Cell-bound complement activation products in antiphospholipid antibody-positive patients without other systemic autoimmune rheumatic diseases.

The objective of this study was to analyze complement activation in antiphospholipid antibody (aPL)-positive patients without other systemic autoimmune rheumatic diseases, using C3/C4 and cell-bound complement activation products (CB-CAPs) (B-lymphocytes [BC4d], erythrocytes [EC4d], and platelets [PC4d]). Persistently aPL-positive patients with or without aPL-related clinical manifestations (thrombotic APS [TAPS], microvascular APS [MAPS], obstetric APS, thrombocytopenia [TP], and/or hemolytic anemia [HA]) were enrolled in a single center study. Blood and clinical data were collected at baseline; a subgroup of patients completed 6- or 12-month follow-up. At baseline, 4/31 (13%) patients had decreased C3/C4, while 7/29 (24%) had elevated BC4d, 11/33 (33%) EC4d, and 12/32 (38%) PC4d. Based on different aPL profiles, all patients with decreased C3/C4 or elevated BC4d, EC4d, and PC4d had triple aPL or isolated lupus anticoagulant positivity. Based on different aPL clinical phenotypes, the number of patients with strongly positive EC4d and PC4d were proportionally higher in those with MAPS/TP/HA, compared to TAPS or no APS. Compared to baseline, the frequencies of BC4d, EC4d, and PC4d positivity were not significantly different in the subgroup of patients during their 6- or 12-month follow-up. There was a weak correlation between C3/C4 and CB-CAPs, especially for PC4d. In summary, complement activation in aPL-positive patients varies based on aPL profiles and clinical phenotypes. Given the higher percentage of aPL-positive patients with abnormal CB-CAPs, compared to C3/C4, and the poor inverse correlation between CB-CAPs and C3/C4, our study generates the hypothesis that CB-CAPs have a role in assessing disease activity and thrombosis risk in aPL-positive patients.

Different aspects of immunological profile in patients with Non-Alcoholic Fatty liver disease.

Background: NAFLD is thought to affect approximately one-fourth of the world's population. Therefore, we evaluated the role of serum complement and immunoglobulins in the NAFLD pathogenesis. Patients and methods: 200 participants were used in this study, divided into two groups; Group I: 100 NAFLD patients and Group II: 100 healthy volunteers. The diagnosis of NAFLD is based on non-invasive methods, following the EASL guideline 2022. IgG, IgM, IgA, C3, and C4 assays were performed on all participants. Results: When the immunological profiles of patients with NAFLD and healthy controls were compared, it was found that the mean IgA in NAFLD patients was (4.20±5.07), whereas the mean IgA in healthy controls was (2.22±1.05) (P=0.000). Additionally, a significant increase in IgG was found in NAFLD patients (17.08±3.87) compared with healthy controls (11.59±3.34), with a P value of (p<0.001). complement C3 and complement C4 levels significantly increased in nonalcoholic fatty liver disease patients (1.28± 0.61 and 0.40 ± 0.19, respectively), compared to healthy controls (0.90 ±0.27 and 0.30 ±0.12, respectively), with a significant P value (p<0.001 for each). Conclusions: Elevated IgA, IgG, C3 and C4 exist in patients with NAFLD and could be associated with fatty liver development and progression of hepatic fibrosis in patients with NAFLD.

Analysis of the complement component C4 gene with schizophrenia subphenotypes.

