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PubMed1986

Development of a rapid kinetic assay for the function of the classical pathway of the complement system and for C2 and C4.

A simple functional complement assay (FCA) is described which is based on kinetic turbidimetry. 25 microliter of sample are combined with 250 microliter of a suspension of antibody coated ovine erythrocytes in a microprocessor controlled photometer. After a lag phase the activation of complement leads to a rapid lysis of the cells which is measured photometrically at 578 nm. The time for a decrease of absorbance of 0.1 is defined as the endpoint of the reaction. Normal citrated plasma which is the preferred specimen for the assay shows a reaction time of about 42 sec whereas pathological or diluted samples show a prolongation. With specific antibodies it was demonstrated that the assay was sensitive for a deficiency of factors of the classical pathway. Factors of the alternative pathway do not influence the assay. In combination with deficient sera a modified form of the assay allows also the determination of C2 and C4. Because of its simplicity, speed and accuracy these assays may be well suited to perform functional complement assays in a routine laboratory.

Animals↗
PubMed1991

[Immunoglobulins A, G and M and C3 and C4 components of the complement in pneumonia in infants under 1 year of age].

The findings of 69 autopsies of children of the first year of life who died from pneumonia were examined. The children were found to have a significant lowering of IgA and IgG and an increase of IgM which correlated with the immunomorphological appearance of the organs of immunogenesis. The concentration of components C3 and C4 of complement was reduced. The reduction appeared most remarkable in +viral and bacterial pneumonias. The conclusion is drawn that in children of the first year of life, pneumonias eventuating in lethal outcomes may occur in primary and secondary immunodeficiency states, since the immune mechanisms are also implicated in the pathogenesis of pulmonary tissue lesions.

Age Factors↗
PubMed2006

Complement as a predictor of further miscarriage in couples with recurrent miscarriages.

BACKGROUND: The clinical significance of complement is unclear in patients with unexplained recurrent miscarriage, though low levels of complement 3 (C3) and/or complement 4 (C4) are reported to be associated with the antiphospholipid syndrome (aPS). We therefore investigated whether C3 and C4 have a predictive value for subsequent miscarriages. METHODS: In total, 215 patients with a history of two consecutive first-trimester miscarriages and no abnormal chromosomes in either partner, no uterine anomalies and no antiphospholipid (aPL) antibodies were examined. Blood tests for C3, C4, total haemolytic complement (CH50), immunoglobulin G (IgG), immunoglobulin A (IgA) and immunoglobulin M (IgM) were performed before subsequent pregnancy. Patients were then followed up without treatment, and their pregnancy outcomes were compared with their previous blood test results. RESULTS: From 215 pregnant patients, 45 subsequently miscarried, whereas the remainder had a live birth. There was no relation with serum CH50, IgG, IgA and IgM levels, but C3 and C4 levels in patients with subsequent miscarriage were significantly higher than in those whose pregnancy was successful. CONCLUSION: In patients with two previous miscarriages, C3 and C4 levels were higher in those women who had a third miscarriage, than in women that went on to have a live birth.

Abortion, Spontaneous↗
PubMed1983

Effect of radiographic contrast media on complement components C3 and C4: generation of C3b-like C3 and C4b-like C4.

Various water soluble iodinated radiographic contrast media (RCM) have been studied for their effect on complement components C3 and C4, purified and in serum. Hepatotropic RCM, and at higher concentration also some nephrotropic RCM, were found to exert a direct effect on purified C3 and C4. RCM treated human C3 and C4 are characterized by (a) loss of haemolytic function, (b) retention of activity in the formation of fluid phase C3 convertases and (c) an antigenic relationship to activated C3 and C4 (C3b and C4b, respectively). This direct alteration of C3 and C4 can probably also occur in serum since loss of haemolytic function is observed at similar RCM concentrations after incubation of serum and of purified components. It is concluded that RCM treated C3 and C4 represent altered forms of these components that resemble C4b and C3b in activity and conformation (C3b-like C3 and C4b-like C4). The alteration is probably caused by binding of RCM, exerting a mild denaturing effect. C3b-like C3 is a potential activator of the alternative pathway, and both C3b-like C3 and C4b-like C4 are known to be cleaved by serum inactivators. A possible pathological significance of the generation of C3b-like C3, C4b-like C4 and their split products remains to be evaluated.

