Search PubMed⌕ Search

SEARCH · Search PubMed

Results for “Complement C1s”

Search indexed PubMed citations on genomics, clinical trials, systematic reviews and public health. Explore titles, authors and supplied subject terms, then open the PubMed record.

Quote a phrase for an exact phrase match. Source license links do not imply unrestricted reuse.

At least 739 records · Page 41Linked to original sources
PubMed1984

Expression of hemolytically active murine fourth component of complement in transfected L cells.

The S region of the murine major histocompatibility complex contains two related genes (C4-X and C4-Y), one of which encodes the fourth component of complement (C4). We have introduced cloned C4-X and C4-Y genes into L cells. C4-X transfectants contained no detectable C4-related RNA, whereas C4-Y transfectants contained large amounts of C4-related RNA. Culture supernatants of C4-Y transfectants contained processed C4 which was indistinguishable from macrophage-derived C4. The L-cell-derived C4 restored hemolytic activity to C4-deficient serum, served as a substrate for C1s, and underwent autolytic cleavage suggesting the presence of an intramolecular thiolester bond. These experiments identify C4-Y as the functional C4 gene in H-2d mice and indicate that L cells can process pro-C4 correctly.

Amino Acid Sequence↗
PubMed1986

A model system for the study of the assembly and regulation of human complement C3 convertase (classical pathway).

The formation of classical C3 convertase of complement and its regulation by C4b-binding protein (C4bp) were studied using two different approaches: (a) the analysis was first carried out in fluid phase; a soluble stabilized C3 proconvertase could be assembled from C4b (or C4b-like C4) and iodine-treated C2 in the presence of Ni2+ ions. Upon activation of this complex by C1s, a C3 convertase C4b(C4b-like C4)-C2a was generated which was able to cleave purified C3. C4bp dissociated both C3 proconvertase and C3 convertase, but its effect was more important on C3 convertase. (b) A model system of phospholipid vesicles has been developed to study the assembly of the C3 convertase on a membrane. Among different phospholipid mixtures tested, P-glycerol/P-choline vesicles were found most effective for C4b binding. Optimal conditions were determined for C4b fixation on these vesicles; bound C4b participated in the formation of a functional membrane-associated C3 convertase. C4bp was found to bind to phospholipid vesicles with a higher affinity than C4b; it was able to dissociate the vesicle-associated C3 convertase.

Buffers↗
PubMed1980

The Croonian Lecture, 1980. The complex proteases of the complement system.

The assembly and activation of the early components of complement, after their interaction with antibody-antigen complexes, are described in terms of the structures of the different proteins taking part. C1q, a molecule of unique half collagen--half globular structure, binds to the second constant domain of the antibody molecules through its six globular heads. A tetrameric complex of C1r2-C1s2 binds to the collagenous tails and leads to formation of the serine-type proteases C1r and C1s. C1s activates C4, which forms a covalent bond between its alpha' chain and the Fab section of the antibody. C2 is also activated by C1s and associates with the bound C4 molecule to form C42, a labile protease that activates C3, but which loses activity as the C2 peptide chains dissociate from C4. C2, by analogy with factor B, the equivalent component of the alternative pathway of activation, appears to be a novel type of serine protease with a similar catalytic site but different activation mechanism to the serine proteases that have been described previously.

Amino Acid Sequence↗
PubMed1998

C1 inhibitor removes the entire C1qr2s2 complex from anti-C1Q monoclonal antibodies with low binding affinities.

