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Biomedical subjects

J I Bell

Publications and source records attributed to J I Bell.

At least 127 records · Page 7Linked to original sources
PubMed1988

Enzymatic amplification of exogenous and endogenous retroviral sequences from DNA of patients with tropical spastic paraparesis.

Using oligonucleotide primers that hybridize to conserved sequences in the reverse transcriptase (RT) gene, we have amplified by the polymerase chain reaction three sequence variants of HTLV-I from the genomic DNA of five patients with tropical spastic paraparesis (TSP), and a fourth sequence variant from a healthy carrier of HTLV-I. These results unequivocally identify the retrovirus associated with TSP as HTLV-I and suggest that no sequence variant is uniquely responsible for the condition. The same primers served to amplify two novel single-copy endogenous retroviral RT sequences related to the exogenous mammalian leukaemia viruses: and three KpnI (LINE1) family DNA repeats. This strategy, combining the sensitivity of PCR with cross-reactive primers, may be useful in the search for known or novel retroviruses in other diseases of possible retroviral aetiology.

Amino Acid Sequence↗
PubMed1988

Genetic factors as determinants of infectious disease transmission in human communities.

Genetic factors may play an important role in individual susceptibility to infection. Hitherto this problem has been investigated by attempting to relate the distribution of genetic polymorphisms in populations to present or past infection, or by analysing specific infections by classical twin studies or group comparisons. There is reasonable evidence that the common red-cell polymorphisms involving haemoglobin, enzymes or membrane have been maintained by relative resistance to malaria. Blood-group heterogeneity, including secretor status, may reflect varying susceptibility to bacterial, virus and yeast infection. There is increasing evidence that the HLA-DR system may be involved in modifying the clinical course of bacterial, virus and parasitic infection. So far no specific resistance or susceptibility loci similar to those found in murine models have been found in man. DNA analysis, particularly involving restriction fragment length polymorphism associations with candidate genes, offers a valuable new approach to this problem.

Communicable Diseases↗
PubMed1988

A molecular basis for MHC class II--associated autoimmunity.

Class II major histocompatibility (MHC) molecules have an immunoregulatory role. These cell-surface glycoproteins present fragments of protein antigens (or peptides) to thymus-derived lymphocytes (T cells). Nucleotide sequence polymorphism in the genes that encode the class II MHC products determines the specificity of the immune response and is correlated with the development of autoimmune diseases. This study identifies certain class II polymorphic amino acid residues that are strongly associated with susceptibility to insulin-dependent diabetes mellitus, rheumatoid arthritis, and pemphigus vulgaris. These findings implicate particular class II MHC isotypes in susceptibility to each disease and suggest new prophylactic and therapeutic strategies.

Amino Acid Sequence↗
PubMed1987

Molecular mapping of class II polymorphisms in the human major histocompatibility complex. I. DR beta.

We have studied 27 cell lines homozygous by consanguinity for the major histocompatibility complex to establish the restriction fragment length polymorphism (RFLP) patterns seen with six different restriction enzymes (Bam HI, Bg1 II, Eco RI, Hinc II, Hind III, Pvu II) and DR beta chain probes. The probes used were a full-length cDNA DR beta probe and a probe specific for the 3' untranslated region. The RFLP obtained represent the first standard patterns for the individual haplotypes DR1 through 7 and DR9 as defined by genetically homozygous lines. The patterns obtained reflect the DR specificities closely, as well as the DRw52 and DRw53 specificities. These latter specificities are associated with the most prominent patterns of RFLP. Bands are present which are unique for the haplotypes DR1, DR2, DR4, DR7, DRw52, and DRw53, and could be used for typing these haplotypes in heterozygotes. Subtypes can be identified for all of the haplotypes except DR1. These subtypes indicate that there is an extensive amount of polymorphism in the DR subregion that has not been identified serologically.

Cell Line↗
PubMed1987

Molecular mapping class II polymorphisms in the human major histocompatibility complex. II. DQ beta.

