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PubMed1979

Evidence for glomerular modulation of complement activation.

Using indirect immunofluorescence, three regulatory proteins of the complement system, C1-inhibitor (C1-INH), C3b inactivator (C3bINA) and beta 1H globulin have been detected in the glomeruli of patients with glomerulonephritis associated with complement activation. C1-INH and beta 1H were found frequently but C3bINA was rarely detected (only 14 biopsies). beta 1H globulin and C3b inactivator which modulate C3b activity were never found in the absence of C3, but C1-INH was sometimes found in the absence of C1s. The patterns for staining for C1s and C1-INH, C3 and beta 1H were almost identical suggesting that the regulatory proteins are binding to the proteins they regulate, as has been demonstrated in vitro. Thus, in tissues undergoing complement-mediated tissue damage, the extent of complement activation is controlled by the normal regulatory mechanisms.

Complement Activation↗
PubMed1996

Biotinylation of proteins via amino groups can induce binding to U937 cells, HL-60 cells, monocytes and granulocytes.

The use of biotinylated ligands for the flow cytometric detection of cell surface receptors has become a popular alternative to radioreceptor assays. Although the biotinylation of a protein is a relatively mild chemical reaction several reports have mentioned the fact that the number and location of biotin moieties coupled to amino groups of a protein can alter its physicochemical properties and impair biological activity. In the present study we show for a variety of biotinylated functionally unaltered ligands that biotinylation by N-hydroxysuccinimide (NHS) esters of biotin can induce a binding to cell surfaces, which is not specific for the respective unlabelled ligand. C1q, C1 inhibitor (C1-INH), alpha 1-antitrypsin (AT), ovalbumin (OV), transferrin and soybean trypsin inhibitor (STI) were labelled with S-NHS-LC-biotin and activated C1s (C1s) with NHS-biotin. Biotinylation of C1q, C1s and C1-INH exerted negligible effects on biological function, antigenicity or electrophoretic mobility but when labelled and unlabelled proteins were assayed for binding to monocytic U937 cells, promyelocytic HL-60 cells, monocytes and granulocytes, a remarkable binding was observed for biotinylated C1q, C1-INH and C1s. In contrast, no binding was observed when we used unlabelled C1q, C1s and C1-INH and employed specific antibodies, alpha-mouse-FITC or alpha-rabbit-FITC for detection. Increasing molar ratios of biotin-to-protein (B : P) for biotinylated AT, OV and STI evoked increased fluorescence intensities of the cells. Most importantly the unlabelled ligands did not compete for cell binding with their biotinylated derivatives, with the exception of transferrin. Preincubation of the cells with an excess of free d-biotin did not reduce binding of biotinylated proteins, thus excluding a potential involvement of biotin receptors. Hydrophobic interaction chromatography revealed a remarkable increase in hydrophobicity of the biotinylated proteins compared to their unlabelled counterparts, suggesting that the biotinylation-induced binding is due to increased hydrophobicity. Our findings indicate that biotinylation by the common amino acid esterification method may be critical for proteins if they are to be used as ligands for receptor binding studies.

Amino Acids↗
PubMed1987

Preoperative prediction of extent and prognosis of gastric carcinoma by four serum proteins and erythrocyte sedimentation rate.

In 195 patients with gastric carcinoma the preoperative ESR and serum concentrations of IgG, C4, C1-INH and CEA varied significantly with the extent of disease. Extent of disease and prognosis were predicted from these variables by discriminant analysis. The discriminant rules were tested on the same patients in an unbiased way. Metastases or no metastases were correctly predicted in 75% of the patients. By an appropriate prior distribution 93% of the patients without metastases were identified. The disease extent was also predicted in subgroups of patients with and without metastases. Survival was correctly predicted preoperatively in 66% of the patients and 83% of the patients with a fair prognosis were identified. Of the patients preoperatively allocated to the non-survival group 94% did actually die during follow-up. When used in addition to other available information, our discriminant rules will contribute to the quality of the preoperative evaluation of patients with gastric carcinoma.

Adult↗
PubMed1995

Changes in the contact system during orthotopic liver transplantation with and without aprotinin.

