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Biomedical subjects

M Carrington

Publications and source records attributed to M Carrington.

At least 91 records · Page 5Linked to original sources
PubMed1997

Novel alleles of the chemokine-receptor gene CCR5.

The CCR5 gene encodes a cell-surface chemokine-receptor molecule that serves as a coreceptor for macrophage-tropic strains of HIV-1. Mutations in this gene may alter expression or function of the protein product, thereby altering chemokine binding/signaling or HIV-1 infection of cells that normally express CCR5 protein. Indeed, homozygotes for a 32-bp deletion allele of CCR5 (CCR5-delta 32), which causes a frameshift at amino acid 185, are relatively resistant to HIV-1 infection. Here we report the identification of 16 additional mutations in the coding region of the CCR5 gene, all but 3 of which are codon altering or "nonsynonymous." Most mutations were rare (found only once or twice in the sample); five were detected exclusively among African Americans, whereas eight were observed only in Caucasians. The mutations included 11 codon-altering nonsynonymous variants, one trinucleotide deletion, one chain-termination mutant, and three synonymous mutations. The high predominance of codon-altering alleles among CCR5 mutants (14/17 [81%], including CCR5-delta 32) is consistent with an adaptive accumulation of function-altering alleles for this gene, perhaps as a consequence of historic selective pressures.

Alleles↗
PubMed1997

DQ microsatellite association studies in three ethnic groups.

Polymorphism at the level of three microsatellite markers (DQCAR, DQCARII, G51152) located in the HLA-DQ region was characterized in 78 10th International Histocompatibility Workshop B-cell lines, 718 random Japanese Asians, 99 Norwegian Caucasians and 95 New Guinean Aborigines with established HLA-DRB1, -DQA1 and -DQB1 typing. DQCAR, DQCARII, and G51152 result in 13, 13, and 11 alleles respectively. All three markers were in tight linkage disequilibrium with HLA-DRB1, -DQA1 and -DQB1. DRB1, DQA1, DQCARII, DQCAR, DQB1, and G51152 haplotypes could be defined for all subjects. In fact, DQ microsatellite typing data could predict DQA1 and DQB1 genotypes with high accuracy and may be used as a simple first pass HLA-DQ typing method. The haplotype data was also used to determine recombination in the DRB1-DQA1 (about 80 kb), DQA1-DQCARII (about 4.5 kb), DQCARII-DQCAR (about 7.5 kb), DQCAR-DQB1 (about 1-1.5 kb) and DQB1-G51152 (about 20-25 kb) genomic segments and the relative rate of slippage microsatellite mutations for DQCAR, DQCARII, and G51152. This led us to conclude that recombination is more frequent in the DRB1-DQA1 and DQCAR-DQCARII segments, thus suggesting cross-overs within small genomic segments are not proportional to genetic distance. We also observed that DQCAR had a higher mutation rate than DQCARII or G51152 and that 1 or 2 CA slippage mutations were arising more frequently from large size microsatellite alleles.

DNA, Satellite↗
PubMed1997

Characterization of recombination in the HLA class II region.

Studies of linkage disequilibrium across the HLA class II region have been useful in predicting where recombination is most likely to occur. The strong associations between genes within the 85-kb region from DQB1 to DRB1 are consistent with low frequency of recombination in this segment of DNA. Conversely, a lack of association between alleles of TAP1 and TAP2 (approximately 15 kb) has been observed, suggesting that recombination occurs here with relatively high frequency. Much of the HLA class II region has now been sequenced, providing the tools to undertake detailed analysis of recombination. Twenty-seven families containing one or two recombinant chromosomes within the 500-kb interval between the DPB1 and DRB1 genes were used to determine patterns of recombination across this region. SSCP analysis and microsatellite typing yielded identification of 127 novel polymorphic markers distributed throughout the class II region, allowing refinement of the site of crossover in 30 class II recombinant chromosomes. The three regions where recombination was observed most frequently are as follows: the 45-kb interval between HLA-DNA and RING3 (11 cases), the 50-kb interval between DQB3 and DQB1 (6 cases), and an 8.8-kb segment of the TAP2 gene (3 cases). Six of the 10 remaining recombinants await further characterization, pending identification of additional informative markers, while four recombinants were localized to other intervals (outliers). Analysis of association between markers flanking HLA-DNA to RING3 (45 kb), as well as TAP1 to TAP2 (15 kb), by use of independent CEPH haplotypes indicated little or no linkage disequilibrium, supporting the familial recombination data. A notable sequence motif located within a region associated with increased rates of recombination consisted of a (TGGA)12 tandem repeat within the TAP2 gene.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Implications of conserved structural motifs in disparate trypanosome surface proteins.

