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PubMed2001

Endothelial targeting with C1-inhibitor reduces complement activation in vitro and during ex vivo reperfusion of pig liver.

Tissue damage during cold storage and reperfusion remains a major obstacle to wider use of transplantation. Vascular endothelial cells and complement activation are thought to be involved in the inflammatory reactions following reperfusion, so endothelial targeting of complement inhibitors is of great interest. Using an in vitro model of human umbilical vein endothelial cells (HUVEC) cold storage and an animal model of ex vivo liver reperfusion after cold ischaemia, we assessed the effect of C1-INH on cell functions and liver damage. We found that in vitro C1-INH bound to HUVEC in a manner depending on the duration of cold storage. Cell-bound C1-INH was functionally active since retained the ability to inhibit exogenous C1s. To assess the ability of cell-bound C1-INH to prevent complement activation during organ reperfusion, we added C1-INH to the preservation solution in an animal model of extracorporeal liver reperfusion. Ex vivo liver reperfusion after 8 h of cold ischaemia resulted in plasma C3 activation and reduction of total serum haemolytic activity, and at tissue level deposition of C3 associated with variable level of inflammatory cell infiltration and tissue damage. These findings were reduced when livers were stored in preservation solution containing C1-INH. Immunohistochemical analysis of C1-INH-treated livers showed immunoreactivity localized on the sinusoidal pole of the liver trabeculae, linked to sinusoidal endothelium, so it is likely that the protective effect was due to C1-INH retained by the livers. These results suggest that adding C1-INH to the preservation solution may be useful to reduce complement activation and tissue injury during the reperfusion of an ischaemic liver.

Animals↗

PubMed1987

Anti-idiotypic antibodies in antisera against human C3 and factor H and their application in the enrichment of antibodies specific for H-binding domains of C3.

Antisera separately raised against C3 and factor H should contain antibodies against the binding domains by which these factors interact. Because these interacting domains are likely to be sterically complementary to each other, antibodies specific for these domains should also be sterically complementary or of anti-idiotypic specificity. To test this hypothesis, rabbit anti-human C3 IgG antibodies which bound to Sepharose-coupled rabbit anti-factor H IgG (anti-H-binding anti-C3) were separated by affinity chromatography. In a control experiment, the anti-human factor H column was found to bind 10 times more anti-C3 antibodies than a Sepharose column coupled with nonimmune rabbit IgG. The binding specificity of the control eluate was indistinguishable from the original anti-C3 preparation, whereas the anti-H-binding anti-C3 was shown to be enriched in regard to antibodies directed against the 42 kd fragment of the C3 alpha-chain of C3c, as demonstrated by immunoblotting of electrophoretically separated polypeptides of C3c and C3d in polyacrylamide gels. In competition binding studies, factor H was 25 times more potent as inhibitor of the anti-H-binding anti-C3 than of the original anti-C3 preparation. This similarity in binding specificity also paralleled a functional similarity in that anti-H-binding anti-C3 in the presence of factor I effected a 20% degradation of the alpha'-chain of C3b into fragments of 65, 45, and 42 kd which are the normal degradation products in the presence of factors I and H. These results suggest that the affinity procedure described resulted in the enrichment of anti-C3 antibodies with selective specificities for factor H-binding domains of C3, from a polyclonal antibody source.

Antibody Specificity↗

PubMed1999

C1-inhibitor attenuates hyperacute rejection and inhibits complement, leukocyte and platelet activation in an ex vivo pig-to-human perfusion model.

Xenotransplantation may be a future alternative due to increased shortage of organs. Classical complement activation is central in hyperacute rejection in pig-to-human combinations. We investigated the effects of C1-inhibitor (C1-INH), a regulator of the complement and contact systems, on hyperacute rejection. Pig kidneys were perfused with fresh human blood to which either C1-INH (n = 6) or human serum albumin (n = 6) was added. The survival of the C1-INH perfused kidneys (mean 327 min) was significantly longer (p < 0.00001) than the controls (79 min). C1-INH substantially inhibited complement activation (C1rs-C1-INH complexes, C4bc, C3bc and terminal complement complex) (p < 0.001 for all) compared with the marked complement activation in the controls. No contact activation was found. Leukocytes and platelets were substantially activated (counts, myeloperoxidase, beta-thromboglobulin, thrombospondin, soluble P-selectin) in the control group, and this activation was markedly reduced by C1-INH (p < 0.02 for all). Immunohistochemistry showed less C1q, C3, TCC, IgG and fibrin deposition in the C1-INH group. C1-INH may be useful to attenuate hyperacute rejection, probably through inhibition of complement. The reduced activation of neutrophils and platelets may mainly be secondary to inhibition of complement.

