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PubMed1994

Receptor-independent activation of guanine nucleotide-binding regulatory proteins by terminal complement complexes.

Activation of heterotrimeric guanine nucleotide-binding proteins (G proteins) by terminal complement complexes (TCC) was investigated on human lymphoblastoid B-cell line JY25 and its mutant JY5 deficient in glycosylphosphatidylinositol-anchored proteins. TCC assembly achieved by antibody-dependent activation of C7-deficient serum reconstituted with C7 increased specific guanosine-5'-(gamma-thio)triphosphate (GTP gamma S) binding, 4- and 8-fold, in JY25 and JY5 membranes, respectively, between 2 and 10 min, over the level without C7. TCC also increased GTPase activity 5- and 4-fold in JY25 and JY5, respectively, between 5 and 10 min. Increased GTPase activity was noted first with C5b-7 assembly, which increased further with C5b-8 and C5b-9. The presence of G proteins in anti-TCC immunoprecipitates of cell lysates was investigated by demonstration of G alpha subunit that can be ADP-ribosylated by pertussis toxin (PTX). Immunoprecipitated TCC complexes contained a PTX-sensitive 41-kDa Gi alpha/Go alpha subunit, as shown by SDS-PAGE and Western blotting. These complexes were functionally active as determined by GTP gamma S binding. We have further shown that enhanced TCC elimination from the plasma membrane induced by TCC-generated signals was inhibited by PTX. In conclusion the biological activities induced by TCC in nucleated cells may be mediated in part by activation of PTX-sensitive G proteins.

B-Lymphocytes↗
PubMed2005

Role of C5 in the development of airway inflammation, airway hyperresponsiveness, and ongoing airway response.

The role of complement component C5 in asthma remains controversial. Here we examined the contribution of C5 at 3 critical checkpoints during the course of disease. Using an mAb specific for C5, we were able to evaluate the contribution of C5 during (a) the initiation of airway inflammation, (b) the maintenance of airway hyperresponsiveness (AHR), and (c) sustainment of an ongoing airway response to allergen provocation. Our results indicate that C5 is probably activated intrapulmonarily after infections or exposures to allergen and C5 inhibition has profound effects at all 3 critical checkpoints. In contrast to an earlier report, C5-deficient mice with established airway inflammation did not have elevated AHR to nonspecific stimuli. In the presence of airway inflammation, C5a serves as a direct link between the innate immune system and the development of AHR by engaging directly with its receptors expressed in airways. Through their powerful chemotactic and cell activation properties, both C5a and C5b-9 regulate the downstream inflammatory cascade, which results in a massive migration of inflammatory cells into the bronchial airway lumen and triggers the release of multiple harmful inflammatory mediators. This study suggests that targeting C5 is a potential clinical approach for treating patients with asthma.

Animals↗
PubMed1990

Human seminal clusterin (SP-40,40). Isolation and characterization.

Molecular cloning of the human complement inhibitor SP-40,40, has revealed strong homology to a major rat and ram Sertoli cell product, sulfated glycoprotein-2, known also as clusterin. This study reports the purification and characterization of human seminal clusterin. Two-dimensional gel electrophoresis revealed charge differences between clusterin purified from semen and the serum-derived material. Both preparations demonstrate comparable hemagglutination (clustering) activity and inhibition of C5b-6 initiated hemolysis. The average clusterin concentration in normal seminal plasma is considerably higher than that found in serum. Mean seminal plasma clusterin concentrations were significantly lower in azoospermia caused by obstruction or seminiferous tubule failure than with oligospermia or normospermia. Only men with vasal agenesis had undetectable seminal clusterin, suggesting that some of the seminal clusterin is produced by the seminal vesicles. Immunofluorescence of human spermatozoa revealed that clusterin was detected on 10% of spermatozoa, predominantly those that were immature or had abnormal morphology. A pilot study of 25 patients suggests that seminal clusterin concentration, together with sperm motility and morphology, is correlated with the fertilization rate in vitro. The function of seminal clusterin is unknown. Its extensive distribution in the male genital tract and its high concentration in seminal plasma suggests an important role in male fertility.

Animals↗
PubMed2002

Effects of C-reactive protein and pentosan polysulphate on human complement activation.

