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Biomedical subjects

N Holmes

Publications and source records attributed to N Holmes.

At least 37 records · Page 2Linked to original sources
PubMed1996

Defective depletion of CD45-null thymocytes by the Staphylococcus aureus enterotoxin B superantigen.

The development of a normal T-cell repertoire is critically dependent on the negative and positive selection events which occur at the CD4+CD8+ (double positive, DP) stage of thymic development. Depending on the avidity of the T-cell antigen receptor (TCR) for peptides presented within the thymus, DP thymocytes are either positively selected for maturation to CD4+/CD8+ single positive cells or are depleted by apoptosis. The addition of superantigen to thymocytes within foetal thymic organ culture (FTOC) mimics the negative selection signal of potentially autoreactive thymocytes and induces the responding population of thymocytes to apoptose. Here we present evidence that the transmembrane phosphotyrosine phosphatase CD45 critically regulates TCR-induced signals in thymic differentiation and present data to show defective depletion of CD45-null transgenic TCR-Vbeta8 DP thymocytes in FTOC by the Staphylococcus aureus Enterotoxin B (SEB) superantigen.

Animals↗
PubMed1995

Localization of HLA-A2.1-restricted T cell epitopes in the circumsporozoite protein of Plasmodium falciparum.

Localization of human MHC class I-restricted T cell epitopes in the circumsporozoite (CS) protein of the human parasite Plasmodium falciparum is an important objective in the development of antimalarial vaccines. To this purpose, we synthesized a series of overlapping synthetic 20-mer peptides, spanning the entire sequence of the 7G8 CS molecule except for the central repeat B cell domain. The P.f.CS peptides were first tested for their ability to bind to the human MHC class I HLA-A2.1 molecule on T2, a human cell line. Subsequently, the use of a series of shorter peptide analogues allowed us to determine the optimal A2.1 binding sequence present in several of the 20-mers. Binding P.f.CS peptides were further tested for their capacity to activate PBL from HLA-A2.1+ immune donors living in a malaria-endemic area. Specific IFN-gamma production was detected in the supernatant of cultures of PBL from exposed individuals. Cytotoxic T cell lines and clones were derived from the PBL of one responder, and their activity was shown to be HLA-A2.1-restricted and specific for the peptide 334-342 of the CS protein. In addition, double transgenic HLA-A2.1 x human beta 2-microglobulin mice were immunized with peptide 1-10 of the CS protein. T cells derived from immune lymph nodes displayed a peptide-specific HLA-A2.1-restricted cytolytic activity after one in vitro stimulation.

Amino Acid Sequence↗
PubMed1994

Resistance of HLA-G and HLA-A2 transfectants to lysis by decidual NK cells.

Trophoblast cells from normal first trimester pregnancies have been shown to express the nonclassical Class I molecule, HLA-G, which is nonpolymorphic and has a heavy chain of 40 kDa. These HLA-G-expressing trophoblast cells infiltrate into maternal decidua, which contains abundant uterine-specific CD56bright natural killer (NK) cells. We believe HLA-G may act as a protective molecule against decidual NK lysis and thus allow trophoblast survival in the maternal tissues. To test this hypothesis, we have constructed HLA-G and HLA-A2 transfectants using LCL 721.221 HLA-null cells. We observed that both of these antigens protected target cells from NK effectors isolated from decidua or peripheral blood, although the effect of HLA-G is not as marked as that of HLA-A2. Our results, therefore, show that in this experimental system expression of a nonclassical Class 1 HLA molecule is also correlated with NK resistance in the same way as a classical Class I HLA molecule.

Blotting, Northern↗
PubMed1994

Generation of an antibody to HLA-G in transgenic mice and demonstration of the tissue reactivity of this antibody.

A method was devised to generate antibodies against the non-classical class I HLA-G antigen. This consisted of immunising HLA-A2/beta 2m double transgenic mice with HLA-G transfected into mouse Ltk- cells. A polyclonal antibody was obtained which appears to be specific for HLA-G. The staining pattern of this antibody was restricted solely to all populations of extravillous trophoblast. No fetal tissues reacted with this antibody, including those where HLA-G mRNA has been demonstrated, such as fetal eye, thymus and liver. This study confirms that HLA-G is a trophoblast-specific protein, although it remains a possibility that the technique of immunohistology is not sufficiently sensitive to detect low level HLA-G antigen expression in non-trophoblast tissues.

Animals↗
PubMed1993

Prevention of epoxy resin dermatitis: failure of manufacturers to use available research information.

Research information is often recommended as a solution for occupational disease and injury. This study asks whether publicly available research information on prevention of a well-documented occupational hazard is acted on by an important sector in industry. The hazard, allergic contact dermatitis (ACD) caused by epoxy resins in paints, is particularly significant for painters, who may have to leave their jobs as a consequence of the condition. No evidence is found, according to a priori criteria, that paint manufacturers/suppliers acted on known prevention measures for epoxy resin ACD that are within their control to implement. The findings suggest that availability of research information alone fails to solve health and safety problems. Recommendations for avenues of direct and indirect enforcement where voluntary implementation is absent in the painting industry are suggested.

