PubMed Health⌕ Search

SEARCH · PubMed Health

Results for “Complement Pathway, Alternative”

Explore indexed PubMed citations for clinical trials, systematic reviews and public health research. Read source abstracts and follow each citation to its original PubMed record.

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

At least 1,369 records · Page 76Linked to original sources
PubMed2004

The alternative activation pathway and complement component C3 are critical for a protective immune response against Pseudomonas aeruginosa in a murine model of pneumonia.

Pseudomonas aeruginosa is a leading cause of hospital-acquired pneumonia, and approximately 80% of patients with cystic fibrosis are infected with this bacterium. To investigate the overall role of complement and the complement activation pathways in the host defense against P. aeruginosa pulmonary infection, we challenged C3-, C4-, and factor B-deficient mice with P. aeruginosa via intranasal inoculation. In these studies, C3(-/-) mice had a higher mortality rate than C3(+/+) mice. Factor B(-/-) mice, but not C4(-/-) mice, infected with P. aeruginosa had a mortality rate similar to that of C3(-/-) mice, indicating that in this model the alternative pathway of complement activation is required for the host defense against Pseudomonas infection. C3(-/-) mice had 6- to 7-fold more bacteria in the lungs and 48-fold more bacteria in the blood than did C3(+/+) mice at 24 h postinfection. In vitro, phagocytic cells from C3(+/+) or C3(-/-) mice exhibited a decreased ability to bind and/or ingest P. aeruginosa in the presence of C3-deficient serum compared to phagocytic cells in the presence of serum with sufficient C3. C3(-/-) mice displayed a significant increase in neutrophils in the lungs and had higher levels of interleukin-1beta (IL-1beta), IL-6, IL-10, KC, and MIP-2 in the lungs at 24 h postinfection than did C3(+/+) mice. Collectively, these results indicate that complement activation by the alternative pathway is critical for the survival of mice infected with P. aeruginosa and that the protection provided by complement is at least in part due to C3-mediated opsonization and phagocytosis of P. aeruginosa.

Animals↗
PubMed1990

Complement activation and white cell sequestration in postischemic skeletal muscle.

After skeletal muscle ischemia, tissue damage is augmented during reperfusion. White blood cells (WBCs) and complement proteins may participate in the reperfusion injury. The purpose of this study was to define the kinetics of classical and alternative pathway complement activation and WBC sequestration by postischemic skeletal muscle during the first 48 h of reperfusion in vivo. The isolated canine gracilis muscle model was used. Systemic levels of the complement proteins factor B (alternative pathway) and C4 (classical pathway) were quantitated by hemolytic assay. WBC sequestration was measured by gracilis arterial-venous WBC differences and tissue myeloperoxidase activity. Reperfusion was associated with an 18% decrease in systemic factor B levels but no consistent change in systemic C4 levels. WBCs were sequestered during the first 4 h of reperfusion, and tissue myeloperoxidase activity was elevated 97-fold after 48 h of reperfusion. These results suggest that skeletal muscle ischemia-reperfusion stimulates 1) activation of the alternative but not the classical complement pathway and 2) an immediate and prolonged sequestration of WBCs.

Animals↗
PubMed1986

The C3 convertase of the alternative pathway of human complement. Enzymic properties of the bimolecular proteinase.

