Relationships between complement activation, complement binding, and EBV absorption by human hematopoietic cell lines.
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Binding Sites↗
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Assays for complement activation.
Complement is a major biologic mediation system that functions in host defense against microorganisms and other pathogens and also aids in the elimination of damaged and abnormal cells. This is accomplished by its ability to mediate the destruction of pathogens and altered cells directly through cytolytic and cytotoxic properties, as well as indirectly by its ability to augment the actions of various effector cells, which in turn destroy or inactivate these substances. Its second major action in vivo is the production of an acute inflammatory response that, by altering blood-vessel permeability, contracting smooth muscles, and promoting an influx of leukocytes, aids in the localization of the injurious process responsible for complement activation and retards its spread and dissemination throughout the body. The actions of the activated complement system upon pathogens and altered cells, as well as its phlogistic properties, are the direct consequence of the actions of complement protein-protein complexes, enzymes, peptides, and cleavage products on the activator, on biologic membranes, and on various effector and other tissue cells. Complement activation is a frequent phenomenon in infectious diseases, autoimmune diseases, and many other conditions having an inflammatory component. Because of the importance of this system in contributing to the resolution of the disease process, monitoring of the status of the system in patients is frequently indicated. Monitoring of the complement status is also appropriate in numerous other diseases, such as those with an inflammatory component, in which complement activation occurs secondarily but in which it is frequently responsible for confining the injurious process and aiding in its resolution. A number of techniques are available to assess the status of the complement system in samples obtained from patients. Among these are a group of newer tests that specifically detect complement activation. They quantitate activation-dependent complement cleavage products, antigenic changes, or protein-protein complexes. These tests are quantitative, highly sensitive, and extremely specific; furthermore, most can be employed with samples obtained from patients. Because all of the biologic actions of the complement system require complement activation, such newer activation-specific assays permit the precise evaluation of the status of this system in human diseases. Further extension of their use to additional patients and other disease complexes will undoubtedly increase the understanding of the biologic importance of the complement system in human disease processes.
Complement Activation↗
A modification of cellulose that facilitates the control of complement activation.
Complement activation by Cuprophan hemodialysis membranes has been linked to a variety of pathological sequelae (neutropenia and various cardiopulmonary manifestations) seen in the clinical setting. The modification of reactive surface hydroxyl groups on regenerated cellulose with various dicarboxylic-acid anhydrides has been found to significantly limit the complement-activating potential of these materials. Of the anhydrides tested, maleic anhydride appears to display the most dramatic and consistent diminution of complement activation compared to unmodified cellulose (0-10% of control values for C3b deposition and C3a/C5a production). Current evidence suggests that this maleated derivative facilitates the factor-H control of C3 and C5 convertase activity and thus may help limit complement activation by normal regulatory mechanisms. In addition, this modification may help limit the production of other inflammatory mediators that may result in diminished levels of cellular activation.
Biocompatible Materials↗
Consecutive enzyme cascades: complement activation at the cell surface triggers increased tissue factor activity.
Complement activation at the cell surface initiates cell damage through a series of reactions occurring at the cell membrane and, after assembly of the terminal membrane attack complex, produces leakage of cytoplasmic contents from the cell. It has been documented that chemical or physical damage to cell membranes can cause a rapid increase in the expression of tissue factor procoagulant activity. In this study, antibody-mediated complement activation at the cell surface resulted in increased tissue factor activity, which correlated with cytolysis, as measured by 51-chromium release. Therefore, complement fixation on the cell surface can have a direct and immediate stimulatory effect on the coagulation cascade at the point of its initiation, with formation of a fibrin clot requiring only three consecutive proteolytic reactions after immunologically mediated cell damage.
Antibodies↗
Blood substitution and complement activation.
