The rare C9 P167S risk variant for age-related macular degeneration increases polymerization of the terminal component of the complement cascade

Age-related macular degeneration (AMD) is a complex neurodegenerative eye disease with behavioral and genetic etiology and is the leading cause of irreversible vision loss among elderly Caucasians. Functionally significant genetic variants in the alternative pathway of complement have been strongly linked to disease. More recently, a rare variant in the terminal pathway of complement has been associated with increased risk, Complement component 9 (C9) P167S. To assess the functional consequence of this variant, C9 levels were measured in two independent cohorts of AMD patients. In both cohorts, it was demonstrated that the P167S variant was associated with low C9 plasma levels. Further analysis showed that patients with advanced AMD had elevated sC5b-9 compared to those with non-advanced AMD, although this was not associated with the P167S polymorphism. Electron microscopy of membrane attack complexes (MACs) generated using recombinantly produced wild type or P167S C9 demonstrated identical MAC ring structures. In functional assays, the P167S variant displayed a higher propensity to polymerize and a small increase in its ability to induce hemolysis of sheep erythrocytes when added to C9-depleted serum. The demonstration that this C9 P167S AMD risk polymorphism displays increased polymerization and functional activity provides a rationale for the gene therapy trials of sCD59 to inhibit the terminal pathway of complement in AMD that are underway.

Tracing and exploring the evolutionary origin and systematic function of fish complement C9

Complement C9, as a member of terminal complement component (TCC) protein, plays important roles in innate immunity. However, some complement components appear to show difference and evolutionary complexity between higher and lower vertebrates. Hence, it is essential to carry on a study of evolutionary origin and systematic function of C9 in fish and non-fish vertebrates. This study aims to explore the complement gene evolution and potential function in fish based on molecular and structural biology. Herein, we found complete divergence of C9 throughout the gene evolution. The optimal codons of C9 sequences tended to be closer to the genomes of lower vertebrates compared to higher vertebrates. Further, conserved amino acids in the C9 TMH1 region were identified, implying their potential functional association with MAC growth and pore formation. Transposons and simple repeats, as gene elements, exhibited a differential distribution in the genomic regions in different animal groups but were sparsely scattered around the sixth exon (TMH1 region). Notably, this demonstrated the regulatory complexity of the C9 gene in higher vertebrates. The negative selection pressures on fish and non-fish groups improved both the sequence conservation and similarity. Through gene/protein regulatory network and pathway analyses, the systematic function of C9 protein was showcased; thus, we could reveal the divergence of the systematic function of C9 across species from different evolutionary positions. In addition, more complicated functions of C9 in higher vertebrates could established by the altered spatial conformation of the protein. Collectively, the present study illustrates the C9 gene evolutionary process and the difference in its systematic function across multiple species. Such advances provide new insights for understanding the evolutionary and potential functions of complement C9.

Cloning, expression profile of the complement component C9 gene and influence of the recombinant C9 protein on peripheral mononuclear leukocytes transcriptome in half-smooth tongue sole (Cynoglossus semilaevis)

The ninth complement component (C9) is a terminal complement component (TCC) that is involved in creating the membrane attack complex (MAC) on the target cell surface. In this study, the CsC9 (C9 of Cynoglossus semilaevis) cDNA sequence was cloned and characterized. The full-length CsC9 cDNA measured 2,150 bp, containing an open reading frame (ORF) of 1,803 bp, a 5'-untranslated region (UTR) of 24 bp and a 3'-UTR of 323 bp. A domain search revealed that the CsC9 protein contains five domains, including two TSP1s, an LDLRA, an EGF, and a MACPF. Quantitative real-time PCR analysis showed that CsC9 at the mRNA level was expressed in all the tested tissues, with the highest expression being observed in the liver. CsC9 expression is significantly upregulated in the tested tissues after challenge with Vibrio anguillarum. To further characterize the role of CsC9, peripheral blood mononuclear cells of C. semilaevis were used for transcriptome analysis after incubation with recombinant CsC9 (rCsC9) protein. A total of 3,775 significant differentially expressed genes (DEGs) were identified between the control and the rCsC9-treated group, including 2,063 upregulated genes and 1,712 downregulated genes. KEGG analyses revealed that the DEGs were enriched in cell adhesion molecules, cytokine-cytokine receptor interactions, T cell receptor signaling pathways, B cell receptor signaling pathways and Toll-like receptor signaling pathways. The results of this study indicate that in addition to participating in MAC formation, CsC9 might play multiple roles in the innate and adaptive immunity of C. semilaevis.

Molecular characterization of complement 9 in Epinephelus coioides and differential expression analysis of classical complement genes following Vibrio alginolyticus challenge

Vibrio alginolyticus is posting an increasing threat to survival of grouper. Classical complement cascade can trigger initiation of immunity, while complement 9 (C9) is a major complement molecule involved in final step of membrane attack complex (MAC) formation. In this study, full-length EcC9 contained an ORF sequence of 1779 bp, encoding a polypeptide of 592 amino acids. A high-level expression of EcC9 mRNA was observed in liver. Following vibrio challenge, increased expression levels of EcC1q, EcBf/C2, EcC4, EcC6, EcC7 and EcC9 mRNA were detected in liver and kidney. These results implied that elevated expression level of classical complement pathway (CCP) and terminal complement components (TCCs) may assess toxicological effect of V. alginolyticus.

Characterization and expression analysis of the C8α and C9 terminal complement components from pufferfish (Takifugu rubripes)

C8α and C9 mediate the membrane attack complex formation and bacterial lysis and are important components in the complement system. The cDNA sequences of the C8α and C9 genes were cloned from Takifugu rubripes. The full-length cDNA of Tr-C8α was 1893 bp and included a 5'-UTR of 69 bp and 3'-UTR of 83 bp. The full-length cDNA of Tr-C9 was 2083 bp and included a 5'-UTR of 72 bp and 3'-UTR of 250 bp. The expression of Tr-C8α and Tr-C9 was detected in newly fertilized eggs of T. rubripes. The expression of these two genes was at a higher level in the liver than in other tissues tested. After lipopolysaccharide (LPS) challenge, the gene expression of Tr-C8α and Tr-C9 increased more significantly in the liver. With these combined results, we further understood how Tr-C8α and Tr-C9 function in the innate immunity of pufferfish. Our findings could deepen the understanding of immune regulation in pufferfish.

Molecular characterization, expression analysis, and ontogeny of complement component C9 in southern catfish (Silurus meridionalis)

The complement system plays an important role in host defense against invading microorganisms. Complement component C9 is the last component that is involved in the formation of the membrane attack complex (MAC) on the surface of target cells. In the present study, the full length C9 cDNA sequence of 1984 bp with an open reading frame (ORF) of 1809 bp was cloned from southern catfish (Silurus meridionalis). The deduced amino acid sequence showed similarity with other teleost fish. The mRNA expression of C9 was detected in the liver, spleen, stomach, intestine, and head kidney, with highest levels detected in the liver. The mRNA of C9 was first detected in the yolk syncytial layer at 34 h post fertilization (hpf) with whole mount in situ hybridization, followed by the liver at 36 h post hatching (hph). The mRNA expression of C9 was upregulated significantly in the liver, spleen, and intestine following the injection with Aeromonas hydrophila, suggesting that C9 played an important role in defense against invading pathogens in southern catfish. Therefore, these results provide important information to understand the functions of C9 during fish early development in fish.

