Alteration of complement protein levels after antiretroviral therapy in HIV-infected persons.
Explore the source record for details and available documents.
Anti-HIV Agents↗
SEARCH · Search PubMed
Results for “Complement Pathway, Classical”
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.
Monoclonal antibodies to complement components without the need of their prior purification. II. Antibodies to mouse C3 and C4.
Rat monoclonal antibodies (MAbs) to mouse complement components C3 and C4 were produced by immunizing rats with cell-bound C3 and C4. This principle involves: a) using mouse thymocytes coated with syngeneic rat antibody isotypes that show high affinity to C1q, b) the intercalation of C1q from serum and c) the subsequent activation of the classical complement pathway leading to deposition of cell-bound complement components. Screening for anti-complement antibodies was performed on antibody coating microtiter plates with mouse serum as source of complement. The reactivity of the MAbs was determined by variations of the ELISA screening system using EDTA-serum to inhibit complement activation by C1 dissociation, serum rendered deficient of functionally active C3 by treatment with cobra venom factor (CVF) or serum of genetically C5-deficient mice. The specificity of the MAbs was confirmed by affinity chromatography followed by SDS-PAGE and immunoblotting. We were able to establish a panel of anti-C3 and anti-C4 MAbs of various isotypes.
Animals↗
Complement component C1q activity and ascorbic acid nutriture in guinea pigs.
When guinea pigs are fed tissue-saturating amounts of ascorbate, C1q concentrations are significantly higher than in those animals fed only enough ascorbate for adequate growth and for the prevention of scurvy. C1q is the recognition protein of the classical complement pathway, a system of blood proteins that constitutes an important part of host defense against pathogens. The observed effect of ascorbate nutriture on C1q concentrations is consistent with the known role of ascorbic acid in hydroxyproline biosynthesis. C1q is a hydroxyproline-containing protein with structural similarities to collagen.
Analysis of Variance↗
The complement system.
Explore the source record for details and available documents.
Complement Pathway, Alternative↗
The complement system in host defense and inflammation.
In this discussion I have reviewed the major role of complement in host defense and inflammation. In addition, I have discussed dificiency states. Although these are rare, their clinical signs and symptoms can be predicted, at least in part, on the basis of our current understanding of the biological activities of complement and the various pathways of complement activation. This is not to say that complement plays no role in a wide variety of other illnesses. However, when complement plays a role in an illness, often this is not because it is functioning in an aberrant fashion. The usual situation is that complement is being activated and is serving its normal function in causing inflammation and damage to tissues under abnormal circumstances. Thus, for example, circulating antigen complexes may be deposited in the kidney, activate complement, and mediate tissue inflammation. In this case, complement is functioning normally but is being activated under abnormal circumstances. The same type of analysis can be made for many diseases of many different organ systems. At present, we have no drugs that are effective in humans in controlling the activation of complement and complement-mediated inflammation. We have not yet even established whether local variations in the activity of complement may affect the course of a clinical infection, but there is certainly strongly suggestive evidence to support this idea. It should be clear that under certain circumstances complement may well be a major factor in controlling the course of an infection. The near future should bring a vast expansion in our understanding of how complement contributes to specific clinical illnesses and to the defense of the host against specific microorganisms.
Angioedema↗
Actions of complement on Junin virus.
Fresh sera from normal rhesus monkeys, guinea pigs, and rabbits inactivated 90%-99% of the infectivity of Vero cell-passaged, attenuated strains of Junin virus (JV) within 60 minutes. Selective depletion studies showed that inactivation occurred by the classical complement pathway. Complement had little effect on virulent JV strains. Adsorption of the fresh sera with JV-infected Vero cells showed that inactivation was not mediated by low levels of antibodies in normal sera. The cells used for propagation of the virus affected inactivation: virus passaged in Vero cells (a continuous African green monkey kidney line) was more susceptible than virus passaged in FRhL-2 cells (a diploid strain derived from fetal rhesus monkey lung). Complement was important for in vitro neutralization of virulent JV strains by immune sera but was unnecessary for neutralization of attenuated strains. Thus, complement may be important in host resistance to Argentine hemorrhagic fever in two ways: first, complement activation may contribute to the attenuated phenotype of some strains; and second, complement may be necessary for efficient neutralization of virulent strains.
Animals↗
Collectin in a non-mammalian species: isolation and characterization of mannan-binding protein (MBP) from chicken serum.
