Independent and consecutive action of C5, C6 and C7 in immune hemolysis. II. Formation and decay of the intermediate complexes EAC1-5 and EAC1-6.
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Animals↗
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A general method for determining helix packing in membrane proteins in situ: helices I and II are close to helix VII in the lactose permease of Escherichia coli.
It was previously shown that coexpression of the lactose permease of Escherichia coli in two contiguous fragments leads to functional complementation. We demonstrate here that site-directed thiol crosslinking of coexpressed permease fragments can be used to determine helix proximity in situ without the necessity of purifying the permease. After coexpression of the six N-terminal (N6) and six C-terminal (C6) transmembrane helices, each with a single Cys residue, crosslinking was carried out in native membranes and assessed by the mobility of anti-C-terminal-reactive polypeptides on immunoblots. A Cys residue at position 242 or 245 (helix VII) forms a disulfide with a Cys residue at either position 28 or 29 (helix I), but not with a Cys residue at position 27, which is on the opposite face of helix I, thereby indicating that the face of helix I containing Pro-28 and Phe-29 is close to helix VII. Similarly, a Cys residue at position 242 or 245 (helix VII) forms a disulfide with a Cys residue at either position 52 or 53 (helix II), but not with a Cys residue at position 54. Furthermore, low-efficiency crosslinking is observed between a Cys residue at position 52 or 53 and a Cys residue at position 361 (helix XI). The results indicate that helix VII lies in close proximity to both helices I and II and that helix II is also close to helix XI. The method should be applicable to a number of different polytopic membrane proteins.
Bacterial Proteins↗
Polymorphonuclear leukocyte chemotactic activity in rabbit serum and Guinea pig serum treated with immune complexes: evidence for c5a as the major chemotactic factor.
A number of polymorphonuclear leukocyte (PMN) chemotactic factors derived from complement components have been described. We sought to determine which of these factors accounted for the majority of PMN chemotactic activity in rabbit serum and guinea pig serum treated with preformed immune complexes. Normal rabbit sera, guinea pig sera, or rabbit sera deficient in C6 were treated with homologous antibovine serum-albumin-bovine serum-albumin complexes. Sera so treated contained one major PMN chemotactic factor which was heat-stable (56 C for 30 min), had a molecular weight of approximately 15,000, and did not require the presence of C6 for its generation. This factor appears to be analogous to C5a.
Journal Article↗
An anticomplementary agent, K-76 monocarboxylic acid: its site and mechanism of inhibition of the complement activation cascade.
A monocarboxylic acid derivative (K-76 COOH) of K-76, purified from the culture filtrate of Stachybotrys complement I nov. sp. K-76, inhibits complement (C) activity. Its inhibitory action is mainly on C5 step. It strongly inhibits the generation of EAC1,4b,2a,3b,5b from C5 and EAC1,4b,2a,3b, and accelerates the decay of EAC1,4b,2a,3b,5b. It also causes some inhibition of the reactions of the reactions of C2,C3,C6,C7 and C9 with their respective preceding intermediate cells. It has no effect on the generation of EAC1,4b from C4 and EAC1, or of EAC-8 from C8 and EAC-7, and apparently increases the generation of EAC1,4b from C1 and EAC4b probably by inhibiting transfer or turnover of C1. It does not affect the rate of decay of EAC1,4b,2a or the T max of generation of EAC1,4b,2a, and it inhibits immune adherence only at high concentration. K-76 COOH also strongly inhibits hemolysis through the alternative pathway of C activation by cobra venom factor, but it does not seem to inhibit the early steps of the alternative pathway, because it has little affect on the consumption of C3 or the conversion of beta 1C to beta 1A on treatment of C serum with zymosan. K-76 COOH probably combines with C5 molecules, forming the inactive complexes, or it causes the structural alteration of C5.
Animals↗
A biotin-avidin sandwich ELISA for quantification of intact complement component C9. The sera from hereditary C9 deficient individuals completely lack C9.
