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Results for “Complement Pathway, Alternative”

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PubMed1989

[Dynamics of inherent interactions between the classical and alternative pathways of complement activation in premature infants with suppurative-inflammatory diseases].

Altogether 57 premature infants were examined. Of these, 15 presented with neonatal sepsis, 36 with local purulent infection (LPI) of different etiology, and 6 children were conventionally normal serving as control. Early activation of the alternative pathway of the complement system was shown by the patients as compared with control. The development of neonatal sepsis was attended by the increased role played by the classical pathway of complement activation. At the same time the course of LPI was characterized by differences in the degree of participation of the classical and alternative pathways in the antiinfectious defence of the neonates. It has been established that high activation of the alternative pathway seen in the premature children may be considered as a prognostic sign enabling one to classify them with the risk group in terms of the possibility of the development in them of an infectious process.

Acute Disease↗

PubMed1985

Activation of the alternative complement pathway in normal human serum by Loa loa and Brugia malayi infective stage larvae.

Infective stage larvae (L3) of Loa loa and Brugia malayi upon in vitro incubation with normal human serum activated the alternative complement pathway. C3 conversion products were detected on larval cuticles by eosinophil adherence and by immunofluorescence with C3c antiserum. No evidence for cuticle binding of IgG, IgA, IgM, Clq, or C4 was found by immunofluorescence. L3-induced C3 activation was inhibited by 10 mM EDTA but unaffected by 10 mM Mg++-EGTA. Human sera deficient in C2, C4, or C6 incubated with L3 resulted in C3 activation. However, sera treated with zymosan or heated for 1 h, 56 degrees C were unreactive with L3. Immunoelectrophoresis of fresh serum exposed to L3 for 1 h at 37 degrees C showed C3 cleavage products. The results indicate that these nematode L3 activate the alternative complement cascade via cuticular surface components. Larval viability was unaffected by complement activation or by adherence of eosinophils.

Animals↗

PubMed1992

Human natural anti-Gal IgG regulates alternative complement pathway activation on bacterial surfaces.

One percent of circulating IgG in humans recognizes galactose alpha 1,3 galactose residues (anti-Gal) and is synthesized in response to stimulation by enteric bacteria. In this study, we found that the prevalence of binding of anti-Gal to blood isolates is significantly higher than its binding to normal stool isolates. When anti-Gal bound onto the lipopolysaccharide of a representative blood isolate, Serratia marcescens #21, it blocked its alternative complement pathway (ACP) lysis and made the organism serum resistant. In contrast, when anti-Gal bound to the capsular polysaccharide of a serum sensitive Serratia, #7, it increased ACP killing of this strain. The mechanism of blockade of ACP lysis by anti-Gal did not involve a decrease in the number of C3 molecules deposited onto Serratia #21 or an inhibition of the binding of C3b to its LPS, nor did it change the iC3b and C3d degradation products of bound C3b or prevent membrane attack complex formation on this organism. Our findings suggest that the effect of anti-Gal on immune lysis is dependent on the bacterial outer membrane structure to which it binds. We postulate that anti-Gal may play a role in the survival of selected Enterobacteriacae in Gram-negative sepsis by blocking ACP-mediated lysis of such bacteria by the nonimmune host, and that this effect depends on where anti-Gal finds its epitope on the bacterial outer membrane.

Complement C3↗

PubMed1987

[Alternative complement pathway activation by anti-band 3 antibodies].

Naturally occurring antibodies against the anion exchange protein of red cells (band 3 protein) can elicit in whole serum a strong C3b deposition to red cells under conditions which favor alternative complement pathway activation. Such a mode of opsonization calls for generation of an alternative C3 convertase nucleated by C3b covalently bound to anti-band 3. Senescent, but not young, red cells should also carry "C3b-anti-band 3" complexes, if clearance of in vivo aged red cells occurred by the same mechanism. We succeeded in isolating covalently linked complexes of C3b and IgG primarily from membranes of senescent red cells.

Anion Exchange Protein 1, Erythrocyte↗

PubMed1992

Studies on activation and levels of haemolytic complement of buffalo (Bubalus bubalis). II. Alternate complement pathway activity in serum.