BACKGROUND: The complement component C4 gene has been identified as a strong marker for schizophrenia (SCZ) risk. The C4 gene has a complex genetic structure consisting of variable structural elements (C4A, C4B, C4L, and C4S) and compound structural forms (C4AL, C4BL, C4AS and C4BS). In addition, the variations in C4 structural forms may have a direct or indirect effect on the brain expression level of C4A and C4B proteins. Previous studies have associated C4AL with higher brain C4A expression and sex-dimorphism of C4 between males and females was observed. STUDY DESIGN: A total of 613 patients with DSM-IV SCZ or schizoaffective disorder (SCZ-AFF) were recruited to investigate the relationship between C4 gene variants and clinical characteristics of SCZ (age of onset, symptom severity, and global assessment of functioning (GAF)). This study also explored the effect of sex on the association of C4 with SCZ. 434 patients were included in the final analyses after genetic quality control. RESULTS: We observed associations between C4 and clinical characteristics of SCZ (age of onset, symptom severity, GAF) and found significant differences when males and females were examined separately. CONCLUSION: Overall, our preliminary findings encourage future investigations of C4 in SCZ-related phenotypes, including antipsychotic response and side effects. The study sample was of moderate size; therefore, further studies in larger samples are needed to extend and validate these results.

Role of serum complement C3 and C4 on kidney outcomes in IgA nephropathy.

IgA Nephropathy (IgAN) is the most prevalent glomerular disease worldwide. Complement system activation is crucial in its pathogenesis. Few studies correlated serum C3 and C4 with disease activity and prognosis. This retrospective study investigated the prognostic value of serum complement at the time of diagnosis in patients with IgAN. Specifically we evaluated whether adding serum C3 and C4 levels to established predictive models-one based on variables related to chronic kidney disease (CKD) progression and another incorporating variables from the International IgA Prediction Tool (IntIgAPT)-enhances the accuracy of outcome prediction. A composite renal outcome was defined as 50% decline in eGFR or onset of kidney failure. 101 patients were stratified according to baseline C3 levels in three groups (Low, Medium and High). During a median follow-up of 54 months, the Low group exhibited higher incidence of primary outcome (16.3 events vs 2.9 and 1.7 events × 100 pts/year, p = 0.0026). Model-1 (M1), consisting of CKD progression variables, and Model-3 (M3), comprising IntIgANPT variables, were implemented with baseline C3 and C4 to create Model-2 (M2) and Model-4 (M4), respectively. M2 demonstrated better predictive performance over M1, showing higher discrimination (lower AIC and BIC, higher C-index and NR2). Similarly, M4 outperformed M3, showing enhanced outcome prediction when C3 and C4 levels were added. Implementation of serum C3 and C4 can enhance prediction accuracy of already-validated prognostic models in IgAN. Lower C3 and higher C4 levels were associated with poorer prognosis, highlighting a more 'Complement-Pathic' subset of patients.

Hydroxychloroquine Improves Low Complement Levels.

OBJECTIVE: Having a low complement level is associated with clinical systemic lupus erythematosus (SLE) disease activity and future organ damage. We studied the association of hydroxychloroquine (HCQ) whole blood levels with changes in complement level. METHODS: We performed two analyses on data prospectively collected from an SLE cohort. In the first (a "new starts on HCQ" analysis), we compared changes in complement level between those starting HCQ and those not starting it. The second analysis evaluated the association between HCQ whole blood levels and low complement level in all cohort visits using conditional logistic regression. RESULTS: In the "new starts on HCQ" analysis, a higher percentage of patients starting HCQ (as reflected in HCQ blood levels >50) experienced a normalization of C4 level compared to those not starting HCQ (23 of 57 [40%] vs. 9 of 56 [13%]; P = 0.011), as well as a significantly greater increase in both C3 and C4 level (P = 0.048 and P = 0.017, respectively). In the "all cohort visits" analysis, there was a statistically significant higher probability of having normal C4 levels in visits with higher HCQ whole blood levels (odds ratio 1.8-2.6 depending on the levels). This relationship was most pronounced for whole blood HCQ levels of 200 ng/mL or more. CONCLUSION: We observed significant improvement in complement levels when HCQ was started and among those with higher whole blood levels of HCQ, particularly with respect to C4. Modulating the pathogenic mechanisms that lead to complement consumption may be one mode by which HCQ prevents poor outcomes in SLE.

Development of clinical and laboratory biomarkers in an international cohort of 428 children with lupus nephritis.

