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PubMed1992

Structural differences between the two human complement C4 isotypes affect the humoral immune response.

An animal model has been used to address the question of the biological importance of the known structural difference between the two isotypes of human C4, i.e., C4A and C4B. Guinea pigs deficient in C4 were reconstituted transiently with either human C4A or C4B protein and immunized with the bacteriophage phi X174. Results from this study showed that C4A-reconstituted animals made a secondary response, i.e., switch from IgM to IgG; whereas the C4B-reconstituted animals did not.

Animals↗
PubMed1994

Is partial deletion of the complement C4 genes associated with sudden infant death?

The two C4 loci C4A and C4B in 61 cases of sudden infant death (SID), 93 living controls and 7 cases of infectious death were studied. In the SID group 13.1% showed deletion of the C4A gene, while 2.5% of the cases showed deletion of the C4B gene. This was not significantly different from neither the controls nor the infectious death group. We were not able to confirm that deletion of the C4B gene is associated with SID. However, in the SID group deletion of either the C4A or the C4B gene was associated with signs of infections prior to death (P = 0.035). This observation may indicate that a proportion of SID victims are more vulnerable to infections than other infants.

Adult↗
PubMed1983

Murine sex-limited protein (Slp) antigenic sites in human complement component C4.

Human complement component C4 is encoded by two HLA-linked loci, A and B. In the mouse, the H-2 region contains structural genes for two serum proteins that react with antibodies to human C4, but one of these proteins (Slp) has no C4 hemolytic activity. Because the product of C4-A locus in man has low hemolytic activity, a previous report suggests it may be the homologue of murine Slp. We show here that Slp antigenic determinants are found in human C4. However, they are expressed in the products of both loci A and B, that is, C4A and C4B, since both proteins were specifically immunoprecipitated by the IgG fraction of alloantisera to mouse Slp. Therefore, Slp-associated structural features are preserved in evolution, although they do not seem to be relevant to the hemolytic properties of C4.

Alleles↗
PubMed1984

Studies on the binding of complement factor C4 in human platelets. Complement activation by means of cold agglutinins.

Normal human platelets were investigated by immunofluorescence techniques for the natural occurrence of and uptake capacity for complement factor C4. Fractions of human platelets were found to carry none or very little C4. Activated C4 was readily taken up by the majority of platelets in vitro. Complement could be activated with pathological cold agglutinins (CA) of mono- or polyclonal types, all with specificity for the I antigen. Complement activation seen in normal human sera was probably due to naturally occurring CA with anti-I specificity. Thrombin potentiated the complement-activating capacity of CA, and complement factor C1 enhanced and stabilized the binding of CA to platelets.

Agglutinins↗
PubMed1992

[Complement C3 and C4 levels in serum from acute viral hepatitis].

Serial measurements of C3 and C4 complement components were performed in 50 patients with acute, uncomplicated viral hepatitis, in the beginning of the symptoms and in the peaks of serum transaminases. There were 17 patients diagnosed as having Hepatitis A virus (HAV) infection and 33 patients diagnosed as having Hepatitis B virus (HBV) infection. There were 4 women and 46 men with a mean age of 22.1 years. In the sera of 50 healthy control subjects serum C3 and C4 complement components measured, this group was composed of 15 women and 35 men with a mean age of 26 years. The complement component levels were observed to be reduced in both viral infections, where the reduction in C3 serum concentration was found to be statistically significant but reduction in C4 serum concentration was not.

Acute Disease↗
PubMed1997

[Early post myocardial infarction syndrome--a trial of assessment based on clinical course and immunologic tests].

The study analysed clinical and immunological course of 22 patients (aged 56.3 +/- 9.5) with fever (38.5 degrees C) and greatly increased erythrocyte sedimentation rate (ESR) in the first week after myocardial infarction. The control group consisted of 25 patients (aged 50.7 +/- 11.2) without inflammatory and infectious diseases. Clinical courses of the disease, chest x-ray, echocardiography, leucocytosis and serial CK-MB levels were analysed. The immunological investigations involved quantitative estimation of IgG, C3 complement, C4 complement and the identification of T and B lymphocytes on the basis of the rosette tests A, E and EAC. Post myocardial infarction syndrome (PMIS) manifested by fever and greatly increased ESR we observed in 64% of examined patients, but fully manifested PMIS in 14% with tendency to recurrences. We found the differences in immunological examinations compared to the control group. Pericardial effusion occurred in 64% of the patients. The treatment with corticosteroids brought dramatic relief of the symptoms with objective improvement of clinical condition. Patients with high temperature with accompanying greatly raised ESR in the first week after MI may demonstrate abortive form of the post myocardial infarction syndrome.