Buffalo serum caused lysis of unsensitized red blood cells (RBC) of sheep, goat, rabbit and guinea-pig. There was minimal lysis of cattle RBC, and homologous RBC were resistant. Lysis of sheep and goat RBC was the result of natural antibodies as adsorption with respective RBC and addition of 8 mmol ethylene glycolbistetraacetate (EGTA) in diluent completely abrogated the haemolytic activity. The lysis of guinea-pig and rabbit RBC was only partially decreased by these treatments, indicating the presence of alternate complement pathway (ACP) activity in buffalo serum. The guinea-pig RBC were the most sensitive to lysis, and 50% CH titre units above 40 ml-1 of serum were obtained. The haemolytic activity of buffalo C for unsensitized guinea-pig RBC was reduced from 47 CH50 units to an undetectable level by heating at 50 degrees C for 20 min and at 56 degrees C for 4 min. Similarly, treatment with zymosan also inhibited this haemolytic activity. Maximum activation of buffalo ACP occurred in the presence of 4 mmol Mg2+ in the diluent. Using standardized conditions, ACP activity was determined in sera of 98 healthy buffaloes of different age groups from 1 month to 12 years. Even young calves less than three months of age showed considerable ACP activity (45.60 +/- 1.21 CH50 units ml-1) which increased with age. The peak mean values of 79.79 +/- 1.45 CH50 units was recorded in 2 to 4-year-old animals. However, in all the 11 animals above 4 years of age, the haemolytic activity was greatly reduced and was even less than that in 1 to 3-month-old buffalo calves.(ABSTRACT TRUNCATED AT 250 WORDS)

Animals↗

PubMed1989

Effect of membrane phospholipids on activation of the alternative complement pathway.

Although some of the membrane glycoproteins that serve as activators or regulators of C activation have been identified, the influence of membrane lipids has not been studied extensively. A model of alternative C pathway activation was established using liposomes composed of cholesterol and synthetic phospholipids. Liposomes containing phosphatidylcholine (PC) as the sole phospholipid did not activate C as measured by C3 binding after incubation in normal human serum containing 2.5 mM MgCl2 and 10 mM EGTA. When phosphatidylethanolamine (PE) was included as 20% or more of the phospholipid, C3 binding was observed. C3 binding to liposomes was inhibited by salicylhydroxamic acid indicating binding through the C3 thioester bond. The phospholipid composition did not influence C3 binding to liposomes in an unregulated system of C3, B, D, and P indicating equivalent C3b binding sites on activating and nonactivating liposomes. When the regulatory proteins H and I were added to the other components, liposomes containing PE bound three times more C3 than PC liposomes suggesting that the phospholipid affects C3 regulation. This was tested directly in a radiolabeled H binding assay. In the presence of equal amounts of C3b, PC liposomes showed a greater number of high affinity H binding sites than PE liposomes. Using different PE derivatives, C activation could be directly related to the phospholipid polar head group. Liposomes containing PE, trinitrophenyl-PE or monomethyl-PE did activate the alternative C pathway, whereas those containing dimethyl-PE, PC, or phosphatidylserine did not. These studies provide evidence that primary and secondary amino groups on lipid membranes can decrease the interaction between H and C3b and provide sites for alternative pathway activation.

Complement Activation↗

PubMed1990

Discrimination between activators and nonactivators of the alternative pathway of complement: regulation via a sialic acid/polyanion binding site on factor H.

The alternative complement pathway is capable of discriminating human cells and tissues from a wide variety of potential pathogens. It has been recently demonstrated that attachment of complement component C3b to activator-derived molecules (e.g., small polysaccharides) restricts inactivation of C3b by factors H and I in a manner similar to activator surfaces. It is now shown that restriction is reversed by certain soluble polyanions (e.g., sialoglycopeptides, heparin, or dextran sulfate) that mimic the effects of sialic acid and glycosaminoglycans on human cells and tissues. Fluid-phase polyanions enhanced binding of factor H to C3b attached to activating particles, indicating that the effect resulted from increased affinity between C3b and factor H. The enhancement was specific for activator-bound C3b since no enhancement was observed on nonactivating particles. While several polyanions could cause this effect, some polyanions could not, indicating specificity. The active polyanions also inhibited lysis of cells via the alternative pathway. The binding site for sialic acid appears to reside on factor H, since factor H bound to heparin-agarose and to sialic acid-bearing fetuinagarose, whereas C3b bound to neither under the same conditions. These observations suggest that occupation of a specific site on factor H by polyanions induces an increase in the C3b-H affinity, resulting in discrimination of host cells and tissues from alternative pathway-activating foreign cells.

