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PubMed1989

In vivo clearance studies of the terminal fluid-phase complement complex in rabbits.

The present study was directed at obtaining information on the in vivo elimination rate of SC5b-9, the terminal fluid-phase product of complement activation. A sandwich ELISA based on the use of mono- and polyclonal antibodies was constructed that permitted quantitation of rabbit SC5b-9 in plasma. Rabbit serum was activated with inulin in vitro to generate SC5b-9, and the activated serum was applied intravenously in normal and C6-deficient rabbits. Elimination of SC5b-9 in normal rabbits was rapid, half-life in the range of 30-50 min. No differences were noted between the clearance of homologous rabbit and heterologous human SC5b-9, SC5b-9 concentrations returned to basal levels 2-3 h after application. Plasma of C6-deficient rabbits contained no SC5b-9 and these animals displayed an even more effective clearance capacity for the complex. Quantitative considerations indicated that basal plasma SC5b-9 levels in healthy animals result from a spontaneous turnover rate of approximately 0.2% of C5-C9 components per h. When multiple doses of SC5b-9 were injected in sequence, the same half-life and total elimination time were found as with single-dose experiments. The results demonstrate the existence of an effective clearance mechanism for SC5b-9, consistent with recent findings that SC5b-9 plasma levels are very low not only in healthy adults, but also in the majority of patients with complement-consuming diseases.

Animals↗
PubMed1983

Beta chain deficiency in three patients with dysfunctional C8 molecules.

Structural and functional studies were performed on a dysfunctional C8 molecule present in the serum of two siblings and an unrelated individual. The C8 in these three sera exhibited a pattern of partial immunologic identity with C8 in normal serum but was devoid of functional activity. The C8 was immunoprecipitated from the three sera and from a control serum with an antihuman C8 antiserum and analyzed by SDS-PAGE using highly purified human C8 as a reference. A selective absence of a band of 62,000 mol. wt was observed in the immunoprecipitates from the sera containing dysfunctional C8. Experiments performed with the purified alpha-gamma and beta subunits showed that the hemolytic activity of the C8 deficient sera could be reconstituted by the addition of the beta chain but not the alpha-gamma dimer. Binding of the dysfunctional C8 to C567 was excluded by the following observations: (1) EAC1-7 treated with the C8 deficient sera and then washed could not be lysed after the addition of the beta subunit and C9; and (2) the abnormal molecules did not interfere with the consumption of normal C8 by the soluble complex SC5b-7.

Binding, Competitive↗
PubMed1989

The release of C5a in complement-activated serum does not require C6.

The influence of terminal complement components on the generation and release of the complement C5a fragment was investigated by comparing the levels of C5a in complement-activated serum with the levels of C5a produced in serum depleted of complement C6. In order to investigate the release of C5a, a modified C5a assay was developed that utilizes an anti-C5b monoclonal antibody to remove C5, C5b, and C5b-C5a complexes from samples prior to C5a assay. The modified assay was developed because the standard methodology, which includes an acid-precipitation step designed to dissociate C5a and C5b, cannot distinguish free C5a from the C5a that is bound to C5b. Therefore, the standard methodology is not capable of monitoring the influence of terminal components on C5a/C5b dissociation. Levels of C5a were measured in complement-activated whole human serum, in serum depleted of C6, and in serum containing inhibitory levels of anti-C6 Fab using both the modified C5a assay and the standard methodology. Sera were complement-activated with either zymosan to activate the alternative complement pathway or with antibody-coated sheep erythrocytes to activate the classical pathway. The levels of free C5a in C6-depleted sera after activation were equivalent to the C5a levels in activated whole serum, indicating that C6 is not required for the release of C5a from C5b. In addition, the quantity of C5a detected in zymosan-activated sera using the standard acid-precipitation methodology was greater than C5a levels when assayed using the modified immunoadsorption technique, confirming that acid-treatment enhances the C5a dissociation and promotes C5a recovery. Since the other terminal components, C7, C8, and C9, bind to C5b only after C5b only after C6 is bound, these results indicate that none of the terminal components are required for the release of C5a. Although the terminal components could influence the rate of C5a release, the quantity of C5a released in serum was entirely independent of terminal components.

