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PubMed1995

Human polymorphonuclear leukocytes store large amounts of terminal complement components C7 and C6, which may be released on stimulation.

Secretion of the C factors C7, C6, and C3 by human polymorphonuclear leukocytes (PMNs) and PBMCs was studied by ELISA and immunoblot. The release of C7 and C6 by PMNs during 24 h of culture was 16-fold and 6-fold higher, respectively, than the C3 release, with median concentrations of 50.2 ng/ml, 18.3 ng/ml, and 3.1 ng/ml, respectively. In PBMC cultures, C release was considerably lower, and there was a different secretory pattern with a 6-fold higher release of C3 compared with C7 and C6. Stimulation with PMA led to a more rapid and complete secretion of the components to the culture media, whereas treatment with unopsonized Candida species did not affect the release. PMN release of C factors was not dependent on protein biosynthesis, and there was no indication of a selective uptake of C7 from serum as demonstrated by incubating PMNs from a subject with allotype C7 N in C7 M serum. Thus, the C components were probably produced by the PMNs or their bone marrow precursors before ex vivo culture. In cell lysates of freshly isolated cells, median C7, C6, and C3 contents of 1 x 10(7) PMNs were 149.7, 60.1, and 10.4 ng/ml, respectively, whereas the corresponding values for 1 x 10(7) PBMCs were 3.2, 2.6, and 14.6 ng/ml, respectively. The C6 and C7 were shown to incorporate into the terminal complement complex, and their molecular integrity was supported by identical m.w. to C6 and C7 present in normal serum. PMNs may represent a major source of C7 and C6 and may be more important than monocytes or macrophages in contributing terminal C components at a site of inflammation. This suggests a new role for the PMN as a C membrane attack modulator.

Candida↗
PubMed1994

Complement component C7. Assessment of in vivo synthesis after liver transplantation reveals that hepatocytes do not synthesize the majority of human C7.

C7 M/N typing, the determination of the allotypes of the recently described C7 M/N protein polymorphism, was conducted on serum samples from donors and recipients of 100 liver transplantations to determine whether the liver is the predominant site of in vivo synthesis of human complement protein C7. Twenty-one cases were informative as the recipient was transplanted with the liver obtained from a donor with a different C7 M/N allotype. The determination of the C7 levels and phenotypes of up to 10 post-transplantation (p.t.) samples revealed that there was at most only a 50% contribution of the transplanted liver toward the C7 M/N allotype at 2 to 3 wk p.t.; that influence decreased with time and was approximately 10% in the samples obtained later than 6 wk after transplantation. C7 is thus the only terminal complement component not predominantly synthesized by hepatocytes, which is compatible with the observation that C7 is not an acute phase reactant. The transient contribution of the donor phenotype appears to be attributable to cells of the mononuclear phagocyte lineage, Kupffer cells in particular that are replaced by cells of recipient origin. Various cells of that lineage that are known to synthesize C7 in vitro, therefore, contribute more toward the C7 concentration than previously anticipated. Enhanced local C7 synthesis at the site of inflammation might add further to the basic C7 level especially because C7 is often the limiting factor for terminal complement complex generation.

Complement C7↗
PubMed1995

Complement component C7 is a plasminogen-binding protein.

Ab deposition, whether by reaction with the specific Ag or by preformed immune complexes, is followed by activation and deposition of complement components. Tissue destruction is observed in the Ab- and complement-induced lesions. The proteolytic enzyme plasmin is thought to participate in the Ab- and complement-mediated organ pathology. Plasmin is generated from plasma-derived plasminogen by cell-derived plasminogen activators (PAs). Two types of PAs are known, urokinase-type PA (uPA) and tissue-type PA (tPA). We investigated whether the PA system and the complement system can interact to promote local plasmin generation. Among the terminal complement components C5b6, C7, C8, and C9, the nonenzymatic component C7 is a plasminogen-binding protein. Radioligand binding studies revealed that the isolated component, as well as C7 after its incorporation into the terminal complement complex C5b-9, can bind plasminogen. Binding was inhibited by the lysine analogues 6-aminohexanoic acid and tranexamic acid, implicating the lysine binding sites of plasminogen into the binding interaction. tPA-mediated plasminogen activation was enhanced in the presence of C7. Based on these findings, an interaction is proposed between the complement system and the plasminogen activator system; a mechanism that may focus plasmin activity to structures that have been tagged by Ab and complement deposition.

Autoradiography↗
PubMed2005

FcgammaRIIIb and complement component C7 codeficiency in a patient with recurrence of fulminant meningococcal septic shock.

