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PubMed1988

Anaphylatoxin-induced release of histamine from in vitro perfused guinea pig kidney.

The effect of porcine C5a des Arg and C3a, given as a bolus injection, in the isolated constant flow pump-perfused guinea-pig kidney was investigated. Only C5a des Arg showed activity which was manifested by a dose-dependent increase in perfusion pressure (PP, due to vasoconstriction) and histamine release. Although histamine release was substantial, it alone could not account for the increase in PP. The two more likely causes are a direct vasoconstrictor effect and the release of other mediators.

Anaphylatoxins↗

PubMed2004

Coronary surgery without cardiotomy suction and autotransfusion reduces the postoperative systemic inflammatory response.

BACKGROUND: Cardiotomy suction and autotransfusion of mediastinal shed blood may contribute to the inflammatory response after cardiac surgery. We compared inflammatory activation, myocardial injury, bleeding, and hemoglobin levels in patients undergoing coronary surgery with or without retransfusion of cardiotomy suction blood and mediastinal shed blood. METHODS: Twenty-nine patients were included in a prospective randomized study. Cardiotomy suction blood and mediastinal shed blood were either retransfused or discarded. Plasma concentrations of the cytokines tumor necrosis factor-alpha and interleukin-6 and complement factor C3a were measured preoperatively and 10 minutes, 2 hours, and 24 hours after cardiopulmonary bypass. C-reactive protein, erythrocyte sedimentation rate, troponin-T, and hemoglobin levels were analyzed preoperatively, and 24 and 48 hours after cardiopulmonary bypass. Postoperative bleeding the first 12 hours was registered. RESULTS: Baseline data did not differ between the groups. Plasma concentrations of tumor necrosis factor-alpha, interleukin-6, and C3a increased after surgery in both groups but significantly less in the group without cardiotomy suction and autotransfusion. The peak delta values in the no-retransfusion group was 36% (tumor necrosis factor-alpha), 47% (interleukin-6), and 75% (C3a) of the values in the retransfusion group. C-reactive protein, erythrocyte sedimentation rate, and troponin-T increased after surgery in both groups without intergroup differences. Postoperative bleeding and hemoglobin levels did not differ between the groups. No patient received homologous blood transfusion. CONCLUSIONS: Coronary surgery without retransfusion of cardiotomy suction blood and mediastinal shed blood reduces the postoperative systemic inflammatory response.

Adult↗

PubMed1987

The phenomenon of leukergy: induction and detection of leukocyte aggregation in whole human blood.

Leukocyte aggregation is involved in the generation of vascular damage during various inflammatory conditions. So far, in vitro leukocyte aggregation has been studied by mixing patients' plasma or serum with leukocytes of a normal donor in a platelet aggregometer. We evaluated the leukergy phenomenon, that is, the occurrence of aggregated leukocytes in peripheral blood of patients with inflammatory disorders, as an alternative tool to the former method. Leukocyte aggregation could be induced by zymosan-activated plasma, phorbol myristate acetate, and formyl-methionyl-leucyl-phenylalanine, as well as by the calcium ionophore A23187 in vitro in whole human blood. This aggregation was blocked by various lipoxygenase and cyclooxygenase pathway inhibitors. Leukergy was diagnosed in peripheral blood of patients with inflammatory disorders and was generally not associated with elevated concentrations of immune complexes, lactoferrin, C3a des Arg, or C5a des Arg. To the best of our knowledge, this is the first report on leukocyte aggregation studies performed in whole blood. Such study permits evaluation of the aggregation phenomena of leukocytes in their natural milieu. Furthermore, it is possible with this method to obtain direct visualization of leukocytic aggregates in the peripheral blood of patients. The significance of our results and their possible implications are discussed in light of the pertinent literature.

Adult↗

PubMed1983

Anaphylatoxins inhibit C2 production.

Anaphylatoxins C5a and C3a and their des Arg derivatives inhibited C2 production by mononuclear phagocytes. C5a and C5adesArg which were approximately equipotent (IC50 = 10(-10) mol/l) were more effective than C3a (IC50 = 5 X 10(-8) mol/l) which was approximately 10-20-fold more potent than C3adesArg IC50 = 5 X 10(-6) mol/l). Inhibition of C2 production was only reversed slightly by the addition of either indomethacin or ETYA to the cultures. Intracellular levels of cAMP, were increased by anaphylatoxins. The level of cAMP showed a good inverse correlation with C2 levels in the culture supernatants. The data suggest that the reduction in C2 production produced by anaphylatoxins may be mediated by an increase in intracellular cAMP.