The restriction fragment length polymorphisms have been determined for six restriction enzymes (Bam HI, Bg1 II, Eco RI, Hinc II, Hind III, and Pvu II) and a DQ beta probe on 25 cell lines that are homozygous by consanguinuity at the MHC. These patterns reflect both DR haplotypes and DQ types of the cells tested. At least one non-polymorphic band is present in all the cell lines with every restriction enzyme except Hinc II. This band most probably represents DX beta hybridization. The polymorphic bands indicate that more polymorphism exists in the DQ subregion than is predicted serologically. Each DR haplotype is associated with a unique set of restriction fragments except for DR2 and DR6. The patterns are largely consistent within each DR haplotype. In addition, some bands reflect the established DQ specificities DQw1 and DQw2. Individual bands can be identified that are unique to the haplotypes DR1, DR4, DR5, and DR6 and the DQw1- and DQw2-associated haplotypes. Subdivisions of haplotypes can be identified with this probe. In particular, MVL (DR1), Akiba (DR2), QBL (DR3), FPF (DR5), and APD (DR6) have polymorphisms that distinguish them from other members of their DR haplotype.

Cell Line↗
PubMed1987

The molecular genetics of HLA-related disorders.

The HLA region on the short arm of chromosome 6 contains a set of highly polymorphic loci responsible for regulating the immune response. Particular haplotypes, defined serologically, have been associated with a risk of developing certain autoimmune diseases such as insulin-dependent (juvenile-onset) diabetes mellitus, multiple sclerosis and rheumatoid arthritis. Recent developments in molecular biology have permitted an improved resolution of the locus and of the sequential arrangement of the susceptibility determinants on these haplotypes. Restriction fragment length polymorphisms have allowed subdivisions of serological haplotypes to be made. These correlate with disease susceptibility in some cases. Amplification of specific HLA class II alleles and nucleic acid sequencing have resulted in the identification of the structural determinants in the HLA that underlie some of these diseases.

Arthritis, Rheumatoid↗
PubMed1987

HLA-DR restriction-fragment-length polymorphisms in narcolepsy.

Seventeen white patients from the Stanford Sleep Disorders Clinic complaining of excessive daytime somnolence (EDS) were selected for restriction-fragment-length polymorphism (RFLP) studies. Fourteen of the patients with clinically diagnosed narcolepsy were seropositive for DR2. RFLP analysis of these patients compared with a homozygous DR2-Dw2 cell line failed to reveal any polymorphism when digested with six restriction endonucleases and hybridized with three different cDNA probes. None of the three patients with central nervous system hypersomnia, a syndrome similar to narcolepsy, were DR2-positive. We conclude that any polymorphism of the DR beta, DQ alpha, or DQ beta genes of DR2 narcoleptics that might distinguish them from DR2 normals cannot be resolved through RFLP analysis.

HLA-D Antigens↗
PubMed1987

Allele-specific DNA identity patterns.

A method of genetic analysis is presented which involves digestion of DNA with a single restriction enzyme (PvuII) and hybridisation with a mixture of five probes. Four of the five probes chosen recognise hypervariable regions (HVRs) of the human genome and hence an allele-specific DNA identity pattern results. An advantage of this approach to genetic characterisation is that the complex identity patterns may be broken down into simple allelic systems of known chromosomal localization by hybridisation with the individual probes. Also different probes may be included in a combined probe designed for particular types of investigation.

DNA Restriction Enzymes↗
PubMed1987

Structural and functional variability among DQ beta alleles of DR2 subtypes.