The main cause of nonsurgical bleeding during orthotopic liver transplantation has been attributed to be hyperfibrinolysis due to high plasma levels of tissue plasminogen activator. The aim of this study was to investigate contact activation and its possible contribution to fibrinolysis during OLT with and without aprotinin. Aprotinin or placebo was given to 20 patients undergoing OLT as part of a randomized double-blind trial. Plasma samples were collected before, during, and after OLT. There were decreased preoperative levels of prekallikrein and factor XIIa (P < 0.05), with a trend for kallikrein and factor XIIa activity to increase during OLT peaking on reperfusion (P < 0.05). Kallikrein inhibition, C1 esterase inhibitor, and alpha-2-macroglobulin levels were normal before surgery, with low normal levels of antithrombin III and alpha-2-antiplasmin; these levels decreased during OLT with no specific change on reperfusion. In the aprotinin-treated group, kallikrein inhibition levels increased (P < 0.05) from preoperative mean (+/- SD) values of 101 +/- 47% to 154 +/- 42% and antiplasmin levels increased (P < 0.05) from 72 +/- 28% to 243 +/- 53% during the anhepatic phase, reflecting the effect of aprotinin. The antifibrinolytic effect of aprotinin was demonstrated by decreased levels of D-dimer on reperfusion (P < 0.05) and at the end of OLT (P < 0.001) in the aprotinin-treated group. We have shown that contact activation during OLT is minimal and that aprotinin does not alter the pattern of contact activation, but provides an antikallikrein effect.

Adult↗
PubMed1985

[Acquired C1 esterase inhibitor deficiency and lymphoproliferative syndromes].

About 20 cases of acquired C1 esterase inhibitor deficiency have been reported in association with malignant lymphomas. We describe 3 such patients. The 3 patients studied were asymptomatic and had low C1q level. Danazol administration resulted in an increase of C1 esterase inhibitor in 2 patients. The complement activation in acquired C1 esterase inhibitor deficiency could be explained by interaction with pathological cells of the spleen, the blood or the bone-marrow. The mechanism of decrease of C1 INH is discussed.

Aged↗
PubMed1979

A rosette assay for the determination of C 1 q receptor-bearing cells.

A rosette assay for the identification of cells with receptors for C 1 q is described. Glutaraldehyde-treated bovine erythrocytes bound C 1 q specifically, and the reagent thus prepared provided a valid indicator for rosette formation mediated by C 1 q receptors. The presence of these receptors on the membrane of a subset of human peripheral lymphocytes (mainly non-G cells) and on B-derived lymphoblastoid cells was confirmed. Rosette formation was dependent on the number of C 1 q molecules bound per indicator cell and was specifically inhibited by soluble native C 1 q and pepsin-resistant C 1 q fragments. These data, together with the reduced binding activity of C 1 r-C 1 s-associated C 1 q, indicated that the C 1 q binding sites for lymphoid membranes are expressed on the collagen-like moiety, C 1 q rosette formation provided a simple new procedure for fractionation of human lymphocyte populations and separation from phagocytes that do not express receptors for C 1 q.

Animals↗
PubMed1999

Increased complement biosynthesis by microglia and complement activation on neurons in Huntington's disease.

In this study complement activation and biosynthesis have been analysed in the brains of Huntington's disease (HD) (n = 9) and normal (n = 3) individuals. In HD striatum, neurons, myelin and astrocytes were strongly stained with antibodies to C1q, C4, C3, iC3b-neoepitope and C9-neoepitope. In contrast, no staining for complement components was found in the normal striatum. Marked astrogliosis and microgliosis were observed in all HD caudate and the internal capsule samples but not in normal brain. RT-PCR analysis and in-situ hybridisation were carried out to determine whether complement was synthesised locally by activated glial cells. By RT-PCR, we found that complement activators of the classical pathway C1q C chain, C1r, C4, C3, as well as the complement regulators, C1 inhibitor, clusterin, MCP, DAF, CD59, were all expressed constitutively and at much higher level in HD brains compared to normal brain. Complement anaphylatoxin receptor mRNAs (C5a receptor and C3a receptor) were strongly expressed in HD caudate. In general, we found that the level of complement mRNA in normal control brains was from 2 to 5 fold lower compared to HD striatum. Using in-situ hybridisation, we confirmed that C3 mRNA and C9 mRNA were expressed by reactive microglia in HD internal capsule. We propose that complement produced locally by reactive microglia is activated on the membranes of neurons, contributing to neuronal necrosis but also to proinflammatory activities. Complement opsonins (iC3b) and anaphylatoxins (C3a, C5a) may be involved in the recruitment and stimulation of glial cells and phagocytes bearing specific complement receptors.

