Functional analysis and quantification of the complement C3 derived anaphylatoxin C3a with a monoclonal antibody

The C3 fragment C3a belongs to the anaphylatoxins. It has immune regulatory activity and contributes to the pathogenesis of the adult respiratory distress syndrome (ARDS). The low molecular weight (9 kD) of C3a complicates the production of antibodies to C3a. We obtained a monoclonal antibody (designated H13) to human C3a. It reacts with C3a or C3a-desArg and with native C3 but not with C5 or C5a. In immunoblot analysis it reacts with the alpha- but not with beta-chain of C3 and binds to a protein with a mol. wt of about 10 kD present in zymosan-activated sera which is only marginally detectable in nonactivated serum and absent in plasma. H13 crossreacts with the analogous proteins of rabbit, guinea pig and sheep. H13 has the capacity to bind 125I-radiolabelled C3a efficiently but fails totally to react with 125I-C5a or with other C3 alpha-chain fragments. H13 blocks C3a functional activity. It markedly inhibits C3a-induced 3H-serotonin release from platelets in vitro and similarly inhibits the C3a-induced extravasation of Evans blue into the skin in vivo. H13 does not interfere with the haemolytic activity of C3. An ELISA system was established using H13 which permits quantification of C3a in sera of polytrauma patients. The antibody H13 should facilitate further functional analysis of C3a in experimental systems. It should be useful for quantification of C3a in diagnostic assays and also for application in immunopathology.

Guillain-Barré syndrome: activated complement components C3a and C5a in CSF

Plasma and spinal fluid levels of complement activation products C3a and C5a were quantitated by radioimmunoassay in a group of 16 patients suffering from acute monophasic Guillain-Barré syndrome (GBS). Median CSF levels of C3a (118 ng/ml) and of C5a (9.6 ng/ml) were significantly elevated when compared with samples from a control group of patients with noninflammatory neurologic diseases. Plasma concentrations of these anaphylotoxic peptides were not significantly different between the two populations. Our findings indicate that the complement system is activated in the CSF of patients with acute GBS. Complement activation products may contribute to the inflammatory changes observed in this disorder.

Trypanosoma lewisi: restriction of alternative complement pathway C3/C5 convertase activity

The rat parasite Trypanosoma lewisi was incubated in vitro with rat or human serum, washed, and extracted in detergent. Extracts were fractionated by electrophoresis in denaturing gels, transferred to nitrocellulose, allowed to renature, then immunoblotted with polyclonal antibodies to rat complement component C3 and human complement components C3, C5, and factor B. Molecules that reacted with these antibodies were detected in the extracts. Fragments of rat C3 were detected in extracts of parasites that had not been exposed to serum in vitro. Additional complement deposition occurred during in vitro incubations; human complement components deposited in vitro could be distinguished from rat components deposited in vivo. Complement deposition in vitro required magnesium ions and did not occur when heat inactivated serum was used. Components reacting with antibodies to human C3 included a group of bands with molecular weights higher than C3 alpha or beta chains. Blotting with affinity purified, chain specific antibodies demonstrated that a 68 kDa component on parasites is C3 beta and that a 44 kDa molecule is derived from C3 alpha. A 73 kDa component that was difficult to resolve from C3 beta is probably also a C3 alpha fragment. This suggests that an inactive iC3b-like molecule is present on parasites. Kinetic studies showed that cleavage of C3 alpha is rapid and that the amount of C3 alpha fragments and C3 beta on intact parasites reached a steady state after 15 min. When parasites were trypsinized prior to incubation in C5 or C6 deficient serum, the rate and extent of C3 and C5 deposition increased. Unprocessed C3 alpha' and C5 alpha' chains were detected. Trypsinized parasites were lysed by the alternative complement pathway in normal serum. Intact parasites could be lysed by complement in the presence of antibody. The data support our previous suggestion that trypsin sensitive surface proteins on intact T. lewisi limit alternative pathway activity by restricting C3/C5 convertase activity.

