Showing papers on "Alternative complement pathway published in 1985"
TL;DR: Alkali supplementation reduces chronic tubulo-interstitial disease in the remnant kidney of the rat, and it is proposed that this results, at least in part, from reduction in cortical ammonia and its interaction with the alternative complement pathway.
Abstract: The human end-stage kidney and its experimental analogue, the remnant kidney in the rat, exhibit widespread tubulo-interstitial disease We investigated whether the pathogenesis of such tubulo-interstitial injury is dependent upon adaptive changes in tubular function and, in particular, in ammonia production when renal mass is reduced Dietary acid load was reduced in 1 3/4-nephrectomized rats by dietary supplementation with sodium bicarbonate (NaHCO3), while control rats, paired for serum creatinine after 1 3/4 nephrectomy, were supplemented with equimolar sodium chloride After 4-6 wk, NaHCO3-supplemented rats demonstrated less impairment of tubular function as measured by urinary excretory rates for total protein and low molecular weight protein and higher transport maximum for para-aminohippurate per unit glomerular filtration rate, less histologic evidence of tubulo-interstitial damage, less deposition of complement components C3 and C5b-9, and a lower renal vein total ammonia concentration Such differences in tubular function could not be accounted for simply on the basis of systemic alkalinization, and differences in tubular injury could not be ascribed to differences in glomerular function Because nitrogen nucleophiles such as ammonia react with C3 to form a convertase for the alternative complement pathway, and because increased tissue levels of ammonia are associated with increased tubulo-interstitial injury, we propose that augmented intrarenal levels of ammonia are injurious because of activation of the alternative complement pathway Chemotactic and cytolytic complement components are thereby generated, leading to tubulo-interstitial inflammation Thus, alkali supplementation reduces chronic tubulo-interstitial disease in the remnant kidney of the rat, and we propose that this results, at least in part, from reduction in cortical ammonia and its interaction with the alternative complement pathway
499 citations
TL;DR: In this paper, the membrane receptors for bound fragments of C3l play a pivotal role in complement activation, and C3-derived fragments are both liberated into the fluid phase and covalently bound to the substrate.
Abstract: Publisher Summary Even though it has been long recognized that the major function of complement receptors was clearance of bacteria by way of opsonization, there are many unknown features about the functions of phagocyte complement receptors. The characterization of the function of complement receptors represents one of the final frontiers of complement research that has detailed the functions of the plasma complement components. Both afferent and efferent limbs of the inflammatory process are dependent upon this coordinating function of complement. The organization of host cell responses by complement is achieved through the interaction of cell membrane receptors with activation products of serum complement proteins. Although a number of different complement components are involved in this complex process, C3l plays a pivotal role. During complement activation, C3-derived fragments are both liberated into the fluid phase and covalently bound to the substrate. The fluid-phase C3 fragments function to induce leukocytosis , increase vascular permeability, and suppress antibody synthesis, whereas the bound C3 fragments participate in assembly of convertase enzymes that amplify C3 activation and further progression of the complement cascade. This chapter focuses on the membrane receptors for bound fragments of C3. The chapter reviews mechanisms for generation and degradation of C3-receptor ligands via the classical and alternative pathways and discusses the abnormalities of expression and/or function that have both clinical relevance and contribute to an understanding of the function of complement receptors in vivo .
333 citations
TL;DR: Results indicate that D is filtered through the glomerular membrane and is probably catabolized in the proximal renal tubules, and enhanced activity of the alternative pathway of complement should be expected in patients with advanced renal failure.
Abstract: Complement protein D, a serine protease participating in the formation of the C3 convertase of the alternative complement pathway, has the lowest molecular weight (23,750) and serum concentration of all complement proteins. In normal serum, D is the rate-limiting protease of the alternative pathway of complement activation. We report that the serum concentrations of D in 20 patients with chronic renal failure (mean ±S.D., 0.42±0.28 mg per deciliter) and in 16 patients on long-term dialysis (1.53±0.39 mg per deciliter) were significantly higher (P<0.001) than in 22 healthy adults (0.18±0.04 mg per deciliter). In chronic renal failure the serum concentration of D correlated with that of creatinine (r = 0.75, P<0.001). The serum concentrations of D found in patients with renal failure reached and in some cases exceeded those at which the protease is no longer rate-limiting. Thus, enhanced activity of the alternative pathway of complement should be expected in patients with advanced renal failure. Ur...
