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Biomedical subjects

N Avrion Mitchison

Publications and source records attributed to N Avrion Mitchison.

7 recordsLinked to original sources
PubMed2006

The role of HLA promoters in autoimmunity.

Population studies reveal HLA class I and class II gene polymorphisms associated with all the common chronic autoimmune diseases, notably spondylarthropathies, rheumatoid arthritis, multiple sclerosis and type I diabetes. We here discuss the exceptionally high levels of nucleotide diversity in the MHC region likely to reflect not only balancing selection acting on the epitope binding sites but also natural selection operating on the promoter region. The latter possibility is supported by functional studies with promoters, higher levels of diversity in the promoters of class II than class I genes and the relatively high frequency of single nucleotide polymorphisms around transcription factor binding sites. This, we argue, reflects the need for an appropriate level of signalling at the immunological synapse. We here summarise our knowledge of HLA promoter polymorphisms and how these translate into differential expression, T cell polarisation and inflammation. We discuss current strategies for pharmaceutical intervention in HLA expression.

Animals↗
PubMed2005

Fundamental immunology and what it can teach us about HIV vaccine development.

This survey covers the immunological background to development of an HIV vaccine, starting from an overview of present understanding of the mechanisms of immunoregulation. It follows the uptake, processing and presentation of an antigen, from its initial uptake by a dendritic cell and its deposit on the dendrites of follicular dendritic cells. It pursues the antigen through uptake by B cells, presentation of epitopes to helper T cells and the eventual production of antibody. In the second arm of the immune response it follows synapse formation between dendritic cell and CD4/CD8 cells leading to production of CTL. It identifies epitope linkage as a key element in directing these pathways. It identifies the principal functions of the various types of cell cooperation. Continuing, it focuses on topics relevant to vaccine development: Th1/Th2 balance: new adjuvants based on ligands of TLRs and other activators of innate immunity, as well as new forms of intervention in antigen processing. We urge that the new vaccine fusion constructs be evaluated against a fusion gold standard rather than against antigen alone. These considerations open new strategies of HIV vaccine development. . Finally we urge that vaccine trials should include storage of individual DNA samples, in order to gain better understanding of the genetic parameters of vaccine efficacy.

AIDS Vaccines↗
PubMed2004

T helper cells and efficacy of Haemophilus influenzae type b conjugate vaccination.

A small number of fully vaccinated children in the UK have experienced invasive Haemophilus influenzae type b (Hib) infection. A rise in disease in recent years has been associated with lower vaccine-induced antibody levels over the first 5 years of life, forcing greater dependence on immunological memory for protection. This has necessitated the introduction of a catch-up campaign, designed to boost immunity in children aged 6 months to 4 years of age. We suggest that the conjugate vaccine's inability to induce pathogen specific helper T cells, combined with a loss of natural boosting due to reduced circulation of Hib, may have contributed to the rising incidence of invasive disease 10 years after introduction of the conjugate vaccine. If so, the changing epidemiology of Hib infection in the UK may in part reflect the failure of a subunit vaccine to activate adequately all the necessary components of the immune system. This observation has implications for optimal scheduling of more recently licensed meningococcal and pneumococcal conjugate vaccines.

Antibodies, Bacterial↗
PubMed2003

Instruction of naive CD4+ T cells by polarized CD4+ T cells within dendritic cell clusters.

Cooperation between CD4(+) T cells can enhance the response and modulate the cytokine profile, and defining these parameters has become a major issue for multivalent-vaccine strategies. We explored cooperation using adoptive transfer of two populations of TCR transgenic T cells of different specificity. One was transferred without prior activation, whereas the second was activated for five days by antigen stimulation under polarizing culture conditions. Both populations were transferred into a single adoptive host and then primed by particle-mediated DNA delivery. Polarized Th1 cells (inducers) raised the frequency of IFN-gamma(+) cells within a naive (target) population, whereas Th2 inducers raised the frequency of IL-4(+) and reduced that of IL-2(+) cells. These effects were obtained when the genes for both antigens were on the same particle, favoring presentation by the same dendritic cell, but not when on different particles delivered to different dendritic cells. Autonomy of DC clusters allows linked sets of antigens (e.g. from a single pathogen) to maintain cytokine bias, but allows other independent responses, each with their own set of autonomous clusters.

Adoptive Transfer↗
PubMed2002

Patterned variation in murine MHC promoters.

To compare variation in regulatory and coding DNA, promoter sequences have been obtained from wild-derived mice and laboratory rats. The sequences are from the proximal promoter of the H2Aa, H2Ab, H2Eb, and H2K genes of 24 wild-derived inbred strains and a sample of the corresponding exon 2 sequences and of the RT1.Ba gene of six strains of laboratory rat. They reveal a high level of variation in the mouse MHC class II promoters (H2A and H2E), a low level in MHC class I (H2K), and none in the rat. The variation is pronounced in and around the cAMP response element, a major binding site for modulating promoter activity in response to external stimulation. This finding, together with the different levels of variation in MHC classes I and II, is suggestive of natural selection. However, selection operating via the MHC coding sequences must also contribute, as indicated by the minimal variation in both the MHC class II promoter and coding sequences of the rat. Furthermore CIITA (trans-activator of class II) of the mouse has been reported to have minimal variation in its promoter and none in its coding sequence. Taken together these data suggest that the regulatory and coding sequences undergo coselection. Each of the mouse class II promoters has a pattern of variation that appears to be basically dimorphic, with further variation added by recombination/mutation. The dimorphic allelic lineages are in marginally detectable linkage disequilibrium with the exon 2 sequences, particularly in H2Aa, thus lending further support to the coevolution hypothesis.

Amino Acid Sequence↗