Evidence is presented for a new C1 Inhibitor (C1 INH) function. C1 INH was capable of dislodging the entire C1qr2s2 complex from C1-activating substances that bound weakly to the globular heads of C1q. Two different mouse IgG1 monoclonal antibodies with different affinities for C1q globular heads were compared for their complement-activating properties in the presence of normal human serum. As expected the higher affinity monoclonal antibody (Qu) was more effective in binding C1q and causing C1-mediated C4b deposition. Unexpectedly, time responses of C1 (C1q) binding to immobilized 3C7 reached a peak then gradually decreased. However, C1q remained constantly bound to immobilized Qu. These results indicated that after C1 activation in human serum, the entire C1 complex (including C1q) was dislodged from 3C7, but not from immobilized Qu. The addition of purified C1 INH to purified C1, which had bound to immobilized 3C7, resulted in removal of C1 (C1q). Removal of the entire C1qr2s2 did not occur when C1 INH preparations were first neutralized by the addition of purified activated C1s. In summary, it is suggested that C1 INH plays a prominent role in dislodging the entire C1qr2s2 from immunoglobulin preparations which have a low binding affinity for the globular heads of C1q.

Animals↗
PubMed1987

Regulation of the activation of C1 in serum.

C1 has been partially purified from serum and its ability to activate has been studied. The activation status of C1 was measured using a sensitive hemolytic assay which allowed the activation status of C1 in serum to be monitored. C1 did not activate in serum but would spontaneously activate when separated from certain other serum proteins, in particular, the C1-inhibitor protein. The activation of C1 was time and concn dependent, but addition of fully activated C1 did not affect either the rate or extent of activation. The activation of C1 could be inhibited reversibly by C1-inhibitor. This action of the C1-inhibitor was over and above its ability to regulate fully activated C1 by covalent bond formation with either the serine esterase of C1s or C1r. The results presented suggest that the C1-inhibitor plays a dual role in the regulation of C1 activation. The regulatory actions of C1-inhibitor would account for the presence of C1 in a zymogen form and for the episodic nature of complement consumption observed in individuals with genetic deficiencies of the C1-inhibitor protein.

Chromatography, Ion Exchange↗
PubMedDate not supplied

[Evaluation of risk factors and blood coagulation parameters in cerebral ischemia].

Different parameters of coagulation and vascular risk factors have been studied in 24 subjects with previous strokes and in 21 control subjects matched by age. The two groups appeared statistically different for arterial pressure (max and min), glycemia, platelet aggregation ADP-induced and C1s-inactivator. Authors suggest to consider the changes of hemostasis as a vascular risk factor.

Aged↗
PubMed2005

The pathophysiology of hereditary angioedema.

Hereditary angioedema (HAE), characterized by recurrent episodes of angioedema involving the skin, or the mucosa of the upper respiratory or the gastrointestinal tracts, results from heterozygosity for deficiency of the serine proteinase inhibitor (serpin), C1 inhibitor (C1INH). The primary biological role of C1INH is to regulate activation of the complement system, the contact system, and the intrinsic coagulation system. During attacks of angioedema, together with decreasing levels of C1INH, the complement and contact systems are activated: C2 and C4 levels fall and high molecular weight kininogen is cleaved. Although previous data suggested that symptoms in HAE might be mediated via complement system activation, a combination of recent clinical data, in vitro studies, and analysis of C1INH-deficient mice all indicate that the major mediator of angioedema is bradykinin: (1) a vascular permeability enhancing factor can be generated in vitro in C1INH-depleted, C2-deficient plasma, but not from C1INH-depleted, contact system-deficient plasma; this factor was identified by sequence analysis as bradykinin; (2) bradykinin can be detected in the plasma of HAE patients during attacks of angioedema; (3) in several members of one family, expression of a C1INH variant that inhibits contact system proteases but has defective inhibition of C1r and C1s does not result in HAE; (4) C1INH-deficient (C1INH-/-) mice have a defect in vascular permeability that is suppressed by treatment with specific plasma kallikrein inhibitors and by bradykinin type 2 receptor (Bk2R) antagonists, and is eliminated in C1INH-/-, Bk2R-/- double-deficient mice.

Angioedema↗
PubMed1980

Immune-complexes in malignant skin melanoma: quantitation by three methods, purification, and characterization of their non-tumor related constituents.

