Formation of C3a and C5a anaphylatoxins in whole human serum after inhibition of the anaphylatoxin inactivator

Complement consumption during cardiopulmonary bypass: bubble versus membrane oxygenators

The purpose of this study was to compare levels of C3 and C4 during cardiopulmonary bypass, using bubble and membrane oxygenators. In vitro studies were performed using human blood in a simple circuit involving an oxygenator, roller pump and connector tubing. In vivo studies were carried out in two separate institutions using a variety of bubble and membrane oxygenators. Samples were taken throughout the pump run (30-1 20 minutes). Complement levels were corrected for haemodilution. All oxygenators tested caused a rapid decrease in C3 and C4 complement levels on institution of bypass. The magnitude and timing of these decreases were similar in the membrane and bubble groups. Thereafter, complement levels were stable throughout the pump run. These data do not suggest that there is any difference in complement activation during relatively short pump runs using bubble and membrane oxygenators.

LIM kinase 1 promotes endothelial barrier disruption and neutrophil infiltration in mouse lungs

RATIONALE

Disruption of endothelial barrier function and neutrophil-mediated injury are two major mechanisms underlying the pathophysiology of sepsis-induced acute lung injury (ALI). Recently we reported that endotoxin induced activation of RhoA in mice lungs that led to the disruption of endothelial barrier and lung edema formation; however, the molecular mechanism of this phenomenon remained unknown.

OBJECTIVE

We reasoned that LIMK1, which participates in the regulation of endothelial cell contractility and is activated by RhoA/Rho kinase pathway, could mediate RhoA-dependent disruption of endothelial barrier function in mouse lungs during ALI. And if that is the case, then attenuation of endothelial cell contractility by downregulating LIMK1 may lead to the enhancement of endothelial barrier function, which could protect mice from endotoxin-induced ALI.

METHODS AND RESULTS

Here we report that LIMK1 deficiency in mice significantly reduced mortality induced by endotoxin. Data showed that lung edema formation, lung microvascular permeability, and neutrophil infiltration into the lungs were suppressed in limk1(-/-) mice.

CONCLUSIONS

We identified that improvement of endothelial barrier function along with impaired neutrophil chemotaxis were the underlying mechanisms that reduced severity of ALI in limk1(-/-) mice, pointing to a new therapeutic target for diseases associated with acute inflammation of the lungs.

Rho GTPases and the regulation of endothelial permeability

Endothelial permeability depends on the integrity of intercellular junctions as well as actomyosin-based cell contractility. Rho GTPases have been implicated in signalling by many vasoactive substances including thrombin, tumour necrosis factor alpha (TNF-alpha), bradykinin, histamine, lysophosphatidic acid (LPA), vascular endothelial growth factor (VEGF), and hepatocyte growth factor (HGF). Two Rho family GTPases, Rho and Rac, have emerged as key regulators acting antagonistically to regulate endothelial barrier function: Rho increases actomyosin contractility, which facilitates breakdown of intercellular junctions, whereas Rac stabilizes endothelial junctions and counteracts the effects of Rho. In this review, we present evidence for the opposing effects of these two regulatory proteins and discuss links between them and other key signalling molecules such as cyclic AMP (cAMP), cyclic GMP (cGMP), phosphatidylinositide 3-kinases (PI3Ks), mitogen-activated protein kinases (MAPKs), and protein kinases C (PKCs). We also discuss strategies for targeting Rho GTPase signalling in therapies for diseases involving altered endothelial permeability.

Complement c3a and c5a induce different signal transduction cascades in endothelial cells

In leukocytes, C3a and C5a cause chemotaxis in a G(i)-dependent, pertussis toxin (PT)-sensitive fashion. Because we found that HUVECs and immortalized human dermal microvascular endothelial cells express small numbers of C3aRs and C5aRs, we asked what the function of these receptors was on these cells. Activation of the C3aR caused transient formation of actin stress fibers, which was not PT-sensitive, but depended on rho activation implying coupling to G(alpha12) or G(alpha13). Activation of the C5aR caused a delayed and sustained cytoskeletal response, which was blocked by PT, and resulted in cell retraction, increased paracellular permeability, and facilitated eosinophil transmigration. C5a, but not C3a, was chemotactic for human immortalized dermal microvascular endothelial cells. The response to C5a was blocked by inhibitors of phosphatidylinositol-3-kinase, src kinase, and of the epidermal growth factor (EGF) receptor (EGFR) as well as by neutralizing Abs against the EGFR and heparin-binding EGF-like factor. Furthermore, immune precipitations showed that the EGFR was phosphorylated following stimulation with C5a. The C5aR in endothelial cells thus uses a signaling cascade-transactivation of the EGFR-that does not exist in leukocytes, while the C3aR couples to a different G protein, presumably G(alpha12/13).

Chronic myelogenous leukemia-derived basophilic granulocytes express a functional active receptor for the anaphylatoxin C3a

The receptor for the inflammatory peptide C3a has scarcely been examined on human cells. This work demonstrates that human tumor-derived basophilic granulocytes express C3a receptors, and presents parts of the hitherto unknown C3a-signal transduction. When incubated with IL-3, these cells specifically liberated histamine on C3a stimulation. Independent from IL-3, 240,000 +/- 100,000 receptors per cell with a Kd of 5.6 +/- 0.9 nM were determined. [Ca2+]i increased from 120 +/- 35 nM to 300 +/- 80 nM after a C3a challenge, as measured by digital imaging fluorescence microscopy, and rested at its basal level in the presence of C3a-desArg, the immediate catabolic product of C3a in vivo. This [Ca2+]i increase could be completely desensitized homologously by C3a as well as inhibited by up to 75% by pertussis toxin. Thus, tumor-derived basophils are suitable for cloning of the human C3a receptor.