A two-site sandwich ELISA method was developed for quantitating intact C9 protein using MoAb P40 (anti-C9b antibody). This antibody reacted with monomeric C9 but not with polymerized C9. MoAb P40 was used as a capture antibody and MoAb X195 (anti-C9a antibody) as a detection antibody. This method is highly sensitive and can detect approximately 0.5 ng/ml of native C9. No cross-reactivities of either C6, C7, or C8 were observed even at concentrations of 10 micrograms/ml per component. In addition, this method allows for measurement of only intact C9 molecules, eliminating the interference of polymerized C9 or inactivated C9. Using this assay, no C9 at all was detected in sera from inherited C9 deficient individuals, including both healthy blood donors and patients with meningococcal meningitis; although by hemolytic assay, C9 levels were reported to be less than 0.2% those of NHS. Therefore, this two-site sandwich ELISA method can replace the hemolytic assay, and is especially useful for measuring small amounts of C9 in serum.
Animals↗
A zinc finger protein from Candida albicans is involved in sucrose utilization.
A sucrose-inducible alpha-glucosidase activity that hydrolyzes sucrose in Candida albicans has been demonstrated previously. The enzyme is assayable in whole cells and was inhibited by both sucrose and maltose. A C. albicans gene (CASUC1) that affects sucrose utilization and alpha-glucosidase activity was cloned by expression in a Saccharomyces cerevisiae suc2 mutant (2102) devoid of invertase genes. CASUC1 enabled the S. cerevisiae mutant to utilize both sucrose and maltose. DNA sequence analysis revealed that CASUC1 encodes a putative zinc finger-containing protein with 28% identity to a maltose-regulatory gene (MAL63) of S. cerevisiae. The gene products of CASUC1 and MAL63 are approximately the same size (501 and 470 amino acids, respectively), and each contains a single zinc finger located at the N terminus. The zinc fingers of CASUC1 and MAL63 comprise six conserved cysteines (C6 zinc finger) and are of the general form Cys-Xaa2-Cys-Xaa6-Cys-Xaavariable-Cys-Xaa2-Cys-+ ++Xaa6-Cys (where Xaan indicates a stretch of the indicated number of any amino acids). Both contain five amino acids in the variable region. CASUC1 also complemented the maltose utilization defect of an S. cerevisiae mutant (TCY-137) containing a defined mutation in a maltose-regulatory gene. The sucrose utilization defect of type II Candida stellatoidea, a sucrase-negative mutant of C. albicans, was corrected by CASUC1. Determinations of alpha-glucosidase activity in whole cells revealed that activity was restored in transformants cultivated on either sucrose or maltose. To our knowledge, this is the first zinc finger-encoding gene, as well as the first putative regulatory gene, to be identified in C. albicans.
Amino Acid Sequence↗
Serum-resistant strains of Borrelia burgdorferi evade complement-mediated killing by expressing a CD59-like complement inhibitory molecule.
Borrelia burgdorferi, the etiological agent of Lyme disease, comprises three genospecies, Borrelia garinii, afzelii, and burgdorferi sensu strictu, that exhibit different pathogenicity and differ in the susceptibility to C-mediated killing. We examined C-sensitive and C-resistant strains of B. burgdorferi for deposition of C3 and late C components by fluorescence microscope and flow cytometry. Despite comparable deposition of C3 on the two strains, the resistant strain exhibited reduced staining for C6 and C7, barely detectable C9, and undetectable poly C9. Based on these findings, we searched for a protein that inhibits assembly of C membrane attack complex and documented an anti-human CD59-reactive molecule on the surface of C-resistant spirochetes by flow cytometry and electron microscopy. A molecule of 80 kDa recognized by polyclonal and monoclonal anti-CD59 Abs was identified in the membrane extract of C-resistant strains by SDS-PAGE and Western blot analysis. The molecule was released from the bacterial wall using deoxycholate and trypsin, suggesting its insertion into the bacterial membrane. The CD59-like molecule acts as C inhibitor on Borrelia because incubation with F(ab')(2) anti-CD59 renders the serum-resistant strain exquisitely susceptible to C-mediated killing and guinea pig erythrocytes bearing C5b-8, unlike the RBC coated with C5b-7, are protected from reactive lysis by the bacterial extract. Western blot analysis revealed preferential binding of the C inhibitory molecule to C9 and weak interaction with C8 beta.