Circulating immune-complexes (ICs) and complement system (C) were studied in sera from 10 patients with malignant skin melanoma. The presence of ICs was demonstrated in all of them by three distinct methods. Moreover, ICs were purified in all the patient sera. The fact that ICs were detected in each serum and that the results of the analysis obtained by the different methods were not overlapping is discussed. It is stressed that the differences among the intrinsic characteristic of each technique are responsible for these discrepancies. The C profile was altered if compared with normal values, but it was not strictly characteristic for an ICs disease. In the purified ICs C3, C4, IgM, IgC1, and IgG3 were demonstrated; C1q, C1s, IgA, IgG2, and IgG4 never. It is noteworthy that a rheumatoid activity was found in the purified material and that this activity was significantly correlated with serum immuno-conglutinins (IKs) titre.

Adult↗
PubMed2003

Complete sequencing and expression of three complement components, C1r, C4 and C1 inhibitor, of the classical activation pathway of the complement system in rainbow trout Oncorhynchus mykiss.

Three complement components, C1r, C4 and C1 inhibitor, of the classical activation pathway have been fully sequenced and their expression investigated in rainbow trout (Oncorhynchus mykiss). Trout C1r cDNA encodes a 707-amino-acid (aa) protein with a theoretical M(r) of 77,200. The trout translation shows highest homology with carp C1r/s, and lower, equal homologies to mammalian C1r and C1s, and MASPs from other vertebrate species. However, phylogenetic analysis and structural features suggest that the trout sequence, together with the two carp sequences, are the orthologues of mammalian C1r. The trout C4 cDNA encodes a 1,724-aa protein with a theoretical M(r) of 192,600. The trout translation shows higher homologies to the carp C4B and medaka C4, but lower homologies to C4 from other species and the carp C4A. It has a predicted signal peptide of 22 aa, a alpha-chain of 773 aa, a beta-chain of 635 aa and a lambda-chain of 288 aa. Trout C1 inhibitor cDNA encodes a 611-aa protein with a theoretical M(r) of 68,700. The trout translation has a C-terminal serpin domain with high homologies with mammalian counterparts (~37% identities), and a longer N-terminus, with no significant homology to other serpins, which contains two Ig-like domains. A molecule containing two Ig-like domains followed by a serpin domain, has also been found in an EST clone from another bony fish, the Japanese flounder. This suggests a unique structural feature of C1 inhibitor in fish. The functional significance of the Ig domains is discussed. The liver is the major site of expression of the three trout complement components, C1r, C4 and C1 inhibitor, although their expression is also detectable in other tissues. The extra-hepatic expression of complement genes may be important for local protection and inflammatory responses. Low-level constitutive expression of the three components was also detectable in a trout monocyte/macrophage cell line RTS-11, but only the expression of C4 could be upregulated by LPS.

Amino Acid Sequence↗
PubMed1999

In vitro analysis of complement-dependent HIV-1 cell infection using a model system.

Previous studies based on the use of human serum as a source of C have provided evidence for the C-dependent enhancement of cell infection by HIV-1. The present study was undertaken to distinguish C from other serum factors and to identify the proteins and the mechanisms involved in C-dependent cell infection by HIV-1. The classical C activation pathway was reconstituted from the proteins C1q, C1r, C1s, C4, C2, C3, factor H, and factor I; each were purified to homogeneity. A mixture of these proteins at physiological concentrations was shown to reproduce the ability of normal human serum to enhance the infection of MT2 cells by HIV-1 at low doses of virus. This enhancing effect was abolished when heat-inactivated serum and C2- or C3-depleted serum were used, and was restored upon addition of the corresponding purified proteins. A mixture of two synthetic peptides corresponding to positions 10-15 and 90-97 of human C receptor type 2 (CD21) as well as soluble CD4 both inhibited the C-dependent infection process. These data provide unambiguous evidence that HIV-1 triggers a direct activation of the classical C pathway in vitro and thereby facilitates the infection of MT2 cells at low doses of virus. These findings are consistent with a mechanism involving increased interaction between the virus opsonized by C3b-derived fragment(s) and the CD21 cell receptors and subsequent virus entry through CD4 receptors.

Acquired Immunodeficiency Syndrome↗
PubMed2004

The critical concentration of C1-esterase inhibitor (C1-INH) in human serum preventing auto-activation of the first component of complement (C1).

