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Biomedical subjects

A Kelso

Publications and source records attributed to A Kelso.

At least 19 recordsLinked to original sources
PubMed2001

CD4 ligation promotes the IL-4-independent development of IL-4-producing clones from naive CD4(+) T cells.

The signals that trigger IL-4-independent IL-4 synthesis by conventional CD4(+) T cells are not yet defined. In this study, we show that coactivation with anti-CD4 mAb can stimulate single naive CD4(+) T cells to form IL-4-producing clones in the absence of APC and exogenous IL-4, independently of effects on proliferation. When single CD4(+) lymph node cells from C57BL/6 mice were cultured with immobilized anti-CD3epsilon mAb and IL-2, 65-85% formed clones over 12-14 days. Coimmobilization of mAb to CD4, CD11a, and/or CD28 increased the size of these clones but each exerted different effects on their cytokine profiles. Most clones produced IFN-gamma and/or IL-3 regardless of the coactivating mAb. However, whereas 0-6% of clones obtained with mAb to CD11a or CD28 produced IL-4, 10-40% of those coactivated with anti-CD4 mAb were IL-4 producers. A similar response was observed among CD4(+) cells from BALB/c mice. Most IL-4-producing clones were derived from CD4(+) cells of naive (CD44(low) or CD62L(high)) phenotype and the great majority coproduced IFN-gamma and IL-3. The effect of anti-CD4 mAb on IL-4 synthesis could be dissociated from effects on clone size since anti-CD4 and anti-CD11a mAb stimulated formation of clones of similar size which differed markedly in IL-4 production. Engagement of CD3 and CD4 in the presence of IL-2 is therefore sufficient to induce a substantial proportion of naive CD4(+) T cells to form IL-4-producing clones in the absence of other exogenous signals, including IL-4 itself.

Animals↗
PubMed2001

A critical role for Dnmt1 and DNA methylation in T cell development, function, and survival.

The role of DNA methylation and of the maintenance DNA methyltransferase Dnmt1 in the epigenetic regulation of developmental stage- and cell lineage-specific gene expression in vivo is uncertain. This is addressed here through the generation of mice in which Dnmt1 was inactivated by Cre/loxP-mediated deletion at sequential stages of T cell development. Deletion of Dnmt1 in early double-negative thymocytes led to impaired survival of TCRalphabeta(+) cells and the generation of atypical CD8(+)TCRgammadelta(+) cells. Deletion of Dnmt1 in double-positive thymocytes impaired activation-induced proliferation but differentially enhanced cytokine mRNA expression by naive peripheral T cells. We conclude that Dnmt1 and DNA methylation are required for the proper expression of certain genes that define fate and determine function in T cells.

Animals↗
PubMed2000

Differential effects of CD4 and CD8 engagement on the development of cytokine profiles of murine CD4+ and CD8+ T lymphocytes.

A simple culture system devoid of antigen-presenting cells was used to examine the ability of immobilized antibodies to lymphocyte function-associated antigen-1 (LFA-1) (CD11a), CD28 and CD4 or CD8 to modulate the responses of normal murine CD4+ and CD8+ lymph node T cells to immobilized anti-CD3 antibody and interleukin-2 (IL-2). All the antibodies enhanced proliferative responses to limiting anti-CD3 antibody. Both CD4+ and CD8+ cells produced substantial titres of IL-3 and interferon-gamma (IFN-gamma) in primary and secondary cultures regardless of the coactivating antibodies used for priming. By contrast, the combination of anti-CD4 with anti-CD3 antibody stimulated significantly higher titres of IL-4 than any other antibody combination in cultures of CD4+ cells. This CD4-dependent IL-4 response was induced in CD4+ T cells of naive (CD44low) phenotype and was similar in magnitude to the response induced by exogenous IL-4 but, unlike the latter, was not associated with elevated IL-3 synthesis. A comparable effect of anti-CD8 antibodies on CD8+ cells was not observed: although IL-4 production by CD8+ cells was induced by exogenous IL-4, it was not detected following coactivation with anti-CD8 or any other antibodies. We conclude that anti-CD4 antibody is a potent inducer of IL-4-secreting CD4+ T cells whose effects can be distinguished from those of anti-CD8 antibody on CD8+ T cells and from those of IL-4 on either subset.

Animals↗
PubMed2000

Regulation of T cell cytokine production by dendritic cells.

Previous work has established that the dendritic cells (DC) of mouse spleen regulate the IL-2 production, and hence the extent of proliferation, of the CD8 T cells they activate. It is now reported here that interaction of primary CD8 T cells with splenic CD8alpha- DC induced much higher production of IL-3, IFN-gamma and granulocyte-macrophage colony-stimulating factor (GM-CSF), as well as IL-2, than did interaction with CD8alpha+ splenic DC. Furthermore, the CD8alpha- DC also induced higher levels of IL-2, IL-3 and IL-10 production in primary CD4 T cells, compared with that induced by CD8alpha+ DC. These quantitative differences did not involve qualitative shifts in the type of cytokine produced. Interleukin-4 production remained low in all the primary T cell cultures and restimulation experiments in secondary cultures did not reveal any bias in the cytokine production profile. When exogenous IL-2 was added to the primary cultures to ensure equal proliferation in response to CD8alpha- or CD8alpha+ DC, the higher level of production of IL-3, IFN-gamma and GM-CSF induced by CD8alpha- DC was maintained. Thus, this general control of T cell cytokine production by splenic DC involves factors additional to those that govern activation of T cells into cell cycle.

