Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Complement C5a”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 559 records · Page 31Linked to original sources
PubMed1998

Receptors for the anaphylatoxin C5a (CD88) on human mesangial cells.

In these studies, we determined whether there are receptors for the anaphylatoxin C5a (C5aR, CD88) on human mesangial cells (HMC). To prepare Abs to C5aR, we first synthesized an immunogenic peptide spanning residues 8-32 of the molecule, and this peptide was used to immunize rabbits. Anti-C5aR antiserum, but not preimmune serum, stained fixed and unfixed HMC in culture. By Western blotting anti-C5aR, Abs identified a 49.6-kDa protein in HMC. By reverse-transcription PCR, a cDNA product of 558 bp was amplified corresponding to the expected size of C5aR cDNA. A cDNA of the same size was amplified simultaneously from human PBL. Restriction mapping of the products amplified from HMC and from PBL gave restriction fragments of the same size. Incubation of HMC with increasing doses of C5a caused a progressive increase in the levels of the transcription factors activator protein-1 (AP-1) and cAMP response element binding protein (CREB), but C5a had no effect on the level of nuclear factor-kappaB (NF-kappaB). The effects of C5a on AP-1 were concentration and time dependent and peaked after 60 min. In contrast, the C5a metabolite C5adesArg had no significant effect on AP-1 levels. Preincubation of HMC with rabbit anti-C5aR antiserum inhibited partially the effect of C5a on AP-1. However, anti-C5aR Abs alone had no appreciable effects on AP-1. C5a caused a significant up-regulation of mRNA for the early response genes c-jun and c-fos on HMC. These results provide evidence for the presence of C5aR in adult HMC in culture and indicate that, after binding to C5aR, the anaphylatoxin C5a causes significant up-regulation of certain transcription factors and early response genes.

Adult↗
PubMed1999

Protein kinase C activation is required for cigarette smoke-enhanced C5a-mediated release of interleukin-8 in human bronchial epithelial cells.

Complement-derived anaphylatoxin C5a is a glycopolypeptide important in the regulation of inflammation. Previously, we have shown that C5a receptors (C5aR) are constitutively expressed on human bronchial epithelial cells (HBECs) grown in culture. We have also shown that the expression of C5aR is increased upon exposure of HBECs to 5% cigarette smoke extract (CSE), and that this subtoxic dose of CSE significantly enhances C5a-stimulated interleukin (IL)-8 release. To determine the intracellular signaling pathway of CSE + C5a-mediated IL-8 release, we assayed protein kinase C (PKC) activity of HBECs after exposing the cells to CSE and/or C5a. No increase in PKC activity was observed when HBECs were treated with 50 nM C5a for various times. However, PKC activity was increased by 2- to 3-fold in HBECs stimulated with 5% CSE for 1 h, as compared with cells incubated with medium only. No additional increase in PKC was observed when HBECs were treated with CSE and C5a together. When HBECs were pretreated with the PKC-specific inhibitor calphostin C (1 microM), no CSE-mediated PKC activation was observed. We then correlated PKC activation with IL-8 release in the same cells. Although HBECs required stimulation by both CSE and C5a to release maximal levels of IL-8, preincubation of CSE-stimulated HBECs with calphostin C inhibited IL-8 release by CSE + C5a. These results suggest that PKC activation by CSE alone does not result in IL-8 release, but that CSE-stimulated PKC activation is required for C5a-mediated IL-8 release from HBECs.

1-(5-Isoquinolinesulfonyl)-2-Methylpiperazine↗
PubMed1994

Gc globulin (vitamin D-binding protein) increases binding of low concentrations of C5a des Arg to human polymorphonuclear leukocytes: an explanation for its cochemotaxin activity.

