PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Complement Pathway, Classical”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 199 records · Page 11Linked to original sources
PubMed1997

Neuronal expression of mRNAs for complement proteins of the classical pathway in Alzheimer brain.

To determine possible sources of complement proteins in the brain, we investigated by in situ hybridization expression of the mRNAs of C1q, C2, C3, C4, C5, C6, C7, C8 and C9 in postmortem Alzheimer disease (AD) and control brain tissue. We found detectable hybridization for all these components in the temporal cortex and hippocampus, with significantly higher levels being found in AD tissue. Hybridization signals were strongest over pyramidal neurons. Low or absent hybridization was seen in the visual cortex or cerebellum. These results suggest that the activated complement components found in association with AD lesions may be, in part, derived from neurons.

Aged↗
PubMed1991

Human serum induced opsonization of immunoglobulin G-coated polystyrene microspheres with complement components C3 and C4 as measured by flow cytometry.

Human IgG-coated polystyrene microspheres (IgG-ms) were incubated with human serum followed by biotinylated monoclonal anti-C3d or anti-C4d antibody, and phycoerythrin-streptavidin. The intensity of fluorescence was measured by flow cytometry and corresponds to the amount of deposited C3 and C4. Binding of C3 and C4 was dependent on the activation of the classical pathway of complement and on the amount of IgG adsorbed to the particles. No deposition was observed on control particles coated with bovine serum albumin or ovalbumin. Incubation of constant amounts of IgG-ms with increasing amounts of normal human serum (NHS) resulted in a dose-dependent increase in C3 deposition. The same result was found for C4 deposition at moderate NHS dilutions, but less C4 was detectable using a higher input of NHS. Half-maximum C3 and C4 deposition was observed at a mean serum dilution of 1/114 and 1/520, respectively (n = 26). No correlation was found between C4 or C3 deposition and either total C4 and C3 serum concentrations as measured by nephelometry or complement-mediated lysis of antibody-coated sheep red blood cells. Reduced or absent C4 or C3 deposition was found in the sera of patients with low amounts or deficiencies of components involved early in classical complement pathway activation whereas essentially normal C4 or C3 deposition was obtained with the sera of patients with deficiencies in components of the membrane attack complex. With this simple and specific functional assay using stable reagents an altered function of early components of the classical pathway of complement may be quickly and reliably detected in routine diagnostic laboratories. Moreover, such opsonized and well characterized particles may be useful in assays of phagocytic cell function.

Complement C3↗
PubMed1993

Biotinylation of monoclonal antibodies prevents their ability to activate the classical pathway of complement.

Biotinylation of mAb has become a standard procedure for a variety of applications that exploit the specific high affinity interaction between biotin and avidin. In the present study, we investigated how biotinylation of mAb affects their ability to sensitize target cells to C-dependent lysis in vitro. mAb were biotinylated by cross-linking biotin covalently with an N-succinimidyl ester to the epsilon-amino groups of lysine residues. Human RBC were treated with two rat mAb, either alone or together: one against glycophorin A (YTH89.1), another against CD59 (protectin; YTH53.1), an inhibitor of the membrane attack complex of C. Melanoma cells (G361) were attacked by a mouse mAb (27A) against an O-acetylated GD3 ganglioside. As compared with the nonbiotinylated mAb, the biotinylated forms of all the investigated mAb were much weaker in causing classical C pathway-mediated lysis of the target cells. Biotinylation did not reduce the ability of the mAb to bind to their Ag, nor of the anti-CD59 mAb to neutralize the C lysis-restrictive effect of CD59. In binding assays using 125I-labeled C1q, significantly less C1q bound to the biotinylated anti-glycophorin-A and anti-CD59 mAb than to the nonbiotinylated mAb. These data show that biotinylated antibodies do not activate the classical C pathway because binding of C1q to the antibody Fc-regions is blocked.

Animals↗
PubMed1997

Inhibition of human complement by beta-glycyrrhetinic acid.