Animals↗

PubMed2003

Excessive matrix accumulation in the kidneys of MRL/lpr lupus mice is dependent on complement activation.

Complement receptor 1-related gene/protein y (Crry) in rodents is a potent membrane complement regulator that inhibits complement C3 activation by both classical and alternative pathways. Complement inhibition with Crry as the recombinant protein Crry-Ig has been demonstrated to prevent MRL/MpJ-Tnfrsf6(lpr) (MRL/lpr) mice from developing proteinuria and renal failure. Crry-Ig-treated mice also showed less glomerulosclerosis compared with control MRL/lpr mice. To clarify how complement inhibition with Crry might affect renal scarring in lupus nephritis, gene transcript profiling was performed comparing Crry-Ig-treated MRL/lpr mice to control-treated MRL/lpr mice as well as to the MRL/+ strain control. Altered gene expression was confirmed by quantitative PCR, and protein quantity with either immunoblotting or immunofluorescence microscopy. Collagens I, III, IV, and VI were overexpressed in control MRL/lpr mice, whereas complement inhibition with Crry reduced the overexpression of these extracellular matrix components toward normal. Plasminogen activator inhibitor 1, connective tissue growth factor, and TGF-beta1 were upregulated in MRL/lpr mice compared with MRL/+ mice and were normalized by Crry-Ig treatment, suggesting that the product of these genes may contribute to the progressive glomerulosclerosis in MRL/lpr mice in a complement-dependent fashion. Thus, complement inhibition with Crry has a prominent effect on matrix-related genes and proteins, which translates into improvement in functional renal disease.

Animals↗

PubMed1984

Partial C4 deficiency in subacute sclerosing panencephalitis.

In an immunogenetic study, 23 subacute sclerosing panencephalitis (SSPE) patients and their families were studied for the HLA region markers HLA-A, B, C, DR, BF, C2, C4A, C4B, GLO I, and PGM3. In addition, C3, C4, and factor B serum levels were determined. A highly significant association of C4A QO with SSPE was found. Furthermore, two rare haplotypes, C4A QOB QO, two C4ACh+ allotypes, and four Ch partial inhibitors were detected, which possibly impair the function of the C4 molecules. HLA-DR5 was increased. In addition, a number of rare HLA-A, C, B, DR haplotypes were observed. It is postulated that rare C4 molecular deficiency might be a predisposing factor in the pathogenesis of SSPE.

Complement C4↗

PubMed1989

Elevated plasma levels of the anaphylatoxins C3a and C4a are associated with a fatal outcome in sepsis.

PURPOSE AND PATIENTS AND METHODS: Both complement and contact system of coagulation have been implicated in the pathophysiology of sepsis. We therefore measured levels of the complement activation products C1-C1-inhibitor complexes and C3a in serial plasma samples (obtained every six hours) from 48 patients with clinically suspected sepsis, and related these levels to the clinical outcome. C4a was also measured in samples obtained on admission. RESULTS: C3a levels were elevated in 47 patients at least once during the observation period. These levels appeared to be considerably higher in patients who died than in patients who survived. This difference was found for the levels on admission (p = 0.0003), as well as for the highest (p = 0.0010) and the lowest (p less than 0.0001) levels encountered in each patient. The mortality in patients with plasma C3a levels of 13 nmol/liter or less on admission (27 patients) was 33 percent, compared with 86 percent in patients with levels of 14 nmol/liter or more. Patients with septic shock had significantly higher C3a levels than normotensive patients (p values between 0.046 and 0.004). No significant differences in C3a were found between patients who had respiratory distress syndrome and those who did not. C4a levels in plasma samples obtained on admission were elevated in 43 patients. These levels correlated very significantly with C3a levels (p less than 0.0001), and showed similar associations with a fatal outcome. C1-C1-inhibitor complexes were elevated in 23 patients at least once during the observation period. These patients had significantly higher levels of C4a and C3a than patients with normal amounts of C1-C1-inhibitor complexes. Patients who died had higher levels of C1-C1-inhibitor complexes than patients who survived. However, this difference was not significant. CONCLUSION: On the basis of our results, we propose that activation of the complement system via the classical pathway is involved in the development of fatal complications in sepsis.

