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PubMed1986

Immobilized doxorubicin increases the complement susceptibility of human melanoma cells by protecting complement component C3b against inactivation.

Human melanoma cells resistant to killing by monoclonal antibody R24 plus human complement became susceptible after treatment with doxorubicin (adriamycin). Treatment with doxorubicin prevented the rapid degradation of surface-bound complement component C3b that has been identified as a protective mechanism of complement-resistant melanoma cells. Doxorubicin caused the increased complement susceptibility as free drug and after immobilization onto glass beads to prevent cellular uptake. Immobilized doxorubicin was more effective than free drug, causing enhanced complement susceptibility at concentrations where the free drug was no longer active. In contrast to free doxorubicin, which exhibited a direct cytotoxic effect leading to cell death within 4 days, immobilized doxorubicin did not affect cell viability. These findings suggest that combination therapy of the complement-activating monoclonal antibody R24 with the complement-enhancing drug doxorubicin may be a promising approach for the treatment of melanoma.

Antibodies, Monoclonal↗
PubMed1972

Role of antibody and complement in the immune clearance and destruction of erythrocytes. II. Molecular nature of IgG and IgM complement-fixing sites and effects of their interaction with serum.

A model for the immune clearance and destruction of homologous erythrocytes has been further explored. In this model, every IgM anti-erythrocyte antibody molecule in an antibody preparation was shown to fix Cl. About 2000 IgG antibody molecules were required to form a Cl-fixing site on the guinea pig erythrocyte surface. 60 IgM complement-fixing sites per erythrocyte were required for the immune clearance of IgM-sensitized erythrocytes. This number of sites could be detected by a direct agglutination test. 1.4 complement-fixing sites were required for immune clearance of IgG-sensitized cells, a number of molecules which could not be detected by direct agglutination. This number could, however, be detected with the use of a Coombs antiglobulin reagent. Depletion of the late components of complement (C3-9) with cobra venom was associated with the loss of ability to clear IgM-sensitized cells and a marked deficit in the ability to clear IgG-coated cells. Thus, late (C3-9) components of complement as well as an early component (C4) were required for normal clearance of sensitized erythrocytes. There was no evidence that activation of the alternate pathway of complement action could lead to accelerated erythrocyte clearance. In vitro incubation of IgG and IgM-sensitized erythrocytes in fresh serum led to deposition of C3 and C4 on the erythrocyte surface. IgM-sensitized cells treated in this way had a normal survival. IgM-sensitized cells also were shown to remain Coombs positive after their release from the liver. The evidence suggests that the interaction of an IgM site with fresh serum in vitro and in vivo leads to formation of a site which allows for sequestration of cells in the liver. With continued exposure to serum components, this site is destroyed or inactivated. This serum-dependent inactivation is complement-dependent as shown by the use of EDTA-treated and C4-deficient serum. IgG complement-fixing sites are only partially inactivated by incubation in fresh serum, further emphasizing the differences in the biologic activity of IgM and IgG antibodies.

Animals↗
PubMed1989

Differential susceptibility of haemolysin-sensitized erythrocytes to complement-mediated cytotoxicity: a biological manifestation of the relationship between antibody availability and complement fixation.

The influence of the concentration of membrane-bound antibody on the susceptibility of individual human erythrocyte populations to complement-mediated haemolysis has been examined using cold competition analysis. It was observed that under conditions where complement is limiting, the relative susceptibility of erythrocytes to complement lysis is dependent on the availability of sensitizing antibody, even when all target red cells possess sufficient membrane antibody to permit maximal lysis in the presence of excess complement. Furthermore, preliminary evidence is presented which suggests that, where the availability of complement is limiting, sensitized blood group A erythrocytes are more susceptible to complement lysis than are sensitized group B cells. Taken together the data indicate that the quantity, and possibly the distribution, of the membrane antibody dictates the relative susceptibility of erythrocytes to complement haemolysis.

ABO Blood-Group System↗
PubMed1992

Assessment of disease activity and impending flare in patients with systemic lupus erythematosus. Comparison of the use of complement split products and conventional measurements of complement.