Complement activation was studied in 45 patients undergoing total hip arthroplasty under epidural anesthesia. The patients were randomly allocated to three groups. In Group I blood loss was replaced with microaggregate-poor erythrocyte concentrate (SAGM-ERC) plus 3% dextran-60 as plasma substitute, and postoperative analgesia was maintained with intramuscular ketobemidone. In Group II blood loss was replaced as in Group I, but epidural anesthesia was prolonged 12 h postoperatively and kept at a level of T4 with 0.5% bupivacaine. In Group III blood loss was replaced with non-frozen stored plasma plus SAGM-ERC, and postoperative analgesia was maintained with ketobemidone as in Group I. All groups received pre- and postoperative thrombo-prophylaxis with dextran. The plasma concentration of C3a-des-arginine (C3a-desArg) was measured by radioimmunoassay preoperatively, immediately after operation and 3, 6 and 18 h postoperatively. No significant differences in plasma C3 and C4 were found between the groups. C3a-desArg was significantly (P less than 0.01) increased up to 6 h postoperatively in Group III compared with both the preoperative value and Groups I and II. It is demonstrated that infusion of plasma can enhance or initiate endogenous complement activation. Blood component therapy with SAGM-ERC and 3% dextran-60, on the other hand, did not significantly increase the plasma level of C3a-desArg irrespective of the type of postoperative analgesia.
Aged↗
The ischaemic leg as a source of complement activation.
Complement activation before and after surgical resection was studied in 40 patients with ischaemic legs (17 with acute and 23 with chronic ischaemia). Plasma anaphylatoxin concentrations (C3a and C5a) and anaphylatoxin inhibitor (AI) activity were studied pre-operatively, and 1 h, 24 h and 1 week postoperatively. Increased plasma anaphylatoxin concentrations were found pre-operatively. Anaphylatoxin levels in plasma had returned to normal one week postoperatively. Patients with acute ischaemia had higher plasma C3a and C5a pre-operatively and during the first 24 h postoperatively than patients with chronic ischaemia. Anaphylatoxins increase vascular permeability, smooth muscle contraction and histamine release from mast cells. Their enhanced activity might be one of the explanations for respiratory, hepatic and renal insufficiency before surgical resection in patients with extensive ischaemia.
Aged↗
Plasmin activity and complement activation during storage of citrated platelet concentrates.
Platelet concentrates were studied for evidence of plasmin activity and complement activation during a 7-to-10-day storage period. When measured by an amidolytic activity assay, plasmin reached a level of 845 +/- 540 nkats/L on day 7 (n = 9). Fibrin(ogen) degradation product (FDP) levels became markedly elevated on the tenth day of storage, rising to 45 +/- 22 micrograms/ml (n = 5). Antiplasmin levels decreased in platelet concentrates by 18% +/- 6% (n = 5) over 7 days, but there was no significant decrease in stored platelet-poor plasma (-1.7%, n = 5, p = 0.5). The amount of plasminogen in platelet concentrate converted to plasmin was estimated to be less than 3% by assay of total plasminogen. Supernatant plasma from stored platelet concentrates was examined for the presence of the complement activation peptides C3a and C5a. From day 0 to day 10 of storage, mean C3a levels rose from 327 ng/ml to 6690 ng/ml. An equivalent increase in C3a levels, from 336 ng/ml at day 0 to 6866 ng/ml at day 10, was also observed in stored platelet-poor plasma. C5a was not detected (less than 10 ng/ml) at any point during the storage period; however, we noted a small decrease of borderline significance (p = 0.04) in total C5 from day 0 (117 micrograms/ml) to day 10 (108 micrograms/ml). Only trace amounts of C3 fragments were found on stored platelets, and there was no evidence of the membrane attack complex. These findings indicate the presence of plasmin activity and conversion of C3 during storage of platelet concentrates.
Blood Platelets↗
The design of cellulosic based membranes that do not activate complement.
Complement is a principal mediator of the acute inflammatory response that works by nonspecific recognition mechanisms to eliminate foreign substances from the body. Because of the non-selective nature of complement, extracorporeal therapies employing hydrophilic cellulosic based materials can result in significant complement activation and systemic exposure to large amounts of C5a which in turn may lead to a variety of pathological sequelae. Several approaches have been identified to produce materials with a limited potential to activate complement. Activation proceeds on a material following the covalent attachment of C3b to surface nucleophiles which leads to the formation of C3 and C5 convertase enzymes. Interference with these enzymes may be achieved at several levels. Surfaces that contain fewer nucleophilic sites bind less C3b and thus generate lower levels of convertase activity. This is exemplified by the Cellulose Triacetate membrane that is produced by exhaustive acetylation of surface hydroxyl groups. This membrane binds only a third of the amount of C3b that a cuprophan membrane will bind. An alternative means of affecting convertase activity can occur by facilitating the regulatory activity of Factors H and I. Evidence is presented here that suggests that Hemophan appears to limit activation by augmenting regulation of bound-C3b. Finally we have begun studies on a new type of modification using dicarboxylic acid anhydrides that produce materials with a very limited potential to activate complement.