Evasion of the host immune system by Trypanosoma brucei is dependent on the sequential expression of individual genes encoding antigenically distinct variant surface glycoproteins (VSG). VSGs are antigenically distinct due to extensive differences in primary sequence; the only obvious conserved feature in the primary sequence is the location of cysteines that form disulphide bridges. Despite this difference, it is believed that VSGs have a conserved tertiary structure which could explain how a range of VSGs with different primary sequences can perform the same apparent function of producing a monolayer barrier that prevents the host antibodies from recognising other cell surface proteins. The main feature of the VSG tertiary structure is two long alpha-helices per monomer that are perpendicular to the cell surface and define the elongated shape of the VSG. The alpha-helices can be identified in the primary sequence by heptad analysis. Here, we briefly review the current understanding of VSG structure and discuss the fact that the cysteine residues and the heptads are conserved in some non-VSG surface proteins from T. brucei, providing strong evidence that these share a similar tertiary structure. These findings suggest that this master structure has evolved to facilitate a range of functions and has implications for understanding the architecture of the trypanosome cell surface and the origins of antigenic variation.

Amino Acid Sequence↗
PubMed1996

Genetic restriction of HIV-1 infection and progression to AIDS by a deletion allele of the CKR5 structural gene. Hemophilia Growth and Development Study, Multicenter AIDS Cohort Study, Multicenter Hemophilia Cohort Study, San Francisco City Cohort, ALIVE Study.

The chemokine receptor 5 (CKR5) protein serves as a secondary receptor on CD4(+) T lymphocytes for certain strains of human immunodeficiency virus-type 1 (HIV-1). The CKR5 structural gene was mapped to human chromosome 3p21, and a 32-base pair deletion allele (CKR5Delta32) was identified that is present at a frequency of approximately0.10 in the Caucasian population of the United States. An examination of 1955 patients included among six well-characterized acquired immunodeficiency syndrome (AIDS) cohort studies revealed that 17 deletion homozygotes occurred exclusively among 612 exposed HIV-1 antibody-negative individuals (2.8 percent) and not at all in 1343 HIV-1-infected individuals. The frequency of CKR5 deletion heterozygotes was significantly elevated in groups of individuals that had survived HIV-1 infection for more than 10 years, and, in some risk groups, twice as frequent as their occurrence in rapid progressors to AIDS. Survival analysis clearly shows that disease progression is slower in CKR5 deletion heterozygotes than in individuals homozygous for the normal CKR5 gene. The CKR5Delta32 deletion may act as a recessive restriction gene against HIV-1 infection and may exert a dominant phenotype of delaying progression to AIDS among infected individuals.

Acquired Immunodeficiency Syndrome↗
PubMed1996

Interleukin 2 production in vitro by peripheral lymphocytes in response to human papillomavirus-derived peptides: correlation with cervical pathology.

Human papillomavirus (HPV) is believed to be the major cause of cervical cancer. To investigate whether a cellular immune response, especially a T helper type 1 response, is related to the natural defense against HPV-related cervical lesions, the interleukin 2 response of peripheral blood lymphocytes in vitro to overlapping peptides from HPV-16 E6 and E7 oncoproteins was compared with the degree of cervical cytological abnormality among 140 women in a cross-sectional study. We compared 66 women diagnosed with low-grade squamous intraepithelial lesions (LSIL), 21 with high-grade squamous intraepithelial lesions (HSIL), and 28 with invasive cervical cancer with 25 women who were cytologically normal but previously HPV-16 DNA positive. The fraction showing strong interleukin 2 production against HPV-16 peptides was greatest among cytologically normal women (35%) and declined with increasing disease severity [LSIL] (20%), HSIL, (17%), and cancer patients (7%); X2 test P for the trend = 0.02], whereas the responses against a recall influenza antigen were not significantly different among groups. Our finding suggests that a T helper lymphocyte type 1 response to HPV antigens is associated with disease status. This result may reflect a targeted effect of the disease on immune function or a protective effect of the immune response against disease progression.

