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PubMed2006

Generation of C5a in the absence of C3: a new complement activation pathway.

Complement-mediated tissue injury in humans occurs upon deposition of immune complexes, such as in autoimmune diseases and acute respiratory distress syndrome. Acute lung inflammatory injury in wild-type and C3-/- mice after deposition of IgG immune complexes was of equivalent intensity and was C5a dependent, but injury was greatly attenuated in Hc-/- mice (Hc encodes C5). Injury in lungs of C3-/- mice and C5a levels in bronchoalveolar lavage (BAL) fluids from these mice were greatly reduced in the presence of antithrombin III (ATIII) or hirudin but were not reduced in similarly treated C3+/+ mice. Plasma from C3-/- mice contained threefold higher levels of thrombin activity compared to plasma from C3+/+ mice. There were higher levels of F2 mRNA (encoding prothrombin) as well as prothrombin and thrombin protein in liver of C3-/- mice compared to C3+/+ mice. A potent solid-phase C5 convertase was generated using plasma from either C3+/+ or C3-/- mice. Human C5 incubated with thrombin generated C5a that was biologically active. These data suggest that, in the genetic absence of C3, thrombin substitutes for the C3-dependent C5 convertase. This linkage between the complement and coagulation pathways may represent a new pathway of complement activation.

Animals↗
PubMed1981

Reduction in alternative complement pathway mediated C3 conversion following burn injury.

Studies were performed to further investigate an abnormality of the alternative complement pathway associated with burn injury. C3 conversion by inulin and cobra venom factor was measured in serial serum samples from 18 burned patients and in the sera from 25 normal controls. C3 conversion by both activating substances in the patients' sera was significantly decreased during 50 days postburn in comparison to C3 conversion in the normal sera. The most marked reduction in C3 conversion occurred in patients with large full-thickness injuries and infectious complications. However, the abnormality was not more severe in patients with pneumonia and bacteremia in comparison to patients with bacteremia only. It was also not predictive of fatal outcome resulting from infectious complications. Preliminary evidence was presented to suggest that the abnormality is caused by a serum inhibitor, which has an affinity for cellulose and/or is inactivated by it.

Adolescent↗
PubMed1992

Hyperosmolality impairs ammonia-mediated inflammation: implications for the renal medulla.

Although ammonia modifies the third component of complement (C3) and activates the alternative pathway, inflammation is not seen in the renal medulla where ammonia concentrations are normally elevated. We examined the effect of the unique hyperosmolar milieu of the renal medulla on the interaction of ammonia with C3 and the capacity of ammonia-modified C3 (NH3.C3) to induce cytolytic injury and stimulate neutrophils (PMN). Incubation of purified human C3 with ammonia in concentrations found in urine results in significant disruption of the C3 thiolester bond compared with ammonia-free controls. Coincubation with urinary osmolytes and hyperosmolar NaCl and urea does not impair thiolester disruption over a range of ammonia concentrations. However, hyperosmolar NaCl and urea virtually abolish cytolytic injury mediated by the alternative pathway. Coincubation with the organic osmolytes betaine, sorbitol, and inositol fails to reverse this inhibitory effect of hyperosmolar NaCl and urea. Hyperosmolar NaCl and urea also suppress lytic injury mediated by ammonia and complement in MDCK, a cell line derived from canine distal tubular epithelium. Both PMN degranulation and respiratory burst responses to NH3.C3 are significantly blunted in the presence of hyperosmolar NaCl and urea. Hyperosmolality also impairs PMN responses to the formyl peptide N-formyl-Met-Leu-Phe and phorbol 12-myristate 13-acetate (PMA). Therefore, in an in vitro setting of hyperosmolar NaCl and urea, amidation of C3 occurs, but subsequent membrane-directed and receptor-mediated functions of NH3.C3 are markedly impaired.(ABSTRACT TRUNCATED AT 250 WORDS)

Ammonia↗
PubMed1990

Expression of complement alternative pathway proteins by endothelial cells. Differential regulation by interleukin 1 and glucocorticoids.

