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Biomedical subjects

J Klein

Publications and source records attributed to J Klein.

At least 397 records · Page 22Linked to original sources
PubMed1994

HLA-B44-directed cytotoxic T cells associated with acute graft-versus-host disease following unrelated bone marrow transplantation.

We describe the recipient of a marrow graft from an HLA-serologically identical unrelated donor from whom highly potent host-reactive CTL of donor origin were isolated in association with acute GVHD. Extensive sequence and biochemical analysis of the HLA complex of this donor and recipient revealed several disparities in class I and class II HLA with the potential to be recognized by T cells from the donor or the host. The donor-derived CTL exclusively recognized a class I HLA difference associated with HLA-B44. Nucleotide sequencing of donor and recipient cells revealed that the patient possessed the HLA-B*4402 allele recognized by IEF as B44.2 while the donor possessed HLA-B*4403 (IEF variant B44.1). These alleles differ at one amino acid residue located at position 156 in the alpha 2 domain. The donor-derived CTL were shown to be specific for B44.2 by blocking studies and by the lysis of five different B44.2+ unrelated cell lines, two of which were confirmed by sequencing to be homozygous for B*4402. A host-specific difference involving a HLA-DRB1 allele was not recognized by the CTL, neither did HLA differences unique to the donor HLA-B*4403 and HLA-DQ8 elicit a host response. These data show that certain HLA disparities may be tolerated at the same time that other disparities elicit a potent immunologic response. The chemical nature of the difference, its structural impact, as well as the conditions of transplant appear to influence the type of response which occurs.

Acute Disease↗
PubMed1993

Release of choline from rat brain under hypoxia: contribution from phospholipase A2 but not from phospholipase D.

Moderate hypoxia induced in rats by inhalation of 10% oxygen led to an increase of the concentration of free choline in the brain and caused a large net-release of choline from the brain into the venous blood as determined by the measurement of the arterio-venous difference. In hippocampal slices from rat brain, hypoxia increased the release of choline into the superfusion medium. The activity of phospholipase D, as measured by the formation of phosphatidylpropanol in the presence of propanol, was not stimulated under these conditions. However, the mobilization of choline was completely depressed by lowering extracellular calcium and by 0.1 mM mepacrine. We conclude that hypoxia leads to a selective activation of phospholipase A2 in the brain and, consequently, to a net loss of choline-containing phospholipids and membrane structures.

Animals↗
PubMed1993

Resolution of the HLA-DRB6 puzzle: a case of grafting a de novo-generated exon on an existing gene.

HLA-DRB6, one of the human major histocompatibility complex genes, lacks exon 1, which normally codes for the leader and the first four amino acid residues of the mature protein. Because it also lacks the HLA promoter, it was surprising to find that the gene is transcribed at a low level in a chimpanzee B-lymphoblastoma cell line, in which the DRB6 homolog is truncated as in humans. The study designed to resolve the paradox has revealed that a retrovirus related to the mouse mammary tumor viruses was inserted into intron 1 of DRB6 > 23 million years ago. The insertion was either accompanied or followed by the deletion of exon 1 and the promoter region of DRB6. In the 3' long terminal repeat of the retrovirus, however, an open reading frame for a new exon arose, which codes for a sequence of mostly hydrophobic amino acid residues; the sequence could function as a leader for the truncated DRB6 gene. This new exon has a functional donor splice site at its 3' end, which enables it to be spliced in register with DRB6 exon 2. Upstream from the new exon is a promoter enabling transcription of the DRB6 gene. Besides providing an example of a de novo generation of an exon, the study suggests a potential mechanism for generating new genes through the replacement of old exons with newly generated ones.

Amino Acid Sequence↗
PubMed1993

The synonymous substitution rate of the major histocompatibility complex loci in primates.

Because the divergence of many allelic lineages at the major histocompatibility complex (MHC) loci predates species divergence, standard methods of calculating synonymous substitution rates are not applicable to this system. We used three alternative methods of rate estimation: one based on the minimum number of substitutions (Dm), another on the nucleotide difference (Dxy), and the third on the net nucleotide difference (Dn). We applied these methods to the protein-encoding sequences of primate MHC class I (A, B, and C) and class II (DRB1) genes. To determine the reliability of the different estimates, we carried out computer simulation. The distribution of the estimates based on Dxy or Dn is generally much broader than that based on Dm. More importantly, the Dm-based method nearly always has the highest probability of recovering true rates, provided that Dm is not smaller than 5. Because of its desirable statistical properties, we used the Dm-based method to estimate the rate of synonymous substitutions. The rate is 1.37 +/- 0.61 for A, 1.84 +/- 0.40 for B, 3.87 +/- 1.05 for C, and 1.18 +/- 0.36 for DRB1 loci, always per site per 10(9) years. Hence despite the extraordinary polymorphism, the mutation rate at the primate MHC loci is no higher than that of other loci.