BACKGROUND: Lupus nephritis (LN) is a very severe manifestation of lupus. There is no consensus on which treatment goals should be achieved to protect kidney function in children with LN. METHODS: We retrospectively analyzed trends of commonly used laboratory biomarkers of 428 patients (≤ 18 years old) with biopsy-proven LN class ≥ III. We compared data of patients who developed stable kidney remission from 6 to 24 months with those who did not. RESULTS: Twenty-five percent of patients maintained kidney stable remission while 75% did not. More patients with stable kidney remission showed normal hemoglobin and erythrocyte sedimentation rate from 6 to 24 months compared to the group without stable kidney remission. eGFR ≥ 90 ml/min/1.73m2 at onset predicted the development of stable kidney remission (93.8%) compared to 64.7% in those without stable remission (P < 0.00001). At diagnosis, 5.9% and 20.2% of the patients showed no proteinuria in the group with and without stable kidney remission, respectively (P = 0.0001). dsDNA antibodies decreased from onset of treatment mainly during the first 3 months in all groups, but more than 50% of all patients in both groups never normalized after 6 months. Complement C3 and C4 increased mainly in the first 3 months in all patients without any significant difference. CONCLUSIONS: Normal eGFR and the absence of proteinuria at onset were predictors of stable kidney remission. Significantly more children showed normal levels of Hb and erythrocyte sedimentation rate (ESR) from 6 to 24 months in the group with stable kidney remission.

Albumin to globulin ratio (AGR) in systemic lupus erythematosus: correlation with disease activity.

OBJECTIVE: To investigate the role of albumin-to-globulin ratio (AGR) in systemic lupus erythematosus (SLE) and its relationship with disease activity. METHODS: This retrospective study consecutively selected patients with SLE and healthy controls. Patients were divided into three groups according to the SLE Disease Activity Index 2000 (SLEDAI-2K): group 1 (mild disease activity, SLEDAI-2K ≤ 6), group 2 (moderate disease activity, SLEDAI-2K 7-12) and group 3 (severe disease activity, SLEDAI-2K > 12). Predictors of SLE disease activity were analysed by ordinal logistical regression. RESULTS: A total of 101 Chinese patients with SLE and 75 healthy Chinese controls were included. Patients with SLE had lower AGR values than healthy individuals, and group 3 patients with SLE displayed lower AGR values than those in group 1, but similar values to group 2. AGR was inversely correlated with SLEDAI-2K (r = -0.543). Ordinal logistic regression analysis showed that lower AGR (ß = -1.319) and lower complement C4 (ß = -1.073) were independent risk factors for SLE disease activity. CONCLUSIONS: AGR was decreased in patients with SLE and may be utilized as a useful inflammatory biomarker for monitoring SLE disease activity.

A complement C4-derived glycopeptide is a biomarker for PMM2-CDG.

BACKGROUNDDiagnosis of PMM2-CDG, the most common congenital disorder of glycosylation (CDG), relies on measuring carbohydrate-deficient transferrin (CDT) and genetic testing. CDT tests have false negatives and may normalize with age. Site-specific changes in protein N-glycosylation have not been reported in sera in PMM2-CDG.METHODSUsing multistep mass spectrometry-based N-glycoproteomics, we analyzed sera from 72 individuals to discover and validate glycopeptide alterations. We performed comprehensive tandem mass tag-based discovery experiments in well-characterized patients and controls. Next, we developed a method for rapid profiling of additional samples. Finally, targeted mass spectrometry was used for validation in an independent set of samples in a blinded fashion.RESULTSOf the 3,342 N-glycopeptides identified, patients exhibited decrease in complex-type N-glycans and increase in truncated, mannose-rich, and hybrid species. We identified a glycopeptide from complement C4 carrying the glycan Man5GlcNAc2, which was not detected in controls, in 5 patients with normal CDT results, including 1 after liver transplant and 2 with a known genetic variant associated with mild disease, indicating greater sensitivity than CDT. It was detected by targeted analysis in 2 individuals with variants of uncertain significance in PMM2.CONCLUSIONComplement C4-derived Man5GlcNAc2 glycopeptide could be a biomarker for accurate diagnosis and therapeutic monitoring of patients with PMM2-CDG and other CDGs.FUNDINGU54NS115198 (Frontiers in Congenital Disorders of Glycosylation: NINDS; NCATS; Eunice Kennedy Shriver NICHD; Rare Disorders Consortium Disease Network); K08NS118119 (NINDS); Minnesota Partnership for Biotechnology and Medical Genomics; Rocket Fund; R01DK099551 (NIDDK); Mayo Clinic DERIVE Office; Mayo Clinic Center for Biomedical Discovery; IA/CRC/20/1/600002 (Center for Rare Disease Diagnosis, Research and Training; DBT/Wellcome Trust India Alliance).

