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PubMed2004

Functional insights from the structure of the multifunctional C345C domain of C5 of complement.

The complement protein C5 initiates assembly of the membrane attack complex. This remarkable process results in lysis of target cells and is fundamental to mammalian defense against infection. The 150-amino acid residue domain at the C terminus of C5 (C5-C345C) is pivotal to C5 function. It interacts with enzymes that convert C5 to C5b, the first step in the assembly of the membrane attack complex; it also binds to the membrane attack complex components C6 and C7 with high affinity. Here a recombinant version of this C5-C345C domain is shown to adopt the oligosaccharide/oligonucleotide binding fold, with two helices packed against a five-stranded beta-barrel. The structure is compared with those from the netrin-like module family that have a similar fold. Residues critical to the interaction with C5-convertase cluster on a mobile, hydrophobic inter-strand loop that protrudes from the open face of the beta-barrel. The opposite, helix-dominated face of C5-C345C carries a pair of exposed hydrophobic side chains adjacent to a striking negatively charged patch, consistent with affinity for positively charged factor I modules in C6 and C7. Modeling of homologous domains from complement proteins C3 and C4, which do not participate in membrane attack complex assembly, suggests that this provisionally identified C6/C7-interacting face is indeed specific to C5.

Amino Acid Sequence↗
PubMed2002

Role of the human C8 subunits in complement-mediated bacterial killing: evidence that C8 gamma is not essential.

Human C8 is one of five complement components (C5b, C6, C7, C8 and C9) that interact to form the cytolytic membrane attack complex (MAC) on bacterial cell membranes. It is an oligomeric protein composed of a disulfide-linked C8 alpha-gamma heterodimer and a non-covalently associated C8 beta chain. Previous studies revealed that C8 alpha and C8 beta have distinct roles in the formation of the MAC on simple cells such as erythrocytes and that both subunits are essential for cell lysis. These studies also determined that C8 gamma is not required for expression of MAC hemolytic activity. To determine if these conclusions are applicable to more biologically relevant systems, the C8 subunits were examined for their ability to support complement-mediated killing of Gram-negative bacteria. Results indicate: (1) C8 alpha-gamma, C8 alpha, C8 beta and C8 gamma have no independent bactericidal activity; (2) bacterial killing requires C8 beta and either C8 alpha-gamma or C8 alpha; (3) C8 alpha is an effective substitute for C8 alpha-gamma in bacterial killing; and (4) C8 gamma enhances, but is not required for C8 bactericidal activity. Together, these data suggest that C8 alpha and C8 beta have correspondingly similar roles in MAC-mediated lysis of erythrocytes and bacterial killing. Furthermore, they provide the first direct evidence that C8 gamma is not required for complement-mediated killing of Gram-negative bacteria.

Blood Bactericidal Activity↗
PubMed2004

Pathological study on the relationship between C4d, CD59 and C5b-9 in acute renal allograft rejection.

In order to evaluate the activation or inhibition of the later phases of classical complement cascade in renal allograft presenting with acute rejection, particularly with C4d deposition on the peritubular capillary (PTC), we observed the expression of CD59 and C5b-9 on the PTC. Subjective cases were divided into two groups, an acute rejection group, of 4 males and 6 females, and a normal donor group, of 5 males and 5 females. Renal biopsies were performed at the onset of acute rejection and at the transplant operation, before reperfusion. C4d deposition on PTC was found in three of 10 cases (30%) with biopsy proven acute rejection, whereas CD59 on PTC was positively expressed in all of the rejection cases. Although C5b-9 was not observed on PTC in the acute rejection group, it was intensively deposited on the tubular basement membrane (TBM) in five cases, including the three with positive C4d on PTC. In the normal donor group, CD59 on PTC was intensively observed, whereas C5b-9 was weakly expressed on TBM. CD59, a complement regulatory factor, works as an inhibitory factor against the formation of C5b-9, a membrane attack complex. From our data, we noted the dissociation between the depositions of C4d and C5b-9 on PTC. The substantially expressed CD59 on PTC may affect this dissociation between C4d and C5b-9 on PTC. The intensive deposition of C5b-9 on TBM in acute rejection cases may suggest an independent immunological injury attacking tubular cells.

Acute Disease↗
PubMed1999

Up-regulated production and activation of the complement system in Alzheimer's disease brain.

