Genetics and the C3 molecule

Complement polymorphism in herpes gestationis: association with C4 null allele

BACKGROUND

Herpes gestationis (HG) is a rare, pregnancy-related skin disease characterized by the production of an autoantibody to a component of the hemidesmosome. It is associated with the class II antigens HLA-DR3 and HLA-DR4, but its potential association with the "class III antigens" C2, C4, and factor B has not previously been studied.

OBJECTIVE

Our purpose was to study complement polymorphism in HG.

METHODS

Using electrophoresis and immunofixation techniques, we determined the allele frequencies of C4A, C4B, C3, and factor B in 42 patients with a history of HG.

RESULTS

Ninety percent of patients carried a C4 null allele (C4*QO). No statistically significant association with C3 or factor B alleles was seen.

CONCLUSION

HG is associated with the presence of a C4*QO. Whether the C4*QO is the primary genetic association, or whether the C4*QO is related to its linkage disequilibrium with DR3 and DR4 has yet to be determined.

Purification of chicken C3 and a structural and functional characterization

A major plasma protein from chicken, analogous to mammalian complement component C3, was purified by the removal of plasminogen, precipitation with polyethyleneglycol, and ion-exchange chromatography. Purification was guided by a rabbit antiserum specific to chicken C3. The yield of native C3 was 27%, and purity and functional activity was assessed by SDS-PAGE, immunoprecipitation techniques, and the ability of the purified C3 to restore the haemolytic activity of C3-depleted chicken serum. Monoclonal antibodies were raised against purified chicken C3. These antibodies were characterized and used to prepare an immunosorbent column to deplete chicken plasma specifically of C3. Chicken C3 has a mol.wt of 185,000-195,000 and a two-chain structure with an alpha chain (118,000) and beta chain (68,000). Complement activation leads to changes in the electrophoretic mobility of chicken C3 and to a decrease in mol.wt to 144,000 corresponding to the release of a 15,000 C3a and a 34,000 C3d/C3dg fragment. Chicken C3 exists in multiple molecular forms with pI values of 6.4-6.6. A genetic polymorphism of chicken C3 based on electrophoretic mobility has not yet been detected after analysis of more than 500 individuals. The function of chicken C3 is dependent on a reactive thioester because treatment of purified chicken C3 with methylamine causes functional inactivation of C3.

Isolation and characterization of the third component of bovine complement

C3 was obtained from bovine serum by polyethylene glycol precipitation and chromatography on DEAE-Sephadex A-50, CM-Sephadex A-50 and Sephacryl S-200. The protein has a molecular weight of 183,000 (alpha-chain 114,000 and beta-chain 69,000). A CVF-induced bovine C3 convertase (Sepharose-CVF.Bb) cleaved C3 into C3a (11,000) and C3b (172,000) as shown by SDS-polyacrylamide gel electrophoresis. Isoelectricfocusing of C3 demonstrated at least three electrophoretic variants with pI 6.55-6.85. The isolated protein promoted the formation and action of a C3 convertase in the presence of purified bovine factors B and D. A monospecific antiserum prepared in rabbits failed to cross react with human C3 or CVF. C3c was identified as a contaminant during the isolation of C3.

Recombination between the t6 complex and linked loci in the house mouse

Recombination between the t6 complex, three allozyme-encoding loci, two antigen-encoding loci, and four molecular markers was studied. The allozyme-encoding loci were complement component-3 (C-3), kidney catalase (Ce-2), and glyoxalase-1 (Glo-1); the antigen-encoding loci were the H-2 Class I genes H-2K and H-2D; the four molecular markers were Tu66, an α-globin pseudogene (Hba-4ps), an unidentified H-2 Class I gene, and the H-2 Class II gene I-Aβ. The latter six loci were used as markers for the t complex. Recombination was detected between Glo-1, Ce-2 and C-3, but not between the markers for the t complex Tu66, Hba-4ps, and the H-2 loci. These data indicate that Ce-2 and C-3 are located outside the t6 complex, while the latter are located within. These data also indicate that the telomeric boundary of the t6 complex is located between H-2 and Ce-2. Recently published studies have shown that complete gametic disequilibrium exists between the t complex and loci located centromeric to the H-2 - Ce-2 interval, while disequilibrium was not detected between loci located telomeric to this interval. Loci included within the region of recombination suppression are also those in disequilibrium with the t complex. As a result, recombination suppression probably resulting from chromosomal rearrangements associated with the t complex appears to be a sufficient explanation for the gametic disequilibrium observed between certain loci and the t complex.

