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Translational Psychiatry Sep 2021Structural variation in the complement 4 gene (C4) confers genetic risk for schizophrenia. The variation includes numbers of the increased C4A copy number, which...
Structural variation in the complement 4 gene (C4) confers genetic risk for schizophrenia. The variation includes numbers of the increased C4A copy number, which predicts increased C4A mRNA expression. C4-anaphylatoxin (C4-ana) is a C4 protein fragment released upon C4 protein activation that has the potential to change the blood-brain barrier (BBB). We hypothesized that elevated plasma levels of C4-ana occur in individuals with schizophrenia (iSCZ). Blood was collected from 15 iSCZ with illness duration < 5 years and from 14 healthy controls (HC). Plasma C4-ana was measured by radioimmunoassay. Other complement activation products C3-ana, C5-ana, and terminal complement complex (TCC) were also measured. Digital-droplet PCR was used to determine C4 gene structural variation state. Recombinant C4-ana was added to primary brain endothelial cells (BEC) and permeability was measured in vitro. C4-ana concentration was elevated in plasma from iSCZ compared to HC (mean = 654 ± 16 ng/mL, 557 ± 94 respectively, p = 0.01). The patients also carried more copies of the C4AL gene and demonstrated a positive correlation between plasma C4-ana concentrations and C4A gene copy number. Furthermore, C4-ana increased the permeability of a monolayer of BEC in vitro. Our findings are consistent with a specific role for C4A protein in schizophrenia and raise the possibility that its activation product, C4-ana, increases BBB permeability. Exploratory analyses suggest the novel hypothesis that the relationship between C4-ana levels and C4A gene copy number could also be altered in iSCZ, suggesting an interaction with unknown genetic and/or environmental risk factors.
Topics: Complement C4; Complement C4a; Endothelial Cells; Genetic Predisposition to Disease; Humans; Schizophrenia
PubMed: 34552056
DOI: 10.1038/s41398-021-01583-5 -
Clinical and Experimental Immunology Apr 2004Although complement is activated in the peritoneal cavity during chronic peritoneal dialysis (PD), little is known about its role in peritoneal defence and injury...
Although complement is activated in the peritoneal cavity during chronic peritoneal dialysis (PD), little is known about its role in peritoneal defence and injury related to long-term PD. We examined the impact of glucose and commercial peritoneal dialysis solutions on complement expression in HPMCs obtained by primary culture from omental tissues of consented patients undergoing elective abdominal surgery. Constitutive expression of C3 and C4 mRNA in HPMCs was up-regulated upon exposure to 75 mm glucose in a time-dependent manner. C3 and C4 protein was secreted in both apical and basolateral directions. Glucose doses beyond 100 mm markedly down-regulated C3 and C4 expression, and stimulated LDH release dose-dependently. Such cytotoxic effects were attenuated using equivalent doses of mannitol instead of glucose. Treatment with conventional lactate-buffered dialysis solution gave rise to down-regulation of C3 and C4 expression, and heightened LDH release in HPMCs. These effects correlated with the glucose strength of the solution, persisted despite replacement with a bicarbonate-buffered solution, aggravated by glycated albumin, and were partially abrogated by supplementation with 10% fetal bovine serum in the culture system. Our findings suggest that the artificial conditions imposed by PD lead to alterations in local complement synthesis that have implications for the role of the peritoneal mesothelium in both inflammation and defence.
Topics: Cell Membrane Permeability; Cell Survival; Cells, Cultured; Complement C3; Complement C4; Dialysis Solutions; Dose-Response Relationship, Drug; Epithelial Cells; Gene Expression Regulation; Glucose; Humans; Mannitol; Peritoneal Dialysis; Peritoneum; RNA, Messenger
PubMed: 15030518
DOI: 10.1111/j.1365-2249.2004.02407.x -
The Biochemical Journal Feb 1998The 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...
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.
Topics: Amino Acid Substitution; Animals; Chromatography, High Pressure Liquid; Complement C3; Complement C4; Cysteine; Esters; Gene Expression; Glutamic Acid; Humans; Mice; Mutagenesis, Site-Directed; Plasmacytoma; Protein Conformation; Sulfhydryl Compounds; Transfection; Tumor Cells, Cultured
PubMed: 9445402
DOI: 10.1042/bj3290705 -
Scandinavian Journal of Immunology Feb 2007Severe forms of chronic periodontitis affect up to 10% of adults. Tumour necrosis factor and lymphotoxin-alpha genes in the major histocompatibility complex are...