We used reverse transcriptase-polymerase chain reaction and Western blotting techniques to measure the levels of complement mRNAs and their protein products in Alzheimer's disease (AD) brain compared with non-AD brain. mRNAs for C1q, C1r, C1s, C2, C3, C4, C5, C6, C7, C8, and C9 were detected in the 11 regions of brain that were investigated. The mRNA levels were markedly up-regulated in affected areas of AD brain. In the entorhinal cortex, hippocampus, and midtemporal gyrus, which had dense accumulations of plaques and tangles, C1q mRNA was increased 11- to 80-fold over control levels, and C9 mRNA 10- to 27-fold. These levels were substantially higher than in the livers of the same cases. Western blot analysis of AD hippocampus established the presence of all of the native complement proteins as well as their activation products C4d, C3d, and the membrane attack complex. These data indicate that high levels of complement are being produced in affected areas of AD brain, that full activation of the classical complement pathway is continuously taking place, and that this activation may be contributing significantly to AD pathology.

Adult↗
PubMed2000

[Immunohistochemical detection of complement factors: a reliable method for the diagnosis of myasthenia gravis].

A 57-year-old woman suffered from generalized muscular weakness without diplopia or dysphagia for about 2 years. An abnormal decremental response on low frequency nerve stimulation and improvement upon administration of edrophonium chloride suggested a diagnosis of myasthenia gravis. However, this diagnosis remained uncertain, since repeated tests for antiacetylcholine receptor antibodies were negative. In addition, the patient reported that she was never able to keep up with peers in prolonged physical activities since childhood. For this reason, a congenital myasthenic syndrome was suspected and an intercostal muscle biopsy performed for special end-plate studies. Immunohistochemistry of the muscle biopsy revealed membrane attack complex deposits at the end-plates. This finding definitely confirmed the diagnosis of autoimmune myasthenia gravis. In conclusion, immunohistochemistry for complement deposits at the end-plates is a simple and reliable method of confirming the diagnosis of myasthenia gravis in uncertain cases.

Biopsy↗
PubMed1996

Protein SIC, a novel extracellular protein of Streptococcus pyogenes interfering with complement function.

The human pathogen Streptococcus pyogenes possesses a chromosomal region, the mga regulon, that contains co-regulated genes important to the virulence of these bacteria. A novel gene located in the mga regulon of a S. pyogenes strain of serotype M1 was cloned and sequenced. It translates into a protein of 305 amino acid residues, including a signal sequence of 32 amino acids and a central region consisting of three tandem repeats. The sequence represents a novel structure with no significant homology to any previously published sequence. The protein was purified from the streptococcal culture media where it is present in substantial amounts. Affinity chromatography of human plasma on Sepharose coupled with the protein specifically absorbed two plasma proteins which were identified as clusterin and histidine-rich glycoprotein (HRG). The interactions between the streptococcal protein and the plasma proteins were further characterized using purified clusterin and HRG. Inhibition experiments indicated that they have affinity for overlapping or closely located sites in the streptococcal protein. Both clusterin and HRG are regulators of the membrane attack complex (C5b-C9) of complement. When the streptococcal protein was added to serum, complement-mediated lysis of sensitized sheep erythrocytes and guinea pig erythrocytes was inhibited. In addition, the streptococcal protein was incorporated into C5b-C9 in serum, indicating the location of its action. The name, protein SIC, streptococcal inhibitor of complement-mediated lysis, is therefore suggested for this novel protein. The occurrence of protein SIC and its gene was investigated in a collection of S. pyogenes strains comprising 55 different M serotypes. Only M1 and M57 strains were positive in this screening, indicating that protein SIC could be a virulence determinant. Thus, during recent years, the M1 serotype has been connected with a world-wide increase of severe and toxic S. pyogenes infections.

Amino Acid Sequence↗
PubMed2000

An indel within the C8 alpha subunit of human complement C8 mediates intracellular binding of C8 gamma and formation of C8 alpha-gamma.