Australia↗
PubMed1993

In situ hybridization and northern blot demonstration of HLA-G mRNA in human trophoblast populations by locus-specific oligonucleotide.

Trophoblast cells from normal first trimester pregnancies have been shown to express the nonclassical class I molecule, HLA-G, which is nonpolymorphic and has a heavy chain of 40 kD. In this study, in situ hybridization experiments were performed using a biotinylated HLA-G specific oligonucleotide on sections of normal placenta including the implantation site. HLA-G mRNA was identified in all extravillous trophoblast populations including the cytotrophoblast cell columns, interstitial trophoblast, endovascular trophoblast, and placental bed giant cells. In addition, villous cytotrophoblast and villous mesenchymal cells also contained HLA-G transcripts, but villous syncytiotrophoblast was always negative.

Blotting, Northern↗
PubMed1991

The pattern of care in families of adults with a mental handicap: a comparison between families of autistic adults and Down syndrome adults.

The pattern of care in 39 families with a mentally handicapped adult member, 20 with Down syndrome, 19 with autism, was studied. There were no significant differences between the mothers, the fathers, or the siblings of Down syndrome and autistic adults in the amount of help offered with physical care, domestic tasks, and supervision duties. However, the brunt of caring fell upon the mothers, with fathers helping mainly with supervision rather than physical care or domestic tasks. Siblings offered less help than fathers. The autistic subjects exhibited significantly more behavior problems. Methods of coping with problems differed: Parents of autistic adults were more likely to "give in" and less likely to tell the handicapped person to stop than parents of Down syndrome adults.

Activities of Daily Living↗
PubMed1990

The human class I MHC gene HLA-F is expressed in lymphocytes.

Genomic and cDNA clones encoding a human, non-classical class I gene, Dew3, have been isolated. The complete coding sequence has been determined. The sequence is capable of directing expression of a protein with high sequence homology to HLA-A,B,C molecules but with a shortened cytoplasmic tail. Sequence comparisons demonstrate that this gene is from a separate locus to the 'classical' HLA-A,B,C and 'non-classical' HLA-E and HLA-G loci. Dew3 is equally distantly related to all of these previously described, functional class I genes. It is, however, extremely homologous to a third 'non-classical' gene, HLA-5.4, and to the chimpanzee gene, Ch28. The RNA species it transcribes is shorter than that of the classical genes, due to an altered acceptor splice site which results in the loss of exon 7. The transcription of Dew3 RNA shows a unique pattern of tissue distribution, being expressed in B cell lines and peripheral blood lymphocytes and absent from T cell lines, fibroblasts and a myelomonocytic leukaemia. A Dew3 protein product was detected after transfection into a human EBV-transformed B cell line but was located intracellularly. The HLA-5.4 gene has been recently designated HLA-F. The Dew3 and X5.1 clones thus represent two new alleles of the HLA-F locus in man. Sequence comparison with its chimpanzee homologue suggests that selective pressure for conservation of amino acid sequence is still maintained at this locus.

Amino Acid Sequence↗
PubMed1989

Expression and function of HLA-A2.1 in transgenic mice.

We have derived a number of transgenic mouse lines which express the human major histocompatibility complex class I gene HLA-A2.1. Two lines carry the complete human HLA-A2.1, the others bear a recombinant gene in which the HLA-A2.1 coding regions are fused to the H-2Kb promoter. Analysis of transgenic spleen cells by immunofluorescence demonstrates that these mouse cells express HLA-A2.1 on their surface in association with mouse beta 2-microglobulin (beta 2m), confirming that HLA-A2 does not require human beta 2m to be expressed at the cell surface. The cells contain more HLA mRNA than endogenous H-2 class I mRNA. There is also a large pool of non-beta 2m-associated HLA heavy chain inside the cell. In contrast the amount of HLA:beta 2m complex is low. Thus, in transgenic mice HLA-A2 seems to compete poorly with H-2 heavy chains for mouse beta 2m. The HLA-A2.1 transgenic mice do not produce influenza-virus-specific cytotoxic T cells (CTL) restricted to the HLA transgene, at least in sufficient numbers to be measured in a direct bulk CTL assay. The dominance of H-2-restricted clones may be the result of quantitative rather than qualitative factors. However, HLA-A2.1 transgenic spleen cells are effective in stimulating an allogeneic CTL response in normal mice. This response is not H-2 restricted. Cold target inhibition studies show that there are at least two populations of CTL, one of which is specific for HLA-A2.1 on mouse cells. This result suggests that at least some allo-CTL are directed against major histocompatibility complex plus "self-peptide".

