the molecular mechanisms underlying amyloid fibril formation are still unclear. Glycosaminoglycans (GAGs) and metal ions have been shown to be related to the onset of protein aggregation and to promote de novo fiber formation. In this study, we show that fibrillogenesis of a cleavage variant of β2m, ΔK58-β2m, which can be found in the circulation of hemodialysis patients and is able to fibrillate at near-physiological pH in vitro, is affected by the presence of copper ions and heparan sulfate. It is found that the fibrils generated when heparan sulfate is present have increased length and diameter, and possess enhanced stability and seeding properties. However, when copper ions are present the fibrils are short, thin and less stable, and form at a slower rate. We suggest that heparan sulfate stabilizes the cleaved monomers in the early aggregates, hereby promoting the assembly of these into fibrils, whereas the copper ions appear to have a destabilizing effect on the monomers. This keeps them in a structure forming amorphous aggregates for a longer period of time, leading to the formation of spherical bodies followed by the assembly of fibrils. Hence, the in vivo formation of amyloid fibrils in DRA could be initiated by the generation of ΔK58-β2m which spontaneously aggregate and form fibrils. The fibrillogenesis is enhanced by the involvement of GAGs and/or metal ions, and results in amyloid-like fibrils able to promote the de novo formation of β2m amyloid by a scaffold mechanism.

Complement activation on degraded polyethylene glycol-covered surface

Surface modification with polyethylene glycol (PEG) has been employed in the development of biomaterials to reduce unfavorable reactions. However, unanticipated body reactions have been reported, with activation of the complement system being suggested as having involvement in these responses. In this study, we prepared a PEG-modified surface on a gold surface using a monolayer of alpha-mercaptoethyl-omega-methoxy-polyoxyethylene. We observed neither protein adsorption nor activation of the complement system on the PEG-modified surface just after preparation. Storage of the PEG-modified surface in a desiccator under ambient light for several days or following ultraviolet irradiation, reflection-adsorption (FTIR-RAS) and X-ray photo spectrometry revealed deterioration of the PEG layer, which became a strong activator of the complement system through the alternative pathway.

Effects of hydrophobicity and electrostatic charge on complement activation by amino groups

Some studies have demonstrated that amino groups, acting as nucleophiles, are potent activators of the complement system, but others not. To clarify these contradictory results, we examined complement activation on two series of NH(2)/CH(3) and NH(2)/COOH mixed self-assembled monolayers (SAMs). NH(2)/CH(3) mixed SAMs were not potent activators of the complement system regardless of the ratio of NH(2)/CH(3) in mixed SAMs. Numerous serum proteins, such as albumin, were adsorbed onto those SAMs and formed a protein layer which inhibited access of C3b to amino groups. In contrast, much C3b and/or C3bBb were deposited on NH(2)/COOH mixed SAMs with approximately 50-60% NH(2) density on the surface and SC5b-9 was found in serum exposed to this SAM, indicating activation of the complement system. These results suggest that C3b can easily access nucleophilic NH(2) groups because of the decrease in electrostatic interaction between negatively charged proteins and the NH(2) SAM surface.

Real-time measurements of coagulation on bacterial cellulose and conventional vascular graft materials

The search for a functional, small diameter (<5mm) vascular graft has been ongoing for over 30 years, but yet there is no consistently reliable synthetic graft. The primary mechanisms of graft failure are intimal hyperplasia, poor blood flow and surface thrombogenicity. Bacterial cellulose (BC) became therefore a proposed new biosynthetic vascular graft material. Since conventional methods are not suited for coagulation measurements on BC, we have adapted the automated calibrated thrombin generation method for measurements of biomaterial-induced coagulation of BC as compared with clinically used graft materials i.e., expanded poly(tetrafluoroethylene) (ePTFE) and poly(ethyleneterephtalat) (PET). We have also visualized the coagulation propagation at the material surfaces. Thrombin generation experiments revealed dramatic differences between the materials tested. Both ePTFE and BC were found to generate longer lag times and ttpeak values than PET. Most importantly, BC was found to generate the lowest "peak", indicating a slower coagulation process at the surface. These results are also supported by the measurements of factor XIIa generation and analysis of surface coagulation times, which were detected in the following increasing order (mean + or - SD): PET (27 + or - 8 min)<BC (46 + or - 9 min)<ePTFE (61 + or - 21 min). Real-time measurement of coagulation seems to have the potential for becoming a powerful tool for evaluation of biomaterials for blood-contacting devices.