Animals↗
PubMed1998

Human complement component C1q inhibits the infectivity of cell-free HTLV-I.

Human T cell leukemia virus type I (HTLV-I) is a retrovirus that is not lysed by human serum or complement. It has not been determined, however, whether HTLV-I directly binds to complement components or whether it retains infectivity after incubation with human serum. We investigated the effects of human serum on the infectivity of cell-free HTLV-I produced by human and animal cells. Plating of vesicular stomatitis virus (HTLV-I) pseudotypes prepared in cat or human cells and formation of HTLV-I DNA after infection of cell-free HTLV-I produced by cat or human cells were markedly inhibited by treatment with fresh human serum, but not by heat-inactivated serum. HTLV-I infection was also inhibited by treatment with C2-, C3-, C6-, or C9-deficient serum, but not by C1q-deficient serum. Inhibitory activities of normal human serum against HTLV-I were neutralized by anti-C1q serum. Furthermore, purified C1q inhibited HTLV-I infection. The direct binding of C1q to HTLV-I was confirmed by comigration of C1q with HTLV-I virion upon sucrose density gradient ultracentrifugation of HTLV-I virion treated with C1q. Binding assay using synthetic envelope peptides indicated that C1q bound to an extramembrane region of the gp21 transmembrane protein. These findings indicate that the human complement component C1q inactivates HTLV-I infectivity.

Animals↗
PubMed1976

Complement-induced ultrastructural membrane lesions: requirement for terminal components.

The step in the complement (C) sequence at which 8- to 11-nm ring-shaped lesions are formed on antibody-coated erythrocytes (EA) has remained controversial. Some workers have concluded that these lesions appear at the C5 step and are not ultrastructural correlates of lysis; others hold that these lesions are formed only after the action of C8 and C9 in association with lysis. We have re-examined this problem by using sheep EA and human sera genetically lacking C5, C6, C7, or C8. Electron micrographs of negatively stained membranes (x 220,000) were read in blind fashion and the results correlated with 125I-C5 binding. Rare structures resemblind C-induced ring lesions were found on EA exposed to C5-deficient (C5D), C6D, C7D and C8D sera or to heated normal serum, with no significant differences among these sera (lesion density 0 to 0.26/mum2). Fresh normal serum (NHS) produced 140 to 220 ring lesions/mum2. C5 binding to EA in C8D serum was 60% of that observed in an NHS control; in C6D and C7D sera C5 binding was 4 to 11% of the normal value. Iodine treatment of sera (to enhance C5 uptake by C2 oxidation) increased C5 binding in C6D serum to 40 to 65% of that seen in native NHS; in iodine-treated C7D and C8D sera C5 binding was 250 and 440%, respectively, of the native NHS value. No increase in ring lesions was observed, however, except in the iodine-treated NHS. Thus, in whole serum, C5 binding is not sufficient to produce ultrastructural membrane rings in the absence of later-acting C components, at least through C8. The formation of ring lesions appears to have C requirements similar to those necessary for lysis.

Binding Sites↗
PubMed1981

How complement kills E. coli. I. Location of the lethal lesion.

We have studied the action of human complement (C) on E. coli membranes. We find, as have others, that C disrupts the outer membrane (OM), allowing the release of periplasmic proteins. In addition, we have found 1) that in the complete absence of lysozyme, C damages the inner membrane (IM), 2) IM damage is different from OM damage in that only small molecules traverse a damaged IM whereas macromolecules traverse damaged OM, 3) IM damage and OM damage occur with identical kinetics and dose response, suggesting that IM and OM damage are closely coupled events, and 4) upon the addition of purified C8 and C9 to the washed cellular intermediate, E. coli C 1-7, both IM and OM are damaged coordinately. These results, taken together, suggest that C damages E. coli membranes by acting at a site contiguous with both membranes. We speculate that C may simultaneously gain access to both membranes by acting at the junctions between IM and OM.