OBJECTIVE: To determine whether increased levels of the complement split products generated in the activation of the alternative or classical pathway accompany more severe disease activity in patients with systemic lupus erythematosus (SLE) and whether these measurements are useful in predicting flares of disease. METHODS: Levels of Ba, Bb, SC5b-9, and C4d were measured in 380 plasma samples obtained from 86 SLE patients who were prospectively followed up for 15 months. RESULTS: In the 20 patients who had inactive disease at the initiation of the study, the mean values of all of the complement split products at entry were within the normal range. In the 47 patients with stable or moderate disease activity, levels of Ba were significantly increased, while the mean values for Bb, SC5b-9, and C4d did not differ significantly from those in patients with inactive disease. The mean entry value of each analyte was highest in the group of 19 patients who had the most severe disease activity at initial evaluation. Traditional measurements of complement, i.e., C3, C4, and CH50, followed similar trends, but did not discriminate between the 3 groups of patients as well as did measurements of the split products. Analysis of the disease course in the patients with inactive or stable/moderate disease revealed that an elevated level of C4d had the most sensitivity with regard to subsequent flare, while an elevated Bb level had the highest specificity and the greatest predictive value. CONCLUSION: These data suggest that elevated levels of complement split products, particularly products of alternative and terminal pathway activation, more accurately reflect disease activity than do conventional measurements of complement in SLE and may be useful in the prediction of impending disease flares.

Complement C3 Convertase, Alternative Pathway↗
PubMed1992

Regulation of complement activity by vaccinia virus complement-control protein.

A major protein secreted by vaccinia virus-infected cells has structural similarity to the super-family of complement-control proteins. This vaccinia complement-control protein (VCP) was studied to determine how it regulates complement activation. VCP was bound by C4b and C3b and served as a cofactor with factor I in cleaving these two molecules. VCP inhibited the formation and accelerated the decay of the classical C3 convertase. It also accelerated decay of the alternative pathway convertase, although higher concentrations were apparently needed. In vitro, therefore, VCP interfered with the classical and alternative complement pathways at several steps. In vivo, this interference may increase the virulence of vaccinia virus by enabling it to escape attack by the host's complement system.

Complement Activation↗
PubMedDate not supplied

In vitro activation of human complement by polyacrilonitrile dialyzer membrane assayed by complement binding to bystander red cells.

Quantitation of complement activation by polyacrilonitrile (PAN) dialyzer membrane is complicated by the high adsorptive capacity of the membrane for fluid phase anaphylotoxins. Assays for these anaphylotoxins, therefore, underestimate the degree of complement activation produced by this membrane. Alternative methods of measuring in vitro complement activation by the PAN and Cuprophan membranes were explored by incubating normal human erythrocytes with the membranes in the presence of serum. This led to deposition of C3d on these "innocent bystander" red cells, and provided an independent parameter for measuring complement activation. The PAN membrane caused significantly more C3d deposition on red cells, and thus more complement activation than Cuprophan. The possible significance of complement activation by PAN membrane, in consideration of its property of binding the resultant anaphylotoxins, is discussed.

Acrylic Resins↗
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↗
PubMed1981

Complement requirement for virus neutralization by antibody and reduced serum complement levels associated with experimental equine herpesvirus 1 infection.

Pony foals, negative for detectable serum-neutralizing antibody to equine herpesvirus 1 by the standard tube-culture virus neutralization test, were experimentally infected with equine herpesvirus 1. Complement-requiring (CR) and non-complement-requiring (NCR) serum-neutralizing antibodies were evaluated in preinfection and postinfection sera by means of a complement-enhanced plaque reduction assay. Low levels of CR antibodies were found in the preinfection sera of only group II ponies. Upon infection, CR antibodies were detected by day 2 postinfection and reached peak titers between 7 and 14 days postinfection in the antisera of all ponies. NCR antibodies were detected later than CR antibodies and at levels approximately 40 to 150 times lower than the latter. CR/NCR ratios indicated that complement requirement was greatest early in the acute stages of disease and that this requirement decreased during the convalescent phase. Fractionation of 1-week and 2-week postinfection antisera of group I ponies indicated the CR antibody activity resided in both the 7S and 19S fractions. Total serum complement levels of the ponies were quantified throughout the infection with an equine anti-goat erythrocyte hemolytic system. In vivo, complement levels were depressed for all ponies during the first 2 weeks of infection. A decline in complement levels was seen as early as day 2, and they decreased to an average of 35% of preinfection levels on day 10 postinfection for all ponies.

Animals↗
PubMed1991

Complement depletion in vitro limits monoclonal antibody 6-19-dependent complement-mediated killing of tumor cells in bone marrow.

