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PubMed1992

The human lymphokine leukoregulin induces cell resistance to complement-mediated lysis.

Leukoregulin (LR) is a lymphokine secreted by human natural killer (NK) cells. Its effect on the susceptibility of K562 human erythroleukemic cells to lysis by antibody and complement was examined. As reported here, treatment of K562 cells with LR for 60 min at 37 degrees C confers on them resistance to complement damage. The LR-induced state of complement resistance is transient and the cells recover within 4-6 h unless a second dose of LR is added. The protective action of LR was observed using both conventional 51Cr-release and trypan blue inclusion assays. The protein synthesis inhibitors puromycin and cycloheximide and the protein kinase inhibitors tamoxifen, polymyxin B and W-7, could each block this action of LR. Fewer membrane attack complexes were found, following complement activation, on LR-treated than control cells. These results suggest that LR increases the capacity of K562 cells to down-regulate complement activation or repair the complement damage, possibly by inducing synthesis of defense proteins and/or activation of protective protein kinases.

Antibodies, Neoplasm↗
PubMed2002

The possible role of complement activation in Alzheimer disease.

Molecular pathological studies of Alzheimer disease (AD) brain have revealed the presence of a spectrum of inflammatory mediators. Epidemiological studies have indicated that the use of anti-inflammatory agents, especially non-steroidal anti-inflammatory drugs (NSAIDs), results in a substantially reduced risk of contracting the disease. It is possible that well targeted anti-inflammatory agents will also be useful in treating established AD. Inhibitors of cyclooxygenase-2 have been unsuccessful in this regard, and traditional NSAIDs have produced mixed results. The complement system, which is strongly activated in AD brain, is an attractive target for therapeutic intervention, particularly through inhibition of the autodestructive action of the membrane attack complex. The complement system works in conjunction with activated microglia, which express high levels of complement receptors. Overactive microglia secrete many toxic materials. Inhibition of microglial activation is another potential therapeutic target.

Alzheimer Disease↗
PubMed2005

Emission of membrane vesicles: roles in complement resistance, immunity and cancer.

Complement-mediated cell death is caused by C5b-9, the membrane attack complex (MAC) composed of the five complement proteins C5b, C6, C7, C8, and C9. Assembly of the C5b-9 complex initiates oligomerization of C9 and production of a transmembrane protein channel that inflicts damage to target cells. For protection, cells eliminate the MAC from their surface either by ectocytosis (direct emission of membrane vesicles) or by endocytosis (internalization). The process of ectosome release is rapid and involves cytosolic Ca(2+) and activation of protein kinases, such as protein kinase C (PKC) and extracellular signal-regulated protein kinase (ERK). Recently, the involvement of mortalin (also known as GRP75 and mitochondrial hsp70) in MAC elimination has been suggested. Extracellular application of antibodies directed to mortalin increases cell sensitivity to MAC-mediated lysis. Release of membrane vesicles is ubiquitous and enhanced in apoptotic or tumor cells and upon cell activation. Composition of the ectosomes (also often referred to as microparticles) membrane proteins and lipids appears to be different from those of the original plasma membrane, indicating involvement of a selective sorting process during ectosome formation. Exosomes (unlike ectosomes) are membrane vesicles generated by endocytosis, endosome sorting into perinuclear multivesicular bodies (MVB) and exocytosis of MVBs. Exosomes appear to be different in size and composition from ectosomes. Exosome-associated MAC has also been described. Although research on ectosomes and exosomes is still limited, physiological roles in coagulation, vascular functions, angiogenesis, wound healing and development have been attributed to these shed membrane vesicles. On the other hand, there are indications that elevated levels of ectosomes and exosomes may predispose to morbidity. Membrane vesicles released by cells exposed to complement MAC may play roles in health and disease beyond protection from cell death.

Animals↗
PubMedDate not supplied

Molecular and cellular characterization of the membrane attack complex, C5b-9, in Alzheimer's disease.