Variation in the antigenic characteristics of venom from the Mojave rattlesnake (Crotalus scutulatus scutulatus)

Venoms from 31 specimens of the Mojave rattlesnake (Crotalus scutulatus scutulatus) were examined to further characterize reported differences among venoms of this species. Twenty-two venoms were recognized by a monoclonal antibody to Mojave toxin, CSS12. Nine venoms were recognized by CA-P-8, a monoclonal antibody produced against the hemorrhagic venom of C. atrox. Seven of these produced strong hemorrhage in mice and were also recognized by polyclonal antibodies (anti-F5) produced against a fraction of Mojave rattlesnake venom that inactivates serum complement. Fractionated venom revealed that CA-P-8 and anti-F5 recognized different proteins. Two of the venoms recognized by CA-P-8 were not recognized by anti-F5 and produced minimal hemorrhage in mice. This suggests that more than one factor may be necessary to induce strong hemorrhage.

Streptococcal products and leukocyte activities

Various streptococcal species are directly responsible for udder infections which should normally be countered by polymorphonuclear neutrophils (PMNs). In order to detect a putative inhibition of streptococcal products on the activities of bovine PMNs, we used a combination of four tests which permits an adequate evaluation of PMNs functions, e.g. PMN adherence on endothelial cells, chemotactic assay, phagocytosis of bacteria labelled with fluorescein isothiocyanate (FITC) and measurement of anion superoxide production. The conclusion is that neither of the two pathogenic streptococcal species isolated from mastitis appeared to produce in vitro factors affecting PMN activities.

A factor in serum lowers resistance and opens tight junctions of MDCK cells

During an inflammatory reaction, factors in blood affect the permeability of endothelium and possibly organ epithelium. In this study we partially characterized a factor in human and canine blood that lowered the transepithelial electrical resistance (TER) of canine kidney epithelial cells (MDCK) and examined whether vascular permeability factors [complement component C3a and C5a and platelet-activating factor (PAF)] were responsible for this reaction. C3a and C5a caused a small (10-13%) dose-related decrease in the TER (alpha = 0.05), whereas PAF had no effect. In contrast, the factor found in both serum and plasma caused a large (60-83%) dose-dependent decrease (saturated at 30%) in the TER that was reversible within 60 min. The blood factor, which does not appear to be albumin, was heat stable and has an apparent molecular mass of 67 kDa. It preferentially decreased the TER of the epithelium when it came in contact with its basolateral surface and significantly lowered the resistance within 60 min by opening the zonula occludentes. These findings suggest that C3a, C5a, and a factor in blood can directly modulate the permeability of renal epithelium.

Interleukin 3 and granulocyte/macrophage-colony-stimulating factor render human basophils responsive to low concentrations of complement component C3a

Complement component C3a is an anaphylatoxin known to induce plasma exudation and smooth muscle contraction in tissues. The effects on inflammatory effector leukocytes, however, are poorly defined and controversial, being at best weak and occurring at very high C3a concentrations. Here, we examined the effect of C3a upon mediator release from human basophils, with and without pretreatment with interleukin 3 (IL-3), a hematopoietic growth factor recently found to profoundly modify the basophil response to various cell agonists. In the absence of cytokines, C3a, even at a concentration of 1 microM, was ineffective or only weakly stimulatory for basophil mediator release. However, when basophils were pretreated with IL-3 at concentrations of only 0.01-1 unit/ml, they became responsive to C3a, releasing large amounts of histamine and also generating leukotrienes. Surprisingly, almost optimal effects occurred with even very low C3a concentrations (1 nM). Another hematopoietic growth factor, granulocyte/macrophage-colony-stimulating factor (GM-CSF), was also found to render basophils capable of responding to C3a, but the effect was weaker than that of IL-3. C3a-induced histamine release and leukotriene generation occurred rapidly in IL-3-primed cells, being complete after 0.5 and 2 min, respectively. The rapid and strong degranulation response, occurring at very low concentrations of C3a, suggests the presence of a high-affinity C3a receptor on basophils, which might be inducible by cytokines. Our results demonstrate that, depending on the presence of IL-3 or GM-CSF, C3a is a potent basophil activator, and such a phenomenon could be of relevance in various inflammatory processes, especially hypersensitivity reactions.

Regulation of the human autologous T cell proliferation by endogenously generated C5a

The immunomodulating role of endogenously synthesized C5 and subsequently generated C5a was studied in a serum-free human autologous mixed leukocyte reaction (AMLR) using either separated T and non-T cell populations or unfractionated mononuclear leukocytes of human peripheral blood. Monoclonal mouse IgG or Fab fragments against human C5/C5a were used as probes for the evaluation of the biological effects of C5a. The reduction of DNA synthesis after the addition of nanogram amounts of anti-C5/C5a mAb was dose-dependent, reaching maximum levels of 30-50%. Of special importance was the availability of a mAb that recognizes a neoepitope present on C5a and not on serum-derived C5. The demonstration of the specificity of its inhibitory effect suggests that C5 is synthesized under the in vitro conditions employed and that the subsequently generated C5a exerts biological effects on T cell proliferation.