A chicken serum lectin was isolated by affinity chromatography on TSK-75 beads derivatized with the monosaccharide N-acetyl-D-mannosamine (ManNAc). Serum was applied to the column in a Ca(2+)-containing buffer and proteins were eluted with EDTA. After recalcification, the eluate was passed through a new ManNAc-derivatized column. Bound proteins were eluted with 50 mM ManNAc. Anti-carbohydrate antibodies present in the eluate were removed by passage through a rabbit anti-chicken immunoglobulin derivatized column, and the lectin was further purified by ion-exchange chromatography and gel-permeation chromatography. The purified chicken lectin shows an overall structure similar to mammalian mannan-binding protein (MBP). SDS-PAGE revealed two polypeptides of M(r) 33 and 34 kDa (reduced) with identical sequence for the first 30 NH2-terminal residues. The NH2-terminal sequence shows 43% identity with the human MBP. Like mammalian MBP, the polypeptides of the chicken lectin are degraded by treatment with collagenase. Residues 26-30 (G-L-P(OH)-G-D) are likely to represent the beginning of the collagenous region. Mobilities on SDS-PAGE of the COOH-terminal collagenase-resistant fragment under reduced and non-reduced conditions indicate the presence of intrachain disulphide bonds, as are also found in mammalian MBP. Gel chromatography showed an intact mol. wt of 750 kDa. Binding of the chicken MBP to mannan was inhibited by monosaccharides in the following order of potency: ManNAc > L-fucose > mannose > N-acetylglucosamine. Other monosaccharides inhibited poorly or not at all. Chicken MBP, bound to mannan, activated the classical complement pathway in human serum. Electron micrographs show structures and dimensions resembling human MBP. Overall, the results show that the purified lectin is the chicken homologue to mammalian MBP and indicate the presence of a MBP-like clearance system outside mammals.
Amino Acid Sequence↗
Killing of virus-infected cells: the role of antiviral antibody and complement in limiting virus infection.
Explore the source record for details and available documents.
Antibodies, Viral↗
Opsonic requirements for phagocytosis of Borrelia hermsii by human polymorphonuclear leukocytes.
Opsonic requirements for phagocytosis by human polymorphonuclear leukocytes (PMNLs) of a laboratory strain of Borrelia hermsii were examined. Intracellular localization of spirochetes was confirmed by electron microscopy and cinephotomicroscopy. Phagocytosis of 3H-labeled spirochetes was increased with higher concentrations of pooled human serum or greater ratios of spirochetes to PMNLs and was unaffected by diminished classical complement pathway activity. Immune rabbit serum markedly increased phagocytosis of spirochetes beyond levels observed with preimmune rabbit serum. Immune rabbit serum also demonstrated direct activity against B. hermsii, which decreased the motility and viability and increased agglutination of the spirochetes independently of complement. Both the direct activity against B. hermsii and the opsonic activity of immune rabbit serum were eliminated by immunoabsorption of immunoglobulins. These observations suggest a role for the alternative complement pathway and for immunoglobulins in the opsonization of spirochetes for phagocytosis by PMNLs. Immunoglobulins may also play a role in the direct clearance of spirochetes.
Animals↗
The role of complement and antibody in opsonophagocytosis of type II group B streptococci.
The role of complement and antibody in the opsonophagocytosis of type II group B streptococci (type II GBS) was defined with sera from healthy adults and two populations with theoretical susceptibility to type II GBS infection--neonates and insulin-dependent diabetics. Significant opsonophagocytosis (bactericidal index, greater than or equal to 90%) of five clinical isolates of type II GBS lacking components of protein antigen c was demonstrated by each of 12 adult sera, as well as by agammaglobulinemic serum, a result indicating that opsonophagocytosis can proceed by antibody-independent activation of the classic complement pathway. Strains containing components of protein antigen c were somewhat more resistant to opsonin-binding activity. Four of 10 neonatal sera and nine of 15 diabetic sera exhibited inefficient opsonophagocytosis. Some of the adult sera with either high or low concentrations of specific antibody to type II GBS promoted opsonophagocytosis via the alternative complement pathway, but this response was not observed with neonatal sera. The addition of sufficient amounts of specific antibody to type II GBS to neonatal and adult diabetic sera in vitro, however, promoted efficient opsonophagocytosis via the alternative pathway.
Adult↗
C4B deficiency: a risk factor for bacteremia with encapsulated organisms.