131 citations
TL;DR: The results show that aqueous whole cigarette smoke solution can modify C3 and activate the alternative pathway of complement, perhaps by a previously unrecognized mechanism, and may partly account for the extensive pulmonary leukocyte recruitment observed in smokers.
Abstract: Cigarette smoking is associated with significant increases in the number of pulmonary mononuclear phagocytes and neutrophils. A potent chemoattractant for these cells is C5a, a peptide generated during complement (C) activation. We, therefore, investigated the possibility that cigarette smoke could activate the complement system in vitro. Our results show that factor(s) (mol wt less than 1,000) present in an aqueous solution of whole, unfiltered cigarette smoke can deplete the hemolytic capacity of whole human serum in a dose-dependent manner. The particle-free, filtered gas phase of cigarette smoke is inactive. The smoke factor(s) do not activate serum C1, but do deplete serum C4 activity. Treatment of purified human C3 with whole smoke solution modifies the molecule such that its subsequent addition to serum (containing Mg/EGTA to block the classical pathway) results in consumption of hemolytic complement by activation of the alternative pathway. Smoke-modified C3 shows increased anodal migration in agarose electrophoresis, but this is not due to proteolytic cleavage of the molecule as evidenced by sodium dodecyl sulfate-polyacrylamide gel electrophoresis. In contrast to methylamine-treated C3, C3 treated with smoke is only partially susceptible to the action of the complement regulatory proteins Factors H and I. In addition, smoke-modified C3 has diminished binding to Factor H as compared with methylamine-treated C3. Finally, smoke-modified C3 incorporates [14C]methylamine which suggests that the thiolester bond may be intact. These data indicate that aqueous whole cigarette smoke solution can modify C3 and activate the alternative pathway of complement, perhaps by a previously unrecognized mechanism. Should this occur in vivo, complement activation might partly account for the extensive pulmonary leukocyte recruitment observed in smokers.
126 citations
TL;DR: These studies indicate that complement and/or other products synthesized by macrophages at extravascular sites could play an important role in opsonization and lysis of pathogens able to activate the alternative pathway and mediate macrophage-neutrophil collaboration in first-line host defence.
Abstract: Macrophages take up zymosan in the absence of exogenous complement via receptors for iC3b (type 3 complement receptors) acting with or without lectin-like receptors for mannosyl-fucosyl-terminated glycoconjugates. We previously provided evidence that macrophages themselves secrete complement-alternative pathway components able to opsonize zymosan locally (Ezekowitz et al., J. Exp. Med. 1984. 159:244-260). We show here that covalently bound C3 cleavage products C3b and iC3b can be eluted from zymosan particles cultivated with 36-h adherent human monocytes in the absence of serum. The ligand binding site of type 3 complement receptors is involved in macrophage-zymosan interactions as shown by inhibition studies of zymosan binding and uptake with Fab fragments of anti-C3 antibodies and monoclonal antireceptor antibodies M01 and OKM10. In contrast, antibody IB4, which binds to a receptor epitope distinct from the binding site, does not inhibit zymosan uptake. Selective modulation of macrophage receptors onto anticomplement receptor antibody and mannose-rich yeast mannan, respectively, confirms that the complement and lectin-like receptors are distinct. Human polymorphonuclear leukocytes, which express receptors for complement, but are not known to secrete complement proteins, bind and ingest only exogenously opsonized zymosan. Unopsonized zymosan is a poor trigger of respiratory burst activity in neutrophils or 7-d adherent human macrophages, but induces cell aggregation and secretion of large amounts of superoxide anion when these cells are co-cultivated in serum-free medium and challenged with zymosan. Our studies indicate that complement and/or other products synthesized by macrophages at extravascular sites could play an important role in opsonization and lysis of pathogens able to activate the alternative pathway and mediate macrophage-neutrophil collaboration in first-line host defence.
106 citations
TL;DR: The results suggest that one of the functions of CRP is to mediate the removal of exposed nuclear DNA by complement-dependent solubilization of chromatin in patients with systemic lupus erythematosus.