[Magnetic resonance imaging T2 mapping could reflect disease status in patients with dermatomyositis or polymyositis].

This study aimed to explore the value of magnetic resonance imaging (MRI) T2 mapping in the assessment of dermatomyositis (DM) and polymyositis (PM). Thirty-three confirmed cases (myosin group) and eight healthy volunteers (healthy control group) at the Department of Rheumatology and Immunology, the First Affiliated Hospital of Kunming Medical University, from October 2016 to December 2017, were collected and analyzed. Multiple parameters of the myosin group were quantified, including creatine kinase (CK), erythrocyte sedimentation rate (ESR), C-reactive protein (CRP), complement C3, and complement C4. Disease status was evaluated using a panel of tools: myositis disease activity assessment tool-muscle (MDAAT-muscle), myositis disease activity assessment tool-whole (MDAAT-all), health assessment questionnaire (HAQ), medical outcomes study health survey short form-36 item (SF-36), hand muscle strength test (MMT-8) score, and MRI T2 mapping of muscle (22 muscles in the pelvis and thighs) T2 values. The results showed that in the myositis group, the measurements for CK, ESR, CRP, complement C3, and complement C4 were 457.2 (165.6, 1 229.2) IU/L, 20 (10, 42) mm/1h, 3.25 (2.38, 10.07) mg/L, 0.90 (0.83, 1.06) g/L, and 0.18 (0.14, 0.23) g/L, respectively. The scores for MMT-8, MDAAT-muscle, MDAAT-all, HAQ, and SF-36 were 57.12±16.23, 5.34 (4.00, 6.00), 34.63±12.62, 1.55 (0.66, 2.59), and 44.66±7.98, respectively. T2 values were significantly higher in all 22 muscles of the pelvis and thighs of patients with DM or PM compared with the healthy controls [(54.99±11.60)ms vs. (36.62±1.66)ms, P<0.001], with the most severe lesions in the satrorius, iliopsoas, piriformis, gluteus minimus, and gluteus medius muscles. The total muscle T2 value in the myositis group was positively correlated with CK, MDAAT-muscle, MDAAT-all, and HAQ (r=0.461, 0.506, 0.347, and 0.510, respectively, all P<0.05). There was a negative correlation between complement C4, SF-36, and MMT-8 scores (r=-0.424, -0.549, and -0.686, respectively, all P<0.05). Collectively, the findings from this study suggest that MRI T2 mapping can objectively reflect the disease status of DM and PM.

Role of Advanced Glycation End Products as New Biomarkers in Systemic Lupus Erythematosus.

Advanced glycation end-products (AGEs) may play a relevant role as inducers in the chronic inflammatory pathway present in immune-mediated diseases, such as systemic lupus erythematosus (SLE). AGEs concentrations have been associated, with discrepant results to date, with some parameters such as disease activity or accrual damage, suggesting their potential usefulness as biomarkers of the disease. Our objectives are to confirm differences in AGEs levels measured by cutaneous autofluorescence between SLE patients and healthy controls (HC) and to study their correlation with various disease parameters. Cross-sectional study, where AGEs levels were measured by skin autofluorescence, and SLE patients' data were compared with those of sex- and age-matched HC in a 1:3 proportion through a multiple linear regression model. Associations of AGEs levels with demographic and clinical data were analyzed through ANOVA tests. Both analyses were adjusted for confounders. AGEs levels in SLE patients were significantly higher than in HC (p < 0.001). We found statistically significant positive associations with SLE disease activity index (SLEDAI) and damage index (SDI), physician and patient global assessment, C-reactive protein, leukocyturia, complement C4, IL-6 and oral ulcers. We also found a negative statistically significant association with current positivity of anti-nuclear and anti-Ro60 antibodies. AGEs seem to have a contribution in LES pathophysiology, being associated with activity and damage and having a role as a new management and prognosis biomarker in this disease. The association with specific antibodies and disease manifestations may indicate a specific clinical phenotype related to higher or lower AGEs levels.

