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Results for “Complement C1 Inhibitor Protein”

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PubMed1996

A solid-phase antibody capture assay for the measurement of C1-inhibitor consumption in vivo.

C1-inhibitor (C1-Inh) is a serine esterase proteinase inhibitor (serpin) which plays an important role in regulating serine proteinases of the early inflammatory response. In this study, we describe a novel and versatile polyclonal antibody capture assay to examine C1-Inh consumption in vivo. This assay has advantages over previously described methods of measuring C1-Inh consumption as it allows the assessment of the relative amounts of native, complexed and cleaved inhibitor circulating in plasma. By using polyclonal antibodies specific for other complement proteins, the C1-Inh capture assay was adapted to measure in vivo activation of C3, C4 and factor B. C1-Inh consumption and complement activation were examined in the plasma of 21 normal individuals, 24 individuals with systemic lupus erythematosus (SLE), nine individuals with adult respiratory distress syndrome (ARDS) and in the paired plasma and synovial fluid from 18 patients with rheumatoid arthritis (RA). The C1-Inh capture assay revealed native, cleaved and complexed C1-Inh migrating at 115 kDa, 96 kDa and 209-225 kDa respectively, in normal plasma. C1-Inh consumption was increased in the plasma of all the inflammatory disorders examined, in comparison to normal plasma. It is proposed that this serpin capture assay could be adapted to the study of serpin involvement in a wide variety of inflammatory disorders.

Arthritis, Rheumatoid↗
PubMed1985

Complement-subcomponent-C1-inhibitor synthesis by human monocytes.

By using a radioimmunoassay, C1-inhibitor was found to accumulate in the supernatants of human monocyte cultures. The production of this protein was inhibited reversibly by cycloheximide. When C1-inhibitor synthesis was compared with C2 synthesis, it was found that C1-inhibitor synthesis continued, whereas synthesis of C2 appeared to cease after about 7 days in culture. Immunoprecipitation of supernatants of monocyte cultures that had been pulsed with [35S]methionine showed a specific band with an Mr of 105 000. Immunoprecipitates of the lysates revealed a band of Mr 83 000; this was thought to represent a partially or non-glycosylated precursor of C1-inhibitor. C1-inhibitor produced by the monocytes was shown, by using a haemolytic assay, to be functionally active. However, the functional activity of C1-inhibitor was reduced by only 44% in the presence of cycloheximide, whereas the concentration of this protein in cycloheximide-treated culture supernatants fell by more than 93%. This finding suggests that monocytes secrete a second molecule, which inhibits C1 activity but is distinct from classical C1-inhibitor.

Cells, Cultured↗
PubMed1988

Effects of fibroblasts and endothelial cells on inactivation of target proteases by protease nexin-1, heparin cofactor II, and C1-inhibitor.

Previous studies have shown that glycosaminoglycans in the extracellular matrix accelerate the inactivation of target proteases by certain protease inhibitors. It has been suggested that the ability of the matrix of certain cells to accelerate some inhibitors but not others might reflect the site of action of the inhibitors. Previous studies showed that fibroblasts accelerate the inactivation of thrombin by protease nexin-1, an inhibitor that appears to function at the surface of cells in extravascular tissues. The present experiments showed that endothelial cells also accelerate this reaction. The accelerative activity was accounted for by the extracellular matrix and was mostly due to heparan sulfate. Fibroblasts but not endothelial cells accelerated the inactivation of thrombin by heparin cofactor II, an abundant inhibitor in plasma. This is consistent with previous suggestions that heparin cofactor II inactivates thrombin when plasma is exposed to fibroblasts and smooth muscle cells. Neither fibroblasts nor endothelial cells accelerated the inactivation of C1s by plasma C1-inhibitor.

Amyloid beta-Protein Precursor↗
PubMed2001

Unmasking of acquired autoimmune C1-inhibitor deficiency by an angiotensin-converting enzyme inhibitor.

BACKGROUND: A majority of angioedema arise from unknown etiologies. Angioedema may also arise from medications or deficiency of C1-esterase inhibitor (C1-INH); either of these may lead to recurrent, sometimes life-threatening attacks of subcutaneous or submucosal edema if the angioedema involves the tongue, throat, or larynx. We describe a patient with unknown acquired C1-INH deficiency, who experienced only mild attacks of angioedema before treatment with an angiotensin-converting enzyme (ACE) inhibitor. This therapy led to life-threatening respiratory distress. OBJECTIVE: To investigate this patient's life-threatening angioedema. METHODS: Serum protein electrophoresis and immunofixation were performed. The titer of anti-C1-inhibitor autoantibody was determined by ELISA, and the specificity of the autoantibody demonstrated by using purified C1-INH to block binding in the ELISA. Finally, fractions from the immunoelectrophoresis gel were tested for C1-INH autoantibody by ELISA. RESULTS: Complement activation was documented by reduced C1-INH, C1q, and C4, and the patient was found to have an autoantibody of IgG2 isotype specific for C1-INH. After discontinuation of the ACE inhibitor, he continued to have decreased C1-INH and positive C1-INH autoantibodies. CONCLUSIONS: This case describes a patient who had a history of mild facial and extremity swelling with abdominal symptoms before ACE inhibitor treatment; this medication resulted in life-threatening respiratory distress. The use of the ACE inhibitor may have unmasked this patient's acquired autoimmune C1-INH deficiency.