Human C8 is one of five complement components (C5b, C6, C7, C8, and C9) that interact to form the cytolytic membrane attack complex, or MAC. It is an oligomeric protein composed of three subunits (C8alpha, C8beta, C8gamma) that are products of different genes. In C8 from serum, these are arranged as a disulfide-linked C8alpha-gamma dimer that is noncovalently associated with C8beta. In this study, the site on C8alpha that mediates intracellular binding of C8gamma to form C8alpha-gamma was identified. From a comparative analysis of indels (insertions/deletions) in C8alpha and its structural homologues C8beta, C6, C7, and C9, it was determined that C8alpha contains a unique insertion (residues 159-175), which includes Cys(164) that forms the disulfide bond to C8gamma. Incorporation of this sequence into C8beta and coexpression of the resulting construct (iC8beta) with C8gamma produced iC8beta-gamma, an atypical disulfide-linked dimer. In related experiments, C8gamma was shown to bind noncovalently to mutant forms of C8alpha and iC8beta in which Cys(164)-->Gly(164) substitutions were made. In addition, C8gamma bound specifically to an immobilized synthetic peptide containing the mutant indel sequence. Together, these results indicate (a) intracellular binding of C8gamma to C8alpha is mediated principally by residues contained within the C8alpha indel, (b) binding is not strictly dependent on Cys(164), and (c) C8gamma must contain a complementary binding site for the C8alpha indel.

Amino Acid Sequence↗
PubMed2006

Activation of kainate receptors sensitizes oligodendrocytes to complement attack.

Glutamate excitotoxicity and complement attack have both been implicated separately in the generation of tissue damage in multiple sclerosis and in its animal model, experimental autoimmune encephalomyelitis. Here, we investigated whether glutamate receptor activation sensitizes oligodendrocytes to complement attack. We found that a brief incubation with glutamate followed by exposure to complement was lethal to oligodendrocytes in vitro and in freshly isolated optic nerves. Complement toxicity was induced by activation of kainate but not of AMPA receptors and was abolished by removing calcium from the medium during glutamate priming. Dose-response studies showed that sensitization to complement attack is induced by two distinct kainate receptor populations displaying high and low affinities for glutamate. Oligodendrocyte death by complement required the formation of the membrane attack complex, which in turn increased membrane conductance and induced calcium overload and mitochondrial depolarization as well as a rise in the level of reactive oxygen species. Treatment with the antioxidant Trolox and inhibition of poly(ADP-ribose) polymerase-1, but not of caspases, protected oligodendrocytes against damage induced by complement. These findings indicate that glutamate sensitization of oligodendrocytes to complement attack may contribute to white matter damage in acute and chronic neurological disorders.

Animals↗
PubMed1985

Characterization of the complement sensitivity of paroxysmal nocturnal hemoglobinuria erythrocytes.

The affected erythrocytes of paroxysmal nocturnal hemoglobinuria (PNH II and PNH III cells) are abnormally sensitive to complement-mediated lysis. Normal human erythrocytes chemically modified by treatment with 2-amino-ethylisothiouronium bromide (AET) have been used as models for PNH cells inasmuch as they also exhibit an enhanced susceptibility to complement. To investigate the bases for the greater sensitivity of these abnormal cells to complement-mediated lysis, we compared binding of C3 and constituents of the membrane attack complex to normal, PNH II, PNH III, and AET-treated cells after classical pathway activation by antibody and fluid-phase activation by cobra venom factor complexes. When whole serum complement was activated by antibody, there was increased binding of C3 and C9 to PNH II, PNH III, and AET-treated cells, although the binding of these complement components to PNH II and PNH III cells was considerably greater than their binding to the AET-treated cells. In addition, all of the abnormal cell types showed a greater degree of lysis per C9 bound than did the normal erythrocytes. PNH III and AET-treated cells were readily lysed by fluid-phase activation of complement, whereas normal and PNH II erythrocytes were not susceptible to bystander lysis. The greater hemolysis of PNH III and AET-treated cells in this reactive lysis system was due to a quantitative increase in binding of constituents of the membrane attack complex. This more efficient binding of the terminal components after fluid-phase activation of whole serum complement was not mediated by cell-bound C3 fragments. These investigations demonstrate that the molecular events that characterize the enhanced susceptibility of PNH II, PNH III, and AET-treated erythrocytes to complement-mediated lysis are heterogeneous.

Cobra Cardiotoxin Proteins↗
PubMed2002

Interaction between the C8 alpha-gamma and C8 beta subunits of human complement C8: role of the C8 beta N-terminal thrombospondin type 1 module and membrane attack complex/perforin domain.