Membrane attack complex-associated molecules from redlip mullet (Liza haematocheila): Molecular characterization and transcriptional evidence of C6, C7, C8β, and C9 in innate immunity

The redlip mullet (Liza haematocheila) is one of the most economically important fish in Korea and other East Asian countries; it is susceptible to infections by pathogens such as Lactococcus garvieae, Argulus spp., Trichodina spp., and Vibrio spp. Learning about the mechanisms of the complement system of the innate immunity of redlip mullet is important for efforts towards eradicating pathogens. Here, we report a comprehensive study of the terminal complement complex (TCC) components that form the membrane attack complex (MAC) through in-silico characterization and comparative spatial and temporal expression profiling. Five conserved domains (TSP1, LDLa, MACPF, CCP, and FIMAC) were detected in the TCC components, but the CCP and FIMAC domains were absent in MuC8β and MuC9. Expression analysis of four TCC genes from healthy redlip mullets showed the highest expression levels in the liver, whereas limited expression was observed in other tissues; immune-induced expression in the head kidney and spleen revealed significant responses against Lactococcus garvieae and poly I:C injection, suggesting their involvement in MAC formation in response to harmful pathogenic infections. Furthermore, the response to poly I:C may suggest the role of TCC components in the breakdown of the membrane of enveloped viruses. These findings may help to elucidate the mechanisms behind the complement system of the teleosts innate immunity.

NetDiff - Bayesian model selection for differential gene regulatory network inference

Differential networks allow us to better understand the changes in cellular processes that are exhibited in conditions of interest, identifying variations in gene regulation or protein interaction between, for example, cases and controls, or in response to external stimuli. Here we present a novel methodology for the inference of differential gene regulatory networks from gene expression microarray data. Specifically we apply a Bayesian model selection approach to compare models of conserved and varying network structure, and use Gaussian graphical models to represent the network structures. We apply a variational inference approach to the learning of Gaussian graphical models of gene regulatory networks, that enables us to perform Bayesian model selection that is significantly more computationally efficient than Markov Chain Monte Carlo approaches. Our method is demonstrated to be more robust than independent analysis of data from multiple conditions when applied to synthetic network data, generating fewer false positive predictions of differential edges. We demonstrate the utility of our approach on real world gene expression microarray data by applying it to existing data from amyotrophic lateral sclerosis cases with and without mutations in C9orf72, and controls, where we are able to identify differential network interactions for further investigation.

Characterisation and expression analysis of two terminal complement components: C7 and C9 from large yellow croaker, Larimichthys crocea

The large yellow croaker Larimichthys crocea, as one of the most economically important marine fish in China and East Asian countries, are facing the fatal attraction of various pathogens in recent years. Elucidation of the organism immunomodulatory mechanism of croaker response to pathogen infection is essential for the disease control. In present study, we reported for the first time the molecular characterization and expression analysis of two terminal complement components (TCCs) of croaker, Lc-C7 and Lc-C9. These two structural conserved TCCs were detected in many tissues in adult healthy fish, with highest levels detected in liver. The transcriptional expression analysis of Lc-C7 and Lc-C9 at different developmental stages showed a continuous increase towards hatch, however the two TCCs mRNA were not detected at the unfertilized stage, hinting the origination of these two TCCs after fertilization. Rapid and drastic responses to Vibrio alginolyticus challenge were observed for Lc-C7 and Lc-C9, suggesting the involvement of component C7 and C9 in innate immune responses to pathogenic invasion in teleost fish. These findings could deepen our understanding about immunomodulatory mechanisms of croaker and shed a new light to the role of component system in teleostean immunomodulation.

Renal C3 complement component: feed forward to diabetic kidney disease

BACKGROUND

Diabetic nephropathy is the main cause of end-stage renal disease and has reached epidemic proportions.

METHODS

Comprehensive genomic profiling (RNAseq) was employed in the ZS (F1 hybrids of Zucker and spontaneously hypertensive heart failure) model of diabetic nephropathy. Controls were lean littermates.

RESULTS

Diabetic nephropathy in obese, diabetic ZS was accelerated by a single episode of renal ischemia (DI). This rapid renal decline was accompanied by the activation of the renal complement system in DI, and to a lesser extent in sham-operated diabetic rats (DS). In DI there were significant increases in renal mRNA encoding C3, C4, C5, C6, C8, and C9 over sham-operated lean normal controls (LS). Moreover, mRNAs encoding the receptors for the anaphylatoxins C3a and C5a were also significantly increased in DI compared to LS. The classic complement pathway was activated in diabetic kidneys with significant increases of C1qa, C1qb, and C1qc mRNAs in DI over LS. In addition, critical regulators of complement activation were significantly attenuated in DI and DS. These included mRNAs encoding CD55, decay accelerating factor, and CD59, which inhibit the membrane attack complex. C3, C4, and C9 proteins were demonstrated in renal tubules and glomeruli. The complement RNAseq data were incorporated into a gene network showing interactions among C3-generating renal tubular cells and other immune competent migratory cells.

CONCLUSIONS

We conclude that local activation of the complement system mediates renal injury in diabetic nephropathy.

The evolutionary analysis on complement genes reveals that fishes C3 and C9 experience different evolutionary patterns

Complement is a humoral factor of innate immunity and plays an essential role in altering the host of the presence of potential pathogens and clearing of invading microorganisms. The third complement component (C3) not only is regarded as the crossing of the three pathways of complement activation, but also serves one of the bridges linking innate and acquired immunity. The nine complement component (C9) can combine with C5b, C6, C7 and C8 to form MAC which bounds to the surface of microorganisms to kill them. The evidence of evolution on C3 genes which have multiple functions and plays central role in innate immunity was documented in our previous study. Now we were interested in the evolution of C9 genes which were the terminal complement components. For these reasons, we want to explore the evolutionary patterns of C9 and whether C3 and C9 experience different evolutionary patterns. In our study, we used the sliding window method to separately calculate the values of ω among fishes and mammals of C3 and C9 codons. In order to detect the positive selection sites, we used the maximum likelihood (ML) method to study the evolutionary pattern on C3 and C9 genes. Positive selection sites were detected in mammalian C9 genes and no positive selection sites were detected in fishes C9 genes. However, no positive selection sites were detected in mammalian C3 genes and positive selection sites were detected in fishes C3 genes. The result indicated that C3 and C9 had different evolutionary patterns on mammals and fishes. In conclusion, different living environments lead to different evolutionary patterns on C3 and C9 in mammals and fishes. Besides, different complement components may have different evolutionary patterns on mammals and fishes.

Molecular characterization and expression analysis of complement component C9 gene in the whitespotted bambooshark, Chiloscyllium plagiosum

Complement system is known as highly sophisticated immune defense mechanism for antigen recognition as well as effector functions. Activation of the terminal pathway of the complement system leads to the assembly of terminal complement complexes (C5b-9), which induces the characteristic complement-mediated cytolysis. The lytic activity of shark complement involves functional analogues of mammalian C8 and C9. In this article, a full-length cDNA of C9 (CpC9) is identified from cartilaginous species, the whitespotted bambooshark, Chiloscyllium plagiosum by RACE. The CpC9 cDNA is 2263 bp in length, encoding a protein of 603 amino acids, which shares 42% and 43% identity with human and Xenopus C9 respectively. Through sequence alignment and comparative analysis, the CpC9 protein was found well conserved, with the typical modular architecture in TCCs and nearly unanimous cysteine composition from fish to mammal. Phylogenetic analysis places it in a clade with C9 orthologs in higher vertebrate and as a sister taxa to the Xenopus. Expression analysis revealed that CpC9 is constitutively highly expressed in shark liver, with much less or even undetectable expression in other tissues; demonstrating liver is the primary tissue for C9synthesis. To sum up, the structural conservation and distinctive phylogenetics might indicate the potentially vital role of CpC9 in shark immune response, though it remains to be confirmed by further study.

