Activation of the early components of the classical complement pathway under physiologic conditions.
Explore the source record for details and available documents.
Binding Sites↗
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.
Nonimmune activation of the classical complement pathway.
Explore the source record for details and available documents.
Amino Acid Sequence↗
C4 does not bind to human and rabbit IgM during activation of the classical complement pathway on the red cell.
It has been known for many years that IgG-C4 complexes are generated during the activation of the classical complement pathway. Information regarding binding of C4 by IgM is not available. We studied the binding of human C4 by natural human and rabbit anti-hapten IgM under conditions in which the IgM was bound to hapten coupled to sheep red cells. We eluted the IgM by excess fluid phase hapten, reattached the eluted IgM to red cells coupled with hapten, and transferred the IgM from red cell-IgM-C4 complexes to red cells coupled with hapten. Analysis of the cells by radioimmunoassay and/or by hemolytic assays showed that no C4 was eluted from the cells with the IgM, that no C4 transferred from cell to cell with the IgM, and that the C4 remaining on the cells was hemolytically active. We concluded that in contrast to IgG, natural human and rabbit IgM at a cell surface failed to bind C4.
Animals↗
Activation of the classical complement pathway in brain tissue of Alzheimer patients.
Positive immunohistochemical staining of Alzheimer brain tissue was obtained with antibodies to proteins associated with classical, but not the alternative, complement pathway. Clq, C3d, C4d are fractions of complement proteins that bind to tissue when the classical complement pathway is activated. Antibodies to these fractions stained senile plaques, dystrophic neurites and some neurofibrillary tangles. C5b-9 is the membrane attack complex which promotes cell lysis when assembled on the plasma membrane. An antibody to a neoantigenic site on this complex stained dystrophic neurites and many neurofibrillary tangles, but not extracellular amyloid. Properdin and fraction Bb of factor B, two proteins that bind to tissue when the alternative complement pathway is activated, were not detected immunohistochemically.
Aged↗
Activation of the classical complement pathway by mannose-binding protein in association with a novel C1s-like serine protease.
Serum mannose-binding protein (MBP) is a C-type lectin that binds to terminal mannose and N-acetylglucosamine moieties present on surfaces of certain pathogens and activates the classical complement pathway. In the present study, we describe the mechanism underlying the activation triggered by MBP. The human serum MBP fraction was obtained by sequential affinity chromatography on mannan-Sepharose, anti-IgM-Sepharose and anti-MBP-Sepharose in the presence of calcium ions. This fraction contained a C1s-like serine protease as assessed by C4 consumption. The C1s-like serine protease, designated MBP-associated serine protease (MASP), was separated from MBP by rechromatography on anti-MBP-Sepharose in the presence of ethylenediaminetetraacetic acid. MASP exhibited both C4- and C2-consuming activities. The molecular mass of MASP was estimated to be 83 kD with two polypeptides of heavy (66 kD) and light (L) (31 kD) chains linked by disulfide bonds. The serine residue responsible for protease activity is located on the L chain. Reconstitution experiments using MASP and MBP revealed that combination of the two components restores C4- and C2-activating capacity on mannan. Based on analyses of molecular size, antigenicity, and 11 NH2-terminal amino acid sequences of the L chain, we conclude that MASP is a novel protein different from C1r or C1s. Our findings are not in accord with a proposed mechanism by which MBP utilizes the C1r2-C1s2 complex to initiate the classical complement pathway.
Amino Acid Sequence↗
Auto-antibody dependent activation of the autologous classical complement pathway by guinea-pig red cells treated with influenza virus or neuraminidase: in vitro and in vivo study.