Aged↗
PubMedDate not supplied

Complement determinations in the synovial fluid and serum of a patient with Erythema nodosum leprosum.

Simultaneous serum and synovial fluid CH50, C1, C4, C2, C1 esterase inhibitor and C3 protein were determined in a patient with acute erythema nodosum leprosum. The pattern of synovial fluid complement activity coupled with the demonstration of multiple lepra bacilli free and within histiocytes is more consistent with an infectious than an immune complex induced synovitis.

Arthritis, Infectious↗
PubMed1986

Inactivation of human plasma serine proteinase inhibitors (serpins) by limited proteolysis of the reactive site loop with snake venom and bacterial metalloproteinases.

Human plasma serine proteinase inhibitors (serpins) gradually lost activity when incubated with catalytic amounts of snake venom or bacterial metalloproteinases. Electrophoretic analyses indicated that antithrombin III, C1-inhibitor, and alpha 2-antiplasmin had been converted by limited proteolysis into modified species which retained inhibitory activity. Further proteolytic attack resulted in the formation of inactivated inhibitors; alpha 1-proteinase inhibitor (alpha 1-antitrypsin) and alpha 1-antichymotrypsin were also enzymatically inactivated, but active intermediates were not detected. Sequence analyses indicated that the initial, noninactivating cleavage occurred in the amino-terminal region of the inhibitors. Inactivation resulted in all cases from the limited proteolysis of a single bond near, but not at, the reactive site bond in the carboxy-terminal region of the inhibitors. The results indicate that the serpins have two regions which are susceptible to limited proteolysis--one near the amino-terminal end and another in the exposed reactive site loop of the inhibitor.

Amino Acid Sequence↗
PubMed1989

Structure and function of C1 inhibitor.

C1 inhibitor (C1 INH) is a plasma protease inhibitor that is essential for regulation of activation of the complement and kinin generating systems. It is the only inhibitor of C1r and C1s in plasma, and is responsible for about half of the kallikrein and the majority of plasma factor XII inactivating activity. Based on sequence homology, C1 INH is a member of the serpin family of protease inhibitors and related proteins, and its mechanism of action is identical to those of the other protease inhibitor members of the family. Susceptible proteases cleave C1 INH at an Arg-Thr peptide bond (the P1 and P1'residues) that is 34 amino acid residues from the carboxy terminus of the protein. A stable bimolecular complex then is formed between the larger amino terminal portion of the C1 INH molecule and the protease. C1 INH inactivation of C1r and C1s within activated macromolecular C1 results in dissociation of C1 with release of complexes consisting of two molecules of C1 INH and one molecule each of C1r and C1s. C1q is thus allowed to interact with zymogen C1r and C1s or with C1q receptors. Autoactivation of intact macromolecular C1 is also prevented by C1 INH. The structure of C1 INH is quite similar to other serpin plasma protease inhibitors, and C1 INH appears to retain all the major structural features required for maintaining tertiary structure and inhibitory function.(ABSTRACT TRUNCATED AT 250 WORDS)

Amino Acid Sequence↗
PubMed1998

Hereditary angioneurotic edema and thromboembolic diseases: I: How symptoms of acute attacks change with aging.

Localized edema of the larynx and pharynx leading to death from asphyxia has long been recognized as a characteristic symptom of hereditary angioneurotic edema (HANE). Long-term follow-up of younger HANE patients has revealed that transient localized acute attacks of edema affect tissues where the microcirculation maintains the blood supply. However, with aging, HANE attacks precipitate disseminated intravascular coagulation (DIC) or multiple organ failure (MOF). Substitution with a C1-inhibitor (C1-INH) has resulted in a fulminant lethal end with a rapid and profound decrease in antithrombin-III (AT-III) activity. A possible mechanism is as follows: Exogenous stimuli activate plasma proteinase systems with the generation of plasma kallikrein that activates the tissue factor pathway (TF) and liberates bradykinin (BK). In younger patients, BK enhances vascular permeability. In the elderly, activated TF is controlled by tissue factor pathway inhibitor (TFPI) and generates thrombin, which is the target enzyme of AT-III and precipitates DIC or MOF. In elderly patients, the characteristic symptom of HANE is hypercoagulation by age-related changes in the biosynthesis of AT-III or TFPI.

Acute Disease↗
PubMed1996

Complement activation on human neuroblastoma cell lines in vitro: route of activation and expression of functional complement regulatory proteins.

