Features of a newly cloned pig C1 esterase inhibitor

The pig cDNA encoding C1 esterase inhibitor (C1-INH) was isolated and the homology of the sequence was compared with that from other animals. The structure of pig C1-INH contains a two disulfide bridge pattern identical to the human C1-INH. In the amino acid sequence of the first Cys-91 to the C-terminal end, the pigC1-INH has a 76.2% homology with the human protein, and the sequence of the reactive site is close to the human. A surface-bound form of pig and human C1-INH, pC1-INH-PI and hC1-INH, respectively, were next constructed. Stable Chinese hamster ovarian tumor (CHO) cell lines and pig endothelial cell (PEC) lines expressing these C1-INH-PI were prepared by transfection. The basic function and the species specificity of pCI-INH were then investigated using these transfectants. pC1-INH and hC1-INH have almost the same suppressive effect on pig, human, dog and rabbit sera in complement-dependent cell lysis, indicating little species specificity.     

The structural basis for neutrophil inactivation of C1 inhibitor.

Limited proteolysis of C1 inhibitor (C1-INH) by neutrophil elastase, Pseudomonas elastase and snake venoms resulted in initial cleavage within the molecule's N-terminus followed by further cleavage within the molecule's C-terminally placed reactive centre. N-Terminal proteolysis occurred at peptide bonds 14-15, 36-37 and 40-41. This had no effect on either the inhibitory activity or the heat-stability of C1-INH. Proteolysis within the reactive centre occurred at peptide bonds 439-440, 440-441, 441-442 and 442-443. Cleavage at any one of these sites inactivated C1-INH and conferred enhanced heat-stability upon a previously heat-labile molecule. Released neutrophil proteinases also cleaved and inactivated C1-INH, suggesting that they may physiologically regulate C1-INH during inflammatory episodes.     

Antibody-independent activation of C1. I. Differences in the mechanism of C1 activation by nonimmune activators and by immune complexes: C1r-independent activation of C1s by cardiolipin vesicles

C1 activation is controlled by the regulatory protein C1-inhibitor (C1-INH). In contrast to immune-complex-induced activation, which is insensitive to C1-INH, antibody-independent activation of C1 is modulated by C1-INH. The mechanisms regulating nonimmune activation were studied with two phospholipids varying in their capacity to activate C1 in the presence of C1-INH: cardiolipin (CL) and phosphatidylglycerol (PG). Whereas C1-INH consistently suppressed activation by PG vesicles, a dose-dependent increase in C1 activation was measured with CL vesicles above 40 mole %. A similar dose-response binding of C1s requiring C1q, but not C1r, was detected only on CL vesicles, but neither on PG vesicles nor on immune complexes. This binding was Ca2+-dependent, suggesting that dimeric C1s is involved and was inhibited by spermine. The C1q-bound C1s was specifically cleaved at 37 degrees C into its active 58 kDa and 28 kDa chains, in the absence of C1r. On the addition of anti-CL antibodies, the C1q-mediated cleavage of C1s by CL vesicles was specifically inhibited. The cleavage of C1r on CL vesicles was also determined. When macromolecular C1 was offered in the presence of C1-INH, C1r cleavage was detected; however, the presence of C1s was a critical factor for C1r activation, because it was required on CL vesicles, but not on immune complexes. These results show that nonimmune activation of C1 presents specific features which distinguish it from immune complex-induced activation. These characteristics varied with the capacity of antibody-independent activators to activate C1 in the presence of C1-INH.     

Potentiation of C1-esterase inhibitor by heparin and interactions with C1s protease as assessed by surface plasmon resonance

Background

Human C1-esterase inhibitor (C1-INH) is a multifunctional plasma protein with a wide range of inhibitory and non-inhibitory properties, mainly recognized as a key down-regulator of the complement and contact cascades. The potentiation of C1-INH by heparin and other glycosaminoglycans (GAGs) regulates a broad spectrum of C1-INH activities in vivo both in normal and disease states.

Scope of research

We have studied the potentiation of human C1-INH by heparin using Surface Plasmon Resonance (SPR), circular dichroism (CD) and a functional assay. To advance a SPR for multiple-unit interaction studies of C1-INH we have developed a novel (consecutive double capture) approach exploring different immobilization and layout.