Adolescent↗

PubMed1986

Incorporation of the purified Epstein Barr virus/C3d receptor (CR2) into liposomes and demonstration of its dual ligand binding functions.

The 145-kDa molecule that has been identified as the C3d receptor CR2 was isolated from lysates of Raji cells by affinity chromatography by using the monoclonal antibody (MoAb)HB-5. The purified protein was incorporated into 14C-phosphatidylcholine liposomes by deoxycholate dialysis followed by flotation on discontinuous sucrose gradients. Incorporation of the receptor was verified by testing the gradient fractions for CR2 by an enzyme-linked immunosorbent assay. Liposomes were shown to be unilamellar vesicles ranging in diameter from 25 to 100 nm by electron microscopy. The external orientation of CR2 in the membranes was demonstrated by immunoelectron microscopy. The functional activities of liposomes containing CR2 and liposomes without protein were compared. CR2 liposomes bound to EC3d, but not to E, and this binding was inhibited by the anti-CR2 MoAb OKB7 and by a MoAb specific for C3d. Control liposomes failed to bind to either E or EC3d. The ability of CR2 to function as a receptor for Epstein Barr virus (EBV) was tested in two ways. First, CR2 liposomes bound to B95-8, a cell line expressing EBV membrane antigens, but not to B95-8 cells treated with the viral DNA polymerase inhibitor phosphonoformic acid. Second, liposomes containing CR2 were shown by ultracentrifugal analyses to bind directly to purified EBV, and this binding was also inhibited by OKB7. Control liposomes did not bind to B95-8 cells or to EBV. These findings show that CR2 purified from detergent extracts of Raji cells can be reconstituted into lipid membranes with maintenance of its dual functions as a receptor for C3d and EBV.

Animals↗

PubMed1987

C3-mediated release of prostaglandin from human monocytes: evidence for independent regulation of thromboxane and prostaglandin synthesis.

Human mononuclear phagocytes (HMP) lose the capacity to respond to C3b, exogenous arachidonic acid (AA), and other stimuli of arachidonic acid (AA) metabolism when precultured for 24 hours prior to the addition of stimulus. Data presented in this report suggest that this reduced capacity is not due to loss of the cyclooxygenase enzyme, to autoinactivation of cyclooxygenase, or to release by the cells of inhibitors of PGE and TxB2 production. Additional metabolism of PGE or a shift of AA metabolism from the cyclooxygenase pathway to the lipoxygenase pathways does not occur and hence cannot account for the observation. HMP precultured for 24 hours with gamma interferon (IFN-gamma) retain the capacity to metabolize AA in response to subsequent exposure to C3b and LPS. HMP precultured with LPS or C3b respond to exogenous AA, but not to restimulation with LPS or C3b, by releasing PGE and to a lesser extent TxB2. The amounts of PGE and TxB2 produced under these conditions are reversed when compared to HMP treated with IFN-gamma LPS, or C3b at the initiation of culture. These data suggest that the production of TxB2 and PGE may be independently regulated in HMP and that IFN-gamma affects HMP AA metabolism by different mechanisms than LPS or C3b.

Arachidonic Acid↗

PubMed1983

The effect of peritoneal lavage and aprotinin in the treatment of severe acute pancreatitis.

Fifty-five patients with severe acute pancreatitis were treated with peritoneal lavage at the Dept. of Surgery at Malmö General Hospital. In a randomized study 26 of the 55 patients received in addition 500,000 KIU aprotinin in the lavage fluid every 2 h. There were no significant differences between the aprotinin- and non-aprotinin-treated groups as to mortality and clinical results. The initial concentration of alpha 1-antitrypsin in plasma was mainly within normal range with increasing values during the treatment. No differences were seen between the two groups. The initial mean level of alpha 2-macroglobulin in plasma was slightly decreased, but 17 patients showed values below normal range. The alpha 2-macroglobulin level during the lavage showed a similar course in the two groups. alpha 1-Antitrypsin and alpha 2-macroglobulin in the lavage fluids showed signs of complexation but in plasma these inhibitors did not show any signs of complexation. On admission to the hospital the mean levels of C3 and kininogen in the plasma were slightly below normal. During the lavage treatment no differences were seen between the two groups. Degradation products of C3 and kininogen were seen in both serum and peritoneal fluids. The electrophoretic patterns of C3 and kininogen normalized in serum as well as in lavage fluids during the lavage treatment without any significant differences in the two groups. High levels of immunoreactive trypsin, pancreatic elastase, PSTI, and leukocyte elastase in serum were seen equally in both groups of patients.