The association of Factor B with C3b (the major fragment of complement component C3) in the presence of Mg2+ results in the formation of a bimolecular zymogen, C3b,B, which is activated by the serine proteinase Factor D, generating the C3 convertase, C3b,Bb (EC 3.4.21.47). Cleavage of native C3 by the C3 convertase was monitored by recording the increase in fluorescence associated with C3b formation in the presence of the fluorescent probe 8-anilinonaphthalene-1-sulphonate. Measurements of initial rates of C3b formation at various C3 concentrations were analysed in accordance with the Michaelis-Menten equation, yielding kcat. = 1.78 +/- 0.08 s-1, Km = 5.86 X 10(-6) M and turnover number = 107 min-1. The assay was used to measure the Ki values of a variety of proteinase inhibitors. The C3 convertase has a short half-life, owing to spontaneous dissociation of the complex. The t1/2 and kcat./Km of the enzyme were determined by fitting an equation modelling both the kinetic reaction and enzyme decay to the fluorimetrically measured progress curve. The enzyme, C3b,Bb, exhibited a t1/2 of 90 +/- 2 s and a kcat./Km of 31.1 X 10(4) +/- 0.8 X 10(4) M-1 X s-1 at physiological pH, ionic strength and temperature. The enzyme that initiates activation of the alternative pathway, C3(H2O),Bb, was also examined. It was slightly less stable (t1/2 = 77 +/- 3 s) and exhibited only half the activity of C3b,Bb (kcat./Km = 16.3 X 10(4) +/- 1.0 X 10(4) M-1 X s-1).

Complement Activating Enzymes↗
PubMedDate not supplied

Rapid activation of the alternative pathway of complement by extracorporeal membrane oxygenation.

Extracorporeal membrane oxygenation (ECMO) is an effective therapy for patients with severe respiratory distress syndromes. However, an inflammatory response has been observed with the use of this therapy. We measured complement activation in vivo in two adults receiving ECMO for acute respiratory distress syndrome (ARDS). Production of complement activation fragments C4d, Bb, iC3b, and SC5b-9 was determined using commercial ELISA kits. In both patients there was intense activation of complement that peaked 1 hour (mean SC5b-9 increase to 1135% of baseline) after the start of ECMO and occurred predominantly via the alternative pathway (Bb production). Early and acute complement activation may be responsible for the initiation of the inflammatory response that has been observed in patients treated with ECMO.

Adult↗
PubMed1990

Activation of the human complement system by phenolic glycolipid 1 of Mycobacterium leprae.

The activation of the complement system by phenolic glycolipid 1 (PGL) from Mycobacterium leprae was studied. It was found that PGL consumed haemolytic complement through both the classical and the alternative pathways. This was further studied at the level of C3. Although the activation was independent of anti-PGL antibodies present in normal human serum, the addition of antibody augmented the activation of complement by PGL. The uptake of C3 through the classical pathway was enhanced predominantly by IgM antibody whereas, IgG antibody against PGL was responsible for the augmentation of the alternative pathway activation. Furthermore, it was found that both the disaccharide and trisaccharide components of PGL were able to activate the complement system.

Antigens, Bacterial↗
PubMed1980

Immunological, structural and functional relationships between an anti-complementary protein from Crotalus atrox venom, cobra venom factor and human C3.

An anti-complementary protein which cross-reacts with antiserum to cobra venom factor (CoF) has been highly purified from Crotalus atrox venom (CAV). On an equal weight basis, the C. atrox factor (CA-F) had one-third the anti-complementary activity of CoF and similarly consumed the terminal components of complement via the alternative pathway. The subunit compositions of CoF and CAV were similar, each being composed of alpha and beta chains held together by covalent and non-covalent bonds. Agarose gel diffusion analysis using monospecific antiserum to CoF detected a reaction of partial immunological identity between CoF and CA-F and between C3 and CA-F with the CoF and C3 precipitin lines spurring over the CA-F lines. Thus CA-F probably represents a C. atrox C3 protein which is capable of activating the alternative complement pathway via the amplification loop in a manner analogous to that of C3b and CoF.

Animals↗
PubMed1990

[Plasma levels of complement fragments during hemodialysis in patients with chronic renal failure].