Homozygous lymphoblastoid cell lines representing various Dw subtypes of DR2 were examined for polymorphism at the DQ beta locus by molecular and cellular techniques. The subtypes studied included Dw2, Dw12, and a group heterogenous by cellular typing that we shall refer to as non-Dw2/non-Dw12. Restriction fragment length polymorphism analysis of cell lines representing these subtypes revealed DQ beta-specific patterns consistent with cellular typing. Two-dimensional gel electrophoresis of DQ molecules from representative cell lines revealed a structural polymorphism of DQ beta among the three subtypes. The DQ beta chain migrated to a position that was unique to each subtype and was consistent among various representative cell lines of each subtype. Nucleotide sequence analysis of cDNA clones of DQ beta from Dw2, Dw12, and non-Dw2/non-Dw12 lines confirmed that the variability resided at the genetic level. Variability was found in the form of numerous scattered nucleotide substitutions throughout the first domain of these alleles. The DQ beta gene of the non-Dw2/non-Dw12 cell line AZH was further found to be almost identical with the DQ beta gene of a DR1 line (Bell et al. 1985b), implicating a common evolutionary origin of these alleles. The only difference between these two sequences was due to an apparent gene conversion event at amino acid 57. T-cell cloning experiments resulted in the derivation of Epstein-Barr virus-specific, DQw1-restricted clones that proliferated against only those cell lines that exhibited the DQ beta gene common to AZH and the DR1 cell line. Thus, the polymorphism among DQ beta alleles within DR2 results in subtype-specific restriction.

Alleles↗
PubMed1987

Allelic variation in the DR subregion of the human major histocompatibility complex.

Allelic variation in the DR subregion of the human major histocompatibility complex has been analyzed by nucleic acid sequencing of cDNA clones obtained from cell lines homozygous by consanguinity for all the common serological types DR1-9. Two expressed loci were identified in the haplotypes DR2, -3, -4, -7, and -9; one locus being present at a much lower frequency (4-7%) than the other. The low-frequency allele was highly conserved between each of the DRw53 (DR4, -7, -9) and the DRw52 (DR3, -5, -6) haplotypes. Analysis of the variation between alleles confirms the presence of three allelic hypervariable regions. At each variable residue, a limited range of amino acid substitutions are found, distinguishing them from immunoglobulin hypervariable regions. Dinucleotide substitutions are extremely common. Individual hypervariable regions are often shared between haplotypes. Much of the variation in these alleles can be attributed to the shuffling of these regions between haplotypes, possibly by the mechanism of gene conversion.

Alleles↗
PubMed1985

DNA sequence and characterization of human class II major histocompatibility complex beta chains from the DR1 haplotype.

Two HLA class II beta-chain clones from a cell line homozygous for the DR1 haplotype have been characterized and sequenced. They represent a DR beta chain (2918.4) and a DQ beta chain (2918.8). Clone 2918.4 has been used to select mRNA from a lymphoblastoid cell line, and this was injected into Xenopus oocytes with mRNA selected with a DR alpha chain. The translation products were immunoprecipitated with a beta-chain-specific monoclonal antibody and electrophoresed on two-dimensional gels. This revealed positive signals in the positions predicted for beta and alpha chains. Sequence comparisons of 2918.4 with previously published DR beta-chain sequences confirm the presence of two regions of variability in the membrane distal domain. Analysis of the sequence of 2918.8 identified it as a DQ beta chain identical to one previously published from a DR3,w6 cell line. We speculate, therefore, that the DQ beta sequence represents the DQ1 specificity shared by the DR1 and DRw6 haplotypes.

Animals↗
PubMed1985

A genetic marker for elevated levels of haemoglobin F in homozygous sickle cell disease?

Ten patients with sickle cell (SS) disease from a Jamaican family were found to have unusually high levels of haemoglobin F for this population. Each of them has inherited one sickle cell gene on a chromosome characterized by an arrangement of restriction fragment length polymorphisms (haplotype) which is very rare in the Jamaican population. Genetic analysis of the family suggests that there is a determinant linked to the beta-globin gene cluster, characterized by this haplotype, which is responsible for increased haemoglobin F production in response to anaemia. Interestingly this particular haplotype appears to be common in patients with SS disease in eastern Saudi Arabia in whom a high level of haemoglobin F is the rule rather than the exception. Hence it is possible that this haplotype (++-++) acts as a genetic marker for elevated levels of haemoglobin F in sickle cell disease.

Anemia, Sickle Cell↗