Selective killing of nonhematopoietic tumor cells in bone marrow harvested for autologous bone marrow transplantation was studied using cultured neuroblastoma cells, monoclonal antibody 6-19, and baby rabbit serum as a source of complement. Monoclonal antibody 6-19, a murine IgG2a antibody, was selected for binding to a cell surface antigen on cultured human neuroblastoma cells that is not expressed by hematopoietic cells. The antigen is an 80-kd sialoglycoprotein present on a wide variety of nonhematopoietic tumors, and it is expressed by normal fibroblast and endothelial cells. The effect of the presence or absence of bone marrow mononuclear cells on target cell survival was evaluated using Hoechst 33342-stained neuroblastoma cells, trypan blue exclusion, and fluorescence microscopy. More than 4 logs of neuroblastoma cells were destroyed in the presence of a more than tenfold excess of bone marrow cells following two incubations with monoclonal antibody 6-19 and complement for 30 min at 37 degrees C. Monoclonal antibody concentrations greater than 5-10 micrograms/ml did not increase cell lysis. The destruction of tumor cells was limited by depletion of complement activity. Tumor cell killing increased with complement concentration and incubation duration but there was no additional cell lysis with incubations greater than 30 min. The percentage of target cells killed was significantly decreased when the target cells were treated in the presence of increasing concentrations of bone marrow mononuclear cells. This decrease in target cell destruction is a result of additional depletion of complement activity by bone marrow mononuclear cells. These results suggest that optimal purging of tumor cells by antibody and complement will be achieved following multiple brief incubations with fresh antibody and complement.

Antibodies, Monoclonal↗
PubMed1975

Complement activation by interaction of polyanions and polycations. I. Heparin-protamine induced consumption of complement.

Interactions of heparin and protamine in fresh human serum, in amounts far below those required for complement depletion by either agent alone, were found to induce virtually complete depletion of total hemolytic complement activity. This depletion was dependent on time, temperature, pH, divalent cations, and serum concentration. The predominant complement component hemolytic activity depleted was C1; under appropriate reaction conditions C4 and C2 were depleted as well. Equivalent amounts of heparin along induced lesser but substantial depletion of C3-9, whereas equivalent amounts of protamine had no effect upon complement component activities. We conclude that interaction of heparin with protamine, like interaction of antibody with antigen, markedly enhances its ability to interact with the first component of complement and activate the classical complement pathway. It is suggested that complement activation by interactions between certain polyanions and polycations, like interactions between antigens and antibodies, may have a role in the initiation of inflammatory reactions.

Adult↗
PubMed1986

Complement, membrane glycoproteins, and complement receptors: their role in regulation of the immune response.

To determine the effect of complement on the normal antibody response we studied seven patients with genetically determined complement component deficiencies, guinea pigs deficient of C4 and C2, respectively, and two patients whose neutrophils and monocytes lack the C3bi receptor. Patients deficient of early complement components (C4, C2, C3) have abnormal antibody responses to the T-cell-dependent antigen, bacteriophage phi X 174. Complement-deficient guinea pigs (C4, C2) produce less antibody than normal guinea pigs and are unable to maintain measurable antibody levels; during secondary immunization they fail to develop amplification and to switch from IgM to IgG. This defect can be overcome by increasing the antigen dose or by injecting normal guinea pig serum at the time of the primary (but not the secondary) immunization. Patients with deficiency of the C3bi receptor were shown to have a significantly depressed antibody response to T-dependent antigens. We postulate that the contribution of complement to the mature humoral immune response is related to activation of C3. The initial production of IgM following antigen injection leads to antigen-antibody complexes which interact with complement, to be nonspecifically trapped by C3b and C3bi receptors on B cells or macrophages. Thus antigen is selectively accumulated within the lymphoid organs and in turn may entrap antigen-specific B cells by interaction of the trapped antigen with surface immunoglobulin. As a result, close approximation between antigen, antibody, and a network of specific and nonspecific lymphoid cells is initiated, allowing generation of specific memory cells and initiation of a prompt mature antibody response on subsequent exposure to antigen.

Animals↗
PubMed1994

Hereditary deficiency of the seventh component of complement and recurrent meningococcal infection: investigations of an Irish family using a novel haemolytic screening assay for complement activity and C7 M/N allotyping.