Complement (C) activation is believed to play an adverse role in several chronic degenerative disease processes, including atherosclerosis, myocardial infarction and Alzheimer's disease. We developed several in vitro quantitative assays to evaluate processes which activate C in human serum, and to assess candidates which might block that activation. Binding of C-reactive protein (CRP) to immobilized cell surfaces was used as a tissue-based method of activation, while immunoglobulin G in solution was used as a surrogate antibody method. Activation was assessed by deposition of C fragments on fixed cell surfaces, or by capture of C5b-9 from solution. We observed that several cell lines, including SH-SY5Y, U-937, THP-1 and ECV304, bound CRP and activated C following attachment of cells to a plastic surface by means of air drying. Treatment of human neuroblastoma SH-SY5Y cells with the reactive oxygen intermediates generated by xanthine (Xa) - xanthine oxidase (XaOx) prior to air drying or by hydrogen peroxide solutions after air drying, enhanced C activation, possibly through oxidation of the cell lipid membrane. Several C inhibitors were tested for their effectiveness in blocking these systems. Pentosan polysulphate (PPS), an orally active agent, blocked C activation in the same concentration range of 1-1000 microg/ml as heparin, dextran sulphate, compstatin and fucoidan. PPS may have practical application as a C inhibitor.

C-Reactive Protein↗
PubMed1988

Comparison between complement and melittin hemolysis: anti-melittin antibodies inhibit complement lysis.

A comparison is made between the hemolytic actions of melittin and the ninth component of complement (C9). Melittin and C9 produce "pores" of similar effective radius in erythrocytes under standardized conditions, and their hemolytic action is suppressed by metal ions at similar concentrations, suggesting a common mechanism. Polyclonal anti-melittin immunoglobulin G (IgG) produced in rabbits retards hemolysis mediated by human C9 in a specific manner. Such antibodies react in several immunoassays with human and monkey C9 but not with C9 from lower animals, and no inhibition of lysis mediated by C9 molecules from these animals is observed. Thus, it is unlikely that anti-melittin IgG reacts with a structural element, such as an amphipathic helix, on human C9 since such structures are also predicted to exist in other C9 molecules. Human C9 and melittin block cross-reactivity in a dose-dependent manner, and anti-melittin IgG recognizes an epitope located between amino acid residues 245 and 390 of human C9 on "Western" blots. Comparison of the melittin and human C9 sequences indicates two regions of complete homology, a tetrapeptide at positions 292-295, and a pentapeptide at positions 527-531 in human C9, corresponding to residues 8-16 in melittin. Inhibition of hemolysis is not caused by blocking of C9 binding to the C5b-8 complex; rather the antibody must dissociate from the bound C9 before lysis ensues, indicating that it interferes with a postbinding event. It is proposed that anti-melittin binds to a conformational epitope on native, folded human C9 and thereby retards unfolding of the molecule, which is required for membrane insertion and hemolysis.

Antibodies↗
PubMed1991

A covalent dimer of complement C4b serves as a subunit of a novel C5 convertase that involves no C3 derivatives.

A C intermediate, LAC14, was prepared from TNP-aminocaproyl liposomes sensitized with anti-TNP antibody (Ab) and purified human C1 and C4. LAC14, containing radiolabeled C4, was analyzed by SDS-PAGE followed by autoradiography, and yielded a 210-kDa band and a predominant 400-kDa band. The 210-kDa band consisted of monomeric C4b bound to low molecular mass acceptors. The 400-kDa band was comprised of a 200-kDa moiety, as well as beta- and gamma-chains of C4. The 200-kDa moiety contained neither C1 nor sensitizing Ab, but it was largely decreased by treatment with NH2OH to the 90-kDa moiety with the mobility corresponding to the alpha'-chain of C4b. A covalent dimer of C4b, therefore, is the predominant form of C4b deposited on liposomes sensitized with antibody. The C4b-C4b dimer formed rapidly (within 5 min) followed by slow dissociation into monomers. The LAC14 bearing the C4b dimer but not the monomer was lysed, although with relatively low efficiency, by the addition of oxyC2 and EDTA-supplemented C3-deficient serum (C3DS), and, furthermore, LAC142 possessed the ability to convert C5 into C5a and C5b. Moreover, lysis was inhibited not by anti-C3 Ab but by anti-C4 Ab. In other experiments, the dimer served as an element of C3 convertase, as well. These findings imply that the C4b dimer, when complexed with C2, expresses C3/C5 convertase activity without participation of C3, and may provide a molecular mechanism whereby sera from patients with complete C3 deficiency retain the ability to induce C-mediated cytolysis.