Severe forms of chronic periodontitis affect up to 10% of adults. Tumour necrosis factor and lymphotoxin-alpha genes in the major histocompatibility complex are associated with severe periodontitis. Complement factor C4 is a nearby, polymorphic, functionally relevant gene region. Although associated with chronic mucosal infections, C4 deficiencies have not been assessed in adult periodontitis patients. We tested whether complement levels are systemically altered and C4 deficiencies associated with severe chronic periodontitis. In a case-control study, we analysed levels of plasma C3, and C4, serum classical pathway haemolytic activity, C4 allotypes and C4 gene numbers in 37 patients with severe chronic periodontitis and in 150 voluntary controls. Plasma levels of C3 were higher, and classical pathway haemolytic activity was lower in patients than in controls. Partial C4 gene deficiencies were more frequent in patients than in controls (odds ratio 2.4, 95% confidence interval 1.1-5.5, P = 0.032). Changes in complement levels may reflect chronic, recurring inflammation. C4 gene deficiencies are associated with predisposition to chronic periodontitis.
Topics: Adult; Alleles; Case-Control Studies; Chronic Disease; Complement C1; Complement C4; Female; Genetic Predisposition to Disease; Humans; Male; Middle Aged; Periodontitis
PubMed: 17257223
DOI: 10.1111/j.1365-3083.2006.01886.x -
Journal of Clinical Laboratory Analysis 2004The two serum proteins of the complement cascade in the highest concentrations, C3 and C4, respond to various conditions in much the same manner as do other positive...
The two serum proteins of the complement cascade in the highest concentrations, C3 and C4, respond to various conditions in much the same manner as do other positive acute-phase proteins. A major difference is that they are relatively sluggish in response to cytokine drive, requiring several days rather than hours to be detectably elevated by serial measurements. As with other acute-phase proteins, there are many processes that up- or down-regulate synthesis, including infection or inflammation, hepatic failure, and immune-complex formation. Clinicians may find it difficult to distinguish among these processes, because they often occur simultaneously. The situation is further complicated by genetic polymorphism, with rare instances of markedly reduced synthesis and circulating levels, and consequent vulnerability to infection. C3 and C4 are measured for clinical purposes to help define certain rheumatic and immunologically mediated renal diseases. Interpreting the measured blood levels of these two components requires one to consider the intensity of the inflammatory drive, the timing of the suspected clinical process, the production of complement-consuming immune complexes, and the possible existence of benign circumstances. In this fifth article in a series, reference ranges for serum levels of two complement proteins (C3 and C4) are examined. The study is based on a cohort of over 55,000 Caucasian individuals from northern New England, who were tested in our laboratory in 1994-1999. Measurements were standardized against certified reference material (CRM) 470/reference preparation for proteins in human serum (RPPHS), and analyzed using a previously described statistical approach. Individuals with unequivocal laboratory evidence of inflammation (C-reactive protein of 10 mg/L or higher) were excluded. Our results show that the levels of C3 and C4 change little during life and between the sexes, except that they increase slightly and then fall after age 20 in males and at about age 45 in females. When values were expressed as multiples of the age- and gender-specific median levels, the resulting distributions fitted a log-Gaussian distribution well over a broad range. When patient data are normalized in this manner, the distribution parameters can be used to assign a centile corresponding to an individual's measurement, thus simplifying interpretation.
Topics: Acute-Phase Proteins; Adolescent; Adult; Age Factors; Aged; Aged, 80 and over; Chemistry, Clinical; Child; Child, Preschool; Cohort Studies; Complement C3; Complement C4; Female; Humans; Infant; Male; Middle Aged; Predictive Value of Tests; Reference Values; Sex Factors; White People
PubMed: 14730550
DOI: 10.1002/jcla.10100 -
The Journal of Biological Chemistry May 2013The complement system is an ancient innate immune defense pathway that plays a front line role in eliminating microbial pathogens. Recognition of foreign targets by...