Guinea-pig erythrocytes that had been exposed to influenza A virus or Vibrio cholerae neuraminidase activated the classical complement pathway in autologous serum. Because all viral particles were eluted from the treated cells, activation was not dependent on anti-viral antibodies or on the particles themselves. After a threshold of 45-55% desialation, had been reached, the relative capacity of treated cells to activate complement increased very rapidly with desialation. Desialation unmasked sites on which natural auto-antibodies of the IgM class were fixed. Antibody fixation on the membrane led to C3b deposition on the cell membrane and activation of the classical complement sequence then cell lysis. The relevance of in vitro lysis of desialated cells to in vivo clearance of these cells is not certain because C4-deficient guinea-pigs were able to eliminate desialated cells from the blood stream as efficiently as did normal guinea-pigs. Nevertheless, membrane desialation occurring during myxovirus infection could lead to autoimmunity and tissue changes, as well as to recovery by eliminating virus-modified cells.
Animals↗
High doses of intravenous immunoglobulin do not affect the recognition phase of the classical complement pathway.
We have recently found that intravenous immunoglobulin (IVIg) prevents deposition of C3 and C4 fragments onto antibody sensitized erythrocytes. To find out if such an effect results from the blockade of the recognition phase of the classical complement cascade, we investigated the ability of human serum containing high concentrations of IVIg to deposit the recognition subunit of the first complement component (C1q) onto targets. Normal human serum supplemented in vitro with IVIg did not demonstrate reduced C1q binding to targets as determined by radiolabeled antihuman C1q antibody uptake. Similarly, methylamine-treated normal human serum to which IVIg was added was equally effective in terms of C1q binding as the same serum without IVIg. At increasing doses of sensitizing antibody, C1q uptake decreased proportionally; however, at all antibody dilution points C1q uptake was not significantly different in the serum with IVIg in comparison with normal serum. Serum from a patient treated with IVIg did not differ in its capacity to deposit C1q from the same patient's serum before therapy. Our data suggest that IVIg does not interfere with the recognition step of classical complement pathway. This is a US government work. There are no restrictions on its use.
Complement C1↗
Natural IgM antibodies in sera from various animals but not the cat kill Toxoplasma gondii by activating the classical complement pathway.
Sera from swine, rabbit, and dog, that had never been exposed to Toxoplasma gondii, demonstrated significant killing of T. gondii tachyzoites in vitro, while cat serum did not. Swine and rabbit sera contained natural IgM antibody against the tachyzoites, and the classical complement pathway was activated by the binding of natural IgM antibody to the tachyzoites, leading to lysis. Anti-T. gondii antibodies, induced in swine or cat infected with T. gondii, had no killing effect by themselves but killed the tachyzoites in the presence of swine complement. However, the anti-T. gondii antibodies of swine or cat demonstrated a very low killing effect in the presence of cat complement. This suggests that T. gondii tachyzoites have an evasion mechanism to prevent lysis which is specific for cat complement.
Animals↗
Classical complement pathway activation by antipneumococcal antibodies leads to covalent binding of C3b to antibody molecules.
We have examined whether or not a physical relationship exists between antipneumococcal antibodies (Ab) and C3b when Ab activate the classical complement pathway on the surface of pneumococci (Pn). After sensitization with 125I-labeled Ab, Pn were sequentially incubated with purified C1, C4, C2, and biotinylated C3. Ab molecules were then eluted from Pn, and C3b-associated molecules were purified on avidin-Sepharose. Both 125I-labeled immunoglobulin G (IgG) and [125I]IgM bound to C3b; the association was stable to incubation in 1% sodium dodecyl sulfate at 37 degrees C. The association was only partially reversed by incubation in 1 M hydroxylamine-0.5% sodium dodecyl sulfate (pH 10.5), implying that Ab and C3b were linked by amide as well as ester bonds. Sodium dodecyl sulfate-polyacrylamide gel electrophoresis of dithiothreitol and NH2OH eluates from the avidin-Sepharose showed that C3b bound to both heavy and light chains of the Ab. Moreover, the ability to bind to erythrocyte C3b receptors could be transferred to unsensitized Pn by eluates from Pn on which Ab had activated the classical pathway. These covalent complexes of Ab and C3b may be especially important in the opsonization of Pn by Ab and complement.
Animals↗
Anti-complement activity of oleanolic acid: an inhibitor of C3-convertase of the classical complement pathway.