Autoradiography↗
PubMed1999

Combined administration of IgA and IgG anti-Thy-1 antibodies enhances renal inflammation in rats.

BACKGROUND: IgA nephropathy (IgAN) is the most common type of immunologically mediated glomerulonephritis (GN) and is characterized by deposition in the glomerular mesangium of IgA together with C3, C5b-9, and properdin. In patients, the codeposition of IgA together with IgG and/or IgM can lead to a more progressive course of disease. In Wistar rats, mesangial proliferative GN can be induced by the injection of mouse IgG anti-Thy-1 antibodies (ER4G). In contrast, the administration of mouse IgA anti-Thy-1 antibodies (ER4A) to rats results in isolated hematuria without detectable albuminuria and without detectable complement deposition. METHODS: To investigate the effect of the combination of IgA and IgG on glomerular injury, Wistar rats were injected with a limiting dose of ER4G in the presence or absence of ER4A in a dose able to induce hematuria. RESULTS: Although the limiting dose of ER4G or the dose of ER4A used did not induce significant albuminuria, the combination of ER4G and ER4A resulted in a synergistic increase in albuminuria. Microhematuria occurred in rats receiving either ER4A or ER4G alone or in combination. Although both ER4A or a limiting dose of ER4G induced minor increases in extracellular matrix expansion, the combination resulted in a pronounced, additive increased matrix expansion. CONCLUSION: We conclude that in this model of IgA-mediated glomerulopathy, a selective complement-dependent synergistic renal injury is induced in Wistar rats by glomerular codeposition of mouse anti-Thy-1 monoclonal isotypes.

Animals↗
PubMed1993

Activated C3 (C3b) in the nephritic glomerulus.

An autoradiographic technique was developed to assess in the nephritic glomerulus the relative amount of C3 which is in the activated form, C3b, compared with the inactivated form, iC3b. Frozen renal biopsy sections from children and young adults with glomerulonephritis were assessed for the C3b fraction of total C3, using a radiolabeled monoclonal anti-C3c. Grain counts with this antibody, before and after reacting the section with 0.0002% trypsin, gave the relative amounts of total C3 and C3b, respectively. C3b was found in all diseases studied. To explain its presence, glomerular C3b acceptors which would restrict C3b inactivation were sought by immunofluorescence studies. C3b acceptor candidates were: IgG in aggregated form, IgA as found in the IgA nephropathies and the C3/C5 convertase, C4b,2a,3b. In acute post-streptococcal glomerulonephritis and membranoproliferative glomerulonephritis type III, diseases in which these acceptors were lacking, it is postulated that the nephritis strain-associated protein and absence of membrane cofactor protein, respectively, may be responsible for C3b deposition. The phlogistic effect of C3b is mediated largely by one of its products, C5b-9. However, the C3b: total C3 ratio failed to correlate with indices of glomerular inflammation, probably in part because the ratio is not a measure of total glomerular C3b.

Adolescent↗
PubMed1999

Derivation of RNA aptamer inhibitors of human complement C5.

Specific aptamer inhibitors of the human complement C5 component were produced by the SELEX methodology of directed evolution of nucleic acid ligands. The SELEX procedure started with a pool of random-sequence, 2'F-pyrimidine-modified nuclease-stabilized RNA, and after twelve rounds of iterative C5 binding and nucleic acid amplification an evolved RNA pool was obtained which contained the highest affinity binders to the C5 protein. The evolved RNA pool was then cloned and sequenced, and individual clones were analyzed for binding and function. Twenty-eight clones (out of sixty) were identified which bound C5 (termed aptamers). Seven of these aptamers formed a closely related sequence homology family; these aptamers bound C5 with a Kd 20-40 nM and also inhibited human serum hemolytic activity. In addition, these aptamers inhibited zymosan-induced generation of C5a. Aptamer inhibition of both C5b and C5a suggests that aptamer binding inhibits cleavage of C5 by the C5 convertase of both pathways. One of the inhibitory aptamer sequences was truncated to yield a 38-mer 2'F RNA aptamer which retained C5 binding and inhibitory activity. The structure of this aptamer is predicted to be a stem-loop containing thirteen base pairs, and also containing two bulges. The affinity of this aptamer was improved by performing a second biased SELEX experiment, where the randomized starting RNA pool uses a template where the individual base compositions are biased toward a specific sequence. This second SELEX experiment produced an aptamer with a Kd of 2-5 nM which retained functional activity. Another SELEX to rat C5 produced an aptamer with binding and inhibitory properties virtually identical with the human aptamer. The human and rat aptamers are being evaluated for complement inhibition in vitro and in vivo as potential therapeutics for treatment of human disease.