[Complement activation following head and brain trauma]

The prognosis for a patient with a severe head injury is dependent not only upon the location and the degree of this trauma, but also upon additional complications. For example, disseminated intravascular coagulation (DIC) can occur because of the thromboplastic activity of the damaged brain tissue that enters the circulation. The complement (C) system is activated by certain enzymes that cleave the clotting factors. Therefore, after head injuries we searched for C activation because it could result in the adult respiratory distress syndrome (ARDS). Patients and methods. We had two groups of patients: (1) 23 with large destruction and (2) 13 with little destruction of the brain tissue. Eighteen patients in group 1 and 8 in group 2 had isolated brain trauma. Blood samples were taken--upon arrival at the hospital and then 1, 3, 7, 12, 24, and 48 h later; after that we took weekly blood samples up to the completion of their treatment in the intensive care unit. We measured the total hemolytic serum C activity (CH50), activation of alternative pathway hemolysis (APH50), cleavage products C3a and C3d, and total protein. Furthermore, we studied the coagulation parameters of the extrinsic (prothrombin time) and intrinsic (partial thromboplastin time) pathways and fibrinogen content. From the patients records we extracted clinical parameters such as neurological status, intracranial pressure, pathological details on computer tomography hemoglobin and arterial-alveolar oxygen difference. Results. Figure 1 shows the different reactions of the C system in both groups: while patients of group 1 suffered from a decrease in total and alternative hemolytic activity, the other group increases in both parameters.(ABSTRACT TRUNCATED AT 250 WORDS)

Neutral endopeptidase-like enzyme controls the contractile activity of substance P in guinea pig lung

The responsiveness of isolated guinea pig lung parenchymal strips to substance P was enhanced by at least 100-fold in the presence of the endopeptidase inhibitors phosphoramidon (1 microM) or thiorphan (1 microM), but not with the converting enzyme inhibitor, captopril, or an inhibitor of serum carboxypeptidase N (both 1 microM). Responses of guinea pig tracheal rings to substance P were also markedly potentiated by phosphoramidon. The increase in tissue responsiveness by these inhibitors was relatively specific for substance P among several other spasmogenic peptides, including formyl-methionyl-leucyl-phenylalanine and the complement peptides C3a and C5a. The enhanced responses appear to result from a decrease in the rate of substance P degradation in the presence of neutral endopeptidase inhibitors. Specific binding of substance P to its receptor on bronchial membranes was increased by three- to fourfold in the presence of phosphoramidon. These data demonstrate an enhanced potential for substance P to contract lung tissues when degradation by a neutral endopeptidase-like enzyme is blocked.

Studies on the procurement of blood coagulation factor VIII in vitro studies on blood components prepared in half-strength citrate anticoagulant

The effect of replacing a standard citrate anticoagulant with one containing half the amount of citrate on the in vitro properties of components prepared from blood donations was investigated. This resulted in a significant improvement in factor VIII stability such that there was little loss during overnight storage, and this was reflected in the factor VIII yield in cryoprecipitate. The quality of cellular components in red cell units stored up to 35 days or platelet concentrates stored up to 7 days was not adversely affected. Although initial levels were similar to those in standard anticoagulant, the extent of fibrinopeptide A generation and complement C3 breakdown in red cell units stored for 35 days in half-strength citrate was somewhat increased.

Acute changes in C3a and C5a in an anaphylactoid reaction in hemodialysis patients

Blood sample were collected from both the arterial and venous lines of the patients undergoing hemodialysis using cuprophan membrane at several time intervals. Radioimmunoassay was then applied to measure the C3a and C5a levels. C3a levels from the arterial lines of patients undergoing uneventful hemodialysis were 463.2 +/- 51.3 ng/ml (mean +/- S.D.), 1112.9 +/- 109.9, 956.0 +/- 72.1, and 721.2 +/- 49.6 at 0, 15, 120 and 360 min, respectively. C5a levels did not change significantly during uneventful hemodialysis. C3a and C5a levels were significantly higher in the blood from the venous lines than those from the arterial lines, a finding indicating that complement activation via alternative pathway takes place in the dialyzer. C3a and C5a levels were markedly elevated in patients with anaphylactoid reaction. Reuses of dialyzers on the patients having a history of an anaphylactoid reaction during hemodialysis suppressed not only the rise of C3a levels, but also the recurrence of the reaction. From these findings, it is concluded that rises of C3a and C5a in the arterial lines of patients are causally related to the induction of anaphylactoid reaction during hemodialysis.