Antibodies, Blocking↗
Characterization of the enhanced susceptibility of paroxysmal nocturnal hemoglobinuria erythrocytes to complement-mediated hemolysis initiated by cobra venom factor.
When whole serum C is activated by cobra venom factor complexes (CoFBb), paroxysmal nocturnal hemoglobinuria (PNH) III E (the most C-sensitive type) are hemolyzed, but normal and PNH II E (the intermediately sensitive type) are not. Previous studies have shown that after exposure to CoFBb and serum, PNH III E bind relatively large amounts of the trimolecular C complex, C5b67, whereas normal and PNH II E bind virtually none. In the studies reported herein, we have observed that when normal and PNH III E are incubated with isolated C5, C6, and 125I-C7 in the presence CoFBb, the normal E bind more C5b-7 than the PNH cells. When C7-deficient serum is included in the reaction mixture, however, the PNH E are once again observed to bind much greater amounts of C5b-7. These observations suggest that plasma and membrane factors act in concert to restrict the assembly of the trimolecular C5b-7 complex on human E. PNH III E appear to be deficient in the membrane component of this inhibitory system.
Animals↗
Clusterin, the human apolipoprotein and complement inhibitor, binds to complement C7, C8 beta, and the b domain of C9.
Clusterin is a heterodimeric multifunctional protein expressed in a variety of tissues and cells. It forms high density lipid complexes in plasma and participates in the control of the lytic activity of the late complement complex (TCC, C5b-9). Together with vitronectin, clusterin binds to the nascent amphiphilic C5b-9 complex, rendering it water soluble and lytically inactive. To define the interactions that underlie the complement-inhibitory function of clusterin, we have examined the binding interactions between [125I]clusterin and the isolated components of the complex, C5b-6, C7, C8, and C9 and vitronectin. By using ligand blotting in the presence of Tween, specific binding of the labeled clusterin with C7, the beta-subunit of C8 and C9 was detected. Binding to C9 was competed by polymerized C9, but not by C8, C7, C6, and CD59, suggesting that the conformational change occurring during the hydrophilic-amphiphilic transition of C9 exposes the interaction site for clusterin. When thrombin-treated C9 was analyzed, clusterin was found to recognize the C9b fragment containing the hydrophobic membrane interaction segment. Both subunits of clusterin interact with C9 and are similarly potent in inhibiting C5b-9-mediated hemolysis and Zn+(+)-induced C9 polymerization. These results show that clusterin exerts its inhibitory effect by interacting with a structural motif common to C7, C8 alpha, and C9b.
Clusterin↗
[Terminal complement complex (TTC) levels in plasma and urine from glomerular diseases: enzyme-linked immunosorbent assay (ELISA) using monoclonal antibody against neoantigens of TCC].
In order to get monoclonal antibodies (MoAbs) against neoantigens of terminal complement complex. MoAbs after immunization of mice with polymerized human C9 were screened for reactivities against native and polymerized C9. MoAb 1B4 reacted with tubular C9 polymer, but did not react with either native or sodium dodecyl sulfate-denatured monomeric C9 as revealed by enzyme-linked immunosorbent assay (ELISA) and Western blotting. Moreover, MoAb 1B4 reacted with the terminal complement complex (TCC), that is, membrane attack complex and the fluid-phase SC5b-9 complex. Thus, MoAb 1B4 recognized a neoantigen in the moiety of C9 polymer in the TCC. Thereafter, we measured TCC in plasma and urine with sandwich ELISA using 1B4 and antihuman C7 antibody to evaluate terminal complement activation in patients with glomerular diseases. TCC was detectable in plasma but not in urine from most of normal controls. In plasma, TCC was elevated in 5 of 23 with lupus nephritis and in 6 of 11 with membranoproliferative glomerulonephritis, but all patients with IgA nephritis, focal glomerulosclerosis, membranous glomerulonephritis and minimal change lesions (MC) showed normal levels. In urine, TCC was detectable in most of patients with severe proteinuria (greater than or equal to 100 mg/dl) except MC. The TCC present in urine was partially purified by gel filtration with Sepharose 6B and was found to contain C5, C6, C7, C8, C9, and S protein by ELISA. Although the molecular weight of SC5b-9 complex is similar to IgM, fractional excretion rate of TCC was about 100 times higher than that of IgM. These results suggest that urinary TCC contains SC5b-9 complex like plasma TCC and is mostly derived from renal origin.