The chemotactic activity of native human C5a des Arg is enhanced significantly by the normal serum and plasma protein Gc globulin (vitamin D-binding protein). Gc globulin attaches to sialic acid residues within the oligosaccharide chain of C5a des Arg to form a complex with potent chemotactic activity for human PMN. We investigated the mechanism whereby this phenomenon may occur and found that Gc globulin enhanced the binding of low concentrations of [125I]C5a des Arg to PMN, but had no effect on C5a-induced displacement of bound [125]C5a des Arg. Gc globulin bound to PMN, and probably acted as a C5a des Arg chaperon. Thus, it appears that Gc globulin, by complexing to C5a des Arg, increases the number of C5a des Arg molecules per unit of PMN membrane without affecting its affinity of binding. This phenomenon provides a plausible explanation for the enhancing effect of Gc globulin on the chemotactic activity of low concentrations of native human C5a des Arg.

Chemotaxis, Leukocyte↗
PubMed1989

1H nuclear magnetic resonance assignments and secondary structure of porcine C5ades Arg.

Sequence-specific assignments of the 1H nuclear magnetic resonance spectrum of porcine C5ades Arg are described. Assignments were facilitated by comparison of spectra obtained in H2O with partially exchanged spectra obtained in 2H2O. The sequence-specific assignments thus obtained were used to characterized the regular secondary structure in the protein, which is helical in the regions 2 to 11, 16 to 27, 35 to 41 and 45 to 64. The structure is very similar to that of human and bovine C5a.

Amino Acid Sequence↗
PubMed1994

Identification of a receptor-binding region in the core segment of the human anaphylatoxin C5a.

In order to identify regions of C5a that contribute to receptor binding and functional activity of the anaphylatoxin, a series of peptides was synthesized in which core segments have been attached to C-terminal segments via native peptidic or disulfide bonds. It has been found that residues Arg40 and Arg46 in the loop-3 region of the core induce a 1000-fold increase in the affinity of the disordered C-terminal segment of C5a. The results obtained from this work lead to the conclusion that the loop-3 region is most likely the core binding site of C5a.

Amino Acid Sequence↗
PubMed1992

Substituted 4,6-diaminoquinolines as inhibitors of C5a receptor binding.

The anaphylatoxin C5a is implicated in a number of inflammatory diseases. It is a highly cationic protein with 13 of 74 amino acids being either arginine or lysine. A search focusing on positively charged molecules, particularly amine-containing functionalities, led to the discovery of substituted 4,6-diaminoquinolines 1 [N,N'-bis(4-amino-2-methyl-6-quinolyl)urea] and 7 [6-N-(2-chlorocinnamoyl)-4,6-diamino-2-methylquinoline] as inhibitors of C5a receptor binding. These two compounds inhibited the binding of radiolabeled C5a to its receptor isolated from human neutrophils with IC50's = 3.3 and 12 micrograms/mL, respectively. Our efforts to enhance their potencies by chemical modification revealed a narrow profile of potency for effective C5a receptor binding inhibition.

Aminoquinolines↗
PubMed2001

Targeting complement in therapy.

With increasing evidence that complement activation significantly contributes to the pathogenesis of a large number of inflammatory diseases, strategies that interfere with its deleterious action have become a major focus in pharmacological research. Endogenous soluble complement inhibitors (C1 inhibitor, recombinant soluble complement receptor 1, antibodies) blocking key proteins of the cascade reaction, neutralizing the action of the complement-derived anaphylatoxin C5a, or interfering with complement receptor 3 (CR3, CD18/11b)-mediated adhesion of inflammatory cells to the vascular endothelium have successfully been tested in various animal models over the past years. Promising results consequently led to clinical trials. Furthermore, incorporation of membrane-bound complement regulators (decay-accelerating factor (CD55), membrane co-factor protein (CD46), CD59) in transgenic animals has provided a major step forward in protecting xenografts from hyperacute rejection. At the same time, the poor contribution of complement to the antitumor response, which is caused by multiple resistance mechanisms that hamper the efficacy of antibody-based tumor therapy, is increasingly recognized and requires pharmacologic intervention. First attempts have now been made to interfere with the resistance mechanisms, thereby improving complement-mediated tumor cell destruction.

Anaphylatoxins↗
PubMed2001

Distinct amplification of the C5a-receptor pathways in normodense and hypodense eosinophils of patients with atopic dermatitis.

