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PubMed1987

DNA polymorphism of human HLA-linked complement C4 allotypes, including C4 null alleles, in the Finnish population.

Human HLA-linked complement C4 gene products, C4A and C4B, show extensive genetic polymorphism. In both loci, an allele without a gene product, C4 null, is also observed. We have performed a restriction enzyme analysis of genomic DNA samples from individuals having all common (frequency over 1%) C4 protein allotypes observed in the Finnish population. Only one allotype-specific RFLP marker was observed. With some enzymes a DNA polymorphism was observed, which was not detectable by C4 protein typing. Analysis of 10 different C4B null haplotypes and 4 C4A null haplotypes suggested that only one haplotype, HLA-B8 C4A0 B1, carried a C4A gene deletion. This was observed in all 4 unrelated individuals homozygous for this haplotype.

Alleles↗
PubMed1994

Association of complement C4 and HLA-DR alleles with systemic lupus erythematosus in Koreans.

OBJECTIVE: To examine the association of complement C4 and HLA-DR to systemic lupus erythematosus (SLE) susceptibility in Korea. METHODS: Complement C4 protein typing was carried out by immunofixation and immunoblotting methods using EDTA-plasma from 60 patients with SLE and 72 healthy controls. Restriction fragment length polymorphism analysis of C4 genes was also carried out using TaqI or HindIII for restriction enzymes. HLA-DR was determined by polymerase chain reaction amplification with sequence specific primers using genomic DNA from 67 patients with SLE and 72 healthy controls. RESULTS: The frequency of the C4AQ0 allele was significantly higher in the patients with SLE than in controls (41.7 vs 25.0%, p < 0.05). The deletion of the C4A gene commonly found in Caucasian patients with SLE was not observed in any patients. For HLA-DR, a significant increase of the haplotype DRB1*1501 was observed in the patients (26.9 vs 12.5%, p < 0.05) and DR9 was also significantly increased (23.9 vs 11.1%, p < 0.05). An increase in each DR2 and DR9 was independent of an increase in C4AQ0. The frequencies of DR2 and DR9 were significantly decreased in patients with renal involvement and alopecia, respectively. CONCLUSION: Our data suggested that the presence of C4AQ0 allele, DRB1*1501-DRB5*0101 haplotype and DR9 contributed to susceptibility to SLE in Koreans and that Korean SLE is based on a different genetic background from Caucasian patients.

Adult↗
PubMed1995

Complement C4, factor B and C3 polymorphism in north India.

Allotype frequencies of complement C4, factor B and C3 proteins were determined in 192 healthy unrelated individuals from North India. The gene frequencies for the most common factor B and C3 alleles were close to the data already published. As expected, significant differences were observed in this first study of C4 allotype frequencies among the North Indian population in comparison to European Caucasians. According to historians, Hungarian Gypsies migrated from India. In this study we demonstrate that our data for some complement allele frequencies are in accordance with the opinion of historians.

Adult↗
PubMed1988

Complement C4 phenotypes in dementia of the Alzheimer type.

Complement C4 phenotype distribution was studied in 64 patients with dementia of the Alzheimer type. In contrast to reported findings we failed to find a significant association between C4B2 gene frequency and Alzheimer's dementia.

Alzheimer Disease↗
PubMed1983

Alpha 1-antitrypsin, alpha 2-macroglobulin and complement C4 in human benign prostatic hyperplasia.

The concentrations of the globulins alpha 1-antitrypsin, alpha 2-macroglobulin and complement C4 have been determined in tissue samples of benign prostatic hyperplasia, from patients with and without prior treatment before open surgery. Globulins have been determined by means of radial immunodiffusion. Results obtained show that alpha 1-antitrypsin is present in high concentrations in human prostate. Treatment with anti-androgens influences the alpha 2-macroglobulin concentration in the different prostatic lobes. Complement C4 concentration is not influenced by the treatment.

Androgen Antagonists↗
PubMed2004

Normal complement C4 values do not exclude hereditary angioedema.

This report describes a patient with hereditary angioedema (HAE) in whom complement C4 values were consistently normal. There was a family history of HAE, for which the patient had previously been screened, but in view of her normal C4 values she was deemed unaffected. However, at 10 years of age she presented with an eight month history of episodes of swelling affecting her hands and recurrent episodes of abdominal pain over the previous few months. In view of the recent clinical history of swellings and the family history of HAE, C4 and C1 inhibitor (C1inh) were measured. The C4 concentration was found to be within the normal range but the C1inh value was low (0.07 g/litre; normal range, 0.18-0.37). The patient was started on tranexamic acid and at an outpatient review three months later her episodes of swelling were occurring less often and were less severe. Although recent papers have suggested that the diagnosis of HAE can be excluded if complement C4 concentrations are normal, this case highlights the fact that C4 concentrations can be normal in this condition, and it is recommended that both C4 and C1inh concentrations should be measured to exclude HAE.