The fourth component of complement (C4) is crucial to the activation of the classical complement pathway, a key defense against invading microorganisms. The two isotypes of C4, C4A and C4B, have very different in vitro activities. An increased incidence of total C4B deficiency was found in white patients with Streptococcus pneumoniae, Haemophilus influenzae, or Neisseria meningitidis infection (14% of bacteremic children vs. 2% of race-matched controls, P = .02). In black patients, however, there was no difference in incidence of C4B deficiency between bacteremic patients and race-matched controls (7% and 5%, respectively, P greater than .5). These data suggest that, at least in whites, total C4B deficiency is a risk factor for invasive disease with these three encapsulated organisms.
Adolescent↗
Molecular characterization of a novel serine protease involved in activation of the complement system by mannose-binding protein.
Mannose-binding protein (MBP) plays an important role in host defense by recognizing sugar residues on certain pathogens and activating the complement cascade. Recently, we described a new protease, designated MBP-associated serine protease (MASP) which is required for complement activation by MBP. We have cloned the cDNA that encodes this protease and found that the deduced amino acid sequence contains an epidermal growth factor-like domain, two short consensus repeats and a serine protease domain. The overall structure of MASP is similar to serine proteases of the first complement component complex, C1r-C1s. Unlike C1r-C1s, however, MASP has a histidine loop structure common to many serine proteases such as trypsin and chymotrypsin. The MASP gene was mapped on the long arm of chromosome 3 which is different from C1r-C1s as well as from trypsin and chymotrypsin. These findings suggest that MASP may have emerged prior to C1r-C1s from a common ancestor. This implies that MBP-MASP, a complex of lectin and serine protease, presumably evolved prior to adaptive immune recognition involving antibody and the classical complement pathway.
Amino Acid Sequence↗
The effect of vitamin C nutriture on complement component C1q concentrations in guinea pig plasma.
This study shows that guinea pigs fed 100 times the amount of vitamin C needed for growth and for prevention of scurvy have elevated levels of complement component C1q. C1q is a plasma protein rich in hydroxyproline, an amino acid whose biosynthesis requires ascorbate. C1q is essential for host defense against pathogens, both as a component of the classical complement pathway and as an opsonin in the phagocytosis process. We measured C1q in vitamin C-depleted guinea pigs that had been repleted for 4 wks with the following daily doses of ascorbate (mg/100 g body wt): 0.50 (suboptimal), 2.0 (adequate), 10 (ample) and 50 (tissue saturating). We measured C1q in three ways: indirectly by quantifying protein-bound hydroxyproline and directly by hemolytic assay and by immunodiffusion against anti-C1q. Regardless of the method, plasma C1q was 30-50% higher in animals fed tissue-saturating ascorbate than in those fed adequate or suboptimal amounts of the vitamin (p less than 0.05, one-way analysis of variance, least significant difference test). These data confirm and significantly extend earlier work that provided indirect evidence for a relationship between C1q and ascorbate nutriture in the guinea pig. They are consistent with a possible relationship between ascorbate nutriture and host defense.
Animals↗
Apoptosis of human polymorphonuclear neutrophils accelerated by dialysis membranes via the activation of the complement system.
BACKGROUND: Haemodialysis (HD) with bioincompatible cellulosic membranes like Cuprophan (CU) is considered to influence negatively the clinical outcome of acute and chronic renal failure. In this effect, apart from the disturbance of phagocytosis or oxygen species production by leukocytes, increased apoptosis also has been implicated recently. The objective of this study was to study the effect of HD membranes on apoptosis induction in polymorphonuclear neutrophils (PMN). METHODS: PMN from healthy donors and uraemic patients were isolated and apoptosis was induced by co-incubation with CU, Hemophan or polyamide hollow fibres in the presence of serum from healthy or uraemic humans. Apoptosis was quantified by flow cytometry using Annexin V-FITC and propidium iodide staining and was confirmed by the detection of DNA fragmentation on gel electrophoresis. The deposition of immunoglobulins (Ig) and complement factors on hollow fibres was detected by direct immunofluorescence. RESULTS: Heat inactivation or the depletion of complement components or Ig significantly reduced apoptosis, indicating its dependence on classical complement activation. The detection of IgG on hollow CU fibres and the restored acceleration of apoptosis by the appropriate replenishment of Ig-deficient sera additionally confirmed these findings. Inhibition experiments revealed that caspases were necessary mainly, but not exclusively, for apoptosis to occur after complement activation. Uraemia led to increased PMN apoptosis in the presence of bioincompatible, but not biocompatible, membranes. CONCLUSIONS: Our results suggest that the acceleration of PMN apoptosis in the presence of CU is mediated via an antibody-dependent activation of the classical complement pathway mobilizing both caspase-dependent and -independent pathways.