Anaphylatoxins↗

PubMed1992

A preclinical screening test for modified hemoglobin to bridge the gap between animal safety studies and use in human.

The infusion of large amount of modified hemoglobin as blood substitute can potentially result in hypersensitivity and anaphylactic reactions, antibody-antigen reactions and others. Animal safety studies are important. However, response in animals may not be the same as in human. Before injecting into human, we may need to use an in-vitro screening procedure. One approach is based on testing the effects of modified Hb on complement activation (C3a) of human plasma. This paper describes this screening test. It also discusses how this may potentially be used. For instance using this to test for contamination from trace membrane fragments with blood group antigen or lipids, antibody-antigen complexes, endotoxin, trace fragments of microorganisms, residual amounts of some polymers, emulsifying agents, and organic solvents. There is also the possibility of obtaining plasma from a very large human population and analyse each of these to study the epidemiology of adverse reactions in different groups and types of patients.

Anaphylaxis↗

PubMed1994

Temporal patterns of hemodynamics, oxygen transport, cytokine activity, and complement activity in the development of adult respiratory distress syndrome after severe injury.

The aim of this study was to search for early inflammatory mediators in severely traumatized patients that could predict the occurrence of adult respiratory distress syndrome (ARDS). We measured sequential plasma levels of tumor necrosis factor (TNF), interleukin 1 (IL-1), interleukin 6 (IL-6), interleukin 8 (IL-8), complement fragment C3a, and endotoxin. In addition, we measured sequentially the values of hemodynamics, oxygen transport, and pulmonary function. The temporal patterns seen in the patients who developed ARDS were compared with those who did not. In the patients who developed ARDS, the first observed findings were low cardiac index (CI) and oxygen delivery (DO2) followed by progressive increases in IL-6, IL-8 and C3a levels, worsening of pulmonary function, and increases in hemodynamic values. The maximum values of IL-6, IL-8, and C3a occurred after the onset of ARDS. In the patients who did not develop ARDS, initial oxygen transport values were not low, the levels of IL-6, IL-8, and C3a decreased rapidly from their initial peaks, and there were no further increases in hemodynamic values. In both ARDS and nonARDS patients, no measurable quantities of TNF, IL-1, or endotoxin were found. We concluded that none of the mediators we measured reached their peaks before the onset of ARDS and none were found to be predictive of posttraumatic ARDS. However, these and other mediators may augment or intensify the development of ARDS.

Adult↗

PubMed2000

Inflammatory response after coronary revascularization with or without cardiopulmonary bypass.

BACKGROUND: We sought to investigate the effect of multiple coronary artery bypass grafting (CABG) with or without cardiopulmonary bypass (CPB) on the perioperative inflammatory response. METHODS: Sixty patients undergoing CABG were randomly assigned to one of two groups: (A) on pump with conventional CPB and cardioplegic arrest, and (B) off pump on the beating heart. Serum samples were collected for estimation of neutrophil elastase, interleukin 8 (IL-8), C3a, and C5a preoperatively and at 1, 4, 12, and 24 hours postoperatively. Furthermore, white blood cell (WBC), neutrophil, and monocyte counts were carried out preoperatively and at 1, 12, 36 and 60 hours postoperatively. Overall incidence of infection and perioperative clinical outcome were also recorded. RESULTS: The groups were similar in terms of age, weight, gender ratio, extent of coronary disease, left ventricular function, and number of grafts per patient. Neutrophil elastase concentration peaked early after CPB in the on-pump group, with a decline with time. Repeated-measures analysis of variance between groups and comparisons at each time point (modified Bonferroni) showed elastase concentrations were significantly higher in the on-pump than the off-pump group (both p < 0.0001). IL-8 increased significantly after surgery in the on-pump group, with no decline during the observation period (p = 0.01 vs off pump). C3a and C5a rose early after surgery in both groups when compared with baseline values. Postoperative WBC, neutrophil, and monocyte counts were significantly higher in the on-pump than the off-pump group (p < 0.01). Finally, the incidence of postoperative overall infections was significantly higher in the on-pump group (p < 0.0001 vs off pump). CONCLUSIONS: CABG on the beating heart is associated with a significant reduction in inflammatory response and postoperative infection when compared with conventional revascularization with CPB and cardioplegic arrest.