The membrane attack complex, C5b-9, is of considerable importance in many inflammatory reactions. It is the terminal, cytolytic component of both classical and alternative pathway activation, and its presence presupposes other potentially destructive complement constituents, including anaphylotoxins and opsonins. We have characterized C5b-9 and its C9 constituent in the Alzheimer's disease (AD) and nondemented elderly (ND) brain using immunohistochemistry at the light and electron microscopic levels, Western blot analysis, and the reverse transcriptase polymerase chain reaction. We have also conducted in vitro ELISA assays of amyloid beta-peptide-stimulated SC5b-9 production. C5b-9 is abundantly present in Alzheimer's disease cortex, associated with neurofibrillary tangle containing neurons, dystrophic neurites within neuritic plaques, and neuropil threads, but is weakly detected, if at all, in nondemented elderly cortex under the same conditions. Staining of Alzheimer's disease sections is abolished both by deletion of primary antibody or preabsorption with purified SC5b-9.

Alzheimer Disease↗
PubMed1998

X-linked vacuolated myopathy: membrane attack complex deposition on the surface membrane of injured muscle fibers is not accompanied by S-protein.

We have studied the expression of S-protein on the muscle from patients with X-linked vacuolated myopathy [characterized by the deposition of the complement C5b-9 membrane attack complex (MAC) over abnormal muscle fibers] and controls by immunocytochemistry and immunoblotting. No expression was detected on muscle from controls and patients with X-linked vacuolated myopathy. These findings suggest that S-protein does not render the MAC inactive in X-linked vacuolated myopathy. This situation may be due to the fact that the pathways of MAC activation and the expression of S-protein in X-linked vacuolated myopathy are different from the ones observed in ischemic and/or necrotic, or immune diseases. These results emphasize the role of the membrane complement regulatory proteins (i.e., CD59) in X-linked vacuolated myopathy.

Adult↗
PubMed1988

The heparin binding domain of S-protein/vitronectin binds to complement components C7, C8, and C9 and perforin from cytolytic T-cells and inhibits their lytic activities.

S-Protein/vitronectin is a serum glycoprotein that inhibits the lytic activity of the membrane attack complex of complement, i.e., of the complex including the proteins C5b, C6, C7, C8, and C9n. We show that intact S-protein/vitronectin or its cyanogen bromide generated fragments also inhibit the hemolysis mediated by perforin from cytotoxic T-cells at 45 and 11 microM, respectively. The glycosaminoglycan binding site of S-protein/vitronectin is responsible for the inhibition, since a synthetic peptide corresponding to a part of this highly basic domain (amino acid residues 348-360) inhibits complement- as well as perforin-mediated cytolysis. In the case of C9, the synthetic peptide binds to the acidic residues occurring in its N-terminal cysteine-rich domain (residues 101-111). Antibodies raised against this particular segment react 25-fold better with the polymerized form of C9 as compared with its monomeric form, indicating that this site becomes exposed only upon the hydrophilic-amphiphilic transition of C9. Since the cysteine-rich domain of C9 has been shown to be highly conserved in C6, C7, and C8 as well as in perforin, the inhibition of the lytic activities of these molecules by S-protein/vitronectin or by peptides corresponding to its heparin binding site may be explained by a similar mechanism.

Animals↗
PubMed1993

Structure of complement poly-C9 determined in projection by cryo-electron microscopy and single particle analysis.