Alkaline Phosphatase↗
PubMed1994

Cardiolipin-protein complexes and initiation of complement activation after coronary artery occlusion.

Specific rabbit anti-cardiolipin (anti-CL) antibodies were used to investigate the hypothesis that cardiolipin, associated with mitochondrial membrane proteins, binds C1 and facilitates activation of the complement cascade following reperfusion of ischemic myocardium. By immunoelectron microscopy, anti-CL localized to subsarcolemmal mitochondria, emerging through breaks in membranes of damaged cardiac myocytes. Anti-CL reacted with > 15 mitochondrial constituents, most of which comigrated with the proteins that bind C1q in transblots of subsarcolemmal mitochondria, fractionated by polyacrylamide gel electrophoresis under reducing conditions in the presence of sodium dodecyl sulfate. A subset of the C1q-binding proteins > 24 to 37 kDa served as stable sites for assembly of C3, C5, and C9. Cardiac lymph, collected during the first hour after reperfusion of ischemic myocardium, contained proteins of diverse size that reacted with both anti-CL and C1q. Cardiac lymph, collected before occlusion and 4 to 5 hours after reperfusion, in comparison, had few if any C1q or anti-CL reactive proteins. Treatment with phospholipase suppressed the C1q-binding activity and anti-CL reactivity of the proteins in reperfusion lymph and those with similar properties in mitochondrial extracts. Our data suggest that during ischemia, mitochondria, extruded through breaks in the sarcolemma, unfold and release membrane fragments in which cardiolipin and protein are intimately associated. By binding C1 and supplying sites for the assembly of later-acting complement components, these fragments provide the means to disseminate the complement-mediated inflammatory response to ischemic injury.

Animals↗
PubMed1983

Cytogenetic analysis of variegation suppressors and a dominant temperature-sensitive lethal in region 23-26 of chromosome 2L in Drosophila melanogaster.

Three suppressor loci for position-effect variegation, one dominant temperature-sensitive (DTS), three Minute genes, and two recessive visible mutants (ed, tkv) have been cytogenetically localized by using duplications and deficiencies in regions 23-25 of chromosome arm 2L of Drosophila melanogaster. Two of the suppressor loci studied proved to represent haplo-abnormal genes localized in regions 23A6-23F6 and 24E2-25A1, respectively. The third one is a strong triplo-abnormal suppressor mapping in 25F4-26B9 which affects white variegation in wm4h when present in three doses. The l(2)2DTS mutation, which belongs to a group of noncomplementing dominant temperature-sensitive mutations, is localized in the 25A4-B1 region. Furthermore, two Minute genes have been localized in region 24 that are included in Df(2L)M11 and can be separated employing translocation (Y;2)P8 (24E2-4): M(2)LS2 in 24D3-4-24E2-4, and M(2)z in 24E4-5-24F5-7. A third Minute gene (M(2)S1) is localized in 25C3-8-25C9-D1. The usefulness of the isolated chromosomal rearrangements for further genetic studies of region 23-26 is discussed.

Animals↗
PubMed1996

Complement activation in the central nervous system following blood-brain barrier damage in man.

The central nervous system (CNS) is virtually isolated from circulating immunological factors such as complement (C), an important mediator of humoral immunity and inflammation. In circulation, C is constantly inhibited to prevent attack on host cells. Since a host of diseases produce an abnormal blood-brain/cerebrospinal fluid (blood-brain/CSF) permeability allowing C protein extravasation, we investigated if C activation occurs in CSF in vitro and in CNS in vivo during subarachnoid hemorrhage (SAH) or brain infarction. After SAH (n = 15), the terminal complement complex (TCC) concentration on days 0 to 2 was higher in the CSF, 210 +/- 61 ng/ml, than in the plasma, 63 +/- 17 ng/ml, but null in the CSF of controls (n = 8) or patients with an ischemic stroke (n = 7). TCC was eliminated from the CSF after SAH (24 +/- 10 ng/ml on days 7 to 10). Incubation of normal human CSF with serum in vitro also activated the terminal C pathway. In 10 fatal ischemic brain infarctions, immunohistochemical techniques demonstrated neuronal fragment-associated deposition of C9 accompanied by neutrophil infiltration. We conclude that the C system becomes activated intrathecally in SAH and focally in the brain parenchyma in ischemic stroke. By promoting chemotaxis and vascular perturbation, C activation may instigate nonimmune inflammation and aggravate CNS damage in diseases associated with plasma extravasation.