In patients with atopic dermatitis two different types of blood eosinophils with distinct density can be isolated. The normodense cells represent the huge majority in count, whereas the hypodense eosinophils are characterized by higher effector activity. To understand the altered functional responsiveness of these two cell subtypes, the expression of C5a receptors as well as C5a-induced signal pathways and the production of reactive oxygen metabolites have been analyzed. Chemiluminescence measurements revealed significant higher production of reactive oxygen metabolites in hypodense eosinophils in comparison to normodense cells. However, no difference in the expression level of C5a receptors as well as in the C5a-induced Ca2+-transients between normodense and hypodense eosinophils were found. In contrast, hypodense eosinophils showed a significantly higher actin polymerization response and phosphatidylinositol 4,5 bisphosphate 3-kinase activation after stimulation with C5a than normodense eosinophils. Therefore, normodense and hypodense eosinophils from the blood of patients with atopic dermatitis are characterized by differential amplification of C5a-receptor signal pathways, which might explain the differences in their proinflammatory activity.

Actins↗
PubMed2002

The complement factor 5a receptor gene maps to murine chromosome 7.

Complement factor 5a (C5a) promotes local inflammation and is a potent chemoattractant for neutrophils and macrophages. We had an interest in C5a and its receptor, C5r1, because we previously identified C5a as a positional candidate gene for the quantitative trait locus Abhr2, which determines allergen-induced bronchial hyperresponsiveness in our murine model of asthma. To study the significance of C5r1 in our asthma model we first had to determine its genomic map location in mice. Genomic sequence surrounding murine C5r1 was analyzed for polymorphisms and two variable microsatellites were identified. These microsatellites were genotyped in A/J x (C3H/HeJ x A/J)F1 backcross mice (n = 355) and mapped in a panel of 164 markers spaced at approximately 10 cM intervals throughout the genome. Multipoint linkage analysis placed C5r1 on murine chromosome 7, 3.9 cM from the top of the linkage group. This map location has been previously identified as containing an additional quantitative trait locus for allergen-induced airway hyperresponsiveness, Abhr3, in this population of mice.

Animals↗
PubMed1997

Biological responses to endovascular treatment of abdominal aortic aneurysms.

PURPOSE: To review the findings of two studies investigating the apparent differences in inflammatory responses demonstrated in patients undergoing endovascular as opposed to classic surgical treatment of abdominal aortic aneurysms (AAAs). METHODS: The clinical course of seven patients treated with an endoluminal procedure (AAA-E) and seven patients undergoing conventional surgery (AAA-C) were compared (all men; ages 52 to 80 years). Blood samples were taken pre-, intra-, and postoperatively for up to 7 days. Inflammatory responses were assessed from measurement of interleukins (IL)-1 beta, IL-6, IL-8, and tumor necrosis factor (TNF-alpha); complement proteins C1q, C4, C5a, and terminal complement complexes, C5b-C9; and C-reactive proteins. Granulocyte and monocyte surface adhesion molecule expression was determined indirectly using a panel of monoclonal antibodies against CD11a, CD11b, CD11c, CD18, and L-selectin in donor white blood cells exposed to patient plasma. RESULTS: In six of the AAA-E patients, blood pressure decreases were recorded during the introduction of the device. Elevated body temperature was sustained for 2 to 5 days postoperatively in the AAA-E group. IL-6 levels were significantly higher in AAA-C patients (p < 0.0005), while TNF-alpha release was recorded in the AAA-E group only. CD11b, CD11c, and CD18 molecules on both granulocytes and monocytes were significantly upregulated 60 minutes after the endovascular procedure compared to conventional surgery. CONCLUSIONS: Endovascular aortic aneurysm repair apparently induces a significant inflammatory response, mainly involving TNF-alpha release, which differs from open AAA repair. These inflammatory responses, which may be related to the observed intraprocedural blood pressure decreases, could be caused by cell activation arising from intra-aneurysmal device manipulation.

Aged↗
PubMed2000

Induction of functional anaphylatoxin C5a receptors on hepatocytes by in vivo treatment of rats with IL-6.

