SEARCH · Search PubMed

Results for “Complement C5a”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

SourceResearch connectionFrom yearThrough year

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 1,693 records · Page 94Linked to original sources

PubMed1986

[A new case of bronchospasm under extracorporeal circulation].

A case of bronchospasm occurring after the termination of cardiopulmonary bypass is reported. The complement fractions C3a, C4a and C5a were measured before and right after CPB. Complement activation is not specific to CPB but may occur in any thoracotomy. The statistically significant increase in complement C3a without any pulmonary symptomatology has been reported by several authors. Complement activation cannot therefore be considered as the explanation of this bronchospasm.

Bronchial Spasm↗

PubMed2004

Complement C3 and C5 play critical roles in traumatic brain cryoinjury: blocking effects on neutrophil extravasation by C5a receptor antagonist.

The role of complement components in traumatic brain injury is poorly understood. Here we show that secondary damage after acute cryoinjury is significantly reduced in C3-/- or C5-/- mice or in mice treated with C5a receptor antagonist peptides. Injury sizes and neutrophil extravasation were compared. While neutrophil density increased following traumatic brain injury in wild type (C57BL/6) mice, C3-deficient mice demonstrated lower neutrophil extravasation and injury sizes in the brain. RNase protection assay indicated that C3 contributes to the induction of brain inflammatory mediators, MIF, RANTES (CCL5) and MCP-1 (CCL2). Intracranial C3 injection induced neutrophil extravasation in injured brains of C3-/- mice suggesting locally produced C3 is important in brain inflammation. We show that neutrophil extravasation is significantly reduced in both C5-/- mice and C5a receptor antagonist treated cryoinjured mice suggesting that one of the possible mechanisms of C3 effect on neutrophil extravasation is mediated via downstream complement activation products such as C5a. Our data indicates that complement inhibitors may ameliorate traumatic brain injury.

Animals↗

PubMed1987

Analysis of density changes and chemotactic receptors of leukocytes from chronic hemodialysis and peritoneal dialysis patients.

Analysis of standard Ficoll-Hypaque (density = 1.077 g/ml) separation profiles of peripheral white blood cells (WBC) from patients undergoing hemodialysis (HD) demonstrated that dialysis caused a marked decrease in the density of polymorphonuclear leukocytes (PMN) resulting in about 50% of these cells separating with the mononuclear cells. In vitro exposure of normal control peripheral blood to HD membranes as well as to the purified chemotactic factors C5a, C5ades-Arg, and formyl-Met-Leu-Phe (fMLP) also resulted in PMN density changes which altered the Ficoll-Hypaque separation profiles of WBC. Therefore, these results imply that C5a generation, resulting from complement activation by the HD membrane, induced the density changes in the PMN from HD patients. Further studies using flow cytometry and fluorescein-labeled chemotactic factors (C5a, formyl-Met-Leu-Phe-Lys [fMLPL] and casein) indicated that HD patients had a significant reduction in the ability of their PMN and monocytes to bind C5a. This contrasted with the findings of no significant difference in the percentage or fluorescence intensity of HD patients' PMN or monocytes binding casein or fMLPL. Functional studies to analyze chemotactic-factor-mediated responses indicated that there was a decreased ability of HD patients' PMN and monocytes to generate superoxide anion, produce H2O2 and release myeloperoxidase in response to both C5a and fMLP. Additional studies evaluated the binding of chemotactic factors to PMN and monocytes from normal blood following passage through a hemodialyzer and from patients undergoing HD. Analysis of receptor binding by control cells passed through the dialyzer showed that there was a progressive decrease in the percentage of C5a-receptor-positive PMN and monocytes but no change with casein or fMLPL. In contrast, peripheral PMN and monocytes from chronic renal failure patients on HD showed no difference in C5a, casein or fMLPL receptors during the course of HD as compared to the predialysis period. This appears to be attributable to a difference in the regulation of the C5a that is generated as a result of the dialysis-membrane-induced activation of the complement system. Although C5a has been shown to be continuously generated during the course of HD, these patients show no modulation of their C5a receptors during the course of HD or when their whole blood is exposed to dialysis membrane fibers. These findings suggest that there are mechanisms functioning in chronically dialyzed patients to protect them from the effects of excessive C5a generation during HD.(ABSTRACT TRUNCATED AT 400 WORDS)

Cell Separation↗

PubMed1995

Streptococcal cysteine proteinase releases biologically active fragments of streptococcal surface proteins.