Biocompatible Materials↗
Effect of exercise on complement activity.
Complement measurements of C1, C1q, C2, C3, C4, C5; the anaphylatoxins, C3a, C4a, and C5a; and total hemolytic activity of the classical and alternative pathways were made in 26 experienced adult runners before and after shortterm aerobic exercise. The baseline results were compared with those of nonexercising age-matched controls. In most subjects tested, running resulted in nanogram increases in C3a and C4a with corresponding decreases in the hemolytic activity of C4 (C4H). Baseline values of C3 and C4H were decreased significantly in runners when compared with nonexercising controls. Preliminary studies measuring the effect of exercise on C3a levels were also done in three asthmatic runners. Mean resting and postexercise levels, and exercise-induced increases in C3a anaphylatoxin in the asthmatic subjects were significantly higher than in the nonasthmatic subjects. The findings indicate that short-term exercise results in the activation of C3 and C4 and subsequent generation of C3a and C4a anaphylatoxins, and suggest that both activation of the classical pathway of complement and a selective downregulation of C3 production may occur in persons regularly engaged in aerobic exercise. The exaggerated generation of C3a by asthmatic subjects during exercise raises the possibility that anaphylatoxins play an etiologic role in exercise-induced asthma.
Adult↗
[Drugs inhibiting complement activation].
Complement may be activated by anaesthetic agents as well as contrast media, and so could anaphylactoid reactions be induced. Efficient and harmless complement blocking agents were still lacking. The only agents actually used by anaesthetists were steroids and/or antifibrinolytic drugs. Other agents were not indicated in surgical patients because of their adverse effects and the impossibility of giving them by the intravenous route.
Adrenal Cortex Hormones↗
Comparative study of assays detecting complement activation. Complement-split product C3d (rocket immuno-electrophoresis) and C3d neodeterminants (ELISA).
The aim of the study was to investigate the correlation between two types of assay measuring specific products of complement C3 activation and their clinical application. Complement C3d split product was estimated using double-decker rocket immunoelectrophoresis (DD-RIE) and measurements of C3d neodeterminants exposed after C3 activation was carried out with an enzyme-linked immunosorbent assay (ELISA). A total of 595 blood samples were measured in parallel in the DD-RIE and the ELISA test systems. The samples originated from blood donors (44), uraemic patients undergoing dialysis (135), serial samples from rheumatoid arthritis (RA) patients during steroid treatment (88) and 328 randomly collected patient samples. The mean values for DD-RIE and ELISA (+/- 1 SD) for the 595 samples were 48 (+/- 20) mU/l and 48 (+/- 28) mU/l respectively. The interassay coefficient of variation (CV) in the ELISA was 18%. The Spearman rho-correlation coefficient between the two assays was 0.63 for all 595 samples. The mean values using ELISA and DD-RIE were practically identical for the 328 successively incoming samples, the samples from the 135 dialysis patients and the 44 donors. In RA patients a higher mean value was found for the 88 samples using DD-RIE than ELISA. In the majority of patient samples there was a good correlation between the two assays. However, the ELISA appears to be more sensitive in detecting acute complement activation and to give lower levels in RA patients with chronic complement activation.
Anaphylaxis↗
The differential ability of human IgG1 and IgG4 to activate complement is determined by the COOH-terminal sequence of the CH2 domain.
Using domain switch chimeric antibodies, we confirm the important role of CH2 in complement activation. In addition, we demonstrate that the structures responsible for the differential ability of human IgG1 and IgG4 to activate complement are located at the COOH-terminal part (from residue 292 to 340) of the CH2 domain. The amino acids in CH2 that might be involved in complement interaction are discussed. While CH3 contributes to efficient complement activation, CH3 from IgG2 and CH3 IgG3 are equally effective.
Complement Activation↗
Complement activating properties of complexes containing rheumatoid factor in synovial fluids and sera from patients with rheumatoid arthritis.