Adult↗
PubMed1994

Soluble recombinant complement receptor 1 inhibits inflammation and demyelination in antibody-mediated demyelinating experimental allergic encephalomyelitis.

Activation of complement may contribute to tissue damage in many inflammatory diseases, including those that are clearly T cell driven. We have previously provided evidence that C is involved in tissue damage in multiple sclerosis and in the animal models of this disease, experimental allergic encephalomyelitis and Ab-mediated demyelinating experimental allergic encephalomyelitis, the latter being a model more closely resembling multiple sclerosis. The development of a soluble recombinant form of human complement receptor 1 (sCR1) with potent C-inhibiting activity both in vitro and in vivo provides a potential means of preventing C-mediated tissue damage in animal models and in human disease. Here, we describe the effects of this agent on clinical disease and pathology in Ab-mediated demyelinating experimental allergic encephalomyelitis in the rat. Daily i.p. injection of sCR1 (20 mg/kg) over 6 days completely suppressed serum C activity, reduced the severity of clinical disease (clinical score 1.33 vs 2.79 in untreated animals), inhibited central nervous system inflammation (inflammatory index 2.76 vs 6.55), and almost completely blocked demyelination (average 2.43% cord cross-section vs 8.81%). Deposition of C components C1, C3, and C9 was also markedly inhibited in sCR1-treated animals. This dramatic effect on a demyelinating disease, achieved using a well-tolerated biologic reagent, offers an exciting new prospect for therapy in multiple sclerosis.

Animals↗
PubMed1985

Fluorescence resonance energy transfer study of the associative state of membrane-bound complexes of complement proteins C5b-8.

Human complement protein C8 was labeled with the fluorescent chromophores fluorescein-5-isothiocyanate (FITC), 3-(4-isothiocyanatophenyl)-7-diethylamine-4-methyl coumarin (IPM), eosin-5-isothiocyanate (EOS), or Texas Red (sulforhodamine-101-sulfonyl chloride; TR) with only minor reduction in the specific hemolytic activity of the protein. The distribution of C5b-8 complexes bound to sheep erythrocyte membranes was investigated by monitoring fluorescence resonance energy transfer (RET) between the following RET donor/acceptor pairs of labeled C8: FITC-C8/EOS-C8, IPM-C8/EOS-C8, and FITC-C8/TR-C8. On binding to membranes containing pre-formed C5b67 complexes, specific RET was detected for each of the donor/acceptor pairs of labeled C8 investigated. In contrast, no energy transfer was observed for these RET donor/acceptor pairs of labeled C8 incubated in the presence of control membranes or in membrane-free solution. On the basis of a consideration of the transfer efficiency that would be expected for donor/acceptor pairs of labeled C8 that were uniformly dispersed on the membrane surface, these results suggest that C5b-8 complexes are aggregated into polymeric clusters when membrane-bound. The efficiency of donor-C8 to acceptor-C8 RET--and the hemolytic activity of membrane-bound C5b-8 (in the absence of C9)--are both related to the surface density of membrane-bound C5b67, suggesting that the physical clustering of the membrane-inserted C5b-8 complex may be related to the expression of its cytolytic activity.

Cell Membrane Permeability↗
PubMed1995

A rapid method for the isolation of analogues of human CD59 by preparative SDS-PAGE: application to pig CD59.