Streptococcus pyogenes are important pathogenic bacteria which produce an extracellular cysteine proteinase contributing to their virulence and pathogenicity. S. pyogenes also express surface molecules, M proteins, that are major virulence determinants due to their antiphagocytic property. In the present work live S. pyogenes bacteria of the M1 serotype were incubated with purified cysteine proteinase. Several peptides were solubilized, and analysis of their protein-binding properties and amino acid sequences revealed two internal fibrinogen-binding fragments of M1 protein (17 and 21 kDa, respectively), and a 36-kDa IgG-binding NH2-terminal fragment of protein H, an IgGFc-binding surface molecule. M protein also plays a role in streptococcal adherence, and removal of this and other surface proteins could promote bacterial dissemination, whereas the generation of soluble complexes between immunoglobulins and immunoglobulin-binding streptococcal surface proteins could be an etiological factor in the development of glomerulonephritis and rheumatic fever. Thus, in these serious complications to S. pyogenes infections immune complexes are found in affected organs. The cysteine proteinase also solubilized a 116-kDa internal fragment of C5a peptidase, another streptococcal surface protein. Activation of the complement system generates C5a, a peptide stimulating leukocyte chemotaxis. C5a-mediated granulocyte migration was blocked by the 116-kDa fragment. This mechanism, by which phagocytes could be prevented from reaching the site of infection, may also contribute to the pathogenicity and virulence of S. pyogenes.

Adhesins, Bacterial↗

PubMed2002

The bacterial peptide N-formyl-Met-Leu-Phe inhibits killing of Staphylococcus epidermidis by human neutrophils in fibrin gels.

To study human neutrophil (polymorphonuclear leukocyte (PMN)) migration and killing of bacteria in an environment similar to that found in inflamed tissues in vivo, we have used fibrin gels. Fibrin gels (1500 microm thick) containing Staphylococcus epidermidis were formed in Boyden-type chemotaxis chambers. PMN migrated < 300 microm into these gels in 6 h and did not kill S. epidermidis when the gels contained heat-inactivated serum, C5-deficient serum, a streptococcal peptidase specific for a fragment of cleaved C5 (C5a), or anti-C5aR IgG. In contrast, in gels containing normal human serum, PMN migrated approximately 1000 microm into the gels in 4 h and into the full thickness of the gels in 6 h, and killed 90% of S. epidermidis in 6 h. fMLP reduced PMN migration into fibrin gels and allowed S. epidermidis to increase by approximately 300% in 4 h, whereas leukotriene B(4) stimulated PMN to migrate the full thickness of the gels and to kill 80% of S. epidermidis in 4 h. We conclude that both complement opsonization and C5a-stimulated chemotaxis are required for PMN bacterial killing in fibrin gels, and that fMLP inhibits PMN bactericidal activity in fibrin gels. The latter finding is surprising and suggests that in the presence of fibrin fMLP promotes bacterial virulence.

Adhesins, Bacterial↗

PubMed1989

Analysis of the interaction of human C5a and C5a des Arg with human monocytes and neutrophils: flow cytometric and chemotaxis studies.

C5a and C5a des Arg are potent complement-derived mediators that bind receptors on peripheral blood leukocytes and tissue-specific cellular elements to elicit and amplify inflammatory and immunomodulatory reactions. To study the interactions of C5a and C5a des Arg with these cells, fluorescein conjugates of these ligands were prepared by a new technique and their binding to monocytes, neutrophils, platelets, and endothelial cells was studied with flow cytometry. Fluoresceinated C5a produced neutrophil myeloperoxidase release and chemotaxis and also bound rabbit anti-C5a antibody much like native anaphylatoxin; likewise, fluoresceinated C5a des Arg demonstrated retention of biologic and antigenic activities. Both fluorescein-conjugated C5a and C5a des Arg bound to monocytes and neutrophils in a concentration-dependent, saturable, and homogeneous manner, but 10- to 15-fold higher concentrations of C5a des Arg were required to attain saturable binding of these leukocytes. Ligand binding was specifically inhibited by native purified human C5a in a concentration-dependent manner, while it was unaffected by C3a or N-formyl-methionyl-leucyl-phenylalanine-lysine. There was no evidence of a C5a receptor-negative subpopulation of monocytes or neutrophils. Moreover, comparative binding experiments with leukocytes from multiple normal volunteers showed that a greater percentage of monocytes than neutrophils bound C5a at less than saturable concentrations of ligand (P less than 0.05, 0.5 to 5.0 nM). A representative half-maximal binding of fluorescein-conjugated C5a (C5a des Arg) binding to monocytes and neutrophils was 1.2 nM (30 nM) and 2.6 nM (68 nM), respectively. In contrast, fluorescein-conjugated C5a did not specifically bind to human platelets or umbilical vein endothelial cells.