Antiinflammatory peptides (antiflammins) inhibit synthesis of platelet-activating factor, neutrophil aggregation and chemotaxis, and intradermal inflammatory reactions

Synthetic peptides corresponding to the region of highest similarity between human lipocortin I and rabbit uteroglobin inhibit phospholipase A2 and show potent antiinflammatory activity on the carrageenan-induced rat footpad edema. The peptide HDMNKVLDL (antiflammin-2) inhibits the synthesis of platelet-activating factor (PAF) induced by TNF or phagocytosis in rat macrophages and human neutrophils, and by thrombin in vascular endothelial cells. The peptide MQMKKVLDS (antiflammin-1) is less inhibitory than antiflammin-2 for macrophages and not inhibitory for neutrophils after a 5-min preincubation. This finding suggests that antiflammin-1 is inactivated by neutrophils secretory products, possibly oxidizing agents. Synthesis of PAF is inhibited by antiflammin-2 without an appreciable lag, but this inhibition is reversed when neutrophils or macrophages are washed and incubated in fresh medium. Therefore, antiflammins must be continuously present to inhibit PAF synthesis. Antiflammins block activation of the acetyltransferase required for PAF synthesis, suggesting that this enzyme is another target for the inhibitory activity of antiflammins. These peptides inhibit neutrophil aggregation and chemotaxis induced by complement component C5a. Antiflammin-2 suppresses the increase in vascular permeability and the leukocyte infiltration induced in rats by an Arthus reaction or by intradermal injection of rTNF and C5a.

Resistance to the Sterne strain of B. anthracis: phagocytic cell responses of resistant and susceptible mice

Inflammatory responses were compared in vivo, and host phagocytic cell functions compared in vitro, of mice resistant (CBA/J) and susceptible (A/J) to lethal infection with the Sterne strain of Bacillus anthracis. Polymorphonuclear leukocyte (PMN) and macrophage responses at the initial site of infection were slower in A/J mice than in CBA/J mice. Whereas in A/J mice, the number of PMN ultimately responding to infection was equal to, or greater than, that in CBA/J mice, fewer macrophages accumulated. A/J mice failed to clear relatively low doses of the organisms and died. In vitro, chemotactic responses to both serum- and bacteria-derived attractants were similar for macrophages from A/J and CBA/J mice but were reduced for PMN from A/J mice. PMN and macrophages from the two mouse strains phagocytosed and killed spores in vitro to a similar extent, although killing by A/J PMN could be blocked by prior uptake of large numbers of killed spores. Thus susceptibility to lethal infection with Sterne strain correlated with the delayed influx (PMN) and reduced accumulation (macrophages) of phagocytes at the initial site of infection, but not with defective in vitro uptake or killing of spores.

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.

A simplified assay for the detection of C3a in human plasma employing a monoclonal antibody raised against denatured C3

A monoclonal antibody raised against SDS-denatured C3 was shown to react with both solid-phase C3a and unfragmented C3. However, in the fluid phase the antibody was found to bind only to C3a and not to native C3. These findings indicated that the antibody could be used in an assay to detect C3a in human EDTA-plasma without prior separation of C3a from native C3. A simple and rapid competition ELISA was developed which monitored soluble C3a. 200 microliter of C3a (8 ng) was absorbed to plastic wells over night at 4 degrees C. Thereafter, 50 microliter of sample and 50 microliter of constant amounts of monoclonal antibody conjugated with beta-galactosidase, were incubated for 60 min at 37 degrees C. After washing, the colour reaction was started by adding nitrophenyl-galactopyridine to the wells. The microtitre plate was incubated at 37 degrees C for 30 min and the staining intensity was quantified at 405 nm. The assay detected both C3a and C3ades arg. A strong correlation was obtained between the new technique and an RIA which used an acid precipitation step for the separation of C3a prior to the determination of C3a (r = 0.9). Significantly higher levels of C3a were detected both in plasma from patients with immune complexes (93 +/- 9 ng/ml; P less than 0.1) and in plasma from patients treated in blood oxygenators (140 +/- 19 ng/ml; P less than 0.05) than in plasma from normal subjects (74 +/- 4 ng/ml). The results were not affected by repeated freezing and thawing of the plasma samples.

The presence of the fifth component of complement (C5) in rabbit uterine flushings in relation to reproductive state

The fifth component of complement (C5) has been detected in rabbit uterine flushings. The C5 activity was evaluated using a hemolytic assay which requires the use of a C5-depleted reagent (C5D) prepared by affinity chromatography of normal human serum. In the absence of C5D, there was no hemolysis of antibody-sensitized erythrocytes by rabbit uterine flushings, whereas the presence of the C5D reagent resulted in substantial hemolysis. The amount of hemolysis was correlated with the reproductive state of the rabbits, with higher amounts of hemolysis (expressed per mg uterine flushing protein) evident in estrous rabbits. In addition, the amounts of immunoglobulin G (IgG), albumin, and total protein were also determined in the uterine flushings. The amounts of total protein and IgG were increased in day-6 pregnant animals compared to estrus while the amount of albumin per ml uterine flushing was not significantly changed.