Human C8 is one of five complement components (C5b, C6, C7, C8, and C9) that interact to form the cytolytic membrane attack complex (MAC). It is an oligomeric protein composed of a disulfide-linked C8alpha-gamma heterodimer and a noncovalently associated C8beta chain. C8alpha and C8beta are homologous; both contain an N-terminal thrombospondin type 1 (TSP1) module, a low-density lipoprotein receptor class A (LDLRA) module, an extended central segment referred to as the membrane attack/perforin (MACPF) domain, an epidermal growth factor (EGF) module, and a second TSP1 module at the C-terminus. In this study, the segment of C8beta that confers binding specificity toward C8alpha-gamma was identified using recombinant C8beta constructs in which the N- and/or C-terminal modules were deleted or exchanged with those from C8alpha. Constructs were tested for their ability to bind C8alpha-gamma in solution and express C8 hemolytic activity. Binding to C8alpha-gamma was found to be dependent on the TSP1 + LDLRA + MACPF segment of C8beta. Within this segment, the TSP1 module and MACPF domain are principally involved and act cooperatively to mediate binding. Results from activity assays suggest that residues within this segment also mediate binding and incorporation of C8 into the MAC.

Amino Acid Motifs↗
PubMed2005

Molecular cloning of the seventh component of complement in rainbow trout.

C7 is an integral component of the lytic pathway of complement, which interacts in a sequence of polymerization reactions with other terminal components to form the membrane attack complex. C7 plays a central role in the terminal complement cascade, since its incorporation into the nascent complex allows its hydrophilic-amphiphilic transition, which subsequently leads to the direct binding of the complex to the target membrane. To date, only human and porcine C7 have been cloned and characterized. Here we report the isolation of a C7 molecule from the rainbow trout (Oncorhynchus mykiss). The full-length trout C7 cDNA was isolated, and the predicted amino acid sequence exhibits 44 and 65% identity with human and Japanese flounder C7, respectively. The cysteine backbone and two putative N-linked glycosylation sites are conserved in trout C7. It also contains the same structural motifs as those found in mammalian C7. Trout C7 mRNA expression was detected in all tissues investigated, except kidney and spleen.

Amino Acid Sequence↗
PubMed1998

Possible arrangement of the five domains in human complement factor I as determined by a combination of X-ray and neutron scattering and homology modeling.

Human factor I is a multidomain plasma serine protease with one factor I-membrane attack complex (FIMAC) domain, one CD5 domain, two low-density lipoprotein receptor (LDLr) domains, and one serine protease (SP) domain and is essential for the regulation of complement. The domain arrangement in factor I was determined by X-ray and neutron scattering on serum-derived human factor I (sFI) and recombinant insect cell factor I (rFI). While the radii of gyration of both were the same at 4.05 nm and both had overall lengths of 14 nm, the cross-sectional radii of gyration were different at 1.70 nm for sFI and 1.57 nm for rFI. This difference was attributed to their different means of glycosylation which is complex-type for sFI and high-mannose-type for rFI. Homology models were constructed for the FIMAC, LDLr, and SP domains of factor I using related crystal structures, and CD5 was represented as a globular protein by referencing its electron microscopy dimensions. In these models, 38 of the 40 Cys residues in factor I were predicted to form internal disulfide bridges. The two remaining Cys residues at the N terminus of the FIMAC domain and at the center of the first LDLr domain were potentially not bridged. It was postulated that, if these two Cys residues were bridged to each other, the FIMAC, CD5, and LDLr-1 domains would form a compact triangular arrangement. This hypothesis was tested by automated scattering curve fit searches based on 9600 bilobal models, setting the FIMAC, CD5, and LDLr-1 domains as one lobe and the large SP domain as the other lobe. The searches gave a single small family of similar structures with a separation of 5.9 nm between the centers of the lobes which gave similar good X-ray and neutron fits for both sFI and rFI, despite the different glycosylations of sFI and rFI. These best-fit structures for factor I showed that this domain model is plausible, and suggested that the SP and the CD5 and LDLr-1 domains may present exposed surfaces in factor I whose roles are to interact separately with its substrates C3b and C4b and with cofactor proteins.

Amino Acid Sequence↗
PubMed1993

Complement activation and C3 allotype distribution in patients with bronchial asthma.