Animals↗

PubMed1973

Activation of the alternate complement pathway by autologous red cell stroma.

The present study demonstrates the ability of human autologous RBC stroma to activate the alternate complement pathway (C3-Activator system, properdin system), as evidenced by the generation of C3-Activator (C3A) from C3-Proactivator (C3PA) when RBC ghosts and sonicated ghosts are incubated with autologous serum. Intact RBC's, hemoglobin, and concentrated platelet stroma, on the other hand, are inactive in this regard. We postulate that this in vitro activity of RBC stroma may occur intravascularly when erythrocytes are damaged by immune or nonimmune mechanisms. The ensuing interaction of activated complement components with platelets leading to release of platelet factor three (PF-3) may constitute a mechanism for activation of the coagulation system during acute hemolytic episodes.

Blood Coagulation↗

PubMed1986

Phagocytosis by human monocytes of unopsonized particulate activators of the human alternative complement pathway: induction by cytokine.

Monocytes isolated from human blood by centrifugal elutriation exhibited little ability to ingest rabbit erythrocytes (ER), zymosan particles, or desialated sheep erythrocytes. In contrast, 85 to 95% of these cells rosetted with C3b- or C3bi-bearing sheep erythrocytes (ES) or ingested IgG-coated ES. Preincubation of the monocytes with human lymphocytes increased their ability to ingest ER. the ER phagocytosis-inducing activity was contained in the 105,000 X G supernatant of lymphocyte lysates. These supernatants increased the percentage of ingesting monocytes from 5 to 15% to 80% within 60 min. The soluble factor was found to be relatively heat stable, inactivated by trypsin, and distinct from IFN-gamma. Its m.w. is less than 13,000. It was present in B and T lymphocytes and also in U937 cells. These results suggest that the ability of human monocytes to ingest nonopsonized particulate activators of the alternative complement pathway is a cytokine-inducible property and that the effect of the cytokine on complement receptor- or Fc receptor-dependent adherence or ingestion of opsonized particles is minor.

Animals↗

PubMed1986

Activation of the alternative complement pathway by Sporothrix schenckii.

We studied the activation of complement by Sporothrix schenckii yeast cells. Total complement activity, and the effect of various activators on this activity, were assayed on aliquots of fresh nonimmune human serum with and without prior treatment with chelators. Both total hemolytic complement and C3 were consumed (activated) in serum chelated with magnesium ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid, which blocks the classical pathway but leaves the alternative pathway intact. Further, C3 was consumed, but C4 (exclusively a component of the classical pathway) was preserved, in nonchelated serum after challenge by S. schenckii yeast cells. Absorption of serum with S. schenckii yeast cells to deplete antibodies did not alter these results. Furthermore, immunofluorescence studies demonstrated that C3, but not immunoglobulin G, was deposited on yeast cells during incubation with nonimmune serum. These data indicate that S. schenckii yeast cells activate the alternative complement pathway in vitro independently of antibody. These data do not define a role for the alternative pathway in in vivo host defenses against infection with this organism but provide a foundation for studies to evaluate such a role.

Chelating Agents↗

PubMed1994

Growth of group B streptococci in human serum leads to increased cell surface sialic acid and decreased activation of the alternative complement pathway.

Group B streptococcus type III is a major cause of neonatal death. The terminal sialic acid moiety of the group B streptococcus type specific capsule has been shown to be an important virulence factor. We demonstrate here that bacteria grown in human serum have increased cell surface sialic acid content compared with cells grown in common laboratory media. This sialic acid was removed by incubation with neuraminidase, showing that it was on the bacterial surface. Serum-dependent sialylation was dependent on metabolic activity, as the addition of chloramphenicol reduced the amount of added sialic acid by more than 90%. Probing the cell surface with an antibody specific for group B streptococcus type III capsular sialic acid showed an increase in antibody binding after growth in human serum. This effect could be lowered by incubating serum-grown cells in neuraminidase prior to antibody exposure. A group B streptococcus mutant that when grown in laboratory media lacks cell surface sialic acid showed significant cell surface sialic acid when grown in human serum. This increase was associated with a significantly decreased ability to bind C3 and hence activate the alternative complement pathway.

Blood↗

PubMed1992

Adipsin and an endogenous pathway of complement from adipose cells.