Aged↗

PubMed1986

Biochemistry and biology of anaphylatoxins.

The molecular architecture of anaphylatoxins has been explored on several levels. Primary, secondary and tertiary structural parameters that dictate function of the C3a, C4a and C5a molecules are being elucidated with the aid of comparative sequence analyses, physical measurements and organic syntheses. Although C3a, C4a and C5a are biologically distinct mediators, as defined by their unique receptor systems, a common genetic origin is apparent from conserved features in their primary structures. Evidence is now available which suggests that similarities in the folding pattern of the anaphylatoxins may dictate a concensus conformation for each factor. We have learned from synthetic peptide studies that the binding (e.g. effector) site in anaphylatoxin molecules exists as a linear sequence contained in the C-terminal portion of the polypeptide. What is also evident is that a preferred conformation is defined for the binding site requiring a proper side chain orientation for optimal bioactivity. It is proposed that folding of the native structure stabilizes this conformation at the binding site. The binding site in C3a contains the essential residues LGLAR folded in an irregular or pseudo-beta-turn and stabilized by an adjacent alpha-helical segment. It is proposed that the alpha-helical segment influences orientation of the side chain residues in the 'binding site'. A similar model is evolving for C5a based on synthetic C5a peptides that express both spasmogenic and chemotactic activities. This helix turn model promises to be representative of an essential structural feature that determines anaphylatoxin activity. We believe that these models contribute significantly to our understanding of the molecular relationships between structure and function for these humoral mediators of inflammation.

Amino Acid Sequence↗

PubMed1983

The active site of human C4a anaphylatoxin.

The human C4 activation peptide C4a has recently been shown to be biologically active and to share common tissue receptors with human C3a anaphylatoxin. Human C3a and C4a each induce contraction and cause cross-desensitization of isolated guinea-pig ileal strips. The essential active site of C3a is comprised in the model peptide containing the five COOH-terminal residues, Leu-Gly-Leu-Ala-Arg. The anaphylatoxic activities of the corresponding C4a pentapeptide, Ala-Gly-Leu-Gln-Arg, and several other synthetic peptides related to the COOH-terminal sequence of human C4a were examined. The C4a pentapeptide induced contraction of guinea-pig ileum at 1 X 10(-3) M and produced a wheal and flare reaction in human or guinea-pig skin when 2-5 mumols were injected intradermally. The corresponding C3a pentapeptide is 500-fold more active, since it induces contraction of guinea-pig ileum at 3-4 X 10(-6) M and only 4-10 nmole induce a visible skin reaction. Although the C4a pentapeptide is relatively inactive compared to the C3a pentapeptide, two analogs of these peptides, Leu-Gly-Leu-Gln-Arg and Ala-Gly-Leu-Ala-Arg, each exhibited significantly greater activity than Ala-Gly-Leu-Gln-Arg and each analog desensitized ileal smooth muscle towards contraction by either C3a or C4a. Thus it is a combination of two amino acid substitutions, the Ala for Leu-73 and Gln for Ala-76, in the COOH-terminal pentapeptide of C3a that accounts for the markedly reduced activity of C4a. The contribution of the COOH-terminal portion of C4a on its activity was further documented by examining the C4a octapeptide, Lys-Gly-Gln-Ala-Gly-Leu-Gln-Arg and a trialanyl analog, Ala-Ala-Ala-Ala-Gly-Leu-Gln-Arg. The C4a octapeptide, C4a (70-77), exhibited 5-fold greater biologic activity than the C4a pentapeptide, while the trialanyl analog was 40-fold more active. Anaphylatoxic activities of the C4a-(73-77) pentapeptide, C4a-(70-77) octapeptide, and the trialanyl octapeptide analog and their ability to specifically block the action of C3a and C4a on smooth muscle tissue support the conclusion that, as in C3a, the essential active site of C4a resides at its COOH terminus. Since C4a functions as an anaphylatoxin and significant quantities of this mediator may be generated in individuals with hereditary angioneurotic edema (HANE), the hypotheses that the kinin-like activity promoting edema in HANE patients is derived solely from component C2 and/or kininogens should be reappraised. The activities previously assigned to C4a and now confirmed by synthetic C4a analog peptides suggest that the kinin-like activity generated in HANE plasma may be derived in part from C4a.