Terminal complement component deficiency predisposes to meningococcal infection and is inherited in an autosomal co-dominant manner. An Irish family is described, in which 2 of 3 brothers had recurrent meningococcal infection. A novel screening assay was used to investigate for terminal complement deficiency and the 2 affected brothers were found to be completely deficient in the seventh component of complement (C7). Enzyme-linked immunosorbent assay for C7 revealed lower than normal levels in the remaining brother and parents. C7 M/N protein polymorphism allotyping, used to investigate the segregation of the C7 deficiency genes, showed that the apparently complement sufficient brother was heterozygous C7 deficient and a carrier of one of the deficiency genes. Complement screening should be carried out in any individual suffering recurrent meningococcal infection or infection with an uncommon meningococcal serogroup. Identification of complement deficient patients allows the implementation of strategies to prevent recurrent infection.

Adolescent↗
PubMed1989

Killing of gram-negative bacteria by complement. Fractionation of cell membranes after complement C5b-9 deposition on to the surface of Salmonella minnesota Re595.

The effect of C5b-9 deposition on the envelope of target Gram-negative bacteria was studied. In order to understand the changes occurring after complement deposition on the bacterial surface, the preparation of Gram-negative bacterial membranes by different methods involving the osmotic lysis of spheroplasts was investigated. Subsequent fractionation of the outer membrane (OM) and cytoplasmic membrane (CM) by sucrose-density-gradient centrifugation showed differences in the membrane profiles obtained. The results indicate that optimum separation of OM and CM components requires effective digestion of DNA in the total membrane preparation before density-gradient fractionation. Salmonella minnesota Re595 carrying the intermediate complement complex C5b-7 (BC1-7) or C5b-8 (BC1-8) were efficiently killed upon incubation with purified C8 + C9 or C9 respectively. Human-alpha-thrombin-cleaved C9 (C9n), which is unable to form tubular poly(C9), was shown to be more effective at killing than native C9. By using an optimized system for the separation of OM and CM, it was found that, subsequent to lethal complement attack, the CM could not be recovered when C9 was used as the terminal complement component, but was recovered with reduced yield when C9n replaced C9. The results show that inability to recover the CM on sucrose density gradients after complement attack may not be a consequence of an essential membrane damage event required for complement-mediated killing of Gram-negative bacteria.

Cell Fractionation↗
PubMed1987

Chemotactic factor-induced low density neutrophils express enhanced complement (CR1 and CR3) receptors and increased complement-dependent cytotoxicity.

We have studied chemotactic factor-induced 'complement receptor enhancement' to determine whether changes in receptor expression and complement-dependent cytotoxicity were associated with alterations in cell density. Ficoll-Paque separated normal human neutrophils (greater than 90%), when further fractionated on discontinuous metrizamide (MTZ) gradients (18, 19, 20, 21, 22, 23% MTZ), consistently gave two major bands at the 20/21% and 21/22% interfaces. Incubation with the synthetic chemotactic peptide, N-formyl-methionyl-leucyl-phenylalanine (fMLP (10(-8) M)), converted virtually all neutrophils to low density cells sedimenting on MTZ at the 18/19% and 19/20% interfaces. There was a time-dependent change of density after fMLP-stimulation which was maximal at 30 min, with cells reverting towards normal density by 60 min. Control unstimulated cells did not alter their density at any of the time points examined. Activated, low density neutrophils had increased expression of CR1 and CR3 (as shown by flow cytometry and the uptake of 125I-F(ab')2 monoclonal anti-CR1 antibody (E11)). These cells also showed enhanced cytotoxic capacity in vitro for helminthic targets (schistosomula of Schistosoma mansoni) opsonized with autologous complement. There were highly significant correlations between cell density and anti-CR1 uptake (P less than 0.001), and between schistosomular killing and change in density (P less than 0.001). Increased CR1 expression also correlated with enhanced helminthicidal capacity of neutrophils (P less than 0.001). Complement dependent cytotoxicity was partially reduced after treatment of cells with anti-human CR1 and/or CR3 antibodies, but only in the presence of a second antibody. These findings indicate that chemotactic factor-induced complement receptor enhancement of human neutrophils is associated with a decrease in cell density and increased complement-dependent cytotoxicity (CTX).

Animals↗
PubMed1995

Soluble complement receptor 1 inhibits both complement and granulocyte activation during ex vivo hemodialysis.