Oleanolic acid is a naturally occurring compound, isolated from Luffa cylindrica, which inhibits the in-vitro immunohaemolysis of antibody-coated sheep erythrocytes by guinea-pig serum. In further experiments this reduced immunohaemolysis was found to be due to inhibition of the C3-convertase of the classical complement pathway. The threshold concentration for inhibition of C3-convertase was 100 micrograms mL-1. However, higher concentrations of oleanolic acid showed constant inhibitory effects on immunohaemolysis. Oleanolic acid also exhibited weak inhibitory effects on individual components of the complement system.
Animals↗
Antibody-independent activation of the classical complement pathway by cytomegalovirus-infected fibroblasts.
Human fibroblasts weakly activated the alternative complement pathway, as assessed by C3b deposition, while 4- to 5-fold more C3b was observed 4 days after infection on cytomegalovirus (CMV)-infected fibroblasts when incubated with human serum. CMV-infected fibroblasts activated via the classical complement pathway independent of specific anti-CMV antibody and incubation of CMV-infected fibroblasts with serum deficient in complement components revealed that C1q, but not mannan-binding lectin, was required for complement activation. The enhanced complement activation by CMV-infected cells was observed as early as 4 h after infection and required the active transcription of CMV genes. No difference in the complement activation by CMV-infected cells was observed with the use of CMV-seropositive or -seronegative serum as a complement source, suggesting that CMV infection induces or up-regulates a protein that binds directly to C1q in a complement-activating conformation.
Blood↗
Anticomplementary activity of boswellic acids--an inhibitor of C3-convertase of the classical complement pathway.
Boswellic acids (BA), an anti-inflammatory and anti-arthritic principle/s of Boswellia serrata, were found to possess anticomplementary activity. It inhibits the in vitro immunohaemolysis of antibody-coated sheep erythrocytes by pooled guinea-pig serum. The reduced immunohaemolysis was found to be due to inhibition of C3-convertase of the classical complement pathway. The threshold concentration for inhibiting C3-convertase was found to be 100 micrograms. However, higher concentrations of BA showed constant inhibitory effects on immunohaemolysis. BA also exhibited weak inhibitory effects on individual components of the complement system. In vivo administration of BA also showed the inhibitory effect on guinea-pig serum.
Animals↗
Myelinated dorsal root ganglion cultures activate both the alternative and classical pathways of complement.
We used rat myelinated dorsal root ganglion (MDRG) cultures to study antibody and complement-mediated mechanisms of peripheral demyelinating diseases. Heat inactivated serum from a patient (LT) with peripheral neuropathy and a monoclonal IgM reactive with myelin-associated glycoprotein (anti-MAG) and sulfated glucuronosyl glycolipids (anti-SGGL) was used as an antibody source. Incubation of whole human serum (WHS) or WHS and anti-SGGL with MDRGs resulted in reduction of classical and alternative pathway hemolytic activities and the development of abnormal myelin sheaths. Incubation of MDRG cultures with C2-deficient serum showed activation of the alternative complement pathway. Classical pathway hemolytic activity was reduced when Factor B-depleted serum was incubated with MDRG cultures. The rat MDRG culture system provides a good model system of a peripheral nerve and has therefore been used by several investigators to study antibody and complement-mediated demyelination associated with peripheral neuropathies. However, our studies indicate a high degree of complement activation and membrane disruption of cultures incubated with WHS.
Animals↗
Repressed classical complement pathway activities and clinical correlations in chronic lymphocytic leukaemia.
Haemolytic activities of the classical and alternative complement pathways, and levels of C1, C4, C3, factor B and C1 inhibitor (C1-INH) were measured in 137 serum samples of 69 patients with chronic lymphocytic leukaemia (CLL). In most sera IgG, IgA and IgM concentrations were determined as well. Clinical correlations of these laboratory parameters have been studied. C1 and C4 activities were found to be depressed in almost 50% of the sera tested, and hypogammaglobulinaemia was observed with a similar frequency. Low C1 and C4 levels were found mainly in the early stages of the disease. A strong association between the occurrence of infections and hypogammaglobulinaemia was observed, although low immunoglobulin levels frequently occurred in patients without a history of infections. Low C1 and C4 levels were significantly correlated with the incidence of infections, too, and this correlation was observed mostly in the early stages of the disease. The reason for this is not known. The present results suggest that not only low immunoglobulin levels but low C1 and/or C4 levels may contribute to the increased susceptibility to infections in patients with chronic lymphocytic leukaemia.