Acute Disease↗

PubMed1980

Aggregation of leukocytes induced by the complement-derived peptides C3a and C5a and by three synthetic formyl-methionyl peptides.

The highly purified hog complement peptides C3a and C5a and three formylmethionyl peptides induced dose-dependent aggregation of human leukocytes. For the effect Ca2+ and Mg2+ ions were required; in their absence the peptides induced specific desensitization. Human serum albumin (1 and 2%) reduced aggregation, whereas equivalent or even higher concentrations of plasma or serum were not inhibitory. SH reagents, protease inhibitors (N-tosyl-L-lysyl-chloromethyl ketone, N-tosyl-L-phenylalanyl-chloromethyl ketone), and colchicine also inhibited aggregation, whereas cytochalasin B greatly enhanced it. Dose-response studies under comparable conditions showed that aggregation is induced in similar dose ranges as chemotaxis. This suggests that complement-derived peptides generated in vivo may contribute to leukocyte accumulation in two ways, first by causing adherence of leukocytes to endothelium (equivalent to aggregation) and then by promoting migration to the inflammatory site.

Calcium↗

PubMed1985

Anaphylatoxin C3a enhances mucous glycoprotein release from human airways in vitro.

Because C3a may be generated during the course of pulmonary inflammatory reactions, we investigated the ability of C3a to affect mucous glycoprotein (MGP) secretion from cultured human airways. C3a, but not C3a des Arg, caused a dose-related increase in MGP release (maximal after 4-6 h), with as little as 15 micrograms of C3a per milliliter stimulating a 40% increase. The experimental evidence suggested that immunologically specific C3a was required for the secretagogue actions, as monospecific anti-C3a inhibited the reaction, as well as specifically absorbing the secretagogue from solution. Moreover, it appeared that C3a does not require mast cell activation, eicosanoid generation, or macrophage-derived mucus secretagogue synthesis for its effect, since (a) no evidence of histamine release accompanied C3a-induced MGP release, and dibutyryl cAMP failed to affect C3a-induced MGP release, while reducing the actions of reversed anaphylaxis; (b) MGP release caused by C3a was not influenced by eicosatetraynoic acid or specific cyclooxygenase inhibitors, and no leukotrienes were detectable on the supernatants of C3a-stimulated airways; and (c) cycloheximide failed to affect C3a secretion-stimulating actions. Thus, C3a is a potent mucus secretagogue, and, possibly, acts directly as a glandular stimulant. It seems likely that C3a generated in the course of pulmonary inflammation might contribute to the mucus secretion associated with pulmonary infections.

5,8,11,14-Eicosatetraynoic Acid↗

PubMed1986

Homologous species restriction in lysis of human erythrocytes: a membrane-derived protein with C8-binding capacity functions as an inhibitor.

An intrinsic membrane protein with a m.w. of 65,000 that can bind human C8 has been identified after separation of human erythrocyte membrane proteins by sodium dodecyl sulfate-polyacrylamide gel electrophoresis and electrotransfer to nitrocellulose sheets. The protein, tentatively designated as the C8-binding protein (C8bp) could be isolated from papain-treated erythrocyte (E) membranes by phenol-water extraction and isoelectric focusing. In a functional assay, with chicken (ch) E as target cells, C8bp inhibited the lysis of ch E C5b67 intermediates by human C8 and C9, whereas the lysis by rabbit C8 and C9 was not affected. Because the decay accelerating factor (DAF) from human erythrocyte membranes also inhibits the activity of C3/C5 convertases in an homologous system, we tested whether or not a DAF activity was present in C8bp. C8bp, however, did not accelerate the decay of the classic C3 convertases. Thus, it appears that C8bp and DAF are two different factors of E membranes with a similar molecular size inhibiting different sites of the activation cascade of complement while they can function synergistically to minimize the self-inflicted damage by complement.

Blood Proteins↗

PubMed2003

Hyperacute lung rejection in the pig-to-human model. 2. Synergy between soluble and membrane complement inhibition.