We have studied the secretion of proteins of the alternative pathway of complement C3, factor B and factor H by human umbilical vein endothelial cells (HUVEC). Results showed that factor H and factor B are quantitatively secreted in abundance whereas C3 could only be detected when the cells are maintained in culture during long periods of time. Interferon-gamma stimulated factor H, factor B and, to a lesser extent, C3 secretions. Interleukin (IL) 1 had a differential effect on spontaneous C3, factor B and factor H secretions. In the presence of IL 1, there was a significant secretion of C3 occurring within a short period of culture. IL 1 also stimulated factor B secretion. There was a synergistic stimulating effect between IL 1 and interferon-gamma to bring C3 and factor B productions by HUVEC to very high levels. In contrast, factor H secretion was consistently inhibited by IL 1. Local increase in C3 and factor B secretions by endothelial cells in the presence of IL 1 may have important implications in the inflammatory reaction. In striking contrast, the glucocorticoid dexamethasone (DXM) had modulatory effects which are consistent with its anti-inflammatory properties. DXM, at therapeutic concentrations, decreased C3 and factor B secretions and increased factor H secretion. Local modulation of complement protein secretion by DXM appears to be a new mechanism by which this glucocorticoid may control inflammation.

Complement C3b Inactivator Proteins↗
PubMed1993

Immune lysis of Trypanosoma congolense: generation of a soluble covalent complex of variant surface glycoprotein and bovine complement component C3b.

Organisms of Trypanosoma congolense variant antigenic type TC13 (VAT TC13) were incubated, at 37 degrees C for 60 min, with fresh bovine serum in the presence of antibody specific for the variant surface glycoprotein (VSG). Upon immune lysis, soluble VSG (54 kDa) and a larger complex (about 225 kDa), containing VSG, was detected in the supernatant fluid of the mixture. Neither soluble VSG nor the VSG complex were detected when fresh bovine serum was incubated with organisms of T. congolense in the absence of specific antibody. Within a narrow range of low antibody concentration, the release of soluble VSG and the formation of the VSG complex were correlated with the amount of specific antibody added to the mixture. The VSG complex could be precipitated with rabbit antibodies specific for VSG of VAT TC13 or antibodies specific for bovine complement C3. The VSG complex was detected by Western blot with rabbit anti-VSG of VAT TC13 as well as rabbit antibovine C3. The complex was found to consist of VSG covalently bound to bovine complement component C3b. Potential pathophysiological implications are discussed.

Animals↗
PubMed2001

Colostral whey concentrate supplement increases complement activity in the sera of neonatal calves.

We evaluated the effect of a commercial bovine colostral whey on the complement-mediated immune responses of calves. Two groups of neonatal calves were fed, in addition to whole milk (WM) and pooled colostrum (PC), different amounts of a commercial immunoglobulin concentrate made from pooled colostral whey (Ig-C) for the first two feedings post natum. The control group was fed WM and PC only. Serum samples were obtained at the ages of 2, 7, 14 and 30 d. Bacteriolytic activity against complement-sensitive Escherichia coli JM103 and opsonic activity against complement-lysis-resistant E. coli IH3080 strains were studied, as well as the levels of C3 complement component and E. coli JM103 specific antibodies in the sera. Groups fed Ig-C had 2-3 times higher bacteriolytic activity than the control group of both the classic (P < 0.005) and alternative pathways (P < 0.0001) at days 2 and 7 post natum. This effect is obviously not caused solely by the antibodies ingested but also involves other unknown colostral factors, possibly lectins. The opsonisation capacities of the sera correlated well with the amounts of immunoglobulins ingested (P < 0.05) at days 2-14. The levels of C3 component in sera did not differ between the groups. In the group fed the largest amount of immunoglobulins levels of E. coli JM103-specific antibodies were highest (P < 0.0001). It can thus be concluded that the antibody independent complement activities of serum can be increased substantially by feeding colostral whey concentrate to calves during their first days of life.

Age Factors↗
PubMed1988

Complements as new diagnostic tools of hepatocellular carcinoma in cirrhotic patients.

Serum complements, C3, C4, and C3 proactivator (C3PA), were evaluated prospectively for their diagnostic power in detecting hepatocellular carcinoma (HCC) in patients with liver cirrhosis (LC). Sixty-three LC patients, including 36 LC with HCC patients, were recruited for this study during the period from March to November 1986. The cutoff values of the complements were set according to retrospective study including 17 LC patients and 20 HCC patients. The values with highest accuracy, 75 mg/dl C3, 16 mg/dl C4, and 18 mg/dl C3PA, were selected. Based on these data, the positive predictive values, negative predictive values, and the accuracies of complements were as follows: C3, 88.9%, 85.2%, and 87.3%; C4, 93.8%, 80.6%, and 87.3%; and C3PA, 66.7%, 90.9%, and 70.9%, respectively. The accuracy elevated to 93.7% when C3, C4, and alpha-fetoprotein were combined as the diagnostic criteria. This study supports the use of complement testing as a new diagnostic tool for HCC screening in LC patients and for follow-up evaluation in posttherapy patients of LC with HCC.