Abstract: We have studied the interaction of C-reactive protein (CRP)-chromatin complexes with serum. The amount of chromatin solubilized by serum is directly proportional to the amount of CRP present. Serum minus C3 did not appreciably solubilize chromatin within the time allowed in these experiments regardless of the amount of CRP present. This indicates that, in addition to CRP, complement is critical to the solubilization process. Studies using genetically C2-deficient serum and purified C2 indicate that the classical complement pathway is primarily involved in the solubilization, however, there may be minor involvement by the alternative pathway. We used an enzyme-linked immunosorbent assay to determine the amounts of CRP in plasma from eight patients with systemic lupus erythematosus; two of the eight had levels of CRP far lower than previously reported for normal individuals, and an additional sample had antibodies reactive with CRP. Together, these results suggest that one of the functions of CRP is to mediate the removal of exposed nuclear DNA by complement-dependent solubilization of chromatin. A defect in this mechanism could (a) facilitate the production of antibodies against chromatin components exposed due to tissue damage or (b) contribute to immune complexes containing the chromatin components released from damaged tissue because they are not rapidly cleared.
99 citations
Journal Article•
TL;DR: It is demonstrated that human PNM consumes complement in vitro in the absence of specific antibody or C1 activation, and activation of complement by PNM via the alternative pathway was shown by cleavage of C3 in normal human serum (NHS) and of B in C2-deficient serum (C2d-HS).
Abstract: Destruction of peripheral nerve myelin (PNM) occurs as a consequence of a variety of pathologic conditions affecting the peripheral nervous system. In certain primary demyelinating neuropathies, several lines of evidence implicate complement in the pathogenesis of demyelination. In this study we demonstrate that human PNM consumes complement in vitro in the absence of specific antibody or C1 activation. Furthermore, activation of complement by PNM via the alternative pathway was shown by cleavage of C3 in normal human serum (NHS) and of B in C2-deficient serum (C2d-HS). Increasing consumption of hemolytic activity of C3 in Mg-EGTA-treated NHS was also noted with increasing amounts of PNM. Pronase treatment of PNM abolished C3 consumption, suggesting that a protein component exposed on the surface of myelin participated in the alternative pathway activation. When P0, the major amphiphilic glycoprotein of PNM, was incorporated into artificial lipid bilayers, the Po-liposomes consumed C3 activity in NHS containing Mg-EGTA. Pronase treatment of Po-liposomes abolished C3 consumption to the level of control liposomes, indicating that P0 was responsible for at least part of the activation seen with peripheral myelin.
80 citations
TL;DR: It was shown that with respect to PAC 1 and PAC 605, the lack of an O-chain resulted in increased sensitivity to serum and decreased virulence, and it was concluded that the structure of the O-antigen polysaccharide chain of lipopolysaccharid is an important virulence factor of P. aeruginosa against the defense mechanisms of the host.
Abstract: When the opsonization of various Pseudomonas aeruginosa strains--PAC 1, its O-chain-deficient mutant PAC 605, and an intermediate strain, P14--was measured either directly by determination of the amount of C3b attached to the bacterial surface or indirectly by assessing phagocytosis by human polymorphonuclear leukocytes and the responses of chemiluminescence, it was demonstrated that PAC 1 was opsonized and phagocytized to a lower extent than P14 and PAC 605. In contrast to PAC 605, PAC 1 showed an increased consumption of complement in the fluid phase and a rapid release of lipopolysaccharide antibodies bound to the bacterial surface due to the alternative pathway of the complement system. Furthermore, it was shown that with respect to PAC 1 and PAC 605, the lack of an O-chain resulted in increased sensitivity to serum and decreased virulence. From both in vivo and in vitro experiments, we concluded that the structure of the O-antigen polysaccharide chain of lipopolysaccharide is an important virulence factor of P. aeruginosa against the defense mechanisms of the host.
78 citations
Journal Article•
TL;DR: The results indicate that in the two species studied, the molecular mechanism of recognition is analogous and that recognition is species-specific.
Abstract: The recognition function of the alternative complement pathway was studied with isolated human and rabbit components. Zymosan and homologous and heterologous erythrocytes were used as representative activators or nonactivators. The binding affinity of Factor B and Factor H for particle-bound C3b was measured. In both species, the average affinity of Factor H for bound C3b on homologous cells (nonactivators) was eight to 10 times higher than on zymosan particles (activators). The interaction between Factor H and C3b on rabbit erythrocytes was species-specific: rabbit Factor H bound strongly to rabbit C3b on rabbit erythrocytes and also on human erythrocytes, which are nonactivators for the rabbit alternative pathway. Human Factor H bound strongly to human C3b on human erythrocytes but seven times weaker on rabbit erythrocytes, which are activators of the human alternative pathway. No substantial differences were found in the binding of Factor B to bound C3b regardless of the nature of the particle to which C3b was bound. The results indicate that in the two species studied, the molecular mechanism of recognition is analogous and that recognition is species-specific.