Hemodialysis with cellulosic membranes results in both complement and granulocyte activation. We investigated the effects of soluble complement receptor 1 (sCR1), a potent complement inhibitor, on both complement and granulocyte activation in an ex vivo model of dialysis. Measurements were made of complement activation (radioimmunoassay for C3a desArg) as well as granulocyte activation (flow cytometric measurements of reactive oxygen species production, granulocyte CD11b/CD18 (MAC-1) expression and CD62L (L-selectin) expression). sCR1 completely abolished the generation of plasma C3a desArg during ex vivo hemodialysis. Without sCR1, C3a desArg levels rose from 968 +/- 373 ng/ml to 4961 +/- 40 ng/ml by the end of the ex vivo procedure (p < 0.001). sCR1 also completely inhibited MAC-1 upregulation and L-selectin shedding from granulocytes during ex vivo hemodialysis. With sCR1 there was still a statistically significant increase in granulocyte reactive oxygen species production (from 2.42 +/- 0.1 fluorescence channels to 6.47 +/- 0.7 fluorescence channels, p < 0.01) but a 50% inhibition when compared with experiments without sCR1 (3.15 +/- 0.5 to 11.2 +/- 1.9, p < 0.01). We conclude that sCR1 completely abolishes complement activation and changes in granulocyte cell adhesion molecules during ex vivo hemodialysis with cellulosic membranes. sCR1 partially inhibits granulocyte reactive oxygen species formation.

Anaphylatoxins↗
PubMed1985

Increased plasma levels of the terminal complement complex in patients with evidence of complement activation.

The terminal C5b-9 complex of human complement has recently been described and quantified in normal human plasma by an enzyme-linked immunosorbent assay (ELISA). We collected EDTA plasma samples from 20 patients clinically suspected to have complement activation. The terminal complement complex (TCC) and C3d split products were measured. The TCC was increased in 8 patients, and 6 of these also had increased C3d values, whereas 4 patients had increased C3d and normal TCC values. Two different double-antibody assays were used to detect terminal pathway activation: the combination of anti-C6 and anti-C9 detecting only the whole complex, and the combination of anti-C6 and anti-C5 detecting intermediate complexes as well. There was a close correlation between the observations in these two assays, suggesting that in general the whole cascade including C9 is involved when the terminal pathway of complement is activated in vivo. Quantification of TCC in plasma is an important supplement to already established methods for the evaluation of complement activation in vivo.

Adult↗
PubMed1991

[The relationship between complement C3 receptors (CR1, CR3) on polymorphonuclear leukocytes and complement fragments during hemodialysis].

The expression of complement receptor type 1 (CR1) and type 3 (CR3) on polymorphonuclear leukocytes (PMNs) and generation of complement fragments, C3a, C5a, C4d, iC3b and Bb, were studied in patients during hemodialysis using cuprammonium rayon (Cu) membranes. Furthermore, the relation between the expression of CR1 and CR3 on PMNs from healthy donors and complement fragments was investigated. The expression of CR1 and CR3 on PMNs increased during hemodialysis. Plasma C3a, C5a and iC3b levels increased in the first 15 minutes and then decreased at 120 minutes of dialysis. But plasma Bb level remained high until the end of hemodialysis. Purified Bb had no effect on the expression of CR1 and CR3 on PMNs, but C5a augmented those expression in vitro. Nafamostat mesilate, an artificial proteinase inhibitor, inhibited augmentation of complement receptors on PMNs in concentration dependent fashion. C5a generated through the activation of complement was thought to take an important role in the increased expression of CR1 and CR3 on PMNs.

Aged↗
PubMed1977

Complementable fraction and complemented enzyme of mutant M15 from Escherichia coli: partial purification by affinity chromatography.

The technique of affinity chromatography has been used in the partial purification of complementable fractions and complemented enzyme of beta-galactosidase from Escherichia coli mutant M15. The crude extract of mutant M15 was incubated with fragment CM-B. The complemented enzyme and complementable fractions were passed through a small column of p-aminophenyl-beta-D-thiogalactoside to which inhibitors had been covalently attached. A high percentage of the nonspecific protein passed directly through the affinity column while the specific enzymatic protein remained bound to the gel. Phosphate buffer with NaCl was used to elute the complementable fractions from the column. Sodium borate buffer was used to elute the bound complemented enzyme from the affinity support. The results of this study show that 100% of the complemented enzyme was bound to the column. The partially purified enzyme had the same position in disc gel electrophoresis as beta-galactosidase from E. coli.

Chromatography, Affinity↗