Angioedema↗
PubMed1980

The cerebrospinal fluid C4 complement component in different meningeal and neurological diseases.

The C4 complement component was measured in CSF from 10 patients without CNS involvement (controls) and 71 with various meningeal and neurological diseases. Serum C4 was also measured in the control group and in 46 of the 71 neurological patients. A significant increase of CSF C4 was observed in all neurological diseases with meningeal involvement independent of the causative agent. Inversely, serum C4 values were within normal limits. Increased CSF C4 with normal serum levels might indicate increased diffusion across the blood-brain barrier, decreased ability for immunocomplex production or increased local production.

Brain Diseases↗
PubMed1975

Serum C3 and C4 complement components in ulcerative colitis and Crohn's disease.

Serum C3 and C4 complement components were estimated in patients with Crohn's disease and ulcerative colitis. In Crohn's disease, serum C4 concentrations were significantly higher than those of controls. In ulcerative colitis, significantly higher concentrations of C3 and C4 were associated with severe or extensive disease, and C4 concentrations may remain high, years after total colectomy.

Adult↗
PubMed1996

Polymorphism of complement C4 and susceptibility to IDDM and microvascular complications.

OBJECTIVE: The aim of this study was to investigate whether or not the inherited polymorphism of complement C4 is associated with genetic susceptibility to microvascular complications in IDDM as previously reported. RESEARCH DESIGN AND METHODS: We determined C4 phenotypes in 241 patients with IDDM and 140 healthy control subjects by agarose gel electrophoresis and immunoprecipitation. C4 allotype frequencies were compared between patients and healthy control subjects. In addition, we compared allotype frequencies of 83 patients with nephropathy with those of 80 patients without nephropathy and compared those of 50 patients with proliferative retinopathy with those of 68 patients without retinopathy or background retinopathy. Duration of IDDM in control patients was at least 21 years. RESULTS: Patients and healthy control subjects differed at both the C4A (P < 0.00001) and C4B (P < 0.0005) loci. The C4 null allele C4AQ0 was significantly increased in IDDM patients (26.8 vs. 11.8%, P < 0.005). C4B2 was more frequently observed in patients (14.5 vs. 6.8%, P < 0.05) compared with healthy control subjects. No differences were observed in C4 allotype distribution between patients with and without nephropathy or retinopathy. CONCLUSIONS: These data confirm previous reports of an association between the C4 null allele C4AQ0 and IDDM. Our results do not support an association of the inherited polymorphism of complement C4 with genetic susceptibility to microvascular complications in patients with IDDM.

Adolescent↗
PubMed2002

Characterization of a de novo conversion in human complement C4 gene producing a C4B5-like protein.

Complement C4 is a highly polymorphic protein essential for the activation of the classical complement pathway. Most of the allelic variation of C4 resides in the C4d region. Four polymorphic amino acid residues specify the isotype and an additional four specify the Rodgers and Chido determinants of the protein. Rare C4 allotypes have been postulated to originate from recombination between highly homologous C4 genes through gene conversions. Here we describe the development of a de novo C4 hybrid protein with allotypic and antigenic diversity resulting from nonhomologous intra or interchromosomal recombination of the maternal chromosomes. A conversion was observed between maternal C4A3a and C4B1b genes producing a functional hybrid gene in one of the children. The codons determining the isotype, Asp(1054), Leu(1101), Ser(1102), Ile(1105) and His(1106), were characteristic of C4B gene, whereas the polymorphic sites in exon and intron 28 were indicative of C4A3a sequence. The protein produced by this hybrid gene was electrophoretically similar to C4B5 allotype. It also possesses reversed antigenicity being Rodgers 1, 2, 3 and Chido-1, -2, -3, 4, -5, and -6. Our case describes the development of a rare bimodular C4B-C4B haplotype containing a functional de novo C4 hybrid gene arisen through gene conversion from C4A to C4B. Overall the data supports the hypothesis of gene conversions as an ongoing process increasing allelic diversity in the C4 locus.

Complement C4a↗
PubMed2002

The variable endogenous retroviral insertion in the human complement C4 gene: a transmission study in type I diabetes mellitus.

A variable endogenous retroviral element has been identified in intron 9 of the complement C4 gene [HERV-K(C4)], which maps to the class III region of the major histocompatibility complex (MHC) on chromosome 6p21.3. Genetic susceptibility to type I diabetes is mainly conferred by the MHC locus and the complement C4 region has been implied to contribute to human leukocyte antigen DQ (HLA-DQ) mediated disease risk. As the HERV-K(C4) insertion has been suggested to modulate expression of homologous genes, we investigated its transmission in 220 families with an offspring affected by type I diabetes as a potential disease susceptibility marker. There was no preferential transmission of the HERV-K(C4) insertion to affected offspring (P(TDT) = 0.79). Although 77.7% of HLA-DQ8 carried the HERV-K(C4) insertion, only 52.9% of -DQ2 haplotypes did (P(chi(2)) < 0.01). However, its insertion or deletion did not modulate the risk conferred by HLA-DQ8 (DQA1*0301-DQB1*0302) (P(chi(2)) = 0.27) or -DQ2 (DQA1*0501-DQB1*0201) (P(chi(2)) = 0.46). Thus, the HERV-K(C4) insertion is not associated with type I diabetes in Germans.