75 citations
TL;DR: The purpose of this chapter is to outline in detail the work done in the laboratory over the last 4 years on complement activation by gramnegative bacteria.
Abstract: The interaction of gram-negative bacteria and the serum complement system has been studied for nearly a century. From the most rudimentary observation that fresh blood could kill certain types of bacteria (Bordet 1985) has evolved detailed understanding of (a) the gram-negative cell wall constituents that activate complement, (b) the role of antibody in initiating or facilitating the process of complement activation, and (c) the biochemical localization and biological consequences of complement deposition and complement activation by pathogenic gram-negative bacteria. The purpose of this chapter is to provide a brief review of existing data in these areas and to outline in detail the work done in our laboratory over the last 4 years on complement activation by gramnegative bacteria.
74 citations
Journal Article•
TL;DR: It is suggested that polymethylmethacrylate lenses with polypropylene loops generate C3a and C5a by activation of the alternative complement pathway.
Abstract: To determine if posterior chamber polymethylmethacrylate lenses with polypropylene loops activate complement, the authors measured levels of C3a, C4a and C5a by radioimmunoassay in human sera incubated with and without these lenses. Human sera incubated with intraocular lenses showed elevated levels of C3a and C5a but no change in C4a. There were no statistically significant differences in the generation of activated complement by polypropylene loops vs polymethylmethacrylate optics. The authors also compared the ability of intraocular lenses to activate complement with that of zymosan and endotoxin, known activators of the alternative pathway. Our results suggest that polymethylmethacrylate lenses with polypropylene loops generate C3a and C5a by activation of the alternative complement pathway.
TL;DR: In this article, the authors examined depolymerized heparin to determine which fragments were capable of inhibiting amplification pathway activation, and they found that as the size of the molecule increases the ability to regulate complement increases; below 1000 Da the fragments were essentially inactive and above 3500 Da they had the same activity as does commercial heparin.
TL;DR: It is demonstrated that purified pneumococcal LTA will bind to sheep erythrocytes and endow them with the ability to activate the alternative pathway of complement.
Abstract: Cell wall teichoic acids of some gram-positive bacteria are potent activators of the alternative pathway of complement. It is unclear, however, whether the other form of teichoic acid, cell membrane lipoteichoic acid (LTA), can also activate the alternative pathway. In the present study, radiolabelled pneumococcal LTA was found to bind spontaneously to sheep erythrocytes in a temperature- and time-dependent fashion. In addition, the presence of pneumococcal LTA on the erythrocyte surface was verified by the fact that they could be agglutinated by a myeloma protein (TEPC-15) specific for choline, a constituent of pneumococcal LTA. Pneumococcal LTA when fixed to the surface of erythrocytes was able to activate the alternative pathway of complement in both guinea pig serum deficient in the fourth component of complement and human serum deficient in the second component of complement, resulting in lysis of the sensitized erythrocytes. The sensitizing principle of the LTA preparation was removed before erythrocyte sensitization by immunoabsorption, using the choline-specific TEPC-15 myeloma protein. These data demonstrate that purified pneumococcal LTA will bind to sheep erythrocytes and endow them with the ability to activate the alternative pathway.
TL;DR: Patients with chronic lymphocytic leukemia (CLL) are at an increased risk for infections with bacteria which require complement for osponization, and the possibility that patients with CLL have a defect in binding the potent opsonin C3b to bacteria is explored.