A rare phenotype C3, F-F0.8 encountered in three successive generations of one family

In the course of a disputed paternity case, a rare phenotype of factor C3 (F-F0.8), not described so far, has been found in three generations of one and the same family. The frequency in the population of such a phenotype is not known.

Structure and expression of the C3 gene

To map the multiple interactive sites on the C3 polypeptide, it is advantageous to combine the approaches of protein chemistry, nucleic acid technology, and molecular biology. This review summarizes the currently known molecular properties of mouse liver C3 mRNA, cloned C3 cDNA, and genomic DNA. Original data communicated have specified the amino acid sequence of the 215 amino-terminal residues of mature mouse C3 beta. Southern blot analysis of liver DNA indicated that the mouse genome contains only one type of C3 gene, that murine and human C3 sequences strongly cross-hybridize, and that the human C3 gene is not somatically rearranged. Included are descriptions of the first human C3 genomic DNA clones, their preparation, and their use to map the human C3 gene to chromosome 19 in linkage with the myotonic dystrophy (DM) locus. After a brief survey of reports describing inherited human C3 deficiencies, we discuss a Dutch family and their three members with total homozygous C3 deficiency who were the subjects of a recent publication. The restricted synthesis of C3 in major and minor producer tissues is discussed and it is proposed that the C3 gene provides a good model system for studying the molecular basis of tissue-specific gene expression. Data are presented documenting the production of C3 in two established mouse macrophage-like cell lines and two rat hepatoma cell lines in tissue cultures. A short account covers the extensive literature on regulation of C3 serum concentrations in acute and chronic inflammation and the very incomplete picture that presently depicts hormonal regulation of C3 synthesis. The final experiment reported demonstrates that nucleic acid hybridization with cloned cDNA probes is a sensitive assay for quantitative determinations of C3 mRNA. With the help of cloned cDNA and genomic DNA, researchers can address questions concerning the functional topography of the C3 polypeptide, the gene's structure, and the molecular nature of inherited C3 deficiencies in humans.

Genetic polymorphism of C3 in Papio and Macaca species

C3 phenotypes were examined in species of Papio and Macaca. Baboons (P. cynocephalus) showed extensive polymorphism, with estimated gene frequencies of 0.815, 0.174, and 0.011 for C3*S, C3*F, and C3*F1 alleles, respectively. Clear segregation patterns showing codominant inheritance were evident in family studies. Such extensive polymorphism was not observed in M. nemestrina or M. fascicularis. The S gene is the most common allele in all the species studied. The F gene is relatively common in baboons.

The minimal length of the differential segment in H-2 congenic lines

One hundred and four H-2 congenic lines were typed for alleles at seven loci, Qa-1, Qa-2, Tla, C3, Ce-2, Pgk-2, and Upg-1, residing distal to the H-2 complex. The results of the typing were used to estimate the length of the segment of chromosome 17 derived from the donor strain of each line--that is, the minimal length of the differential segment. The results indicate that only lines derived by intra-H-2 crossing-over in such a way that they inherited the right-hand portion of H-2 from the inbred partner have the telomeric half of chromosome 17 identical with that of the inbred-partner strain. In other lines the differential segment is at least 3 to 10 cM long. It is argued that in some lines the entire telomeric half of chromosome 17 might be of donor-strain origin.

Genetic polymorphism of C3 and serum levels of immunoglobulins, C3, C4 components of complement and C3-proactivator in four different populations of Afghanistan

The C3 phenotype distribution was studied in 4 different populations from Afghanistan. The gene frequencies of C3S allele were: Tajiks (0,8547), Pushtoons (0.8812), Hazaras (0.9036) and Osbeks (0.8530). These values were significantly higher than in European populations studied previously. No significant differences were found between the mean serum levels of C3, C4 and C3-proactivator among 4 population groups. A higher concentration of IgG, IgA and IgM was observed in Afghanistan sera than reported for Europeans.

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.