Adolescent↗
Complement expression in human brain. Biosynthesis of terminal pathway components and regulators in human glial cells and cell lines.
C biosynthesis at extrahepatic sites remote from plasma C may be important in the protection of tissues against inflammation and infection but may also contribute to tissue injury. This latter possibility is particularly relevant in the central nervous system (CNS), where several cell types are susceptible to damage by C. We have previously shown that human astrocyte-derived tumor cell lines synthesize and secrete all of the components of the activation pathways of C. In this study, we demonstrate that these cells also produce the components (C6, C7, C8, and C9) and regulators (S-protein and clusterin) of the lytic terminal C pathway. The terminal components produced are hemolytically active, and secretion is markedly up-regulated by the inflammatory cytokine IFN-gamma. Primary human fetal astrocytes also expressed C6, C7, S-protein, and clusterin. The human monocyte/macrophage cell line, used here as a model for microglia, also produced all terminal components and regulators when appropriately stimulated. These studies raise the prospect of the intrathecal synthesis of a complete, functional C system and its regulators in the inflamed CNS. Intrathecal C synthesis may be important in the resolution of infection and inflammation but, given the C susceptibility of some CNS cell types, may also exacerbate damage in demyelination and neurodegeneration.
Antibodies, Monoclonal↗
Human complement component C1q inhibits the infectivity of cell-free HTLV-I.
Human T cell leukemia virus type I (HTLV-I) is a retrovirus that is not lysed by human serum or complement. It has not been determined, however, whether HTLV-I directly binds to complement components or whether it retains infectivity after incubation with human serum. We investigated the effects of human serum on the infectivity of cell-free HTLV-I produced by human and animal cells. Plating of vesicular stomatitis virus (HTLV-I) pseudotypes prepared in cat or human cells and formation of HTLV-I DNA after infection of cell-free HTLV-I produced by cat or human cells were markedly inhibited by treatment with fresh human serum, but not by heat-inactivated serum. HTLV-I infection was also inhibited by treatment with C2-, C3-, C6-, or C9-deficient serum, but not by C1q-deficient serum. Inhibitory activities of normal human serum against HTLV-I were neutralized by anti-C1q serum. Furthermore, purified C1q inhibited HTLV-I infection. The direct binding of C1q to HTLV-I was confirmed by comigration of C1q with HTLV-I virion upon sucrose density gradient ultracentrifugation of HTLV-I virion treated with C1q. Binding assay using synthetic envelope peptides indicated that C1q bound to an extramembrane region of the gp21 transmembrane protein. These findings indicate that the human complement component C1q inactivates HTLV-I infectivity.
Animals↗
Pathogenesis of renal ischemia/reperfusion injury: lessons from knockout mice.
