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At least 1,621 records · Page 90Linked to original sources
PubMed1987

Molecular genetics of the fourth component of human complement.

The fourth component of complement in humans is coded for by two closely linked loci, i.e., C4A and C4B, that have been positioned within the class III region of the human major histocompatibility complex along with the genes for C2, Bf, and steroid 21-OH. Both C4 loci are highly polymorphic and certain alleles, particularly the nulls, are associated with susceptibility to autoimmune disease. About one-half of the null alleles are due to a large deletion that includes both a C4 and flanking 21-OH gene. Despite the near identity of the products of the two loci, the proteins differ dramatically in their efficiency of covalent binding to antigen. The amino acid substitutions responsible for the functional differences have been identified and they are clustered relatively near the covalent binding site within the C4d region of the alpha chain. These observations support the hypothesis that the susceptibility to autoimmune disease is related to the structural variation of the C4 protein.

Alleles↗
PubMed1999

Inhibitory effect of bilirubin on complement-mediated hemolysis.

We investigated the in vitro action of the bile pigments, unconjugated bilirubin (UB) and bilirubin monoglucuronide (BMG) on complement (C) cascade reaction. Both UB and BMG inhibited hemolysis in the classical pathway (CP) in a dose-dependent manner at low micromolar concentrations, UB showing a stronger effect than BMG. The analysis of the action of UB on the hemolytic activity of the C1, C4, C2 and C-EDTA components of the C cascade revealed that the C1 step was the most inhibited. An enzyme immunoassay was developed to evaluate the effect of UB on the binding of C1q, one of the subcomponents of C1, to human IgM and IgG. The study demonstrated that the unconjugated pigment interferes both the C1q-IgM and -IgG interactions, thus tentatively explaining the inhibitory action of UB on hemolytic activity of C1. We conclude that the anti-complement effect of UB is mainly exerted on the C1 component, the recognition unit of CP. The potential clinical implication of the reported effects in hyperbilirubinemia is discussed.

Animals↗
PubMed1986

Susceptibility of Campylobacter jejuni to strain-specific bactericidal activity in sera of infected patients.

Campylobacter jejuni is a common cause of inflammatory enteritis, which in normal hosts is usually self-limited and resolves without antibiotic therapy. C. jejuni bacteremia is very rare. We examined sera for bactericidal activity that might be important in limiting the extent of C. jejuni infection in man. We studied the ability of nonimmune sera and homologous and heterologous immune sera from infected patients to kill different fresh case isolates of C. jejuni in vitro. The reduction of the log10 concentration of viable C. jejuni (log10 killing) by fresh sera from nonimmune donors was only 0.2. Log10 killing by homologous acute sera varied from 0 to 3.8 (mean, 1.8). Convalescent sera showed remarkable log10 killing of only homologous C. jejuni, with values of 2.7 to 4.4 (mean, 3.7). The bactericidal effects of acute and convalescent sera were abrogated by heat and EDTA chelation, indicating mediation by complement. The role of classical complement pathway activation was supported by chelating sera with magnesium EGTA [ethylene glycol-bis(beta-aminoethyl ether)-N, N, N', N'-tetraacetic acid] and by reconstitution experiments with heat-inactivated sera, C2-deficient serum, and purified C2. The requirement of specific antibody for the serum bactericidal effect was indicated by the loss of bactericidal activity when immune sera were absorbed with homologous but not heterologous whole C. jejuni isolates. The presence of specific antibodies was further documented by agglutination of only homologous C. jejuni suspensions by heat-inactivated immune sera. Studies with polymorphonuclear leukocytes suggested that ingestion and killing of two C. jejuni strains were modest and variable in the presence of heat-inactivated homologous serum. In summary, the data document a potent serum bactericidal effect that develops rapidly and specifically during C. jejuni enteritis and may be an important factor in host defense against C. jejuni.

Antibodies, Bacterial↗
PubMed1995

Influence of humoral immunity on leukotriene B4 production by neutrophils in response to Trichomonas vaginalis stimulation.