In vitro--transcriptional response of polymorphonuclear leukocytes following contact with different antigens

Background Human polymorphonuclear neutrophils (PMN) are activated and undergo apoptosis if brought into contact with cuprophane haemodialysis membranes, a phenomenon not observed if more 'biocompatible' polysulfone dialysers are used. It remains yet to be defined if this differential response is due to mechanisms regulated on a transcriptional or protein level. Furthermore, it is not clear if the contact of PMN with membranes ('frustrated' phagocytosis) activates the same response as phagocytosis of bacteria (complete phagocytosis). Materials and methods We performed a genome-wide differential gene expression study using cDNA microarrays to analyse the impact of different dialysis fibres on the transcriptional response of PMN of human healthy volunteers. These results were compared to transcriptional response of PMN during phagocytosis of Escherichia coli. Results We did not detect significant differences in gene expression between PMN stimulated with cuprophane or pulysulfone. Compared to unstimulated PMN the 'frustrated' phagocytosis of either dialysis membrane resulted in increased expression of 50 genes, with a marked up-regulation of FOS - and JUN - transcripts, but with only little activation of immune response genes, and virtually no activation of apoptosis related RNA transcripts. In contrast, phagocytosis of E.coli was associated with a striking up-regulation of 88 genes, most of them involved in pro- and antiapoptotic pathways, immune response and activation of nuclear factor kappa B and inhibitor of NF-kappa B. Conclusions Our results suggest that the response of PMN to artificial surfaces is not controlled on transcriptional level. Complete and 'frustrated' phagocytosis activate markedly distinct transcriptional regulatory pathways in PMN.

An update on pruritus associated with CKD

The prevalence of chronic kidney disease (CKD) and end-stage renal disease is increasing worldwide. Despite improvements in dialysis methods, including the development of novel biocompatible membranes and ultrapure dialysate, CKD-associated pruritus remains a common and significant public health issue. Not only does this distressing symptom profoundly impact on quality of life and sleep, recent evidence showed that pruritus also was associated with poor patient outcome. Nonetheless, nephrologists and other health care professionals often fail to recognize and adequately address the pruritus associated with CKD. The pathophysiological mechanism of CKD-associated pruritus is poorly defined, and, as a result, the development of specific therapies has proved to be a challenge. The purpose of this review is to highlight the importance of this neglected topic by providing an overview of recent epidemiological studies, outcomes data, proposed pathophysiological mechanisms, and emerging treatment options.

The role of complement in biomaterial-induced inflammation

Biomaterials are regularly used in various types of artificial tissues and organs, such as oxygenators, plasmapheresis equipment, hemodialysers, catheters, prostheses, stents, vascular grafts, miniature pumps, sensors and heart aids. Although progress has been made regarding bioincompatibility, many materials and procedures are associated with side effects, in particular bioincompatibility-induced inflammation, infections and subsequent loss of function. After cardiopulmonary bypass, coagulopathies can occur and lead to cognitive disturbances, stroke and extended hospitalization. Hemodialysis is associated with anaphylatoid reactions that cause whole-body inflammation and may contribute to accelerated arteriosclerosis. Stents cause restenosis and, in severe cases, thrombotic reactions. This situation indicates that there is still a need to try to understand the mechanisms involved in these incompatibility reactions in order to be able to improve the biomaterials and to develop treatments that attenuate the reactions and thereby reduce patients' discomfort, treatment time and cost. This overview deals with the role of complement in the incompatibility reactions that occur when biomaterials come in contact with blood and other body fluids.

uPAR (CD87) as a biocompatibility marker of dialysis membrane

BACKGROUND/AIMS

Hemodialysis (HD) therapy may lead to functional changes in patient leukocytes. For example, the upregulation of inflammatory cytokines, such as IL-1beta and TNFalpha, has been well characterized. However, these findings do not explain the entire response of leukocytes in HD. In this study, we carried out a comprehensive gene expression analysis in leukocytes treated with various dialysis membranes using DNA microarrays. The identified gene has the potential to be a new marker for testing dialysis membrane biocompatibility.