The alternative complement pathway is best known for its role in humoral suppression of infectious agents. We have previously shown that adipose cells synthesize adipsin, the mouse homolog of human complement factor D, and that the synthesis of this protein is reduced in several rodent models of obesity. We show here that adipose cells and adipose tissue also synthesize two other essential components of the alternative pathway of complement, factors C3 and B, and activate the proximal portion of this pathway. This activation occurs in the absence of infectious agents and without triggering the terminal, lytic part of this pathway. We demonstrate the production in vitro of several polypeptides characteristic of complement activation that are known to have potent biological activities, including the anaphylatoxin C3a. Cultured adipocytes require stimulation with cytokines to activate complement, while explanted adipose tissue has no such requirement. The adipose tissue from obese mice is deficient in this localized activation of the alternative pathway. These results indicate that complement activation occurs in a localized site, adipose tissue, in normal mice and is impaired in a state of metabolic dysfunction. This suggests a novel function for the proximal portion of this complement pathway related to adipose cell biology or energy balance.

3T3 Cells↗

PubMed1981

The role of immunoglobulins in alternative complement pathway activation by zymosan. I. Human IgG with specificity for Zymosan enhances alternative pathway activation by zymosan.

Prior absorption of normal human serum (NHS) or C2-deficient human serum (C2D) with zymosan at 0 degrees C results in diminished consumption of C3 and factor B during subsequent incubation of the sera in Mg-EGTA buffer with zymosan at 37 degrees C for 30 min. An acid eluate from the zymosan restores the defect of absorbed NHS and C2D, and also enhances C3 and factor B utilization in hypogammaglobulinemic serum (H gamma S) in a dose-dependent fashion. The activity is specific in that the eluate from zymosan fails to enhance C3 and B depletion in H gamma S or absorbed NHS by lipopolysaccharide or Sepharose. The active component of th zymosan eluate emerges from both Sepharose 4B and Sephacryl S-200 in the region of molecules with m.w. of 150,000. Absorption with protein A-Sepharose removes the activity, demonstrating that it is IgG. Digestion of the IgG with pepsin fails to diminish activity, indicating that the Fc region is not required for activity; reduction to monovalent Fab' fragments, however, abrogates activity. When IgG antibody is bound to Protein A-Sepharose, it fails to enhance C3 depletion in H gamma S by Sepharose, indicating that binding of IgG antibody by the Fab region is necessary for enhancement of alternative pathway activity in human serum.

Antibody Specificity↗

PubMed1997

A novel mechanism of alternative pathway complement activation accounts for the deposition of C3 fragments on CR2-expressing homologous cells.

Complement receptor type 2 (CD21, CR2), the receptor for the C3 fragment C3dg, activates complement via the alternative pathway and also serves as a preferential acceptor site for C3 fragments. The molecular basis for this phenomenon, which has recently been demonstrated for B lymphocytes in vivo, is currently not understood. Here we present a model for this CR2-dependent complement activation. The inactive C3 (iC3), which forms spontaneously in serum in low amounts by reaction of native C3 with H2O, binds noncovalently to the N-terminal part of CR2. Subsequent association of properdin and factor B, and cleavage of factor B by factor D lead to formation of a C3 convertase associated with CR2, thus focussing covalent C3 deposition to CR2 itself. This model is supported by the following experimental findings. 1) By FACS analysis and radioreceptor assays we showed that iC3, properdin, and factor B bound to CR2 on Raji B cells, MT2 T cells, and peripheral blood B cells. 2) Both binding of these proteins and complement activation by CR2-expressing cells were reduced in parallel by Abs against CR2. 3) 125I-labeled C3b was covalently deposited on CR2, when hemolytically active 125I-labeled C3 was added to Raji cells preincubated with iC3, factor B, properdin, and factor D, thus proving functionality of CR2-bound C3 convertase. This model of C3 convertase activity formed on CR2 domains inaccessible for decay-accelerating factor offers an explanation for the deposition of C3 found on CR2-expressing cells.

B-Lymphocytes↗

PubMed1983

[Effective method of simultaneous isolation from human serum of highly purified factors B and D of the alternative pathway of complement activation].

A simple method for isolation from human serum of the complement alternative pathway factor B, in a yield over 40% and purity over 80% with respect to protein, has been developed. Such a high yield was reached due to rejection of ammonium sulphate fractionation and employment of only two chromatographic stages: on CM-Sephadex C-50 and on DEAE-Sepharose CL-6B. An additional chromatography on QAE-Sephadex A-50 provides factor B of 100% purity but with a loss of some amount of protein (yield approximately 20%). One of the fractions, obtained at the first stage of factor B purification, contained also factor D. After rechromatography on CM-Sephadex C-50 and gel filtration on Sephadex G-75 it afforded factor D in yield more than 60% and purity above 100%.