Genomic characterization and expression analysis of complement component 9 in rock bream (Oplegnathus fasciatus)

The complement component 9 (C9) is a single-chain glycoprotein that mediates formation of the membrane attack complex (MAC) on the surface of target cells. Full-length C9 sequence was identified from a cDNA library of rock bream (Oplegnathus fasciatus), and its genomic sequence was obtained by screening and sequencing of a bacterial artificial chromosome (BAC) genomic DNA library of rock bream. The rock bream complement component 9 (Rb-C9) gene contains 11 exons and 10 introns and is composed of a 1782 bp complete open reading frame (ORF) that encodes a polypeptide of 593 amino acids. Sequence analysis revealed that the Rb-C9 protein contains two thrombospondin type-1domains, a low-density lipoprotein receptor domain class A, a membrane attack complex & perforin (MACPF) domain, and an epidermal growth factor (EGF)-like domain. Important putative transcription factor binding sites, including those for NF-κB, SP-1, C/EBP, AP-1 and OCT-1, were found in the 5' flanking region. Phylogenetic analysis revealed a close proximity of Rb-C9 with the orthologues in puffer fish, and Japanese flounder. Quantitative real-time RT-PCR analysis confirmed that Rb-C9 was constitutively expressed in all the examined tissues isolated from healthy rock bream, with highest expression occurring in liver. Pathogen challenge, including Edwardsiella tarda, Streptococcus iniae, lipopolysaccharide endotoxin and rock bream iridovirus led to up-regulation of Rb-C9 in liver but no change in peripheral blood cells. The observed response to bacterial and viral challenges and high degree of evolutionary relationship to respective orthologues, confirmed that Rb-C9 is an important immune gene, likely involved in the complement system lytic pathway of rock bream.

Topology of the membrane-bound form of complement protein C9 probed by glycosylation mapping, anti-peptide antibody binding, and disulfide modification

The two N-linked oligosaccharides in native human C9 were deleted by site-specific mutagenesis. This aglycosyl-C9 did not differ from its native form in hemolytic and bactericidal activity. A new N-glycosylation site (K311N/E313T) was introduced into the turn of a helix-turn-helix [HTH] fold that had been postulated to form a transmembrane hairpin in membrane-bound C9. This glycosylated form of human C9 was as active as the native protein suggesting that the glycan chain remains on the external side of the membrane and that translocation of this hairpin is not required for membrane anchoring. Furthermore, flow cytometry provided evidence for the recognition of membrane-bound C9 on complement-lysed ghosts by an antibody specific for the HTH fold. A new N-glycosylation site (P26N) was also introduced close to the N-terminus of C9 to test whether this region was involved in C9 polymerization, which is thought to be required for cytolytic activity of C9. Again, this glycosylated C9 was as active as native C9 and could be induced to polymerize by heating or incubation with metal ions. The two C-terminal cystines within the MACPF domain could be eliminated partially or completely without affecting the hemolytic activity. Free sulfhydryl groups of unpaired cysteines in such C9 mutants are blocked since they could not be modified with SH-specific reagents. These results are discussed with respect to a recently proposed model that, on the basis of the MACPF structure in C8alpha, envisions membrane insertion of C9 to resemble the mechanism by which cholesterol-dependent cytolysins enter a membrane.

Molecular cloning, promoter analysis and induced expression of the complement component C9 gene in the grass carp Ctenopharyngodon idella

Complement-mediated killing of pathogens through lytic pathway is an important effector mechanism of innate immune response. C9 is the ninth member of complement components, creating the membrane attack complex (MAC). In the present study, a putative cDNA sequence encoding the 650 amino acids of C9 and its genomic organization were identified in grass carp Ctenopharyngodon idella. The deduced amino acid sequence of grass carp C9 (gcC9) showed 48% and 38.5% identity to Japanese flounder and human C9, respectively. Domain search revealed that gcC9 contains a LDL receptor domain, an EGF precursor domain, a MACPF domain and two TSP domain located in the N-terminal and C-terminal, respectively. Phylogenetic analysis demonstrated that gcC9 is clustered in a same clade with Japanese flounder, pufferfish and rainbow trout C9. The gcC9 gene consists of 11 exons with 10 introns, spacing over approximately 7 kb of genomic sequence. Analysis of gcC9 promoter region revealed the presence of a TATA box and some putative transcription factor such as C/EBP, HSF, NF-AT, CHOP-C, HNF-3B, GATA-2, IK-2, EVI-1, AP-1, CP2 and OCT-1 binding sites. The first intron region contains C/EBPb, HFH-1 and Oct-1 binding sites. RT-PCR and Western blotting analysis demonstrated that the mRNA and protein of gcC9 gene have similar expression patterns, being constitutively expressed in all organs examined of healthy fish, with the highest level in hepatopancreas. By real-time quantitative RT-PCR analysis, gcC9 transcripts were significantly up-regulated in head kidney, spleen, hepatopancreas and down-regulated in intestine from inactivated fish bacterial pathogen Flavobacterium columnare-stimulated fish, demonstrating the role of C9 in immune response.

Activation of complement C3, C5, and C9 genes in tumors treated by photodynamic therapy

Cancer therapies, which deliver a rapidly induced massive tumor tissue injury, such as photodynamic therapy (PDT), provoke a strong host response raised for dealing with the inflicted local trauma. Activated complement system was identified as an important element of host response elicited by tumor PDT. The expression of genes encoding complement proteins C3, C5, and C9 was studied following tumor PDT mediated by photosensitizer Photofrin using mouse Lewis lung carcinoma (LLC) model. Treated tumors and the livers of host mice were collected at different times after PDT and the expression of the investigated genes was analyzed by RT-PCR. The results show a significant up-regulation of C3, C5, and C9 genes in PDT-treated tumors at 24 h after therapy, while no significant increase in the expression of these genes was found in the liver tissues. The expression of C3, C5, and C9 genes also became up-regulated in untreated tumor-associated macrophages (TAMs) co-incubated in vitro with PDT-treated LLC cells. This effect was abolished or drastically reduced in the presence of antibodies blocking heat shock protein 70 (HSP70), Toll-like receptor (TLR) 2 and TLR4, and specific peptide inhibitors of TIRAP adapter protein and transcription factor NF-kappaB. The presented study reveals that complement genes C3, C5, and C9 become up-regulated in tumors treated by PDT, but not in the host's liver. Tumor-localized up-regulation of these genes can be largely attributed to monocytes/macrophages invading the treated lesion after PDT. This effect appears to be induced by the recognition of danger signals from PDT-treated tumor cells such as HSP70 by TAMs that involve the TLR2- and TLR4-triggered signal transduction pathways leading to the activation of NF-kappaB.