A method for the rapid isolation of functionally active analogues of human CD59 from erythrocytes (E) is described. The method, here applied to pig E, is based on the fractionation of a butanol extract of E ghosts by preparative SDS-PAGE followed by gel filtration on Superose 12. Purification was monitored using a functional complement inhibition assay. SDS-PAGE analysis of the product of this procedure indicated a single protein band with apparent M(r) of 20 kDa under reducing and non-reducing conditions. The preparation could be incorporated into guinea pig E to inhibit both CVF-reactive lysis and lysis through C8 and C9 using preformed C5b-7 sites, demonstrating that it contained a CD59-like activity. PIPLC treatment of the isolated protein abolished the inhibition. In contrast to SDS-PAGE analysis, amino-terminal sequence analysis of the preparation showed that it comprised two components. One was identified from databank searches as a fragment of pig glycophorin. These two components could not be separated by either standard or affinity chromatographic techniques. The second component was novel and had high sequence homology with human CD59, identifying it as the pig analogue. Further functional studies showed that the pig analogue of human CD59 was effective in the protection of guinea pig E against lysis by serum from a variety of species, including human.

Amino Acid Sequence↗
PubMed1983

Surface-dependent modulation by H of C5 cleavage by the cell-bound alternative pathway C5 convertase of human complement.

Regulation by H of formation of the C3 and C5 alternative pathway convertases of complement on cells is dependent on such chemical characteristics of the cell surfaces as their membrane content in sialic acid. Properdin-stabilized C5 convertase sites were assembled on the non-activating cells of the alternative pathway, sheep erythrocytes (Es), and on the activating cells, desialated Es and rabbit erythrocytes (Er). C5 hemolytic sites were revealed by incubation of the convertase-bearing cells with limiting C5 and excess C6-C9. H inhibited generation of C5 hemolytic sites in a dose-related fashion on Es, Er, and desialated Es at molar ratios of H/C5 of 0.03 to 0.5. H similarly inhibited C5 utilization by the cell-bound C5 convertase on Es and desialated Es regardless of the cell membrane sialic acid content; however, H was three to five times less effective on Er. Kinetic experiments also suggested that C5 hemolytic sites are generated more rapidly on Er than on Es and desialated Es. The inhibition effect of H was independent of the number of C5 convertase sites per cell on all cell types; two to three times more residual hemolytic sites were found on convertase-bearing Es that had been incubated with C5 and H as compared with cells that had been decayed by H before incubation with C5. Furthermore, H also inhibited C5 interaction with a preformed classical pathway C5 convertase. These results suggest that H interacts with C5 so as to alter C5 binding and/or cleavage by the cell-bound C5 alternative pathway convertase. Sialic acid-independent modulation by H of C5 cleavage by the C5 convertase represents an additional regulatory step in the activation of the human alternative complement pathway.

Animals↗
PubMed1991

Alternative complement pathway-mediated myeloid cell cytotoxicity: repertoire of membrane factors participating in regulation of C3 deposition and cytolysis.

Most human nucleated cells and cell lines possess C3 step regulators, decay-accelerating factor (DAF; CD55) and membrane cofactor protein (MCP; CD46) and an inhibitor of membrane attack complex (MAC) formation (p18; CD59). Unless DAF and MCP were simultaneously blocked by their antibodies, Mg(2+)-EGTA-human serum treatment did not induce C3 deposition on most nucleated cells. Furthermore, less than 20% lysis occurred even after the block of all the three factors. In contrast, three myeloid cell lines, U-937, HL-60 and p39, were found to exhibit unusual C3 deposition or cytolysis. U-937 possessed DAF and MCP but lacked p18, and about 50% was lysed by treatment with anti-DAF and anti-MCP followed by Mg(2+)-EGTA-serum, which caused C3, C5 and C8 deposition. Anti-DAF evoked similar but less complement (C) deposition and cytolysis while anti-MCP alone did not, although it enhanced the anti-DAF-mediated C deposition and cytolysis. Thus, once the C3 step is overcome, U-937 is attacked by the late components leading to cytolysis because of the absence of p18. On the other hand, HL60 allowed the deposition of C3 by blocking of either DAF or MCP followed by the Mg(2+)-EGTA-serum treatment. C5, C8 and C9 were subsequently deposited but resulted in no lysis. Lysis of 60% was attained by the additional blocking of p18. Thus, HL60 is poorly protected by C3 and C9 step regulation. Strikingly, extensive C3 deposition occurs on p39 without any antibody treatment, suggestive of the presence of unique alternative pathway activators. However, little cytolysis was induced on p39 even by blocking of all three inhibitors with antibodies. These results suggest that in activation of the alternative pathway on myeloid cells, C3 step is controlled by the inhibitors and alternative pathway activators, and C-mediated cytolysis is blocked by p18 and additional regulatory mechanisms or factors which assist in protection of nucleated host cells from MAC attack. Susceptibility to homologous C of these cell lines, therefore, reflects relatively low potency of C regulation on their membrane.