Animals↗
PubMed1984

[Complement markers Bf and C4 in multiple sclerosis].

Some immunogenetic HLA markers are significantly correlated with multiple sclerosis, e.g.: the antigens B7, DR2, and the associations B7-DR2, A3-B7-DR2. In addition, the polymorphism of the allotypes Bf and C4 is also controlled by chromosome 6; a study of these markers is therefore of interest. The study of Bf and C4 in multiple sclerosis included a population of genotyped unrelated patients: 50 patients for Bf markers and 41 for C4A and C4B markers. This study revealed an over-representation of allotype S and homozygous BfSS in multiple sclerosis. BfSS homozygote was significantly more frequent in the B7 negative and/or DR2 negative patients, i.e. when the risk markers per se were absent. No correlation could be evidenced with the remittent or progressive character of the disease. These data, obtained from the study of C4, are still preliminary ones. The results found with the Bf markers confirm the existence of a genetic factor in multiple sclerosis and suggest that the susceptibility gene of the disease could be closer to locus Bf than to locus DR.

Chromosomes, Human, 6-12 and X↗
PubMed1982

[Determination of various fractions of complement (Cl, C3c, C3a, C4) in a population of healthy neonates].

The authors have studied plasma levels of various complement fractions (C1,C3c,C3att.,C4) in 127 newborns. Referring to gestation period the studied subjects were divided as follows: 25 newborns (less than 37 weeks), 78 newborns (37-41 weeks), 21 newborns (more then 41 weeks). The mean values of various fractions results higher in the newborns with higher gestation period. Considering the gestational ages, the mean values obtained for each complement fraction are not different from those considered "normals". The range of single value turned out very wide. This fact should lead to prudence in the diagnostic valuation.

Complement C1↗
PubMed1990

Structural homologies of component C5 of human complement with components C3 and C4 by neutron scattering.

The complement component C5 is one of a family of structurally related plasma proteins that includes components C3 and C4. Activation of C5 is the initial step in the formation of the membrane attack complex of complement. Analysis of the solution structure of C5 and comparisons with similar analyses of the structures of C3 and C4 are reported here. Neutron solution scattering gave an Mr for C5 of 201,000, which demonstrates that C5 is monomeric in solution. The radius of gyration RG of C5 at infinite contrast is 4.87 nm and corresponds to an elongated structure. The longest length of C5 was determined to be at least 15-16 nm from three calculations on the basis of the RG, the scattering intensity at zero angle I(0), and the indirect transformation of the scattering curve into real space. Comparison of the RG and contrast variation data and indirect transformations of the scattering curves for C3, C4, and C5 show that these have very similar structures. Comparisons of the C5 scattering curve with Debye small-sphere models previously employed for C4 and C3 show that good curve fits could be obtained. Unlike previous studies that have suggested significant differences, these experiments indicate that, while C5 differs from C3 and C4 in its activation and inactivation pathways, significant structural homology exists between the native proteins, as might be predicted from their high (and similar) sequence homology.

Complement C3↗
PubMed1976

[Plasma level of complement fractions C3 and C4 in children with glomerular nephropathies. Correlations with morphological and immunopathological studies of renal biopsies].

The measurement of the plasmatic level of C3 may easily be included in the record of all glomerular nephropathies. Its decrease is an important argument for the diagnosis of post-infectious acute glomerulonephritis, or renal involvement in sepsis supervening to a ventriculo-atrial diversion. Variations of C3 level are of major importance in the management of the nephropathies in systemic lupus. Besides these special etiological circumstances, a persisting low level of C3 most often cooresponds to a membrano-proliferative glomerulonephritis especially of the type characterized by intra-membranous dense deposits.

Adolescent↗
PubMed1984

Secretion rates of immunoglobulins, albumin, haptoglobin and complement factors C3 and C4 in the perfused jejunum and ileum of human Salmonella carriers.