Alleles↗
PubMed1993

Extensive MHC variability in cichlid fishes of Lake Malawi.

Lake Malawi in East Africa harbours 500-1,000 endemic species of cichlid fishes, all presumably derived by adaptive radiation from a single founding population within the past two million years. The species of this 'flock' differ strikingly in their ecology and behaviour, moderately in their external morphology and very little in their molecular characteristics. Here we describe high sequence variability of class II major histocompatibility complex genes in a sample of species from Lake Malawi. The variability provides a set of molecular markers for studying adaptive radiation and should be useful for estimating the size of the population that founded the species flock.

Africa, Southern↗
PubMed1993

Time to step back.

Explore the source record for details and available documents.

Health Policy↗
PubMed1993

Comparison of carboplatin pharmacokinetics between an anephric child and two children with normal renal function.

Carboplatin, a promising second generation platinum compound, is an effective antitumor drug and appears to be less nephrotoxic than cisplatin. We report comparative pharmacokinetics of carboplatin in an anephric child and two children with normal renal function. All three children were infused with carboplatin over 4 hours, the anephric child receiving 100 mg/m2 (25% of the dose received by the other two children). This dose was well tolerated and 18 days later the anephric patient received a second course of carboplatin at 50% of the regular dose received by the control patients. Following this dose the girl experienced severe pancytopenia and recovered with the use of GM-CSF, blood, and platelet transfusion. Blood samples were obtained at timed intervals for 24 hours in the control subjects and for 40 hours in the anephric patient. Plasma and plasma ultrafiltrates were analyzed for total and free platinum. The results show that elimination half-life of total platinum was 13 hours in the children with normal renal function and 42 hours in the anephric child following the 100 mg/m2 dose. The elimination T1/2 of free platinum was 8 hours in a child with normal GFR and 32 hours in the anephric child. In the anephric child the clearance of ultrafiltrable platinum was 10% of the normal total body clearance. We suggest that, in children with renal insufficiency, the dose of platinum derivatives should be carefully chosen, proportionally to the degree of renal impairment.

Blood Proteins↗
PubMed1993

Class I major histocompatibility complex genes of the red-necked Wallaby, Macropus rufogriseus.

Marsupials are one of three main evolutionary lineages in mammals, the other two being the monotremes and the placental mammals. The marsupial and the placental lineages separated between 120 and 156 million years ago. In this communication, we provide the first molecular description of class I major histocompatibility complex (Mhc) genes in a representative of the marsupial lineage, the red-necked wallaby, Macropus rufogriseus. Three different, nearly full-length class I Mhc sequences were identified in the cDNA library prepared from spleen mRNA of a single wallaby. The three sequences identify at least two loci. Under the assumption that two of the identified sequences are alleles, we designate the three wallaby genes Maru-Mhc-UA*01, Maru-Mhc-UA*02, and Maru-Mhc-UB*01. The three Maru sequences share several codon deletions and insertions not found in the class I genes of placental mammals. Comparisons of genetic distances among the known class I genes suggest that the Maru genes arose from one ancestral element, whereas the class I genes of the placental mammals arose from another, different ancestral element. The absence of an identifiable defect in the three Maru sequences suggests that the genes from which they were derived are functional. Hence, as in placental mammals, there appear to be two functional class I Mhc loci in the marsupials as well.

Animals↗
PubMed1993

Zebrafish Mhc class II alpha chain-encoding genes: polymorphism, expression, and function.

