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PubMed1976

Induction of platelet aggregation by the complement-derived peptides C3a and C5a.

The effect of two complement-derived peptides, hog serum C3a and C5a, on platelet aggregation in platelet-rich plasma and suspensions in Tyrode solution was investigated. 1. Guinea-pig platelets were aggregated by both C3a and C5a; the spasmogenically inactive product of C3a, C3ai, also induced aggregation. Threshold concentrations were in the range of 10(-6)--10(-9) M depending on the peptide and platelet preparation. 2. Cat platelets were aggregated by C5a (threshold concentrations 10(-7)--10(-8) M) but not by C3a. 3. Platelets from pig, rabbit and man were not aggregated by either of the two peptides in concentrations of up to 5 X 10(-6) M. 4. When C5a was administered repeatedly in subthreshold doses guinea-pig platelets became tachyphylactic to C5a but were still aggregable by C3a or ADP. Conversely, platelets desensitized to C3a still reacted to C5a or ADP. Tachyphylaxis towards C5a developed also when platelets were incubated with C5a in the absence of free Ca2+ under which condition they do not react. The tachyphylaxis in this case became evident after recalcification of the medium. The lack of cross-desensitization indicates that C3a and C5a react via different receptors. 5. C3a and C5a were injected i.v. into guinea pigs. Histological examination of the lungs revealed that some of the smaller vessels (20-30 mu in diameter) were occluded by platelet aggregates. In addition signs of severe acute emphysema were seen in animals treated with C5a, but only slight emphysema in C3a-treated animals. Intravenous injections of C3a into guinea pigs caused but weak respiratory distress and drowsiness and never killed an animal (at doses of up to 20 mg per kg body weight), whereas C5a caused the well-known severe respiratory failure and death already at doses of 0.03 mg/kg body weight.

Anaphylatoxins↗

PubMed1991

FUT-175 as a potent inhibitor of C5/C3 convertase activity for production of C5a and C3a.

We examined the inhibitory effect of FUT-175 on the C3/C5 convertase activity of the cobra venom factor-derived enzyme CVF,Bb by measuring C5b6-mediated reactive lysis of unsensitized guinea pig erythrocytes and by measuring directly the released fragments C3-des-Arg and C5a-des-Arg. In this study, we showed that the concentration of 4.5 X 10(-6) M of FUT-175 caused 50% inhibition of C5 convertase activity of CVF,Bb in reactive hemolysis assays, and that 4.0 X 10(-6) M FUT-175 caused 50% inhibition of the production of C3a and C5a generated by the C3/C5 convertase activity of CVF,Bb.

Animals↗

PubMed1996

Complement anaphylatoxin C3a and C5a formation in premature children with respiratory distress.

UNLABELLED: Premature children (n = 25) with respiratory distress (RD) were studied regarding complement activation and formation of the anaphylatoxins C3a and C5a. Blood samples were drawn on admission to the paediatric intensive care unit. In 18 of the patients RD was accompanied by other perinatal complications like pneumothorax or intracerebral haemorrhages. Seven of the premature children had RD without such complications. Preterm children with RD and with peri- and postnatal complications such as pneumothorax or intracerebral haemorrhage had increased concentrations in plasma of the anaphylatoxins C3a and C5a compared with preterm children with RD without these complications. There was a positive correlation between the plasma C3a and C5a concentrations in the preterm children. CONCLUSION: The present study indicates that isolated RD will appear without signs of complement activation and that complications like pneumothorax or intracerebral haemorrhages are associated with release of the anaphylatoxins C3a and C5a.

Analysis of Variance↗

PubMed1986

Chemotactic peptides modulate adherence of human polymorphonuclear leukocytes to monolayers of cultured endothelial cells.