Adult↗
PubMed2004

Exocytosis of a complement component C3-like protein by tunicate hemocytes.

This study investigates the exocytic responses of invertebrate hemocytes to pathogen-associated antigens. It demonstrates that a homologue of complement component C3, a key defensive protein of the innate immune system, is expressed by phagocytic hemocytes (non-refractile vacuolated cells) of the tunicate, Styela plicata. C3-like molecules are localized in sub-cellular vesicles and are rapidly exocytosed after stimulation with bacterial, fungal or algal cell surface molecules. Signal transduction analysis indicated that the induced secretion of C3-like molecules is mediated by a G-protein dependent signaling pathway, which modulates tubulin microtubules. All of this evidence indicates that hemocytes can contribute to host defense responses by rapidly exocytosing C3-like proteins at sites of infection.

Alkaloids↗
PubMed1976

Persistence of immunoglobulin and complement components C4 and C3 bound to guinea pig tumor cells.

Guinea pig hepatoma cells (line-10) growing as ascites were studied for the presence of immunoglobulin, C4, and C3 (components of complement) on their surfaces. Immunoglobulin, C4, and C3 content increased with length of time spent in the peritoneal cavity. The persistence of these factors bound in vivo or in vitro was also determined. Complement-fixing (CF) activity of cellbound antibody disappeared from the surface more rapidly at 37 degrees C than at 4 degrees C; the continued presence of cellbound immunoglobulin in non-complement-fixing form could be demonostrated at either temperature. No CF activity was released into the medium. C4 and C3 were released into the medium and could be demonstrated in the medium by immunochemical methods.

Animals↗
PubMed1979

Complement fixation in acute serum sickness: assembly of glomerular-bound C3-convertase.

Complement (C) fixing properties of glomerular immune deposits were studied in vitro in two groups of rabbits with acute serum sickness (ASS). Deposits were studied early in decomplemented (cobra venom factor-treated) rabbits (Group I) and during the evolution of the nephritis in non-decomplemented rabbits (Group II). Following perfusion of kidneys of animals from Group I (which contained no autologous C3) with rabbit serum deficient in factor B (classical pathway) or serum pre-treated with Mg++EGTA (alternative pathway), fixation of C3 was observed in both systems. No C3 deposition was found when EDTA-rabbit serum was used. When kidney sections obtained from serial biopsies and autopsy material from Group II (which contained rabbit C3-C3rb) were incubated with purified factors B and D, followed by either purified human C3 (C3hu) or EDTA-guinea-pig serum (C3gp), fixation of C3hu or C3gp to early C3 deposits was observed. When sections were pre-incubated with heat-inactivated rabbit serum (source of C3b-inactivator), C3 fixation was substantially reduced. Little or no C3 fixation was found after incubation of sections with human or guinea-pig serum depleted of factor D (classical pathway). Thus, in ASS, glomerular complement deposition appears to be predominantly dependent on the activation of the alternative pathway (C3b-feedback) which is progressively lost during the evolution of the nephritis.

Animals↗
PubMed1995

The complement control protein homolog of herpesvirus saimiri regulates serum complement by inhibiting C3 convertase activity.

The herpesvirus saimiri genome encodes a complement control protein homolog (CCPH). Stable mammalian cell transfectants expressing a recombinant transmembrane form of CCPH (mCCPH) or a 5'FLAG epitope-tagged mCCPH (5'FLAGmCCPH) conferred resistance to complement-mediated cell damage by inhibiting the lytic activity of human serum complement. The function of CCPH was further defined by showing that the mCCPH and the 5'FLAGmCCPH transfectants inhibited C3 convertase activity and effectively reduced cell surface deposition of the activated complement component, C3d.

Amino Acid Sequence↗
PubMed1988

Expression of CR2/EBV receptors on human thymocytes detected by monoclonal antibodies.