Effects of endotoxin administration and cerebral hypoxia-ischemia on complement activity and local transcriptional regulation in neonatal rats

It is not known whether up-regulation of complement components, either circulating or locally synthesized, contributes to an increased susceptibility to neonatal hypoxic-ischemic (HI) cerebral injury. Therefore, we tested the hypothesis that in neonatal rats subjected to a unilateral HI cerebral insult, prior administration of E. coli lipopolysaccharide (LPS) augments (1) complement-mediated serum hemolytic activity, and (2) C3 mRNA and C9 mRNA levels in hepatic and cerebral tissue. Pregnant rats were injected subcutaneously with sterile normal saline (NS) or 500 microg/kg of LPS on gestational days 18 and 19. Following birth, the pups received intraperitoneal injections of NS or 250 microg/kg of LPS on postnatal days 3 and 5. On postnatal day 7, each animal was subjected to ligation of the right common carotid artery followed by 2.5h of hypoxia (8% O(2)). At 3, 6,18, 24 and 48 h after hypoxia, the complement-mediated hemolytic activity of pooled serum was measured. Hepatic and cerebral C3 mRNA and C9 mRNA were quantified by qRT-PCR at 3, 6, and 18 h after HI. Serum hemolytic activity, hepatic C3 mRNA, and hepatic C9 mRNA were up-regulated after cerebral HI. LPS administration potentiated the effect of HI on serum hemolytic activity and increased cerebral C3 mRNA levels. Cerebral C9 mRNA was not detected and was not affected by HI, with or without the prior LPS administration. These observations support the theory that previously reported C9-mediated neurotoxicity following cerebral HI is induced by circulating, rather than locally synthesized C9.

Complement activation by direct C4 binding to thyroperoxidase in Hashimoto's thyroiditis

Biosynthesis of thyroid hormones is an oxidative process that generates reactive oxygen species (ROS) and involves thyroperoxidase (TPO) that is one of the main autoantigens involved in autoimmune thyroid diseases. The ectodomain of TPO consists of a large N-terminal myeloperoxidase-like module followed by a complement control protein (CCP)-like module and an epidermal growth factor-like module. The presence of these two additional gene modules suggests that they may play some crucial, hitherto unsuspected role associated with thyroid function. Because the CCP module is a constituent of the molecules involved in the activation of C4 complement component, we investigated the possibility that C4 may bind to TPO and activate the complement pathway in autoimmune conditions. We showed that TPO via its CCP module directly activated complement without any mediation by Ig. We suggested that this additional complement pathway requires the production of ROS and specially hydroxyl radicals that aggregate TPO and oxidize methionines of C4. Moreover, we found, in patients with Hashimoto's thyroiditis, that thyrocytes overexpress C4 and all the downstream components of the complement pathway. These results indicate that TPO has some as yet unknown function, which may contribute along with other mechanisms to the massive cell destruction observed in Hashimoto's thyroiditis. Investigating this complement pathway, therefore, would provide an excellent means of reaching a better understanding of the etiology of other degenerative diseases.

Founder effect of the C9 R95X mutation in Orientals

A nonsense mutation at codon 95 (R95X) in the C9 gene is responsible for most Japanese C9 deficiency (C9D) cases, with a carrier frequency of 6.7%. Upon analysis of microsatellite markers and newly identified dinucleotide repeat number polymorphisms in the 3' flanking region of the C9 gene, a founder effect was demonstrated for the R95X mutation of the C9 gene in Japanese. Screening for the R95X mutation in Korean and Chinese individuals showed that the R95X carrier frequencies in Koreans and Chinese were 2.0% and 1.0%, respectively. Although homozygotes for the R95X mutation were not found in Korea or China, the shared haplotype of the dinucleotide repeat number polymorphisms appeared to be associated with the R95X mutation in the heterozygotes in Korea and China. The founder effect found in East Asians (Japanese, Koreans and Chinese) but not in Caucasians, as well as the haplotype sharing in only a small chromosomal interval, suggested that the R95X mutation of C9 gene was ancient and had occurred after the divergence of East Asians and Caucasians, and before migration of the Yayoi people to Japan. Since the mortality of meningococcal infections in complement-deficient patients is lower than that in normal individuals, a founder effect and a selective advantage in isolation might be the main reasons for the high frequency of the R95X mutation in Japan.

An abnormal but functionally active complement component C9 protein found in an Irish family with subtotal C9 deficiency

Two independently segregating C9 genetic defects have previously been reported in two siblings in an Irish family with subtotal C9 deficiency. One defect would lead to an abnormal C9 protein, with replacement of a cysteine by a glycine (C98G). The second defect is a premature stop codon at amino acid 406 which would lead to a truncated C9. However, at least one of two abnormal proteins was present in the circulation of the proband at 0.2% of normal C9 concentration. In this study, the abnormal protein was shown to have a molecular weight approximately equal to that of normal C9, and to carry the binding site for monoclonal antibody (mAb) Mc42 which is known to react with an epitope at amino acid positions 412-426, distal to 406. Therefore, the subtotal C9 protein carries the C98G defect. The protein was incorporated into the terminal complement complex, and was active in haemolytic, bactericidal and lipopolysaccharide release assays. A quantitative haemolytic assay indicated even slightly greater haemolytic efficiency than normal C9. Epitope mapping with six antihuman C9 mAbs showed the abnormal protein to react to these antibodies in the same way as normal C9. However, none of these mAbs have epitopes within the lipoprotein receptor A module, where the C98G defect is located. The role of this region in C9 functionality is still unclear. In conclusion, we have shown that the lack of a cysteine led to the production of a protein present in the circulation at very much reduced levels, but which was fully functionally active.

The human complement C9 gene: structural analysis of the 5' gene region and genetic polymorphism studies

C9 is the last of the human complement components creating the membrane attack complex. The single chain serum protein is encoded by a gene located on chromosome 5p13 that is composed of 11 exons. With the aid of inverse PCR, the hitherto unknown regions flanking exon 1 and the 3' part of exon 11 (3'UTR) have been sequenced. A computer-based analysis of the 300-bp region located just upstream of the AUG start codon showed homologies to known DNA modules which affect the transcriptional regulation of certain genes. The most striking of these is a sequence that may substitute the missing TATA box in initiating C9 transcription. In the 3'UTR, three successive polyadenylation signals were found. Although the C9 protein is invariant, four different single nucleotide polymorphisms (SNPs) have been observed at the DNA level by exon-specific PCR and direct sequencing. None of them changes the amino acid composition of the mature protein. Due to a C --> T transition in exon 1 at cDNA position 17, the fifth amino acid of the leader peptide may be either an arginine or a tryptophane. Using either PCR/ RFLP analysis (exons 1 and 11) or allele-specific PCR (intron 1 and exon 4), each polymorphism can be characterized without sequencing. All of the exon 1, intron 1 and exon 11 variants could be detected in small population samples of European, Thai or South American Indian origin. In contrast, the exon 4 C variant was observed only once in a European. The first three SNPs can be combined to designate eight different 'C9 alleles'. Of these, six have actually be found. These data provide strong evidence that several mutation and recombination events occurred in the course of C9 gene evolution.

Induction of complement C9 messenger RNAs in human neuronal cells by inflammatory stimuli: relevance to neurodegenerative disorders

Neurons express proteins of the classical complement pathway, including C9. Both the mRNA and protein levels for C9 are sharply upregulated in brain areas affected by Alzheimer's disease (AD). Since little is known about the signals that are responsible for this upregulation, we evaluated in human SH-SY5Y neuroblastoma cells the factors which stimulate C9 production. Interferon-gamma, phorbol myristate acetate and interleukin-6 all stimulated C9 mRNA expression but the inflammatory cytokines tumor necrosis factor-alpha, interleukin-1 beta, as well as the anaphylatoxin C5a and the bacterial lipopolysaccharide, were ineffective. Immunohistochemical analysis of postmortem human brains for C9 protein demonstrated its presence in many cortical pyramidal neurons in AD, Down's syndrome, the parkinsonism dementia complex of Guam and pallido-ponto-nigral degeneration, as well as in thalamic neurons of progressive supranuclear palsy and ballooned neurons of Pick's disease. Since C9 is required for the membrane attack complex of complement to become functional, interfering with signaling pathways that stimulate its production could offer new therapeutic strategies for treating various neurodegenerative disorders.