The ring-like complement 'lesions' found on membranes of complement lysed cells comprise a complex of components C5b through C9 that coalesce to form hollow cylinders which penetrate the membrane bilayer and create lytic pores. Walls of these C5b-9 membrane attack complex cylinders may consist primarily of the C9 component, since samples of purified, isolated C9 can polymerize into cylindrical structures which appear identical with the fully assembled C5b-9 complex. The structure of these poly-C9 molecules has been investigated using the techniques of cryo-electron microscopy and single particle analysis. Sets of single poly-C9 particles viewed as rings were selected from cryo-EM images, then particles were aligned and treated by correspondence analysis to identify the principle interparticle similarities and variations. The highest ranking variation found was the presence or absence of a dense inner ring of protein density. Other important variations were interpreted as different types of particle tilt. These results were used in selecting a subgroup of untilted particles for averaging and symmetry analysis. The rotational power spectrum of the initial average suggested 13-fold symmetry. The 13-fold symmetry was used to select and group particles for further analysis. Individual particles were 13-fold rotational averaged and those with enhanced peripheral features were placed into either a right-handed subgroup or into a left-handed subgroup based on orientation of the peripheral features. Particles within each group were aligned and averaged, and a poly-C9 structure was produced which shows important structural details and from which the C9 monomer structure can be deduced. The poly-C9 structure contains a dense inner ring of diameter between 113-181 A and which is modulated into 13 discrete peaks with peak-to-peak separation of approx. 35 A. The dense inner ring is surrounded by a less dense, concentric outer rim extending to 254 A diameter. The outer rim contains projections that are contiguous with the inner peaks but are skewed relative to the ring radius to produce the appearance of a pin-wheel. These projections correspond with the peripheral features picked up in the rotationally averaged individual particles; the left- or right-handed orientation of projections may result from the up/down orientation of individual particles in ice. The C9 monomer structure within the cylinder is suggested by the density distribution. The monomer would be a rod with diameter of 35 A, oriented parallel to the cylinder axis and would be roughly perpendicular to a membrane.(ABSTRACT TRUNCATED AT 400 WORDS)

Complement C9↗
PubMed2000

The terminal complement complex C5b-9 stimulates interleukin-6 production in human smooth muscle cells through activation of transcription factors NF-kappa B and AP-1.

Activation of the complement system plays an important role in the pathogenesis of atherosclerosis. The proinflammatory cytokine interleukin (IL)-6 is potentially involved in the progression of the disease. We therefore investigated whether the terminal complement complex C5b-9 affects IL-6 production from vascular smooth-muscle cells (VSMC) and set out to determine the underlying signal transduction pathway. Stimulation of human VSMC with C5b-9 resulted in an increase of IL-6 transcript and production of IL-6 protein. Pretreatment with pertussis toxin or pyrrolidine dithiocarbamate inhibited complement-dependent IL-6 mRNA expression and IL-6 release, suggesting the involvement of Gi-proteins and nuclear factor-kB (NF-kB). C5b-9 also induced formation of reactive oxygen species, which, along with IL-6 release, was inhibited by the antioxidant N-acetylcysteine. C5b-9 activated the redox-sensitive transcription factors NF-kB and activator protein-1 (AP-1), which were both involved in the induction of IL-6 by C5b-9, as demonstrated by cis element double-stranded (decoy) oligonucleotides (ODN). The results demonstrate that activation of the complement system induces IL-6 release from human VSMC by a Gi-dependent pathway involving the generation of oxidative stressand the activation of the redox sensitive transcription factors NF-kB and AP-1. Our data support a new mechanism for the proatherogenic effect of the terminal complement complex.

Acetylcysteine↗
PubMed1994

Immunohistochemical studies of vitronectin, C5b-9, and vitronectin receptor in membranous nephropathy.

To investigate the involvement of vitronectin, the terminal complement complex (C5b-9), and the vitronectin receptor in the pathogenesis of membranous nephropathy, the immunohistochemical localization of these antigens in the kidney was determined using the immunoperoxidase method and monoclonal antibodies: antivitronectin, anti-SC5b-9 (neoantigen), and antivitronectin receptor (specific for alpha v beta 3 and alpha v). The subjects were 6 patients with membranous nephropathy, and the controls were 2 patients with minimal-change nephrotic syndrome. In membranous nephropathy, vitronectin was localized in subepithelial deposits and in epithelial cell foot processes and was intensely positive in the foot processes adjacent to subepithelial deposits. C5b-9 showed a similar pattern of localization to vitronectin. Both alpha v beta 3 and alpha v were localized in the basal portions of the foot processes of visceral epithelial cells as well as along the borders of these cells adjacent to the urinary space. Deposition at the former site was heavier than at the latter, and localization was especially prominent adjacent to the subepithelial deposits. In addition, alpha v was localized around and within some of the electron-lucent subepithelial deposits in the basement membrane. In contrast, the deposition of vitronectin, C5b-9, alpha v beta 3, and alpha v was always less intense in minimal-change nephrotic syndrome than in membranous nephropathy. Vitronectin and C5b-9 were localized to small parts of mesangium and glomerular basement membrane, while alpha v beta 3 and alpha v deposits showed no difference in intensity between the basal portions of the foot processes and the urinary border of the visceral epithelial cells. Thus, membranous nephropathy featured increased localization of vitronectin, C5b-9, and vitronectin receptors both within and around the subepithelial deposits, suggesting that the mechanism of immune complex disposal via the vitronectin receptor and the vitronectin-C5b-9 complex, associated with complement activation due to subepithelial immune complex formation, may also be active.