Blood Platelets↗

PubMed2005

Disulfide trapping to localize small-molecule agonists and antagonists for a G protein-coupled receptor.

A key question regarding the signaling mechanism for G protein-coupled receptors (GPCRs) is what triggers agonism versus antagonism. Peptide analogs derived from the chemokine, complement fragment 5 anaphylatoxin (C5a), can act as agonists or antagonists to the C5a receptor, a member of the GPCR family [Gerber, B. O., Meng, E. C., Dotsch, V., Baranski, T. J. & Bourne, H. R. (2001) J. Biol. Chem. 276, 3394-4000]. Recently, we showed that two Cys residues engineered near a proposed binding site in the C5a receptor on transmembrane helices III and VI can selectively and reversibly trap short Cys-containing 3-mer peptides derived from C5a by disulfide bond formation [Buck, E. A., Bourne, H. & Wells, J. A. (November 18, 2004) J. Biol. Chem., 10.1074/jbc.C400500200]. Here, a library of 10,000 compounds, each containing an exchangeable thiol, was screened to identify specific small-molecule mimics that block binding of C5a. Some of the selected compounds acted as agonists and were as potent as the natural C5a ligand, and some acted as antagonists. A residue near these compounds, Ile-116 in helix III, functions as a "gatekeeper" to modulate these effects. A small substitution, Ile-116-Ala, enhanced affinity for some compounds and allowed antagonists to function as agonists; a larger substitution, Ile-116-Trp, decreased affinity and agonism. Thus, subtle changes in either the structure of the ligand or the receptor at the site between helix III, VI, and VII can switch the receptor on or off. This ligand binding and activation site may be similarly positioned in other members of the chemokine receptor family. Selective ligand trapping by reversible disulfide formation may serve to nucleate the development of small-molecule mimics.

Binding Sites↗

PubMed1993

Hemofiltration modifies complement activation after extracorporeal circulation in infants.

Complement and fibrinolytic factors were measured in 9 infants undergoing hemofiltration immediately after cardiopulmonary bypass in an attempt to reduce activation of these systems. Plasma levels of C3a, C5a, and terminal complement complexes increased during bypass by 460%, 85%, and 745%. Plasma levels were reduced after hemofiltration in 8 of the 9 infants, and C3a and C5a fractions were recovered in the ultrafiltrate. The observed activation of the fibrinolytic system seemed to be unaltered by hemofiltration. Fibrinolytic factors were not filtered. Our study shows that increased concentrations of complement factors in the plasma after bypass in infants may be reduced by hemofiltration.

Complement Activation↗

PubMed1999

C5a receptor antagonists.

The anaphylatoxin C5a is an extremely potent proinflammatory peptide produced during activation of the complement system. The structure of C5a includes a core region (N-terminal residues 1-63) consisting of four, antiparallel alpha-helices held together by three disulfide linkages and a structured C-terminal tail (residues 64-74). The C5a receptor belongs to the large class of seven transmembrane, G-protein-linked receptors. C5a appears to interact with its receptor at two sites: the C5a core binds to the receptor s N-terminal extracellular domain while C5a s tail binds the receptor near Arg206, near the membrane surface of transmembrane helix V. C5a receptors are concentrated on blood granulocytes (neutrophils, eosinophils, and basophils) and tissue inflammatory cells (macrophages, mast cells, microglia); thus the main effects of C5a are manifest as inflammation. Additionally, C5a receptors are also present, albeit in lower concentrations, on non-myeloid cells, e.g. endothelial and smooth muscle cells where they may further influence inflammatory reactions such as blood cell emigration and tissue edema. C5a has been implicated in myriad disorders, both acute and chronic; therefore a C5a receptor antagonist is predicted to have utility as a therapeutic agent. Unfortunately, few specific C5a receptor antagonists have been reported, and only two have demonstrated activity in vivo. Furthermore, those reported are peptidic and hence have limited application therapeutically. The current state of C5a receptor antagonists is discussed as well as the potential for their use against various human disorders. A model of C5a receptor dimerization is presented to account for the high potency of the disulfide antagonist C5aRAD.