We have used a new centrifugation assay to examine the effects of highly purified human C5a and C5a des Arg, as well as effects of N-formyl-methionyl-leucyl-phenylalanine (FMLP), on both the extent and strength of human polymorphonuclear leukocyte (PMN) adherence to monolayers of cultured human umbilical vein endothelial cells. At concentrations that were chemotactic for PMN, C5a (0.1 nM), C5a des Arg (5.0 nM), and FMLP (1.0 nM) significantly reduced the percentage of PMN that adhered to endothelial monolayers. Adherence also was reduced by C5a des Arg that was generated by incubating (37 degrees C, 30 min) fresh human serum with either zymosan or purified C5a. High concentrations of C5a (greater than 1.0 nM) and FMLP (greater than 50 nM) that diminished PMN chemotaxis significantly enhanced the percentage of PMN that adhered tightly to endothelial cells (adherent cells resisted a dislodgment force of 1200 X G). Tight adherence of PMN to endothelial cells also was increased by high concentrations of C5a that were added to human serum in which carboxypeptidase N activity was destroyed by heating (56 degrees C, 30 min), and by C5a that was generated by incubating (37 degrees C, 30 min) fresh human serum with zymosan in the presence of the carboxypeptidase N inhibitor, epsilon-aminocaproic acid. High concentrations of C5a des Arg (up to 80 nM) neither enhanced adherence of PMN to endothelial cells nor decreased PMN migration. Thus, a reciprocal relation exists between PMN migration and PMN adherence to endothelial cells in response to chemotactic factors. At concentrations that are chemotactic for human PMN, C5-derived peptides and FMLP reduce the adherence of PMN to endothelial monolayers. Only at concentrations that decrease PMN migration do C5a and FMLP augment PMN adherence.

Adult↗

PubMed2003

C5L2, a nonsignaling C5A binding protein.

C5a anaphylatoxin, a potent inflammatory mediator, is known to act through a specific G protein coupled receptor. However, some of the complex effects of C5a in vivo may not be explained solely by the deletion of the known receptor. Here, we show that an orphan receptor, identified as C5L2, is a high affinity C5a binding protein. Unlike the previously described C5aR, C5L2 is obligately uncoupled from heterotrimeric G proteins, in part by virtue of an amino acid alteration in the so-called DRY sequence at the end of the third transmembrane segment. Both human and murine C5L2 bear a leucine for arginine replacement at this site. C5L2, when transfected into several cell types, is weakly phosphorylated in transfected cells following binding of C5a but does not induce significant activation of MAP kinases, mediate calcium flux, or stimulate chemotaxis. Bone marrow cells from wild type respond robustly to C5a with induction and suppression of a number of inflammation related genes. In contrast, C5a receptor deficient mice, which bear C5L2 alone, do not respond to C5a with changes in gene transcription by microarray analyses. Biophysical properties of the C5L2, including slow ligand on and off rates, absence of internalization, and relatively high affinity for the C5a des Arg metabolite, suggest that this receptor may serve to modulate C5a biological functions in vivo. Finally, in contrast to previous reports, we find absolutely no interaction of C5L2 with other anaphylatoxins C3a and C4a.

Amino Acid Sequence↗

PubMed1994

Inactivation of human anaphylatoxin C5a and C5a des-Arg through cleavage by the plasminogen activator activity of a human fibrosarcoma cell line.

The HT-1080 human fibrosarcoma cell line exhibited a plasminogen-dependent ability to inactivate recombinant anaphylatoxin C5a or zymosan-activated serum. The inactivation was obtained at physiological levels of both plasminogen (2 microM) and C5a (1-5 nM). Inactivated C5a and zymosan-activated serum were no longer able to induce chemotaxis and degranulation of neutrophils. Inactivation of C5a paralleled the emergence of plasmin activity, assayed by cleavage of the synthetic substrate H-D-valyl-L-leucyl-L-lysine-p-nitroanilide (S-2251). Both C5a inactivation and S-2251 cleavage were inhibited by the plasmin inhibitor alpha 2-antiplasmin, the urokinase inhibitor amiloride, and by anti-urokinase antibodies. In a cell-free system, inactivation of C5a was shown to depend on the simultaneous presence of urokinase and plasminogen and was inhibited by alpha 2-antiplasmin and by anti-urokinase antibodies. SDS-polyacrylamide electrophoresis demonstrated the cleavage of C5a by the plasminogen activation system and inhibition of the cleavage by amiloride. Amino acid sequencing of the band corresponding to the C5a degradation product revealed that C5a was cleaved at positions Lys14-His15 and Arg40-Ile41; cleavage at position Arg40-Ile41 seemed to be responsible for the loss of activity. Since neoplastic cells extensively produce and exhibit plasminogen activator activity, the present observations suggest that plasminogen activation may, by inactivation of C5a, reduce the anti-tumor immune response and support the immunological escape phenomenon of tumors.

Amino Acid Sequence↗

PubMed1986

Anaphylatoxin C5a generation and dialysis-induced leukopenia with different hemodialyzer membranes.

Leukocyte counts and plasma C5a anaphylatoxin levels were studied during hemodialysis in patients using Cuprophan, polycarbonate and polyacrylonitrile membrane dialyzers. Cuprophan induced a marked leukopenia with significant plasma C5a generation. Polycarbonate promoted the same trend of changes in both parameters but significantly less pronounced, while polyacrylonitrile did not affect leukocyte counts nor plasma C5a levels. These data suggest that complement-derived C5a generation may be an important factor in the mechanism of hemodialysis-induced leukopenia.