Neutrophils are the predominant inflammatory cells found in vaginal discharges from patients with Trichomonas vaginalis infection. In this study, we investigated the effect of humoral immunity on leukotriene B4 (LTB4) generation by neutrophils in the inflammatory response of vaginal trichomoniasis. As quantitated by a radioimmunoassay, no release of LTB4 was detected from neutrophils (5 x 10(6)/ml) interacted with trichomonads (1 x 10(6)/ml). However, specific immunoglobulin G(IgG) but not F(ab')2, at a titre of 1:256 directed against T. vaginalis, augmented LTB4 production (1.4 +/- 0.4 ng/ml, n = 5) by neutrophils, suggesting that this enhancement is Fc gamma receptor-mediated. Moreover, addition of the specific IgG (1 mg/ml) to C2-deficient serum or Factor B-deficient serum, but not C5-deficient serum, significantly increased LTB4 production by neutrophils in response to trichomonad stimulation. This indicates that the complement common pathway activation is crucial for the amplification of host defence mechanisms against T. vaginalis. An LTB4 receptor antagonist, SC-41930, completely abolished neutrophil chemotactic activity induced by LTB4. Taken together, these results indicate that humoral immunity could promote the interaction of neutrophils with T. vaginalis and augment the inflammatory response through the amplification of LTB4 production.

Animals↗
PubMed2002

Activation of the lectin complement pathway by H-ficolin (Hakata antigen).

Ficolins are a group of proteins which consist of a collagen-like domain and a fibrinogen-like domain. In human serum, there are two types of ficolins named L-ficolin/P35 and H-ficolin (Hakata Ag), both of which have lectin activity. We recently demonstrated that L-ficolin/P35 is associated with mannose-binding lectin (MBL)-associated serine proteases (MASP) 1 and 2 and small MBL-associated protein (sMAP), and that the complex activates the lectin pathway. In this study, we report the characterization of H-ficolin in terms of its ability to activate complement. Western blotting analysis showed the presence of MASP-1, MASP-2, MASP-3, and sMAP in H-ficolin preparations isolated from Cohn Fraction III. The MASPs in the preparations had proteolytic activities against C4, C2, and C3 in the fluid phase. When H-ficolin preparations were bound to anti-H-ficolin Ab which had been coated on ELISA plates, they activated C4, although no C4 activation was noted when anti-MBL and anti-L-ficolin/P35 were used. H-ficolin binds to PSA, a polysaccharide produced by Aerococcus viridans. C4 was activated by H-ficolin preparations bound to PSA which had been coated on ELISA plates. These results indicate that H-ficolin is a second ficolin which is associated with MASPs and sMAP, and which activates the lectin pathway.

Antibodies, Monoclonal↗
PubMed1982

On the lysis of paroxysmal nocturnal hemoglobinuria erythrocytes by complement: dual role of C3b.

The efficiency of cytolysis by the terminal complement proteins C5b-9 can be markedly enhanced by C3b molecules bound on the target cell membrane (Hammer et al. 1976). This enhancement was shown to be proportional to the number of C3b molecules on the cell membrane. The present experiments have shown that the hemolytic efficiency of the complement membrane attack system is two to five times greater on paroxysmal nocturnal hemoglobulinuria erythrocytes (PNHE) than on normal human E. This difference is attribute to a derivative of C3, probably C3b, on PNHE since it was abolished by anti-C3 but not by anti-C2. The efficiency of C5b-9 to lyse PNHE was only partially decreased by C3b inactivator and beta 1 H, indicating that the C3b on PNHE is not readily inactivated by its regulatory proteins. Furthermore, cells from a single severely affected patient consumed 3-fold more C5b6 than normal human E yet concommitantly measured membrane fluidity was normal. From these observations we conclude that cell-bound C3b on PNHE serves two functions: (a) it increases the hemolytic efficiency of membrane attack components of the complement system; and (b) it provides sites for assembly of the alternative pathway convertases.

Complement C3b↗
PubMed1993

Activation of the alternative complement pathway and production of factor H by skeletal myotubes.

Skeletal muscle myotubes from neonatal rats were used to study the interaction of skeletal muscle with complement. Serum from guinea pig, rabbit, and human, in the absence of muscle-specific antibody, caused creatine phosphokinase release, which required activation of the terminal complement cascade. Cleavage of serum C3 and Factor B in the presence of myotubes was dependent on Mg2+, but not Ca2+, and C3 cleavage occurred only in the presence of Factor B. Rat myotubes caused significant consumption of C8 and C9 in rat serum, which also required Mg2+, but not Ca2+. All of these findings are typical of a tissue capable of activating the alternative pathway. In addition, the C2 myotube cell line was shown to produce Factor H, an inhibitory protein of the alternative pathway, as demonstrated by Factor H mRNA expression and immunoprecipitation of the protein.