Adult↗
PubMed1997

Evidence for increased synthesis of complement C4 in the renal epithelium of rats with passive Heymann nephritis.

Passive Heymann nephritis (PHN) is a complement-dependent model of immune complex glomerulonephritis. This study investigated the contribution of local complement synthesis by studying gene expression of the classical pathway component C4 in relation to the site of the tissue injury and the development of proteinuria induced by the pathogenic antibody (sheep anti-GP330). This study, using in situ hybridization, found that C4 mRNA expression was increased in the glomerular epithelium and the proximal renal tubular epithelium in a distribution similar to that of the targeted GP330 antigen. The total cortical C4 mRNA expression assessed by semiquantitative polymerase chain reaction (PCR) increased in a time-dependent manner (P < 0.05), coincident with the onset and progression of proteinuria, and peaking 11 to 14 days after the induction of the disease. These data suggest a link, in place and time, between local complement gene expression and glomerular barrier dysfunction induced by anti-GP330. It is postulated that increased epithelial synthesis of C4 stimulated by the engagement of GP330 enhances the formation of the membrane attack complex of complement through its classical pathway, and, hence, the formation of complement-mediated injury.

Animals↗
PubMed1998

High-dose intravenous immunoglobulin treatment activates complement in vivo.

Several complement modulating effects of high-dose intravenous immunoglobulins (IVIG) have been proposed from in vitro studies and experimental animal models. However, the in vivo effects of IVIG on plasma complement in humans are yet not known. We have investigated the in vivo effects of IVIG on complement in seven women with unexplained recurrent spontaneous abortion who were without evidence of autoimmune disease. Samples were obtained before and after the very first infusion of IVIG. There was a marked increase in immunoglobulin G (IgG) from (median and range) 12.4 (9.4-15.9) to 26.8 (22.4-30.0) g/l but no change in immunoglobulin A (IgA) or immunoglobulin M (IgM). A significantly increased complement activation was demonstrated using neoepitope-specific enzyme immunoassays to the activation products C3bc (median increased from 9.8 to 31.2 AU/ml), Bb (0.66-1.66 g/ml), C5a (10.5-12.7 ng/ml), and TCC (0.81-2.19 AU/ml) (P = 0.015 for all). There were no changes in antigenic concentrations of individual complement components or regulators (C1q, C4, C3, C1-inhibitor, C4b-binding protein) and no decrease in complement haemolytic activity (classical and alternative CH50), which were all within the normal range. The classical pathway activation products C1rs/C1-inhibitor complexes, C4bc and C4d were elevated in all patients before IVIG treatment and did not change significantly during treatment. In conclusion, IVIG induced a significant activation of complement in vivo.

Abortion, Habitual↗
PubMed2000

Sublytic complement attack reduces infarct size in rabbit isolated hearts: evidence for C5a-mediated cardioprotection.