Hereditary complement (C9) deficiency associated with dermatomyositis

A 28-year-old Japanese woman with hereditary complement (C9) deficiency and dermatomyositis is reported. She had a 3-year history of facial erythema and a 1-month history of progressive muscle weakness. Clinical and laboratory findings were suggestive of dermatomyositis; muscle biopsy confirmed an inflammatory myopathy. An unexpected finding, however, was the low titre of serum haemolytic complement (CH50). Treatment with prednisolone resulted in marked clinical improvement but did not affect the CH50 titre. Further investigation revealed a selective and total absence of the ninth complement component (C9), with direct DNA sequence analysis revealing a non-sense mutation at Arg95 of the C9 gene. This case demonstrates that the muscle lesions of dermatomyositis can occur in the presence of a complement defect that would prevent the formation of the C5b-9 membrane attack complex.

Complement component 9 deficiency is not a susceptibility factor for SLE

Almost all complement component 9 (C9) deficiency in Japan shows Arg95 Stop mutation of C9 gene. Therefore, we studied the prevalence of Arg95Stop mutation of C9 gene among 78 patients with SLE to elucidate the association of SLE and C9 deficiency. The Arg95Stop carrier frequency showed no significant difference between SLE patients and controls. Thus, C9 deficiency is not implicated in SLE susceptibility.

Detection of mRNA for the terminal complement components C5, C6, C8 and C9 in human umbilical vein endothelial cells in vitro

Human umbilical vein endothelial cells (HUVEC) have previously been shown to synthesize the functional terminal pathway of complement based on the detection by radioimmunoassay of the terminal complement complex (TCC) on coincubated agarose beads. In addition, C7 secretion by these cells in amounts comparable to C3, as well as C7 mRNA, has recently been demonstrated. However, it has not been possible to detect C5-6 and C8 in the fluid phase, and only trace amounts of soluble C9. Against this background we examined whether mRNA for the remaining terminal complement factors was present in HUVEC. By the use of reverse transcription (RT)-polymerase chain reaction (PCR) and Northern blot the presence of mRNA for complement factors C5, C6, C8 and C9 was demonstrated.

Deficiency of complement defense protein CD59 may contribute to neurodegeneration in Alzheimer's disease

Complement defense 59 (CD59) is a cell surface glycophosphoinositol (GPI)-anchored protein that prevents complement membrane attack complex (MAC) assembly. Here, we present evidence from ELISA assays that CD59 protein levels are significantly decreased in the frontal cortex and hippocampus of Alzheimer's disease (AD) compared with nondemented elderly (ND) patients, whereas complement component 9, a final component to form MAC, is significantly increased. To further confirm the CD59 deficit, PI-specific phospholipase C (PIPLC) was used to cleave the CD59 GPI anchor at the cell surface in intact slices from AD and ND cortex. CD59 released by PIPLC cleavage was significantly reduced in AD compared with ND samples. By the use of a ribonuclease protection technique, amyloid beta-peptide was found to downregulate CD59 expression at the mRNA level, suggesting a partial explanation of CD59 deficits in the AD brain. To evaluate the pathophysiological significance of CD59 alterations in neurons, we exposed cultured NT2 cells, which normally underexpress CD59, and NT2 cells transfected to overexpress CD59 to homologous human serum. Lactic acid dehydrogenase assays revealed significant complement-induced cell lysis in CD59-underexpressing NT2 cells and significant protection from such lysis in CD59-overexpressing NT2 cells. Moreover, cells expressing normal levels of CD59 showed no evidence of MAC assembly or damage after exposure to homologous serum, whereas pretreatment of these cells with a CD59-neutralizing antibody resulted in MAC assembly at the cell surface and morphological damage. Taken together, these data suggest that CD59 deficits may play a role in the neuritic losses characteristic of AD.

Reference typing report for complement components C6, C7 and C9 including mutations leading to deficiencies

The results of the present (VIIth Complement Genetics Workshop and Conference, Mainz, May 1998) and past reference typing workshops for the terminal complement components C6, C7 and C9 are compiled and discussed both on the protein level and on the DNA level. This report also focuses on the molecular bases of expressed and silent polymorphisms and reviews the molecular bases of subtotal and complete deficiencies of these proteins and their associations with protein and DNA markers. The results of the protein typing for C6 are published in the following paper of this issue.

Free radicals upregulate complement expression in rabbit isolated heart

Both free radicals and complement activation can injure tissue. Our study determined whether free radicals alter complement production by the myocardium. Isolated hearts from New Zealand White rabbits were perfused on a Langendorff apparatus and exposed to xanthine (X; 100 microM) plus xanthine oxidase (XO; 8 mU/ml) (X/XO). The free radical-generating system significantly (P < 0.05) increased C1q and also increased C1r, C3, C8, and C9 transcription compared with controls. Immunohistological examination revealed augmented membrane attack complex deposition on X/XO-treated tissue. X/XO-treated hearts also exhibited significant (P < 0.05) increases in coronary perfusion pressure and left ventricular end-diastolic pressure and a decrease in left-ventricular developed pressure. N-(2-mercaptopropionyl)-glycine (3 mM), in conjunction with the superoxide dismutase mimetic SC-52608 (100 microM), significantly (P < 0.05) reduced the upregulation of C1q, C1r, C3, C8, and C9 mRNA expression elicited by X/XO. The antioxidants also ameliorated the deterioration in function caused by X/XO. Local complement activation may represent a mechanism by which free radicals mediate tissue injury.

Molecular analysis of complement component C8beta and C9 cDNAs of Japanese flounder, Paralichthys olivaceus

The amino acid sequences of the human terminal complement components show extensive structural similarity to each other. In this study the C8beta and C9 cDNAs of Japanese flounder, Paralichthys olivaceus, were cloned and analyzed. The derived deduced amino acid sequences of the two terminal components were homologous to those of humans, in that the sequences of both species contained LDL receptor, EGF precursor, and two thrombospondin domains. Japanese flounder C9 was found to have a second thrombospondin region in the C-terminus, similar to that reported for rainbow trout and pufferfish. Moreover, these two complement component cDNAs of Japanese flounder had partial similarity to human perforin. These findings show that Japanese flounder C8beta and C9 have similar structures, which supports the hypothesis that the terminal complement genes originated from the same ancestral gene. Collectively, these features emphasize the strong similarity among the members of the terminal complement family.

Phylogenetic analysis of the homologous proteins of the terminal complement complex supports the emergence of C6 and C7 followed by C8 and C9

The plasma complement system comprises several activation pathways that share a common terminal route involving the assembly of the terminal complement complex (TCC), formed by C5b-C9. The order of emergence of the homologous components of TCC (C6, C7, C8alpha, C8beta, and C9) has been determined by phylogenetic analyses of their amino acid sequences. Using all the sequence data available for C6-C9 proteins, as well as for perforins, the results suggested that these TCC components originated from a single ancestral gene and that C6 and C7 were the earliest to emerge. Our evidence supports the notion that the ancestral gene had a complex modular composition. A series of gene duplications in combination with a tendency to lose modules resulted in successive complement proteins with decreasing modular complexity. C9 and perforin apparently are the result of different selective conditions to acquire pore-forming function. Thus C9 and perforin are examples of evolutionary parallelism.