Acrylic Resins↗

PubMed1996

Effects of interleukin (IL)-3 and IL-5 on human eosinophil degranulation induced by complement components C3a and C5a.

It is suggested that eosinophils (Eos) play an important role in the pathogenesis of bronchial asthma by releasing cytotoxic cationic eosinophil granule proteins and damaging bronchial epithelial cells. However, the exact nature of the actual inducer of eosinophil degranulation in vivo is unclear. We examined eosinophil cationic protein (ECP) release from human Eos in response to soluble agonists such as C5a, C3a, platelet-activating factor, and FMLP with or without interleukin (IL)-3 or IL-5 priming. Eosinophil degranulation induced by these soluble agonists required the pretreatment of Eos by cytochalasin B even in IL-3 priming. Among four agonists, C5a was the most effective stimulus of ECP release either with or without IL-5 priming. IL-3 and IL-5 remarkably enhanced ECP release in Eos triggered by C3a and C5a. The enhancement of ECP release by IL-3 and IL-5 occurred at 0.1-0.3 ng/ml and became maximal at 10-30 ng/ml, concentration-dependently. The enhancement of ECP release by cytokines became optimal at an interval of 10 min. Our data support the importance of complement components and cytokines in eosinophil degranulation in vivo.

Blood Proteins↗

PubMed1983

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.

Antibody Specificity↗

PubMed1991

A sensitive enzyme immunoassay for the quantitation of human C5a/C5a(desArg) anaphylatoxin using a monoclonal antibody with specificity for a neoepitope.

The direct quantitation of C5a/C5a(desArg) in human plasma was achieved by a specific and highly sensitive ELISA which is based on the neoepitope-specific monoclonal antibody C17/5. The error-prone removal of C5 from plasma prior to the assay is therefore not required. With a detection limit of 20 pg C5a/ml plasma, the sensitivity of this assay allowed to define normal ranges (1.94 +/- 1.49 ng C5a/nl, mean +/- SD) of C5a/C5a(desArg) in human blood plasma. This assay will also be applicable to the quantitation of C5a in specimens with low protein content where precipitation-based assays fail to accurately determine C5a. In addition, the mAb C17/5 turned out to efficiently block the binding of C5a/C5a (desArg) to its cellular receptor and therefore provides a valuable tool in the delineation of C5a effects in complex biologic systems in the presence of native C5, such as under in vivo conditions.

Adenosine Triphosphate↗

PubMed1986

Attachment of human C5a des Arg to its cochemotaxin is required for maximum expression of chemotactic activity.

The chemotactic activity of human C5a des Arg is enhanced significantly by an anionic polypeptide (cochemotaxin) in normal human serum and plasma. We have found that the cochemotaxin attaches to the oligosaccharide chain of native C5a des Arg to form a complex with potent chemotactic activity for human polymorphonuclear leukocytes. Although capable of enhancing the chemotactic activity of native C5a des Arg, the cochemotaxin had no effect on the chemotactic activity of either deglycosylated C5a des Arg, native C5a, or N-formyl-methionyl-leucyl-phenylalanine. Of the known components of the oligosaccharide chain, only sialic acid prevented enhancement by the cochemotaxin of the chemotactic activity exhibited by native C5a des Arg. Sialic acid also prevented the formation of C5a des Arg-cochemotaxin complexes, detected by acid polyacrylamide gel electrophoresis, molecular sieve chromatography on polyacrylamide gels, and sucrose density gradient ultracentrifugation.

Anaphylatoxins↗

PubMed1989

Inflammatory properties of human C5a and C5a des Arg/ in mast cell-depleted human skin.