C1-esterase inhibitor (C1-INH) was depleted from normal human serum (NHS) at 4 degrees C by affinity chromatography with a monoclonal anti-C1-INH antibody (mAb 13 E1) coupled to CNBr-activated Sepharose 4B. The C1-INH-depleted serum (C1-INH-depl-HS) had normal levels of C1, C4, and CH 50 and C1-INH concentration was less than 10% of normal (15 microg/ml in C1-INH-depl-HS compared to 230 microg/ml in NHS). C1-auto-activation in C1-INH-depl-HS was followed by measuring C4-consumption in a haemolytic assay and by detection of activated C1s in a C1s-ELISA. After a lag phase of 10-20 min, C1-auto-activation in C1-INH depl-HS occurred and reached its maximum after 40 min at 37 degrees C. In contrast, neutralization of C1-INH activity in NHS by addition of monoclonal antibodies directed against its C1s-binding site, resulted in an immediate, spontaneous C1-activation without a lag-phase and reached its maximum already after 20 min (mAb 140) and 25 min (mAb 88G2). Addition of highly purified C1-INH or NHS as source of C1-INH to C1-INH-depleted serum to a final concentration of 55 microg/ml (22% of normal C1-INH concentration in HS) was sufficient to control spontaneous C1-activation.

Animals↗
PubMed1987

Human complement proteins D, C2, and B. Active site mapping with peptide thioester substrates.

The specificity and reactivity of complement serine proteases D, B, Bb, C2, and C2a were determined using a series of peptide thioester substrates. The rates of thioester hydrolysis were measured using assay mixtures containing the thiol reagent 4,4'-dithiodipyridine at pH 7.5. Each substrate contained a P1 arginine residue, and the effect of various groups and amino acids in the P2, P3, P4, and P5 positions was determined using kcat/Km values to compare reactivities. Among peptide thioesters corresponding to the activation site sequence in B, dipeptide thioesters containing a P2 lysine residue were the best substrates for D. Extending the chain to include a P3 or P4 amino acid resulted in loss of activity, and neither the tripeptide nor the tetrapeptide containing the cleavage sequence of B was hydrolyzed. Overall, D cleaved fewer substrates and was 2-3 orders of magnitude less reactive than C1s against some thioester substrates. C2 and fragment C2a had comparable reactivities and hydrolyzed peptides containing Leu-Ala-Arg and Leu-Gly-Arg, which have the same sequence as the cleavage sites of C3 and C5, respectively. The best substrates for C2 and C2a were Z-Gly-Leu-Ala-Arg-SBzl and Z-Leu-Gly-Leu-Ala-Arg-SBzl, respectively, where Bzl is benzyl. B was the least reactive among these complement enzymes. The best substrate for B was Z-Lys-Arg-SBzl with a kcat/Km value of 1370 M-1 s-1. The catalytic fragment of B, Bb, had higher activity toward these peptide thioester substrates. The best substrate for Bb was Z-Gly-Leu-Ala-Arg-SBzl with a kcat/Km similar to C2a and 10 times higher than the value for B. Both C2a and Bb were considerably more reactive against C3-like than C5-like substrates. Bovine trypsin hydrolyzed thioester substrates with kcat/Km approximately 10(3) higher than the complement enzymes. These thioester substrates for D, B, and C2 should be quite useful in kinetic and active site studies of the purified enzymes.

Animals↗
PubMed2003

Expression of H-ficolin/Hakata antigen, mannose-binding lectin-associated serine protease (MASP)-1 and MASP-3 by human glioma cell line T98G.