Animals↗
PubMed1982

Photolabeling of a hydrophobic domain of the ninth component of human complement.

Recent experiments with membrane-restricted, photoactivatable probes indicated a preferential labeling of C9 within the assembled membrane attack complex (MAC) of complement, suggesting a direct role for C9 in the interaction of the MAC with membrane lipids. To further characterize the lipid-binding sites on C9, we have now used C9 that has been cleaved by alpha-thrombin. This enzyme cleaves C9 at one site but the newly generated peptides, C9a and C9b, respectively, remain noncovalently associated and the cleaved protein suffers no loss in hemolytic activity. When cleaved C9 was incorporated into the MAC during assembly on phospholipid vesicles and photolabeled, subsequent sodium dodecyl sulfate-polyacrylamide gel electrophoresis analysis and fluorography revealed that only the larger fragment C9b, but not the smaller fragment C9a, became labeled. C9 attached alone to vesicles through heat aggregation in the absence of the precursor complex C5b-8 is also accessible to the hydrophobic photolabel. When cleaved C9 is used in the heat-induced assembly on vesicles and the polymerized C9 is photolabeled, the label associates again predominantly with C9b and not C9a. These results not only show that, within C9 polymers or within the assembled MAC, C9 possesses a two-domain structure, but also lend considerable support to the structure proposed for C9 by Biesecker et al. (Biesecker, G., Gerard, C., and Hugli, T. E. (1982) J. Biol. Chem. 257, 2584-2590) who classified C9a as hydrophilic and C9b as hydrophobic.

Azides↗
PubMed1984

Residual hemolytic and proteolytic activity expressed by Bb after decay-dissociation of C3b,Bb.

Bb (Mr = 63,000) is the catalytic site-bearing subunit of the C3 convertase of the alternative complement pathway, C3b,Bb, which is dissociated from the complex upon decay of the enzyme. Because purified Bb induced certain leukocyte activities, we examined whether it expresses residual hemolytic or proteolytic activity. Hemolytic activity of Bb was tested by using Factor B- or Factor D-depleted normal human serum and rabbit or sheep erythrocytes. Proteolytic activity of Bb was assessed by using purified C3 or C5 as substrates and SDS-PAGE to detect protein cleavage. Bb expressed metal-dependent hemolytic activity that was approximately 100-fold lower than that of Factor B. This activity could be inhibited by Factor H and enhanced by properdin. Low but statistically significant binding of 125I-labeled Bb to C3b on erythrocytes was demonstrated. Monoclonal antibodies that bind to Bb but not to intact Factor B inhibited the Bb hemolytic activity. Purified Bb cleaved C3 to C3a and C3b, as evidenced by the appearance of the alpha'-chain of C3b. It also cleaved C5 to C5a and C5b when cobra venom factor was present in the reaction mixture. Metal ions were required for expression of proteolytic activity, and Ni supported the activity better than Mg. These results indicate that decayed Bb has residual C3 and C5 cleaving activity and hemolytic activity, expression of which appears to require its association with C3b, C3(H2O), or cobra venom factor. These observations may aid in explaining the mechanism of action of Bb on leukocytes.

Antibodies, Monoclonal↗
PubMed2005

Complement inhibitor of C5 activation from the soft tick Ornithodoros moubata.