Chromatography, DEAE-Cellulose↗

PubMed1977

Activation of the alternative complement pathway due to resistance of zymosan-bound amplification convertase to endogenous regulatory mechanisms.

The surface of zymosan (Zy), by affording a protected microenvironment for C3b and the amplification convertase stabilized by properdin, P,C3b,Bb, shifts the alternative complement pathway from slow fluid phase turnover to the amplification phase of its expression. This mode of activation is in contradistinction to that of the classical pathway, which follows conversion of a proenzyme, Cl, to its active form, C1. Under conditions in which the control proteins, C3b inactivator (C3bINA) and beta1H, completely, inactivated C3b on the sheep erythrocyte intermediate, EAC4b,3b, the activity of C3b bound to Zy,ZyC3b, was diminished by only one-third. Further, when ZyC3b was converted to ZyC3b,Bb,P there was an additional point of deregulation in that the convertase was resistant to beta1H-mediated decay-dissociation while P,C3b,Bb on the sheep erythrocyte exhibited the usual susceptibility to beta1H. That Zy alone could indeed promote rapid C3 cleavage by the alternative pathway through assembly and protection of the amplification convertase on its surface was demonstrated with a mixture of alternative pathway proteins, C3,B,D,P, C3bINA, and beta1H, that had each been purified to homogeneity. Interaction of these proteins at one-tenth their relative serum concentrations with Zy permitted low-grade inactivation of C3 and B to advance to the level of amplification after a 15 min lag period. Because the reaction of the purified proteins proceeded spontaneously when either regulatory protein was deleted, the effect of Zy was attributed to deregulation rather than to conversion of one of the proteins to a specific initiating state. The alternative pathway, through the normal presence of D, interacts with a microbial surface, such as Zy, to amplify deposition of C3b by circumvention of endogenous regulatory mechanisms, thereby augmenting host defense.

Animals↗

PubMed1977

Interaction of zymosan and of activated properdin with factor D-depleted guinea pig serum: implications for the mechanism of initial C3 cleavage via the alternative complement pathway.

Factor D of the alternative C pathway was specifically removed from guinea pig serum. The resulting serum reagent (RD) supported neither the formation of a C3-cleaving enzyme on zymosan (Z) nor the inactivation of C3 or of factor B in the presence of Z or activated properdin (P). Addition of purified D to RD restored these properties. Studies were limited amounts of purified D were added to RD with Z or P as activating substances, gave the following results: (1) Inactivation of B and of C3 occurs in the presence of minute amounts of D. (2) C3 inactivation is more efficient than B inactivation and proceeds even in the absence of detectable enzymatic B activation. (3) C3 cleavage at any D concentration tested is always accompanied by uptake of C3 fragments onto Z. With respect to initial C3 cleavage via the alternative C pathway these data suggest that the initiating reaction is D-dependent, very efficient in depositing C3 fragments on particulate activating substances such as Z and able to utilize factor B in an apparently uncleaved form.

Animals↗

PubMed1986

Formation of the functional alternative pathway of complement by human monocytes in vitro as demonstrated by phagocytosis of agarose beads.

Native agarose beads (diameter 5-10 micron), activators of the alternative complement pathway, are slowly phagocytosed when incubated with human monocytes cultured under serum-free conditions. Agarose beads preincubated with monocyte cultures and then transferred to new cultures are more easily phagocytosed than native beads. These results indicate that the phagocytosis of agarose beads depends on opsonization of the beads by one or several substances of monocyte origin. By using antihuman C3 antibodies, trypsin treatment, and sodium dodecyl sulphate washing, we were able to demonstrate C3b and iC3b on the agarose beads. The molecules were covalently bound to the surface of the beads. We conclude that in vitro human monocytes produce and secrete the essential factors for activation and propagation of the alternative complement pathway (factors C3, B, D, H and I), which becomes evident with an external activator like agarose beads in the cultures. The activation of complement by agarose beads results in the attachment of C3b and iC3b to the surface of the beads, which are then phagocytosed by means of C3b and iC3b receptors on the monocytes.

Cell Communication↗