Major conclusions

Our SPR experiments conducted in three different design versions showed marked acceleration in C1-INH interactions with complement protease C1s as a result of potentiation of C1-INH by heparin (from 5- to 11-fold increase of the association rate). Far-UV CD studies suggested that heparin binding did not alter C1-INH secondary structure. Functional assay using chromogenic substrate confirmed that heparin does not affect the amidolytic activity of C1s, but does accelerate its consumption due to C1-INH potentiation.

General significance

This is the first report that directly demonstrates a significant acceleration of the C1-INH interactions with C1s due to heparin by using a consecutive double capture SPR approach. The results of this study may be useful for further C-INH therapeutic development, ultimately for the enhancement of current C1-INH replacement therapies.     

Human C1 inhibitor: improved isolation and preliminary structural characterization

An improved procedure for the isolation of the C1 inhibitor (C1-INH) component of human complement is reported. Following preliminary steps to remove plasminogen, fibrinogen, and aggregated material, three conventional chromatographic steps are used to isolate C1-INH in high (70%) overall yield. An extinction coefficient (E 1%, 1 cm 280nm) of 3.60 has been determined. The isolated protein exhibits a single band on sodium dodecyl sulfate-polyacrylamide gel electrophoresis, with a mobility corresponding to an apparent molecular weight (Mr) of 105 000. After removal of carbohydrate, the protein shows an increased mobility, corresponding to an apparent Mr of 78 000. A total carbohydrate content of 33% has been calculated, and from this and the size of the deglycosylated polypeptide, a true molecular weight of 116 000 was estimated. Further analysis of the carbohydrate has indicated a galactose:mannose ratio of 2:1 and approximately equimolar amounts of N-acetylglucosamine and N-acetylgalactosamine. This composition is unusual for a plasma protein and suggests that much of the carbohydrate is contained in linkages other than the typical N-glycosidic structures. Values found for the amino acid composition are compared with those reported previously. The amino-terminal sequence (40 residues) of C1-INH is also reported. Asparagine lies at the amino terminus. Neither high-performance liquid chromatography of the released phenylthiohydantoin derivative nor back-hydrolysis of the thiazolinone permitted identification of the residue contained at position 3. The sequence around this position is compatible, however, with an N-glycosidic linkage to residue 3.(ABSTRACT TRUNCATED AT 250 WORDS)     

StcE,a metalloprotease secreted by Escherichia coli O157:H7, specifically cleaves C1 esterase inhibitor

Escherichia coli O157:H7 causes diarrhoea, haemorrhagic colitis, and the haemolytic uraemic syndrome. We have identified a protein of previously unknown function encoded on the pO157 virulence plasmid of E. coli O157:H7, which is the first described protease that specifically cleaves C1 esterase inhibitor (C1-INH), a member of the serine protease inhibitor family. The protein, named StcE for secreted protease of C1 esterase inhibitor from EHEC (formerly Tagn), cleaves C1-INH to produce (unique) approximately 60-65 kDa fragments. StcE does not digest other serine protease inhibitors, extracellular matrix proteins or universal protease targets. We also observed that StcE causes the aggregation of cultured human T cells but not macrophage-like cells or B cells. Substitution of aspartic acid for glutamic acid at StcE position 435 within the consensus metalloprotease active site ablates its abilities to digest C1-INH and to aggregate T cells. StcE is secreted by the etp type II secretion pathway encoded on pO157, and extracellular StcE levels are positively regulated by the LEE-encoded regulator, Ler. StcE antigen and activity were detected in the faeces of a child with an E. coli O157:H7 infection, demonstrating the expression of StcE during human disease. Cleavage of C1-INH by StcE could plausibly cause localized pro-inflammatory and coagulation responses resulting in tissue damage, intestinal oedema and thrombotic abnormalities.     

Binding of activated Factor XII to endothelial cells affects its inactivation by the C1-esterase inhibitor.