Abstract: Patients with chronic lymphocytic leukemia (CLL) are at an increased risk for infections with bacteria which require complement for osponization. We explored the possibility that patients with CLL have a defect in binding the potent opsonin C3b to bacteria. Bacteria selected for these experiments included Streptococcus pneumoniae type 3, which binds C3 by activating the classical complement pathway (CCP), type 25, which can bind normal amounts of C3b by the alternative complement pathway (ACP), type 14, which can activate both the CCP and ACP, and Staphylococcus aureus and Escherichia coli, both of which activate the CCP. Bacteria were treated with normal serum or serum from 15 patients with CLL, and the bound C3b was quantified spectrophotofluorometrically. Despite normal serum concentrations of C3, C4, Factor B, C-reactive protein, and total hemolytic complement activity, all 15 CLL sera bound reduced amounts of C3b to at least one bacterial species; 9 to S pneumoniae type 3, 8 to types 14 and 25, 11 to S aureus, and 13 to E coli. Mixing normal serum with CLL serum restored C3b binding to all bacteria, suggesting a deficiency rather than an inhibitor of activity. Serum from ten hypogammaglobulinemic CLL patients bound less C3b (62.7 +/- 5% of normal) (means +/- SEM) than those with normal immunoglobulin levels (81.9 +/- 5%) (p less than .005). Nevertheless, the addition of specific antibacterial antibodies to CLL serum did not enhance C3b binding to any of the bacteria. Serum from patients with a history of a bacterial infection bound less C3b (62.3 +/- 5%) than those without a history of infections (76.1 +/- 6%) (p less than .05). Thus, there is a defect in either the activation or activity of C3 in CLL serum which may contribute to the increased incidence of infections in these patients.
TL;DR: Results provide strong evidence that cleaved macrophage-derived C3 (iC3b) mediates promastigote binding to CR3, and may be important determinants of the infectivity and survival of Leishmania parasites in the vertebrate host.
Abstract: This paper examines briefly receptors and recognition mechanisms involved in binding Leishmania parasites to the lumen of the sandfly gut and to cells of the vertebrate host's mononuclear phagocyte system. In particular, work carried out in our laboratory on the relative roles of the macrophage plasma membrane receptor (CR3) for the cleaved third complement component (iC3b) and the mannosyl/fucosyl receptor (MFR) in binding, ingestion and respiratory burst (RB) response elicited by promastigotes versus amastigotes of L. donovani , is discussed. In the absence of serum, soluble inhibitors (e.g. mannan) of the MFR cause a dose-dependent reduction in promastigote binding to murine resident peritoneal macrophages and in the proportion of bound parasites eliciting a RB response. For amastigotes, no consistent reduction in binding in the presence of mannan is observed but the proportion of parasites eliciting a RB is reduced. Serum-independent binding of promastigotes, which are good activators of the alternative complement pathway, is also inhibited by the anti-CR3 monoclonal antibody Ml/70, by Fab anti-C3, and by an inhibitor of C3 fixation, sodium salicyl hydroxamate. With amastigotes, which are poor activators of the alternative pathway, a lesser effect is observed. These results provide strong evidence that cleaved macrophage-derived C3 (iC3b) mediates promastigote binding to CR3. Modulation experiments in which either CR3 or MFR are rendered inaccessible demonstrate that both receptors must be present on the segment of macrophage membrane with which the promastigote makes contact to mediate binding and ingestion. These receptor interactions may be important determinants of the infectivity and survival of Leishmania parasites in the vertebrate host.
TL;DR: Lymphocyte-mediated lysis of cells of the Raji, Daudi, Jijoye, and Bjab lines was elevated when fresh human serum was added to the assay and it is assumed that the bridge of C3 molecules between targets and effectors increases the avidity of their interaction.
Abstract: Lymphocyte-mediated lysis of cells of the Raji, Daudi, Jijoye, and Bjab lines was elevated when fresh human serum was added to the assay. A higher proportion of effector-target conjugates was observed in the presence of human serum. In similar experiments lysis of 1301, Rael, and P3HR-1 cells was unaltered. All cell lines activated the alternative pathway of complement but they varied in the expression of receptors for complement component 3 (C3) and in the ability to fix the C3 cleavage products on their membrane. The enhancement of lysis in the presence of human serum occurred only with those cells that bound C3. This characteristic was correlated to the expression of C3 receptors. Analysis of the nature of the deposited C3 was performed with Raji cells. Raji cells exposed to human serum bound C3b as indicated by the immunoadherence test. The C3b was further processed to C3bi, because the immunoadherence declined with time and conjugate formation increased with Daudi cells, which carry the C3 receptors CR2 and CR3. This suggests that in the lytic assay lymphocytes with C3bi receptors are recruited in the presence of human serum. We assume that the bridge of C3 molecules between targets and effectors increases the avidity of their interaction.
TL;DR: The data suggest, that complement abnormality seen in Crohn's disease patients does not simply reflect mucosal inflammation or hypercatabolism of complement, and raised levels of circulating complement C3c split products suggested complement involvement in Crochn's disease probands.