C5a and thromboxane generation associated with pulmonary vaso- and broncho-constriction during protamine reversal of heparin

The authors conducted a study in humans to determine the mediators associated with acute pulmonary vaso- and broncho-constriction occurring episodically with protamine reversal of heparin anticoagulation. Of 48 adult patients investigated prospectively after termination of cardiopulmonary bypass, two presented a sudden increase of airway pressure, acute pulmonary hypertension, and systemic hypotension 1-3 min after right atrial protamine injection. In these two subjects, plasma levels of C5a increased from 0.7 and 2.2 to 9.8 and 9.9 ng/ml, respectively, and thromboxane B2 increased from 0.26 and 0.34 to 7.5 and 16.2 ng/ml 1 minute after drug injection. A third subject not identified prospectively had an identical reaction and mediator profile (C5a, 10.2 ng/ml; TxB2, 18.6 ng/ml at 1 min). The plasma levels of these mediators were unchanged in the remaining patients (C5a, 0.7 +/- 1.1 [x +/- S.D.] to 0.6 +/- 0.9 ng/ml; TxB2, 0.16 +/- 0.12 to 0.15 +/- 0.07 ng/ml). Plasma histamine was not involved in this type of reaction, but increased from 0.7-10.4 ng/ml in a fourth patient who became hypotensive without acute pulmonary hypertension, bronchoconstriction, or elevation of C5a or TxB2. The authors' data indicate that the generation of high plasma levels of C5a anaphylatoxins and thromboxane is associated with pulmonary vaso- and broncho-constriction induced by protamine reversal of heparin in humans.

Ex vivo biocompatibility evaluation of a new modified cellulose membrane

To evaluate membrane biocompatibility, an open loop ex vivo model was designed simulating the hemodialysis procedure. Blood was withdrawn continuously from healthy nonuremic donors, heparinized, and pumped through a module containing the membrane to be studied. C3a generation in the module was determined at various time points comparing the cuprammonium cellulose (CC) membrane and four types of modified cellulose (MC) membrane, each with a different degree of hydroxyl (OH-) group substitution. In other studies, C3a generation in the ex vivo mode was compared with that during in vivo dialysis. In the ex vivo model, C3a generation with MC membranes was reduced by 70% compared with CC. However, within the MC group, the degree of C3a generation did not correlate with the degree of OH-group substitution. In vivo studies confirmed the reduced degree of C3a generation with the MC membrane compared with CC. Additionally, validation studies using the CC membrane showed excellent agreement between C3a generation during ex vivo perfusion and in vivo dialysis. The results suggest that a group of new MC membranes causes substantially less complement activation than the CC membrane but that the degree of complement activation with various subtypes of MC membranes is not related to the degree of OH-group substitution.

Is contact activation of the coagulation system involved in the genesis of the first-use syndrome?

A number of mechanisms have been thought to be involved in the pathogenesis of the first-use syndrome. These include IgE antibody-mediated response to ethylene oxide-related antigens, membrane activation of the alternative complement pathway, activation of tissue mast cells and basophils by materials released from the dialyzer into the circulation, and transfer of bacterial products through high flux dialyzer. However, the possible role of the activation of blood coagulation system and platelets during dialysis has not been considered. The present communication reviews the theoretical basis for a possible connection between dialysis-induced activation of platelets and coagulation system with the first-use syndrome. Although the available data concerning the activation of intrinsic coagulation pathway during dialysis are conflicting, there is no controversy as to the occurrence of platelet activation. It is suggested that biochemical events triggered by activation of these systems may in part contribute to the genesis of first-use syndrome.