Sublytic complement attack can elicit protective cellular responses without precipitating cell death. Our investigation examined the effects of non-lethal complement activation in isolated hearts. New Zealand white rabbit hearts were subjected to 30 min of ischemia followed by 1 h of reperfusion. Prior to ischemia, hearts were perfused for 20 min with 0.5% normal human plasma (NHP). Hearts treated with NHP developed significantly (p<0.05) smaller infarcts compared with controls, expressed as percent of area at risk (AAR) (25.3+/-4.0% vs. 40.9+/-4.3%, respectively). Heat-inactivation, soluble complement receptor 1 (sCR1; 20 nM), and anti-C5a antibody reversed the protective effect of NHP (39.0+/-3.1%, 41.7+/-5.1% and 38.4+/-2.3% AAR, respectively). Hearts treated with 3 nM C5a exhibited infarct sizes similar to those exposed to NHP (27.6+/-5.0% AAR). sCR1 alone did not affect infarct size (37.9+/-4.5% AAR). The results suggest that non-lethal complement activation attenuates reperfusion injury through formation of C5a.

Animals↗
PubMed1995

Complement inhibitory therapeutics and xenotransplantation.

Once complement-mediated HAR has been inhibited, the full spectrum of cellular and antibody-mediated inflammatory and immune responses characteristic of acute and chronic rejection will need to be counter-manded. But the fact remains that if xenotransplantation is to become a clinical reality, a clinically relevant means of inhibiting complement activation will be required. Soluble complement receptor type 1 provides such a therapeutic option and an option where the dosing regimen is under the control of the physician and can be adjusted in response to the needs of the patient.

Animals↗
PubMed1992

Interaction of complement and clusterin in renal injury.

Clusterin is a heterodimeric glycoprotein that has been associated with such diverse biologic functions as reproduction, cell regression, cell aggregation, and regulation of the cytolytic activity of the membrane attack complex of complement. Clusterin is a component of glomerular immune deposits in the kidney, and increased clusterin expression occurs in a number of renal injury states. To further explore the interaction between clusterin and complement, the requirement for an intact complement system for renal clusterin induction in an acute (folic acid nephropathy) and a chronic (subtotal renal ablation) model of renal injury was examined. After it was first demonstrated that folic acid increased renal clusterin mRNA in the rat, a species in which renal clusterin was highly inducible by other stimuli, the effects of folic acid (250 mg/kg ip) on clusterin mRNA and immunoreactivity were examined in mice sufficient and deficient for the fifth component of complement. Similar increases in clusterin mRNA and immunoreactivity were seen in both the C5-sufficient and C5-deficient mice compared with their respective vehicle-injected control groups. Renal clusterin mRNA was also increased to a similar extent in the remaining kidney of both C5-sufficient and C5-deficient mice 10 days after subtotal nephrectomy. In conclusion, the induction of clusterin after folic acid administration or subtotal nephrectomy was independent of the presence of an intact complement system, because similar increases in clusterin expression were observed in C5-sufficient and C5-deficient mice.

Acute Disease↗
PubMed2001

Immunization against tumor cell surface complement-regulatory proteins.

Complement is an enzymatic cascade that results in the release of pro-inflammatory anaphylatoxins, C3b deposition and the assembly of the membrane attack complex (MAC), which results in cell lysis. Cells express complement regulatory proteins or inhibitors to protect themselves from bystander attack by complement. Expression of the complement-regulatory proteins CD55, CD46 and CD59 are deregulated in cancer with tumors showing loss of one or more inhibitors and strong overexpression of others. This results in tumors that are resistant to attack by complement and is a major limitation in the use of monoclonal antibodies as monotherapies. However, tumor sensitivity to complement can be restored by co-administration of antibodies that bind to the functional domains of complement-regulatory proteins. Overexpression of complement-regulatory proteins on tumors also makes them potential targets for cancer vaccines. However, these vaccines have to be carefully designed to induce immune responses that recognize inhibitors overexpressed on tumors and that do not detect the levels expressed by normal cells. A human anti-idiotypic antibody that mimics CD55 has been used successfully in over 200 colorectal cancer and osteosarcoma patients. 70% Of patients show CD55-specific immune responses with no associated toxicity. Similar vaccines targeting CD46 and CD59 would eliminate any cell overexpressing a complement inhibitor. Any remaining tumor cell or any tumor cell that loses complement-regulatory proteins in response to therapy would become highly susceptible to in situ complement deposition. In summary, targeting complement-regulatory proteins is a very attractive approach to tumor therapy, although great care must be taken in preventing normal tissue recognition as this could lead to uncontrolled complement deposition and massive cell lysis.