It is well known that activated Factor XII (FXIIa) and kallikrein are rapidly inactivated in plasma as a result of reaction with endogenous inhibitors. The purpose of this may be to prevent uncontrolled deleterious spreading and activation of target zymogens. Both FXII and the complex plasma prekallikrein/high molecular mass kininogen become activated when they bind, in a Zn2+-dependent manner, to receptors on human umbilical vein endothelial cells (HUVEC). The C1-esterase inhibitor (C1-INH) is by far the most efficient inhibitor of FXIIa. In the present study it has been investigated whether binding of FXIIa to HUVEC might offer protection against inactivation by C1-INH. It appeared that the relative amidolytic activity of purified FXIIa bound to the surface of HUVEC decreased according to the concentration of C1-INH in medium; however, the decrease was smaller than that measured for inactivation of FXIIa in solution. The secondary rate constant for the inactivation was 3-10-fold lower for cell-bound than for soluble FXIIa. The inactivation was found to be caused by C1-INH binding to cell-bound FXIIa. Accordingly, the amidolytic activity of saturated amounts of cell-bound FXIIa was reduced in the presence of C1-INH and was theoretically nonexistent at physiological C1-INH concentrations. Amidolytic activity was, however, present on HUVEC incubated with plasma indicating that the endogenous C1-INH did not completely abolish the activity of FXIIa generated during the incubation period. This supports the hypothesis that binding to endothelial cells protects the activated FXII against inactivation by its major endogenous inhibitor. Hence, the function of FXII may be localized at cellular surfaces.     

Increased plasma concentrations of C9, C1-inhibitor and alpha 1-protease inhibitor associated with cigarette smoking

The association between various parameters of acute and chronic smoking status and plasma levels of three proteins, C9, C1-inhibitor (C1-INH) and alpha 1-protease inhibitor (alpha 1-PI) were determined for 49 male cigarette smokers and 49 age-matched nonsmokers (mean age = 32.2 years). The mean number of cigarettes smoked was 28.7 per day while the cumulative consumption was only 18.1 pack-years. Plasma levels of all three proteins were significantly higher in the smokers than nonsmokers. Plasma C9 and alpha 1-PI concentrations correlated with cumulative cigarette consumption and plasma nicotine concentrations. While C1-INH concentration did not correlate with either cumulative cigarette consumption or plasma nicotine concentration, it correlated significantly with serum thiocyanate concentration. No consistent correlation was found between plasma concentration of these proteins and parameters of pulmonary function.     

Antibody-independent activation of C1. II. Evidence for two classes of nonimmune activators of the classical pathway of complement

Nonimmune activation of the first component of complement (C1) by cardiolipin (CL) vesicles present specific features which were not demonstrated on immune complexes. CL vesicles which activate C1 in the presence of C1-inhibitor (C1-INH) were found to bind C1s in the absence of C1r, and to induce a specific C1r-independent cleavage of C1q-bound C1s. Therefore, several known natural nonimmune activators were analyzed by comparing their ability to activate C1 in the presence of C1-INH and to mediate a C1r-independent cleavage of C1s. Freshly isolated human heart mitochondria (HHM) activated C1 only in the absence of C1-INH. However, mitoplasts derived from HHM (HHMP) activated C1 regardless of the presence of C1-INH, and induced a specific cleavage of C1q-bound C1s. The same pattern was observed in the case of smooth E. coli and a semi-rough E. coli strain. DNA, known to activate C1 only in the absence of C1-INH, does not induce C1s cleavage in the absence of C1r. Thus, nonimmune activators can be classified into two distinct categories. "Strong" activators, such as CL vesicles, HHMP, or the semi-rough E. coli strain J5 can activate C1 in the presence of C1-INH. By using C1qs2 as a probe, they exhibit a specific, C1r-independent cleavage of C1s. C1s-binding to C1q is a critical factor for the activation process in this group. In the case of "weak" activators, such as E. coli smooth strains, DNA, or HHM, no C1s-binding to activator-bound C1q was detected, and C1r-independent C1s cleavage and C1 activation in the presence of C1-INH were not observed. As in the case of immune complexes, C1r activation appears to play a key role in the C1 activation by "weak" activators.     

Antithrombin III,but not C1 esterase inhibitor reduces inflammatory response in lipopolysaccharide-stimulated human monocytes in an ex-vivo whole blood setting