Dialyzer membranes: effect of surface area and chemical modification of cellulose on complement and platelet activation

Using an ex vivo model, the effects of membrane composition and surface area on both the complement system (as reflected by plasma C3a levels) and platelets [as indicated by plasma concentrations of thromboxane B2 (TXB2) and platelet factor 4 (PF4)] were studied. In this model, polyacrylonitrile (PAN) was associated with less complement activation than cuprammonium cellulose (CC). A new "modified cellulose" (MC) membrane, in which a small number of the free hydroxyl groups on cellulose are substituted with a tertiary amino compound, was also associated with a low degree of complement activation, similar to that with PAN. However, the extent of hydroxyl group substitution in four MC membrane subtypes did not correlate with the reduction in complement activation. In studies using CC, the amount of generated C3a correlated with the membrane surface area, although the relationship was curvilinear. Plasma concentrations at the "dialyzer" outlet of TXB2 and PF4 were similar with CC, PAN, and MC. In studies with the MC subtypes, increasing the extent of hydroxyl group substitution paradoxically increased, albeit slightly, the amount of TXB2 generation. In studies with CC, a linear relationship between membrane surface area and TXB2 generation was found. The results suggest a dissociation between platelet and complement effects among different dialyzer membranes, and underline the importance of membrane surface area.

Complement activation during hemodialysis: laboratory evaluation of hemodialyzers

A laboratory method that facilitates delineation of the complement-activating characteristics of various dialyzers under defined conditions has been developed. Results obtained by circulating reconstituted human serum through these devices and measuring time-dependent production of both C3a and C5a antigens are entirely consistent with previous clinical observations. For example, the complement-activating potential of dialyzer membranes could be described as high (cuprammonium cellulose), moderate (cellulose acetate), or low (polycarbonate or polyacrylonitrile). Furthermore, these techniques provided the opportunity to identify membrane characteristics that are not readily defined by clinical studies alone. Specifically, membranes that transported and absorbed C5a antigen were readily identified by these methods. Additionally, laboratory evaluation provided the unique ability to define the efficiency of complement activation taking place on the membrane surface. Results of these investigations are compatible with a hypothetical model that not only describes the properties of a typical dialyzer membrane but may be generally applicable to other biomaterials as well.

Mast cells are not required for anaphylatoxin-induced ileal smooth muscle contraction

The complement-derived anaphylatoxin peptides, C3a and C5a, have long been considered to manifest their spasmogenic activities primarily through stimulation of mast cells. Although mast cells represent the major non-circulating repository for histamine, these cells also elaborate a number of additional, highly potent spasmogenic mediators derived from arachidonic acid. The same lipid mediators can be released by many other cell types. As a result, evaluation of the role of mast cells in anaphylatoxin-dependent responses cannot be based exclusively upon an analysis of the mediators released. We evaluated the role of mast cells in anaphylatoxin-induced ileal smooth muscle contractions by testing isolated segments of ileal tissues derived from genetically mast cell-deficient mice and their congenic normal (+/+) littermates. Isolated tissues from either congenic normal (+/+) or mast cell-deficient Sl/Sld mice responded similarly to acetylcholine, histamine, serotonin, prostaglandin E2, and the thromboxane A2 analog, U-46619. At 1 microgram/ml, histamine induced contractions of greater magnitude in tissues from mast cell-deficient animals; however, this mediator also desensitized the tissues to repeat challenge with histamine at the same concentration. C5a at 1 nM resulted in contractions equivalent to approximately 50% of the maximal KCl response; normal and mast cell-deficient tissues responded in a similar manner. C5a also released histamine from the normal mouse ileum, in addition to causing contraction of the tissues. C3a at 200 nM also produced similar contractile responses in both +/+ and S1/S1d tissues. These studies show that the anaphylatoxin peptides C3a and C5a are capable of contracting smooth muscle-containing tissues by a mechanism completely independent of mast cells. In addition, we also demonstrated that mast cell degranulation does not necessarily provoke ileal contraction. Thus compound 48/80, a mast cell degranulating agent unrelated to the anaphylatoxins, did not induce contractions in ileal tissues, even when used at concentrations as high as 100 micrograms/ml. Compound 48/80 did release histamine from the +/+ ileum, however, indicating that the agent was able to cause degranulation of ileal mast cells. Taken together, these data indicate that spasmogenic responses to anaphylatoxins (and possibly other agents) that are associated with mast cell degranulation need not necessarily require mast cell mediator release for their expression.