The architectural transition of human complement component C9 to poly(C9)

Several regions of C9 including three cysteine-rich modules homologous to those in thrombospondin (TS), the low density lipoprotein receptor (LDL), the epidermal growth factors (EDGF), as well as two middle sections of the polypeptide chain were expressed in bacteria. Antibodies derived from these segments were used to probe the relative exposure of epitopes in C9 and poly(C9) using ELISAs. The results indicated that the TS and LDL modules are fully exposed in both monomer and polymer; however, the middle region of the polypeptide chain is buried in the monomer but external in the polymer. Using specified conditions, Fab fragments to the TS and LDL modules did not block C9 polymerization, but those to the middle region of the polypeptide chain and to some extent to the EDGF module did so. Immuno-electron microscopy of poly(C9) indicated that the C9 polypeptide chain assumes a 'U' shape, in which the TS and LDL modules are located on the upper rim. The EDGF module is located on the lower edge of the upper rim, and midsection of the polypeptide chain constructs the barrel of the tubule. Computer assisted contrast enhancement of select electron micrograph images of poly(C9) allowed the clear visualization of each subunit. These were seen to have a volute shape. The upper rim is composed of whorls that are apparently not in lateral contact. It is concluded that the TS and LDL modules do not participate directly in polymerization but cover the hydrophobic central region of the polypeptide chain in the monomer. As a consequence of circular polymerization the midsection of the polypeptide chain becomes exposed as each C9 lengths to fashion a volute form. reserved.

[Clinical findings and genetic bases of congenital complement deficiencies]

The clinical findings and genetic bases of inherited deficiencies of plasma complement components and complement control proteins are reviewed. In Japan, since the frequencies of late complement component deficiencies (LCCD) are high, clinical features of neisserial infections associated with LCCD are described in details. C 9 deficiency is one of the most frequent genetic disorders in Japan and most of them are healthy. However, C 9 deficiency is weakly but significantly associated with the development of meningococcal meningitis but not of systemic lupus erythematosus. The common Arg 95 Stop mutation was found in most individuals with C 9 deficiency. Molecular epidemiologic study revealed that homozygous and heterozygous Arg 95 Stop mutation of C 9 gene is found in approximately one of 1000 individuals and one of 15 individuals, respectively. Complement studies including C 9 antigen and DNA analyses should be performed in patients with meningococcal meningitis or recurrent bacterial infections.

Molecular epidemiology of C9 deficiency heterozygotes with an Arg95Stop mutation of the C9 gene in Japan

Deficiency of the ninth component of human complement (C9) is the most common complement deficiency in Japan, with an incidence of approximately one homozygote in 1000, but is very rare in other countries. Genetic analyses of Japanese C9 deficiency have shown that a C-to-T transition leading to TGA stop codon for Arg95 in exon 4 of the C9 gene (Arg95Stop) is common in Japanese C9 deficiency. To determine the prevalence of heterozygous carriers of the Arg95Stop mutation in a Japanese population, we collected DNA samples from 300 individuals in two of the four main islands of Japan. Heterozygote detection was performed with an allele-specific polymerase chain reaction (PCR) system designed to detect exclusively only one of the normal and mutant alleles, followed by confirmation with PCR/single-strand conformation polymorphism (SSCP) analysis and direct sequencing. Twenty individuals were heterozygous for the Arg95Stop mutation. None was homozygous. The prevalence of carriers of the Arg95Stop mutation was 6.7% (20/300). An estimated frequency (0.12%) of complete C9 deficiency due to homozygous Arg95Stop mutation was consistent with frequencies determined by serological studies.

Expression of complement C4 and C9 genes by human astrocytes

Evidence exists that complement activation is involved in the pathogenesis of Alzheimer's disease (AD). It has been previously demonstrated that central nervous system (CNS) resident cells can synthesize complement proteins. Two key proteins in the complement pathway are the complement C4 and C9 proteins. Using reverse transcription-polymerase chain reaction, ELISA, immunocytochemical and immunoblot techniques, we showed that primary human astrocytes constitutively expressed complement C4 mRNA and protein, and that this was increased when cells were treated with interferon-gamma, but inhibited when cells were treated with interleukin-1beta (IL-1beta). C4 immunoreactivity could be localized to GFAP-positive astrocytes when protein secretion was inhibited. These results indicated that astrocytes could be a source of complement C4 in the human CNS. In addition it was shown that stimulated astrocytes could also express complement C9 mRNA, though C9 protein was not detectable in culture supernatants.

Complement gene expression by rabbit heart: upregulation by ischemia and reperfusion

Activation of the complement system has been implicated in the pathogenesis of myocardial ischemia/reperfusion injury. It has always been assumed that liver is the primary source of complement components. In the present study, we used the reverse-transcriptase polymerase chain reaction technique to establish that the mRNAs for complement proteins C3 and C9 are expressed in rabbit heart. Rabbit liver, brain, spleen, and kidney were also shown to express C3 and C9 mRNAs. We used Western blotting to establish that these mRNAs in heart are translated into the corresponding proteins. We further established that dramatic upregulation of the mRNAs occurred in Langendorff-perfused isolated hearts subjected to ischemia and reperfusion. C3 mRNA was always expressed at higher levels than was C9 mRNA, but C9 mRNA showed greater upregulation under stress. Compared with levels in control hearts subjected to 5 minutes of normoxic perfusion, hearts subjected to 0.5 hours of ischemia followed by 1 hour of reperfusion had a 4.72-fold increase in C3 mRNA and a 19.5-fold increase in C9 mRNA. By contrast, C3 mRNA in hearts subjected to 3.5 hours of normoxic perfusion showed no change, and those subjected to 3.5 hours of ischemia showed only a 1.72-fold increase, whereas C9 mRNA levels increased by 5.17-fold after 3.5 hours of normoxic perfusion and 12.5-fold after 3.5 hours of ischemia. The results of this study demonstrate for the first time that heart tissue is capable of expressing genes and proteins of the complement system, although it is not yet known which cell types are responsible. They further demonstrate that ischemia and reperfusion of the heart promotes a rapid upregulation of the mRNAs encoding the complement proteins C3 and C9 and that these abnormal levels considerably exceed those of normal liver. These observations are consistent with the hypothesis that local production of complement proteins may contribute significantly to the degree of ischemic injury to the myocardium and that complement expression is augmented by reperfusion.

Nonsense mutation in exon 4 of human complement C9 gene is the major cause of Japanese complement C9 deficiency

Deficiency of the ninth component of human complement (C9) is the most common complement deficiency in Japan but is rare in other countries. We studied the molecular basis of C9 deficiency in four Japanese C9-deficient patients who had suffered from meningococcal meningitis. Direct sequencing of amplified C9 cDNA and DNA revealed a nonsense substitution (CGA-->TGA) at codon 95 in exon 4 in the four C9-deficient individuals. An allele-specific polymerase chain reaction system designed to detect exclusively only one of the normal and mutant alleles indicated that all the four patients were homozygous for the mutation in exon 4 and that the parents of patient 2 were heterozygous. The common mutation at codon 95 in exon 4 might be responsible for most Japanese C9 deficiency.