Amino Acid Sequence↗

PubMedDate not supplied

Inflammatory response after implantation of a left ventricular assist device: comparison between the axial flow MicroMed DeBakey VAD and the pulsatile Novacor device.

The implantation of a ventricular assist device (VAD) is associated with a stimulation of the inflammatory system. We compared changes in the inflammatory response after implantation of a pulsatile Novacor left (L) VAD and the axial flow MicroMed DeBakey VAD. Six consecutive patients after implantation of a Novacor LVAD (NC) and six patients after implantation of a MicroMed DeBakey VAD (MD) were included in the investigation. Patients received LVADs for medically non treatable end-stage heart failure. Tumor necrosis factor alpha (TNF), C3a, C5a, interleukin 6 (IL-6), and neutrophil elastase were measured twice a week over a period of 3 months after implantation of the device. All tests were performed with an enzyme-linked immunosorbent assay. There was no significant difference in the clinical course of the two groups. All inflammatory parameters were elevated in both groups during the entire period of the investigation. There was no difference in TNF, polynuclear leukocyte elastase, or C3a levels between the two groups; however, IL-6 (NC: 23.6+/-37.6 pg/ml vs. MD: 63+/-114 pg/ml, p < 0.001) and C5a (NC: 708+/-352 microg/L vs. MD: 1,745+/-1,305 microg/L, p < 0.001) were increased significantly more in patients following implantation of the axial flow MicroMed DeBakey VAD. Compared with the pulsatile Novacor device, the implantation of the axial flow MicroMed DeBakey LVAD seems to be associated with an increased stimulation of one part of the inflammatory system. Further investigations are necessary for evaluation of the pathophysiologic mechanism and clinical implications of these findings.

Adult↗

PubMed1986

C3 activation by a new factor B-dependent enzyme detected in culture supernatant from guinea-pig peritoneal macrophages.

Culture supernatants (c.s.) collected from thioglycollate-elicited macrophages were concentrated and incubated with purified C3. In this reaction mixture loss of haemolytic C3 according to classical enzyme kinetics was observed. As revealed by SDS-PAGE, c.s.-catalysed fragmentation of the C3 alpha-chain occurred. The cleavage products were identified by size and function as C3a and C3b. The apparent molecular weight of this C3-activating enzyme in c.s. was approximately 220,000 according to ultracentrifugation studies. This large enzyme showed the following characteristics: it had no activity against C5; it was inhibited by EDTA; Mg2+ was required for its optimal function; its half-life at 37 degrees was approximately 35 min; it was completely inhibited by anti-B IgG. Thus, we were able to detect a C3-activating enzyme in c.s. containing B but differing otherwise from a preformed C3 convertase of the alternative pathway. The exact component composition of this new enzyme is under further investigation.

Animals↗

PubMed2004

Inflammatory response in an immunosuppressed patient with Wegener's granulomatosis.

BACKGROUND: The use of cardiopulmonary bypass (CPB) triggers a systemic inflammatory response (IR), but it is not known if a similar response occurs in an immunosuppressed patient with autoimmune disease. METHODS AND RESULTS: Observational study in a 56-year-old man receiving immunosuppressive therapy for Wegener's granulomatosis (WG) who underwent aortic valve replacement on CPB. The following markers for IR were studied in the perioperative period: C3a, C5a, neutrophil elastase (NE), interleukin eight (IL-8), white cell count (WCC) and C-reactive protein (CRP). Results were compared with published literature on the IR in patients undergoing coronary revascularisation with and without the use of CPB. All inflammatory markers increased in the perioperative period. The intensity of IR was markedly reduced compared to published literature for patients undergoing coronary revascularisation on CPB and the temporal patients and extend resembled that for off-pump. CONCLUSION: In a patient with WG on immunosuppressive therapy the CPB-related IR is reduced.

Aortic Valve Insufficiency↗

PubMed1999

Hemofiltrate from patients with severe sepsis and depressed left ventricular contractility contains cardiotoxic compounds.