Adolescent↗
PubMed1996

Simultaneous but independent activation of adenylate cyclase and glycosylphosphatidylinositol-phospholipase C under stress conditions in Trypanosoma brucei.

Previous observations suggested a concomitant relationship between the release of the variant surface glycoprotein (VSG) and the activation of adenylate cyclase in the bloodstream form of the parasitic protozoan Trypanosoma brucei. In order to evaluate this hypothesis, adenylate cyclase activity was measured in live trypanosomes subjected to different treatments known to induce the shedding of the VSG coat, namely low pH and trypsin digestion. In both cases adenylate cyclase activation occurred in parallel with the release of the VSG. The latter was found to be mediated by the glycosylphosphatidylinositol-specific phospholipase C that cleaves the glycosylphosphatidylinositol anchor of the protein (VSG lipase). Furthermore, both adenylate cyclase and VSG release were activated by the incubation of trypanosomes with specific inhibitors of protein kinase C, suggesting a repressive role for protein kinase C on both VSG lipase and adenylate cyclase activities. Significantly, in mutant trypanosomes lacking VSG lipase, adenylate cyclase was activated under conditions where VSG release did not occur. Moreover,VSG release was also found to occur in the absence of activation of the cyclase, as observed in the presence of low concentration of the thiol modifying reagent p-chloromercuriphenylsulfonic acid. These observations provide the first demonstration that release of the VSG in response to cellular stress is mediated by the VSG lipase and that while both release of the VSG and activation of adenylate cyclase occur in response to the same stimuli they are not obligatorily coupled.

Adenylyl Cyclases↗
PubMed1996

Expression of HLA class I molecules and the transporter associated with antigen processing in hepatocellular carcinoma.

The expression of the HLA class I molecules on the cell surface was investigated in hepatocellular carcinoma (HCC) cell lines using complement-mediated cytotoxicity (CMC) and flow cytometric analysis. Although HLA-A antigens were detected by CMC in all cell lines tested, HLA-B and -C antigens were not detectable in six of seven HCC cell lines. These results were also confirmed by flow cytometric analysis focusing on HLA-Bw4 and Bw6 public antigens. Furthermore, complementary DNA (cDNA) from each cell line was tested for the expression of HLA-A, -B, -C and the transporter associated with antigen processing genes (TAP1 and TAP2). Two cell lines showed a reduced level of one or both of the TAP messenger RNAs (mRNAs), and one of these showed a reduction of HLA-B and -C gene expression as well, but the others had detectable mRNA levels. These results demonstrate that hepatocellular carcinoma cell lines tested in the current study lose or decrease the expression of HLA-B and -C alleles on the cell surface, even though mRNA encoding these alleles is present, suggesting that the loss of the HLA molecules might be caused by posttranscriptional events or failure to transport and load peptides necessary for HLA expression. The selective loss of HLA-B and -C, but not -A, molecules (which also excludes a beta 2-microglobulin defect) is intriguing, and may be attributable to the ability of some of the HLA-A molecules to load signal peptides not requiring TAP transport, or to natural selection of HLA-B or -C locus-specific immune surveillance.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Persistently seronegative men from whom HIV-1 has been isolated are genetically and immunologically distinct.

Studies in both monkeys and humans have suggested that transient infection with HIV-1 can occur without provoking a measurable humoral immune response. The objective of this study was to look for genetic and immunologic correlates of transient HIV-1 infection in antibody-negative men from whom HIV-1 had been isolated. The distributions of MHC class I, class II, and TAP (transporter protein associated with antigen processing) region genes were compared between 23 persistently seronegative men from whom HIV-1 was isolated at least once (isol+/Ab-) and 137 men who seroconverted. A subset of 13 of the 23 isol+/Ab- men were compared to 27 seronegative men for distribution of CD25+CD4+ and CD25+CD8+ cells in the absence of exogenous immunologic stimulation. The prevalences of the TAP1.4, and a combination of TAP1.4, and TAP2.3 variants were significantly higher in the isol+/Ab- men. The proportion of CD8+ cells that expressed CD25+ antigen was also significantly higher in the isol+/Ab- men than in the seronegative men. We conclude that isol+/Ab- men may be genetically and immunologically distinct from HIV-1 susceptible men. We hypothesize that activated CD8+ cells may have cleared HIV-1 infection in these men through genetically mediated influences of the TAP genes on the presentation of peptides by HLA class I molecules.