A non-sense mutation at Arg95 is predominant in complement 9 deficiency in Japanese

Deficiency of the ninth component of complement (C9D) is one of the most common genetic abnormalities in Japan, with an incidence of one homozygote in 1000. Although C9D individuals are usually healthy, it has been shown that they have an significantly increased risk of developing meningococcal meningitis. In the present study we report the molecular bases for C9D in 10 unrelated Japanese subjects. As a screening step for mutations, exons 2 to 11 of the C9 gene were analyzed using exon-specific PCR/single-strand conformation polymorphism analysis, which demonstrated aberrantly migrating DNA bands in exon 4 in all the C9D subjects. Subsequent direct sequencing of exon 4 of the C9D subjects revealed that eight of the 10 C9D subjects were homozygous for a C to T transition at nucleotide 343, the first nucleotide of the codon CGA for Arg95, leading to a TGA stop codon (R95X). R95X is a novel mutation different from those recently identified in a Swiss family with C9D. Cases 6 and 7 were heterozygous for the R95X mutation. Family study in case 10 confirmed the genetic nature of the defect. In case 6, the second mutation for C9D of the C9 gene was identified to be the substitution of Cys to Tyr at amino acid residue 507 (C507Y), while the genetic defect(s) in the other allele in case 7 remains unknown. Our results indicate that a novel mutation, R95X, is present in most cases of C9D in Japan.

Cloning and sequencing of complement component C9 and its linkage to DOC-2 in the pufferfish Fugu rubripes

The Japanese pufferfish Fugu rubripes has a 400 Mb genome with high gene density and minimal non-coding complexity, and is therefore an ideal vertebrate model for sequence comparison. The identification of regions of conserved synteny between Fugu and humans would greatly accelerate the mapping and ordering of genes. Fugu C9 was cloned and sequenced as a first step in an attempt to characterize the region in Fugu homologous to human chromosome 5p13. The 11 exons of the Fugu C9 gene share 33% identity with human C9 and span 2.9 kb of genomic DNA. By comparison, human C9 spans 90 kb, representing a 30-fold difference in size. We have also determined by cosmid sequence scanning that DOC-2, a tumour suppresser gene which also maps to human 5p13, lies 6-7 kb from C9 in a head-to-head or 5' to 5' orientation. These results demonstrate that the Fugu C9/DOC-2 locus is a region of conserved synteny. Sequence scanning of overlapping cosmids has identified two other genes, GAS-1 and FBP, both of which map to human chromosome 9q22, and lie adjacent to the Fugu C9/DOC-2 locus, indicating the boundary between two syntenic regions.

Difficulties in the ascertainment of C9 deficiency: lessons to be drawn from a compound heterozygote C9-deficient subject

A group of patients with long-surviving mismatched kidney allografts were investigated for complement function using haemolytic assays in agarose gels. One patient was found to have no alternative pathway activity but a low normal classical pathway. Surprisingly, investigation revealed that the patient's complement was normal for all components except C9, which was functionally absent. The patient was shown to be heterozygous for DNA markers in the C6, C7 and C9 region of chromosome 5 and therefore appears to be a compound heterozygote for two uncharacterized C9 deficiency genes. Serological analysis by ELISA revealed that he has trace concentrations of a non-functional C9 molecule. Western blot analysis was not sufficiently sensitive to permit detection of this molecule. We hypothesize that the patient is heterozygous for a complete deficiency of C9 and for a gene directing hyposynthesis of a defective C9. We also suggest that C9 deficiency may be more common among Caucasians than has been reported.

The human complement C9 gene: identification of two mutations causing deficiency and revision of the gene structure

The ninth component of human complement (C9) is the last of the terminal complement components creating the membrane attack complex. C9 is a single-chain serum protein that is encoded by a gene located on chromosome 5p. Deficiency of terminal complement components is generally associated with recurrent neisseria infections. We studied a previously described Swiss family with inherited C9 deficiency. To identify the genetic basis of C9 deficiency, we developed an approach using exon-specific PCR and direct DNA sequencing. As a cause of C9 deficiency, we found two different point mutations, both generating TGA stop codons in the coding sequence. One mutation, a C to A exchange, was detected in exon 2 at cDNA position 166, the other, a C to T exchange, was located in exon 4 (cDNA position 464). In family studies of three first-degree relatives with heterozygous C9 deficiency, we demonstrated that the two mutations are segregating independently. Therefore, these mutations are sufficient to explain the complete deficiency of both the probands studied. DNA sequencing of the exon-intron junctions revealed a number of revisions regarding the boundaries between exons 4, 5, and 6 as well as between exons 10 and 11. No additional introns were detected in exons 6 and 10. Furthermore, DNA marker studies were conducted using known polymorphisms of the C6, C7, and C9 genes, confirming the linkage of the observed C9 mutations with defined haplotypes.

Horse complement protein C9: primary structure and cytotoxic activity

Lack of hemolytic activity of horse serum is an inherent property of horse C9. To understand the molecular reasons for this deficiency we have cloned C9 cDNA from a horse liver cDNA library and have sequenced the cDNA yielding the complete coding sequence for horse C9. Purification of C9 from horse plasma and microsequencing established the N-terminus of the mature protein and verified that the correct horse C9 cDNA clone had been isolated. The deduced amino acid sequence corresponds to a mature protein of 526 amino acids that is 77% identical to human C9. It has the same domain structure as human C9 and contains 22 cysteines and four invariant tryptophans. The few differences include the N-terminus, which is an unblocked glycine in horse C9 but pyroglutamine in human C9, and three potential N-glycosylation sites compared to two in human C9. The N-terminal difference is unimportant since microsequencing of bovine C9, which is strongly hemolytic, established that it also has an unblocked glycine identical to horse C9. There are no obvious structural differences apparent that could resolve the differences in hemolytic potency between the two molecules. Aside from a few conservative replacements, both C9 sequences are identical between positions 250 and 360. This region includes the membrane interaction domain in C9 and the postulated transmembrane segment that is thought to constitute the wall of a putative transmembrane pore and, therefore, should be required for cytotoxicity. In agreement with this prediction we have observed that, in contrast to the marked decrease in hemolytic activity, horse C9 is very efficient in killing a variety of Gram-negative bacteria. These results demonstrate that horse C9 is a structurally competent molecule with efficient cytotoxic activity. Its inability to lyse erythrocytes may be related to the action of control proteins on target cell membranes.

Role of a disulfide-bonded peptide loop within human complement C9 in the species-selectivity of complement inhibitor CD59

CD59 antigen is a membrane glycoprotein that inhibits the activity of the C9 component of the C5b-9 membrane attack complex (MAC), thereby protecting human cells from lysis by human complement. The complement-inhibitory activity of CD59 is species-selective, and is most effective toward C9 derived from human or other primate plasma. The species-selective activity of CD59 was recently used to map the segment of human C9 that is recognized by this MAC inhibitor, using recombinant rabbit/human C9 chimeras that retain lytic function within the MAC [Husler, T., Lockert, D. H., Kaufman, K. M., Sodetz, J. M., & Sims, P. J. (1995) J. Biol. Chem. 270,3483-3486]. These experiments suggested that the CD59 recognition domain was contained between residues 334 and 415 in human C9. By analyzing the species-selective lytic activity of recombinant C9 with chimeric substitutions internal to this segment, we now demonstrate that the site in human C9 uniquely recognized by CD59 is centered on those residues contained between C9 Cys359/Cys384, with an additional contribution by residues C-terminal to this segment. Consistent with its role as a CD59 recognition domain, CD59 specifically bound a human C9-derived peptide corresponding to residues 359-384, and antibody (Fab) raised against this C9-derived peptide inhibited the lytic activity of human MAC. Mutant human C9 in which Ala was substituted for Cys359/384 was found to express normal lytic activity and to be fully inhibited by CD59. This suggests that the intrachain Cys359/Cys384 disulfide bond within C9 is not required to maintain the conformation of this segment of C9 for interaction with CD59.