METHODS

Gene expression profiles were compared between a group of leukocytes treated with various dialysis membranes and an untreated group by using DNA microarray analysis. Expression was confirmed by quantitative RT-PCR. The expression of the gene product (leukocyte surface protein) was examined in 20 chronic HD patients by flow cytometry.

RESULTS

In addition to the inflammatory cytokines, the urokinase plasminogen activator receptor (uPAR or CD87) gene was induced in leukocytes treated with each dialysis membrane. The extent of induction depended on the membrane's material composition. The expression of the uPAR (CD87) protein on leukocytes was markedly increased in patients undergoing dialysis therapy. The magnitude of uPAR (CD87) protein expression was correlated with clinical findings, i.e., the degree of leukopenia and the expression of adhesion molecules.

CONCLUSIONS

The gene and protein expression of uPAR (CD87) depended on the dialysis membrane material and correlated closely with clinical findings. These results suggest that uPAR has the potential to serve as a marker not only for clinical use but also for the development of new dialysis membranes.

Binding of C3 fragments on top of adsorbed plasma proteins during complement activation on a model biomaterial surface

In the present study we investigate whether complement activation in blood in contact with a model biomaterial surface (polystyrene) occurs directly on the material surface or on top of an adsorbed plasma protein layer. Quartz crystal microbalance-dissipation analysis (QCM-D) complemented with enzyme immunoassays and Western blotting were used. QCM-D showed that the surface was immediately covered with a plasma protein film of approximately 8 nm. Complement activation that started concomitantly with the adsorption of the protein film was triggered by a self-limiting classical pathway activation. After adsorption of the protein film, alternative pathway activation provided the bulk of the C3b deposition that added 25% more mass to the surface. The build up of alternative pathway convertase complexes using purified C3 and factors B and D on different protein films as monitored by QCM-D showed that only adsorbed albumin, IgG, but not fibrinogen, allowed C3b binding, convertase assembly and amplification. Western blotting of eluted proteins from the material surface demonstrated that the C3 fragments were covalently bound to other proteins. This is consistent with a model in which the activation is triggered by initiating convertases formed by means of the initially adsorbed proteins and the main C3b binding is mediated by the alternative pathway on top of the adsorbed protein film.

Biomaterial-associated thrombosis: roles of coagulation factors, complement, platelets and leukocytes

Our failure to produce truly non-thrombogenic materials may reflect a failure to fully understand the mechanisms of biomaterial-associated thrombosis. The community has focused on minimizing coagulation or minimizing platelet adhesion and activation. We have infrequently considered the interactions between the two although we are generally familiar with these interactions. However, we have rarely considered in the context of biomaterial-associated thrombosis the other major players in blood: complement and leukocytes. Biomaterials are known agonists of complement and leukocyte activation, but this is frequently studied only in the context of inflammation. For us, thrombosis is a special case of inflammation. Here we summarize current perspectives on all four of these components in thrombosis and with biomaterials and cardiovascular devices. We also briefly highlight a few features of biomaterial-associated thrombosis that are not often considered in the biomaterials literature: The importance of tissue factor and the extrinsic coagulation system. Complement activation as a prelude to platelet activation and its role in thrombosis. The role of leukocytes in thrombin formation. The differing time scales of these contributions.

Apoptosis of human polymorphonuclear neutrophils accelerated by dialysis membranes via the activation of the complement system

BACKGROUND

Haemodialysis (HD) with bioincompatible cellulosic membranes like Cuprophan (CU) is considered to influence negatively the clinical outcome of acute and chronic renal failure. In this effect, apart from the disturbance of phagocytosis or oxygen species production by leukocytes, increased apoptosis also has been implicated recently. The objective of this study was to study the effect of HD membranes on apoptosis induction in polymorphonuclear neutrophils (PMN).

METHODS

PMN from healthy donors and uraemic patients were isolated and apoptosis was induced by co-incubation with CU, Hemophan or polyamide hollow fibres in the presence of serum from healthy or uraemic humans. Apoptosis was quantified by flow cytometry using Annexin V-FITC and propidium iodide staining and was confirmed by the detection of DNA fragmentation on gel electrophoresis. The deposition of immunoglobulins (Ig) and complement factors on hollow fibres was detected by direct immunofluorescence.

