Purification and characterization of subcomponent C1q of the first component of mouse complement

Role of complement in a murine model of peanut-induced anaphylaxis

Peanut allergy is severe and persisting from childhood to adulthood. However, there is no effective prophylaxis or treatment for peanut allergy. Little is known to about the molecular process in the pathogenesis of peanuts allergy, especially in innate immunity. Thus we investigated the role of complement activation in murine peanut anaphylaxis. Complement component C3 deposition on peanut extract (PE) was evaluated using sera from wild-type (WT), mannose-binding lectin associated serine protease (MASP)-1/3 deficient, MASP-2 deficient, and C4 deficient mice. Sera from interferon regulatory factor-4 (IRF-4) deficient mice, which lack serum immunoglobulin, were also used. In anaphylaxis study, mice were pretreated with propranolol and a long-acting form of IL-4, and injected with PE. Mice were then assessed for plasma C3a levels and hypothermia shock by ELISA and rectal temperature measurement, respectively. C3 deposition on PE was abolished in immunoglobulin- and C4-deficient sera. No difference in C3 deposition levels were observed among WT, MASP-1/3 deficient and MASP-2 deficient sera. IgM, IgG2b, IgG3, C1q, and ficolin-A deposits were detected on PE. In anaphylaxis study, MASP-1/3 deficient mice showed elevation of plasma C3a levels similar to WT mice. However, they were significantly reduced in C4- and MASP-2-deficient mice compared to WT mice. Consistently, PE-induced anaphylactic shock was prevented in C4 deficient mice and partially in MASP-2 deficient mice. In conclusion, PE activates complement via both the lectin and classical pathways in vivo, and the complement activation contributes to hypothermia shock in mice.

C1q, the recognition subcomponent of the classical pathway of complement, drives microglial activation

Microglia, central nervous system (CNS) resident phagocytic cells, persistently police the integrity of CNS tissue and respond to any kind of damage or pathophysiological changes. These cells sense and rapidly respond to danger and inflammatory signals by changing their cell morphology; by release of cytokines, chemokines, or nitric oxide; and by changing their MHC expression profile. We have shown previously that microglial biosynthesis of the complement subcomponent C1q may serve as a reliable marker of microglial activation ranging from undetectable levels of C1q biosynthesis in resting microglia to abundant C1q expression in activated, nonramified microglia. In this study, we demonstrate that cultured microglial cells respond to extrinsic C1q with a marked intracellular Ca(2+) increase. A shift toward proinflammatory microglial activation is indicated by the release of interleukin-6, tumor necrosis factor-alpha, and nitric oxide and the oxidative burst in rat primary microglial cells, an activation and differentiation process similar to the proinflammatory response of microglia to exposure to lipopolysaccharide. Our findings indicate 1) that extrinsic plasma C1q is involved in the initiation of microglial activation in the course of CNS diseases with blood-brain barrier impairment and 2) that C1q synthesized and released by activated microglia is likely to contribute in an autocrine/paracrine way to maintain and balance microglial activation in the diseased CNS tissue.

C1q, the collagen-like subcomponent of the first component of complement C1, is a membrane protein of guinea pig macrophages

C1q, a subcomponent of C1--the first component of complement, is synthesized by macrophages (M phi). Immunofluorescence and immunoperoxidase studies first indicated the presence of C1q on the surface of guinea pig (gp) and human peritoneal M phi (Loos, M., Storz, R., Müller, W. and Lemmel, E. M., Immunobiology 1981. 158: 213). In our study different methods for labeling of gp serum and gp M phi C1q were employed. The presence of C1q protein on the surface of gp peritoneal M phi is shown by cell surface labeling with the biotin derivative sulfosuccinimdyl-6-(biotinamido)-hexanoate and subsequent immunoprecipitation. The mechanism by which C1q is attached to the cell membrane was also investigated. Intact cells were treated with acid stripping-buffers or phosphatidylinositol-specific phospholipase C and separated membranes were extracted with a buffer containing 1 M KCl and 3 M urea. Regardless of which method was used, C1q remained attached to the membrane. When surface-labeled cells were cultured, they were found to release the C1q from their surface membrane into the culture medium. Lysates of biosynthetically labeled cells were used to show that, like secreted or serum C1q, cellular M phi C1q binds to immobilized homologous IgG. This implies that the globular regions of the cellular C1q are functionally active. The results reveal that (i) cellular M phi C1q is firmly located in the membrane throughout the biosynthetic pathway, such that it is comparable with an integral membrane protein, (ii) cellular M phi C1q is not reversibly bound to the cell surface via a receptor. We suggest that C1q, as a membrane protein of M phi, serves as an Fc binding factor that also is secreted into the environment.