In normal rat liver, anaphylatoxin C5a receptors (C5aR) are only expressed by nonparenchymal cells, mainly Kupffer cells and hepatic stellate cells, but not by parenchymal cells, i.e., hepatocytes (HC). Nevertheless, C5a stimulates glucose output by HC. This HC-specific defense reaction is induced indirectly via prostanoids secreted by the C5aR-expressing Kupffer cells and hepatic stellate cells. It is shown here that under inflammatory conditions simulated by in vivo treatment of rats with IL-6 C5aR mRNA and protein were induced in HC in a time-dependent manner. Maximal mRNA and protein expression were observed at 4-8 h and 8-10 h, respectively, after IL-6 injection. The newly expressed receptors were functional, because recombinant rat C5a significantly activated glycogen phosphorylase in HC isolated from IL-6-treated but not in HC from control rats. In perfused livers of IL-6-treated animals in contrast to control animals, recombinant rat C5a-induced glucose output was not impaired by inhibition of prostanoid synthesis and function with the cyclooxygenase inhibitor indomethacin and the thromboxane receptor antagonist daltroban. These results indicate that HC-specific defense reactions might be differently regulated under normal and inflammatory conditions as shown here for the indirect prostanoid-dependent or direct C5a-induced activation of hepatocellular glycogen phyosphorylase and glucose output in control or IL-6-treated rats, respectively.

Animals↗
PubMed1991

In vitro activation of human complement by nitrogen bubbles.

Complement activation may be responsible for some of the symptoms of decompression sickness. In the present study, complement activation was studied by exposing human sera with or without red blood cells to nitrogen bubbles. Nitrogen bubbles activated human complement as measured by generation of the fluid-phase, complement-split product C5a des Arg. In addition, we found that complement activation continued after exposure to bubbles was stopped. This continued complement activation may explain the failure of recompression treatment in some patients. Complement activation induced by nitrogen bubbles in human sera was enhanced when red cells were present. Red cells may be able to provide a stable membrane surface on which complement activation by bubbles can occur more efficiently. Complement activation by nitrogen bubbles in serum also led to the binding of activated C3 to red cells. Quantitation of bystander red-cell-bound C3d may allow the assessment of complement activation occurring by nitrogen bubbles in individuals undergoing decompression.

Complement Activation↗
PubMed1993

Regulation of eosinophil migration by adult T cell leukemia-derived factor.

Adult T cell leukemia-derived factor (ADF), originally defined as an IL-2 receptor alpha-chain (IL-2R alpha)/p55 (Tac) inducer, is a human thioredoxin homologue and has many cytokine-like activities. In this study, we examined the regulatory effect of ADF on eosinophil migration using human eosinophils and an eosinophilic subline of HL-60 human promyelocytic leukemia cells, YY-1. rADF induced migration of eosinophils from patients with hypereosinophilia, although rADF exhibited little activity on eosinophils from healthy donors. When human eosinophils were incubated with rADF (0.1-10 micrograms/ml) at 37 degrees C for 24 h, both chemotactic and chemokinetic activity of the complement anaphylatoxin peptide C5a on eosinophil migration was markedly enhanced in a dose-dependent manner. Similarly, this enhancing effect of rADF was observed in the migration assay using YY-1 cells. In contrast, rADF showed no modulation of migratory behavior of human eosinophils and YY-1 cells by IL-3, IL-5, nor granulocyte-macrophage colony-stimulating factor. Scatchard analysis of C5a receptors on YY-1 cells using 125I-C5a showed that rADF modulated neither the density nor the affinity of the cell membrane significantly. Furthermore, mutant ADF (mADF), which had no reducing activity, had no enhancing effect on C5a-induced eosinophil migration. These results indicate a possible involvement of ADF in the recruitment of eosinophils through redox regulation by a dithiol reductase activity.

Adult↗
PubMed1984

Amino-acid sequence and disulfide linkages of the anaphylatoxin, des-Arg omega-C5a, from porcine serum.