Myocardial dysfunction due to sepsis is common in patients with multiple organ dysfunction syndrome and is believed to be produced by inflammatory mediators. Some of these mediators may be eliminated by continuous hemofiltration, which is a standard procedure in an ICU for renal replacement therapy. This study was designed to directly compare the effects of ultrafiltrates from patients with sepsis (UFs) with ultrafiltrates from healthy volunteers (UFh) in well-characterized cardiomyocyte culture systems. Isovolemic hemofiltration (filtration rate: 2 L/h, polyamide membrane) was performed during 12 hours in 5 patients with severe sepsis (Elebute Score >20) and simultaneously reduced left ventricular contractility (left ventricular stroke work index [LVSWI] <30 g m/m2) and in 5 healthy volunteers. Inflammatory mediator concentrations (interleukin [IL]-1beta, IL-6, IL-8, tumor necrosis factor [TNF] alpha, C3a, and C5a) were measured in plasma and ultrafiltrate samples taken shortly after the beginning of the hemofiltration procedure. Cell culture experiments were done comparing UFs with UFh by using spontaneously beating or electrically driven neonatal rat cardiomyocyte cultures. UFs contained significantly higher amounts of IL-1, IL-8, and C3a when compared to UFh. Simultaneously, UFs induced a decrease in the contraction frequency of electrically-stimulated cardiomyocytes, whereas UFh had no effect. The cardiotoxic effect could be reversed by the addition of a high concentration (2.4 mM) of Ca++. Hemofiltration did not alter parameters of cardiac performance during 12 hours in patients with sepsis. UFs induced significant cardiotoxic effects in rat cardiomyocytes, whereas UFh showed no cardiotoxicity. Contact of blood with the hemofiltration membrane did not induce activation of cardiotoxic mediators. Significantly higher filtration rates may be required to improve left ventricular contractility in patients with sepsis by hemofiltration.

Adult↗

PubMed1982

Modulation of the immune response by anaphylatoxin in the microenvironment of the interacting cells.

It was shown that the anaphylatoxins C3a and C5a can modulate in vitro immunological reactivities. C3a suppresses both the in vitro polyclonal antibody response and the specific antibody response to sheep red blood cells (SRBC) of both mouse spleen cells and human peripheral blood cells. The target cell in the mouse for C3a appears to be an Lyt-1+2- suppressor-inducer cell and macrophages appear not to be required. In contrast to C3a, C5a enhances in vitro responses of mice. Both the response to SRBC and the mixed lymphocyte reaction are enhanced by C5a. This enhancement appears to be through an Ia- macrophage that contains receptors for C5a. It appears that enhancement may be brought about by interleukin 1, which is released when Ia- macrophages are pulsed with C5a. It is suggested that these anaphylatoxins, when present in high concentrations in the microenvironment of the interacting cells of the immune system, play a dynamic role in the regulation of the immune response. Peptide fragments cleaved from the Fc portion of antibody, complexed with antigen in this microenvironment, may have a similar regulating role.

Animals↗

PubMed1994

The pharmacophore of the human C5a anaphylatoxin.

We have determined which amino acids contribute to the pharmacophore of human C5a, a potent inflammatory mediator. A systematic mutational analysis of this 74-amino acid protein was performed and the effects on the potency of receptor binding and of C5a-induced intracellular calcium ion mobilization were measured. This analysis included the construction of hybrids between C5a and the homologous but unreactive C3a protein and site-directed mutagenesis. Ten noncontiguous amino acids from the structurally well-defined 4-helix core domain (amino acids 1-63) and the C-terminal arginine-containing tripeptide were found to contribute to the pharmacophore of human C5a. The 10 mostly charged amino acids from the core domain generally made small incremental contributions toward binding affinity, some of which were independent. Substitutions of the C-terminal amino acid Arg 74 produced the largest single effect. We also found the connection between these 2 important regions to be unconstrained.

Alanine↗

PubMed2001

Detection of anaphylatoxin receptors on CD83+ dendritic cells derived from human skin.

Dendritic cells (DC) are recruited to sites of inflammation for the initiation of immune responses. As the anaphylatoxins C5a and C3a are important mediators of inflammation, we investigated the expression of their receptors (C3aR and C5aR) on human DC. DC were isolated from human skin or generated from purified blood monocytes and were identified by their expression of CD1a or CD83. Freshly isolated or cultured dermal CD1a+ and CD83+ DC bound anti-C5aR and anti-C3aR monoclonal antibodies (mAbs), as detected by flow cytometry. C5a induced calcium fluxes in dermal CD1a+ and CD83+ DC, which could be inhibited by C17/5, an anti-C5a mAb. C3a did not induce calcium fluxes in these cells. Anaphylatoxin receptor expression was down-regulated on dermal DC by adding tumour necrosis factor-alpha (TNF-alpha) to the culture medium. On CD1a+ CD83- cells generated from isolated blood monocytes by culture with 6.25 ng/ml of granulocyte-macrophage colony-stimulating factor (GM-CSF) and 125 U/ml of interleukin-4 (IL-4), expression of both C5aR and C3aR was observed. In these cells, both C5a and C3a induced calcium fluxes. After addition of TNF-alpha to the culture medium, the majority of the CD1a+ cells expressed CD83+. These cells - expressing a phenotype of 'mature DC' - down-regulated the expression of the anaphylatoxin receptors and lost their reactivity to the respective ligands. Our results demonstrate the expression of the anaphylatoxin receptors C5aR and C3aR on human skin-derived DC and blood-derived cells expressing the DC-associated membrane molecule, CD1a. Furthermore, the expression of anaphylatoxin receptors on CD83+ dermal DC is indicative of an intermediate stage of maturation of these cells, which was not observed on in vitro-differentiated CD83+ cells.