In order to examine the immunomodulatory effects of antithrombin III (AT-III) and C1 esterase inhibitor (C1-INH) in human monocytes, we investigated the intracellular expression of interleukin (IL)-6, IL-8, and tumor necrosis factor (TNF)-α in an ex-vivo laboratory study in a whole blood setting.Heparinized whole blood samples from 23 healthy male and female volunteers (mean age: 27 ± 7 years) were pre-incubated with clinically relevant concentrations of AT-III (n = 11) and C1-INH (n = 12), then stimulated with 0.2 ng/mL lipopolysaccharide (LPS) for 3 h. After phenotyping CD14⁺ monocytes, intracellular expression of IL-6, IL-8, and TNF-α was assessed using flow cytometry. In addition, 12 whole blood samples (AT-III and C1-INH, n = 6 each) were examined using hirudin for anticoagulation; all samples were processed in the same way. To exclude cytotoxicity effects, 7-amino-actinomycin D and Nonidet P40 staining were used to investigate probes.This study is the first to demonstrate the influence of C1-INH and AT-III on the monocytic inflammatory response in a whole blood setting, which mimics the optimal physiological setting. Cells treated with AT-III exhibited significant downregulation of the proportion of gated CD14⁺ monocytes for IL-6 and IL-8, in a dose-dependent manner; downregulation for TNF-α did not reach statistical significance. There were no significant effects on mean fluorescence intensity (MFI). In contrast, C1-INH did not significantly reduce the proportion of gated CD14⁺ monocytes or the MFI regarding IL-6, TNF-α, and IL-8. When using hirudin for anticoagulation, no difference in the anti-inflammatory properties of AT-III and C1-INH in monocytes occurs.Taken together, in contrast to TNF-α, IL-6 and IL-8 were significantly downregulated in monocytes in an ex-vivo setting of human whole blood when treated with AT-III. This finding implicates monocytes as an important point of action regarding the anti-inflammatory properties of AT-III in sepsis. C1-INH was unable to attenuate the monocytic response, which supports the hypothesis that other cellular components in whole blood (e.g., neutrophils) might be responsible for the known effects of C1-INH in inflammation.     

Study of the effect of high molecular weight kininogen upon the fluid-phase inactivation of kallikrein by C1 inhibitor

Plasma kallikrein and factor XIa circulate bound to high molecular weight kininogen, and such binding has been reported to protect these enzymes from inactivation by their respective inhibitors. However, this observation is controversial, and the effect of high molecular weight kininogen upon the interaction between kallikrein and C1 inhibitor (C1-INH) has been questioned. We have re-evaluated this reaction and studied the rate of inhibition of kallikrein by C1-INH in the presence and absence of high molecular weight kininogen. The second-order rate constant of inhibition of kallikrein by C1-INH was unaffected by saturating concentrations of high molecular weight kininogen. Our results suggest that although high molecular weight kininogen clearly augments the rate of formation of kallikrein and other enzymes of the contact activation pathway, it has no effect on the rate of enzyme inhibition by C1-INH.     

Activation of human C1: analysis with Western blotting reveals slow self-activation

The first component of human complement was separated from C1-INH by sucrose linear gradient ultracentrifugation. Activation of C1 was studied in the absence and presence of immune complexes; activation was monitored by SDS-PAGE and Western blot. When the partially purified native C1 preparation was incubated at 37 degrees C without immune complexes, activated C1s appeared after 30 min in the case of eightfold dilution with respect to the original serum, and after 45 min with 32-fold dilution. Kinetics of appearance of activated C1r was the same as that of activated C1s. From the following results, we concluded that spontaneous activation may be partially due to proteolytic enzymes contaminating the preparation: 1) a nonspecific protease inhibitor, PMSF, completely inhibited spontaneous activation but did not inhibit the activation of C1 by immune complexes; 2) alpha 2-macroglobulin partially inhibited spontaneous activation, and 3) although spontaneous activation in the absence of PMSF was relatively slow, activated C1 accelerated spontaneous activation that was completely blocked by C1-INH. In contrast to spontaneous activation, the partially purified native C1 was rapidly activated by immune complexes: within 5 min almost all C1 was activated by rabbit IgG anti-human IgM-human IgM complexes. These results support conclusions derived from activation studies when using native C1 and hemolytic assays, and do not support those derived from the activation studies with reconstituted C1 and SDS-PAGE analysis. We suggest that the contradictions can be resolved if one assumes that C1 activation can be both an intra- and intermolecular process; which process dominates is determined by the state of C1 and by experimental conditions.     

Activation of human C1r: Western blot analysis reveals slow and dose-dependent activation

Spontaneous activation of C1r in the presence of EDTA was examined by a Western blot. Partially purified native C1r was prepared by ultracentrifugation of fresh serum in 10 to 30% sucrose gradient; final concentration of C1r was one-sixth of the original serum. C1(-)-INH was not detectable by a single radial immunodiffusion (less than 0.5% of serum). The results demonstrated that 1) the rate of spontaneous activation of C1r was slow (less than 10% in 30 min); 2) it was concentration-dependent; 3) it was enhanced by activated C1r; and 4) it was almost completely suppressed by serine protease inhibitors up to 1 h. These results were inconsistent with an intramolecular autoactivation model of C1r in the fluid phase and suggested intermolecular activation by contaminating protease or activated C1r.     