Individuals with deficiencies of the late components of complement exhibit a susceptibility to the recurrence of meningococcal disease with a usually mild clinical presentation. We report the recurrence of fulminant meningococcal disease in a complement component C7-deficient patient. We found a total deficiency of FcgammaRIIIb on neutrophils, which could partially explain the unusually severe clinical presentation.

Adolescent↗
PubMed1982

Characterization of human complement components C6 and C7.

Human complement components C6 and C7 have been purified and characterized. Component C6 is a single-chain plasma protein of mol. wt 104,800 containing 3.8% carbohydrate and it has alanine as the amino terminal residue. Component C7 is a single-chain plasma protein of mol. wt 92,400 containing 6.4% carbohydrate and it has serine as the amino terminal residue. Primary sequence analysis failed to provide evidence of homology between these two proteins.

Amino Acid Sequence↗
PubMed1994

A novel human complement component C7 phenotype detected in South Africa and proposed designation of the allele as C7*10.

A novel allotype of the seventh component of human complement was detected by isoelectric focusing. The band pattern showed a complete band-interval shift towards the cathode compared with the C7 1 allotype and it is proposed that the designation is C7 10. The allele C7*10 segregated in two South African Cape Coloured families and had a gene frequency of 0.006. It was also found to segregate together with a C6*rare allele.

Alleles↗
PubMed1994

Paradoxical reconstitution of complement activity following plasma transfusion of an individual with deficiency of the seventh component of complement.

A subject deficient in the seventh component of complement (C7) was plasmapheresed with 660 ml C7-sufficient plasma. The expected reconstitution of C7 activity, followed by exponential decay, was not observed. During day 1, serum haemolytic C7 and total haemolytic complement were undetectable and C7 levels were very low by C7 ELISA. However, low levels of circulating fluid phase terminal complement complex (TCC) were detected. On day 2 about microgram C7/ml serum was detected and this rose to 6 micrograms/ml by day 17. Functional complement activity was also present. At day 28 the serum C7 and total haemolytic complement had dropped to pretransfusion levels. A low level of C5b6 was present in pretransfusion serum and this increased markedly immediately following transfusion when the patient's serum also acquired C7 consuming activity. Throughout the study low levels of anti-C7 antibodies were present but there was no evidence that antibody was directly responsible for the C7 consumption. Nevertheless antibody-antigen interactions could have generated circulating C5b6. C5b6 has been shown previously to have the capacity to inhibit C7 activity in vitro. Investigations of the C7 circulating on days 2-17 demonstrated normal molecular weight, functionally active C7. The donor sera and the recirculating C7 allotyped C7-1 by isoelectric focusing; however, the recirculating C7 showed additional weak bands with C7 functional activity, suggesting a possible genetic or acquired abnormality. Although the disappearance of C7 immediately post-transfusion may be explained by the presence of C5b6, there is no satisfactory explanation for the rising C7 levels on days 2-17 and we cannot exclude temporary C7 secretion by the patient.

Adult↗
PubMed1990

DNA polymorphism of the human complement component C7 gene in familial deficiencies.

A C7 cDNA probe detecting a TaqI restriction fragment length polymorphism has been used to examine the segregation of the "silent allele" (C7*Q0) in two familial deficiencies. Carrier diagnosis in healthy children is possible when both parents are heterozygotes. Only one of these two families was informative. The "silent allele" is linked to different TaqI alleles in both families. This suggests that at least two different C7*Q0 alleles are present in our population. This paper gives a protocol for genetic studies of hereditary traits in which the C7 gene and other genes tightly linked to it are involved.

Alleles↗
PubMed1986

[Meningococcal meningitis in isolated familial deficiency of the 7th complement component, C7].

Based on recent reports of a hereditary disposition to neisserial infections in subjects deficient in one of the hemolytic components of the complement system, we have studied 2 siblings who had had "sporadic" meningococcal meningitis in 1976 and 1977 respectively. In neither was C7 detectable, which suggested a homozygous deficiency. The two children of the first propositus showed values compatible with a heterozygous state.

Adult↗
PubMed1988

The heparin binding domain of S-protein/vitronectin binds to complement components C7, C8, and C9 and perforin from cytolytic T-cells and inhibits their lytic activities.

