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PubMed1983

The genetics of the sixth and seventh components of complement in the dog: polymorphism, linkage, locus duplication, and silent alleles.

The complement components C6 and C7 exhibit genetic polymorphism in the domestic dog. In the case of C6, there is a single locus with a null allele and two structural alleles; in the case of C7, there are two linked loci, each with three structural alleles. There is a null allele or locus deletion at one of these loci. In all cases, inheritance is autosomal and codominant. The C7 loci are closely linked to each other and to C6. This complex is not close to the dog major histocompatibility complex (MHC) locus.

Alleles↗
PubMed1987

Terminal complement components play a role in the expression of C5a.

This study examined the expression of C5a detected antigenically (RIA) and functionally (PMN-myeloperoxidase release) consequent to classical or alternative pathway convertase cleavage. Maximal C5a expression occurred when C5 was cleaved in the presence of the later-acting complement components, C6, C7, and C8. This effect was detected by using both purified components and normal human serum immunochemically depleted of C7 or C8 and reconstituted with the purified component. C6 alone was not sufficient to augment C5a expression. Subsequent incubation of C6 and C7 with C5 cleaved in the absence of the terminal components was not sufficient for C5a release. Repeated freezing and thawing of C5 cleaved in the absence of C6 and C7 produced C5a equivalent to that detected when convertase cleavage occurred in the presence of the terminal components. Mild detergent treatment of convertase-cleaved C5 was not sufficient for C5a release. We believe that these data indicate a role for the terminal complement components in the expression of both C5a antigen and function. The mechanism for this effect is not known, but it may involve conformational changes in the C5 molecule that occur during membrane attack complex formation.

Complement C5↗
PubMed1997

Factors involved in rejection of concordant xenografts in complement-deficient rats.

BACKGROUND: Factors that contribute to xenograft (Xg) rejection were investigated in complement C6-deficient (C-) PVG rats. METHODS: First and second hamster hearts were transplanted in C6-deficient and C6-sufficient PVG rats. Xenoantibody (XAb) formation, hemolytic C (CH50) activity and immunohistochemistry were studied. RESULTS: PVG C6-deficient rats rejected Xgs 3 days later than PVG C6-sufficient rats. Surprisingly, C activation participated in the rejection in PVG C- rats, as shown by partially recovered serum CH50 levels and deposition of C factors in the Xgs. As we found that cultured endothelial cells produced C6 in vitro, we hypothesized that Xg endothelial cells corrected the C6 defect in PVG C- rats. This was probably induced by IgM XAbs as: (1) it did not occur in immunosuppressed PVG C- rats in which XAb formation was prevented, and (2) transfer of IgM XAbs to naive, xenotransplanted PVG C- rats accelerated the recovery of CH50 and concomitantly Xg rejection. Thirty days after rejection of a first Xg, when no IgM XAbs or CH50 activity but high levels of IgG XAbs were detected in PVG C- rats, second Xgs underwent a hyperacute rejection. This time, complement was not involved, as no serum CH50 nor C deposition was found in the Xg. Instead, IgG antibody-dependent cellular cytotoxicity was involved as: (1) IgG XAbs were deposited in the Xg and (2) hyperacute rejection was induced in naive PVG C- rats by transfer of IgG XAbs, and (3) this rejection was delayed to 5+/-3 days if the adoptive hosts were first irradiated. CONCLUSIONS: In the face of a defect of host C factors, IgM XAb may induce cells of the Xg to secrete C factors which may correct the C defect of the host. Even if activation of lytic C can be prevented, IgG XAb may still provoke an acute Xg rejection by antibody-dependent cellular cytotoxicity.

Animals↗
PubMed1975

Consumption of classical complement components by heart subcellular membranes in vitro and in patients after acute myocardial infarction.

Experiments were conducted to characterize the antibody-independent activation of complement in human serum by isolated human heart mitochondrial membranes in vitro and to determine whether similar patterns of complement consumption occurred in patients after acute myocardial infarction. Direct evidence for the interaction of C1 and heart mitochondrial membranes was obtained by mitochondria-C1 binding and elution experiments. Exposure of normal human sera to isolated human heart mitochondria at 37 degrees C resulted in the consumption of C1, C4, C2, and C3 without significant consumption of the terminal components of the complement system (C6 through C9). The consumption occurred in the absence of detectable anti-heart mitochondria autoantibody, was demonstrated to be calcium dependent, and was inhibited by either 0.01 M EDTA or ethylene glycol bis(bets-aminoethyl ether) N,N,N',N',-tetraacetic acid (EDTA). Although specific absorption of C1q from human sera inhibited the mitochondria-dependent activation of C4, C3 donsumption was not affected. These data indicate that the consumption of C4 and C2 likely occurred due to the mitochondrial membrane-mediated activation of C1, but that the consumption of the C3 did not necessarily involve either the classical or alternative complement pathways. After the in vitro characterization of the mitochondria-dependent activation of the complement system, additional studies were performed to determine whether similar consumption occurred in patients after acute myocaridal infarction. During a 72-h period after hospital admission significant decreases in C1, C4, and C3 occurred in six patients with recent chest pain but no evidence of acute myocardial infarction. These studies suggest that myocardial cell necrosis results in the release of subcellular membrane constituents capable of activating the complement system in the absence of detectable anti-heart autoantibodies; such activation may be responsible in part for the development of acute inflammation and evolution of the infarct size following coronary artery occulusion.