Antigens, CD↗
PubMed1989

Arachidonic acid mobilization and phosphoinositide turnover by the terminal complement complex, C5b-9, in rat oligodendrocyte x C6 glioma cell hybrids.

Previously, we have shown that rat oligodendrocytes release phospholipid and generate arachidonic acid (AA) and leukotriene B4 in response to sublytic C5b-9 formation. In the present study, we investigated the biochemical pathways by which C5b-9 generates AA from clone ROC-1, a fusion product of rat oligodendrocytes and C6 glioma. Cells were incubated for 24 h in the presence of [3H]AA or [3H]myoinositol. They were then sensitized with antibody against hybrid cell stroma and treated for 1 h with C9-depleted human serum (C9D-HS) or C9D-HS reconstituted with C9. Alternatively, cells were treated with C8,C9D-HS or C8,C9D-HS reconstituted with C8 or C8 plus C9 for 1 h. Qualitative and quantitative analysis of the released [3H]AA and [3H]myoinositol radiolabeled products were performed by thin layer chromatography/autoradiography and anion exchange chromatography, respectively. The major [3H]AA radiolabeled products after C5b-9 stimulation comigrated with intact phospholipid and AA standards, and the major [3H]myoinositol radiolabeled product was inositol-1-phosphate. Treatment of cells with phospholipase A2 inhibitors, mepacrine and bromophenacyl bromide, abolished AA release by C5b-9. In the absence of extracellular Ca2+, C5b-9 also failed to induce the release of AA. Interestingly, 1-(5-isoquinolinsulfonyl)-2-methylpiperazine (H-7), a potent inhibitor of protein kinases, inhibited AA release by C5b-9, whereas AA release stimulated by the calcium ionophore A23187 was not blocked by H-7. The results suggest that AA generation by C5b-9 from the ROC-1 clone involves activation of Ca2+-dependent phospholipase A2 which is regulated by protein kinase-dependent mechanisms.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMedDate not supplied

Enhanced generation of O2- by human neutrophils via a complement iC3b/Mac-1 interaction.

There is evidence for a tumor necrosis factor alpha (TNF alpha)-initiated and CD11b/CD18-dependent burst of superoxide anion (O2-) and hydrogen peroxide production by human polymorphonuclear leukocytes which are adherent to surfaces bearing a variety of proteins. In the current studies neutrophils were stimulated with opsonized (by fresh human serum) zymosan particles in the presence of cytochalasin B, to prevent internalization of particles and to simulate the interaction of neutrophils with protein-bearing surfaces. Under these conditions, the cells demonstrated 2.9-fold greater production of O2- when compared to nonopsonized zymosan particles. Heat inactivation or cobra venom factor treatment of human serum prior to opsonization resulted in 98% and 66% reductions, respectively, in O2- responses. C3 and factor B were required for this response, since sera deficient in either component caused 56 and 68% reductions, respectively, in O2- production. Sera deficient in Clq, C2, C4, C5, C6, C7 or C9 showed no defect in their ability to enhance O2- responses to zymosan particles. Monoclonal antibody to iC3b, but not monoclonal antibodies to C3c or C3d, caused a 29% reduction (p < 0.01) in O2- generation. Antibodies to CD18 (R15.7) or CD11b (CL44 and 60.1) reduced the incremental production of O2- by 76, 71 and 77%, respectively. Two antibodies directed against CD11a as well as the isotype-matched control (MOPC 21) were without effects. These data suggest that, in this model of neutrophil activation, the pathway for O2- generation is a Mac-1 (but not LFA-1)-dependent pathway and also requires iC3b. These findings may be relevant to complement-mediated, neutrophil-dependent vascular injury in vivo.