S-Protein/vitronectin is a serum glycoprotein that inhibits the lytic activity of the membrane attack complex of complement, i.e., of the complex including the proteins C5b, C6, C7, C8, and C9n. We show that intact S-protein/vitronectin or its cyanogen bromide generated fragments also inhibit the hemolysis mediated by perforin from cytotoxic T-cells at 45 and 11 microM, respectively. The glycosaminoglycan binding site of S-protein/vitronectin is responsible for the inhibition, since a synthetic peptide corresponding to a part of this highly basic domain (amino acid residues 348-360) inhibits complement- as well as perforin-mediated cytolysis. In the case of C9, the synthetic peptide binds to the acidic residues occurring in its N-terminal cysteine-rich domain (residues 101-111). Antibodies raised against this particular segment react 25-fold better with the polymerized form of C9 as compared with its monomeric form, indicating that this site becomes exposed only upon the hydrophilic-amphiphilic transition of C9. Since the cysteine-rich domain of C9 has been shown to be highly conserved in C6, C7, and C8 as well as in perforin, the inhibition of the lytic activities of these molecules by S-protein/vitronectin or by peptides corresponding to its heparin binding site may be explained by a similar mechanism.

Animals↗
PubMed2006

Cutaneous immune responses in the common carp detected using transcript analysis.

In order to detect new immune-related genes in common carp (Cyprinus carpio L.) challenged by an ectoparasitic infection, two cDNA libraries were constructed from carp skin sampled at 3 and 72h after infection with Ichthyophthirius multifiliis. In a total of 3500 expressed sequence tags (ESTs) we identified 82 orthologues of genes of immune relevance previously described in other organisms. Of these, 61 have never been described before in C. carpio, thus shedding light on some key components of the defence mechanisms of this species. Among the newly described genes, full-length molecules of prostaglandin D2 synthase (PGDS), the CC chemokine molecule SCYA103, and a second gene for the carp beta(2)-microglobulin (beta(2)m), beta(2)m-2, were described. Transcript amounts of the genes PGDS, interferon (IFN), SCYA103, complement factor 7 (C7), complement factor P (FP), complement factor D (FD) and beta(2)m-2 were evaluated by real-time quantitative PCR (RQ-PCR). Samples from skin, blood and liver from fish challenged with I. multifiliis were taken at 3, 12, 24, 36 and 48h post infection. Higher expression levels of most of these transcripts were observed in skin from uninfected fish, compared to the transcript levels detected in blood and liver from the same animals. Also, there was significant down-regulation of the genes PGDS and beta(2)m-2 in skin, whilst significant up-regulation was observed for the C7 and SCYA103 genes in liver of fish infected with the parasite. These results confirm the active role of fish skin in the immune response against infections, acting as an important site of expression of immune-related molecules.

Amino Acid Sequence↗
PubMed2005

Recombinant C345C and factor I modules of complement components C5 and C7 inhibit C7 incorporation into the complement membrane attack complex.

Complement component C5 binds to components C6 and C7 in reversible reactions that are distinct from the essentially nonreversible associations that form during assembly of the complement membrane attack complex (MAC). We previously reported that the approximately 150-aa residue C345C domain (also known as NTR) of C5 mediates these reversible reactions, and that the corresponding recombinant module (rC5-C345C) binds directly to the tandem pair of approximately 75-residue factor I modules from C7 (C7-FIMs). We suggested from these and other observations that binding of the C345C module of C5 to the FIMs of C7, but not C6, is also essential for MAC assembly itself. The present report describes a novel method for assembling a complex that appears to closely resemble the MAC on the sensor chip of a surface plasmon resonance instrument using the complement-reactive lysis mechanism. This method provides the ability to monitor individually the incorporation of C7, C8, and C9 into the complex. Using this method, we found that C7 binds to surface-bound C5b,6 with a K(d) of approximately 3 pM, and that micromolar concentrations of either rC5-C345C or rC7-FIMs inhibit this early step in MAC formation. We also found that similar concentrations of either module inhibited complement-mediated erythrocyte lysis by both the reactive lysis and classical pathway mechanisms. These results demonstrate that the interaction between the C345C domain of C5 and the FIMs of C7, which mediates reversible binding of C5 to C7 in solution, also plays an essential role in MAC formation and complement lytic activity.

Amino Acid Motifs↗
PubMed2006

Two mutations of the C7 gene, c.1424G > A and c.281-1G > T, in two Korean families.

Complement C7 deficiency is associated with increased susceptibility to meningococcal infection. The genetic alterations of C7 deficiency are known to be sporadic and heterogeneous worldwide. We investigated molecular basis of C7 deficiency in two unrelated Korean families, in which the index cases suffered from meningococcal meningitis. Exon-specific PCR and direct sequencing of the C7 gene revealed two different mutations: c.1424G > A and c.281-1G > T. In family 1, index case and her brother revealed a homozygous mis-sense mutation (c.1424G > A), a novel mutation, which results in the change of cysteine to tyrosine (C475Y) in exon 10. Index case in family 2 was found to be a homozygote carrying point mutation at the 3' splice acceptor site of intron 3 (c.281-1G > T), which was previously reported in a Korean C7-deficient subject.