Amino Acid Sequence↗

PubMed2005

Expression of the anaphylatoxin receptors C3aR and C5aR is increased in fatal asthma.

BACKGROUND: The mechanisms leading to death from asthma are not completely understood. Recent studies suggest the involvement of the anaphylatoxins C3a and C5a, generated during complement activation, and their receptors C3aR and C5aR in the pathogenesis of asthma. OBJECTIVE: The aim of our study was to investigate the expression of C3aR and C5aR in fatal asthma. METHODS: We analyzed lung tissue from 14 subjects who died of asthma (fatal asthma; FA) and 14 subjects who died of nonpulmonary causes (controls) and bronchial biopsy specimens from 16 subjects with mild intermittent asthma (MIA). C3aR and C5aR expression was evaluated by immunohistochemistry, and a semiquantitative analysis of the intensity of staining was performed according to a visual analogue scale (score, 0-3). RESULTS: C3aR was expressed on airway epithelium, smooth muscle, submucosal, and parenchymal vessels. C5aR was expressed on myeloid cells infiltrating the submucosa and on airway epithelium. Statistical analysis demonstrated higher expression of C3aR on submucosal vessels in FA compared with controls and MIA (median [minimum-maximum], controls, 0.24 [0-1.48]; MIA, 0.0 [0-1.00]; FA, 1.56 [0.13-3]; P = .002). C3aR was also increased on parenchymal vessels in FA (controls, 0.56 [0-2.00]; FA, 1.81 [0.5-3]; P = .0004). C5aR expression on airway epithelium was increased in FA compared with controls and MIA (controls, 1.25 [0.25-3]; MIA, 1.00 [0-2.00]; FA, 3.00 [1.13-3.00]; P = .001). CONCLUSION: The results of our study suggest a role of complement in FA.

Adult↗

PubMed1999

A comparison of C3a and C5a-mediated stable adhesion of rolling eosinophils in postcapillary venules and transendothelial migration in vitro and in vivo.

The comparative ability of the complement anaphylatoxins C3a and C5a to mediate leukocyte adhesion and transendothelial migration in vivo and in vitro was investigated. Superfusion of IL-1beta-stimulated rabbit mesentery with C3a resulted in a rapid and stable adhesion of rolling eosinophils, but not neutrophils, to postcapillary venules. However, C3a failed to evoke subsequent transmigration of the adherent eosinophils. In contrast, C5a induced both the rapid activation-dependent firm adhesion and transmigration of eosinophils and neutrophils through venular endothelium. C3a induced selective shedding of L-selectin and an increase in alphaMbeta2 integrin expression on eosinophils but not neutrophils, while C5a induced shedding of L-selectin and up-regulation of alphaMbeta2 integrin on both eosinophils and neutrophils. Both C3a- and C5a-dependent adhesion to venular endothelium was blocked by ex vivo treatment of eosinophils with anti-alpha4 and anti-beta2 integrin mAbs. In vitro, both C3a (but not C3a(desArg)) and C5a (including C5a(desArg))-dependent transmigration of eosinophils across IL-1beta-stimulated endothelial monolayer was mediated by alpha4beta1 and alphaMbeta2 integrins. Overall these studies suggest that C3a is eosinophil-specific chemotactic mediator that influences selectively eosinophil adhesion but not transmigration in vivo. C5a in contrast is a complete activator of integrin-dependent adhesion as well as transmigration of eosinophils and neutrophils.

Animals↗

PubMed1985

High dose corticosteroids and cell-cell interactions.