C5a and its degradation product, C5a des Arg, elicit immediate cutaneous inflammatory reactions after intradermal injection. Histologically, these reactions are characterized by neutrophil-rich leukocytic infiltrates, leukocytoclasis, edema, and dermal mast cell degranulation. It has not been possible to assess in vivo the relative contributions of resident mast cells and circulating leukocytes to this reaction because the accumulation of leukocytes and degranulation of mast cells occur simultaneously after injection of these anaphylatoxins. To assess the role of mast cells in these inflammatory reactions, we have examined the reactivity of human skin selectively depleted of dermal mast cells by local corticosteroid treatment. Corticosteroid-treated skin became virtually devoid of dermal mast cells within 4-6 wk as assessed by light microscopy, immunofluorescence with fluorescein-conjugated avidin, or electron microscopy. Mast cell-depleted skin demonstrated normal vasopermeability and vasodilatory responsiveness to intradermal injection of histamine, but the reactivity of these sites to the mast cell secretagogue, morphine, was absent. Moreover, no clinical reactions were detectable in mast cell-depleted human skin after intradermal challenge with 50 ng of either C5a or C5a des Arg, despite the fact that biopsies of these sites revealed substantial, neutrophil-rich infiltrates. These infiltrates were qualitatively and quantitatively identical to C5a or C5a des Arg-induced infiltrates in mast cell replete skin. This experimental approach in vivo has allowed the independent analysis of the anaphylactogenic and chemoattractant activities of human C5a and C5a des Arg in human skin, demonstrated the importance of dermal mast cells in these clinical responses, and shown that leukocytes can accumulate at these injection sites directly in response to these mediators.

Adrenal Cortex Hormones↗

PubMed1986

Chemotactic activity for polymorphonuclear and mononuclear leukocytes in rheumatoid synovial fluids.

In order to why polymorphonuclear leukocytes (PMNs) are predominant and mononuclear leukocytes (MNLs) are few in rheumatoid synovial fluids, chemotactic factor(s) for PMNs and MNLs were studied in the synovial fluids of rheumatoid arthritis (RA-SF) and osteoarthritis (OA-SF) using both Boyden's and agarose methods. The RA-SF showed strong chemotactic activity for human peripheral blood PMNs compared with non-rheumatoid OA-SF. The chemotactic activity for PMNs was well correlated with the number of PMNs in RA-SF, suggesting that it was a natural mediator for PMN emigration into rheumatoid joint cavity. The major chemotactic factor for PMN in RA-SF was of apparent molecular weight of 14,000 and its activity was suppressed to less than 10 percent by anti-C5a antibody, but it failed to show any anaphylatoxin activity which was an attribute of C5a. It was, therefore, suggested to be C5a-like molecule but not C5a itself. The possibility that the factor may be a C5a des-Arg was discussed. On the contrary, the chemotactic activity for MNLs was not found neither in RA-SF nor OA-SF. These findings may explain the fact that PMNs are predominant in rheumatoid synovial fluids.

Arthritis, Rheumatoid↗

PubMed2006

Drusen complement components C3a and C5a promote choroidal neovascularization.

Age-related macular degeneration (AMD) is the leading cause of irreversible blindness in industrialized nations, affecting 30-50 million people worldwide. The earliest clinical hallmark of AMD is the presence of drusen, extracellular deposits that accumulate beneath the retinal pigmented epithelium. Although drusen nearly always precede and increase the risk of choroidal neovascularization (CNV), the late vision-threatening stage of AMD, it is unknown whether drusen contribute to the development of CNV. Both in patients with AMD and in a recently described mouse model of AMD, early subretinal pigmented epithelium deposition of complement components C3 and C5 occurs, suggesting a contributing role for these inflammatory proteins in the development of AMD. Here we provide evidence that bioactive fragments of these complement components (C3a and C5a) are present in drusen of patients with AMD, and that C3a and C5a induce VEGF expression in vitro and in vivo. Further, we demonstrate that C3a and C5a are generated early in the course of laser-induced CNV, an accelerated model of neovascular AMD driven by VEGF and recruitment of leukocytes into the choroid. We also show that genetic ablation of receptors for C3a or C5a reduces VEGF expression, leukocyte recruitment, and CNV formation after laser injury, and that antibody-mediated neutralization of C3a or C5a or pharmacological blockade of their receptors also reduces CNV. Collectively, these findings establish a mechanistic basis for the clinical observation that drusen predispose to CNV, revealing a role for immunological phenomena in angiogenesis and providing therapeutic targets for AMD.

Aged, 80 and over↗

PubMed1995

IgE-independent interleukin-4 expression and induction of a late phase of leukotriene C4 formation in human blood basophils.