The kinetics of hemodialysis-induced leukopenia and generation of complement fragments including C3a, C5a, C4d, iC3b and Bb were investigated in 14 patients during hemodialysis using cellulose acetate (CA), cuprophan (Cu) and ethylenevinyl alcohol (EVA) membranes. A marked leukopenia in the first 15 minutes was observed in CA and Cu. Plasma C3a levels were higher in CA than in Cu and EVA. Plasma C5a levels were higher in CA and Cu than in EVA. There was a negative correlation between the white blood cell counts and plasma C5a levels at 15 minutes (gamma = -0.85, p less than 0.001). Plasma C4d levels showed no increase in all membranes. Plasma iC3b levels were higher significantly in Cu than in CA and EVA. Plasma Bb levels in the first 15 minutes increased significantly in all membranes, and furthermore continued to increase till the end of hemodialysis in CA and Cu. This study revealed that all the membranes tested activated the complement via the alternative pathway to produce Bb, iC3b, C3a and C5a. C5a was thought to take an important role in transient leukopenia. Furthermore, Bb was accumulated during hemodialysis in CA and Cu, and its biological effects on patients undergoing hemodialysis should be studied.

Adult↗
PubMed1981

The binding of complement component C3 to antibody-antigen aggregates after activation of the alternative pathway in human serum.

Preformed immune aggregates, containing antigen and either IgG (immunoglobulin G) or F(ab')2 rabbit antibody, were incubated with normal human serum under conditions allowing activation of only the alternative pathway of complement. Both the IgG and F(ab')2 immune aggregates bound C3b, the activated form of the complement component C3, in a similar manner, 2-3% of the C3 available in the serum being bound to the aggregates as C3b, and the rest remaining in the fluid phase as inactive C3b or uncleaved C3. It was found that the C3b was probably covalently bound to the IgG in the aggregates, since C3b-IgG complexes could be demonstrated on sodium dodecyl sulphate/polyacrylamide-gel electrophoresis, after repeated washing with buffers containing high salt or boiling under denaturing conditions. Incubation of the C3b-antibody-antigen aggregates in buffers known to destroy ester linkages had little effect on the C3b-IgG complexes, which suggested that C3b and IgG might be linked by an amide bond. Two main types of C3b-IgG complexes were found that had apparent mol.wts. of 360000 and 580000, corresponding to either one to two C3b molecules respectively bound to one molecule of antibody. On reduction of the C3b-IgG complexes it was found that the beta-chain, but not the alpha'-chain, of C3b was released along with all the light chain of IgG but only about half or less of the heavy chain of IgG. These results indicate that, during activation of the alternative pathway of complement by immune aggregates containing IgG antibody, the alpha'-chain of C3b may become covalently bound at one or two sites in the Fd portion of the heavy chain of IgG.

Antigen-Antibody Complex↗
PubMed2001

Pediatric cardiac surgery with cardiopulmonary bypass: pathways contributing to transient systemic immune suppression.

Cardiovascular surgery with cardiopulmonary bypass (CPB) can lead to postoperative complications like postpericardiotomy syndrome (PPS), capillary leak syndrome, or multiple organ failure. In children, PPS morbidity is up to 30%, and intra- and immediate postoperative mortality is up to 4%. For these complications, the CPB is made responsible. Its etiology is not yet clarified in detail, but is thought to be of immunologic origin. The exact knowledge of these reactions is crucial for the selection of treatment strategies. The immune response to CPB surgery in children comprises of a cascade of pro- and anti-inflammatory events. Proinflammatory responses are indicated by the release of interleukin (IL)-6 and IL-8, and the activation of alternative complement pathway. This reaction is mainly a response to surgical trauma and medication and only activation of the alternative complement pathway is CPB specific. Antiinflammatory response during CPB surgery is serologically indicated by the systemic release of the immunosuppressive cytokine IL-10 already before that of proinflammatory cytokines. CPB surgery induces population shifts of the leukocyte subsets, changes their degree of activation, and contributes to the phenotype of a peripheral immune suppression. Circulating neutrophils are selectively filtered and inactivated. T-helper (Th) cells shift transiently to the Th2 phenotype, indicating the prevalence for a humoral immune response. These alterations start immediately after the onset of the CPB. Increased immunosuppression may be involved in PPS development and may be linked to an allergic/atopic predisposition. A generalized model of the immune sequela to pediatric cardiovascular surgery with CPB is drawn. CPB induces a systemic transient anti-inflammatory response by elimination of activated cells, by compensatory reaction to local, systemically not observable, proinflammatory responses, by IL-10 release, by anesthetics and medication, and by leukocyte extravasation. The subsequent proinflammatory reaction is the reaction to surgical trauma modulating the anti-inflammatory reaction. Possible therapeutic consequences of these findings may include treatment strategies that modulate the anti-inflammatory response. More studies are needed to test this hypothesis.