Adult Respiratory Distress Syndrome (ARDS) is a feared complication of trauma or sepsis, characterized by an interstitial and alveolar edema due to increased pulmonary microvascular permeability. In ARDS polymorphonuclear granulocytes (PMN) aggregate and accumulate in the pulmonary microvessels and activation of the complement system, especially C5a, is suggested to be of importance supporting this aggregation. Such complement activated PMN can increase vascular permeability, probably by initiating endothelial cell (EC) damage. Addition of PMN and C5a to cultured EC monolayers in vitro produced both morphological and functional EC damage. A similar EC damage could be reproduced in the absence of white cells by exposing EC monolayers to oxygen free radicals induced by xanthine and xanthine oxidase or hydrogen peroxide. High dose corticosteroid (HDC) administration has been advocated in shock and ARDS and it has been experimentally demonstrated that methylprednisolone or hydrocortisone at a concentration corresponding approximately to a dose of 30 mg/kg i.v. inhibited both PMN aggregation and adhesion to the endothelium. On the other hand, no effect of HDC on PMN thromboxane synthesis or cell membrane morphology alterations was found. It has been suggested that HDC increases PMN hydrophobicity and thus reduces the tendency of the white cells to adhere to the endothelium of the microvasculature. Furthermore, it has been demonstrated that HDC can inhibit PMN production of oxygen free radicals. Platelets seem to play a role in ARDS. Serotonin released from platelets increased the cytotoxic effect of PMN on EC more than 100% in vitro, and activated PMN seemed to recruit platelets and release vasoactive substances. On the other hand, platelet serotonin enhanced the adhesion of complement stimulated PMN to EC, thus creating a vicious circle. To conclude, complement activated PMN aggregate and adhere to the pulmonary microvascular EC which are injured by e.g. PMN-generated oxygen free radicals. Platelet aggregation and release of serotonin augments this injury and activated PMN probably stimulate platelet aggregation and release. Agents capable of diminishing PMN activation and aggregation, e.g. HDC, might be of value in attenuating these cell-cell interactions in ARDS.

Adrenal Cortex Hormones↗

PubMed2006

Effect of an anti-C5a monoclonal antibody indicates a prominent role for anaphylatoxin in pulmonary xenograft dysfunction.

BACKGROUND: In contrast to renal or cardiac xenografts, the inhibition of complement using cobra venom factor (CVF) accelerates pulmonary xenograft failure. By activating C3/C5 convertase, CVF depletes complement while additionally generating C5a and other anaphylatoxins, to which pulmonary xenografts may be uniquely susceptible. The current study investigates the role of C5a in pulmonary xenograft failure in baboons. METHODS: Left orthotopic pulmonary xenografts using swine lungs expressing human CD46 were performed in baboons receiving: I) no other treatment (n=4), II) immunodepletion (n=5), and III) immunodepletion plus a single dose of mouse anti-human C5a monoclonal antibody (anti-C5a, 0.6 mg/kg administered intravenously) (n=3). The extent to which anti-C5a inhibits baboon C5a was assessed in vitro using a hemolytic reaction involving baboon serum and porcine red blood cells and by ELISA. RESULTS: Baboons in Group III exhibited significantly prolonged xenograft survival (mean=722+/-121 min, P=0.02) compared to baboons in Group I (mean=202+/-24 min) and Group II (mean=276+/-79 min). Furthermore, baboons in Groups I and II experienced pronounced hemodynamic compromise requiring inotropic support whereas those in Group III remained hemodynamically stable throughout experimentation without the need for additional pharmacologic intervention. CONCLUSIONS: These findings indicate that C5a exacerbates pulmonary xenograft injury and compromises recipient hemodynamic status. Moreover, blockade of anaphylatoxins, such as C5a, offers a promising approach for future investigations aimed at preventing pulmonary xenograft injury in baboons.

Animals↗

PubMed1985

Effects of the C5a anaphylatoxin and its relationship to cyclo-oxygenase metabolites in rabbit vascular strips.