Animals↗
PubMed1997

Role of T cells in the mediation of Heymann nephritis. ii. Identification of Th1 and cytotoxic cells in glomeruli.

The role of immunoglobulin (Ig) and complement as mediators of Heymann nephritis (HN) has been questioned by recent studies showing that HN can be induced in a C6-deficient rat that cannot assemble the membrane attack complex of complement. Also, the severity of HN can be reduced by therapy directed at CD8+ T cells, which has no effect on antibody (Ab) production or immune deposits. To identify whether T cells may contribute to the glomerular injury of active HN in Lewis rats, the mononuclear infiltrate and cytokine mRNA in glomeruli and kidney interstitium were examined. Groups of Lewis rats immunized with Fx1A in CFA developed HN, and were compared to controls that received CFA only. Proteinuria, the marker of glomerular filtration barrier dysfunction, was absent at four weeks but present at eight weeks in HN. Serum anti-Fx1A Ab and glomerular Ig were present in HN at both time points. Immunoperoxidase staining with monoclonal Abs identified, at eight weeks, a glomerular infiltrate of CD4+ and CD8+ T cells, and macrophages, but not NK cells. Semiquantitative RT-PCR of isolated glomeruli at eight weeks demonstrated expression of cytokine mRNA for Th1 CD4+ cells (IFN-gamma and TNF-beta/LT, but not IL-2), cytotoxic CD8+ T cells (granzyme A and perforin), and macrophages (TNF-alpha and IL-10), but not Th2 CD4+ cells (no increase in IL-4, IL-5 and IL-6). At eight weeks, the cellular infiltrate and pattern of cellular activation in glomeruli was different to that in renal cortex. In the cortical infiltrate CD8+ cells were a lesser component, and NK cells were increased, as were CD4+ cells and macrophages. RT-PCR identified increased cytokine mRNA for macrophages, Th1 and Th2 cells, but not cytotoxic effector T cells. At four weeks, T cells including CD4+ and CD8+ cells were identified in the isolated glomeruli of rats with HN, but there was no increase in cytokine mRNA expression. There was no infiltrate or increase in cytokine mRNA detected in renal cortex at four weeks. Anti-Fx1A Ab's and glomerular deposition of Ig develop many weeks before the onset of proteinuria, when there is only a small cellular infiltrate present. The progressive development of infiltrates of activated T cells, principally Th1 and cytotoxic effector cells, and macrophages, within glomeruli is coincident with the development of proteinuria. These findings raise the possibility that these cells contribute to the mediation of the glomerular injury and proteinuria of HN.

Animals↗
PubMed1988

Induction of expression of cell-surface homologous restriction factor upon anti-CD3 stimulation of human peripheral lymphocytes.

Homologous restriction factor (HRF) is a 65-kDa membrane protein that inhibits transmembrane channel formation by the membrane-attack complex of complement and by the complement component C9-related cytolytic lymphocyte protein. Stimulation of resting peripheral human lymphocytes with the anti-CD3 monoclonal antibody OKT3 has been shown to induce cytotoxicity in the CD8+ subpopulation. As demonstrated here, OKT3 stimulation also induces expression of cell-surface HRF by CD4+ and CD8+ T lymphocytes. The small proportion of Leu 19+ natural killer lymphocytes present in peripheral blood mononuclear cells was found to express HRF prior to stimulation. Whereas unstimulated peripheral blood mononuclear cells were susceptible to lysis by the membrane-attack complex or by the C9-related protein, OKT3-stimulated peripheral blood mononuclear cells were relatively resistant to both the membrane-attack complex and C9-related protein. This acquired resistance was abrogated by blocking surface HRF with F(ab')2 anti-HRF, suggesting that resistance was due to lymphocyte-membrane HRF. By using solid-phase anti-HRF, a 65-kDa protein was isolated from the activated peripheral blood mononuclear cells and shown to be capable of conferring upon sheep erythrocytes the characteristic activity of human HRF.

Antibodies, Monoclonal↗