Molecular Interactions Required for Activation of Complement Component C2 Include Exosites Located on the Serine Protease Domain of C1s and Mannose-Binding Lectin Associated Protease-2.

The activation of the CP/LP C3 proconvertase complex is a key event in complement activation and involves cleavage of C4 and C2 by the C1s protease (classical pathway) or the mannose-binding lectin-associated serine protease (MASP)-2 (lectin pathway). Efficient cleavage of C4 by C1s and MASP-2 involves exosites on the complement control protein and serine protease (SP) domains of the proteases. The complement control protein domain exosite is not involved in cleavage of C2 by the proteases, but the role of an anion-binding exosite (ABE) on the SP domains of the proteases has (to our knowledge) never been investigated. In this study, we have shown that the ABE on the SP of both C1s and MASP-2 is crucial for efficient cleavage of C2, with mutant forms of the proteases greatly impaired in their rate of cleavage of C2. We have additionally shown that the site of binding for the ABE of the proteases is very likely to be located on the von Willebrand factor domain of C2, with the precise area differing between the enzymes: whereas C1s requires two anionic clusters on the von Willebrand factor domain to enact efficient cleavage of C2, MASP-2 apparently only requires one. These data provide (to our knowledge) new information about the molecular determinants for efficient activation of C2 by C1s and MASP-2. The enhanced view of the molecular events underlying the early stages of complement activation provides further possible intervention points for control of this activation that is involved in a number of inflammatory diseases.

Serum concentrations of complement C3 and C4 in dogs with idiopathic epilepsy.

BACKGROUND: High concentrations of complement factors are presented in serum of animal epilepsy models and human patients with epilepsy. OBJECTIVES: To determine whether complement dysregulation occurs in dogs with idiopathic epilepsy (IE). ANIMALS: The study included 49 dogs with IE subgrouped into treatment (n = 19), and nontreatment (n = 30), and 29 healthy dogs. METHODS: In this case-control study, the serum concentrations of the third (C3) and fourth (C4) components of the complement system were measured using a canine-specific ELISA kit. RESULTS: Serum C3 and C4 concentrations were significantly higher in dogs with IE (C3, median; 4.901 [IQR; 3.915-6.673] mg/mL, P < .001; C4, 0.327 [0.134-0.557] mg/mL, P = .03) than in healthy control dogs (C3, 3.550 [3.075-4.191] mg/mL; C4, 0.267 [0.131-0.427] mg/mL). No significant differences were observed in serum C3 and C4 concentrations between dogs in the treatment (C3, median; 4.894 [IQR; 4.192-5.715] mg/mL; C4, 0.427 [0.143-0.586] mg/mL) and nontreatment groups (C3, 5.051 [3.702-7.132] mg/mL; C4, 0.258 [0.130-0.489] mg/mL). Dogs with a seizure frequency >3 times/month had significantly higher serum C3 (6.461 [4.695-8.735] mg/mL; P < .01) and C4 (0.451 [0.163-0.675] mg/mL; P = .01) concentrations than those with a seizure frequency ≤3 times/month (C3, 3.859 [3.464-5.142] mg/mL; C4, 0.161 [0.100-0.325] mg/mL). CONCLUSIONS AND CLINICAL IMPORTANCE: Dysregulation of classical complement pathway was identified in IE dogs. Serum C3 and C4 concentrations could be diagnostic biomarkers for IE in dogs with higher seizure frequency.