Psoriasis and leukocyte chemotaxis

Transepidermal migration of leukocytes, with resultant formation of microscopic or macroscopic sterile subcorneal pustules is a phenomenon characteristically noted in psoriasis and related sterile pustular dermatoses. It is natural to assume the presence of potent neutrophil chemotactic substances in the subcorneal portion of the lesional epidermis, because this location is the target of the in vivo leukocyte chemotaxis. In fact, crude psoriasis scale extracts show remarkably high neutrophil chemotactic and activating properties as compared with those of other non-psoriatic inflammatory dermatoses. We isolated a psoriatic leukotactic factor (PLF) having a molecular mass of around 12 kD, distinct from those common to other inflammatory changes involving the skin or those released by bacteria. Further analysis of PLF identified C5 cleavage fragments, together with other chemotactic peptides, such as those derived from monocytes. Likewise, potent low-molecular-mass chemotactic factors, including cell membrane lipid derived chemotactic factor, e.g. leukotriene B4, are also increased in psoriatic lesions, as in other nonpsoriatic inflammatory dermatoses. However, their activity to stimulate the generation of oxygen radicals in neutrophils was found to be much weaker than that of PLF. The peripheral blood leukocytes from active psoriatic patients show enhanced function in chemotaxis, phagocytosis, active oxygen production, and enzyme release; patients' sera contain substances such as anaphylatoxins that activate leukocyte function. Further research is required for clearer understanding of the series of events resulting in the leukocyte chemotaxis, as well as for the elucidation of the background immunoregulatory mechanisms.

Relationships of serum opsonins and complement in human experimental gingivitis

This study assessed the phagocytosis of polymorphonuclear neutrophils and the opsonic capacity of serum in experimental human gingivitis. Relationships were sought among these two measurements, clinical indices of gingivitis and complement-related opsonins. Measurements of chemiluminescence provided an index of phagocytosis and of opsonic capacity. Test group Plaque Index scores were higher than the control group on Days 7, 14, and 21, while the Gingival Index of the test group was elevated only on Day 21. Phagocytosis of test subjects' PMNs and opsonic capacity of their sera were no different from that of the controls'. Levels of C3 in both nonactivated and activated sera of the test group were significantly lower than that of the control group only on Day 14. In the test group, differences of per cent C3 conversion occurred between Days 14 and 21, and Plaque Index scores were inversely correlated with the order of per cent C3 data on these same days. Our results also indicate that complement contributes significantly to the serum opsonic capacity. The levels of developing plaque and subsequent gingival inflammation are apparently related to the degree of complement activation.

Relation between complement activation and susceptibility to decompression sickness

The consequences of complement activation and the symptoms of decompression sickness are similar. Consequently, the relation between the sensitivity of individuals to complement activation by air bubbles and their susceptibility to decompression sickness has been examined. Plasma samples from 34 individuals were incubated with air bubbles, and the concentration of the fluid phase metabolites of complement activation C3a, C4a, and C5a were measured with radioimmunoassays. It was found that both the anaphylatoxins C3a and C5a were produced by the presence of air bubbles but that the anaphylatoxin C4a was not. This finding indicates that air bubbles activate the complement system by the alternate pathway. One group of individuals was found to be particularly sensitive to complement activation by this pathway. They produced 3.3 times more C3a and 5.3 times more C5a in their plasma samples incubated with air bubbles as did the other group. Sixteen individuals were subjected to a series of pressure profiles that were severe enough to produce bubbles in their circulatory system that could be detected by Doppler ultrasonic monitoring. The group of individuals that had been identified as being more sensitive to complement activation by the alternate pathway was also found to be more susceptible to decompression sickness.