Ischemia/reperfusion-induced acute renal failure is a common clinical problem associated with a high morbidity and mortality. Upon hypoxic injury, the depletion of ATP causes mitochondrial dysfunction, and accumulation of intracellular sodium, calcium and reactive oxygen species. Subsequently, multiple enzyme systems including proteases, nitric oxide synthases, phospholipases and endonuclease are activated and responsible for cytoskeleton disruption, membrane damage, and DNA degradation, and eventually cell death. Ischemia/reperfusion injury also activates complement, cytokines, and chemokines, which are cytotoxic themselves, but also attract leukocytes into the ischemic area to cause further damage. The vascular endothelial cell injury and dysfunction prolong ischemia and induce vascular congestion, edema, and further infiltration of inflammatory cells. Many players in renal ischemia/reperfusion injury and their mechanisms have been investigated using genetically manipulated mouse models. In this review, we focus on the information gathered from these studies. Deficiency of the Na/Ca exchanger, inducible nitric oxide synthase, Caspase-1, A3 adenosine receptor, C3, C5, C6, Factor B, or midkine protects the kidney against I/R injury. Conversely, deficiency of the interleukin-1 receptor, osteopontin, C4, or recombination activation gene-1 is not protective, while the absence of adrenomedullin or endothelin receptor B delays the recovery of ischemia/reperfusion injury. The knowledge obtained from these studies provides new direction for designing potential therapeutic agents for treating ischemia/reperfusion injury.
Adenosine↗
Consequences of cell membrane attack by complement: release of arachidonate and formation of inflammatory derivatives.
Treatment of [3H]arachidonic acid [( 3H]C20:4)-labeled and antibody-sensitized Ehrlich ascites tumor cells with guinea pig or rabbit serum complement (C) released up to about 20 or 25% of the incorporated [3H]C20:4 into the aqueous phase as a consequence of C-induced hydrolysis of cellular phospholipid. The dose-response curve of release of [3H]C20:4 from Ehrlich ascites tumor cells, with respect to C, was approximately in the same range as the cytolytic response. In the case of [3H]C20:4-labeled and antibody-sensitized peritoneal mouse macrophages, treatment with C induced release of about 11% of the incorporated 3H as C20:4 and about 6% as prostaglandins, thromboxane B2, and hydroxyicosatetraenoic acids. C6- and C8-deficient rabbit and human sera, respectively, induced release of small amounts of [3H]C20:4 from Ehrlich ascites tumor cells and macrophages; these deficient sera also released traces of oxygenated derivatives from macrophages. Addition of purified C6 or C8 effectively restored release from both cell types, indicating that the terminal C proteins, up to and including C8, are required for the major part of the release. Our results do not rule out a possible requirement for C9.
Animals↗
Loxosceles sphingomyelinase induces complement-dependent dermonecrosis, neutrophil infiltration, and endogenous gelatinase expression.
Envenomation by the spider Loxosceles can result in dermonecrosis and severe ulceration. Our aim was to investigate the role of the complement system and of the endogenous metalloproteinases in the initiation of the pathology of dermonecrosis. Histological analysis of skin of rabbits injected with Loxosceles intermedia venom and purified or recombinant sphingomyelinases showed a large influx of neutrophils, concomitant with dissociation of the collagenous fibers in the dermis. Decomplementation, using cobra venom factor, largely prevented the influx of neutrophils, while influx of neutrophils was also reduced in genetically C6-deficient rabbits, suggesting roles for both C5a and the membrane attack complex in the induction of dermonecrosis. However, C-depletion and C6 deficiency did not prevent the haemorrhage and the collagen injury. Zymography analysis of skin extracts showed the induction of expression of the endogenous gelatinase MMP-9 in the skin of envenomated animals. Rabbit neutrophils contained high levels of MMP-9, expression of which was further increased after incubation with venom, suggesting that these cells may be a source of the MMP-9 found in the skin of envenomated animals. Furthermore, skin fibroblasts also secreted MMP-9 and MMP-2 upon incubation with venom, suggesting that locally produced MMPs can also contribute to proteolytic tissue destruction.
Animals↗
Distinctive roles of neutrophils and monocytes in anti-thy-1 nephritis.