The primary structure of the porcine complement-derived peptide, des-Arg omega-C5a, has been analysed. Des-Arg omega-C5a is the natural secondary product of the activation fragment of the fifth component of complement, C5a, and represents a classical anaphylatoxin. The elaborated amino-acid sequence confirms the structure of porcine C5a proposed earlier by Gerard and Hugli, with one exception. Further, by end-group determination and sequencing of the unreduced core of des-Arg omega-C5a the position of its three disulfide bridges has been determined, now allowing insight into the tertiary structure of des-Arg omega-C5a.

Amino Acid Sequence↗
PubMed1991

Expression cloning of a receptor for C5a anaphylatoxin on differentiated HL-60 cells.

A cDNA clone encoding the human C5a anaphylatoxin receptor has been isolated by expression cloning from a CDM8 expression library prepared from mRNA of human myeloid HL-60 cells differentiated to the granulocyte phenotype with dibutyryladenosine cyclic monophosphate. The cDNA clone was able to transfer to COS-7 cells the capacity to specifically bind iodinated human recombinant C5a. The cDNA was 2.3 kb long, with an open reading frame encoding a 350-residue polypeptide. Cross-linking of iodinated C5a to the plasma membrane of transfected COS cells revealed a complex with an apparent molecular mass of 52-55 kDa, similar to that observed for the constitutively expressed receptor in differentiated HL-60 cells or human neutrophils. Although differentiated HL-60 cells display a single class of binding sites, with a dissociation constant of approximately 800-900 pM, the C5a-R cDNA, expressed in COS cells, generates both high-affinity (1.7 nM) and low-affinity (20-25 nM) receptors. Sequence comparison established that the degree of sequence identity between the C5a receptor and the N-formylpeptide receptor is 34%.

Amino Acid Sequence↗
PubMed1997

Internalization and recycling of the C5a anaphylatoxin receptor: evidence that the agonist-mediated internalization is modulated by phosphorylation of the C-terminal domain.

The C5a anaphylatoxin receptor is a member of the G protein-coupled receptor family involved in chemoattraction and activation of myeloid cells, as well as in host defence against infection by Pseudomonas aeruginosa. Upon challenge by C5a, the C5a receptor undergoes a rapid phosphorylation on serine residues in the carboxyl-terminal region. In this study, we used cells stably transfected with either the wild-type C5a receptor, or mutants affected in their capacity to be phosphorylated, to examine the role played by phosphorylation in the intracellular trafficking of the C5a receptor. Upon agonist binding, the wild-type receptor was rapidly internalized into endosomes that cluster near the nucleus after 10 minutes. Internalization of a non-phosphorylable mutant was severely impaired relative to wild-type receptor, whereas a mutant phos-phorylated on serine 327 and/or serine 338, showed a rate of internalization intermediate between that of wild-type receptor and that of the non-phosphorylable mutant. Under continuous exposure to C5a and in the absence of protein synthesis, the C5a receptor was maintained in a highly phosphorylated state but was not degraded. Confocal microscopy and ligand-binding studies indicated that internalized receptors were recycled to the plasma membrane. During this process, receptors were dephosphorylated with kinetics that correlated with the kinetics of receptor recovery on the cell surface. Altogether, our data suggest that phosphorylation plays a key role in the intracellular trafficking of the C5a receptor. Phosphoryl-ated receptors might be recognized by an adaptor protein that interacts with the endocytic machinery.

Amino Acid Sequence↗
PubMed1994

Generation of chimeric C5a/formyl peptide receptors: towards the identification of the human C5a receptor binding site.

We employed the polymerase chain reaction to produce a series of chimeric C5a/formyl peptide receptors. Chinese hamster ovary cells transfected with these constructs were tested for their ability to bind C5a. Substitution of three of the extracellular domains of the C5a receptor with the corresponding domains of the formyl peptide receptor abolished C5a binding, whilst replacement of the first extracellular loop of the C5a receptor with that of the formyl peptide receptor had little effect on the affinity of the receptor for C5a. We therefore conclude that this first outer loop of the C5a receptor does not participate in ligand binding, whilst involvement of the other extracellular domains of the receptor cannot be ruled out.

Animals↗