61 patients suffering from intrinsic (idiotypic) or extrinsic (allergic) asthma were investigated for signs of complement activation and for C3 phenotype distribution. Activation of both the classical and alternative pathway of the complement system and generation of the membrane attack complex could be assessed by ELISAs for the activation-specific protein-protein complexes C1rsC1 inhibitor, C3b(Bb)P and SC5b-9, respectively. A possible deficiency of the complement regulatory proteins C1 inhibitor, factor H and factor I was excluded. In contrast to earlier studies, C3 allele frequencies did not differ from those found in the healthy population. Our results support the role of complement activation during bronchial asthma and, thereby, provide further evidence for the inflammatory nature of the disease.

Alleles↗
PubMed1998

Human heart generates complement proteins that are upregulated and activated after myocardial infarction.

In human heart, we detected mRNAs and proteins for C1q, C1r, C1s, C2, C3, C4, C5, C6, C7, C8, and C9 with the use of reverse transcriptase-polymerase chain reaction, Western blotting, and immunohistochemical techniques. We found an upregulation of both mRNAs and proteins in areas of recent and old myocardial infarctions. In both situations, the classical complement pathway was activated, with C4d, C3d, and the membrane attack complex (C5b-9) being deposited on damaged cardiac myocytes. These activated complement components were also identified on Western blots of infarcted tissue. Complement mRNAs in infarcted heart tissue were higher than those in liver, and liver complement mRNAs were not upregulated in cases with infarcted hearts. Our results establish that (1) complement proteins are endogenously produced by human heart; (2) the classical complement pathway is fully activated after myocardial infarction; (3) complement activation is directly involved in myocardial damage after ischemic insults; and (4) damage from complement activation may be chronically sustained. These data suggest that inhibition of the complement system should be effective in treating myocardial infarction.

Adult↗
PubMed2005

The Arabidopsis gene CAD1 controls programmed cell death in the plant immune system and encodes a protein containing a MACPF domain.

To clarify the processes involved in plant immunity, we have isolated and characterized a single recessive Arabidopsis mutant, cad1 (constitutively activated cell death 1), which shows a phenotype that mimics the lesions seen in the hypersensitive response (HR). This mutant shows spontaneously activated expression of pathogenesis-related (PR) genes, and leading to a 32-fold increase in salicylic acid (SA). Inoculation of cad1 mutant plants with Pseudomonas syringae pv tomato DC3000 shows that the cad1 mutation results in the restriction of bacterial growth. Cloning of CAD1 reveals that this gene encodes a protein containing a domain with significant homology to the MACPF (membrane attack complex and perforin) domain of complement components and perforin proteins that are involved in innate immunity in animals. Furthermore, cell death is suppressed in transgenic cad1 plants expressing nahG, which encodes an SA-degrading enzyme. We therefore conclude that the CAD1 protein negatively controls the SA-mediated pathway of programmed cell death in plant immunity.

Amino Acid Sequence↗
PubMed1995

Identity of the segment of human complement C8 recognized by complement regulatory protein CD59.

CD59 antigen is a membrane glycoprotein that inhibits the activity of the C5b-9 membrane attack complex (MAC), thereby protecting human cells from lysis by human complement. The inhibitory function of CD59 derives from its capacity to interact with both the C8 and C9 components of MAC, preventing assembly of membrane-inserted C9 polymer. MAC-inhibitory activity of CD59 is species-selective and is most effective when both C8 and C9 derive from human or other primate plasma. Rabbit C8 and C9, which can substitute for human C8 and C9 in MAC, mediate virtually unrestricted lysis of human cells expressing CD59. In order to identify the segment of human C8 that is recognized by CD59, recombinant peptides containing human or rabbit C8 sequence were expressed in Escherichia coli and purified. CD59 was found to specifically bind to a peptide corresponding to residues 334-385 of the human C8 alpha-subunit, and to require a disulfide bond between Cys345 and Cys369. No specific binding was observed to the corresponding sequence from rabbit C8 alpha (residues 334-386). To obtain functional evidence that this segment of human C8 alpha is selectively recognized by CD59, recombinant C8 proteins were prepared by co-transfecting COS-7 cells with human/rabbit chimeras of the C8 alpha cDNA, and cDNAs encoding the C8 beta and C8 gamma chains. Hemolytic activity of MAC formed with chimeric C8 was analyzed using target cells reconstituted with CD59. These experiments confirmed that CD59 recognizes a conformationally sensitive epitope that is within a segment of human C8 alpha internal to residues 320-415. Our data also suggest that optimal interaction of CD59 with this segment of human C8 alpha is influenced by N-terminal flanking sequence in C8 alpha and by human C8 beta, but is unaffected by C8 gamma.