T-helper cells can differentiate into at least two subtypes secreting distinct profiles of cytokines, Th1 and Th2, regulating immunoprotection and different immunopathologies. Interleukin-4 (IL-4) is both the product and the inducer of Th2 cells, raising the question whether IL-4 can be produced in response to antigen-independent stimuli. Here we show that human basophils produce IL-4 on stimulation with IL-3 and C5a or C5adesarg in similar amounts as induced by IgE-receptor-cross-linking. C5a-induced IL-4 production requires the presence of IL-3, with little effect of the sequence of stimuli addition. No "Th1-cytokines" (interferon-gamma and IL-2) and even no "Th2-cytokines" (IL-3, IL-5, IL-10, and granulocyte-macrophage colony-stimulating factor) are produced by basophils in response to either IgE-dependent or IgE-independent activation. The generation of leukotriene C4 (LTC4) is regulated in a similar manner. However, C5a induces a rapid, transient burst of leukotriene formation only if added after IL-3. Interestingly, upon prolonged culture, a late phase of continuous LTC4 production is observed, which also requires two signals (IL-3 and C5a), but rather depends on their continuous presence than on their sequence of action. These data describe an antigen-independent pathway of very restricted IL-4 expression. Thus, basophils must be considered as central immunoregulatory cells of the innate immune system. Furthermore, the results show that LTC4 can also be generated more continuously for many hours, a phenomenon that may be of particular importance in chornic allergic inflammation, such as asthma.

Basophils↗

PubMed1982

Cardiopulmonary bypass-induced complement activation. Evidence for C5a participation.

Plasma activity inducing polymorphonuclear neutrophils (PMN) aggregation, augmenting PMN adherence, plasma chemotactic activity as well as peripheral PMN count were estimated in patients during cardiopulmonary bypass. In the course of the surgical procedure the chemotactic activity and the activity inducing PMN aggregation were detected in plasma. The top of these two activities was always followed by the significant fall of the peripheral PMN count. The increase of the activity augmenting PMN adherence was observed in a part of cases, but when noticed, always preceded the maximum of the remaining evaluated activities.

Adult↗

PubMed1983

Acute lung inflammation induced in the rabbit by local instillation of 1-0-octadecyl-2-acetyl-sn-glyceryl-3-phosphorylcholine or of native platelet-activating factor.

The intratracheal instillation into rabbits of 1-0-octadecyl-2-acetyl-sn-glyceryl-3-phosphorylcholine (AGEPC) or native platelet-activating factor (PAF) was shown to induce a dose-dependent acute pulmonary inflammation characterized by accumulation of macrophages in the alveolar space, degenerative and necrotic changes of alveolar epithelium, and accumulation of polymorphonuclear leukocytes (PMNs) and platelets in the alveolar capillary lumens with degenerative changes of endothelial cells. Infiltration of alveolar septa by inflammatory cells and, in a later stage, pulmonary fibrosis were also observed. Intrabronchial instillation of lysoglyceryl ether phosphorylcholine (lyso-GEPC) produced no inflammatory changes or only mild ones. In comparison with acute inflammation induced by intratracheal instillation of C5a des Arg, which is mainly characterized by the presence of neutrophils, red blood cells, and fibrin in the alveolar space, AGEPC and native PAF seem to induce a more severe accumulation of macrophages in the alveolar space and septa and of platelet and PMNs in the lumens of alveolar capillaries. These results are compatible with the concept that during inflammatory reaction an intraalveolar release of PAF contributes to the development of pulmonary injury.

Acute Disease↗

PubMed1992

Characterization of the binding of Bolton-Hunter labeled [125I]C5a to human neutrophil, monocyte and U-937 cell membranes.

The fifth component of the complement cascade, C5a, was iodinated using the Bolton-Hunter reagent. Results from the present study, using the high affinity ligand, [125I]Bolton-Hunter-labeled C5a ([125I]BH-C5a), revealed a single binding site on membranes prepared from human neutrophils, U-937 cells and human monocytes. Saturation studies demonstrated Bmax values in these cells of 11.5, 47.3 and 16.6 fmol/10(6) cells, respectively. The C5a receptor demonstrated a very high affinity for [125I]BH-C5a of approximately 4 pM in each cell type. Competition studies using analogs of C5a generated a similar order of potency in each of the cell types of C5a > or = C5a(1-74), Ser66Ala > C5a(1-73) > C5a(1-69). These studies indicate that [125I]BH-C5a labels a similar receptor in neutrophil, U-937 cell and monocyte membranes. Furthermore, C5a(1-73) produced shallow inhibition curves in competition experiments in each cell type. Computer analysis of the binding data revealed two components of binding. When 10 nM unlabeled C5a was used to initiate dissociation of [125I]BH-C5a binding in neutrophil membranes, two binding components were observed. In addition, dissociation of [125I]BH-C5a binding by 10 nM unlabeled C5a in the presence of 1 mM GppNHp decreased the percentage of binding to the slowly dissociating, high affinity binding component from 84 to 58%. These results suggest that multiple states of the C5a receptor exist.

Binding, Competitive↗