The relationship between complexes containing rheumatoid factor and complexes activating complement was examined in synovial fluids and sera from patients with rheumatoid arthritis (RA). In each case this was performed by quantifying the amount of rheumatoid factor bound by solid phase Fab'2 anti-C3 and/or solid phase conglutinin. Both anti-C3 coated and conglutinin coated microtitre plates bound high levels of complexes containing rheumatoid factor from sera of RA patients with vasculitis. Unexpectedly, these complexes were detected in synovial fluids from only a minority of RA patients with synovitis. However, RA synovial fluids did contain other complexes as shown by the presence of complement consuming activity, C1q binding material and immunoglobulin attaching to conglutinin. It is considered that in RA synovial fluids the complexes containing RF and those activating complement are not necessarily the same whilst in vasculitic sera the complexes containing rheumatoid factor also activate complement.
Adult↗
Biomedical polymers differ in their capacity to activate complement.
Conventionally, complement activation by biomedical polymers has been evaluated by determining the C3a concentration in the fluid phase only. According to this criterion, biomaterials such as hemodialysis membranes made from cellulosic or various synthetic polymers were classified as activators or nonactivators of complement. Since certain membranes bind large quantities of C3a from the fluid phase, classification based on fluid-phase C3a concentration has in some instances been inaccurate. As follows from the comparison of complement activation by cuprophane and polyacrylonitrile membranes, the capacity of a biomedical polymer to activate complement is not determined by the number of potential covalent binding sites on its surface. Biomaterial itself may lack hydroxyl and/or amino groups, and yet it may activate C3 in human serum very efficiently. Some of the biomaterials may also bind unactivated/unfragmented C3 whether in the absence or presence of other serum proteins. In addition, binding of factor B (a promotor of C3 activation) and binding of factor H (an inhibitor of C3 activation) to certain biomaterials have been found to be independent of complement activation and unaffected by the presence or absence of C3. Thus, it is becoming apparent that the requirements for the formation and stability of the C3 convertase on artificial surfaces differ from those on biological membranes, and that the relative magnitude of binding of factor B and factor H to the surface per se cannot be used as a reliable indicator of the capacity of the biomaterial to activate complement. Further studies are necessary to elucidate the molecular mechanisms of C3 and C5 activation on the surfaces of biomedical polymers.(ABSTRACT TRUNCATED AT 250 WORDS)
Blood Proteins↗
Complement activation and complement receptors in systemic lupus erythematosus.
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Antigen-Antibody Complex↗
The effect of immune complex composition on complement activation and complement dependent complex release.
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Animals↗
Complement activation in acne vulgaris: in vitro studies with Propionibacterium acnes and Propionibacterium granulosum.
To better define the role of bacteria in inflammatory acne vulgaris, we have investigated the ability of four strains of Propionibacterium acnes and three strains of Propionibacterium granulosum to activate complement. Complement activation was assayed by incubating normal human serum with varying concentrations of each strain and measuring residual total hemolytic complement activity. When serum was tested unaltered, P. acnes strains were approximately threefold more potent than an equal weight of P. granulosum in consuming complement, which could reflect classical and/or alternative pathway activation. All strains also consumed complement in serum chelated with ethyleneglycol-bis (beta-aminoethyl ether)-N,N'-tetraacetic acid, which selectively assays alternative pathway activation. Incubation of unaltered serum with both P. acnes and P. granulosum resulted in immunoelectrophoretic conversion of C4, C3, and factor B of the alternative pathway. Incubation of chelated serum resulted in conversion of C3 and factor B. These data taken together suggest that both species can activate complement through either pathway. Serum incubated with P. acnes was chemotactic for polymorphonuclear leukocytes, and this chemotactic activity was largely C5 dependent as shown by antibody inhibition. It is suggested that complement activation may occur in vivo in acne, and the inflammatory response may be contributed to by the generation of C5-dependent chemotactic factors.
Acne Vulgaris↗
Complement, complement activation and anaphylatoxins in human ovarian follicular fluid.
Functionally active complement was sought and detected in human follicular fluids obtained during the pre-ovulatory period. All the functional complement activities tested, including total haemolytic complement, classical pathway activity and alternative pathway activity were present in nine fluids from four different donors with values within the normal serum range. The immunochemical analysis demonstrated the presence of complement factors from C1 to C9, of B and of C1 INH, H, I. Complement anaphylatoxins were found employing RIA techniques in amounts significantly higher than in human plasma, thus demonstrating that follicular fluid complement, at least during the pre-ovulatory period, is partially activated. A possible role for urokinase-like substances in such an activation was indicated by further in vitro experiments. The presence of active complement in follicular fluid can be relevant for the function of the enzymatic multi-factorial mechanism of ovulation.
Anaphylatoxins↗