Blood-feeding ticks must control C activation or be damaged by the host inflammatory response. We report the characterization and expression of a novel, relatively small, broad-acting C inhibitory protein (termed OmCI) from the soft tick Ornithodoros moubata. The native 17-kDa nonglycosylated protein inhibits both human and guinea pig classical and alternative C activation pathways. The IC50 values for each pathway were 12 and 27 nM, respectively, in hemolytic assays using human serum diluted 40-fold. The cDNA encodes a protein of 168 aa, including an 18-aa secretion signal sequence that is absent in the mature form. The inhibitor has 46% amino acid identity with moubatin, a platelet aggregation inhibitor also from O. moubata that is an outlying member of the lipocalin family. Native OmCI had no inhibitory effect on the addition of C8 and C9 to preformed C5b-C7 and C5b-C8 to form the membrane attack complex and no effect on the rate of C3a production by the C3 convertase enzymes C4bC2a, C3(H2O)Bb, or C3bBb. Both recombinant and native OmCI abolish production of C5a by human classical (C4bC3bC2a) and alternative (C3bC3bBb) C5 convertases. Addition of excess C5 but not C3 competes away the inhibitory activity of OmCI, indicating that OmCI targets C5 itself rather than inhibiting the C5 convertase C4bC3bC2a itself. Direct binding of OmCI to C5 was demonstrated by Western blotting and gel filtration chromatography using 125I-labeled proteins. OmCI is the first lipocalin family member shown to inhibit C and also the first natural inhibitor that specifically targets the C5 activation step.

Amino Acid Sequence↗
PubMed1993

Small angle neutron scattering studies of C8 and C9 and their interactions in solution.

Small angle neutron scattering (SANS) results revealed that contrary to most reports C9 is not a globular protein. Its radius of gyration (Rg) at pH 8 and an ionic strength of 0.5 is 32.2 +/- 1.4 A increasing to 35 A at physiologic ionic strength. In contrast, C8, which has a 2.2-fold larger mass, has a similar Rg value [34.6 +/- 1.6 A]. Calibration plots of Rg vs. M(r) indicate that native C8 is a spherical protein whereas native C9 is elongated. From previous reports it was known that native C8 and C9 associate in solutions of low ionic strength. SANS results confirmed this observation but also demonstrated that C8-C9 heterodimers are already formed at physiologic ionic strength. The dimeric complex is globular [Rg = 40 +/- 0.8 A] indicating that the proteins associate side-by-side rather than end-to-end. In contrast, in presence of the drug Suramin, a potent inhibitor of the assembly of the C5b-9 complex, C9 forms a complex with twice the molecular mass that is still elongated (Rg = 48.8 +/- 0.8 A), suggesting that in this case the protein dimerizes end-to-end via a bridging Suramin molecule.

Biophysical Phenomena↗
PubMed1990

Bacterial killing and inhibition of inner membrane activity by C5b-9 complexes as a function of the sequential addition of C9 to C5b-8 sites.

The assembly of the C5b-9 complex on the outer membrane of C-sensitive cells of Escherichia coli results in a rapid inhibition of inner membrane function and ultimately a loss of cell viability. Cells bearing C5b-8 sites suffer no deleterious effects; however, the addition of C9 results in a rapid inhibition of inner membrane function and cell death. An attempt was made to examine the relationship between the toxic effects of the C5b-9 complex and the number of C9 molecules per C5b-8 site. Cells bearing C5b-8 sites were exposed to excess C9 at 0 degrees C and washed three times at 4 degrees C. The number of C9 molecules bound to each cell was equivalent to the number of C5b-8 sites present on each cell, and no additional C9 molecules could be bound when the cells were maintained at 4 degrees C. These cells were then incubated at 37 degrees C for 3 min and returned to 0 degrees C, a technique which exposed additional C9-binding sites equivalent to the number of C9 molecules previously bound to the cells. This technique was repeated and demonstrated that the sequential build-up of a C5b-9 site with two C9 molecules per C5b-8 site was capable of inhibiting both inner membrane function (respiration and amino acid transport) and cell viability. Three C9 molecules per complex had effects that approached the inhibitory effects of complexes formed in the presence of excess C9.

Bacterial Physiological Phenomena↗
PubMed1986

The ninth component of human complement (C9). Functional activity of the b fragment.