Animals↗
PubMed1996

Effect of chorioamnionitis on the levels of serum proteins in the cord blood of premature infants.

OBJECTIVE: To determine the relationships among complements, other serum proteins (including acute-phase reactant), and the cytokine interleukin-6. DESIGN: Prospective observational study. SETTING: A perinatal center, children's hospital, and research institute in Osaka, Japan. PATIENTS: Two hundred fifteen newborn infants ranging from 17 to 42 weeks in gestational age. MAIN OUTCOME MEASURES: We measured the serum levels of several proteins and complements in the cord blood of neonates with and without chorioamnionitis by immunological assays. RESULTS: The levels of C3d, haptoglobin, interleukin-6, IgM, C-reactive protein, and IgA were not influenced by gestational age, and levels of C5, C1q, C2, albumin, C9, and IgG were not influenced by chorioamnionitis status. The levels of C3, C4, CH50, factor B, and orosomucoid were influenced by both factors. CONCLUSIONS: Our investigation of the mutual relation of the data suggests that the increase of cytokine interleukin-6 affects each other component. We suggest that, compared with the serum levels of proteins in neonates with chorioamnionitis, levels in neonates without chorioamnionitis are more similar to those in the normal fetus.

Blood Proteins↗
PubMed1997

Surface loops adjacent to the cation-binding site of the complement factor B von Willebrand factor type A module determine C3b binding specificity.

The interaction of factor B with C3b deposited on the surface of pathogens is the first step in the activation of the alternative complement pathway. The role of the von Willebrand factor type A (VWFA) module of factor B in this interaction has been investigated by generating three chimeras, Ch1-Ch3, in which surface loops of the VWFA module flanking the cation-binding residues were replaced by the corresponding sequences of C2, a factor B-like molecule which does not bind C3b. The location of the three loops was inferred from a homology model based on the structure of the integrin alphaM VWFA module [Ch1, betaA-alpha1 loop: Ch2, alpha3-alpha4 loop; and Ch3, betaD-alpha5 loop; Lee, J.-O., et al. (1995b) Cell 80, 631-638]. The function of the chimeras was studied by means of hemolytic assays and assays of the individual steps of the alternative complement pathway, i.e., binding to the C3b analogue cobra venom factor and factor D cleavage. These experiments showed that Ch1 and Ch3 define regions that are involved in C3b binding whereas Ch2 does not appear to be involved in binding specificity. The inability of Ch1 to register the enhancement of cobra venom factor binding normally seen after factor D cleavage suggested that the betaA-alpha1 loop mediates the conformational regulation of ligand binding affinity. Homology modeling of the chimeras has been used to visualize the surface structures which potentially define the C3b binding site.

Amino Acid Sequence↗
PubMed1981

Hypocomplementemia in Reye syndrome: relationship to disease stage, circulating immune complexes, and C3b amplification loop protein synthesis.

Measurement of C1q, C2, C4, C5, C6, factor B, properdin, beta1H, and C3bINA were made in acute sera from 31 patients with Reye syndrome. Abnormalities were found in 18 patients. The magnitude of the complement component depression correlated with disease severity. Sera from patients with stage IV illness had significantly lower complement levels than did sera from patients with state I (P less than 0.001), II (P less than 0.05), and III (P less than 0.05) disease. Circulating immune complex measurements were performed on all 31 acute sera and were present in six (19%). However, from the results of the present study, it would appear that in the majority of the patients circulating immune complexes are not the cause of the lowered levels of, at least, C3 and factor B. Rather, these low levels could be explained as secondary to reductions in the levels of the C3b amplification loop control proteins beta1H and C3bINA.

Antigen-Antibody Complex↗
PubMed1988

Hereditary C3 hypocomplementemia in the rabbit.