Licorice, the root extract of Glycyrrhiza glabra I., is used as a medicine for various diseases. Anti-inflammatory as well as anti-allergic activities have been attributed to one of its main constituents, glycyrrhizin. These activities are mainly ascribed to the action of the aglycone, beta-glycyrrhetinic acid. beta-Glycyrrhetinic acid has a steroid-like structure and is believed to have immunomodulatory properties. To determine whether interference with complement functions may contribute to the immunomodulatory activity of beta-glycyrrhetinic acid, its effects on the classical and alternative activation pathways of human complement were investigated. We found that beta-glycyrrhetinic acid is a potent inhibitor of the classical complement pathway (IC50 = 35 microM), whereas no inhibitory activity was observed towards the alternative pathway (IC50 > 2500 microM). The anticomplementary activity of beta-glycyrrhetinic acid was dependent on its conformation, since the alpha-form was not active. It was also established that naturally occurring steroids, e.g. hydrocortisone and cortisone, did not inhibit human complement activity under similar conditions. Detailed mechanistic studies revealed that beta-glycyrrhetinic acid acts at the level of complement component C2.

Administration, Topical↗
PubMed1980

Killing of the S and Re forms of Salmonella minnesota via the classical pathway of complement activation in guinea-pig and human sera.

The S (wildtype) and Re form (heptose-deficient, core-defective mutant) of Salmonella minnesota were killed by treatment with normal guinea-pig serum (GPS). Using C4-deficient GPS and serum containing 0.02 M ethyleneglycol-bis-(beta-aminoethylether)-tetraacetic acid and 0.02 M MgCl2 (EGTA-Mg2+) a reduced killing rate was observed. In normal GPS diluted 1:10 containing 0.02 M EGTA-Mg2+ or in C4-deficient GPS diluted 1:10 no killing occurred, whereas the same serum dilution without EGTA-Mg2+ showed a strong bactericidal effect indicating a dependency upon C4 and Ca2+ ions. Furthermore, in contrast to normal human serum (NHS) no killing occurred in a selective complete C1q-deficient human serum. The bactericidal effect, however, could be restored by addition of highly purified C1q; this is a further indication for a dependency upon the classical pathway of C activation. The C-dependent bactericidal activity was totally abolished when phosphate buffer was used, partially reduced in the presence of veronal-buffered saline (VBS), and not affected by tris-(hydroxymethyl)-aminomethane(Tris) or thioglycollate-buffered system EGTA-Mg2+ alone slightly reduced the growth rate of the bacteria whereas disodium ethylene diaminetetraacetate (EDTA) had a bacteriostatic effect on the S-form. The inhibition of the growth of the Re-form by EDTA was amplified by the addition of serum. Pre-incubation of bacteria with serum for absorption of antibodies did not increase the killing rate of such pre-treated bacteria excluding an antibody-mediated bactericidal reaction. Furthermore, pre-treatment of the bacteria with GPS at 0 degrees reduced the serum sensitivity of both types of bacteria.

Animals↗
PubMed1996

Immune evasion properties of herpes simplex virus type 1 glycoprotein gC.

Herpes simplex virus type I (HSV-1) glycoprotein gC binds complement component C3b, and purified gC inhibits complement activation. Two HSV strains carrying mutations in the gC gene which rendered them unable to bind C3b were compared with wild-type and marker-rescued viruses to evaluate the role of gC on the virion in protecting HSV-1 from complement-mediated neutralization. The gC mutant viruses were markedly susceptible to neutralization by nonimmune human serum, showing up to a 5,000-fold decline in titer after 1 h of incubation with serum. In contrast, wild-type or marker-rescued viruses showed a twofold reduction in titer. Studies with hypogammaglobulinemic and immunoglobulin G-depleted serum supported the observation that neutralization occurred in the absence of antibody. Neutralization of gC mutant strains by nonimmune serum was rapid; their half-life was 2 to 2.5 min, compared with 1 h for wild-type virus. Ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid (EGTA)-treated human serum or C4-deficient guinea pig serum failed to neutralize gC mutant strains, indicating a role for components of the classical complement pathway. gC had little additional effect on neutralization by the combination of antibody plus complement compared with complement alone. The results indicate that the magnitude of the protection offered by gC-1 is larger than previously recognized; that in the absence of gC-1, complement neutralization is rapid and is mediated by components of the classical complement pathway; and that gC mainly protects against antibody-independent complement neutralization, suggesting a probable role for gC early in infection, before antibodies develop.

Animals↗
PubMed1975

Interaction of peptidoglycans with anti-IgGs and with complement.