Its small size and short generation time renders the zebrafish (Brachydanio rerio) an ideal vertebrate for immunological research involving large populations. A prerequisite for this is the identification of the molecules critical for an immune response in this species. In earlier studies, we cloned the zebrafish genes coding for the beta chains of the class I and class II major histocompatibility complex (Mhc) molecules. Here, we describe the cloning of the zebrafish alpha chain-encoding class II gene, which represents the first identification of a class II A gene in teleost fishes. The gene, which is less than 3 kilobases (kb) distant from one of the beta chain-encoding genes, is approximately 1.2 kb long and consists of four exons interrupted by very short (< 200 base pairs) introns. Its organization is similar to that of the mammalian class II A genes, but its sequence differs greatly from the sequence of the latter (36% sequence similarity). Among the most conserved parts is the promoter region, which contains X, Y, and TATA boxes with high sequence similarity to the corresponding mammalian boxes. The observed striking conservation of the promoter region suggests that the regulatory system of the class II genes was established more than 400 million years ago and has, principally, remained the same ever since. Like the DMA, but unlike all other mammalian class II A genes, the zebrafish gene codes for two cysteine residues which might potentially be involved in the formation of a disulfide bond in the alpha 1 domain. The primary transcript of the gene is 1196 nucleotides long and contains 708 nucleotides of coding sequence. The gene is expressed in tissues with a high content of lymphoid/myeloid cells (spleen, pronephros, hepatopancreas, and intestine). The analyzed genomic and cDNA sequences are probably derived from different loci (their overall sequence similarity in the coding region is 73% and their 3' untranslated regions are highly divergent from each other). The genes are apparently functional. Comparison of genes from different zebrafish populations reveals high exon 2 variability concentrated in positions coding for the putative peptide-binding region. Phylogenetic analysis suggests that the zebrafish class II A genes stem from a different ancestor than the mammalian class II A genes and the recently cloned shark class II A gene.

Amino Acid Sequence↗
PubMed1993

Primate ABO glycosyltransferases: evidence for trans-species evolution.

The human ABO blood group system is controlled by alleles at a single locus on chromosome 9. The alleles encode glycosyltransferases, which add different sugar residues to the terminal part of the oligosaccharide core, thus generating the A or B antigens; an allele encoding enzymatically inactive protein is responsible for the blood group O. The A and B antigens are present not only in humans, but also in many other primate species and it has been proposed that the AB polymorphism was established long before these species diverged. Here we provide molecular evidence for the trans-species evolution of the AB polymorphism. Polymerase-chain reaction (PCR) amplification and sequencing has revealed that the critical substitutions differentiating the A and B genes occurred before the divergence of the lineages leading to humans, chimpanzees, gorillas, and orangutans. This polymorphism is therefore at least 13 million years old and is most likely maintained by selection. Comparison of the sequences derived from different species indicates that the difference in enzymatic activities between the A and B transferases is caused by two single nucleotide substitutions responsible for Leu-Met and Gly-Ala replacement at positions 265 and 267 in the polypeptide chains, respectively.

ABO Blood-Group System↗
PubMed1993

Mhc-DRB genes of platyrrhine primates.

The two infraorders of anthropoid primates, Platyrrhini (New World monkeys) and Catarrhini (Old World monkeys and the hominoids) are estimated to have diverged from a common ancestor 37 million years ago. The major histocompatibility complex class II DRB gene and haplotype polymorphism of the Catarrhini has been characterized in several recent studies. The present study was undertaken to obtain information on the DRB polymorphism of the Platyrrhini. Fifty-five complete exon 2 DRB sequences were obtained from six species of Platyrrhini representing both the Callitrichidae and the Cebidae families. Combined with the results of a parallel contig mapping study, our data indicate that at least three loci (DRB1*03, DRB3, and DRB5) are shared by the Catarrhini and the Platyrrhini. However, the three loci are occupied by functional genes in the former infraorder and mostly by pseudogenes in the latter. Instead of the pseudogenes, the Platyrrhini have evolved a new set of apparently functional genes-DRB11 and DRB*W12 through DRB*W19, which have thus far not been found in the Catarrhini. The DRB*W13, *W14, *W15, *W17, *W18, and *W19 genes seem to be restricted to the Cebidae family, whereas the DRB*W16 locus has so far been documented in the Callitrichidae family only. The DRB alleles of the cotton-top tamarin, and perhaps also those of the common marmoset (both members of the family Callitrichidae), are characterized by low nucleotide diversity, possibly indicating that they diverged from a common ancestral gene relatively recently.

Amino Acid Sequence↗
PubMed1993

Exon-intron organization of fish major histocompatibility complex class II B genes.