Adult↗
PubMed1991

C1 esterase inhibitor deficiency: three presentations.

We have presented three patients representing three of the four reported forms of C1 esterase inhibitor deficiency. The C1INH deficiencies are in general distinguishable from each other and from other forms of angioedema by their complement patterns. The acquired C1INH deficiency must be part of the differential in patients without a family history of angioedema since it may precede the diagnosis of more serious medical conditions such as lymphoproliferative disorders.

Adolescent↗
PubMed1980

Interaction between Schistosoma mansoni and the complement system: binding of C1q to schistosomula.

In earlier studies we have found that activation of the classical complement pathway (CCP) by the immature schistosomes involves the presence of IgG. By investigating the first step of this activation we have demonstrated in the present work that binding of C1q to schistosomula can occur by two different routes: 1) directly, by specific C1q receptors, and 2) indirectly through the IgG previously attached to Fc receptors present on the parasite surface. Only this second mechanism appears to be involved in CCP activation by schistosomula. Moreover, certain low m.w. schistosome antigens (less than 20,000), which activate CCP, also directly fixed C1q. In this case, IgG are not required for C activation. The presence of receptors for host protein, essentially in 2- to 3-hr-old schistosomula, i.e., the life stage of Schistosoma mansoni that are first in contact with the host, could be the first mechanism by which the schistosomes evade the immune attack.

Animals↗
PubMed1996

The catabolism of intact, reactive centre-cleaved and proteinase-complexed C1 inhibitor in the guinea pig.

Clearance rates in the guinea pig were determined for intact guinea pig and human C1 inhibitor, the complexes of both inhibitors with human Cls, beta factor XIIa and kallikrein, and for each inhibitor cleaved at its reactive centre with trypsin. Intact human and guinea pig C1 inhibitor were cleared from the circulation more slowly (t1/2s of 9-7 h and 12.1 h and fractional catabolic rates (FCRs) of 0.09 and 0.117) than any of their cleaved or complexed forms. The reactive centre-cleaved inhibitors were cleared with half-lives of 6.75 h for humans and 10.1 h for the guinea pig. The complexes with target proteases were catabolized much more rapidly, with half-lives ranging from 3-08 h to 4.3 h. The complexes with kallikrein were cleared more slowly than those with Cls and beta factor XIIa. Complexes prepared with the guinea pig and human inhibitors were cleared at equivalent rates. The free inactivated proteases were cleared at rates similar to the equivalent complexes, except for kallikrein, which was cleared more rapidly than its complex. The fact that the complexes with different target proteases differed in their catabolism and that protease and complex catabolism were similar suggests that protease may play a direct role in clearance.

Amino Acid Sequence↗
PubMed1986

The metabolism of C1 inhibitor and C1q in patients with acquired C1-inhibitor deficiency.

The metabolism of 125I-labeled C1 inhibitor (C1INH) and C1q was studied in five patients with B cell lymphoproliferative disorders, C1INH deficiency, and angioedema. C1INH catabolism was markedly accelerated in these patients. The fractional catabolic rate (FCR) was 0.053 of the plasma pool per hour compared to that of normal subjects (0.025) or patients with hereditary angioneurotic edema (HANE) (0.035). The catabolism of two dysfunctional proteins Wel and Ta was studied. Protein Wel was catabolized at an accelerated rate (0.041) compared to that in patients with HANE (0.029) or in normal subjects (0.020). In contrast, the FCR of protein Ta was 0.012, which is similar to that in normal patients and in patients with HANE. The extravascular to plasma ratio (E/P) of the normal C1INH in patients was 1.55 compared to 0.60 in normal patients. This is consistent with the rapid extravascular sequestration of the C1INH. The synthesis rate of the C1INH was 0.29 mg/kg/hr in patients that is similar to that in control subjects. The metabolism of C1q was studied in two normal control subjects and three patients. The FCR of C1q was 0.051 in patients compared to 0.023 in control subjects. The E/P was increased in patients (2.8) compared to E/P in control subjects (0.6). The acquisition of C1INH deficiency results from increased consumption of C1INH in vivo.