Complement C3b↗
PubMed1994

Antibody-mediated complement activation on nucleated cells. A quantitative analysis of the individual reaction steps.

The sequential molecular events of the initiation, amplification, and membrane attack phases of classical C pathway activation on nucleated cells were investigated. As a model system, C-susceptible human melanoma cells (SK-MEL-93-2) expressing the disialoganglioside Ag GD3 were studied. Activation of the classical C pathway was initiated by the anti-GD3 mAb R24 (murine IgG3). The initiation phase is characterized by a very inefficient molar ratio of deposited C1q per Ab molecule. At an Ab density of 5.86 x 10(6) molecules/cell, only 3% of cell-bound R24 molecules form suitable pairs for C1q binding. During the amplification phase maximally 2.44 x 10(6) molecules of C4 and 0.67 x 10(6) molecules of C2/cell are being bound to form the C3 convertase. Despite the rather inefficient binding of C2, the C3 convertase is highly active in depositing high numbers of C3b molecules on the cell surface. Maximum binding of C3b occurred within 5 min of incubation with a total number of 2.1 x 10(7) molecules/cell. This indicates amplification factors at the level of C4 and C3 of 28 (C4/C1q) and 241 (C3/C1q), respectively. C3b was found to be rapidly cleaved into iC3b. As a result of this rapid C3b degradation, the membrane attack phase is initiated with a relatively inefficient C5 activation. The maximal number of 9.5 x 10(5) molecules C5b/cell corresponds to a molar ratio of C5:C3 of only 1:22. The deposition of C5b led to the subsequent maximum binding of the following numbers of molecules of terminal C components per cell: C6, 0.8 x 10(6); C7, 0.89 x 10(6); C8, 0.82 x 10(6); C9, 1.8 x 10(6). These numbers correspond to average molar ratios (calculated per C5b molecule) of C5b/C6/C7/C8/C9 of 1/0.85/0.94/0.86/1.88. In addition to the monomeric C9, dimeric and polymeric (12- to 16-mer) forms of the molecule could be demonstrated. Collectively, our data represent a first comprehensive quantitative analysis of classical pathway activation on a nucleated cell.

Antibodies, Monoclonal↗
PubMed1995

Complement expression in human brain. Biosynthesis of terminal pathway components and regulators in human glial cells and cell lines.

C biosynthesis at extrahepatic sites remote from plasma C may be important in the protection of tissues against inflammation and infection but may also contribute to tissue injury. This latter possibility is particularly relevant in the central nervous system (CNS), where several cell types are susceptible to damage by C. We have previously shown that human astrocyte-derived tumor cell lines synthesize and secrete all of the components of the activation pathways of C. In this study, we demonstrate that these cells also produce the components (C6, C7, C8, and C9) and regulators (S-protein and clusterin) of the lytic terminal C pathway. The terminal components produced are hemolytically active, and secretion is markedly up-regulated by the inflammatory cytokine IFN-gamma. Primary human fetal astrocytes also expressed C6, C7, S-protein, and clusterin. The human monocyte/macrophage cell line, used here as a model for microglia, also produced all terminal components and regulators when appropriately stimulated. These studies raise the prospect of the intrathecal synthesis of a complete, functional C system and its regulators in the inflamed CNS. Intrathecal C synthesis may be important in the resolution of infection and inflammation but, given the C susceptibility of some CNS cell types, may also exacerbate damage in demyelination and neurodegeneration.

Antibodies, Monoclonal↗