Experimental and clinical immunogenetics最新文献

'Human Immunoglobulin Heavy Variable Genes', the fourth report of the 'IMGT Locus on Focus' section, comprises five tables entitled: (1) 'Number of human germline IGHV genes at 14q32.33 and potential repertoire'; (2) 'Human germline IGHV genes at 14q32.33'; (3) 'Human IGHV orphons on chromosome 15 (15q11.2)'; (4) 'Human IGHV orphons on chromosome 16 (16p11.2)', and (5) 'Human IGHV allele table'. These tables are available at the IMGT Marie-Paule page from IMGT, the international ImMunoGeneTics database (http://imgt.cnusc.fr:8104) created by Marie-Paule Lefranc, Université Montpellier II, CNRS, France.

Ethnic comparisons are extremely important and useful for studying the HLA component involved in insulin-dependent diabetes mellitus (IDDM) predisposition. To date there have been only a few reports on the association of HLA loci and IDDM in Chinese. We report here a study on DQA1*Arg52, DQB1*nonAsp57, and DRB1*04 in IDDM children and control adults among Han Chinese living in Taiwan. One hundred and fourteen unrelated children (62 boys) with IDDM were studied. Their ages at diagnosis were between 0.3 and 15.0 years (6.8 +/- 3.6 years). The control population consisted of 120 randomly selected normal adults. DQA1*Arg52(+/+), DQB1*nonAsp57(+/+), and DRB1*04(+/-) were associated with IDDM (RR = 11.50, 2.21, and 2.82; p = 1.11 x 10(-15), 2.84 x 10(-3), and 1.98 x 10(-4), respectively). DQA1*Arg52, DQB1*nonAsp57, and DRB1*04 conferred risks for IDDM (RR = 12.79, 7.11, and 2.83; pc = 8.22 x 10(-4), 5.35 x 10(-3), and 5.68 x 10(-4), respectively). Combinations of DQA1*Arg52 and DRB1*04 conferred the highest risk for IDDM (RR = 19.64, pc = 5.4 x 10(-5)). DQA1*Arg52 was associated with IDDM in subjects with DQB1*nonAsp57+ (RR = 14.87, pc = 2.41 x 10(-4)) and DQB1*nonAsp57 was also associated with IDDM in subjects with DQA1*Arg52+ (RR = 8.41, pc = 1.54 x 10(-3)), suggesting that DQA1*Arg52 and DQB1*nonAsp57 are interacting. This study demonstrates that DQA1*Arg52, DQB1*nonAsp57, and DRB1*04 confer susceptibility for IDDM to Chinese children. A combination of DQA1*Arg52 and DRB1*04 confers the highest risk and it is suggested that a susceptibility gene might be situated between DQA1*Arg52 and DRB1*04 or both are synergistic. There is an interaction between DQA1*Arg52 and DQB1*nonAsp57 and homozygosity for DQA1*Arg52/DQB1*nonAsp57, which encodes four susceptibility DQ heterodimers, confers a high risk.

Variants of the mannose-binding lectin (MBL) have been shown to be associated with low serum concentrations of the protein and to predispose to bacterial, fungal and viral infections. A recent small study on 33 Caucasian patients had suggested that a mutation at codon 52 of the MBL gene is associated with chronic hepatitis B virus (HBV) infection. Exon 1 of the MBL gene was amplified by PCR in 61 patients with chronic HBV infection, 28 patients with acute infection and in 60 controls. MBL variants were detected by subsequent restriction enzyme digestion and agarose gel electrophoresis. The occurrence of the codon 52 mutation in patients with chronic HBV infection did not differ significantly from that in controls or patients with acute infection (9 vs. 7%), nor were there any significant differences for the codon 54 mutation. The frequency of MBL variants at codon 52 and 54 is not increased in patients with chronic HBV infection. Thus, the previously reported association of MBL deficiency with chronic HBV infection in adults could not be confirmed.

Complement component C4 genes are located within the central region of the human MHC. The genomic arrangement of these genes is complex, with each chromosome usually encoding either one or two C4 genes. C4 allotyping of a group of Western Australian Aborigines demonstrated certain discrepancies in the densitometric ratios between the C4A4 and the C4A3 protein bands; however, the mechanism causing the increase in density of the C4A4 band was unknown. Our aim was to determine whether the increase in densitometry was due to an increase in the expression of the C4A4 isotype, or whether these individuals carried a new complotype characterised by an increased gene copy number. Using pulsed-field gel electrophoresis and Taq I RFLP analysis we will show that the apparent increase in C4A4 protein expression was due to the existence of new, previously uncharacterised Aboriginal complotypes defined by at least three C4 genes. Segregation analysis from an extensive family suggests that one of the new C4 complotypes is likely to contain the duplicated C4A4 isotype together with a C4B2 gene (C4A4, C4A4, C4B2) and is the first such chromosomal arrangement seen in this population group.