Adult↗
PubMed1991

Inactivation of human plasma C1-inhibitor by human PMN leucocyte matrix metalloproteinases.

Highly purified human polymorphonuclear (PMN) leucocyte matrix metalloproteinases, collagenase and gelatinase, cleaved human plasma C1-inhibitor at the carboxyl site of Ala439 (P6). This led to a concomitant loss of C1-inhibitor activity. An additional cleavage site, at the carboxyl site of Ser441 (P4), was observed during PMN leucocyte gelatinase-induced inactivation, and a minor fragment of the plasma C1-inhibitor was generated.

Amino Acid Sequence↗
PubMed1997

Probing the structure of C1 with an anti-C1s monoclonal antibody: the possible existence of two forms of C1 in solution.

Anti-human C1s monoclonal antibody H1532, a mouse gamma-1-immunoglobulin elicited by a C1r2C1s2 immunogen, appeared to bind to the beta-domain of C1s by electron microscopy. In agreement with this observation, Western blotting demonstrated good binding to unreduced C1s, but no binding to the alpha or gamma-B domains. When added to solutions of the C1r2C1s2 tetramer, HI532 converted the 8.7 S tetramer into an 18 S complex, which was seen by electron microscopy to be a dimer of parallel C1s x C1r x C1r x C1s molecules cross-linked by two bivalent monoclonal antibodies. If increasing amounts of HI532 were added to C1r2C1s2 followed by addition of equivalent C1q, there was a progressive loss of hemolytic activity, which became zero when two equivalents of antibody HI532 were added. When two equivalents of HI532 were added to serum or C1 reconstituted overnight from purified subcomponents, there was an immediate loss of approximately 50% of the hemolytic activity; thereafter, activity decayed slowly and even after 24 hr, 10-30% of the activity remained. The rapid loss of only 50% of the activity would be readily explained by the existence of two conformations of C1, one of which was rapidly disassembled by antibody, and the other was resistant to disassembly. These two conformations may correspond to two previously proposed structures for the C1 complex.

Animals↗
PubMed1981

The role of sialic acid in the functional activity and the hepatic clearance of C1-INH.

The immunochemical properties, catabolic clearance, and organ distribution of highly purified radiolabeled human C1-INH were studied after treatment with glycosidases. The antigenicity and C1s inhibitory activity of C1-INH were unimpaired after removal of sialic acid residues (60%) or sialic acid and galactose residues (60 and 20%, respectively) with immobilized neuraminidase and beta-galactosidase. Treatment of C1-INH with neuraminidase was associated with increased cathodal migration of the glycoprotein. In vivo studies in the rabbit, however, showed that removal of sialic acid residues resulted in rapid blood clearance of C1-INH and enhanced localization of the asialo C1-INH in the liver. Subsequent removal of penultimate galactose residues returned the survival time in the circulation and organ distribution to near normal. Additionally, simultaneous infusion of asialo-C1-INH with asialo alpha 1-acid glycoprotein, a protein known to bind to hepatic asialoglycoprotein receptors, dramatically extended the intravascular survival time of asialo C1-INH. In agreement with the observations on other plasma glycoproteins, these results indicate that desialylation of C1-INH results in rapid clearance by hepatic asialoglycoprotein receptors.

Animals↗
PubMed1996

Phosphatase 2A participates in interferon-gamma's induced upregulation of C1 inhibitor mRNA expression.