Two human neuroblastoma cell lines activated the classical pathway of complement in serum. Activation caused the opsonisation of these cells with complement fragments but with moderate cell killing. Neuroblastoma expressed regulators MCP and CD59 but did not express DAF or CR1. Neutralisation of CD59 rendered the cells susceptible to killing. Neuroblastoma also expressed C1-inhibitor, factor H, clusterin and S-protein. Expression of several regulators was enhanced by incubation with cytokines. Complement inhibition using soluble CRI markedly reduced opsonisation and killing of neuroblastoma. Our results suggest that complement might play a role in neuronal loss and that treatment with complement inhibitors might be of therapeutic value.

Antigens, CD↗
PubMed1989

A new simplified procedure for C1 inhibitor purification. A novel use for jacalin-agarose.

C1 inhibitor (C1-INH), the major regulatory protein of the classical pathway of complement activation, is also involved in the regulation of several other plasma proteolytic systems including the coagulation, fibrinolytic and contact systems. All the previously published methods for the purification of C1-INH are time-consuming and some do not yield highly pure protein. Recently, it was reported that Jack fruit (Artocarpus integrifolia) lectin, also called jacalin, binds C1-INH. Since jacalin binds only a small number of human serum proteins it appeared that jacalin-agarose affinity chromatography would constitute a very selective early step for the purification of C1-INH. Consequently we have designed a new, simplified three-step procedure for the purification of C1-INH which includes PEG fractionation, jacalin-agarose chromatography and hydrophobic interaction chromatography on phenyl-Sepharose which takes advantage of the marked hydrophilicity of the inhibitor. This procedure has three major advantages over those which have been the most frequently used. Firstly, it includes only two fast chromatographic steps. Secondly, because the C1-INH pool is cleanly and predictably separated from the unwanted proteins by differential elution conditions in both chromatographic steps, no antigenic or functional assays are required to define the desired peaks. Thirdly, only the final product is dialyzed while all other methods required several buffer changes. For these reasons this procedure is much faster and simpler than the previously published methods. About 10-12 mg of highly purified and fully active C1-INH can be obtained within 1 day from 120 ml of plasma giving an average yield of 40-45%. This method may thus be highly adaptable to bulk purification for clinical use or for preparation of genetically or pathologically altered C1-INH from clinical specimens.

Blotting, Western↗
PubMed1993

Perspectives for the future.

The pathophysiology of sepsis and septic shock is extremely complex and ultimately involves every physiological pathway. The initiating event is the entrance of endotoxin or similar substances into the blood which initiates the release of multiple mediators. These are designed to react locally and to protect the organism. Their constant release, however, sets in motion up- and down regulations, ultimately resulting in "metabolic anarchy". Tumor necrosis factor alpha and other cytokines trigger several systems, especially coagulation to yield DIC, and the complement system. Many treatment modalities have been developed, most recently those which substitute inhibitors of various systems. Antithrombin III concentrates and potentially protein C concentrates are designed to arrest DIC. C1-esterase inhibitor concentrates should intercept the activation of the complement system and the contact phase of coagulation and its relationship to kinin generation. Even newer approaches entail antibodies to tumor necrosis factor alpha or endotoxin itself. The complex process of sepsis will undoubtedly require a multifaceted therapeutic approach.

Antibodies, Monoclonal↗
PubMed2001

K562 erythroleukemic cells are equipped with multiple mechanisms of resistance to lysis by complement.

Resistance of tumor cells to lysis by complement is generally attributed to several protective mechanisms. The relative impact of these mechanisms in the same tumor cell, however, has not been assessed yet. We have analyzed the interaction of the human erythroleukemia tumor cell line K562 with human complement. K562 cells express the membrane complement regulatory proteins CD59, CD55 and CD46. As shown here for the first time, K562 also spontaneously release the soluble regulators C1 inhibitor, factor H, and soluble CD59. Complement resistance of K562 cells is augmented upon treatment with PMA, TNF or even with sublytic complement. Unlike TNF and sublytic complement, PMA enhanced the expression of membrane-bound CD55 and CD59 and led to increased secretion of soluble CD59. In addition, we show that complement-resistant K562 cells express a membrane-associated proteolytic activity, higher than the complement-sensitive K562/S cells. Treatment of complement-resistant K562 cells with serine protease inhibitors enhance their sensitivity to complement-mediated lysis. Inhibitors of protein kinase C (PKC) also sensitize K562 cells to complement lysis, implicating PKC-mediated signaling in cell resistance to complement. Neutralization of the CD55 and CD59 but not of CD46 regulatory activity with specific antibodies significantly increases complement-mediated K562 cell lysis. Treatment of K562 cells with a mixture of inhibitory reagents results in a significant additive enhancing effect on complement-mediated lysis of K562. In conclusion, K562 cells resist a complement attack by concomitantly using multiple molecular evasion strategies. Future attempts in antibody-based tumor therapy should include strategies to interfere with those resistance mechanisms.

Antigens, CD↗