Plasma-Derived Human C1-Esterase Inhibitor Does Not Prevent Mechanical Ventilation-Induced Pulmonary Complement Activation in a Rat Model of Streptococcus pneumoniae Pneumonia

Mechanical ventilation has the potential to cause lung injury, and the role of complement activation herein is uncertain. We hypothesized that inhibition of the complement cascade by administration of plasma-derived human C1-esterase inhibitor (C1-INH) prevents ventilation-induced pulmonary complement activation, and as such attenuates lung inflammation and lung injury in a rat model of Streptococcus pneumoniae pneumonia. Forty hours after intratracheal challenge with S. pneumoniae causing pneumonia rats were subjected to ventilation with lower tidal volumes and positive end-expiratory pressure (PEEP) or high tidal volumes without PEEP, after an intravenous bolus of C1-INH (200 U/kg) or placebo (saline). After 4 h of ventilation blood, broncho-alveolar lavage fluid and lung tissue were collected. Non-ventilated rats with S. pneumoniae pneumonia served as controls. While ventilation with lower tidal volumes and PEEP slightly amplified pneumonia-induced complement activation in the lungs, ventilation with higher tidal volumes without PEEP augmented local complement activation more strongly. Systemic pre-treatment with C1-INH, however, failed to alter ventilation-induced complement activation with both ventilation strategies. In accordance, lung inflammation and lung injury were not affected by pre-treatment with C1-INH, neither in rats ventilated with lower tidal volumes and PEEP, nor rats ventilated with high tidal volumes without PEEP. Ventilation augments pulmonary complement activation in a rat model of S. pneumoniae pneumonia. Systemic administration of C1-INH, however, does not attenuate ventilation-induced complement activation, lung inflammation, and lung injury.     

Characterization of the StcE protease activity of Escherichia coli O157:H7

The StcE zinc metalloprotease is secreted by enterohemorrhagic Escherichia coli (EHEC) O157:H7 and contributes to intimate adherence of this bacterium to host cells, a process essential for mammalian colonization. StcE has also been shown to localize the inflammatory regulator C1 esterase inhibitor (C1-INH) to cell membranes. We tried to more fully characterize StcE activity to better understand its role in EHEC pathogenesis. StcE was active at pH 6.1 to 9.0, in the presence of NaCl concentrations ranging from 0 to 600 mM, and at 4 degrees C to 55 degrees C. Interestingly, antisera against StcE or C1-INH did not eliminate StcE cleavage of C1-INH. Treatment of StcE with the proteases trypsin, chymotrypsin, human neutrophil elastase, and Pseudomonas aeruginosa elastase did not eliminate StcE activity against C1-INH. After StcE was kept at 23 degrees C for 65 days, it exhibited full proteolytic activity, and it retained 30% of its original activity after incubation for 8 days at 37 degrees C. Together, these results show the StcE protease is a stable enzyme that is probably active in the environment of the colon. Additionally, k(cat)/K(m) data showed that StcE proteolytic activity was 2.5-fold more efficient with the secreted mucin MUC7 than with the complement regulator C1-INH. This evidence supports a model which includes two roles for StcE during infection, in which StcE acts first as a mucinase and then as an anti-inflammatory agent by localizing C1-INH to cell membranes.     

New possibilities of treating acute angioedema caused by C1-inhibitor deficiency

The authors discuss diagnostic difficulties in 12 cases of hereditary angioneurotic edema due to C1-esterase inhibitor (C1-INH deficiency). Emphasis is on the treatment of the acute attacks with intravenous infusions of C1-inhibitor concentrate (Boehring, West Germany). This proved to be a very efficient and safe therapy, leading to a prompt disappearance of all clinical symptoms. Throughout 12 months following the infusions, indices of the liver function remained within the normal range, and anti-Hbs and anti-HIV tests were negative.     

Secondary structure changes stabilize the reactive-centre cleaved form of SERPINs. A study by 1H nuclear magnetic resonance and Fourier transform infrared spectroscopy.