Mannose-binding lectin (MBL) is a C-type lectin involved in the first line of host defense and it requires MBL-associated serine proteases (MASP) for activation of the lectin complement pathway (LCP). Recently we reported that human ficolins, L-ficolin/P35 and H-ficolin/Hakata antigen, as well as MBL activate the LCP in association with MASP. We investigated in vitro expression of complements of the lectin complement pathway in several cell lines. Out of 17 cell lines tested using RT-PCR, a human glioma cell line, T98G, expressed high levels of H-ficolin/Hakata antigen, MASP1 and MASP3 mRNAs. Similar results were obtained in four other glioma lines. In addition, mRNAs for C1r, C1s, C2, C3, C4, C5 and C6 were also detected in T98G cells, but very low amount of mRNAs for C1q and MBL. MBL mRNA was seen in two of the other glioma cell lines. An ELISA of culture supernatants showed that T98G cells secreted a considerable amount of MASP-1 and MASP-3 proteins. SDS-PAGE and immunoblotting analyses showed the secreted H-ficolin/Hakata antigen, MASP-1 and MASP-3 to be 34, 81 and 105 kDa in size respectively, similar to their serum counterparts. Since the glioma cells used are derived from astrocytes, this suggests that human astrocytes may be a source of some components of the LCP in the brain.

Cell Line↗
PubMedDate not supplied

Complement activating rheumatoid factors in rheumatoid arthritis studied by haemolysis in gel: relation to antibody class and response to treatment with podophyllotoxin derivatives.

Complement (C) activating rheumatoid factors (RF) were measured in 16 patients with rheumatoid arthritis (RA) by a simple haemolysis in gel (HIG) assay. IgM-RF, but not IgG-RF or IgA-RF, measured by an enzyme linked immuno-sorbent assay, were closely correlated with C activating RF (r = 0.86). In neither assay did the concentrations of RF appear to be directly related to C1 activation as expressed by serum concentrations of C1r-C1s-C1 inactivator complexes or of C4. In the sera, C1q binding substances, measured by C1q binding assay, were markedly correlated with C activating RF (r = 0.88), whereas C1q binding substances detected by the C1q deviation test were not. Treatment with podophyllotoxin derivatives for 6 months clearly reduced patients' RF concentrations. The decrease of IgG-RF, IgA-RF and IgM-RF was significantly more pronounced than that of the IgG, IgA and IgM concentrations, respectively.

Adult↗
PubMed1987

Regulation of the alternative pathway of human complement by C1q.

The interaction of C1q with C3b and its effect on C3b activities in the alternative pathway of complement (APC) have been studied. Purified C1q markedly inhibited C3b deposition on and lysis of rabbit erythrocytes by the isolated cytolytic APC. It also blocked formation of the C3 convertase, C3b, Bb as well as binding of Factors B and H to sheep erythrocytes (E) bearing C3b. The direct and specific binding of C1q to C3b was clearly demonstrated using the hemagglutination technique at low ionic strength (0.1 M NaCl). C1q concns of 2 micrograms/ml and higher agglutinated, in a dose-dependent fashion, EC3b but not E, EC3bi or EC3d. Addition of C1r and C1s to C1q and formation of C1 did not affect its capacity to agglutinate EC3b. The C1q-mediated agglutination of EC3b was inhibited by EDTA, MgEGTA, C3b and Factor B but not by native C3 or collagen. Heating C1q (56 degrees C) markedly potentiated its agglutinating activity whereas collagenase-treated C1q lost most of its activity. Taken together, these results suggest that C1q binds through its "heads" and in the presence of calcium ions to a site on C3b that is adjacent to the Factor B and Factor H binding sites. This interaction may down-regulate the activity of the alternative pathway of complement on surfaces which activate both the classical and alternative pathways of complement.

Animals↗
PubMed1979

Purification of soluble immune complexes from serum using polymethylmetacrylate beads coated with conglutinin or C1q. Application to the analysis of the components of in vitro formed immune complexes and of immune complexes occurring in vivo during leishmaniasis.