Adolescent↗
PubMed1996

A new intronic polymorphism in the C7 gene 36 bp from the common expressed C7 M/N polymorphism.

We report a new polymorphism in the complement C7 gene that results from an A-C transversion in intron 12, 27 bp upstream of exon 13 (C712.-27) and 36 bp upstream of the point mutation that underlies the C7 M/N antigenic polymorphism. The C7 12.-27 polymorphism subdivides C7 M haplotypes, but not C7 N. It also sheds light on the evolution of the various types of deficiency genes at the adjacent C6 locus.

Base Sequence↗
PubMed1989

Complete primary structure and functional characterization of the sixth component of the human complement system. Identification of the C5b-binding domain in complement C6.

Complement C6 is one of five plasma proteins that are incorporated into the lytic terminal complement complex on lipid membranes (C5b-9m) upon activation of the complement cascade. Oligonucleotide probes derived from partial amino acid sequences of purified C6 were used to isolate cDNA clones from a human liver cDNA library. The complete polypeptide structure of mature C6 deduced from the cDNA sequence consists of 913 amino acid residues preceded by a typical 21-residue signal peptide. C6 is most similar in structure to complement C7, sharing 33.5% identical residues with C7 including all 56 cysteine residues. The low density lipoprotein receptor class A and B modules, the thrombospondin type I module at the carboxyl terminus, and the two short consensus repeat modules are arranged in the same way as in C7. In contrast to C7 and other terminal complement proteins, the thrombospondin type I module at the amino terminus occurs as a tandem repeat in C6. The last tandem repeat at the carboxyl terminus of C6 and C7 has been identified as a new distinct module (factor I module), which is closely related to a segment in the heavy chain of complement control factor I. Binding studies with filter-bound C6 fragments generated by proteolysis showed that the C5b-binding domain of C6 was located in the 34-kDa carboxyl terminal fragment consisting of two short consensus repeats and two factor I modules.

Amino Acid Sequence↗
PubMed2004

Two cDNAs from the purple sea urchin, Strongylocentrotus purpuratus, encoding mosaic proteins with domains found in factor H, factor I, and complement components C6 and C7.

The vertebrate complement system is composed of about 30 serum and cell surface proteins that make up three activation pathways, a lytic pathway, and a set of proteins that regulate complement. Regulatory proteins are required for host protection against autologous complement attack and to control the amplification feedback loop of the alternative pathway. Purple sea urchin, Strongylocentrotus purpuratus, homologues of complement C3 (SpC3) and factor B (SpBf) have been identified, suggesting the presence of an alternative complement pathway. This implies that echinoderms require a complement regulatory system for the same reasons that it is required in higher vertebrates. Two cDNAs, Sp5 and Sp5013, have been characterized from coelomocytes and the deduced structures of the encoded mosaic proteins, SpCRL ( S. p urpuratus complement related protein, long form) and SpCRS ( short form), have domains that are also found in regulatory proteins such as factor H and factor I and the terminal pathway components C6 and C7. These domains include multiple short consensus repeats, a fucolectin domain, Ser/Thr/Pro-rich regions, a Cys-rich region, and a factor I-membrane attack complex domain. The genes are constitutively expressed in all tissues of the sea urchin and are not induced in response to immune challenge. Multiple bands of varying intensity on both genome blots and RNA blots suggest that Sp5 and Sp5013 are members of a small gene family and that they might undergo alternative splicing. Based on the domains present in SpCRL and SpCRS, they might be either examples of complement regulatory proteins or members of the terminal pathway of complement.

Amino Acid Sequence↗
PubMed1986

Family study on the polymorphisms of the sixth and seventh components (C6 and C7) of human complement: linkage and haplotype analyses.

Genetic polymorphisms of the sixth and seventh complement components (C6 and C7) have been studied in Japanese family material using polyacrylamide gel isoelectric focusing followed by immunoblotting. Three common and four rare alleles were observed at the locus for C6. Inheritance of the two rare C6 variants, M11 and B3, was first confirmed. Three common C7 allotypes were classified as C7 1, C7 2, and C7 4, respectively. Linkage analysis confirmed the close linkage between the loci for C6 and C7. The maximum lod score was 8.43 at phi = 0 (95% confidence limits: phi = 0 and phi = .07). No significant linkage disequilibrium was found between C6 and C7 in directly determined haplotypes of unrelated parents.

Alleles↗