This report describes the interaction of peptidoglycan (Streptococcus group A, Staphylococcus epidermidis and Micrococcus lysodeikticus) with 2 serum mediator systems, namely with the anti-IgG system and with complement. The observation that the majority of rabbits hyperimmunized with A-variant streptococcal vaccine produced anti-group carbohydrate antisera containing anti-IgGs and antibodies directed to peptidoglycan suggested that the production of these 2 latter antibodies was related. This view was supported by the finding of a monoclonal 7S anti-IgG with antibody specificity for the pentapeptide of peptidoglycan as evidenced by inhibition of the coprecipitation of 7S anti-IgG with antigen-antibody complexes by the pentapeptide. Inhibition of the anti-idiotype reaction by the pentapeptide provided further evidence for the antibody specificity of 7S anti-IgG for peptidoglycan. When added to normal human sera all peptidoglycan preparations inhibited the hemolytic activity of the sera. Consumption of C3 in C2 deficient serum and consumption of C2 in normal serum indicated the activation of both known complement pathways. Activation of the classical pathway of complement was more efficient since 50 mug of peptidoglycan consumed approximately 70% of C2 per ml normal serum whereas more than 2 mg of the same preparations was required to inactivate 17-24% of C3 in C2 deficient sera. Each of the different peptidoglycan preparations consumed similar amounts of complement in all 20 sera tested. This finding suggested that activation of the classical complement pathway by peptidoglycan was not mediated by anti-peptidoglycan antibodies present in only 20-40% of normal human sera.

Animals↗
PubMed1992

DNA binds and activates complement via residues 14-26 of the human C1q A chain.

The mechanism by which DNA activates the classical complement pathway was investigated, with emphasis upon the C1q binding sites involved. DNA bound to both the collagen-like and globular regions of C1q. Binding reactivity with DNA was retained after reduction/alkylation and sodium dodecyl sulfate treatment of C1q. DNA bound preferentially to the A chain of C1q. Binding sites for DNA were localized by using synthetic C1q A chain peptides to two cationic regions within residues 14-26 and 76-92, respectively. Peptides 14-26 and 76-92 avidly bound DNA in enzyme-linked immunosorbent and gel shift assays. Peptide 14-26 also precipitated with DNA and blocked its ability to bind C1q and activate C. Replacement of the two prolines with alanines or scrambling the order of the amino acids resulted in loss of ability of peptide 14-26 to inhibit C1q binding and complement activation by DNA; similar investigations showed a sequence specificity for peptide 76-92 as well. These experiments identify C1q A chain residues 14-26 as the major site, and residues 76-92 as a secondary site, through which DNA binds C1q and activates the classical complement pathway, and demonstrate that a peptide identical to residues 14-26 can modulate C1q binding and complement activation by DNA.

Amino Acid Sequence↗
PubMed1990

Binding of the pentamer/hexamer forms of mannan-binding protein to zymosan activates the proenzyme C1r2C1s2 complex, of the classical pathway of complement, without involvement of C1q.

The serum lectin, mannan binding protein (MBP), was isolated in a yield of 40 micrograms/liter from pooled normal human serum by affinity chromatography on mannan-Sepharose, followed by gel-filtration and ion-exchange chromatography and finally by passage down an anti-IgM Sepharose column. A rabbit antiserum was prepared against the purified MBP and an enzyme-linked immunoassay developed that used both the specificity of the polyclonal antibody and the Ca+(+)-dependent carbohydrate binding property of MBP. Assay of the sera from 103 blood-donors showed a wide range of MBP levels, ranging from 0 to 870 micrograms/liter. MBP, after interaction with zymosan, caused efficient activation of a C1r2 125I-C1s2 complex that was prepared by incubation of 125I-C1s2 with serum, from a patient with a complete genetic deficiency of C1q, followed by gel-filtration on Sepharose 6B. The purified MBP is composed of a mixture of trimers, tetramers, pentamers, and hexamers of an approximate 90-kDa structural unit as judged by chromatography, SDS-PAGE and electron microscopy studies. Only the molecules in the pentamer/hexamer fraction, which have a similar overall structure to that of C1q, appeared to cause efficient, zymosan-dependent, activation of C1s within the C1r2C1s2 complex. The pentamer/hexamer form of MBP may therefore play an important role in antibody-independent activation of the C system during the early stages of certain infections.

Calcium↗
PubMed1987

Antibody-independent activation of C1. II. Evidence for two classes of nonimmune activators of the classical pathway of complement.