Abstract: Complement was studied in Crohn's disease probands with early onset and in their first degree relatives Controls included 24 healthy volunteers and 24 patients with ulcerative colitis or peptic ulcers Subnormal generation of chemotactic activity by the alternative pathway was shown in eight of 21 probands and in six of 33 relatives, a frequency in both groups significantly different from controls (p less than 0005), with a strong connection between findings in patients and relatives As previously shown in patients with Crohn's disease, the subnormal generation was related to decreased utilisation of complement C3 in relatives Raised levels of circulating complement C3c split products suggested complement involvement in Crohn's disease probands In contrast, plasma C3c was normal in all relatives, and none of the six cases with complement dysfunction had gastrointestinal symptoms or a history of inflammatory bowel disease Our data suggest, that complement abnormality seen in Crohn's disease patients does not simply reflect mucosal inflammation or hypercatabolism of complement
TL;DR: Results obtained with these three independent inhibitors provide strong evidence that cleaved macrophage-derived C3 (iC3b), which can be visualised on the parasite surface in electron microscope sections following addition of anti-C3 antibody and a protein A-gold conjugate, mediates binding to CR3.
TL;DR: The results suggest that the immune IgG transforms TBF into ACP activators by blocking the capacity of some parasite cell surface components that are known inhibitors of C activation.
Abstract: In this report we examined the capacity of immune IgG fragments to prepare trypomastigote bloodstream forms (TBF) of Trypanosoma cruzi for lysis. F(ab')2 fragments were capable of presensitizing TBF for complement (C) lysis, thus excluding the participation of Fc domains in the C activation process. An intact hinge region of the IgG molecule was not involved either, since the corresponding Fab' were almost as active as the original molecules in preparing TBF for lysis. Fab also retained such activity even after further reduction and alkylation. These findings indicate that neither the portions of heavy chains that make up the hinge region nor the intrachain disulphide bonds are involved in the process. The IgG fragments promoted lysis through the activation of the alternative C pathway (ACP). These results suggest that the immune IgG transforms TBF into ACP activators by blocking the capacity of some parasite cell surface components that are known inhibitors of C activation.
TL;DR: In this article, the authors measured activation of the alternative pathway in sera from patients with sickle cell disease utilizing an enzyme immunoassay which detects C3b,P complexes, derivative of the C 3b,Bb-P alternative pathway convertase.
TL;DR: The results indicate that the surface of the ameba can promote complement activation by the classical pathway, without the participation of specific antibodies, and that the magnitude of this activation is greater than that induced by the alternative pathway.
Abstract: Entamoeba histolytica HM1 supported the activation of human alternative and classical complement pathways in the absence of ameba-reactive antibodies. Nonimmune serum depleted of C1q and factor D (NHS s C1q + D) and reconstituted with C1q was able to specifically deposit C3b onto trophozoites and produce lysis. This activity was not modified by the absorption of serum on E. histolytica. Serum depleted of factor B allowed C3b binding to amebae. Serum devoid of C4 effected only small amounts of C3 uptake. The kinetics of lysis of E. histolytica by serum in the presence of Mg-EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N,N,N',N'-tetraacetic acid] (lacking classical pathway function) or by NHS s C1q + D and reconstituted with factor D was slow and only produced one-half the amount of lysis produced by NHS s C1q + D supplemented with C1q. These results indicate that the surface of the ameba can promote complement activation by the classical pathway, without the participation of specific antibodies, and that the magnitude of this activation is greater than that induced by the alternative pathway.
Journal Article•
TL;DR: It is suggested that macrophages may deposit enough C3b onto desialated E to cause CR1-mediated phagocytosis in the presence of Fn, which may be critically important in areas of inflammation where concentrations of serum-derived specific opsonins may be inadequate.