Animals↗
PubMed1988

Nature of polymorphism in HLA-A, -B, and -C molecules.

Diversity in 39 HLA-A, -B, and -C molecules is derived from 20 amino acid positions of high variability and 71 positions of low variability. Variation in the structurally homologous alpha 1 and alpha 2 domains is distinct and may correlate with partial segregation of peptide and T-cell receptor binding functions. Comparison of 15 HLA-A with 20 HLA-B molecules reveals considerable locus-specific character, due primarily to differences at polymorphic residues. The results indicate that genetic exchange between alleles of the same locus has been a more important mechanism in the generation of HLA-A, -B, and -C diversity than genetic exchange events between alleles of different loci.

Amino Acid Sequence↗
PubMed1987

Multiple genetic mechanisms have contributed to the generation of the HLA-A2/A28 family of class I MHC molecules.

The genetic events that produce diversity in class I MHC genes and proteins has been investigated by using a family of closely related HLA-A alleles. Five genes coding for HLA-A2.2Y, HLA-A2.3, and HLA-Aw68.2 have been isolated. Exon sequences are compared with the known sequences for HLA-A2.1, HLA-A2.2F, HLA-A2.4, HLA-Aw68.1, and HLA-Aw69. Pairwise comparison of the eight unique sequences shows that point mutation, reciprocal recombination, and gene conversion have all contributed significantly to the diversification of this family of alleles. These results are compared with those of other studies that have emphasized the role of gene conversion. A predominance of coding substitutions in the alpha 1 and alpha 2 domains is found, consistent with positive selection for polymorphism being a major factor in the fixation of these alleles. In the three cases examined, genes for phenotypically identical proteins gave identical nucleotide sequences, indicating that most, if not all, of the class I polymorphism is detectable by immunological methods. The apparent stability of the sequences suggests that the events generating some of the alleles occurred before the origin of modern Homo sapiens.

Alleles↗
PubMed1987

Locally-based residential services for mentally handicapped adults: a comparative study.

The patterns of daily living, occupation and leisure activities, skills, behaviour and the structure and organization of living units were assessed for 2 groups of mentally handicapped adults, first in a large hospital and second, a year later in the new local units to which they were transferred. Similar assessments were carried out for individually matched control subjects who remained in the large hospital. For the less severely handicapped, more sociable residents who moved to an NHS hostel in the community, there were significant improvements on several of these measures. For the more severely handicapped, socially aloof people who moved to a ward in a small converted hospital in the district from which they had originally come, some changes on the environmental measures were found, but on the whole the unit was run along similar lines to the wards of the large hospital. There was little change in the pattern of the residents' day to day life. The controls who remained in the large hospital experienced very little change in environmental and life-style measures. The discussion focuses on the interaction between environmental factors and the handicaps of the individuals, and the influence of this interaction upon quality of care and life-style. The study was carried out during the early stages of the rundown to closure of the large mental handicap hospital.

Adult↗
PubMed1986

The primary structure of HLA-A32 suggests a region involved in formation of the Bw4/Bw6 epitopes.

All HLA-B locus molecules have either the Bw4 or Bw6 epitopes. In addition, the Bw4 epitope is found on HLA-Aw23, Aw24, and A32, and Bw6 is also found on HLA-Cw3. The structural basis for these determinants and the evolution of their distribution among products of the HLA-B locus has been a long standing puzzle. To identify residues that may be involved in these determinants, we have cloned a gene for A32 and sequenced the protein encoding exons. Comparison of the predicted protein sequence with other HLA-A,B,C sequences identified residues 79 through 83 of the alpha 1 domain as having a pattern of polymorphic substitution that correlates with the presence and absence of the Bw4 and Bw6 epitopes.

Amino Acid Sequence↗
PubMed1986

Acetylcholinesterase is regulated by action potential generation and not by muscle contractile activity per se in mouse muscle in vitro.

Dysgenic (mdg/mdg) skeletal muscle of the mouse, grown in primary cell culture, fires action potentials in the absence of contractions, thus allowing analysis of the role of electrical activity (without contraction) on the specific activity and molecular forms of acetylcholinesterase (AChE). Specific activity of AChE was assessed by the spectrophometric method of Ellman (Biochem. Pharmacol., 7 (1961) 88-95) and found to increase by 2-5 times in the active myotubes (contraction and action potentials in normal and action potentials, alone in dysgenic muscle) compared to quiescent muscle. Sucrose density sedimentation analysis of muscle homogenates revealed an increase, by 2-3 times, in the proportion of the asymmetric (16S) molecular form of AChE in active muscle of both genotypes. Thus, electrical membrane activity, and not contraction per se, is directly involved in the regulation of levels of specific activity of and accumulation of the asymmetric (16S) form of AChE in muscle cells in culture.

Acetylcholinesterase↗