RESULTS

Heat inactivation or the depletion of complement components or Ig significantly reduced apoptosis, indicating its dependence on classical complement activation. The detection of IgG on hollow CU fibres and the restored acceleration of apoptosis by the appropriate replenishment of Ig-deficient sera additionally confirmed these findings. Inhibition experiments revealed that caspases were necessary mainly, but not exclusively, for apoptosis to occur after complement activation. Uraemia led to increased PMN apoptosis in the presence of bioincompatible, but not biocompatible, membranes.

CONCLUSIONS

Our results suggest that the acceleration of PMN apoptosis in the presence of CU is mediated via an antibody-dependent activation of the classical complement pathway mobilizing both caspase-dependent and -independent pathways.

Interactions between surface-bound actin and complement, platelets, and neutrophils

Actin exists as globular (G) monomers or polymeric filaments (F) in the cytoplasm of eukaryotic cells, mediating cell morphologic changes and motility. Large amounts of this protein may be released out to the extracellular compartment during tissue injury, but little is known about its role in biomaterial-related inflammation. We immobilized actin to methylated glass, methylated and aminated silicon, and gold model surfaces and studied the subsequent blood serum deposition and complement activation, generation of reactive oxygen species (ROS), and adhesion and aggregation of neutrophils and platelets. Null ellipsometry showed that approximately one monolayer of G-actin can be immobilized onto the model surfaces and that actin in buffer polymerized on top of this by the addition of K(+) and Mg(2+) ions to form a thicker layer of firmly bound F-actin. After serum incubation, F-actin bound low amounts of anti-complement factor 1q (anti-C1q). Cell responses upon contact with actin-coated surfaces were analyzed by luminol-amplified chemiluminescence, lumi-aggregometry, and fluorescence microscopy. It was shown that surface-triggered aggregation, spreading, and generation of ROS are down-regulated and comparable to the response by adsorbed albumin. However, F-actin on gold surfaces recruited platelets in a C1q-dependent manner. We conclude that in vitro adsorbed actin is a weak complement, platelet, and neutrophil activator, but that F-actin associates with both C1q and platelets.

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.

C1q-independent activation of neutrophils by immunoglobulin M-coated surfaces

Neutrophil granulocytes are known to rapidly adhere and undergo frustrated phagocytosis upon contact with immunoglobulin and/or complement protein opsonized artificial surfaces. In this study, we examined the relation between serum protein deposition and human neutrophil activation on hydrophobic glass and silicon model surfaces that were coated with immunoglobulin G or M (IgG/IgM), both initiators of the classical complement pathway. Protein adsorption from normal human serum (NHS) was quantified with null-ellipsometry combined with antibody techniques. The neutrophil oxygen radical production was registered by luminol-amplified chemiluminescence (CL) and the morphology, as well as changes in the content of filamentous actin (F-actin), were documented by fluorescence microscopy. Complement factor 3 (C3) bound to both IgG- and IgM-coated surfaces, but surprisingly C1q was found only on IgG-coated surfaces. Both immunoglobulins triggered complement dependent neutrophil activation. However, CL and F-actin accumulation were found sensitive to the presence of C1q in the serum only at the IgG-coated surface. We suggest that spontaneously adsorbed IgM activates the complement system and interacts with neutrophils by C1q-independent mechanisms.

The interleukin-10 promoter genotype determines clinical immune function in hemodialysis patients

BACKGROUND

Immune dysfunction and the impaired hepatitis B vaccination response are complications of chronic renal failure that are tightly associated with inflammation induced by uremia and blood-membrane contacts. Proinflammatory cytokines, such as interleukin (IL)-6, are counter-regulated by IL-10 with a large interindividual variability. Part of the variability of cytokine production is genetically determined since polymorphisms in the cytokine gene promoters lead to high or low production. The aim of this study was to detect the genetic influence of the IL-10 promoter on immune function of chronic hemodialysis patients.

METHODS

The IL-10 genotype (polymorphic bases at positions -1082 and -819) was determined in 272 chronic hemodialysis patients using highly specific PCR and related to the patients' response to a triple vaccination against hepatitis B. Secretion of IL-10 and IL-6 by peripheral blood leucocytes in vitro was determined by ELISA.