A procedure for the isolation of immune complexes from human sera has been developed. Two steps are involved: (1) lipid-free serum is precipitated by polyethylene glycol; (2) the solubilized precipitate is absorbed on a column of polymethylmethacrylate beads coated with conglutinin (K) or C1q; the column is washed, the complexes are then eluted, using 0.02 M EDTA (for K column) or 0.5 M NaCl (for C1q column). This procedure permitted the purification and the characterization of soluble 125I-BSA-anti-BSA, 125 I-tetanus toxoid-anti-tetanus toxoid, and 125-I-HBsAg-anti-HBsAg complexes made in vitro in the presence of fresh human serum. The isolated complexes were shown to contain antigen, antibody, C1q, C1r, C1s and C3. When normal human serum was submitted to such a procedure, no detectable amount of protein was present in the final eluted fraction. Immune complexes formed in vivo were also purified by conglutinin column from the serum of a patient with disseminated leishmaniasis. The isolated material was found to contain IgM, IgG, C1q, C1r, C1s, C3c and C3d. The purified complexes dissociated at acid pH were found to contain anti-IgG and anti-leishmania antibodies.

Adult↗
PubMed2001

Complement components, but not complement inhibitors, are upregulated in atherosclerotic plaques.

Complement activation occurs in atherosclerotic plaques. The capacity of arterial tissue to inhibit this activation through generation of the complement regulators C1 inhibitor, decay accelerating factor, membrane cofactor protein (CD46), C4 binding protein (C4BP), and protectin (CD59) was evaluated in pairs of aortic atherosclerotic plaques and nearby normal artery from 11 human postmortem specimens. All 22 samples produced mRNAs for each of these proteins. The ratios of plaque versus normal artery pairs was not significantly different from unity for any of these inhibitors. However, in plaques, the mRNAs for C1r and C1s, the substrates for the C1 inhibitor, were increased 2.35- and 4.96-fold, respectively, compared with normal artery; mRNA for C4, the target for C4BP, was elevated l.34-fold; and mRNAs for C7 and C8, the targets for CD59, were elevated 2.61- and 3.25-fold, respectively. By Western blotting and immunohistochemistry, fraction Bb of factor B, a marker of alternative pathway activation, was barely detectable in plaque and normal arterial tissue. These data indicate that it is primarily the classical, not the alternative pathway, that is activated in plaques and that key inhibitors are not upregulated to defend against this activation.

Antigens, CD↗
PubMed1980

Purified proenzyme C1r. Some characteristics of its activation and subsequent proteolytic cleavage.

1. Upon incubation for 1 h at 37 degrees C, proenzymic C1r was activated by a proteolytic cleavage comparable to that observed in vivo; after reduction and alkylation, two fragments of apparent molecular weights 57 000 and 35 000 were evident on sodium dodecyl sulphate (SDS)-polyacrylamide gel electrophoresis. The activation kinetics were slightly sigmoidal and nearly independent of C1r concentration. They were characterized by a marked thermal dependence (activation energy = 45 kcal/mol). The reaction was inhibited by calcium and p-nitrophenyl-p'-guanidinobenzoate, but poorly sensitive to di-isopropyl phosphorofluoridate. The dependence of the activation rate on pH was unusual; it decreased progressively in the acid range (pH 4.5-6.5) which coincides with the dissociation of the C1r-C1r dimer. Above pH 6.5, the rate increased slightly and showed no clear maximum. These results are consistent with an intramolecular autocatalytic activation mechanism involving the pro-site of each subunit of the C1r-C1r dimer. 2. During a 5 h incubation period at 37 degrees C, C1r underwent two proteolytic cleavages which led to the successive removal of two fragments, alpha (35 000) and beta (7000-11 000) from each subunit, leaving a dimeric molecule of reduced size (Mr = 110 000; s20,w = 6.1 S). The proteolytic process was nearly independent of C1r concentration and characterized by a pH optimum at 8.5-9.0, and a high activation energy (36.8 kcal/mol). Calcium and p-nitrophenyl-p'-guanidinobenzoate, and also di-isopropyl phosphorofluoridate and benzamidine were inhibitors of this reaction. The product, C1r II, retained the original antigenic properties of C1r and a functional active site, but lost the capacity to bind C1s. These results are consistent with an autocatalytic intramolecular proteolysis mediated by the active site of each subunit of the C1r-C1r dimer.

Complement Activating Enzymes↗