Antigens, CD↗

PubMed1997

Clinical characterization of Dicea a new cellulose membrane for haemodialysis.

A prospective randomised clinical study comparing the functional performance and biocompatibility of a new cellulose diacetate variant (Dicea) in which the degree of hydroxyl group substitution differs, with cellulose diacetate and low flux polysulfone incorporated into commercially produced hollow fiber hemodialysers with a surface area 1.5-1.6 m2 has been undertaken. All dialysers studied demonstrated clinically acceptable performance in terms of their small molecular removal characteristics, with minor statistical but not clinical differences. Use of both cellulose diacetate membranes but not low flux polysulfone resulted in a reduction in plasma beta(2) microglobulin levels. The membranes were impermeable to albumin, but showed some permeability to low molecular weight proteins. The average protein recovery from the dialysis fluid was 3105 mg for Dicea, 2913 mg for cellulose diacetate and 2842 mg for low flux polysulfone. For Dicea the white cell count by 15 minutes had declined to 68% of pre treatment value, compared with 59% and 86% for cellulose diacetate and low flux polysulfone. The differences between Dicea and cellulose diacetate were not significant, but both cellulose based membranes differed from low flux polysulfone (p = 0.0015). There was a strong evidence of differences between the membranes in respect of C5a and C5b-9 generation (p = 0.0001) but not for C3a (p = 0.16) furthermore the levels of C5b-9 generated during dialysis also showed a significant positive correlation compared to C5a for all membranes. (Pearson's correlation coefficient = 0.856, p = 0.0001). It is concluded that the two cellulose diacetate membranes are not identical, with the differences observed being a consequence of the degree of acetyl substitution, resulting in alteration of membrane structure and the method of sterilization. The clinical significance of these differences are difficult to characterize but the modification of the cellulose structure appears to be a promising method to improve the biocompatibility of cellulose membranes. The improved biocompatibility offered by this method still falls short of that achieved with low flux synthetic membranes such as Fresenius Polysulfone.

Adult↗

PubMed2005

Characterization of a C3a receptor in rainbow trout and Xenopus: the first identification of C3a receptors in nonmammalian species.

Virtually nothing is known about the structure, function, and evolutionary origins of the C3aR in nonmammalian species. Because C3aR and C5aR are thought to have arisen from the same common ancestor, the recent characterization of a C5aR in teleost fish implied the presence of a C3aR in this animal group. In this study we report the cloning of a trout cDNA encoding a 364-aa molecule (TC3aR) that shows a high degree of sequence homology and a strong phylogenetic relationship with mammalian C3aRs. Northern blotting demonstrated that TC3aR was expressed primarily in blood leukocytes. Flow cytometric analysis and immunofluorescence microscopy showed that Abs raised against TC3aR stained to a high degree all blood B lymphocytes and, to a lesser extent, all granulocytes. More importantly, these Abs inhibited trout C3a-mediated intracellular calcium mobilization in trout leukocytes. A fascinating structural feature of TC3aR is the lack of a significant portion of the second extracellular loop (ECL2). In all C3aR molecules characterized to date, the ECL2 is exceptionally large when compared with the same region of C5aR. However, the exact function of the extra portion of ECL2 is unknown. The lack of this segment in TC3aR suggests that the extra piece of ECL2 was not necessary for the interaction of the ancestral C3aR with its ligand. Our findings represent the first C3aR characterized in nonmammalian species and support the hypothesis that if C3aR and C5aR diverged from a common ancestor, this event occurred before the emergence of teleost fish.

Amino Acid Sequence↗