The Complement Component 4 Binding Protein α Gene: A Versatile Immune Gene That Influences Lipid Metabolism in Bovine Mammary Epithelial Cell Lines.

Complement component 4 binding protein α (C4BPA) is an immune gene which is responsible for the complement regulation function of C4BP by binding and inactivating the Complement component C4b (C4b) component of the classical Complement 3 (C3) invertase pathway. Our previous findings revealed that C4BPA was differentially expressed by comparing the transcriptome in high-fat and low-fat bovine mammary epithelial cell lines (BMECs) from Chinese Holstein dairy cows. In this study, a C4BPA gene knockout BMECs line model was constructed via using a CRISPR/Cas9 system to investigate the function of C4BPA in lipid metabolism. The results showed that levels of triglyceride (TG) were increased, while levels of cholesterol (CHOL) and free fatty acid (FFA) were decreased (p < 0.05) after knocking out C4BPA in BMECs. Additionally, most kinds of fatty acids were found to be mainly enriched in the pathway of the biosynthesis of unsaturated fatty acids, linoleic acid metabolism, fatty acid biosynthesis, and regulation of lipolysis in adipocyte. Meanwhile, the RNA-seq showed that most of the differentially expressed genes (DEGs) are related to PI3K-Akt signaling pathway. The expressions of 3-Hydroxy-3-Methylglutaryl-CoA Synthase 1 (HMGCS1), Carnitine Palmitoyltransferase 1A (CPT1A), Fatty Acid Desaturase 1 (FADS1), and Stearoyl-Coenzyme A desaturase 1 (SCD1) significantly changed when the C4BPA gene was knocked out. Collectively, C4BPA gene, which is an immune gene, played an important role in lipid metabolism in BMECs. These findings provide a new avenue for animal breeders: this gene, with multiple functions, should be reasonably utilized.

Renin-angiotensin-aldosterone-system inhibitors increase the serum level of complement component 4 in patients with immunoglobulin A nephropathy.

OBJECTIVE: To investigate the impact of renin-angiotensin-aldosterone-system (RAAS) inhibitors on complement component 4 (C4) serum levels in patients with immunoglobulin A nephropathy (IgAN). METHODS: A total of 423 patients diagnosed with IgAN at Shanxi Provincial People's Hospital, China, between 1 January 2017 and 31 December 2021 were divided into two groups, a RAAS inhibitor group and a non-RAAS inhibitor group, for comparative analysis. RESULTS: The RAAS inhibitor group exhibited significantly increased C4 and eGFR levels and had a higher proportion of patients with hypertension compared with the non-RAAS inhibitor group. Serum C4 levels were positively correlated with 24-hour urine protein, serum C3 levels and blood uric acid levels but negatively correlated with eGFR levels. In addition, serum C4 levels were positively correlated with the severity of mesangial hypercellularity and interstitial/tubular injury. Through prognostic analysis, serum C4 was identified as an independent risk factor for the progression of IgAN. CONCLUSION: Renin-angiotensin-aldosterone-system inhibitors can increase serum C4 levels in patients with IgAN and may represent an independent risk factor for disease progression.

Soluble terminal complement complex blood levels are elevated in schizophrenia.

The role of the complement system in schizophrenia (Sz) is inconclusive due to heterogeneity of the disease and study designs. Here, we assessed the levels of complement activation products and functionality of the classical pathway in acutely ill unmedicated Sz patients at baseline and after 6 weeks of treatment versus matched controls. The study included analyses of the terminal complement complex (sTCC) and C5a in plasma from 96 patients and 96 controls by enzyme-linked immunosorbent assay. Sub-group analysis of serum was conducted for measurement of C4 component and activity of the classical pathway (28 and 24 cases per cohort, respectively). We found no differences in levels of C5a, C4 and classical pathway function in patients versus controls. Plasma sTCC was significantly higher in patients [486 (392-659) ng/mL, n = 96] compared to controls [389 (304-612) ng/mL, n = 96] (p = 0.027, δ = 0.185), but not associated with clinical symptom ratings or treatment. The differences in sTCC between Sz and controls were confirmed using an Aligned Rank Transformation model considering the covariates age and sex (p = 0.040). Additional analysis showed that sTCC was significantly associated with C-reactive protein (CRP; p = 0.006). These findings suggest that sTCC plays a role in Sz as a trait marker of non-specific chronic immune activation, as previously described for CRP. Future longitudinal analyses with more sampling time points from early recognition centres for psychoses may be helpful to better understand the temporal dynamics of innate immune system changes during psychosis development.