Nonimmune activation of the first component of complement (C1) by cardiolipin (CL) vesicles present specific features which were not demonstrated on immune complexes. CL vesicles which activate C1 in the presence of C1-inhibitor (C1-INH) were found to bind C1s in the absence of C1r, and to induce a specific C1r-independent cleavage of C1q-bound C1s. Therefore, several known natural nonimmune activators were analyzed by comparing their ability to activate C1 in the presence of C1-INH and to mediate a C1r-independent cleavage of C1s. Freshly isolated human heart mitochondria (HHM) activated C1 only in the absence of C1-INH. However, mitoplasts derived from HHM (HHMP) activated C1 regardless of the presence of C1-INH, and induced a specific cleavage of C1q-bound C1s. The same pattern was observed in the case of smooth E. coli and a semi-rough E. coli strain. DNA, known to activate C1 only in the absence of C1-INH, does not induce C1s cleavage in the absence of C1r. Thus, nonimmune activators can be classified into two distinct categories. "Strong" activators, such as CL vesicles, HHMP, or the semi-rough E. coli strain J5 can activate C1 in the presence of C1-INH. By using C1qs2 as a probe, they exhibit a specific, C1r-independent cleavage of C1s. C1s-binding to C1q is a critical factor for the activation process in this group. In the case of "weak" activators, such as E. coli smooth strains, DNA, or HHM, no C1s-binding to activator-bound C1q was detected, and C1r-independent C1s cleavage and C1 activation in the presence of C1-INH were not observed. As in the case of immune complexes, C1r activation appears to play a key role in the C1 activation by "weak" activators.

Calcium↗
PubMed1979

Activation of the classical pathway of complement by the C3NeF-stabilized cell-bound amplification convertase.

C3 nephritic factor (C3NeF) has been shown to be composed of two heavy and two light chains, like IgG; in addition it shares antigenic determinants with IgG. C3NeF, purified from the sera of eight patients by incorporation of C3NeF into the stabilized fluid phase amplification C3 convertase, C3bBb(C3NeF), followed by its release after decay of convertase function, was investigated for its ability to bind 125I-C1q and to activate 125I-C1. It was found that although fluid phase C3b,Bb(C3NeF) is fully capable of binding 125I-C1q, it is not able to activate 125I-C1 even at concentrations of 1.3 x 10(12) C3bBb(C3NeF) complexs/ml. On the other hand, cell-bound C3bBb(C3NeF) is capable of both binding 125I-C1q and activating 125I-C1. This discrepancy between fluid phase and cell-bound, C3bBb(C3NeF) was found for C3NeF preparations from eight different patients and therefore seems to apply to all C3NeF preparations.

Binding Sites↗
PubMed1980

Alternate and classical pathway components of complement in the normal cornea.

Activation of complement by either the classical or alternate pathway may be involved in corneal inflammation. This study was undertaken to determine whether the normal human cornea contains components for both classical and alternate pathway activation of complement. Direct immunofluorescence of corneas from human donors using fluorescein-labeled antiserums was used to demonstrate C1q, C3, C4, and C5. The C1q component (the recognition unit of the classical pathway and largest complement component) was found in the periphery of the cornea. Normal donor corneas were also eluted in phosphate-buffered saline at 4 degrees C for one to four days. Ouchterlony plates, in which the corneal eluate was reacted against antiserums to complement components, disclosed the presence of C1q, C3, C4, C5, properdin, and properdin factor B. Plasminogen was also found. Radial immunodiffusion was used to obtain estimates of the concentrations of C3, C4, and C5 in the cornea.

Aged↗
PubMed1982

Immunological aspects of adverse reactions to althesin.

Sequential plasma samples from 30 patients showing clinical signs of hypersensitivity to Althesin were investigated to determine if a specific immune response to the drug was present (as measured by classical complement pathway activation) or if a non-antibody-dependent alternative complement pathway activation was taking place. The patients were classified as those reacting on first exposure to Althesin and those who reacted adversely only on a second exposure. The alternative complement pathway, but not the classical pathway, was activated in five of the 13 first-time reactors, while in the remaining eight no complement activation was detected. In contrast, classical complement pathway activation was demonstrated in the blood samples of all 17 patients reacting on repeat exposure. Severe reactions occurred in nine of the 17 previously exposed patients compared with only one of the 13 reacting on first exposure to Althesin.

Adolescent↗