ATP Binding Cassette Transporter, Subfamily B, Mem↗
PubMed1996

Selective metabolic labelling of intracellular parasite proteins using ricin.

The characterization of protein synthesis by eukaryotic intracellular parasites is inherently difficult because it may represent only a small fraction of host cell protein synthesis. Here, Mark Carrington, Yael Shochat and Anne Gurnett describe a method for overcoming this problem through the use of the toxin ricin to inhibit host cell protein synthesis specifically.

Journal Article↗
PubMed1996

Peptide binding function and the paradox of HLA disease associations.

Many studies have found associations between HLA loci and susceptibility or resistance to both infectious and autoimmune diseases, but often subsequent studies fail to find the same association. Such inconsistencies are not surprising if we consider what is known of the population biology and evolution of HLA genes, especially the consequences of natural selection favouring heterozygosity in the peptide binding regions (PBR) of HLA molecules. Because of past recombination event and/or convergent evolution, alleles that are not closely related in overall sequence may come to resemble each other in the PBR. Because peptide binding is likely to be important for the role of HLA molecules in both infectious and autoimmune disease, a strategy of searching for HLA disease associations that groups alleles in functional categories based on PBR motifs may prove more successful than conventional strategies. Likewise, in developing approaches for molecular typing, it may be advisable to develop methods that group alleles on the basis of shared PBR motifs rather than simply on the basis of shared primer sites in less functionally important regions.

Animals↗
PubMed1996

Influence of combinations of human major histocompatibility complex genes on the course of HIV-1 infection.

Major histocompatibility complex (MHC) genes (HLA in humans) regulate the immune response to foreign antigens. Molecular and serologic techniques were used to identify products of HLA class I, class II and transporter (TAP) genes (also part of the MHC) in homosexual seroconverters to human immunodeficiency virus type 1 (HIV-1). Comprehensive statistical analysis produced an HLA profile that predicted time from HIV-1 infection to the onset of AIDS. The profile was developed in a cohort of 139 men and evaluated in a second unrelated cohort of 102 men. In the evaluation cohort, the profile discriminated a sixfold difference between groups with the shortest and longest times to AIDS (P = 0.001). These findings support current theory about control of antigen processing by HLA genes and have implications for immunopathogenesis of HIV-1 and other infections.

Acquired Immunodeficiency Syndrome↗
PubMed1996

The isolation and characterization of genomic and cDNA clones coding for a cdc2-related kinase (ThCRK2) from the bovine protozoan parasite Theileria.

The tick-transmitted protozoan parasites Theileria annulata and Theileria parva are important intracellular pathogens of domestic cattle in tropical and subtropical regions. Proliferative phases take place within both lymphocytes and erythrocytes. The lymphocyte is stimulated to enter the cell cycle by the parasite and the multinucleate parasite can establish a state in which karyokinesis and cytokinesis occur in phase with the host cell. The link between parasite nuclear division and cytokinesis is altered during the formation of merozoites (a non-dividing, invasive, extracellular stage). These features imply a high degree of control over parasite nuclear division and cytokinesis. Two different approaches have been used to identify clones from both species which are extremely highly conserved homologues. These encode a cdc2-related kinase which is > 60% identical to eukaryotic cyclin-dependent kinases of the p34cdc2/p32CDK2 subfamily. There is typical conservation of kinase domains, implying an in vivo protein kinase activity for the polypeptide. The PSTAIRE region, implicated in cyclin binding, is well conserved suggesting that ThCRK2 will bind cyclin molecules closely related to the eukaryotic A/B-type cyclins. However, there is divergence in certain key motifs potentially associated with binding of molecules that regulate the activity of the kinase. Expression patterns of RNA and protein indicate that ThCRK2 is likely to function in all dividing stages of the parasite and, taken together, the results point to a central role in the regulation of nuclear division.

Amino Acid Sequence↗