Synergism between inflammatory mediators in vivo. Induction of airway hyperresponsiveness to C3a in the guinea pig

The complement anaphylatoxin C3a causes acute bronchoconstriction after intravenous infusion in guinea pigs. At doses of 6 to 600 micrograms/kg, the peptide causes significant and dose-dependent increases in resistance (RL) and decreases in dynamic compliance (Cdyn). Inhibition of serum carboxypeptidase N, the enzyme thought to be responsible for control of C3a activity in blood, by pretreating animals with DL-2-mercaptomethyl-3-guanidinoethylthiopropanoic acid (MGPA), resulted in a 4-fold potentiation of the response to 200 micrograms/kg C3a. Responses to lower C3a doses were not significantly affected. Pretreating animals intravenously with histamine prior to administration of C3a resulted in potentiation of C3a-induced bronchoconstriction at all doses tested, decreasing the amount of C3a required to double RL by 15-fold, from 110 to 7 micrograms/kg. The effect appears to be relatively specific for C3a since histamine pretreatment did not alter airway responsiveness to methacholine. Similarly, pretreatment with methacholine at a dose that caused an increase in RL comparable to histamine did not alter subsequent responses to C3a. Administration of capsaicin, under conditions that elicit acute release of endogenous substance P, also resulted in potentiation of C3a responses, to an extent similar to that observed for histamine. These data are consistent with an increase in pulmonary vascular permeability facilitating accessibility of C3a for its receptor to cause bronchoconstriction before it is inactivated by serum carboxypeptidase N. Further, when C3a is generated in the presence of histamine-and/or substance-P-releasing agents, it may be responsible for a greater fraction of altered pulmonary mechanics than has previously been appreciated.

Differential effects of the complement peptides, C5a and C5a des Arg on human basophil and lung mast cell histamine release

The ability of purified anaphylatoxins to induce human lung mast cell mediator release was investigated. In eight anti-IgE responsive (histamine release = 22 +/- 5%, mean +/- SEM) mast cell preparations of 1-96% purity, C5a and C5a des Arg (0.55 pg/ml to 55 micrograms/ml), failed to elicit or potentiate histamine release; lung fragments were similarly unresponsive. The related peptide C3a was also inactive. All anaphylatoxins failed to induce mast cell leukotriene C4 (LTC4) and prostaglandin D2 (PGD2) release. LTC4 release was also negligible from basophils where C5a was a potent histamine release stimulus. Supernatants from C5a-challenged mast cells remained fully active on basophils, excluding carboxypeptidase inactivation of C5a as an explanation for the lung mast cell results. In contrast to lung, skin mast cells were C5a-responsive (histamine release = 8 +/- 1%, at 55 micrograms/ml, n = 2). We conclude that C5a, though devoid of activity on the human lung mast cell, is a human basophil and skin mast cell secretagogue. These findings demonstrate significant organ-specific heterogeneity in mast cell responsiveness.

Preparation and characterization of monoclonal antibodies against the fifth component of rabbit complement (C5)

By immunizing mice genetically deficient in C5 we were able to obtain a group of monoclonal antibodies to rabbit C5 that cross-react with C5 from a wide variety of mammalian sera, including mouse. The specificity of the monoclonal antibodies was against native C5 and C5b but not C5a. The antibodies strongly inhibit the expression of C5 hemolytic activity. We suggest that these monoclonal antibodies will be useful for studying C5 as well as providing a way to selectively deplete C5 from plasma in vitro or in vivo.

A low molecular weight, heat-labile factor enhances neutrophil Fc receptor-mediated lysosomal enzyme release and phagocytosis

When exposed to solid-phase immune complexes, polymorphonuclear neutrophils (PMN) degranulate and release proteases capable of degrading the major structural macromolecules of the joint. Evidence indicates that the PMN response to such activators may be modified by factors present at the sites of inflammation. We have evaluated the effects of a low molecular weight factor present in synovial fluid from rheumatoid arthritis (RA) patients on Fc receptor-mediated PMN degranulation and phagocytosis. Synovial fluid samples from 11 RA patients were studied; 10 of them contained factor(s) which augmented phagocytosis and degranulation mediated through the Fc receptor. This factor(s) alone, however, did not initiate neutrophil degranulation: its MW is less than 10,000 daltons and it is unstable when heated to 56 degrees C. We also examined supernatants that were produced by coculturing adherent human mononuclear cells stimulated by IgG-coated sheep red blood cells with autologous nonadherent mononuclear cells. A factor(s) with properties similar to those found in the synovial fluids (i.e., heat-labile at 56 degrees C and capable of augmenting Fc receptor-mediated degranulation and phagocytosis) was found in the stimulated human mononuclear cell culture supernatants. Filtration studies indicated that the MW of this factor(s) is between 2,000 and 10,000 daltons. No such activity was detected in culture supernatants of unstimulated mononuclear cells. Production of the cytokine was blocked by cycloheximide, indicating that protein synthesis was necessary. This factor(s), by enhancing PMN degranulation, may augment PMN-mediated tissue destruction in diseases such as RA.

Anaphylotoxin levels following thermal injury

Following thermal injury, anaphylotoxins (C3a and C5a) are generated by complement activity. We measured C3a and C5a levels serially in 18 seriously burned patients (mean burn size = 37.9 per cent body surface area) over the initial 3 weeks following injury. Values for C3a were significantly increased when compared with normal controls, with maximum levels during the second week, while C5a levels were slightly elevated initially. These levels did not correlate with the extent of tissue injury, the development of septic complications or the clinical outcome. However, it appears likely that C3a and C5a may be responsible for some of the pathophysiological alterations observed following thermal injury.

The effects of histamine and serotonin on polymorphonuclear leukocyte accumulation in the rat

Histamine and serotonin were evaluated for their effects on rat polymorphonuclear leukocyte (PMN) accumulation in vivo and PMN migration in vitro. Both of the mediators inhibited the accumulation of PMNs when injected into the pleural cavity in a saline vehicle, and reduced the PMN content of the peripheral blood. Histamine also reduced the cellular influx when administered in combination with an intrapleural injection of carrageenan. Peripheral blood leukocytes removed from rats injected intrapleurally with histamine and carrageenan had a lesser chemotactic responsiveness compared with those removed from rats injected only with carrageenan. The effects of histamine in reducing PMN accumulation was abolished by treatment with cimetidine, an H2 antagonist, but not by treatment with chlorpheniramine, an H1 antagonist. These results suggest that a local release of histamine may play a role in reducing cellular infiltration into an inflammatory site.