Secretion rates of immunoglobulins and other proteins were assessed by luminal perfusion of jejunum and distal ileum, and the jejunal histology was evaluated in eight Danish chronic Salmonella typhi and paratyphi carriers compared to nine healthy controls who previously had suffered from typhoid or paratyphoid fever not followed by a carrier state. The median secretion rates for each protein investigated in the distal ileum as well as in the jejunum revealed no significant differences between the two groups. The secretion rate of secretory IgA was raised in both groups compared to previously investigated normal persons. The histological examination revealed no signs of inflammation or presence of bacteria. It was concluded that no primary humoral immune defect was revealed in the carriers.

Adult↗
PubMed1996

Regulation of early complement components C3 and C4 in the synovium.

To determine the cytokine inducibility of early complement component (C3 and C4) expression in the synovium, explant tissue was maintained in culture for 7 days. C3 and C4 production was measured by specific enzyme-linked immunosorbent assay, and RNA was evaluated by semiquantitative PCR. The effects of leukemia inhibitory factor (LIF), gamma interferon (IFN-gamma), IFN-alpha, and estrogen on C3 and C4 expression were evaluated. C3 levels were unaffected by 7 days of LIF, IFN-gamma, or IFN-alpha treatment. In contrast, C4 levels were significantly induced in synovial samples treated for 7 days with either IFN-gamma or IFN-alpha. LIF had no effect on C4 levels in this system. Estrogen was found to down-modulate the induction of expression due to IFN-gamma. These data provide evidence for cytokine regulation of C4 expression in the synovium and for estrogen modulation of those effects.

Base Sequence↗
PubMed1998

Native conformations of human complement components C3 and C4 show different dependencies on thioester formation.

The thioester bond in complement components C3 and C4 and the protease inhibitor alpha2-macroglobulin have traditionally been thought of as fulfilling the dual roles of mediating covalent attachment and maintaining the native conformational states of these molecules. We previously reported that several human C3 thioester-region mutants, including variants E1012Q and C1010A, in the latter of which thioester-bond formation is precluded, display an unexpected phenotype. Despite the lack of a thioester bond in these mutants, they appear to adopt a native-like conformation as suggested by the finding that they are cleavable by the classical pathway C3 convertase, C4b2a, whereas the C3b-like C3(H2O) species is not. Subsequently, a species referred to as C3(NH3)* was described which potentially could account for the observations with the above mutants. C3(NH3)* is a transient species formed on aminolysis of native C3 that can spontaneously re-form the thioester bond. Importantly, it has a mobility on cation-exchange HPLC that is distinct from both native C3 and C3(H2O), but like the native molecule, it is cleavable by an alternative-pathway C3 convertase. In this study we showed by using cation-exchange HPLC as an additional conformational probe that C3 C1010A and E1012Q mutant proteins did not resemble C3(NH3)*. Instead they displayed a chromatographic behaviour that was indistinguishable from that of native C3. To assess the general applicability of these observations, we engineered the equivalent mutations into human C4, specifically C4 C1010A and C4 E1012Q. As expected, thioester-bond formation did not occur in either of these C4 mutants, but in contrast with the results with C3 we found no evidence for the formation of a stable native-like conformation in either C4 mutant, as assessed using cleavability by C1s as the conformational probe. A possible interpretation of our data is that the adoption of the native conformational state during biosynthesis of C3 and C4 is an energetically permissible process, even if it is not locked in via thioester-bond formation. Whereas this conformational state is stable in mature C3, it is unstable in mature C4, perhaps reflecting the additional post-translational cleavage of C4 before its secretion.

Amino Acid Substitution↗
PubMed1975

Studies on the polymorphism of C3, Tf and Bg in Down's syndrome and other diseases.

The distribution of phenotypes C3, Ff and Bg was investigated in sera of patients with Down's syndrome, oligophrenia, Wilson's disease and heart infarct. Quantitative determination of the concentration of C3 and C4 components of human complement was also carried out in these patients. The results are compared to healthy controls and are discussed with already reported data from other authors. Despite differences in the percentage distribution of various phenotypes in the patients' sera as compared to that of the controls, no statistically significant association could be established.