The complement system is an ancient innate immune defense pathway that plays a front line role in eliminating microbial pathogens. Recognition of foreign targets by antibodies drives sequential activation of two serine proteases, C1r and C1s, which reside within the complement Component 1 (C1) complex. Active C1s propagates the immune response through its ability to bind and cleave the effector molecule complement Component 4 (C4). Currently, the precise structural and biochemical basis for the control of the interaction between C1s and C4 is unclear. Here, using surface plasmon resonance, we show that the transition of the C1s zymogen to the active form is essential for C1s binding to C4. To understand this, we determined the crystal structure of a zymogen C1s construct (comprising two complement control protein (CCP) domains and the serine protease (SP) domain). These data reveal that two loops (492-499 and 573-580) in the zymogen serine protease domain adopt a conformation that would be predicted to sterically abrogate C4 binding. The transition from zymogen to active C1s repositions both loops such that they would be able to interact with sulfotyrosine residues on C4. The structure also shows the junction of the CCP1 and CCP2 domains of C1s for the first time, yielding valuable information about the exosite for C4 binding located at this position. Together, these data provide a structural explanation for the control of the interaction with C1s and C4 and, furthermore, point to alternative strategies for developing therapeutic approaches for controlling activation of the complement cascade.
Topics: Complement C1s; Complement C4; Enzyme Precursors; Humans; Protein Binding; Protein Structure, Quaternary; Protein Structure, Secondary; Protein Structure, Tertiary; Structure-Activity Relationship
PubMed: 23592783
DOI: 10.1074/jbc.M113.464545 -
F1000Research 2023The complement system is made up of an abundance of unique plasma proteins that play an important role in innate immunity and inflammation, aiding in the fight against...
The complement system is made up of an abundance of unique plasma proteins that play an important role in innate immunity and inflammation, aiding in the fight against pathogenic microbes and viral diseases. The purpose of this study was to evaluate the serum complement C4 concentration in COVID-19 patients in Khartoum and compare them to healthy controls. A total of 100 samples were collected, 50 samples from COVID-19 patients who presented as cases and 50 samples from people who were evidently healthy. Overall, 33 (66%) the patient populations in the case group were not in the hospital's intensive care unit (ICU), compared to 17 (34%) who were. The concentrations of C4 in each serum sample were calculated in milligrams per deciliter. SPSS version (20) was used to analyze the data. The means level of complement C4 (mg/dL) were 37.44 18.618, 23.90 10.229 in the case group and in the control group, respectively. There was a statistically significant difference in complement C4 level between case and control (p-values ≤0.01). In addition, the mean complement C4 level in the ICU and non-ICU case groups was 25.00±17.85 and 43.85±15.712 mg/dL, respectively. There was a statistically significant variance in complement C4 level between ICU and non-ICU (p-values ≤0.01). Furthermore, the cases were divided into four age groups: 20-40, 40-60, 60-80, and over 80 years old. The one-way ANOVA test showed no statistically significant differences between age categories in complement C4 level (P = 0.735) The case group had a higher mean level of complement C4 than the control group, which could be understood by the stimulation of the complement cascade during the COVID-19 illness. Furthermore, the complement C4 level in severe COVID-19 patients was lower than in non-severe COVID-19.
Topics: Humans; Young Adult; Adult; Aged, 80 and over; Complement C4; COVID-19; Complement C3; Case-Control Studies
PubMed: 37533483
DOI: 10.12688/f1000research.132670.1 -
Infection and Immunity May 1981In experimentally induced malnutrition in rats, there was no significant difference between the measured level of complement activity of the classical pathway (50%...
In experimentally induced malnutrition in rats, there was no significant difference between the measured level of complement activity of the classical pathway (50% hemolytic complement [CH50]) and that of the alternative pathway (ACH50), although the levels of complement components C1, C4, C2, and C3 were depressed significantly. The complement activity showed a temporary elevation with a peak at 2 or 3 days after bacterial challenge with Staphylococcus aureus in rats, and we call this the complement response. After 3 days, CH50 and C3 in the malnourished rats and ACH50, CH50, and C3 in the well-nourished rats showed a significant increase, and C1, C4, and C2 in both groups tended to elevate. On the basis of these observations, the significance of the elevation of C3 in the complement response to bacterial infection showed a strong influence by enhancing the activation of both the classical and the alternative pathways, since C3 is known to be the junction of both complement pathways. In this way, C3 responded to an earlier stage than did the other components and may contribute to maintaining the body defense system against infection.