Proteinase inhibitor members of the SERPIN superfamily are characterized by the presence of a proteolytically sensitive reactive-site loop. Cleavage within this region results in a conformational transition from an unstable "stressed" native protein to a more stable "relaxed" cleaved molecule. In order to identify the principal molecular aspects of this transition, 1H nuclear magnetic resonance (n.m.r.) and FT-IR spectroscopy were applied to the study of four SERPINs. 1H n.m.r. spectra of approximately 20 high-field ring-current-shifted methyl signals exhibited slightly different chemical shifts in the native and cleaved forms of alpha 1-antitrypsin (alpha 1-AT), alpha 1-antichymotrypsin (alpha 1-ACT) and C1 inhibitor (C1-INH), but not ovalbumin, between 20 degrees C and 90 degrees C. Ring current calculations based on crystal co-ordinates for cleaved alpha 1-AT and alpha 1-ACT and native ovalbumin showed that these signals originate from highly localized interactions between different buried residues corresponding to alpha-helix and beta-sheet segments of the SERPIN fold. The small shift changes correspond to small relative conformational side-chain rearrangements of about 0.01 nm to 0.05 nm in the protein hydrophobic core, i.e. the tertiary structure interactions in the two forms of the SERPIN fold are well-preserved, and changes in this appear unimportant for the stabilization found after reactive centre cleavage. Fourier transform infrared (FT-IR) spectroscopic studies of the amide I band showed that the native and cleaved forms of alpha 1-AT, alpha 1-ACT and C1-INH contain 28% to 36% alpha-helix and 38% to 44% beta-sheet. Second derivative FT-IR spectra using H2O and 2H2O buffers revealed very large differences in the amide I band between the native and cleaved forms of alpha 1-AT, alpha 1-ACT and C1-INH, but not for ovalbumin. The alpha-helix band was most sensitive to 1H-2H exchange, while the beta-sheet bands were not, and greater amounts of antiparallel beta-sheet were detected in the cleaved form. 1H n.m.r. showed that polypeptide amide 1H-2H exchange was greater in the native forms of alpha 1-AT, alpha 1-ACT and C1-INH than in their cleaved forms, whereas for ovalbumin it was unchanged. The FT-IR and 1H-2H exchange data show that alterations in the secondary structure are central to the stabilization of the cleaved SERPIN structure.(ABSTRACT TRUNCATED AT 400 WORDS)     

Fluid-phase interaction of C1 inhibitor (C1 Inh) and the subcomponents C1r and C1s of the first component of complement, C1.

Interactions between proenzymic or activated complement subcomponents of C1 and C1 Inh (C1 inhibitor) were analysed by sucrose-density-gradient ultracentrifugation and sodium dodecyl sulphate/polyacrylamide-gel electrophoresis. The interaction of C1 Inh with dimeric C1r in the presence of EDTA resulted into two bimolecular complexes accounting for a disruption of C1r. The interaction of C1 Inh with the Ca2+-dependent C1r2-C1s2 complex (8.8 S) led to an 8.5 S inhibited C1r-C1s-C1 Inh complex (1:1:2), indicating a disruption of C1r2 and of C1s2 on C1 Inh binding. The 8.5 S inhibited complex was stable in the presence of EDTA; it was also formed from a mixture of C1r, C1s and C1 Inh in the presence of EDTA or from bimolecular complexes of C1r-C1 Inh and C1s-C1 Inh. C1r II, a modified C1r molecule, deprived of a Ca2+-binding site after autoproteolysis, did not lead to an inhibited tetrameric complex on incubation with C1s and C1 Inh. These findings suggest that, when C1 Inh binds to C1r2-C1s2 complex, the intermonomer links inside C1r2 or C1s2 are weakened, whereas the non-covalent Ca2+-independent interaction between C1r2 and C1s2 is strengthened. The nature of the proteinase-C1 Inh link was investigated. Hydroxylamine (1M) was able to dissociate the complexes partially (pH 7.5) or totally (pH 9.0) when the incubation was performed in denaturing conditions. An ester link between a serine residue at the active site of C1r or C1s and C1 Inh is postulated.     

Autoimmune Angioneurotic Edema in a Patient with Helicobacter pylori Infection

Association of acquired autoimmune angioneurotic edema with other diseases is increasing. However, the precise mechanism by which antibodies to C1-esterase inhibitor (C1-INH) are produced, is not elucidated. We describe a patient with IgA antibodies against C1-INH without other autoimmune markers. Our patient had gastritis and Helicobacter pylori infection, proven by biopsy. This case suggests that H. pylori infection can act as triggering factor for acquired autoimmune angioneurotic edema.