RESULTS

The prevalence of the IL-10 genotypes in dialysis patients with well-preserved immune function (vaccination responders) was similar to the general population. In contrast, prevalence of the -1082G* allele (associated with high production of IL-10) was low in the nonresponders. The relative risk of vaccination nonresponse in patients homozygous for the -1082A* allele was 1.394 (95% CI, 1.091 to 1.781, P < 0.05) compared to those homozygous for -1082G*. There was no relationship between the IL-10 genotype and the type of renal disease.

CONCLUSIONS

The IL-10 genotype determines IL-10 production in dialysis patients, which down-regulates uremia- and dialysis-induced chronic inflammation and helps to preserve immune defense functions.

What really is blood compatibility?

The criteria for nonthrombogenicity are classically defined as long clotting times and minimal platelet deposition. The inability to point to unequivocal progress in the development of truly nonthrombogenic materials, highlights the inadequacy if not actually invalidity of these criteria. Our approach is to define nonthrombogenicity in terms of: (1) a thrombin production rate constant, kp < 10(-4) cm s(-1); (2) low platelet consumption and low degree of platelet activation (e.g., microparticle formation); (3) perhaps some platelet spreading; and (4) low complement and leukocyte activation. Only when the target becomes clear, will it be possible to identify clear strategies for producing the materials we need.

Flow cytometric evaluation of material-induced platelet and complement activation

Flow cytometry is used to characterize the activation state of platelets and leukocytes within whole blood after contact for 4 h at 37 degrees C with various materials under conditions of low shear. The contact involved adding heparinized whole blood to small diameter tubes that were connected to two arms extending from a rocking platform. For all surfaces (polyethylene, polypropylene, Silastic, PVA hydrogel) tested there was strong evidence of platelet activation in the bulk blood: platelet-derived microparticles. P-selectin expression and platelet-leukocyte aggregates. Only contact with PVA hydrogel surfaces led to dramatic increases in CD11b up-regulation on monocytes and neutrophils that was inhibited by complement inhibition (sCRI). Flow cytometry was also used to evaluate the effectiveness of various agents to inhibit material-induced complement activation. The assay involved incubating 10 microm polystyrene beads for 1 h with serum at 37 degrees C before isolating the beads so as to label them with a monoclonal antibody against a neoantigen on SC5b-9. The beads were then identified by flow cytometry and the fluorescence associated with their SC5b-9 level recorded. The ability of C1-INH, pentamidine and benzamidine to moderately inhibit SC5b-9 levels suggests a role for classical complement activation in material-induced complement activation.

Inhibition of complement, neutrophil, and platelet activation by an anti-factor D monoclonal antibody in simulated cardiopulmonary bypass circuits

OBJECTIVES

Patients undergoing cardiopulmonary bypass frequently manifest generalized systemic inflammation and occasionally manifest serious multiorgan failure. Inflammatory responses of bypass are triggered by contact of blood with artificial surfaces of the bypass circuits, surgical trauma, and ischemia-reperfusion injury. We studied the effects of specific inhibition of the alternative complement cascade by using an anti-factor D monoclonal antibody (166-32) in extracorporeal circulation of human whole blood used as a simulated model of cardiopulmonary bypass.

METHODS

Five healthy blood donors were used in the study. Monoclonal antibody 166-32 was added to freshly collected, heparinized human blood recirculated in a pediatric cardiopulmonary bypass circuit at a final concentration of 18 microg/mL. An irrelevant monoclonal antibody was used as a negative control with the same donor blood in a parallel bypass circuit on the same day. Blood samples were collected at different time points during recirculation for measurement of activation of complement, neutrophils, and platelets by immunofluorocytometric methods and enzyme-linked immunosorbent assays.

RESULTS

Monoclonal antibody 166-32 inhibited the alternative complement activation and the production of Bb, C3a, sC5b-9, and C5a. Upregulation of CD11b on neutrophils and CD62P on platelets was also significantly inhibited by monoclonal antibody 166-32. This is consistent with the inhibition of the release of neutrophil-specific myeloperoxidase and elastase and platelet thrombospondin. The production of proinflammatory cytokine interleukin 8 was also suppressed by the antibody.

CONCLUSIONS

The alternative complement cascade is predominantly activated during extracorporeal circulation. Anti-factor D monoclonal antibody 166-32 is effective in inhibiting the activation of complement, neutrophils, and platelets. Inhibition of the alternative complement pathway by targeting factor D could be useful in reducing systemic inflammation in patients undergoing cardiopulmonary bypass.