Cardiac Surgical Procedures↗
PubMed1991

Molecular cloning of the cDNA coding for properdin, a positive regulator of the alternative pathway of human complement.

Northern blot analysis indicated that the mRNA for human properdin is approximately 1.5 kb long and that its level in U-937 cells is increased by pretreating the cells with phorbol 12-myristate 13-acetate (PMA). Using a human genomic probe clones coding for human properdin were isolated from a lambda gt10 cDNA library derived from PMA-treated U-937 cells. The sequence of the 1474-bp cDNA insert of the longest clone revealed an open reading fram of 1326 bp coding for the entire 442 amino acids of the mature form of human properdin and 67 bp coding for 22 amino acids of typical, but incomplete leader sequence. Polymerase chain reaction "RACE" experiments identified the start site ATG and revealed the complete, 27-amino acid-long, leader peptide sequence. Within the 81-bp 3' non-translated extension a polyadenylation signal was identified 41 bp downstream from the stop codon, TAA, and 12 bp upstream of a 19 nucleotide long poly(A) tail. The amino acid sequence of human properdin is clearly divided into three distinct regions: a 49 residue-long N-terminal region, a 32 residue-long C-terminal region and a middle region, covering residues 50 to 411, composed of six tandemly repeated thrombospondin repeat (TSR) motifs of the type first described in the adhesive glycoprotein thrombospondin and also known to be present in the C6, C7, C8 alpha, C8 beta and C9 terminal components of complement. Human and mouse properdin sequences show a high (approximately 76%) degree of identity with almost complete conservation of the relatively large number of Cys (44) and Trp (20) residues.

Amino Acid Sequence↗
PubMed1987

Covalent conjugates of monoclonal antibody and cobra venom factor mediate specific cytotoxicity via alternative pathway of human complement activation.

Because of lack of unspecific toxicity autologous serum is the optimal source of complement for in vitro cell depletion in human bone marrow transplantation. Covalent binding of cobra venom factor to an antibody leads to a specific complement activating conjugate with cytolytic potential independent of the capacity of the antibody to fix complement itself. Therefore this conjugation allows the use of various sera, including human as the source of complement. The kinetics of cobra venom factor-initiated cytolysis is compatible with in vitro treatment of bone marrow prior to transplantation.

Antibodies, Monoclonal↗
PubMed1980

Factor D of the alternative pathway of human complement. Purification, alignment and N-terminal amino acid sequences of the major cyanogen bromide fragments, and localization of the serine residue at the active site.

The serine esterase factor D of the complement system was purified from outdated human plasma with a yield of 20% of the initial haemolytic activity found in serum. This represented an approx. 60 000-fold purification. The final product was homogeneous as judged by sodium dodecyl sulphate/polyacrylamide-gel electrophoresis (with an apparent mol.wt. of 24 000), its migration as a single component in a variety of fractionation procedures based on size and charge, and its N-terminal amino-acid-sequence analysis. The N-terminal amino acid sequence of the first 36 residues of the intact molecule was found to be homologous with the N-terminal amino acid sequences of the catalytic chains of other serine esterases. Factor D showed an especially strong homology (greater than 60% identity) with rat 'group-specific protease' [Woodbury, Katunuma, Kobayashi, Titani, & Neurath (1978) Biochemistry 17, 811-819] over the first 16 amino acid residues. This similarity is of interest since it is considered that both enzymes may be synthesized in their active, rather than zymogen, forms. The three major CNBr fragments of factor D, which had apparent mol.wts. of 15 800, 6600 and 1700, were purified and then aligned by N-terminal amino acid sequence analysis and amino acid analysis. By using factor D labelled with di-[1,3-14C]isopropylphosphofluoridate it was shown that the CNBr fragment of apparent mol.wt. 6600, which is located in the C-terminal region of factor D, contained the active serine residue. The amino acid sequence around this residue was determined.