Complement components regulates ferroptosis in CVB3 viral myocarditis by interatction with TFRC.

BACKGROUND: Dysregulated cell death machinery and an excessive inflammatory response in Coxsackievirus B3(CVB3)-infected myocarditis are hallmarks of an abnormal host response. Complement C4 and C3 are considered the central components of the classical activation pathway and often participate in the response process in the early stages of virus infection. METHODS: In our study, we constructed a mouse model of CVB3-related viral myocarditis via intraperitoneal injection of Fer-1 and detected myocarditis and ferroptosis markers in the mouse myocardium. Then, we performed co-IP and protein mass spectrometry analyses to explore which components interact with the ferroptosis gene transferrin receptor (TFRC). Finally, functional experiments were conducted to verify the role of complement components in regulating ferroptosis in CVB3 infection. RESULTS: It showed that the ferroptosis inhibitor Fer-1 could alleviate the inflammation in viral myocarditis as well as ferroptosis. Mechanistically, during CVB3 infection, the key factor TFRC was activated and inhibited by Fer-1. Fer-1 effectively prevented the consumption of complement C3 and overload of the complement product C4b. Interestingly, we found that TFRC directly interacts with complement C4, leading to an increase in the product of C4b and a decrease in the downstream complement C3. Functional experiments have also confirmed that regulating the complement C4/C3 pathway can effectively rescue cell ferroptosis caused by CVB3 infection. CONCLUSIONS: In this study, we found that ferroptosis occurs through crosstalk with complement C4 in viral myocarditis through interaction with TFRC and that regulating the complement C4/C3 pathway may rescue ferroptosis in CVB3-infected cardiomyocytes.

High-throughput complement component 4 genomic sequence analysis with C4Investigator.

The complement component 4 gene loci, composed of the C4A and C4B genes and located on chromosome 6, encodes for complement component 4 (C4) proteins, a key intermediate in the classical and lectin pathways of the complement system. The complement system is an important modulator of immune system activity and is also involved in the clearance of immune complexes and cellular debris. C4A and C4B gene loci exhibit copy number variation, with each composite gene varying between 0 and 5 copies per haplotype. C4A and C4B genes also vary in size depending on the presence of the human endogenous retrovirus (HERV) in intron 9, denoted by C4(L) for long-form and C4(S) for short-form, which affects expression and is found in both C4A and C4B. Additionally, human blood group antigens Rodgers and Chido are located on the C4 protein, with the Rodger epitope generally found on C4A protein, and the Chido epitope generally found on C4B protein. C4A and C4B copy number variation has been implicated in numerous autoimmune and pathogenic diseases. Despite the central role of C4 in immune function and regulation, high-throughput genomic sequence analysis of C4A and C4B variants has been impeded by the high degree of sequence similarity and complex genetic variation exhibited by these genes. To investigate C4 variation using genomic sequencing data, we have developed a novel bioinformatic pipeline for comprehensive, high-throughput characterization of human C4A and C4B sequences from short-read sequencing data, named C4Investigator. Using paired-end targeted or whole genome sequence data as input, C4Investigator determines the overall gene copy numbers, as well as C4A, C4B, C4(Rodger), C4(Ch), C4(L), and C4(S). Additionally, C4Ivestigator reports the full overall C4A and C4B aligned sequence, enabling nucleotide level analysis. To demonstrate the utility of this workflow we have analyzed C4A and C4B variation in the 1000 Genomes Project Data set, showing that these genes are highly poly-allelic with many variants that have the potential to impact C4 protein function.