Protection of gingival epithelium against complement-mediated damage by strong expression of the membrane attack complex inhibitor protectin (CD59)

Adult periodontitis (AP) is a chronic inflammatory disease of the tooth-supporting apparatus. Activation products of the inflammation-inducing complement system have been detected in the gingival crevicular fluid at the site of gingival inflammation. In the present study, we examined whether evidence for ongoing complement activation in gingival tissues of patients with AP can be obtained. In light of the potential tissue-damaging effects of the complement system, we also examined how the gingival tissue is protected against the cytolytic activity of complement. Surgical and autopsy samples of AP (n = 18) and healthy (n = 11) gingiva were analyzed for the expression or deposition of the complement regulators protectin (CD59) and vitronectin (S-protein) and complement components C3d and C9 by indirect immunofluorescence microscopy with specific antibodies. In healthy gingiva, protection was strongly expressed on the membranes of epithelial cells and on the vascular endothelia of the underlying connective tissue. In AP, protectin was also strongly expressed by endothelial cells, but in the epithelia the expression was granular and weaker than in the healthy gingiva. Coarse granular deposits of complement components were seen in the subepithelial tissues of 61% (C3d), 39% (C9), and 33% (vitronectin) of AP patients, compared with 9% (one case in 11) in healthy controls. In addition, deposits of C3d, C9, and vitronectin were observed on the basement membranes of both pocket and oral epithelium of healthy and AP gingiva but not at sites of protectin expression. The results suggest an increased turnover of the complement system in the gingival tissues of AP patients. The gingival epithelium and connective tissue endothelia are well-protected against damage by the membrane attack complex of complement (MAC). Protection of the underlying connective tissue is insufficient, however, and may allow for deposition of MAC and autologous tissue damage in AP.

Structure of the human C7 gene and comparison with the C6, C8A, C8B, and C9 genes

The seventh component of complement is a single chain plasma glycoprotein that is involved in the cytolytic phase of complement activation. We have determined the structure of the C7 gene, which is encoded by 18 exons whose sizes vary from 56 to 244 bp. For the most part, the exons do not correspond to the protein homology units. However, two intron/exon boundaries occur at junctions between different functional parts of the protein. The first is at a site between the end of the C9 homology unit and the carboxyl-terminal extension which is also a feature of C6. The second of these boundaries occurs between the regions encoding two pairs of cysteine-rich modules (the short consensus repeats and the factor I modules) located in the carboxyl-terminal part of C7. In contrast to the exons, the introns range considerably in size from 0.5 to 8.5 kbp. The complete analysis indicates that the gene encoding C7 is approximately 80 kbp in length. We show here that the C7 gene is highly homologous to that for C6, and also to C8A, C8B, and C9, confirming and extending the published data. With the exception of exon 1, all intron/exon boundaries are preserved with respect to phase when compared with C6.

Chimeras of human complement C9 reveal the site recognized by complement regulatory protein CD59

CD59 antigen is a membrane glycoprotein that inhibits the activity of the C9 component of the C5b-9 membrane attack complex, thereby protecting human cells from lysis by human complement. The complement-inhibitory activity of CD59 is species-selective and is most effective toward C9 derived from human or other primate plasma. By contrast, rabbit C9, which can substitute for human C9 in the membrane attack complex, mediates unrestricted lysis of human cells. To identify the peptide segment of human C9 that is recognized by CD59, rabbit C9 cDNA clones were isolated, characterized, and used to construct hybrid cDNAs for expression of full-length human/rabbit C9 chimeras in COS-7 cells. All resulting chimeras were hemolytically active, when tested against chicken erythrocytes bearing C5b-8 complexes. Assays performed in the presence or absence of CD59 revealed that this inhibitor reduced the hemolytic activity of those chimeras containing human C9 sequence between residues 334-415, irrespective of whether the remainder of the protein contained human or rabbit sequence. By contrast, when this segment of C9 contained rabbit sequence, lytic activity was unaffected by CD59. These data establish that human C9 residues 334-415 contain the site recognized by CD59, and they suggest that sequence variability within this segment of C9 is responsible for the observed species-selective inhibitory activity of CD59.

Genetic detection of the silent allele (*Q0) in hereditary deficiencies of the human complement C6, C7, and C9 components

DNA polymorphisms (RFLPs) of the human complement component C6, C7, and C9 genes were studied in three C7-deficient (C7D) families, one C6-deficient (C6D) family, and one C9-deficient (C9D) family. The 3 loci are closely linked on human chromosome 5. The haplotypes carrying the "silent" allele (C7*Q0, C6*Q0, and C9*Q0) were defined in each family, allowing for the detection of carriers among asymptomatic relatives. This paper describes familial studies on a type of hereditary trait, characterized by recurrent Neisseria infections in individuals homozygous for "silent" alleles at the C6, C7, or C9 loci.

Altered glycosylation and selected mutation in recombinant human complement component C9: effects on haemolytic activity

Recombinant wild-type and mutated forms of human complement component C9 have been synthesized in baculovirus-infected insect cells. Wild-type recombinant C9 was indistinguishable from native C9, as judged by haemolytic activity, trypsin and alpha-thrombin digestion, reaction with antibodies to C9, enzymatic deglycosylation to the same core size and polymerization in the presence of Zn2+. Replacement of the native signal peptide with the honey-bee melittin signal peptide, and replacement of Spodoptera frugiperda (Sf9) cells with Trichoplusia ni cells produced yields of 5 micrograms C9/ml supernatant. Three C9 mutants were generated; one mutant, with four acidic residues changed to alanines in a putative calcium-binding site, had the same biological activity as recombinant C9. Another mutant, lacking 23 N-terminal amino acids, previously showing increased polymerization when produced in vitro, polymerized on secretion, rendering it inactive. It was not possible to demonstrate haemolytic activity of the third mutant, cysteines 33 and 36 mutated to alanine, as it was secreted a hundredfold less than the wild-type protein.

A method for in vitro synthesis of unglycosylated recombinant complement component C9

A method for in vitro synthesis of human complement component C9 has been established in order to generate unglycosylated normal and mutant proteins without the need to sub-clone. One or two step polymerase chain reaction (PCR) was used to add the T7 RNA polymerase promoter and introduce multiple mutations within the cDNA. The cDNA was then transcribed by T7 RNA polymerase and the mRNA translated in a rabbit reticulocyte lysate or wheat germ system. Successful synthesis was confirmed by: the correct size of PCR product DNA on agarose gel electrophoresis, incorporation of [alpha-32P]UTP into mRNA, and formation of [35S]methionine-labelled protein of the correct molecular mass for full length C9. The wheat germ extract generated up to 1.5 micrograms of recombinant C9. This unglycosylated C9 had at least 10% of the haemolytic activity of native C9. Unglycosylated C9 polymerised more readily than the native protein. This spontaneous polymerisation was increased by removal of the first 23 amino acids or mutating two cysteines at positions 33 and 36. This therefore provides a rapid method for screening the effect of multiple mutations on the biological activity and polymerisation of pore forming proteins.