BACKGROUND: The role of complement in hyperacute lung xenograft rejection has not been elucidated. The present study evaluates the effect of complement (C) C3/C5 convertase inhibition on hyperacute rejection of pig lung by human blood. METHODS: In an established ex-vivo model, lungs from pigs heterozygous for human decay accelerating factor (hDAF), non-transgenic littermate control pigs, or farm-bred pigs were perfused with fresh human blood that was either unmodified or treated with soluble complement receptor type 1 (sCR1: TP10, 100 microg/ml). RESULTS: Non-transgenic lungs from littermate controls had a median survival time of 35 min (range 5 to 210; P = 0.25 vs. farm-bred piglets: median 5 min, range 5 to 10). Lungs expressing hDAF survived for a median of 90 min (range 10 to 161; P = 0.5 and 0.01 vs. littermate and farm-bred controls, respectively), with sCR1, whereas hDAF (-) lungs failed by 35 min (range 6 to 307), hDAF (+) lungs survived for 330 min (range 39 to 577) [P = 0.002 vs. farm-bred; P = 0.08 vs. hDAF (-); P = 0.17 vs. sCR1/hDAF (-)]. The rise in pulmonary vascular resistance (PVR) at 5 min was blunted only by hDAF (+) with sCR1 (0.26 +/- 0.2 vs. 0.5 to 0.7 mmHg/ml/min for other groups). Plasma C3a and sC5b-9 and tissue deposition of C5b-9 were dramatically diminished using sCR1, and further decreased in association with hDAF. Histamine and thromboxane were produced rapidly in all groups. CONCLUSION: Complement plays an important role in lung HAR. However, even potent inhibition of C3/C5 convertase, both membrane bound in lung and by a soluble-phase inhibitor in the blood, does not prevent activation of inflammatory responses known to be particularly injurious to the lung. Our findings implicate a role for innate immune pathways resistant to efficient complement regulation. The role of anti-species antibody, coagulation pathway dysregulation, and additional environmental or genetic influences remain to be defined.

Acute Disease↗

PubMed1995

Protection of retroviral vector particles in human blood through complement inhibition.

The rapid inactivation of murine-derived retroviral vectors in human or nonhuman primate sera is largely attributed to the activity of complement mediated through the classical pathway. In this study, we have further investigated the relationship between the human complement cascade and retrovirus inactivation. Preincubation in normal human serum effectively inactivated LXSN retroviral vector particles, whereas the vector maintained the ability to transduce cells following incubation in sera deficient in either the C1, C2, C3, C5, C6, C8, or C9 human complement proteins. Preincubation of serum with monoclonal antibodies (mAbs) that functionally block specific complement components, including C5, C6, C8, and C9, successfully protected the LXSN vector from complement-mediated inactivation. Treatment of serum with cobra venom factor, which consumes terminal complement, also effectively protected the vector from inactivation. LXSN vector survival in serum corresponded inversely to the level of complement activity following treatment of serum with anti-C5 mAb as assessed in an erythrocyte hemolytic assay. Additionally, pretreatment of human whole blood with anti-C5 mAb effectively inhibited inactivation of the LXSN vector. Taken together, these data demonstrate that formation of the membrane attack complex (MAC, C5b-9) is required for the inactivation of the murine-based LXSN retroviral vector in human blood and that this process can be abrogated with the use of soluble complement inhibitors.

3T3 Cells↗

PubMed1999

Alpha 1-acid glycoprotein-induced tumor necrosis factor-alpha secretion of human monocytes is enhanced by serum binding proteins and depends on protein tyrosine kinase activation.

The acute phase protein, alpha1 acid glycoprotein (AGP), stimulated human mononuclear cells as well as monocytes to secrete tumor necrosis factor-alpha (TNFalpha) which was demonstrated by ELISA, RT-PCR and functional assays. AGP-induced TNFalpha secretion of monocytes was enhanced in the presence of human plasma and inhibited by protein kinase inhibitors, indicating it is serum and tyrosine kinase dependent. The activation of tyrosine kinase in AGP-stimulated monocytes was further confirmed by immunoblotting of tyrosine phosphorylated proteins of monocytes at different time after AGP stimulation. Furthermore, several serum proteins such as C3, sCD14 and IgG were able to bind to AGP and enhanced TNFalpha secretion of human monocytes induced by AGP. Taken together, these results suggest serum proteins binding to AGP enhance its ability to stimulate human monocytes to secrete pro-inflammatory cytokines through a tyrosine kinase dependent pathway.