C1 inhibitor (C1 INH) is the major inhibitor of the proteolytically active subcomponents of C1, kallikrein, activated forms of factor XII, and factor XIa in plasma. We determined the mechanism(s) how interferon-gamma (IFN-gamma) regulates C1 INH mRNA expression in HepG2 cells. Cycloheximide or anisomycin treatment alone did not increase C1 INH mRNA nor did it potentiate C1 INH mRNA expression after IFN-gamma stimulation. C1 INH mRNA levels on Northern blot from untreated and IFN-gamma-treated cells did not change for more than 20 hours after actinomycin D treatment. Actinomycin D and 5,6-dichloro-1-beta-ribofuranosylbenzimidazole abolished IFN-gamma-induced C1 INH mRNA expression. Relatively more C1 INH mRNA precursor (heterogeneous nuclear RNA [hnRNA]) was detected in total RNA from IFN-gamma-treated HepG2 cells than unstimulated cells. Treatment of HepG2 cells with the phosphatase 1 and 2A inhibitors, okadaic acid (> or = 50 nmol/L) and calyculin (> or = 25 nmol/L), decreased IFN-gamma's ability to upregulated C1 INH mRNA. The phosphatase 2A inhibitor, cantharidin (> or = 10 micromol/L), also blocked the IFN-gamma induction of the C1 INH gene. In HepG2 cells total phosphatase 2A activity was significantly increased by C6 ceramide but not IFN-gamma. However, C6 ceramide itself did not increase C1 INH mRNA expression. These data indicate that phosphatase 2A is required to dephosphorylate a substrate in order for IFN-gamma to induce the transcriptional upregulation of C1 INH mRNA, but phosphatase 2A is not a direct stimulator of C1 INH gene expression.

Complement C1 Inactivator Proteins↗
PubMed1981

Purification and characterization of two functionally distinct forms of C1 inhibitor from a patient with angioedema.

A minority of patients with hereditary angioedema (HAE) have normal concentrations of a dysfunctional C1 inhibitor protein (C1INH) in their plasmas. We purified C1INH from the plasmas of one such patient before and during treatment with the anabolic steroid stanozolol. Both the pretreatment plasma and plasma obtained during stanozolol treatment contained varying amounts of two extremely similar C1INH proteins that were functionally distinct. The pretreatment plasma contained primarily (94%) dysfunctional C1INH that did not inactivate or complex with either purified C1s, activated Hageman factor, or kallikrein and small amounts (6%) of functionally normal C1INH. Stanozolol treatment increased the plasma concentrations of both of these proteins as well as the proportion (23%) of functional C1INH in the plasma. The purified dysfunctional and functional C1INHs had identical or nearly identical molecular sizes, charges, amino acid compositions, and amino sugar contents, and could not be distinguished physicochemically from each other or from normal C1INH. From these studies of purified C1INH proteins we concluded that HAE associated with dysfunctional C1INH is due to a defect at the structural locus for one C1INH gene and that both the dysfunctional C1INH gene and the normal C1INH gene products are present in the plasma of the affected subject. Treatment with stanozolol comparably increased the synthesis of both C1INH proteins. The disproportionate rise in the level of the normal C1INH protein is consistent with the view that it is more rapidly catabolized as a consequence of its interaction with the proteases it inactivates.

Adult↗
PubMed2001

C1 inhibitor: analysis of the role of amino acid residues within the reactive center loop in target protease recognition.

Previous analysis of a naturally occurring C1 inhibitor P2 mutant (Ala(443)-->Val) indicated a role for P2 in specificity determination. To define this role and that of other reactive center loop residues, a number of different amino acids were introduced at P2, as well as at P6 (Ala(439)) and P8'/9' (Gln(452)Gln(453)). Ala(439)-->Val is a naturally occurring mutant observed in a patient with hereditary angioedema. Previous data suggested that Gln(452)Gln(453) might be a contact site for C1s. Reactivity of the inhibitors toward target (C1s, C1r, kallikrein, beta factor XIIa, and plasmin) and nontarget proteases (alpha-thrombin and trypsin) were studied. Substitution of P2 with bulky or charged residues resulted in decreased reactivity with all target proteases. Substitution with residues with hydrophobic or polar side chains resulted in decreased reactivity with some proteases, but in unaltered or increased reactivity with others. Second order rate constants for the reaction with C1s were determined for the mutants with activities most similar to the wild-type protein. The three P2 mutants showed reductions in rate from 3.35 x 10(5) M(-1)s(-1) for the wild type to 1.61, 1.29, and 0.63 x 10(5) for the Ser, Thr, and Val mutants, respectively. In contrast, the Ala(439)-->Val and the Gln(452)Gln(453)-->Ala mutants showed little difference in association rates with C1s, in comparison with the wild-type inhibitor. The data confirm the importance of P2 in specificity determination. However, the P6 position appears to be of little, if any, importance. Furthermore, it appears unlikely that Gln(452)Gln(453) comprise a portion of a protease contact site within the inhibitor.

Amino Acid Substitution↗