Complement Activation↗
Low activity of the classical complement pathway predicts short survival of patients with chronic lymphocytic leukaemia.
The activities of the classical (CP) and alternative (AP) complement pathways as well as the levels of some complement components and circulating immune complexes were measured in 43 patients with chronic lymphocytic leukaemia (CLL) between 1980 and 1984. Depressed CP activities were frequently found in these patients. Clinical course of the disease in the patients was followed until 1992, and compared with the initial complement values. During the follow-up period 36 patients died, death of 33 patients being related to the underlying disease. A strong positive correlation (P < 0.01) was found between the length of survival of the patients and the initial CP values. Patients were divided into two groups: group A, short-term survivors, i.e patients who died in CLL-related complications within 3 years after the complement measurements; and group B, long-term survivors who died > or = 4 years after the complement measurements due to any cause, or were alive at the end of the follow-up period. Average CP values in Group B were almost twice those in group A (P = 0.002), and a similar but less pronounced difference was found in C3 levels (P = 0.055). These differences were even more marked (P = 0.0006 and P = 0.0015, respectively) when only patients in Rai stage 2 and 3 were considered. Low classical pathway activities predicted short survival time: according to the logrank test, patients in Rai stage 2-3 with low (< mean - 2s.d. of the normal values), and normal CP levels survived for 2.0 +/- 1.1, and 4.6 +/- 3.0 years, respectively. All the nine and 11/13 patients with low CP and C4 levels, respectively, died within 3 years after the complement measurements were made. These findings indicate that complement measurements performed in CLL patients have a clinical value.
Aged↗
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↗
Glomerular C4d deposition indicates in situ classic complement pathway activation, but is not a marker for lupus nephritis activity.
This study was designed to evaluate whether glomerular C4d deposition may be a useful marker of lupus nephritis activity. Twenty-one patients diagnosed as having lupus nephritis (WHO class III: 4 cases; IV: 12 cases; V: 5 cases) were included. Mean patient age was 29.3 +/- 13.5 years (range: 7-55 years). The presence and intensity of glomerular C4d deposition were compared with the corresponding histologic activity index for each case. Immunofluorescence for C4d showed diffusely granular staining along glomerular capillary loops, in all cases examined (1+, in 8 cases; 2+, in 7 cases; 3+, in 6 cases). In eight cases, C4d deposition was found in the absence of capillary or mesangial C4 deposits. Moreover, the intensity of C4d deposits correlated with those of capillary IgG, IgA, C4, C1q, and fibrinogen deposits. However, C4d staining intensity did not correlate with the lupus nephritis activity index. Although glomerular capillary C4d deposition is a sensitive marker of classic complement pathway activation, it is not a sensitive marker for active lupus nephritis.
Adolescent↗
Effect of sequential glycolysis of the lectin of Euonymus europaeus on activation of the classical complement pathway in normal human serum.
The lectin of Euonymus europaeus at concentrations of 5-21 micrograms/ml causes activation of the classical complement (C) pathway (C1, C4, C2) when added to normal human serum at 37 degrees C. At higher concentrations, C3 is also consumed. The effect is dependent on a 'natural antibody' in serum of the IgM class which reacts with an epitope of the lectin. With physicochemical methods, the carbohydrate of the lectin was shown to be involved in the activation of C, but not involved in the agglutination of group B erythrocytes. Removal of N-acetyl-D-glucosamine from the lectin with an exoglycosidase greatly reduced the activation of C in serum, but it did not affect erythroagglutination. Using competitive binding studies with various sugars, it was confirmed that N-acetyl-D-glucosamine is the dominant specificity of a determinant for activation of the classical C pathway in serum.
Binding, Competitive↗