Strips of rabbit blood vessels were suspended in vitro and responses to complement peptides C3a and C5a were recorded isotonically. Human C3a (up to 1.5 microM) was inactive on rabbit vascular strips. Human C5a (2.9-59 nM) decreased spontaneous activity of the rabbit portal vein under resting baseline tension. The C5a relaxed strips of portal vein and pulmonary artery that were precontracted with noradrenaline (NA, 200 nM). On the portal vein, C5a-induced relaxation was preceded by a transient contractile phase which decreased with repeated applications of C5a. The magnitude of C5a-induced relaxation of both vessels increased with repeated stimulation by C5a. Maximal levels of relaxation for the third application of C5a at 59 nM averaged 44% and 17% of the NA-induced contraction plateau in portal vein and pulmonary artery, respectively. Strips of rabbit aorta responded minimally to C5a. Indomethacin (5.6 microM) significantly inhibited C5a-induced relaxation of the portal vein and pulmonary artery but had no effect on the early contractile response of the portal vein. Mepyramine (10 microM) failed to modify the C5a response from either vessel, but it reduced the contractile phase of the C5a response on the portal vein when applied in conjunction with indomethacin. The drug SKF 88046, an end organ antagonist of thromboxane (TX) A2 and some contractile prostaglandins, reduced the contractile phase and increased relaxation of the portal vein to C5a but did not modify the response of the pulmonary artery. Radioimmunoassays for 6-keto-prostaglandin F1 alpha (6-keto-PGF1 alpha) and TXB2 were performed on the fluid bathing rabbit isolated blood vessels. C5a promoted release of 6-keto-PGF1, over the basal release rate in rabbit tissues. Only trace quantities of TXB2 were produced by rabbit vessels exposed to C5a. 7 It is concluded that the mechanical response of blood vessels to C5a is mainly determined by the type of cyclo-oxygenase products released and by the sensitivity of each blood vessel to these active lipids. Tissue histamine release is also responsible for a component of the response of rabbit portal vein to C5a. The relaxant effect of C5a on rabbit blood vessels may be a phenomenon related to the previously reported hypotensive action of classical anaphylatoxins in vivo.

6-Ketoprostaglandin F1 alpha↗

PubMed2005

Complement activation-related cardiac anaphylaxis in pigs: role of C5a anaphylatoxin and adenosine in liposome-induced abnormalities in ECG and heart function.

Cardiac anaphylaxis is a severe, life-threatening manifestation of acute hypersensitivity reactions to allergens and drugs. Earlier studies highlighted an amplifying effect of locally applied C5a on the process; however, the role of systemic complement (C) activation with C5a liberation in blood has not been explored to date. In the present study, we used the porcine liposome-induced cardiopulmonary distress model for 1) characterizing and quantifying peripheral C activation-related cardiac dysfunction; 2) exploring the role of C5a in cardiac abnormalities and therapeutic potential of C blockage by soluble C receptor type 1 (sCR1) and an anti-C5a antibody (GS1); and 3) elucidating the role of adenosine and adenosine receptors in paradoxical bradycardia, one of the symptoms observed in this model. Pigs were injected intravenously with different liposomes [Doxil and multilamellar vesicles (MLV)], zymosan, recombinant human (rhu) C5a, and adenosine, and the ensuing hemodynamic and cardiac changes (hypotension, tachy- or bradycardia, arrhythmias, ST-T changes, ventricular fibrillation, and arrest) were quantified by ranking on an arbitrary scale [cardiac abnormality score (CAS)]. There was significant correlation between CAS and C5a production by liposomes in vitro, and the liposome-induced cardiac abnormalities were partially or fully reproduced with zymosan, rhuC5a, adenosine, and the selective adenosine A1 receptor agonist cyclopentyl-adenosine. The use of C nonactivator liposomes or pretreatment of pigs with sCR1 or GS1 attenuated the abnormalities. The selective A1 blocker cyclopentyl-xanthine inhibited bradycardia without influencing hypotension, whereas the A(2) blocker 4-(2-[7-amino-2-(2-furyl)[1,2,4]triazolo[2,3-a][1,3,5]triazin-5-ylamino]ethyl)phenol (ZM-24135) had no such effect. These data suggest that 1) systemic C activation can underlie cardiac anaphylaxis, 2) C5a plays a causal role in the reaction, 3) adenosine action via A1 receptors may explain paradoxical bradycardia, and 4) inhibition of C5a formation or action or of A1-receptor function may alleviate the acute cardiotoxicity of liposomal drugs and other intravenous agents that activate C.

Adenosine↗

PubMed2003

Differential cytokine expression of human retinal pigment epithelial cells in response to stimulation by C5a.

Human retinal pigment epithelial (RPE) cells form part of the blood-retina barrier where they potentially can regulate leucocyte function. RPE cells are known to secrete several cytokines in response to stimulation by other cytokines. Anaphylatoxin C5a, a potent inflammatory mediator produced during complement activation, binds to G-protein coupled C5a receptors (C5aR) on monocytes/macrophages and releases various cytokines from the cells. We previously reported that the human RPE cell line ARPE-19 possesses C5aR and expresses IL-8 mRNA in response to C5a stimulation. In this study, we used a primary human RPE cell line (RPE43) and found that C5a induces increased expression of IL-1beta, IL-6, MCP-1 and GM-CSF mRNAs as well as IL-8 mRNA. ARPE-19 cells showed similar increases in the same cytokines. Interestingly, the kinetics of expression of the various cytokines differed. These results provide further evidence that C5a stimulation of RPE cells may play a role in regulating leucocyte function during ocular inflammation in which there is complement activation.