Amino Acid Sequence↗
PubMed1991

Pathogenesis of intraabdominal abscess formation: abscess-potentiating agents and inhibition of complement-dependent opsonization of abscess-inducing bacteria.

Bacteroides fragilis and Escherichia coli are synergistic in the production of intraabdominal abscesses. However, these bacteria initiate abscess formation only when inoculated with an agent such as autoclaved colonic contents (ACC) or bran (a fiber analogue). The mechanism of action of the abscess-potentiating agent was studied. Opsonins in normal mouse serum were determined for phagocytic killing by murine neutrophils of B. fragilis and E. coli. Opsonization required fixation of complement by the alternative pathway. ACC (0.2 mg/ml) and bran (1.0 mg/ml) inhibited phagocytic killing of Proteus mirabilis in the presence of normal but not immune serum. Assay of the alternative pathway of complement activation indicated that both bacterial components and abscess-potentiating agents in an abscess-inducing mixture activated complement. These findings suggest that abscess-potentiating agents inhibit opsonization and therefore the subsequent phagocytic killing of bacteria in the nonimmune host.

Abscess↗
PubMed2004

Heterozygous and homozygous factor h deficiencies associated with hemolytic uremic syndrome or membranoproliferative glomerulonephritis: report and genetic analysis of 16 cases.

Factor H (FH) is the major regulatory protein of the complement alternative pathway, with a structure consisting of a tandem array of 20 homologous units, called short consensus repeats (SCR). Reported are 16 FH-deficient patients. Among six patients with homozygous deficiency, four presented with membranoproliferative glomerulonephritis, and two with atypical hemolytic uremic syndrome (HUS). The ten other patients had heterozygous FH deficiency and developed atypical HUS. HUS onset occurred from birth to midadulthood, and disease progression was variable. Four children with homozygous or heterozygous FH deficiency and HUS underwent renal transplantation, which was successful in three but failed as a result of recurrence of HUS in one patient. All but one patient exhibited alternative pathway-mediated complement consumption, with no detectable FH antigenic levels or with 50% immunochemical or functional FH levels in the case of complete or partial deficiency, respectively. The molecular mechanisms of the deficiency were documented in all cases by exon-specific sequencing analysis. These mechanisms included nucleotide substitutions, insertion, or deletion located in SCR 2, 7, 11, 13, 15, and 20, leading to an amino acid substitution or to a stop codon. This report emphasizes the variability in the clinical progression of kidney diseases associated with FH deficiencies. Genetic analysis reveals the molecular abnormalities associated with FH deficiencies to be polymorphous.

Adult↗
PubMed1978

Activation of classical complement pathway by naturally occurring heteroantibodies in normal rabbit serum. Effect on subpopulations of human lymphoid cells.

Heteroantibodies present in normal rabbit serum (NRS) are toxic to human B lymphocytes, T lymphocytes, and monocytes. Even NRS, which exhibits little back ground cytotoxicity for human lymphoid cells in conventional HLA or B-cell lymphocytotoxic assays, can be shown to contain considerable activity by making two modifications in usual procedures: by washing cells in saline or balanced salt solutions devoid of protein or sugar substances, and by increasing incubation time for 1 h to 3--4 h. Using such modifications, the cytotoxic activity of NRS towards human lymphoid cells was investigated and was found to involve activation of the classical complement pathway rather than activation of the alternate complement pathway. Residual unwanted background cytotoxicity of NRS toward human lymphoid cells can be decreased without loss of desired complement activity either by heating NRS for 15 min at 50 degrees C or by mixing NRS with small amounts of normal human serum.

Animals↗