Abstract: We examined the ability of human monocytes and culture-derived macrophages under serum-free conditions to phagocytose desialated sheep erythrocytes (E), an activator of the alternative pathway of human complement Freshly derived monocytes ingested desialated erythrocytes, but the degree of phagocytosis varied among individual donors However, exposing the phagocyte to intact plasma fibronectin (Fn) had no effect on monocyte phagocytosis Macrophages derived from monocytes in culture were far more efficient at ingesting desialated E, and the extent of phagocytosis was proportional to the degree of desialation Although exposure of macrophages to substrate-bound Fn or fluid-phase Fn enhanced the phagocytosis of desialated E, pretreatment of desialated E with Fn did not enhance phagocytosis, demonstrating that Fn acted through an interaction with the macrophages Fn-enhanced phagocytosis of desialated E was inhibited by treating macrophages with a monoclonal antibody to the C4b/C3b receptor (CR1), but not with a monoclonal antibody to the receptor for C3bi (CR3) Addition of cobra venom factor (CVF) to the macrophages also inhibited Fn-enhanced phagocytosis of desialated E Phagocytosis of IgG-sensitized E, either in the absence or in the presence of Fn, was not significantly affected by anti-CR1 or CVF, demonstrating that these reagents did not lead to a general inhibition of phagocytosis These experiments suggest that macrophages may deposit enough C3b onto desialated E to cause CR1-mediated phagocytosis in the presence of Fn The ability of macrophages to opsonize and ingest foreign particles that activate complement may be critically important in areas of inflammation where concentrations of serum-derived specific opsonins may be inadequate
TL;DR: The results indicate that the cobra has a complement system with an alternative pathway very similar to mammalian complement that is susceptible to activation by the human C5 convertase.
Abstract: The complement system of the cobra snake is of particular interest because cobra venom contains cobra venom factor (CVF), a protein that is related to C3 and forms a stable C3 convertase with mammalian Factor B. We investigated the alternative pathway of cobra complement. Cobra plasma lysed erythrocytes in presence of Mg-EGTA of some mammalian species, but not cobra erythrocytes. The hemolytic activity was inhibited by EDTA and destroyed by heating. Preincubation of cobra plasma with alternative pathway activators (zymosan, inulin, lipopolysaccharide), with small nucleophiles (methylamine, hydrazine), or with chaotropes (KSCN) abrogated the hemolytic activity. The activity of cobra plasma was not affected by CVF. Cobra plasma also lysed EAC1423 cells in presence of EDTA but not EAC142 cells (prepared with sheep erythrocytes, rabbit antibody, and human complement proteins) indicating the presence of C5 in cobra plasma that is susceptible to activation by the human C5 convertase. These results indicate that the cobra has a complement system with an alternative pathway very similar to mammalian complement.
Journal Article•
TL;DR: Amastigotes of the disseminating strains of leishmania represent the first example of a group of protozoa that activate early complement components leading to fixation of C3, but that are resistant to inactivation by complement.
Abstract: Amastigote forms of Leishmania major are sensitive to lysis by fresh serum, whereas those of L. donovani are resistant. To understand the basis for this resistance we have examined the interaction of complement with amastigotes of seven strains of leishmania. Complement activation was determined by measuring the ability of amastigotes to consume complement from normal serum and by identifying parasite surface-bound C3. All of the strains that were tested activated complement, including both those that are resistant and those that are susceptible to inactivation by fresh serum. Complement consumption by amastigotes was measured as a decrease in the ACH 50 titers of serum exposed to parasites. L. major, L. donovani, and L. mexicana mexicana (strain 1VLM) amastigotes decrease titers by 35.7, 33.5, and 40.3%, respectively. The binding of C3 to amastigotes was judged qualitatively by immunofluorescence and quantitatively by a C3 radiobinding assay. L. major amastigotes bind an average of 6.6 X 10(4) molecules of C3 per parasite. L. mexicana amazonensis, L. mexicana mexicana, and L. donovani bind an average of 3.9 X 10(4), 5.9 X 10(4), and 3.7 X 10(4) molecules, respectively. In all cases, C3 binding is the result of alternative pathway activation requiring Mg++ but not Ca++. Amastigotes of the disseminating strains of leishmania represent the first example of a group of protozoa that activate early complement components leading to fixation of C3, but that are resistant to inactivation by complement.
TL;DR: The hypothesis that humoral immune mechanisms may contribute to morbidity and mortality in CF is supported, as well as the possibility that complement abnormalities and circulating immune complexes were an independent risk factor for death.
Abstract: Serum samples from 139 patients with cystic fibrosis (CF) were tested for complement abnormalities and circulating immune complexes (CIC). We found no consistent changes in whole complement activity. However, we found CIC in 29% of these patients and decreased activity of the alternative complement pathway (ACP) in 36%. During 5 yr of observation, mortality was much higher in patients whose sera contained CIC (p less than 0.001) or decreased ACP activity (p less than 0.01). Of patients with both abnormalities, 31% died; however, no deaths occurred in patients with normal ACP activity and negative tests for CIC (p less than 0.001). During a subsequent 2.5-yr period, 55% of patients greater than or equal to 21 yr old with both findings died. In contrast, no deaths occurred in older patients lacking this combination (p = 0.0062). Circulating immune complexes but not decreased ACP activity were an independent risk factor for death. Our findings support the hypothesis that humoral immune mechanisms may contribute to morbidity and mortality in CF.