Topics: Animals; Complement Activation; Complement C1; Complement C3; Complement C4; Complement System Proteins; Male; Nutrition Disorders; Rats; Staphylococcal Infections
PubMed: 7251136
DOI: 10.1128/iai.32.2.553-556.1981 -
Fertility and Sterility Nov 2007To assess whether complement components iC3b, C3c, C4, and SC5b-9 may be involved in the pathogenesis of endometriosis. (Comparative Study)
Comparative Study
OBJECTIVE
To assess whether complement components iC3b, C3c, C4, and SC5b-9 may be involved in the pathogenesis of endometriosis.
DESIGN
Prospective, experimental trial.
SETTING
Medical university.
PATIENT(S)
112 women infertile women undergoing laparoscopy.
INTERVENTION(S)
Venipuncture and laparoscopic peritoneal fluid collection.
MAIN OUTCOME MEASURE(S)
Peritoneal fluid and serum iC3b, C3c, C4, and SC5b-9 levels were measured by the enzyme-linked immunosorbent assay (ELISA) method.
RESULT(S)
Higher levels of C3c, C4, and SC5b-9 complement components were found in the serum compared with the peritoneal fluid, but the levels of iC3b were higher in the peritoneal fluid. We observed higher concentrations of C3c, C4, and SC5b-9 in the peritoneal fluid and serum of women with endometriosis compared with healthy women. However, the levels of iC3b in both peritoneal fluid and serum were statistically significantly lower than in the control group.
CONCLUSION(S)
The impairment of the mechanisms involved in the regulation of activation of complement system may be an important factor in the pathogenesis of endometriosis and endometriosis-associated infertility.
Topics: Adult; Ascitic Fluid; Complement Activation; Complement C3b; Complement C3c; Complement C4; Complement Membrane Attack Complex; Complement System Proteins; Endometriosis; Female; Humans; Infertility, Female; Prospective Studies
PubMed: 17482181
DOI: 10.1016/j.fertnstert.2006.12.061 -
American Journal of Human Genetics Mar 2012Systemic lupus erythematosus (SLE) is a chronic, multisystem autoimmune disease. Complete deficiency of complement component C4 confers strong genetic risk for SLE....
Systemic lupus erythematosus (SLE) is a chronic, multisystem autoimmune disease. Complete deficiency of complement component C4 confers strong genetic risk for SLE. Partial C4 deficiency states have also shown association with SLE, but despite much effort over the last 30 years, it has not been established whether this association is primarily causal or secondary to long-range linkage disequilibrium. The complement C4 locus, located in the major histocompatibility complex (MHC) class III region, exhibits copy-number variation (CNV) and C4 itself exists as two paralogs, C4A and C4B. In order to determine whether partial C4 deficiency is an independent genetic risk factor for SLE, we investigated C4 CNV in the context of HLA-DRB1 and MHC region SNP polymorphism in the largest and most comprehensive complement C4 study to date. Specifically, we genotyped 2,207 subjects of northern and southern European ancestry (1,028 SLE cases and 1,179 controls) for total C4, C4A, and C4B gene copy numbers, and the loss-of-function C4 exon 29 CT indel. We used multiple logistic regression to determine the independence of C4 CNV from known SNP and HLA-DRB1 associations. We clearly demonstrate that genetically determined partial C4 deficiency states are not independent risk factors for SLE in UK and Spanish populations. These results are further corroborated by the lack of association shown by the C4A exon 29 CT insertion in either cohort. Thus, although complete homozygous deficiency of complement C4 is one of the strongest genetic risk factors for SLE, partial C4 deficiency states do not independently predispose to the disease.
Topics: Alleles; Case-Control Studies; Cohort Studies; Complement C4a; Complement C4b; DNA Copy Number Variations; Exons; Gene Dosage; Gene Frequency; Genetic Predisposition to Disease; HLA-DRB1 Chains; Haplotypes; Homozygote; Humans; Linkage Disequilibrium; Logistic Models; Lupus Erythematosus, Systemic; Major Histocompatibility Complex; Polymorphism, Single Nucleotide; Risk Factors; Spain; United Kingdom; White People
PubMed: 22387014
DOI: 10.1016/j.ajhg.2012.01.012