Antigens, CD↗

PubMed2000

Comparison of the suppressive effects of soluble CR1 and C5a receptor antagonist in acute arthritis induced in rats by blocking of CD59.

We investigated the effects of suppression of complement activation at C3 level and inhibition of C5a on acute synovitis in rats. Acute synovitis was induced in Wistar rats by intra-articular (i.a.) injection into one knee of 0.3 mg of MoAb 6D1 (anti-rat CD59 antibody). In the treatment groups, soluble CR1 (sCR1) or C5a receptor (C5aR) antagonist was administered intra-articularly or intravenously and effects on the course of the acute synovitis were monitored. Synovitis induced by 6D1 was characterized by joint swelling, thickening of synovial tissue, cellular infiltration and deposition of membrane attack complex (MAC) on the synovial surface. Neither inflammatory change nor MAC deposition was found in rats which received an i.a. injection of sCR1 to suppress complement activity in the joint. Intra-articular injection of sCR1 did not reduce plasma complement activity. Intravenous administration of sCR1 suppressed plasma complement activity but had no effect on the course of the arthritis and synovitis with MAC deposition was observed. Neither i.a. nor i.v. injection of C5aR antagonist had any suppressive effects on inflammatory change or MAC deposition in synovium. The data show that inflammatory change induced by 6D1 was mediated by local complement activation and was not accompanied by systemic complement activation. C5a generation was not responsible for the observed inflammation, suggesting that other complement activation products, possibly MAC, mediate the inflammatory change observed in this model of acute synovitis in rats.

Acute Disease↗

PubMed2000

Complement activation in heart diseases. Role of oxidants.

Increasing evidence demonstrated that atherosclerosis is an immunologically mediated disease. Myocardial ischemia/reperfusion injury is accompanied by an inflammatory response contributing to reversible and irreversible changes in tissue viability and organ function. Three major components are recognized as the major contributing factors in reperfusion injury. These are: (1) molecular oxygen; (2) cellular blood elements (especially the neutrophils); and (3) components of the activated complement system. The latter two often act in concert. Endothelial and leukocyte responses are involved in tissue injury, orchestrated primarily by the complement cascade. Anaphylatoxins and assembly of the membrane attack complex contribute directly and indirectly to further tissue damage. Tissue damage mediated by neutrophils can be initiated by complement fragments, notably C5a, which are potent stimulators of neutrophil superoxide production and adherence to coronary artery endothelium. The complement cascade, particularly the alternative pathway, is activated during myocardial ischemia/reperfusion. Complement fragments such as the anaphylatoxins C3a and C5a, are produced both locally and systematically, and the membrane attack complex is deposited on cell membranes and subsequent release of mediators such as histamine and platelet activating factor (PAF), thereby causing an increase in vascular permeability with concomitant manifestation of cellular edema. Complement increases the expression of CD18 on the neutrophils and increases P-selectin expression on the surface of the endothelium. Mitochondria may be a source of molecules that activate complements during ischemia/reperfusion injury to myocardium, providing therewith a stimulus for infiltration of polymorphonuclear leukocytes. Tissue salvage can be achieved by depletion of complement components, thus making evident a contributory role for the complement cascade in ischemia/reperfusion injury. The complexities of the complement cascade provide numerous sites as potential targets for therapeutic interventions designed to modulate the complement response to injury. The latter is exemplified by the ability of soluble form of complement receptor 1 (sCR1) to decrease infarct size in in vitro models of ischemia/reperfusion injury. The mechanism(s) that initiates complement activation is not clearly known, although loss of CD59 (protectin) from cells compromised by ischemia/reperfusion may contribute to direct damage of the coronary vascular bed by the terminal complement complex. Therapeutic approaches to ischemia/reperfusion injury in general, and especially those involving complements, are at the very beginning and their potential benefits have still to be adequately evaluated. It may be noted that complement activation has both positive and negative effects and, therefore, might be modulated rather than abruptly blunted.

Animals↗