Molecular cloning and characterization of the complementary DNA coding for the B-chain of murine Clq

cDNA clones coding for the B-chain of murine Clq were isolated from a mouse macrophage library. The characterized clones include the total coding region plus a leader sequence. High homology was found with human Clq B-chain in the coding region (81%). Northern blot analysis of total RNA from different tissues of Balb/c mice showed one band of approximately 1.2 kb. The highest signal was found in RNA preparations of thioglycolate-activated peritoneal macrophages. The probe also hybridized with mRNA from spleen, thymus and heart. Extremely weak signals were found in liver, kidney, lung and intestine tissues.

Mechanism of complement activation after coronary artery occlusion: evidence that myocardial ischemia in dogs causes release of constituents of myocardial subcellular origin that complex with human C1q in vivo

To evaluate whether ischemic myocardium releases molecules that react with the first component of complement, we studied cardiac lymph from eight dogs before and at intervals after coronary artery occlusion and reperfusion. Before occlusion, the dogs were injected intravenously with radiolabeled human C1q. Labeled C1q could be detected in the cardiac lymph within minutes following injection. Rabbit antisera, prepared against substances precipitated from postreprefusion cardiac lymph by anti-human C1q, also reacted with specific constituents of isolated cardiac sarcoplasmic reticulum and mitochondria. To evaluate whether mitochondria are the source of these C1q-binding proteins, we isolated intramyofibrillar and subsarcolemmal mitochondria from canine heart and incubated sonicates of these with purified C1q, immobilized on nitrocellulose. Molecules bound to the immobilized C1q were removed with 0.1% sodium dodecyl sulfate, fractionated under reducing conditions by polyacrylamide gel electrophoresis, and transferred electrophoretically to nitrocellulose paper. Antisera prepared against postreperfusion lymph reacted with a 31,000-32,000-dalton protein in these nitrocellulose paper replicas. Since this protein originates from mitochondria, binds to C1q, and is recognized by antibodies made against postreperfusion lymph, this protein is likely to be one of the subcellular constituents that, upon release from ischemic cells, activates the complement cascade. To evaluate the clinical relevance of these observations, we tested sera from 53 patients obtained 48-72 hours after hospitalization for suspected myocardial infarction.(ABSTRACT TRUNCATED AT 250 WORDS)

cDNA clones coding for the complete murine B chain of complement C1q: nucleotide and derived amino acid sequences

We have isolated cDNA clones covering the complete B chain of the complement subunit C1q from mouse; this subunit initiates the classical complement pathway. Deoxynucleotide sequence analysis shows that these clones contain 156 nucleotides of the 5' untranslated region, followed by sequences coding for the 25 amino acids of the signal peptide, all of the 228 amino acids of the mature protein and 140 nucleotides of the 3' untranslated region, including a poly A addition signal. The coding region for the mature protein contains 261 nucleotides for the Gly-X-Y repeat and 408 nucleotides for the globular portion of C1q. By comparing the nucleotide sequence of the mouse B chain of C1q with the B chain from human (Reid, K. B. M., 1985, Biochem. J. 231, 729), we find a high homology (80%) within the mature protein, a lower homology within the signal peptide (59%) and the 3' untranslated region (47%) and no homology (26%) in the 5' untranslated region.

cDNA clones coding for the complete murine B chain of complement Clq: nucleotide and derived amino acid sequences

We have isolated cDNA clones covering the complete B chain of the complement subunit Clq from mouse; this subunit initiates the classical complement pathway. Deoxynucleotide sequence analysis shows that these clones contain 156 nucleotides of the 5' untranslated region, followed by sequences coding for the 25 amino acids of the signal peptide; all of the 228 amino acids of the mature protein; and 140 nucleotides of the 3' untranslated region, including a poly A additional signal. The coding region for the mature protein contains 261 nucleotides for the Gly-X-Y repeat and 408 nucleotides for the globular portion of Clq. By comparing the nucleotide sequence of the mouse B chain of Clq with the human B chain (Reid, K.B.M., 1985, Biochem. J. 231, 729), we find a high homology (80%) within the mature protein, a lower homology within the signal peptide (59%) and the 3' untranslated region (47%) and no homology (26%) in the 5' untranslated region.

Purification, identification and characterization of chicken C1q, a subcomponent of the first component of complement

A component, having the equivalent haemolytic activity to that of human complement subcomponent C1q, was purified by a combination of precipitation with EGTA, gel filtration, ion exchange and adsorption chromatography from chicken serum. Yields ranged from 8 to 15 mg/litre of serum. The finally purified preparation generates full Cl haemolytic activity when assayed with human complement subcomponents C1r and C1s, and have been identified as chicken C1q. The molecular weight of undissociated C1q, as estimated on polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulphate (SDS), is 504,000. Under dissociating but non-reducing conditions, the C1q was shown to consist of 2 subunits having molecular weights of 52,700 and 51,200 in a molar ratio of 2:1. On reduction, the 52,700 molecular weight subunit gave chains with molecular weights of 25,900 and 24,800 in equimolar ratio, and the 51,200 molecular weight subunit decreased to 24,800. The C1q contains hydroxyproline, hydroxylysine, a high percentage of glycine and approximately 7% carbohydrate. Collagenase digestion of C1q caused a rapid loss of haemolytic activity and produced much smaller peptide fragments.