Apoptosis↗
Fatal anaphylactoid response to protamine after percutaneous transluminal coronary angioplasty.
A generalized skin erythema and severe hypotension developed following administration of protamine for the reversal of heparin anticoagulation after an unsuccessful attempt at percutaneous transluminal angioplasty in a patient who had never been exposed to protamines before. Evidence of classical pathway complement activation was present indicating that this reaction could have been triggered by a non-immunological mechanism. The patient could not adequately be resuscitated because of the presence of severe coronary artery disease.
Aged↗
Host defense against opportunist microorganisms following trauma. I. Studies to determine the association between changes in humoral components of host defense and septicemia in burned patients.
Total hemolytic complement (CH(50)), conversion of C3 by inulin, and immunochemical levels of Clq, C4, C2, C3, C5, factor B, C3b inactivator (KAF), and properdin were measured in the sera of 15 patients with severe thermal injury during nine weeks postburn. Five of the 15 patients had multiple episodes of septicemia as documented by positive blood cultures and clinical findings. Decrease in CH(50), Clq, C4, C2, C3, and C5 occurred prior to and during septic episodes in these patients. Although conversion of C3 by inulin was often reduced during septic episodes, levels of factor B and KAF were generally normal or elevated. In only one patient did consumption of complement occurring during septicemia decrease the opsonic capacity of the patient's sera for the patient's infecting microorganism, an isolate of E. coli; sera from the same patient opsonized her infecting strain of S. aureus normally. The microorganisms isolated from the other septic patients, which were opsonized normally by the patients' sera despite complement consumption, were also with one exception strains of Staphylococci. In the nonseptic burned patients, decrease in properdin and C3 conversion by inulin, and increase in C3, factor B and KAF were demonstrated as we have previously reported. The results indicate that the classical complement pathway was activated during septicemia in burned patients and that activation of this pathway occurred preferentially due to inhibition of the alternative pathway. In addition, the data show that complement consumption may reduce the opsonic capacity of a patient's sera for certain microorganisms and not for others.
Adolescent↗
Complement activation by cross-linked truncated and chimeric full-length beta-amyloid.
The activation of complement by beta-amyloid (A beta) has been implicated in the local inflammatory response in Alzheimer's disease. To assess the structural parameters required for this activation, beta-sheet-containing fibrils of A beta1-28 were induced by low pH and then chemically cross-linked to constrain the beta-sheet conformation. Chimeric A beta peptides with a substituted C-terminal sequence derived from two different transmembrane proteins were also assessed for the ability to form fibrils rich in beta-sheet structure and to activate complement. Both the cross-linked A beta1-28 and the chimeric A beta peptides were strong activators of the classical complement pathway. These results suggest that the C-terminal residues (29-42) of A beta facilitate fibril assembly required for complement activation but do not contain the interaction sites required for complement activation, further supporting the hypothesis that C1q binds to the N-terminal hydrophilic domain of A beta, and that a fibrillar beta-sheet-rich conformation is required for effective binding and activation of C1.
Amino Acid Sequence↗
Complement activation upon binding of mannan-binding protein to HIV envelope glycoproteins.
OBJECTIVE: Retroviruses can activate the complement system in the absence of antibodies, and the purpose of this study was to examine whether the serum collection, mannan-binding protein (MBP), could mediate such complement activation. DESIGN: Virus envelope proteins gp120 and gp110 from HIV-1 and HIV-2 were incubated in microtitre wells coated with anti-gp120 or anti-gp110 antibodies. After further incubation with serum, complement activation was measured as deposition of complement factor C4 and C3 onto the wells. Deposited C4 and C3 were detected with enzyme-labelled antibodies. Normal human serum depleted of endogenous lectins by affinity chromatography was used as the complement source. Serum from C1q-deficient patients was used in some experiments. Complement activation was then assessed with and without prior addition of MBP to the wells. Complement activation was also correlated with the quantity of endogenous MBP in a number of normal sera. RESULTS: Complement activation by HIV envelope glycoproteins was found to be mediated by the binding of MBP to carbohydrates on natural envelope protein produced in virus-infected cells, as well as on glycosylated recombinant envelope proteins produced in insect cells. Non-glycosylated recombinant envelope proteins produced in Escherichia coli did not induce this type of complement activation. CONCLUSIONS: Activation of the classical complement pathway by retrovirus envelope proteins can be initiated by the binding of MBP to carbohydrate side chains of envelope glycoproteins.
Carrier Proteins↗