Complement C4↗
PubMed1992

Synthesis and regulation of the fourth component of complement (C4) in the human monocytic cell line U937: comparison with that of the third component of complement (C3).

Production of the fourth component of complement (C4) by the human monocytic cell line U937 and its regulation were investigated in comparison with the production of the third component of complement (C3) in a cell culture system. Although no detectable C4 was produced by U937 without stimulation, U937 was induced by recombinant interferon-gamma (IFN-gamma) to synthesize C4 in a dose- and time-dependent fashion. The production of C4 was reversibly inhibited by cycloheximide, indicating that it resulted from de novo synthesis. The C4 synthesized by U937 cells was functionally active as assessed by haemolytic assay. SDS-PAGE following biosynthetic labelling showed that subunit structure of C4 synthesized by U937 cells was identical with that of plasma C4 but that molecular weight of alpha-chain was greater than that of plasma C4. We compared the regulation of C4 synthesis with that of C3 synthesis. Although C3 synthesis by U937 cells was enhanced by IFN-gamma, lipopolysaccharide (LPS) and phorbol myristate acetate (PMA), C4 synthesis was induced only by IFN-gamma. LPS and IFN-gamma induced a synergistic increase in C3 synthesis by U937 cells. U937 cells incubated with LPS and IFN-gamma synthesized a greater amount of C4 than those incubated with IFN-gamma alone. Thus it was demonstrated that the synthesis of C3 and C4 was independently regulated. This study shows that the U937 cell line provides a useful model for studies on the synthesis of complement proteins and on the regulation of complement production.

Cell Line↗
PubMed1994

The dichotomous size variation of human complement C4 genes is mediated by a novel family of endogenous retroviruses, which also establishes species-specific genomic patterns among Old World primates.

The human complement C4 genes in the HLA exhibit an unusual, dichotomous size polymorphism and a four-gene, modular variation involving novel gene RP, complement C4, steroid 21-hydroxylase (CYP21), and tenascin-like Gene X (RCCX). The C4 gene size dichotomy is mediated by an endogenous retrovirus, HERV-K(C4). Nearly identical sequences for this retrotransposon are present precisely at the same location in the long C4 genes from the tandem RCCX Module I and Module II. Specific nucleotide substitutions between the long and short C4 genes have been identified and used for diagnosis. Southern blot analyses revealed that HERV-K(C4) is present at more than 30 locations in the human genome, exhibits variations in the population, and its analogs exist in the genomes of Old World primates with species-specific patterns. Evidence of intrachromosomal recombination between the two long terminal repeats of HERV-K(C4) is found near the huntingtin locus on chromosome 4. It is possible that members of HERV-K(C4) are involved in genetic instabilities including the RCCX modules, and in protecting the host genome from retroviral attack through an antisense strategy.

Amino Acid Sequence↗
PubMed2000

Complement C4 inhibits systemic autoimmunity through a mechanism independent of complement receptors CR1 and CR2.

The complement system enhances antibody responses to T-dependent antigens, but paradoxically, deficiencies in C1 and C4 are strongly linked to autoantibody production in humans. In mice, disruption of the C1qa gene also results in spontaneous autoimmunity. Moreover, deficiencies in C4 or complement receptors 1 and 2 (CR1/CR2) lead to reduced selection against autoreactive B cells and impaired humoral responses. These observations suggest that C1 and C4 act through CR1/CR2 to enhance humoral immunity and somehow suppress autoimmunity. Here we report high titers of spontaneous antinuclear antibody (ANA) in C4(-/)- mice. This systemic lupus erythematosus-like autoimmunity is highly penetrant; by 10 mo of age, all C4(-)(/)- females and most males produced ANA. In contrast, titers and frequencies of ANA in Cr2(-)(/)- mice, which are deficient in CR1 and CR2, never rose significantly above those in normal controls. Glomerular deposition of immune complexes (ICs), glomerulonephritis, and splenomegaly were observed in C4(-)(/)- but not Cr2(-)(/)- mice. C4(-)(/)-, but not Cr2(-)(/)-, mice accumulate activated T and B cells. Clearance of circulating ICs is impaired in preautoimmune C4(-)(/)-, but not Cr2(-)(/)-, mice. C4 deficiency causes spontaneous, lupus-like autoimmunity through a mechanism that is independent of CR1/CR2.

Animals↗