Blood Proteins↗

PubMed1993

A role for complement as the major opsonin in the sequestration of erythrocytes from elderly and young donors.

Erythrocytes from elderly donors (> 70 years), but not young donors (18-35 years), are shown to undergo sequestration in an in vitro erythrophagocytosis assay. Comparable levels of sequestration are observed for high density erythrocytes from young individuals and both low density and high density erythrocytes from elderly individuals. These cells, which are susceptible to phagocytosis with no additional treatment are collectively termed 'in situ aged' erythrocytes. We present evidence for the involvement of complement in the sequestration of 'in situ aged' erythrocytes and correlate levels of complement bound to 'in situ aged' erythrocytes from young and elderly donors with levels of phagocytosis. We also demonstrate that the in vitro sequestration of erythrocytes from elderly donors can be inhibited by beta-galactosyl sugars and arginine-glycine-aspartic acid (RGD) but not by mannose nor by Protein-G, a specific inhibitor of Fc-gamma mediated phagocytosis. These experiments show that IgG is not the major opsonin in the sequestration of red cells from elderly donors. In support of the role of complement rather than IgG as the major opsonin in red cell sequestration, we further demonstrate that C'3 bearing immune complexes block in vitro sequestration of erythrocytes from elderly donors. This competition is not dependent upon the isotype of the immunoglobulin (IgM or IgG) in the complex but rather on the presence of active complement.

Adolescent↗

PubMed1988

C-reactive protein-mediated complement activation in polymyalgia rheumatica and other systemic inflammatory diseases.

An immunoglobulin-independent deposition of the complement (C) components C4 and C3 occurs on rat kidney medullary structures, when sera of patients with various inflammatory diseases are studied by indirect immunofluorescence. The diagnostic value of this new test (C4-C3-IFT) for polymyalgia rheumatica (PMR) is stressed, since all sera from patients with active disease yielded positive reactions. Though highly sensitive with respect to PMR, C4/C3-IFT is not specific for this syndrome. Examples of positive reactions in systemic inflammatory diseases other than PMR are documented. Besides the clinical studies, C4/C3-IFT reactivity was analyzed with regard to the mechanisms of the reaction. Experimental data are presented which suggest that C-reactive protein (CRP) binds to rat kidney structures, thereby activating the classical C cascade. As a result of CRP-C interaction, C4 and C3 components are fixed to distinct renal medullary structures. Because of its technical simplicity, C4/C3-IFT can routinely be used to screen patients' sera for CRP-mediated C activation. This ex vivo test system may contribute to a better understanding of pathophysiological functions of serum CRP in various inflammatory diseases.

Antigen-Antibody Complex↗

PubMed2003

A surface amebic cysteine proteinase inactivates interleukin-18.

Amebiasis is a major cause of morbidity and mortality worldwide. Invasion by Entamoeba histolytica trophozoites causes secretion of proinflammatory cytokines from host epithelial cells, leading to a local acute inflammatory response, followed by lysis of colonic cells. Extracellular cysteine proteinases from amebic trophozoites are key virulence factors and have a number of important interactions with host defenses, including cleavage of immunoglobulin G (IgG), IgA, and complement components C3 and C5. Amebic lysates have also been shown to activate the precursor to interleukin 1-beta (proIL-1beta), mimicking the action of caspase-1. IL-18 is also a central cytokine, which induces gamma interferon (IFN-gamma) and activates macrophages, one of the main host defenses against invading trophozoites. Because proIL-18 is also activated by caspase-1, we evaluated whether amebic proteinases had a similar effect. Instead, we found that recombinant proIL-18 was cleaved into smaller fragments by the complex of surface-associated and released amebic proteinases. To evaluate the function of an individual proteinase from the complex pool, we expressed an active surface proteinase, EhCP5, which is functional only in E. histolytica. Recombinant EhCP5 expressed in Pichia pastoris had kinetic properties similar to those of the native enzyme with respect to substrate specificity and sensitivity to proteinase inhibitors. In contrast to the activation of proIL-1beta by amebic lysates, the purified proteinase cleaved proIL-18 and mature IL-18 to biologically inactive fragments. These studies suggest that the acute host response and amebic invasion result from a complex interplay of parasite virulence factors and host defenses. E. histolytica may block the host inflammatory response by a novel mechanism, inactivation of IL-18.

Amino Acid Sequence↗