Major histocompatibility complex (Mhc) molecules bind self and foreign peptides and present them to lymphocytes for recognition. Activation of lymphocytes by Mhc-bound foreign peptides leads to specific immune response against parasites. The Mhc genes have been studied extensively in mammals and birds but much less in other vertebrate classes. In this communication we provide the first description of the exon-intron organization of class II beta-chain-encoding genes from the teleost fish Aulonocara hansbaenschi, family Cichlidae. Each of the genes consists of six exons, E1 through E6, encoding the leader peptide (E1), beta 1 domain (E1+E2), beta 2 domain (E3+E4), connecting peptide (E5), transmembrane region (E5), cytoplasmic domain (E5+E6), and the 3' untranslated region (E6). The exons are separated by relatively short introns, the length of the longest intron being 1.3 kilobase pairs. An important difference between these and all other known class II B genes is that the beta 2 domain-encoding exon is split by an intron 97 base pairs in length. The intron is absent in other teleost fishes such as Brachydanio rerio. A change in the 3' splice site of intron 4 in some of the genes of A. hansbaenschi and of another cichlid fish, Cyphotilapia frontosa, has produced two extra codons at the 5' end of exon 5. Comparison of the A. hansbaenschi coding sequences with those of C. frontosa has revealed a concentration of variability in exon 2 and part of exon 3. Taken together, these observations provide evidence for the existence in cichlid fishes of at least two class II B loci which are functionally equivalent to the corresponding loci in mammals. The exon-intron organization and sequence similarities indicate that the two loci arose by duplication from a common ancestral gene.

Amino Acid Sequence↗
PubMed1993

Cloning of the beta 2-microglobulin gene in the zebrafish.

The beta 2-microglobulin (beta 2m) is a protein found in the serum in a free form and on the cell surface in a form noncovalently associated with the alpha chain of the class I major histocompatibility complex (Mhc) molecules. In mammals, the beta 2m-encoding gene (B2m) is found on a chromosome different from the Mhc proper. We have isolated and characterized the B2m gene of the zebrafish, Brachydanio rerio, family Cyprinidae. We obtained both cDNA and genomic clones of the Brre-B2m gene. The cDNA clones contained the entire coding sequence, the entire 3' untranslated (UT) region, and at least part of the 5'UT region. The genomic clone contained the entire Brre-B2m gene. The coding sequence specifies 97 amino acid residues of the mature protein so that the zebrafish beta 2m is two residues shorter than human and one residue shorter than cattle, fowl, or turkey beta 2m (codons at positions 85 and 86 have been deleted in the Brre-B2m gene). The amino acid and nucleotide sequence similarities between zebrafish and human beta 2m (B2m) are 45% and 59%, respectively. Approximately 24% of the positions are invariant and an additional 9% show only conservative substitutions in comparisons which include all known beta 2m sequences (fish, avian, and mammalian). Most of the conserved positions are in the beta strands (some 47% of the beta-strand positions are conserved in the three vertebrate classes). The Brre-B2m gene consists of four exons separated by three introns. All of the introns are considerably shorter than the corresponding introns in the mammalian B2m genes. The coding sequences of the cDNA and the genomic clones are almost identical but the sequences of the 3'UT regions differ at 1.7% of the sites, suggesting that the genes borne by these clones might have diverged at least 0.7 million years (my) ago. In contrast to the human B2m gene, the Brre-B2m gene shows no bias in the distribution of the CpG dinucleotides: the dinucleotides are distributed evenly along the entire available sequence. The haploid genome of the zebrafish contains only one copy of the B2m gene.

Amino Acid Sequence↗
PubMed1993

Degradation of diphenylether by Pseudomonas cepacia Et4: enzymatic release of phenol from 2,3-dihydroxydiphenylether.

2,3-Dihydroxybiphenyl dioxygenase from Pseudomonas cepacia Et 4 was found to catalyze the ring fission of 2,3-dihydroxydiphenylether in the course of diphenylether degradation. The enzyme was purified and characterized. It had a molecular mass of 240 kDa and is dissociated by SDS into eight subunits of equal mass (31 kDa). The purified enzyme was found to be most active with 2,3-dihydroxybiphenyl as substrate and showed moderate activity with 2,3-dihydroxydiphenylether, catechol and some 3-substituted catechols. The Km-value of 1 microM for 2,3-dihydroxydiphenylether indicated a high affinity of the enzyme towards this substrate. The cleavage of 2,3-dihydroxydiphenylether by 2,3-dihydroxybiphenyl dioxygenase lead to the formation of phenol and 2-pyrone-6-carboxylate as products of ring fission and ether cleavage without participation of free intermediates. Isotope labeling experiments carried out with 18O2 and H2(18)O indicated the incorporation of 18O from the atmosphere into the carboxyl residue as well as into the carbonyl oxygen of the lactone moiety of 2-pyrone-6-carboxylate. Based on these experimental findings the reaction mechanism for the formation of phenol and 2-pyrone-6-carboxylate is proposed in accordance with the mechanism suggested by Kersten et al. (1982).

Biodegradation, Environmental↗