Anti-Thy-1.1 glomerulonephritis as an experimental model for mesangial proliferative glomerulonephritis was induced in Wistar rats by a single injection of monoclonal IgG2a-anti-Thy-1.1 antibody (ER4G). This transient model is complement-mediated and leads to mesangial-cell (MC) lysis followed by MC proliferation, glomerular microaneurysm formation, glomerular influx of polymorphonuclear leukocytes (PMNs) and macrophages, proteinuria, and hematuria. In this study we investigated the distinctive roles of infiltrating PMNs or monocytes/macrophages by treating rats with an antibody against rat integrin CD11b/CD18 (ED7) or by depletion of monocytes with multilamellar clodronate liposomes, respectively. ED7 administration resulted in reduction of the influx of PMNs in glomeruli during the first 6 days after induction of Thy-1.1 nephritis, whereas treatment with an isotype-matched irrelevant antibody (PEN9) or with phosphate-buffered saline had no effect on macrophage influx. Increased glomerular C3 and C6 deposition on days 1 and 3 was seen in the ED7-treated rats but not seen in the control groups. In addition, the ED7-treated group showed an increased number of aneurysmatic glomeruli and more severe hematuria. Monocyte/macrophage depletion led to a significant reduction of mesangial matrix expansion, although mesangial proliferation, proteinuria, and hematuria remained unaltered. These results, together with the known effects of PMN-derived enzymes on C3 cleavage, suggest that a reduction in the influx of PMNs results in sparing of C3 and consequently of more complement activation in the glomerulus with increased complement-mediated damage. Our data indicate that infiltrating PMNs and monocytes/macrophages play distinctive roles during inflammation in this model of MC glomerulonephritis.
Animals↗
The complement SC5b-9 complex mediates cell adhesion through a vitronectin receptor.
Adhesion of cells to the terminal complement complex of C5b through C9 containing the serum S-protein (SC5b-9) was investigated using a microtiter plate attachment assay with L8 myoblast indicator cells. The skeletal muscle-derived L8 myoblasts bound and spread on substratum coated with SC5b-9, and with the vitronectin/S-protein component of SC5b-9. The myoblasts did not adhere to substratum coated with collagen, laminin, or fibronectin. The cell attachment was blocked by antibody to vitronectin/S-protein, whereas antibody to the other components C5, C6, C7, C8, or C9 had minimal effect. The cells were not bound to free vitronectin because attachment activity was removed by adsorption with an anti-C6 antibody column. The L8 cell attachment was dependent on divalent cations, was blocked by synthetic peptides containing the amino acid sequence Arg-Gly-Asp, and was inhibited by antivitronectin receptor antibody. These results indicate that cells adhere to the SC5b-9 complex through interaction of the vitronectin component with an integrin vitronectin receptor. Cell attachment to terminal C complexes could be used for leukocyte adherence and migration during inflammation, and also for attachment of tissue cells during regeneration after disease or traumatic injury.
Animals↗
Complement-mediated lipopolysaccharide release and outer membrane damage in Escherichia coli J5: requirement for C9.
Lipopolysaccharides (LPS) are major antigenic components of the outer membrane of Gram-negative bacteria and can stimulate activation of the complement system. Such activation leads to formation of the complement membrane attack complex (MAC) on the cell walls, LPS release and, in serum-sensitive strains, to cell death. In this study, Escherichia coli J5 strains, which incorporate exogenous galactose exclusively into LPS, were used to generate target strains with different LPS chemotypes, and the LPS of the strains was labelled with tritium (3H-LPS). The ability of normal human serum (NHS) and human complement-deficient sera to release LPS was subsequently monitored. NHS-induced release of 64-95.7% of 3H-LPS within 30 min; overall, no significant difference was observed between release of LPS from E. coli J5 strains with different LPS chemotypes. In functional assays, maximum LPS release had occurred by 30 min and before maximum bacterial killing. Electron microscopy revealed NHS-induced outer-membrane disruption in the form of blebs at 15 min; at this time-point the inner membrane remained intact. Background LPS release and no bactericidal activity were detected in heat-inactivated serum or human sera deficient in C6, C7 or C8. The C9-deficient (C9D) serum had low bactericidal activity and failed to induce LPS release; however, addition of purified human C9 reconstituted its ability to release LPS. This study demonstrated the need for functional C9 molecules for LPS-releasing activities in serum-sensitive E. coli J5 strains.
Blood Bactericidal Activity↗