TL;DR: The findings of the in vitro experiments accurately mimic some old, but as yet insufficiently understood, in vivo effects of complement activation on circulating blood cells.
TL;DR: The results indicate that an opsonic defect of cord blood serum affects mainly microorganisms requiring opsonization via the alternative pathway of complement, and implies that IgG concentrations, as assessed by immunochemical methods, in cord blood and adult sera represent functionally similar IgG activities.
Abstract: In this study opsonic activity of fresh and heat inactivated cord blood/CB/sera for S.aureus, E.coli and group B streptococci concentrations of immunoglobulins and complement components as well as activity of the classical and alternative pathways of complement activation were investigated.The opsonic activity of a serum was determined as its capacity to promote ingestion of bacteria.Concentrations of IgA,IgM and IgG were measured by immunodiffusion.The activity of complement pathways was determined by hemolytic titration. -The results showed that activity of heat inactivated CB sera in promoting phagocytosis was equal to that of sera of healthy adults which implies that IgG concentrations in CB sera and in adult sera represent functionally similar IgG activities.Ingestion of micro-organisms in the presence of fresh sera was found to be of the same level for CB sera and sera from adults when opsonisation occured via the classical pathway of complement activation.However due to the decreased concentrations of factors B,P and D in CB sera, optimal opsonisation of micro-organisms requiring the alternative pathway of complement was impaired.These findings clearly show the need to determine the opsonising activity of serum for each specific micro-organism.A normal or defective activity of a serum for one organism does not predict its activity for other micro-organisms.
TL;DR: It is concluded that inhibition of human complement by heparin is independent of its anticoagulant activity and of its size and it is suggested that a fraction ofheparin with reduced risk for bleeding and platelet aggregation is a potential anti-inflammatory agent.
TL;DR: Retrospective data were suggestive of an increased incidence of pneumococcal bacteremia occurring in association with reduction in opsonic activity, and auxiliary serum factors rather than an intrinsic defect in the complement system in the o Simpsonic alterations were implicate.
Abstract: Opsonic activity for Streptococcus pneumoniae mediated by the alternative and classic complement pathways and concomitant binding of activated C3 to the bacteria were measured in sera from children with sickle cell disease and normal siblings of similar age. Uptake of radiolabeled serotypes 7F, 10A, 15B, and 24F by normal human polymorphonuclear leukocytes and intracellular killing were the parameters used to assess opsonization. C3 fixation was quantitated by radioimmunoassay under conditions identical to those used for opsonic measurements. Both classic and alternative pathway-mediated opsonic activities were significantly reduced in a subset of patients. These alterations were associated with reduction in C3 fixation by way of the classic pathway and normal C3 fixation by way of the alternative pathway. The data implicate auxiliary serum factors rather than an intrinsic defect in the complement system in the opsonic alterations. Retrospective data were suggestive of an increased incidence of pneumococcal bacteremia occurring in association with reduction in opsonic activity.
TL;DR: Spermatozoa were able to activate PMN in the presence of heat-inactivated serum (only antibody, no complement), serum obtained from a patient with agammaglobulinemia (without antibodies and only complement as opsonin), and in MgEGTA agammglobulinemic serum ( only the alternative pathway of complement intact).
Abstract: Human spermatozoa activated human polymorphonuclear leukocytes (PMN) in the presence of serum. Activation of PMN was studied by measuring the emission of chemiluminescence by the PMN. The amount of chemiluminescence emitted depended on the number of spermatozoa and the serum concentration, and the presence of antibody or complement. Spermatozoa were able to activate PMN in the presence of heat-inactivated serum (only antibody, no complement), serum obtained from a patient with agammaglobulinemia (without antibodies and only complement as opsonin), and in MgEGTA agammaglobulinemic serum (only the alternative pathway of complement intact). In the presence of heat-inactivated agammaglobulinemic serum no significant chemiluminescence was observed. It was concluded that spermatozoa activate the alternative pathway of complement. Dead spermatozoa were more able to activate PMN than viable spermatozoa.