The domain structure of human complement protein C9 was investigated by determining the functional activities of the NH2-terminal (C9a) and COOH-terminal (C9b) fragments obtained by cleavage of C9 with alpha-thrombin. The two fragments were separated by preparative sodium dodecyl sulfate-polyacrylamide gel electrophoresis and renatured by dialysis against buffers containing zwitterionic detergents. The C9b fragment produced membranolytic activities in three independent assays. First, it produced single, ion-conducting channels of varying conductances in planar lipid membranes. Most of the channels had an average conductance of 11 picoSiemens and an average lifetime of about 30 s. The channels showed lipid specificity and a 3-fold preference for conducting K+ over Na+. Second, the fragment also caused specific marker release from liposomes which was inhibitable by a C9b-specific monoclonal antibody, and third, it lysed erythrocytes in the absence of a fully assembled C5b-8 complex. The isolated C9a fragment did not produce single channels in planar lipid membranes but was also effective in releasing markers from liposomes and in lysing erythrocytes. Secondary structure predictions indicate the presence of several amphiphilic, "surface-seeking" segments in the primary structure of C9 which are mainly alpha-helices in C9b and beta-sheets in C9a. These results may indicate the presence of surface-binding domains in the NH2-terminal half and channel-forming domains in the COOH-terminal portion of native, monomeric C9.

Antibodies, Monoclonal↗
PubMed2003

Fatal trauma to the neck: immunohistochemical study of local injuries.

As fatal trauma to the neck is often associated with short survival times, proof of vitality may often be difficult using standard histochemical techniques. Soft tissue neck injuries resulting from strangulation by ligature or manual strangulation were examined immunohistochemically using antibodies to myoglobin, fibronectin, C5b-9 and MRP14, and compared to controls consisting of accidental soft tissue neck injuries as well as undamaged neck soft tissue. Although survival times in the study and control groups were unknown and certainly some individual variation may be expected in the time course of normal wound development, both the study and control groups demonstrated similar time courses in the immunohistochemical detection of antigen. Myoglobin was always found in those samples in which only one antigen was shown to be involved in an injury-specific pattern; myoglobin and fibronectin were found in samples with dual antigen involvement. Samples involving three antigens always included C5b-9 in addition to myoglobin and fibronectin. The single positive MRP14 sample in the study and control groups was simultaneously positive for the other markers used. Myoglobin, fibronectin, C5b-9 and MRP14 are therefore suitable for immunohistochemical detection of vital reactions and estimation of temporal relationships in the early posttraumatic period after neck trauma.

Adolescent↗
PubMed1994

Susceptibility of C5b-9(m) to postmortem changes.

C5b-9(m) is a specific and sensitive marker for myocardial cell necrosis. The diagnostic value of this marker would be considerably limited in forensic practice if its immuno-histochemical demonstration were hampered by putrefaction or autolysis. We could demonstrate C5b-9(m) immunohistochemically in necrotic myocardium due to infarction up to the 11th day of experimentally induced putrefaction and autolysis, when reliable demonstration of myocardial infarction with hematoxylin-eosin was no longer possible. Under the experimental conditions of this study, no false positive immunohistochemical staining occurred.

Bias↗
PubMed1991

Complement-mediated killing of the Lyme disease spirochete Borrelia burgdorferi. Role of antibody in formation of an effective membrane attack complex.

Lyme disease is a multisystemic illness caused by the spirochete Borrelia burgdorferi. In the absence of specific antibody, the spirochete is resistant to the bactericidal activity of C, despite the capacity of B. burgdorferi to activate both C pathways. We examined the mechanism of serum resistance by measuring the deposition of C3 and terminal C components on B. burgdorferi in the presence and absence of immune IgG. In normal human serum antibody-sensitized borreliae bound similar amounts of C3, and similar or increased amounts of C8 and C9, in comparison to unsensitized bacteria. However, at comparable levels of C3, C8, or C9 uptake, only sensitized bacteria were killed. The requirement of antibody for killing could not be explained by differences in the rate of C deposition or by differences in the C9 to C8 ratio in the membrane attack complex (MAC). We found that bacteria incubated in C5-depleted human serum, but not in C6-depleted serum, were killed when this treatment was followed by antibody and the missing C components. Bacteria were also killed by reactive lysis (C5b-9) provided that antibody was present. Therefore, the effect of bactericidal IgG occurred at the stage of C5b binding to the bacterial surface. Elution studies of bound C9 indicated that the MAC was stably bound to the outer membrane of B. burgdorferi, whether or not the bacteria were treated with antibody. However, treatment with 0.1% trypsin released 48% of 125I-C9 from the surface of unsensitized borreliae and 24% from IgG-sensitized cells, demonstrating that the presence of the antibody changed the accessibility to trypsin of C9 in the MAC. These results indicate that the effect of antibody in the killing process is not to enhance the rate or extent of initial or terminal component binding, but rather to alter the bacterial outer membrane to allow effective MAC formation.

Antibodies, Bacterial↗