Complement.

The role of complement in human autoimmune, inflammatory, and infectious diseases is reviewed, focusing on clinical applicability. A typical case is presented in which serum testing for C3 and C4 is performed to help assess a syndrome with a broad differential diagnosis. The review includes a discussion of complement deficiency states, consumption of complement by diseases characterized by immune-complex formation and deposition, usefulness and interpretation of laboratory tests for complement, and development of drugs targeting specific components of the complement pathway for a growing number of indications.

IMMUNOLOGICAL DISORDERS AND COLON DYSBIOSIS IN OBESE PATIENTS WITH HYPOTHYROIDISM.

OBJECTIVE: The aim: To investigate the peculiarities of immunological changes and their relationship with colon dysbiosis in obese patients with HT. PATIENTS AND METHODS: Materials and methods: The examined patients included 48 patients with HT and obesity (group 1) and 34 patients with obesity (group 2). Patients under¬went fecal analysis for dysbiosis. The levels of complement, namely C3 and C4 and the concentration of immunoglobulins (IgA, Ig M, IgG) were determined by means of chromogenic analysis. RESULTS: Results: During the clinical examination, constipation and flatulence were more often diagnosed in patients of group I (58.3% and 66.7%, respectively - p<0.001), while in patients of group 2 with increased BMI without thyroid dysfunction, a tendency to diarrhea was more often found, accompanied by periodic pain along the colon (50.0% and 32.3% of patients, respectively - p<0.001). Changes in the immunological status of patients in both groups were found. In patients with HT and increase of BMI an increase in serum IgA, IgM, IgG levels were found. An increase in serum immunoglobulins (A, M and G) was also diagnosed in group 2 of examined patients too. CONCLUSION: Conclusions: 1. In patients with obesity decrease in the concentration of Bifidobacterium, Lactobacillus and increase in the number of Staphylococcus, Clostridium, Proteus and Klebsiella were detected, which is more pronounced in patients with a combination of obesity and hypothyroidism. 2. Impairment distinct of immu¬nological status in patients with hypothyroidism and obesity was diagnosed, which was manifested by increased levels of immunoglobulins, namly (A, M, G), as well as a decrease in blood serum complements (C3, C4). 3. The level of IgA, G directly depends on the decrese of Bifidobacterium, Lactobacillus and increse of Staphylococcus, Clostridium and Klebsiella in patients with obesity, which is more pronounced in patients with a combination of obesity and hypothyroidism.

Cerebrospinal Fluid Complement 4 Levels Were Associated with Alzheimer's Disease Pathology and Cognition in Non-Demented Elderly.

BACKGROUND: Numerous studies have shown that the complement system plays an important role in Alzheimer's disease (AD). However, whether complement 4 (C4) protein in cerebrospinal fluid (CSF) was associated with AD pathology, especially in the early stage of AD, is still unclear. OBJECTIVE: We aimed to explore the association of CSF C4 with AD pathology and cognition in the preclinical AD. METHODS: The study included a total of 287 participants from the Alzheimer's Disease Neuroimaging Initiative (ADNI) database. Based on the A/T scheme, they were divided into four groups to access the changes of CSF C4 in the preclinical AD. Linear regression models were used to test the associations between CSF C4 and AD core biomarkers, namely Aß42, P-tau, and T-tau. RESULTS: The level of CSF C4 decreased in the A + T- group compared with the A-T- group (p = 0.04) and it increased in the A-T+ group compared to the A + T- group (p = 0.01). In pooled samples, C4 was significantly associated with AD core biomarkers (all p < 0.05), but only in the A + group after stratification according to the A/T scheme. Furthermore, CSF C4 levels at baseline were associated with longitudinal cognitive changes. CONCLUSIONS: Our results showed that CSF C4 levels changed dynamically in the preclinical AD, and that the responses of CSF C4 to brain Aß pathology, tau pathology and neurodegeneration were found only in the presence of amyloid plaques, both of which indicates the complex link between C4 and AD.