Amino Acid Sequence↗
PubMed2026

Complement expression profiles in human glomerular mesangial cells, endothelial cells, podocytes and proximal tubular epithelial cells.

BACKGROUND: Local expression of complement components in the kidney has been reported sporadically in both diseased and normal kidneys. This study aimed to comprehensively characterize the expression of complement components in human glomerular mesangial cells (GMCs), glomerular endothelial cells (GECs), podocytes, and proximal tubular epithelial cells (PTECs) in non-diseased renal tissue. METHODS: Complement expression in cultured human renal intrinsic cells was initially evaluated using reverse transcription polymerase chain reaction and immunofluorescence staining. These findings were further examined using publicly available single-cell RNA-sequencing datasets and 10×Genomics single-cell RNA sequencing of non-diseased human kidney tissue. The analyses focused on complement components involved in the initiation of the classical, lectin, and alternative pathways, as well as components shared among these activation pathways, terminal pathway components, complement regulators, and complement receptors. RESULTS: Complement components unique to the initial phase for classical pathway (C1S, C1R, C2, C4), lectin pathway (MBL2, FCN1, MASP1), alternative pathway (CFB, CFD), and the C3 component shared by the three activation pathways were detected in these cells. The components shared by the terminal pathways including C5, C6, C7, C8 and C9 exhibited lower expression, while complement regulators (CFH, CFI, CD55/DAF, CD46/MCP, CD59, C4BPB, PROS1/Protein S) or receptors (CD93/C1QR1, CR1), particularly membrane-bound proteins, such as DAF, MCP and CD59, which inhibit complement activation and the formation of the membrane attack complex, showed relatively high expression. CONCLUSION: These results showed that all four types of intrinsic renal cells expressed multiple complement components associated with the classical, lectin, and alternative pathways. In non-diseased kidney tissue, complement regulatory molecules involved in the control of complement activation showed relatively higher expression, whereas components of the terminal complement pathway were expressed at relatively lower levels, suggesting that renal intrinsic cells maintain a locally poised but tightly regulated complement system.

Humans↗
PubMed1996

Amplification of the inflammatory response: adhesion molecules associated with platelet/white cell responses.

Cardiopulmonary bypass (CPB) causes leukocyte and platelet activation, resulting in upregulation of the adhesion receptor CD11b/CD18 on leukocytes and upregulation of P-selectin, the adhesion receptor that binds the activated platelet to polymorphonuclear neutrophils (PMNs) and monocytes. Our laboratory has studied the expression of activation-dependent adhesion receptors during in vivo CPB. Both PMN and monocyte CD11b were upregulated during CPB but with differing time courses. Peak PMN CD11b levels occurred at the end of the hypothermic phase of bypass, whereas monocyte CD11b levels increased steadily throughout the course of CPB, peaked at 2-4 h after CPB, and remained significantly elevated as late as 18-24 h post CPB. The percentage of P-selectin-positive platelets increased significantly during bypass, peaking around the end of bypass and remaining elevated in the early post-bypass period. The level then returned to normal by 18 h post-bypass. Monocyte-platelet binding paralleled the increase in P-selectin-positive platelets during bypass and similarly remained elevated in the post-bypass period. PMN-platelet binding also increased but peaked early during CPB. Upregulation of these adhesive receptors and formation of platelet-leukocyte conjugates may influence the prothrombotic activity of monocytes and the proinflammatory activity of PMNs in the post-CPB period. Our laboratory has developed an in vitro model of extracorporeal circulation, and recirculation of blood on this circuit results in significant activation of PMNs and monocyte CD11b expression, increasing progressively over time. Likewise, the percentage of P-selectin-positive platelets increased and was paralleled by the formation of leukocyte-platelet conjugates comparable to the pattern found in vivo. Generation of the complement fragments C5a and the C5b-9 membrane-attack complex may contribute to platelet P-selectin expression and formation of leukocyte-platelet conjugates during CPB. The in vitro model has been used to test the cellular effects of complement inhibition employing a monoclonal antibody that blocks cleavage of C5 into C5a and C5b to determine the role of early vs. late complement components in the cellular activation induced by CPB. Preliminary results demonstrate that blockage of the formation of C5a and the C5b-9 membrane-attack complex during simulated extracorporeal circulation effectively inhibits platelet and PMN activation and the formation of leukocyte-platelet conjugates.

Blood Platelets↗