A simplified method for purification of human C5a from citrated plasma

A simplified immunoadsorption technique has been developed to purify human C5a. the 11 000 Da glycopeptide produced by C5 convertase cleavage of the fifth component of complement. In this method, human C5 fragments, including C5a, are isolated from zymosan-activated plasma by affinity chromatography, concentrated on CM 52 cellulose, and then purified to homogeneity by gel filtration on Sephadex G-75 in phosphate-buffered saline. Human C5a prepared by this technique demonstrates characteristic immunochemical and biological activity. This method has also been adapted for the purification of 125I-C5a in phosphate-buffered saline. This technique offers a simplified approach to the purification of this important soluble mediator of inflammation.

Cardiopulmonary effects of cuprophane-activated plasma in the swine

Hemodialysis with cuprophane membrane is associated with complement activation and the formation of anaphylatoxins. Frequently, it is also complicated by various adverse reactions which include hypoxemia and hemodynamic changes. This study examined the cardiopulmonary effects of cuprophane membrane on experimental animals. To support the hypothesis that these effects were mediated by complement activation products, the effects of zymosan-activated plasma and C5adesArg challenge on the same variables were compared. We showed that intravenous infusion of autologous cuprophane-activated plasma into swine produced severe pulmonary hypertension, hypoxemia and leukopenia. In addition, mean systemic arterial pressure fluctuated and cardiac output fell. Infusion of zymosan-activated plasma produced similar results, suggesting that complement activation products are responsible for these alterations. Similar responses to porcine C5adesArg infusion suggested further that this polypeptide was the mediator. When swine were subjected to extracorporeal circulation using cuprophane membrane but without dialysis, acute pulmonary hypertension was seen preceding the onset of significant leukopenia. These data suggest that blood contact with cuprophane membrane produces both pulmonary and systemic hemodynamic changes, which are mediated by complement activation products. Furthermore, these products and/or other humoral factors, but not leukoagglutination, cause the pulmonary hypertension.

Species variability in the cardiovascular and hematologic effects of zymosan-activated plasma infusion

The anaphylatoxins have been implicated in the pathogenesis of endotoxin shock and the adult respiratory distress syndrome. Both endotoxin and zymosan activate the complement pathway. Because there are marked species differences in the cardiovascular and hematologic effects of endotoxin infusion, the purpose of this study was to compare the effects of zymosan-activated plasma (ZAP) infusion in dogs, sheep, and baboons. ZAP was infused (0.11 ml/kg/min for 60 min) into dogs (n = 5), baboons (n = 5), and sheep (n = 3). The infusion of ZAP resulted in significant changes in heart rate (HR) (P less than 0.03), mean arterial pressure (MAP) (P less than 0.002), pulmonary artery pressure (PAP) (P less than 0.004), cardiac index (CI) (P less than 0.034), and extra vascular lung water (EVLW) (P less than 0.001). A specific difference between the species' response to ZAP infusion was present when evaluating the effect of ZAP on MAP (P less than 0.02), HR (P less than 0.003). EVLW (P less than 0.001), platelet count (P less than 0.01), and white blood cell count (P less than 0.01). The main species differences in the changes in MAP, HR, and platelet count were an increase in MAP, decrease in HR, and decrease in platelet count that occurred in dogs. The species difference in the WBC count was the result of ZAP-induced neutropenia in sheep versus a leukocytosis in dogs. Unlike dogs and baboons, sheep developed an increase in EVLW. Like endotoxin, the cardiovascular and hematologic effects of ZAP infusion are species dependent.(ABSTRACT TRUNCATED AT 250 WORDS)

Biocompatibility of haemoperfusion

To evaluate the influence of haemoperfusion on haemodynamics, complement system, leucocyte and thrombocyte concentration, a controlled study was performed in three groups of five dogs each. During the first 30 min of haemoperfusion with columns containing cellulose-coated activated charcoal, a significant decrease of mean aortic pressure, cardiac output and stroke volume was observed, while heart rate and total systemic resistance decreased. A comparable phenomenon, although to a much lesser extent, was observed during perfusion using columns containing polystyrene resin. Perfusion with columns containing cellulose-coated activated charcoal caused a significant decrease in total haemolytic complement, indicating activation of the complement system. A significant decrease in the leucocyte and thrombocyte concentration due to sequestration of granulocytes and thrombocytes in the columns was observed during the first 30 min of perfusion in both groups. Pulmonary leucostasis, without decrease of arterial oxygen tension, occurred during perfusion with columns containing cellulose-coated activated charcoal. Both the simultaneous occurrence and the transient character of the haemodynamic changes, complement activation and sequestration of granulocytes and thrombocytes in the perfusion column suggest a relationship between these various changes. The results stress the importance of close monitoring of the haemodynamic parameters of the intoxicated patient, particularly during the early phase of haemoperfusion.