Rat Clq: isolation and purification from normal serum and development of a sensitive hemolytic assay

Rat Clq was isolated and purified from normal rat serum by a two-step procedure: affinity chromatography on a human IgG-Sepharose 4B column and Bio-Gel A 5m column chromatography. From 1.8 l of normal serum, the procedure yielded 4.5 mg of homogeneous and hemolytically active rat Clq as shown by three bands of peptide in SDS polyacrylamide gel electrophoresis under reducing conditions and by a single precipitin line between rat Clq and rabbit anti-rat Clq antibody. Rabbit anti-rat Clq antibody prepared by immunizing a rabbit with 225 micrograms of rat Clq was specific as shown by a single precipitin line between the antibody and normal rat serum and rat Clq with complete identity. The amino acid composition of rat Clq was very similar to that of human Clq. The purification procedure also yielded Clq-depleted rat serum which was used with the homogeneous Clq to establish a sensitive hemolytic assay: 4.5-13.5 ng of rat Clq can be reproducibly quantitated. The concentration of Clq in Brown Norway rats was estimated to be 41.5 +/- 3.0 micrograms/ml serum.

A study of the role of the asparagine-linked sugar chains of human complement subcomponent C1q in its biological activities

The sialic acid residues were removed from asparagine-linked sugar chains on the C-terminal non-collagenous globular regions of human C1q by sialidase digestion. Both the haemolytic activity and the binding ability to immunoglobulin G (IgG) (Fc-binding ability) of C1q were unimpaired, even after the complete removal of sialic acid from these sugar chains. On the other hand, the rate of disappearance of C1q from the circulation was greatly accelerated by its desialylation, that is, the radioactivity of the infused intact and desialylated C1q was reduced to half for 200 min and for 140 min in the circulation of rats, respectively. A mixture of entire asparagine-linked sugar chains consisting of neutral, monosialyl and disialyl oligosaccharides was isolated from the intact C1q molecule by hydrazinolysis. The oligosaccharide-mixture isolated, after NaBH4 reduction, was added to assay system of C1q, but neither the haemolytic activity nor the Fc-binding ability was influenced.

Binding of complement subcomponent C1q to mouse IgG1, IgG2a and IgG2b: a novel C1q binding assay

A C1q binding assay is presented which is suitable for use in comparison of the binding ability of different antibodies, and which allows the quantitative determination of their binding constants. The assay system uses IgG bound to a hapten-derivatized Affigel support. No non-specific binding is observed to a DNP-derivatized support, allowing the use of anti-DNP antibodies. With mouse anti-DNP hybridoma IgGs it was found that C1q binding followed the series IgG2a greater than IgG2b much greater than IgG1, in accordance with the complement fixing ability of these subclasses. Since it is relatively simple to couple any antigen to Affigel , this assay system should be generally applicable to any antibody-antigen system.

Comparative studies on biological activities of subcomponents C1q of the first component of human, bovine, mouse and guinea-pig complement

Both the haemolytic activity and the binding ability to immunoglobulin G(IgG) (Fc-binding ability) were comparatively assayed among human, bovine, mouse and guinea-pig C1q. The haemolytic activity was measured by using the sensitized sheep erythrocytes with rabbit immunoglobulin M(IgM)- or IgG-haemolysin. The Fc-binding ability was assayed by using immune complexes made of rabbit IgG-antibody against human serum albumin as well as agglutination of latex particles coated with human, bovine or rabbit IgG (IgG-latex). The specific haemolytic activity was comparable with between bovine and mouse C1q, while those of guinea pig and human C1q were significantly lower than those of the others. Only the human and mouse C1q showed significantly positive agglutinating activity of human or bovine IgG-latex. In the case of the use of rabbit IgG-latex, each of these C1q gave much weaker agglutination. On the other hand, the ability of all these C1q to bind to Fc of immune complexes specifically was almost comparable. The discrepancy in specific activities between the haemolysis and the Fc-binding ability may suggest that these two biological activities are not always correlative and that these are independent biological phenomena.