Complement C3↗
PubMed1978

[Recurrence of intramembraneous glomerulonephritis in 2 consecutive kidney transplantations].

A case of dense intramembranous deposit disease, partial lipodystrophy, hypocomplementemia, and nephritic factor-like activity in the serum is presented. Recurrence of underlying renal disease was noted in two consecutive renal allografts. The first transplant was lost 7 months after implantation, chronic renal rejection being an additional cause of graft failure. A favourable clinical course, however, was observed after the second renal transplantation. 22 months after surgery, the patient was fully rehabilitated and transplant function only slightly reduced despite electron microscopic evidence of typical dense intramembranous deposit lesions. Low C3-serum complement and normal C4-serum complement levels were constant findings throughout observation time. The case supports the assumption that patients with dense intramembranous deposit disease should not be excluded from renal transplantation As shown in the literature, maintenance of satisfactory graft function is usually obtained for a long period of time despite recurrence of original disease.

Adult↗
PubMed1990

The complements and immunoglobulins in different media of healthy pregnant women and in pregnant women with increased blood pressure.

We have determined the levels of complement C3, C4 and immunoglobulin G, M, A in mothers' and cord blood serum. Parallelly properdin factor B and immunoglobulin G tests were done in urine samples. All estimations were performed on Immunochemistry Analyzer "Beckman". The investigations were made on 30 healthy pregnant women and 30 with arterial hypertension at the end of third trimester. In the mothers' serum C3 was not significantly changed. In the cord blood of healthy pregnant women it was 0.69 g/L. (SD 0.12) and in those with hypertension 0.38 g/L. (SD 0.15), which means significantly decreased. Complements C4 was not significantly increased in mothers' and cord blood serum. Properdin factor B was significantly increased in mothers' and cord blood serum (healthy pregnant women in serum 0.38 g/L., SD 0.07; with hypertension 0.48 g/L., SD 0.15; while in the cord blood serum of healthy women it was 0.14 g/L., SD 0.06; and hypertensive it was 0.22 g/L., SD 0.10). The same parameter was significantly decreased in the urine of healthy subjects 3.94 mg/L., SD 1.91; and in the hypertensive too, 2.42 mg/L., SD 0.90. The IgG level was significantly increased in the urine of healthy pregnant women 4.42 mg/L., SD 2.24; with hypertension 6.64 mg/L., SD 3.61. IgM was not significantly changed in mothers' and cord blood serum. IgA was significantly increased in the cord blood serum of healthy mothers', 0.02 g/L., SD 0.01, with hypertension 0.12 g/L., SD 0.05.

Complement C3↗
PubMed1985

Common evolutionary origin of alpha 2-macroglobulin and complement components C3 and C4.

A comparison of the sequence of the subunit of human alpha 2-macroglobulin (alpha 2M; 1451 amino acid residues) with that of murine complement component pro-C3 (1639 amino acid residues) reveals eight extended regions of sequence similarity. These regions contain between 19% and 31% identically placed residues and account for 75% and 67%, respectively, of the polypeptide chains of alpha 2M and pro-C3. Published sequence data for complement component C4 show that segments of this protein match well with corresponding stretches in alpha 2M and pro-C3. It is proposed that alpha 2M, C3 and C4, which all contain a unique activatable beta-cysteinyl-gamma-glutamyl thiol ester, have a common evolutionary origin and are homologous proteins. Several larger regions of low sequence similarity indicate the presence of structural domains in each of these proteins that specifically modify an underlying common gross structure. The quartets of basic residues in pro-C3 and pro-C4, at which cleavage takes place to produce the mature subunits of these proteins, and most of the residues forming the anaphylatoxin peptides of C3 and C4 (C3a and C4a) are absent in alpha 2M. In addition, C3 and C4 contain large portions, which extend beyond the COOH terminus of alpha 2M.

Amino Acid Sequence↗