Hereditary hypocomplementemia of the third component of complement (C3) was found in a strain of rabbits in which hereditary C8 alpha-gamma deficiency was also found. The serum C3 concentration, haemolytic C3 activity and total complement haemolytic activity (CH50) of these animals were, respectively, 6-12%, 8-13% and 27-37% of the normal levels. The haemolytic complement activity in the C3 hypocomplementemic (C3-hypo) rabbit serum was restored in a dose-dependent manner by the addition of purified rabbit C3. The levels of factor H and properdin and components C2 and C6 were in the normal range, and the levels of factors B and D and component C8 were higher than normal. The low level of serum C3 in C3-hypo rabbits was not due to C3 conversion, partial C3 antigenicity, presence of a C3 inhibitor or hypercatabolism of normal C3. Furthermore, no change in the ratio of C3 protein levels was observed between C3-hypo and normal rabbits, even after turpentine injection. In addition, the C8 alpha-gamma deficiency condition does not affect C3 activity and C3 catabolism in vivo. Mating tests showed that the C3 hypocomplementemia is transmitted as a simple autosomal co-dominant trait. C3-hypo rabbits have a lower survival at 3 months than normal rabbits. C3-hypo rabbit serum also has a lower bactericidal activity than normal rabbit serum. The PAGE under reducing conditions showed no difference in the molecular weights of C3 alpha and C3 beta chains between C3-hypo, heterozygous and normal animals.

Aging↗
PubMed1986

Activation of the alternative pathway of complement by DL-2-mercaptomethyl-3-guanidinoethylthiopropanoic acid (Mergetpa).

Incubation of normal human serum with 3-5 mM Mergetpa causes activation of the alternative pathway of complement as indicated by fragmentation of C3 and factor B, dependent on the presence of divalent cations. Mergetpa inhibits the regulatory protein factor I and, as a consequence, may allow initiation of the feedback cycle of the alternative pathway by deregulation. The classical pathway is not or only to a minor extent activated. A decrease in the hemolytic activity of C2, C5 and one or several of the components C6-9 in the presence of 5 mM Mergetpa may be explained by direct inactivation. The described effects are probably mediated by Mergetpa acting as a thiol.

3-Mercaptopropionic Acid↗
PubMed1996

Activation of the complement, coagulation, fibrinolytic and kallikrein-kinin systems during attacks of hereditary angioedema.

Five patients with hereditary angioedema (HAE) were studied during attacks and remission as were healthy controls. The high levels of C1/C1-INH complexes, low C4 and high ratio C4 activation products (C4bc)/C4 also differed significantly during remission compared to controls. During attacks C4bc/C4 increased (922-2007; P = 0.022, remission versus attacks, median values throughout), C2 and CH50 dropped (111-31%; P = 0.043 and 110-36%; P = 0.016, respectively), TCC (C5b-9) increased (0.88-1.23 AU/ml; P = 0.028). Cleavage of HK increased to be almost complete during attacks (20-90%; P = 0.009). While factor XIa/serpin-complexes did not increase, a more than twofold rise in thrombin/antithrombin-complexes (0.20-0.50 microgram/l; P = 0.009) and in plasmin/alpha-2-antiplasmin-complexes (7.3-17 nmol/l; P = 0.028) was observed. For the first time cascade activation in HAE was studied simultaneously, and corroborates that attacks lead to activation of the kallikrein-kinin system, fibrinolysis and early part of the classical complement pathway. In addition, the authors present novel data of terminal complement and coagulation activation, the latter apparently not via FXIa.

Angioedema↗
PubMed1990

[Mapping of the c-region of the temperate phage 59 of Erwinia carotovora 268].

The present communication deals with the genetic mapping of the temperate bacteriophage 59 immunity region. Morphological mutants of the c-type of the temperate bacteriophage 59 were isolated after UV-treatment of the phage. Complementation analysis of 36 c-mutants has shown that the bacteriophage 59 c-region consists of at least four genes responsible for the establishment of lysogenization. The two-factor crosses were used to determine the mutual positions (order and distances) of the c-mutations. The order of the c-genes is C1--C3--C2--C4. The three c-genes are localized in a short region of the phage 59 chromosome, but the fourth gene is located in the separate locus.

Bacteriophages↗
PubMed1986

Sheep serum complement sensitisation of sheep erythrocyte-rabbit antibody complexes for haemolysis by guinea-pig complement plus EDTA or Mg2+-EGTA.