Inhibition of complement dependent experimental inflammation in human skin by different heparin fractions

The anticoagulant activity of heparin is dependent on its affinity for antithrombin III (AT III) and on its molecular weight. In contrast, heparin fractions differing in these respects are equally effective inhibitors of the human complement system in vitro. In this study we designed and evaluated a model to investigate the effects of different heparin fractions on a complement dependent inflammation. Locally administered heparin, in a dose-dependent manner, inhibited the flare, itch and wheal responses induced by intradermal injection of heat-aggregated human IgG (HAGG). These reactions were also inhibited by the antihistamine mepyramine, favouring the view that HAGG activates complement and that the observed inflammatory response is mediated by anaphylatoxin liberation of histamine. Similar cutaneous reactions induced by trypsin, which can generate C3a and C5a by proteolysis of C3 and C5, the histamine liberator compound 48/80 or histamine were inhibited by mepyramine but not by heparin. Thus it is strongly suggested that heparin inhibits the HAGG induced reactions by modulating the early pre-C3 steps of complement activation. On a weight basis heparin fractions differing in AT III-affinity or in average molecular weight (5,000 and 16,000 D) were equally potent modulators of the HAGG-induced inflammation. We conclude that heparin can inhibit an apparently complement-dependent inflammation irrespective of its AT III-affinity or of its size, and suggest that a heparin with low anticoagulant activity could be of value as a modulator of inflammation and should be useful in investigating the consequences of complement inhibition in inflammation.

Complement proteins and C3 anaphylatoxin in the tears of patients with conjunctivitis

Previous studies in our laboratory have demonstrated pollen-specific IgG antibodies in the tears of patients with vernal conjunctivitis (VC) and elevated tear IgG levels in patients with contact lens-induced giant papillary conjunctivitis (GPC). Tear secretions were examined for complement (C) proteins to determine the role of this effector system in the pathogenesis of these ocular disorders. The tears of VC (15) and GPC (10) patients with active disease had elevated tear levels of both C3 and factor B. By use of transferrin as a marker for the leakage of plasma proteins into the tears, most C3 was locally produced by the conjunctival tissues. Although immune complexes could not be detected in the tear secretions, increased levels of C3 des Arg were present in the tears that suggested complement activation with the generation of anaphylatoxins. These studies suggest that complement may be important in the inflammatory ocular process of VC and GPC and that the generation of anaphylatoxins (C3a), even by nonimmune mechanisms, may contribute to basophil and mast cell activation with the release of inflammatory mediators into the tear secretions.

Functional characteristics of leukotriene C4- and D4-metabolizing enzymes (gamma-glutamyl transpeptidase, dipeptidase) within human plasma

Several properties of the leukotriene C4- and leukotriene D4-metabolizing enzymes within human plasma were studied after fractionation of the plasma proteins using ammonium sulfate precipitation. Leukotriene D4-metabolizing enzymes were widely distributed among the fractions obtained. They showed different pH optima (pH 6.5, pH 7.0 and pH greater than or equal to 8.5) and revealed a different degree of thermal stability. The results indicate the presence of more than one enzyme in plasma which interacts with leukotriene D4. EDTA and L-cysteine inhibited the metabolism of leukotriene D4. Two leukotriene C4-metabolizing activities (gamma-glutamyl transpeptidases) differing in their molecular weights were detected after gel filtration. Their molecular weights were estimated to be Mr greater than or equal to 150 000 and Mr between 55 000 and 100 000.

Subnormal sensitivity of neutrophils to complement split product C5a in rheumatoid arthritis: relation to complement catabolism and disease extent

The capacity of circulating neutrophils for activation by complement was studied in outpatients with classical or definite rheumatoid arthritis during treatment with dextropropoxyphene only. Analysis of dose-response in the Boyden chamber assay of chemotaxis showed that sensitivity to the potent, complement derived anaphylatoxin, C5a, was markedly decreased, especially in those patients with few joints involved. In contrast, peak response to C5a was within the normal range. Increased complement 3c split products in plasma of the patients suggested involvement of complement cascade reactions. Subnormal sensitivity of neutrophils to phlogistic mediators released by complement may tend to limit their recruitment and potentially tissue destroying secretion locally in rheumatoid arthritis.

Studies of human C5a as a mediator of inflammation in normal human skin

C5a is an 11,000-D fragment of the fifth component of complement (C5) with potent anaphylatoxic and leukocyte chemotactic activities. C5a is believed to play an important role in the pathophysiology of certain skin disorders and systemic diseases with cutaneous manifestations. However, there is very little known about the in vivo reactivity of C5a in man. In this study we examined the effects of intradermal injections of human C5a in 17 normal volunteers. C5a was prepared by interacting highly purified human C5 with zymosan bound alternative pathway C5 convertase under conditions resulting in consumption of approximately 90% of the C5 substrate. C5a produced in this manner was chemotactic for human neutrophils and monocytes (0.5 X 10(-7) to 10(-9) M) and caused neutrophil aggregation and myeloperoxidase release (concentrations greater than or equal to 10(-10) M) in vitro. In vivo, C5a produced immediate wheal and flare reactions in all volunteers, and was active in doses as low as 1 ng (10(-13) mol). Intradermal testing with 20 ng of C5a in eight volunteers produced a maximal mean wheal of 11.75 mm (+/- 0.80 mm SEM) 20 min after anaphylatoxin injection, and a maximal mean erythema of 62.50 mm (+/- 3.27 mm SEM) 10 min after C5a administration. Reactions at C5a test sites were dose-related, associated with marked pruritus in some subjects, resolved without lesion formation, and were not associated with late phase reactions. In vivo testing revealed that human C5a was a more potent mediator of wheal and flare reactions than histamine, 48/80, human C3a, or morphine sulfate. Skin biopsies from eight volunteers 20 min after intradermal injection of 20 ng of C5a revealed a neutrophil-predominant perivascular infiltrate, endothelial cell edema, and sites of leukocytoclasis. Mast cell degranulation was observed on both light and electron microscopy of biopsies from C5a test sites. Although erythema at C5a injection sites was reduced by pretreating volunteers with hydroxyzine, whealing reactions and cellular infiltrates in biopsies were unaffected by this H1-antihistamine. Moderate doses of systemic corticosteroids did not alter clinical or histologic reactions at C5a injection sites in two volunteers. This study, using doses within the potential physiologic range of the anaphylatoxin, provides a comprehensive assessment of the effect of human C5a on normal human skin.