The data on the structure and relationships of the TCC genes are reviewed and a model is presented for the processes of gene duplication by which the modern genes might have evolved. Data on variations of the overall gene numbers and relationships in modern species are also reviewed, together with the polymorphisms found in man. The apparent contradictions of lack of allelic association between markers and lack of direct evidence for recombination in the C6/C7 gene region is also discussed.

The human major histocompatibility complex (MHC) complement gene cluster (MCGC) is a highly variable region that is characterized by polymorphisms, variations in gene size and gene number, and associations with diseases. Deficiencies in complement C2 are either due to abolition of C2 protein synthesis by mini-deletions that caused frameshift mutations, or blocked secretion of the C2 protein by single amino acid substitutions. One, two or three C4 genes may be present in a human MCGC haplotype and these genes may code for C4A, C4B, or both. Deficiencies of C4A or C4B proteins are attributed to the expression of identical C4 isotypes or allotypes from the C4 loci, the absence or deletion of a C4 gene, 2-bp insertion at exon 29 or 1-bp deletion at exon 20 that caused frameshift mutations. The C4 genes are either 21 or 14.6 kb in size due to the presence of endogenous retrovirus HERV-K(C4) in the intron 9 of long C4 genes. A deletion or duplication of a C4 gene is always accompanied by its neighboring genes, RP at the 5' region, and CYP21 and TNX at the 3' region. These four genes form a genetic unit termed the RCCX module. In an RCCX bimodular structure, the pseudogene CYP21A, and partially duplicated gene segments TNXA and RP2 are present between the two C4 loci. The RCCX modular variations in gene number and gene size contributed to unequal crossovers and exchanges of polymorphic sequences/mutations, resulting in the homogenization of C4 polymorphisms and acquisitions of deleterious mutations in RP1, C4A, C4B, CYP21B and TNXB genes. RD, SKI2W, DOM3Z and RP1 are the four novel genes found between Bf and C4. RD and Ski2w proteins may be related to RNA splicing, RNA turnover and regulation of translation. The functions of Dom3z and RP1 are being investigated. The complete genomic DNA sequence between C2 and TNX is now available. This should facilitate a complete documentation of polymorphisms, mutations and disease associations for the MCGC.

The first report of the 'IMGT Locus on Focus' section comprises five tables entitled: (1) 'Number of human germline IGLV genes at 22q11.1-q11.2 and potential repertoire'; (2) 'Human germline IGLV gene table'; (3) 'Human IGLV allele table', (4) 'Human germline IGLJ table' and (5) 'Human IGLJ allele table'. These tables are available at the MariePaule page from IMGT, the international ImMunoGeneTics database (http:/(/)imgt.cnusc.fr:8104) created by Marie-Paule Lefranc, CNRS, Université Montpellier II, Montpellier, France.

Deficiency of the complement component C4 at the functional, protein and gene level and deficiency of complement component C2 at the functional level were investigated and HLA analysis was performed on patients with limited and diffuse systemic sclerosis (SSc). One of the patients with limited SSc (n = 15) had subnormal C4, 1 subnormal C2 and 1 subnormal C4 and C2 activities; the latter patient had HLA alleles A11;B35;Dw1 associated with type II C2 deficiency and therefore most likely had a defect at the C2 locus. One of the patients with diffuse SSC (n = 12) had subnormal C4 and 1 subnormal C4 and C2 activities. C2 deficiencies in patients other than the one with the haplotype associated with C2 deficiency appeared not to be determined by the gene at the C2 locus. The incidence of partial C2 deficiency in a normal Caucasian population is reported to be 16 in 10,000, and that of partial C4 deficiency also appears to be very low. The percentages of C4A*Q0 and C4B*Q0 alleles in normal controls (n = 45) were within the reported range. Seven patients with limited SSc (n = 14) had one or two C4A*Q0 alleles and 2 with diffuse SSc (n = 13) had one C4A*Q0 allele. Thus, the incidence of C4A*Q0 was higher than normal in limited SSc and within the normal range in diffuse SSc. The two-sided Fisher's exact test applied on these data revealed that the association of C4A*Q0 with limited SSc did not reach a significant level (p = 0.10). Two of the 3 patients with limited SSc, who had two C4A*Q0 alleles, carried a heterozygous C4A-21-hydroxylase A (OHA) gene segment deletion as detected by Southern blotting. There was no correlation between the subnormal activity of C4 and the occurrence of one or two C4A*Q0 (and C4A-21-OHA segment deletion). HLA alleles A1, B8 and DR3 (p = 0.002) were associated with limited SSc (n = 23) and DR5(w11) (p = 0.018) with diffuse SSc (n = 17).

The results of the present (VIIth Complement Genetics Workshop and Conference, Mainz, May 1998) and past reference typing workshops for the terminal complement components C6, C7 and C9 are compiled and discussed both on the protein level and on the DNA level. This report also focuses on the molecular bases of expressed and silent polymorphisms and reviews the molecular bases of subtotal and complete deficiencies of these proteins and their associations with protein and DNA markers. The results of the protein typing for C6 are published in the following paper of this issue.