Autoantibodies↗
PubMed2002

Modulation of leukocyte recruitment and IL-8 expression by the membrane attack complex of complement (C5b-9) in a rabbit model of antigen-induced arthritis.

The complement system is thought to be a major physiological mediator of injury in a number of diseases including rheumatoid arthritis (RA). The membrane attack complex (MAC) of complement has been detected in RA tissue, suggesting that the MAC may be relevant to the pathogenesis of the disease. Deposition of sublytic concentrations of the MAC has been shown to promote the expression of proinflammatory mediators. In the present study, we utilized rabbits deficient in the complement protein C6 to elucidate the role of the MAC in mediating the pathogenesis of antigen-induced arthritis. Swelling, leukocyte accumulation, IL-8 expression, proteoglycan, and hydroxyproline content were assessed. Analysis of synovial tissue demonstrated a significant decrease in leukocyte influx and a parallel decrease in tissue associated IL-8 in joints of C6-deficient animals as compared to C6-sufficient animals. However, this did not correlate with the preservation of connective tissue. The results derived from this study provide evidence that the MAC has an important function in mediating leukocyte recruitment in antigen-induced arthritis but does not play a direct role in connective tissue breakdown.

Animals↗
PubMed2000

[C6 deficiency].

Explore the source record for details and available documents.

Autoimmune Diseases↗
PubMed1993

Structure of the human C6 gene.

The terminal components of the complement system (C6-C9) are related proteins, differing in size and complexity. They seem to be typical mosaic proteins, composed of modules which are homologous with parts of other proteins. Individual elements in a mosaic protein are often bounded by introns in the gene, and where they are duplicated within a polypeptide, partial gene duplication within the gene is responsible. It is often found in such genes that the intron/exon boundaries are of the class 1 type. We have examined the boundaries of 17 of the 18 exons of C6 and five of C7. When considered with published data for C9, only one of the protein elements appears to follow the conventional pattern. These data suggest a more complex evolutionary history for the genes of the terminal complement components than had been anticipated and challenge the notions both that discovery of a recognized protein module is of predictive value in relation to gene structure and that these genes evolved from the simple to the complex.

Amino Acid Sequence↗
PubMed1998

Complement contributes to the rejection of complete and class I major histocompatibility complex--incompatible cardiac allografts.

BACKGROUND: We have demonstrated previously that the terminal complement component C6 contributes to the acute rejection of ACI cardiac allografts by PVG recipients. ACI rats differ from PVG rats at major and minor histocompatibility antigens and ACI cardiac allografts stimulate vigorous alloantibody responses in PVG rats. We have now bred the C6 deficiency onto four PVG congenic rat strains to determine the effects of C6 on cardiac allograft survival across individual donor-recipient major histocompatibility complex (MHC) disparities. METHODS: Hearts from C6-deficient PVG.1A (RT1a) donors were transplanted heterotopically to fully MHC-incompatible C6-sufficient and C6-deficient PVG.1L (RT1(1)) recipients, as well as from C6-deficient PVG.R8 (RT1.AaBu) donors to MHC class I incompatible C6-sufficient and C6-deficient PVG. 1U (RT1.AuBu) recipients. RESULTS: Hearts from PVG.1A (C6-) female donors were rejected acutely (7 to 9 days; n = 5) by fully MHC disparate female PVG.1L (C6+) recipients, but they survived significantly longer in female PVG.1L (C6-) recipients (13 to >50 days; n = 6). Slightly better survival resulted in male PVG.1L (C6-) heart transplant recipients of male PVG.1A (C6-) hearts (19 to >50 days [n = 5] vs 6 to 9 days for C6+ male PVG.1L recipients [n = 10]). The C6 deficiency had an even greater effect in PVG.1U recipients of class I MHC disparate PVG.R8 hearts (>50 day survival in C6- PVG.1U recipients [n = 5] vs 6 to 7 days in C6+ recipients [n = 8]). The cardiac allografts elicited similarly vigorous immunoglobulin M and G alloantibody responses in the C6- and C6+ recipients as measured by flow cytometry. At the time of acute rejection, the hearts in the C6+ recipients demonstrated extensive vascular endothelial destruction. In contrast, rejection of hearts by C6- recipients was characterized by endothelialitis, but there was little destruction of the endothelium and limited proliferation of smooth muscle cells in the intima. CONCLUSIONS: These results demonstrate that the terminal complement component C6 can contribute to the rejection of class I or complete MHC-incompatible hearts in rats that have been characterized as "high" alloantibody responders.