Subcomponents C1q of the first component of guinea pig and mouse complement. Comparative study of their asparagine-linked sugar chains

Guinea pig and mouse C1q, subcomponents of the first component of complement, contained six asparagine-linked sugar chains on the C-terminal non-collagenous globular regions of each molecule. After N-acetylation and successive NaB3H4-reduction of asparagine-linked sugar chains liberated by hydrazinolysis, their structure was analysed by sequential exoglycosidase digestion in combination with sugar composition analyses. The sugar chains of C1q molecules of both animals were very similar and composed of the biantennary complex type sugar chains with the following outer chains in various combination is: (+/- NeuNAc alpha leads to)Gal beta 1 leads to GlcNAc beta 1 leads to and Gal beta 1 leads to Gal beta 1 leads to GlcNAc beta 1 leads to. These outer chain moieties were found to be linked to a common core structure of Man alpha 1 leads t o (Man alpha 1 leads to)Man beta 1 leads to GlcNAc beta 1 leads to (Fuc alpha 1 leads to)GlcNAc.

Stimulation of locomotion of peripheral blood monocytes by human plasma fibronectin

The motility of human peripheral blood granulocytes and monocytes in response to human plasma fibronectin was quantified by an in vitro assay using blind-well chemotaxis chambers. Purified fibronectin under nondenaturing conditions produced increased migration of granulocytes only at concentrations higher than 100 nM, and induced increased chemotactic and random locomotion of monocytes at concentrations higher than 0.1 nM. The monocyte migration-inducing activity of fibronectin was concentration dependent, and was strongly inhibited by low concentrations of colchicine (100 nM-100 microM). These findings suggest the possibility that plasma fibronectin serves as a chemotactic stimulus for monocytes in vivo and attracts these cells to sites of microscopic tissue injury where plasma fibronectin is deposited.

Chemical studies on the isolated collagen-like and globular fragment of complement component C1q. Comparative studies on bovine and human C1q

Both the collagen-like and the globular fragments of a subcomponent C1q of the first component of bovine and human complement were highly purified by enzymic digestion followed by gel filtration. Analyses by polyacrylamide gel electrophoresis showed that the former was composed of covalently linked peptide chains with an average molecular weight of 14 000, and that the latter was composed of three non-covalently linked peptide chains each having a molecular weight of approximately 15 000. Great similarities between amino acid compositions of the globular fragments and some similarities between those of the collagen-like fragments were found. Moreover, great similarities of amino acid compositions were found among three non-covalently linked chains of each globular fragment as well as between the corresponding chains of both globular fragments. These results suggested that both the collagen-like and the globular domains on the C1q molecule remained highly conserved in its evolution.

The subcomponent Clq of the first component of guinea pig complement: purification and characterization

Guinea pig C1q was purified, in a highly active hemolytic form, by a combination of precipitation with chelating agents, CM-cellulose and Sepharose 6B. Yields ranged from 30 to 35% protein, and the activity of final preparations was in the range of 2 x 10(13)--3 x 10(13) C1q effective molecules/mg. The molecular weight of C1q was approximately 430,000, as determined by polyacrylamide gel electrophoresis in the presence of sodium dodecyl sulfate (SDS). C1q was shown to be composed of two non-covalently liked subunits of approximate molecular weights 46,500 and 45,000 in a molar ratio 2:1. One reduction, the higher molecular weight subunit gave two chains having approximate molecular weights of 24,500 and 23,000 in equimolar ration, and the lower weight subunit gave one chain with a molecular weight of approximately 22,300. C1q contained hydroxyproline, hydroxylysine and high percentage of glycine. Thus, the overall molecular structure of guinea pig C1q appears similar to that of human C1q. The antiserum against the purified C1q showed only one precipitation band with guinea pig whole serum or purified C1q on immunodiffusion analyses and was found to be monospecific.

Comparable content of hydroxylysine-linked glycosides in subcomponents C1q of the first component of human, bovine and mouse complement

The hydroxylysine-glycosides in bovine and mouse C1q are directly quantified in parallel with those in human C1q after the alkaline hydrolysis of these molecules. Human, bovine and mouse C1q contain 68.3, 66.3 and 64.0 hydroxylysine-galactosylglucose residues in each of these molecules respectively. Only human C1q contains 2.5 residues of hydroxylysine-galactose per molecule, and both of bovine and mouse C1q contain no detectable hydroxylysine-monosaccharides in their molecules. The percentage of hydroxylysine residues glycosylated to total hydroxylysine residues in each of these molecules is calculated to be 86.4, 92.0 and 95.1% for human, bovine and mouse C1q respectively and is comparable with each other. The percentages of hydroxylysine residues resistant to periodate oxidation to total hydroxylysine residues in these molecules were 61.1, 65.3 and 74.3% for human, bovine and mouse C1q respectively and were significantly lower than those estimated by the direct quantification of hydroxylysine-glycosides after the alkaline hydrolysis of these molecules.