The biologic effects of the third component of complement, C3, are mediated via receptors which specifically bind the enzymatic degradation products resulting from the cleavage of C3. One of the products, C3d, has been associated with binding to the second complement receptor CR2 (CD21). This receptor, which is identical to the receptor for Epstein-Barr virus (EBV), has been primarily found on cells of the B lineage, but not on mature T cells or other cells of erythroid or myeloid lineages. In the present investigation, we report the presence of CR2 on human thymocytes. Indirect immunofluorescence analysis employing monoclonal anti-CR2 antibodies revealed a range of thymocyte reactivity from 15% to 63% in thirteen experiments using cells of different donors. Reactivity was always greater with the monoclonal anti-CR2 (CD21) antibody HB-5 than with two other antibodies which recognize distinct epitopes on the CR2 molecule. Two-color immunofluorescence analysis indicated that the brightest of the HB-5-stained thymocytes also reacted with the monoclonal anti-CD1 antibody T6 (immature thymocyte marker) while some of the duller HB-5-staining cells reacted with the monoclonal anti-CD3 antibody Leu-4 (mature thymocyte marker). Immunoprecipitation of CR2 on thymocytes with antibody HB-5 and polyacrylamide gel electrophoretic analysis revealed a protein of 145 kDa molecular mass which is consistent with the size of CR2 found on B lymphocytes. These findings raise several questions regarding the biologic role of CR2-EBV receptor on cells of the T lineage.

Antibodies, Monoclonal↗
PubMed1992

[Concentration of serum proteins in children with down syndrome].

In the serum of 41 children with trisomy 21 (Down syndrome) the concentration was determined of 10 proteins by the radial immunodiffusion method. It was found that the concentration of prealbumin and alpha 2-macroglobulin was lower than in healthy children. The concentration of acid alpha 1-glycoprotein, alpha 1-antitrypsin, haptoglobin, C4 complement component, and hemopexin was higher than in healthy children. The concentration of ceruloplasmin, C3 complement component, and transferrin was similar as in healthy children.

Blood Proteins↗
PubMedDate not supplied

Complement activation and serum beta-glucuronidase level during hemodialysis.

Peripheral white blood cell counts, complement and serum beta-glucuronidase activity were examined in 15 chronic hemodialysis patients, ranging in age from 8 to 10 years, precisely at initiation of dialysis, at 15 min after the initiation and at the end of the dialysis. At the initiation of dialysis, a rapid decline of neutrophils from the predialysis value was observed. The complement C3 level fell simultaneously but C4 was not changed. We have observed that the complement activation which follows hemodialysis is accompanied by a rise in the activities of plasma beta-glucuronidase. A rise in the serum beta-glucuronidase level was considered to be the result of complement activation and leukopenia. Granulocytopenia significantly increased the risk of infection of hemodialysis.

Child↗
PubMed1976

[Direct immunofluorescence in cutaneous lupus erythematosus].

A study of the Direct Immunofluorescence Method in skin biopsies of 62 patients with discoid lupus erythematosus is presented. All the specimens were examined to determine the presence of immunoglobulins (IgG, IgM, IgA) and complement (C3) on the different histological structures of the skin. The presence of immunoglobulins and complement was detected not only in the basement membrane of the lesion but also on the hyaline bodies, collagen fibres, dermal capillaries, basal membrane of hair follicles, dermal inflammatory cells, sweat glands and arrector pili muscles. The significance of these findings is discussed.

Complement System Proteins↗
PubMed1995

Complement C1q and C3 mRNA expression in the frontal cortex of Alzheimer's patients.

The levels and cellular localization of mRNA for complement C1q and C3 were examined by RNA gel blot and nonradioactive in situ hybridization in the frontal cortex of patients with Alzheimer's disease (AD) and age-matched controls. We found that the hybridization signal for C1q mRNA was markedly increased (approx. 3.5-fold) in the frontal cortex of AD patients compared to that in age-matched controls. In contrast to previous reports we also found that the levels of C3 mRNA, although well expressed, did not differ significantly between AD cases and age-matched controls. Nonradioactive in situ hybridization using digoxigenin-labeled ribo-probes revealed that transcripts coding for both C1q and C3 were closely associated with neurons. These results support the hypothesis that complement could play a role in neuronal degeneration which has been observed in the brain of AD patients.

Aged↗