Animals↗
PubMed2000

Molecular cloning of the C6A form cDNA of the mouse sixth complement component: functional integrity despite the absence of factor I modules.

The sixth complement component (C6) is an essential component of the biologically active C5b-9 membrane attack complex of the complement system. The multimolecular C5b-9 complex is an important mediator of the biological effects of the activated complement system through its prominent cell signaling and cytolytic functions. To begin to provide essential information and reagents needed to analyze the functions of the complement system in mouse models of human diseases, the cDNA of the A form of mouse C6, which is present in all mouse strains, was cloned and characterized structurally and functionally. Although strikingly homologous in deduced amino acid sequence and modular structure to human C6 (75% identity), mouse C6 is substantially smaller due to the absence of the two carboxyl-terminal factor I modules (FIMs) found in human C6. Various approaches, including studies with antibody generated to recombinant mouse C6, failed to reveal evidence for FIMs in this form of mouse C6. Despite the absence of these modules in C6A, reported to be important for interactions with C5 in the human system, mouse C6A is functionally active and is readily incorporated into the mouse C5b-9 complex.

Amino Acid Sequence↗
PubMed1999

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.

Amino Acid Sequence↗
PubMed1977

Deviated lysis (d.l.): III. Kinetics of interaction of d.l. activity with chicken erythrocytes: evidence for E formation.

The interaction of d.l. activity with chicken red cells (CE) generates a cell intermediate with the properties of classical E*. Generation of CE* by d.l. activity at 37 degrees C is rapid, while there is a considerable lag in the conversion of CE* to ghost and hemoglobin. Conversion of CE* to ghosts can be blocked by high concentration of EDTA and/or 0 degrees C. CE* contain at least C6 and C9 on their surface.

Animals↗
PubMed2000

Membrane attack complex formation on yeast as trigger of selective release of terminal complement proteins from human polymorphonuclear leukocytes.

It has recently been shown that measurable amounts of complement proteins, C6 and in particular C7, are released from human polymorphonuclear leukocytes (PMNs). The aim of the present study was to investigate the impact of opsonized Candida albicans on this release. Stimulation with opsonized C. albicans led to a rapid and sustained increase of C6 and C7 in the cell culture supernatant beginning within 5 min of placing in co-culture, whereas co-culture with unopsonized C. albicans or C. albicans mock-opsonized with inactivated human serum did not affect the release. In contrast, even after stimulation employing opsonized C. albicans, no release of the complement component C8 and only trace amounts of C9 were detected. The presence of the membrane attack complex (MAC) on C. albicans after opsonization was demonstrated by indirect immunofluorescence. Opsonization of C. albicans with human serum deficient in or depleted of a terminal complement component resulted in only minor stimulation of C6 and C7 release, although C3 deposition on the surface of C. albicans was not affected as determined by direct immunofluorescence. Detailed analyses with inactivated or deficient sera showed that detection of C6 and C7 was not due to insufficient washing of the opsonized yeast prior to co-culture and suggest that only a small proportion of these proteins was derived from the membrane bound and then cleaved off MAC. Thus, these findings imply that MAC on the fungal surface may represent an additional trigger for the release of C6 and C7 from PMNs, suggesting a new role for the terminal complement complex (TCC) on target membranes as modulator of PMN functions locally at the site of inflammation.

Candida↗
PubMed1991

Human umbilical vein endothelial cells synthesize functional C3, C5, C6, C8 and C9 in vitro.

Human endothelial cells (EC), cultured serum-free, synthesize de novo protein which increasingly bind to agarose beads (an alternative pathway activator), until a plateau phase is reached after 24-48 h. EC synthesize functional C3, C5, C6, C8 and C9, which were detected on co-cultured agarose beads, using relevant polyclonal anti-complement antibodies. Two monoclonal anti-C9 neoepitope antibodies (aE11, poly C9-MA) bound to the co-cultured beads, showing that the terminal complement complex (TCC) (C5b-9) was assembled on the beads. This also suggests that C7 is synthesized. There seems to be a positive correlation between the amount of agarose-bound labelled protein and agarose-bound complement. The results indicate that EC produce and secrete the components for the functional alternative and terminal pathways of complement.

Antibodies, Monoclonal↗