Effect of leukocyte activation on the formation of heterotypic tumor-cell aggregates in vitro

Walker tumor cell (1 x 10(6) cells/ml) were incubated at 37 degrees C in a stirred cuvette with rat peritoneal exudate cells (9 x 10(6) cells/ml) with or without the synthetic leukocyte chemo-attractant fMLP (2 x 10(6) M) or biologically active concentrations of the major endogenous chemo-attractant, C5a. Aggregation, induced by the chemo-attractants, was detected after 3 min by a platelet aggregometer and by studying cytocentrifuge preparations. The response was amplified in the presence of cytochalasin B (5 micrograms/ml). Tumor cells could be identified in the aggregates by their morphology or by autoradiography after labeling with 3H-thymidine. Although tumor cells were incorporated into the leukocyte aggregates, there was no appreciable change in the number of aggregates formed between tumor cells themselves. Levine III human breast tumor cells (1 x 10(6)/ml) in heparinized human blood were incorporated into leukocyte aggregates within 30 min of adding 50 U cobra venom factor to activate complement. Aggregation correlated with a decrease in complement hemolytic activity (CH50). The aggregation reaction was not cytotoxic to tumor cells when evaluated by Trypan blue exclusion or by 51Cr release. We conclude that local tumor cells can be incorporated into aggregates formed when leukocytes are stimulated by chemo-attractants. We postulate that intravascular activation of neutrophils might affect the localization of circulating tumor cells by incorporating them into microembolic cell aggregates and by causing damage to the pulmonary endothelium.

Fast deactivation of guinea-pig isolated ileum to C5adesArg: a possible cyclic AMP-dependent mechanism

The fast component of deactivation of guinea-pig isolated ileum to the spasmogenic action of the complement peptide C5adesArg was further differentiated from the slow component which had been previously analysed (Damerau et al., 1985a, b). Fast deactivation differs from the slow component in the following characteristics: (a) it is unspecific in that it is also induced by C3a, another complement peptide, (b) it depends on the spasmogenic effect of the peptides, and (c) it does not occur at 16 degrees C. In contrast to the slow component, in which the deactivation is thought to be caused by blockade of C5a receptors, fast deactivation seems to be due to a transient increase of intracellular cyclic AMP evoked by C5adesArg and C3a; it is prevented by GDP beta S (5 X 10(-4) M) which blocks activation of adenylate cyclase, and prolonged by agents which sustain cyclic AMP elevations, namely 5 X 10(-4) M theophylline and 5 X 10(-4) M) GTP gamma S.

Inulin-induced activation of factor B in whole serum: description of structural modifications in the Ba fragment

The investigation of inulin-induced conversion of human factor B in serum by isoelectrofocusing revealed physiological modifications in the primary structure of the Ba fragment. Evidence has been obtained that a nascent Ba, generated by the hydrolytic action of the D component on B in serum, was a short-lived product and that a fast release of carboxy-terminal arginine and lysine residues occurred involving a serum carboxypeptidase B enzyme.

Subnormal activation of phagocytes by complement in chronic inflammatory bowel disease? Neutrophil chemotaxis to complement split product C5a

The capacity of circulating phagocytes for activation by complement was investigated in consecutive, untreated cases of chronic inflammatory bowel disease. The major complement derived chemotactic factor, C5a, served as chemoattractant in dose response studies of neutrophil chemotaxis. A similar, significantly decreased sensitivity and peak response was revealed in patients with Crohn's disease and ulcerative colitis. This subnormal function of neutrophils could be shown even in cases of complete clinical remission. Chemotactic response to casein and spontaneous motility was within the normal range showing an unaffected basic cell function of neutrophils in the patients. The study shows a dysfunction of phagocytic cells, related to potentially important phlogistic mediators, in chronic inflammatory bowel disease.

Structure and function of the anaphylatoxins

Chemical and physical characterization of the anaphylatoxin molecules have provided a reasonably clear description of the architecture of these bioactive proteins. The primary structures of C3a, C4a, and C5a from man and from a number of animal species have been elucidated, and it is apparent that the three anaphylatoxins are genetically related. The anaphylatoxin protein chains very in length from 74 to 78 residues and no fewer than 30% of the residues are homologous when comparing C3a, C4a, and C5a within or between species. Synthetic peptide studies have been instrumental in identifying molecular features essential for the function of anaphylatoxins. Information gleaned from the structure-function studies with synthetic analogue peptides of the anaphylatoxins define putative "active sites" in these effector molecules. Linear sequences at the carboxy-terminus of C3a and C4a fulfill all of the criteria of an "active site," in that synthetic peptides of an identical sequence can mimic the biologic actions of the natural factors. In the case of human C3a, a crystallographic analysis has been performed and a three-dimensional structure was elucidated at the 3.2 A level. The crystalline structure of C3a provides valuable new information regarding the alpha helical regions and identifies the arrangement of intra-chain disulfide linkages. Taken together, the structural data now accumulated for anaphylatoxins permit molecular modelling of these proteins, designates favored conformational arrangements of the native structures, and specifically localizes the effector sites. Furthermore, elements at the essential active site have been defined with such precision that models are proposed detailing the exact nature of ligand interactions between anaphylatoxins and specific cellular receptors. Biologic characterization of the anaphylatoxins continues at a rapid pace and each advance provides a clearer view of the role of these humoral mediators in host defense. A variety of responses to anaphylatoxins are known to occur at the cellular level and are mediated in a hormone-like fashion. Diversity of action for these factors at the tissue level is readily explained by the numerous cell types stimulated by the anaphylatoxins. Cellular responses to the anaphylatoxins are perhaps the most easily defined and studied; however, tissue and systemic effects more accurately reflect the physiologic role of anaphylatoxins. Considerable progress has been made in understanding the mechanisms whereby anaphylatoxins mediate two major tissue effects, namely enhancement of vascular permeability and induction of smooth muscle contraction.(ABSTRACT TRUNCATED AT 400 WORDS)