Plasma anaphylatoxin concentrations in inflammatory skin diseases

To study the possible involvement of the complement system in inflammatory skin disorders, we measured the concentrations of C3a and C4a anaphylatoxins in the peripheral blood of 148 patients with various inflammatory skin disorders and 48 healthy control subjects by radioimmunoassay. Significant increases in mean levels of both C3a and C4a anaphylatoxins were found in 59 patients with psoriasis. Remarkable increases in both C3a and C4a anaphylatoxins were also noted in some patients with leukocytoclastic vasculitis, urticarial vasculitis or unspecified toxic erythema. On the other hand, elevation of C4a alone was noted in a case of systemic lupus erythematosus. In contrast, using the mean of the normal control +/- 2 S.D., no significant anaphylatoxin elevation was found in 16 patients with pustulosis palmaris et plantaris, 7 with pityriasis rosea, 3 with erythema multiforme, and 3 with erythema nodosum or autoimmune bullous dermatoses.

Plasma levels of main granulocyte components in patients dialyzed with polycarbonate and cuprophan membranes

Plasma levels of granulocyte lactoferrin, granulocyte myeloperoxidase and granulocyte elastase in complex with alpha 1-proteinase inhibitor (E-alpha 1PI) were investigated in regular hemodialysis patients dialyzed with hollow-fiber dialyzers made from polycarbonate (FD 100) or cuprophan (GFS 120 H). Plasma levels of all these main granulocyte components increased significantly during hemodialysis. E-alpha 1PI levels were significantly higher in patients dialyzed with the polycarbonate compared with the cuprophan membrane, whereas the increases of myeloperoxidase and lactoferrin were not different for the two dialyzers. On the other hand, plasma C3a levels were higher in patients dialyzed with the cuprophan compared with the polycarbonate dialyzer. Therefore, granulocyte activation during hemodialysis does not necessarily need complement activation.

Non-IgE antibody mediated mechanisms in food allergy

Food sensitivity or intolerance is not necessarily based on the Type I allergic reaction. Non-IgE antibody reactions, complement-dependent reactions, enzyme deficiencies such as lactase and non-immunologic histamine release (such as with some sea foods) have been described. Even the detection of specific antibodies on their own does not necessarily indicate that a given symptom is due to that antibody. Food allergy nevertheless exists. It is important that those observers fortunate enough to see many cases document their observations carefully and eventually publish them for the education of their less fortunate colleagues. Is food allergy more common in infants and young children? What happens as they grow older? How often is atopic eczema due to food allergy? Why are some foods more likely to be implicated than others? Does a negative RAST result eliminate the diagnosis or a positive one confirm it? Until the answers to these and other questions are known, the mainstay of diagnosis will be the history, and that of treatment will be the elimination diet.

Anaphylatoxin-induced neutrophil chemotaxis and aggregation. Limited aggregation and specific desensitization induced by human C3a and synthetic C3a octapeptides

Human neutrophil aggregation was induced by highly purified human C3a and chemically synthetic COOH-terminal peptides of C3a (C3a-8R; Ala-Ala-Ala-Leu-Gly-Leu-Ala-Arg) in a dose-dependent manner and was 40% of human C5a-induced aggregation at each optimal concentration. In contrast to C5a and formyl-Met-Leu-Phe (f-MLP), C3a and C3a-8R showed little chemotactic activity. Specific desensitization of neutrophil aggregation was observed with C3a, C3a-8R, C5a and f-MLP, but not with C3a-des-Arg-7R, indicating that the human neutrophil has C3a-specific binding sites which are different from C5a and f-MLP receptors. An additive effect on aggregation was observed at suboptimal concentrations of C5a (1 X 10(-8) M) and C3a (1 X 10(-6) M) or C3a-8R (1 X 10(-5) M). These studies suggest that a subpopulation of human neutrophils have specific binding sites for C3a and C3a may work cooperatively with C5a during the process of neutrophil activation by increasing aggregation and lysosomal enzyme release.

Biocompatibility of artificial organs: an overview

Papers that are presented in this symposium on biocompatibility of foreign surfaces used in artificial organs are commented upon and set in an overall context of the biocompatibility of foreign surfaces to blood. A working formulation of the events comprising lack of biocompatibility of hemodialysis membranes to the complement system is given as a possible model to which other foreign surfaces may be compared.