Aged↗
PubMed1985

Complement factor C4 in schizophrenia.

The complement factor C4 was studied in 165 schizophrenic patients and in 330 controls. A highly significant increase in the frequency of C4B deficiency (BQO) was found among the schizophrenic patients compared with controls (p less than 0.0005).

Complement C4↗
PubMed1989

Sequence of the gene for murine complement component C4.

The gene for murine complement component C4 lies in the S region of the murine major histocompatibility (H-2) complex; in this paper, we report the nucleotide sequence of this gene. The present sequence extends from a SmaI restriction enzyme cleavage site near the 5' end of the gene to a KpnI restriction enzyme cleavage site 569 nucleotides 3' of the polyadenylation site. The sequence spans 15,956 base pairs and together with previously reported data provides a complete sequence extending from the site of transcriptional initiation to the polyadenylation site. The sequence reveals that the C4 gene has 40 introns which range from 75 to 1089 base pairs in length and which include three murine B1 middle repetitive elements, a MT repeat element, and an apparently novel repeat sequence that is also found in noncoding regions of the murine beta-glucuronidase, lymphotoxin (TNF-beta), and rat alpha-crystallin genes. An intron splits the protein coding sequence precisely at the site of proteolytic activation of C4 by complement protease C1s; however, except for this one case, the intron positions show no striking relationship to the structural features of the C4 protein. The length of the murine C4 gene relative to the isotypic C4A and C4B genes in man suggests the independent loss of a 6-kilobase intron from both murine and human C4 genes.

Animals↗
PubMed1985

The origin of the very variable haemolytic activities of the common human complement component C4 allotypes including C4-A6.

The human complement component C4 occurs in many different forms which show big differences in their haemolytic activities. This phenomenon seems likely to be of considerable importance both physiologically and pathologically. C4 is coded by duplicated genes between HLA-D and HLA-B loci in the major histocompatibility complex in man. Several fold differences in haemolytic activity between products of the two loci C4-A and C4-B have been correlated with changes of six amino acid residues in this large protein of 1722 residues and with differences of several fold in the covalent binding of C4 to antibody-antigen aggregates. Some allotypes of one locus also differ markedly, notably C4-A6 which has 1/10th the haemolytic activity of other C4-A allotypes. A monoclonal antibody affinity column has been prepared which is able to separate C4-A from C4-B proteins and, using serum from an individual expressing only the C4-A6 allele at the C4-A locus, C4-A6 protein has been prepared. Investigation has shown C4-A6 to have the same reactivity as other C4-A allotypes except in the formation of the complex protease, C5 convertase. This protease is formed from C4, C2 and C3 and if C4-A6 is used it has approximately 1/5th the catalytic activity compared with other C4-A allotype. Allelic differences in sequence identified in C4 proteins so far are few and it is probable that the big difference in catalytic activity of C5 convertase is caused by very small changes in structure.

Alleles↗
PubMed1990

The complement component C4 of mammals.

Human complement component C4 is coded by tandem genes located in the HLA class III region. The products of the two genes, C4A and C4B, are different in their activity. This difference is due to a degree of 'substrate' specificity in the covalent binding reactions of the two isotypes. Mouse also has a duplicated locus, but only one gene produces active C4, while the other codes for the closely related sex-limited protein (Slp). In order to gain some insight into the evolutionary history of the duplicated C4 locus, we have purified C4 from a number of other mammalian species, and tested their binding specificities. Like man, chimpanzee and rhesus monkey appear to produce two C4 types with reactivities similar to C4A and C4B. Rat, guinea pig, whale, rabbit, dog and pig each expresses C4 with a single binding specificity, which is C4B-like. Sheep and cattle express two C4 types, one C4B-like, the other C4A-like, in their binding properties. These results suggest that more than one locus may be present in these species. If this is so, then the duplication of the C4 locus is either very ancient, having occurred before the divergence of the modern mammals, or there have been three separate duplication events in the lines leading to the primates, rodents and ungulates.

Animals↗