Localized heat urticaria associated with a decrease in serum complement factor B (C3 proactivator)

A case of localized heat urticaria is reported in a 51-year-old woman who within a few minutes of contact with warm water developed erythema and swelling sharply localized to the heated area. After a hot bath urticarial lesions appeared over large areas of her body, accompanied by a feeling of weakness, but no other systemic symptoms. After challenge with heat by immersing her left arm in water heated to 42 degrees C, a rapid decrease of her serum complement level of factor B was demonstrated, suggesting that activation of an alternative complement pathway plays a role in this form of urticaria. Biopsies for immunofluorescent study of complement and immunoglobulins were negative at 30 and 180 min after heat challenge. The dermal fibres and endothelial cells of dermal vessels were capable, in vitro, of complement binding before and after exposure to heat.

Mechanisms of leukocyte regulation by complement-derived factors

Progress over the past five years has drawn attention to the fact that the anaplylatoxins are important factors in both leukocyte activation and regulation events. The C5 anaphylatoxin has been proposed to play major role in leukocyte aggregation and adherence phenomenon. Influences of C5a on the leukocyte may lead to clinical manifestations such as respiratory distress syndrome after trauma or postpump syndrome after cardiopulmonary bypass, both effects derived from leukocyte sequestration. Many other clinical conditions involving repeated transient sequestration of leukocytes, particularly in the pulmonary vasculature, may eventually be recognized as a complication of systemic complement activation. Dramatic pathologic changes observed in the lungs of animals exposed to either C3a or C5a emphasizes the potential damage that these factors may exert via cellular activation mechanisms (Huey et al., 1983). More recent evidence that the anaphylatoxins are potent immunoregulatory factors under in vitro conditions suggests a physiologic role for these humoral factors in nonspecific modulation of the immune response. It is an attractive hypothesis to suggest that once activated, complement is capable of relaying information to the cellular immune system via the anaphylatoxins. Other components of the complement system have long been known to exert regulatory influences on the immune system, and perhaps molecular description of such entities as the C3d-K fragment will serve to unravel this seemingly more complex effector system. In any case, as our understanding of both the chemical and biologic nature of factors derived from blood complement components advances, it has become apparent that a major function of complement may be to modulate the immune response. We have already demonstrated that these factors are selective both for cell type and for eliciting a variety of cellular responses. From this, one can infer that manipulation of the cellular events will eventually be possible. Hence a therapeutic value may be realized once involvement of these complement factors under in vivo conditions is better characterized.

Biologically active complement (C5)-derived peptides and their relevance to disease

In man and in most mammals, activation of the complement system via either the classical or the alternative pathway results in the generation of biologically active peptides. The most active peptides are C5a and C5a des Arg generated by cleavage of the alpha-chain of native C5. C5a is a potent anaphylatoxin and can induce human polymorphonuclear leukocytes to migrate in a directed fashion, to degranulate, to undergo a burst of oxidative metabolism and to aggregate. Upon generation C5a is converted in serum and plasma to C5a des Arg with loss of the noxious anaphylatoxin activity. C5a/C5a des Arg play important roles in host defenses against bacterial infections and possibly in the mediation of some pathologic lesions such as the leukocyte infiltration seen in the lungs during acute respiratory distress syndrome.

Inherited disorders of complement

Isolated complement component deficiencies are uncommon. Deficiencies of all eleven components and two inhibitors of the classical pathway have been described. Complete absence of the components of the alternative pathway has not been described. The consequences of a single defect in complement are often predictable from an understanding of the biologic activities associated with activation of the complement system. Deficiency of C1 esterase inhibitor gives rise to the disease, hereditary angioedema; deficiency of the early components of the classical pathway are associated with lupus erythematosus; C3 and C3 inactivator deficiencies with pyogenic infections; C5 dysfunction with Leiner's disease; deficiencies of the terminal components with recurrent Neisseria bacteremia; and C9 deficiency with normal health. The complement system and its associated biologic activities are reviewed. The present knowledge of the inherited complement deficiencies and associated diseases, with particular emphasis on the dermatologic manifestations, genetics, and diagnosis, is summarized.

A specific enzyme-linked immunosorbent assay (ELISA) for the determination of human C5a antigen

An enzyme-linked immunosorbent assay has been developed to detect human C5a antigen. This ELISA methodology has been shown to be a highly sensitive technique capable of detecting C5a antigen concentrations below 10 ng/ml. The microELISA technique used in this study is specific for human C5a and C5a des arg (C5a antigen) but not for human C5. Conditions to establish sensitivity and specificity are outlined in ths report.