Sheep erythrocyte (E)-rabbit antibody (A) complexes incubated with sheep serum diluted up to 1:5120 or 1:20480 and washed can be haemolysed by guinea-pig (g-p) serum (complement, C) containing EDTA or Mg2+-EGTA respectively as haemolytic finishing reagents. Sheep E carrying a high dose of rabbit A were necessary for this reaction, particularly with g-p C-EDTA. G-p serum (stored by freezing) was active as a haemolytic finishing reagent with both EDTA and Mg2+-EGTA. Reconstituted freeze-dried g-p serum (also stored by freezing) was haemolytically active with Mg2+-EGTA only. G-p serum preserved by Richardson's method did not function as a finishing reagent with EDTA or Mg2+-EGTA. A non-haemolytic prozone occurred with sheep E-rabbit A treated with dilutions of sheep serum or body fluid up to 1:160, particularly when g-p C (frozen)-EDTA was used as the finishing reagent. Sheep E-rabbit A were sensitized by serum, foetal lamb serum, pericardiac-, synovial- or ovarian follicle-fluids colostrum or milk for haemolysis by g-p C (frozen)-EDTA or -Mg2+-EGTA. With the C3 inhibitors cobra venom factor or salicylaldoxime, serum sensitisation of sheep E-rabbit A for haemolysis by g-p C (frozen)-EDTA or -Mg2+-EGTA was not blocked. Sensitisation by serum heated at 50 degrees C for 30 min (partial inactivation of C2) was incomplete. Inhibitors of C1 (antrypol, chelators of Ca2+ or heating serum at 56 degrees C for 30 min) partially or fully blocked sensitisation for haemolysis by both g-p C (frozen)-EDTA or -Mg2+-EGTA. These results show that at a minimum, components C1, C4 and C2 are present and functionally active in serum and some body fluids of sheep.

Animals↗
PubMed1985

Angioedema.

Angioedema is characterized by a well-demarcated swelling on the skin, oropharyngolaryngeal tissue, or the gastrointestinal wall. Underlying mechanisms may include IgE-mediated reactions, complement activation, inhibition of the cyclo-oxygenase pathway of arachidonic acid metabolism, direct release of mediators from mast cells, and activation of the kinin-forming system. Foods, drugs, inhalants, insect bites, blood transfusion, collagen vascular disease, infections, physical factors, neoplasms, and hereditary factors can cause angioedema through one or more of these mechanisms. Chronic angioedema lasts more than 6 weeks or recurs during this period. Acute angioedema is a self-limited disorder and resolves spontaneously, or with simple therapy, in several days; the patient rarely requires a complete work-up. Chronic angioedema may necessitate a detailed history, physical examination, and limited clinical or laboratory tests to exclude serious underlying illnesses. The H1 antihistamines are used for the treatment of both acute and chronic angioedema. An H2 antihistamine, a second H1 antihistamine, or rarely even a low dose of corticosteroid may be added to the regimen if H1 antihistamine alone fails to control chronic angioedema. Hereditary angioedema is an autosomal dominant disease that is caused by C1INH deficiency. In patients with this disorder, swelling of the lip, pharynx, and extremities may follow trauma to soft tissue. Other clinical manifestations include abdominal pain, nausea, vomiting, and suffocation because of laryngeal swelling. Diagnosis can be confirmed by the finding of low levels of C4 and C2 and the absence of nonfunction of C1INH. Androgens reverse the biochemical defects.

Angioedema↗
PubMed1985

The complement components coded in the major histocompatibility complexes and their biological activities.

The complement system has two pathways of activity, both dependent on the sequential conversion of proteolytic zymogens to active proteases leading to a common lytic complex and both with control proteins which inhibit or inactivate different steps in the cascade. Three of the components--C2, factor B and C4--are coded by closely linked genes in the MHC of man and mouse and have been placed relative to each other. The genes are polymorphic, particularly C4, with variable numbers of loci as well as many mutant forms. Some alleles of C4 show strikingly different reactivities in their haemolytic activity and this may be relevant to the association of susceptibility to autoimmune diseases with particular haplotypes in this section of HLA.

Alleles↗