Animals↗
PubMed2000

Cytokines and their receptors: an overview.

Cytokines participate in the induction and effector phases of all immune and inflammatory responses. They are therefore obvious candidates for exploitation as drugs or drug targets to promote, limit, or alter these responses in infection, allergy, autoimmunity, and other disease states. Although some cytokines and related molecules are already in clinical use, the full therapeutic potential of this class of hormones has yet to be realized, and this will depend in part on understanding their normal functions and regulation in health and disease. An overview is given of the cytokines and their receptors, their genetic and structural relationships, and the regulation of their activities by naturally occurring antagonists and other physiologic mechanisms. Some of the ways in which new therapeutic strategies are being developed from knowledge of the structure, function, and regulation of these various components of the cytokine network are outlined.

Animals↗
PubMed1999

The activated type 1-polarized CD8(+) T cell population isolated from an effector site contains cells with flexible cytokine profiles.

The capacity of activated T cells to alter their cytokine expression profiles after migration into an effector site has not previously been defined. We addressed this issue by paired daughter analysis of a type 1-polarized CD8(+) effector T cell population freshly isolated from lung parenchyma of influenza virus-infected mice. Single T cells were activated to divide in vitro; individual daughter cells were then micromanipulated into secondary cultures with and without added IL-4 to assess their potential to express type 2 cytokine genes. The resultant subclones were analyzed for type 1 and 2 cytokine mRNAs at day 6-7. When the most activated (CD44(high)CD11a(high)) CD8(+) subpopulation from infected lung was compared with naive or resting (CD44(low)CD11a(low)) CD8(+) cells from infected lung and from normal lymph nodes (LNs), both clonogenicity and plasticity of the cytokine response were highest in the LN population and lowest in the activated lung population, correlating inversely with effector function. Multipotential cells were nevertheless detected among clonogenic CD44(high)CD11a(high) lung cells at 30-50% of the frequency in normal LNs. The data indicate that activated CD8(+) T cells can retain the ability to proliferate and express new cytokine genes in response to local stimuli after recruitment to an effector site.

Animals↗
PubMed1999

Methodological issues in volumetric magnetic resonance imaging of the brain in the Edinburgh High Risk Project.

The Edinburgh High Risk Project is a longitudinal study of brain structure (and function) in subjects at high risk of developing schizophrenia in the next 5-10 years for genetic reasons. In this article we describe the methods of volumetric analysis of structural magnetic resonance images used in the study. We also consider potential sources of error in these methods: the validity of our image analysis techniques; inter- and intra-rater reliability; possible positional variation; and thresholding criteria used in separating brain from cerebro-spinal fluid (CSF). Investigation with a phantom test object (of similar imaging characteristics to the brain) provided evidence for the validity of our image acquisition and analysis techniques. Both inter- and intra-rater reliability were found to be good in whole brain measures but less so for smaller regions. There were no statistically significant differences in positioning across the three study groups (patients with schizophrenia, high risk subjects and normal volunteers). A new technique for thresholding MRI scans longitudinally is described (the 'rescale' method) and compared with our established method (thresholding by eye). Few differences between the two techniques were seen at 3- and 6-month follow-up. These findings demonstrate the validity and reliability of the structural MRI analysis techniques used in the Edinburgh High Risk Project, and highlight methodological issues of general concern in cross-sectional and longitudinal studies of brain structure in healthy control subjects and neuropsychiatric populations.

Adolescent↗
PubMed1999

Cutting edge: stable epigenetic inheritance of regional IFN-gamma promoter demethylation in CD44highCD8+ T lymphocytes.

Genomic DNA methylation patterns influence the development and maintenance of function during cellular differentiation. Methylation of regulatory sequences can have long-lasting effects on gene expression if inherited in an epigenetic manner. Recent work suggests that DNA methylation has a regulatory role in differential cytokine gene expression in primary T lymphocytes. Here we show, by clonal lineage analysis, that methylation patterns in the IFN-gamma promoter exhibit long term faithful inheritance in CD44highCD8+ T cells and their progeny, through 16 cell divisions and a clonal expansion of 5 orders of magnitude. Moreover, the demethylated IFN-gamma promoter is faithfully inherited following the withdrawal of T cell stimulation and the loss of detectable IFN-gamma mRNA, consistent with passive rather than active maintenance mechanisms. This represents a form of stable cellular memory, of defined epigenetic characteristics, that may contribute to the maintenance of T cell cytokine expression patterns and T cell memory.

Animals↗
PubMed1999

Nature versus nurture in T cell cytokine production.

Both extrinsic and intrinsic factors influence the development of cytokine expression patterns in T lymphocytes. The models proposed to accommodate these factors are often separated into two types: deterministic (or instructional) and probabilistic (or stochastic). In this review we compare these two types of models and examine how they account for different stages of T cell cytokine responses to antigen stimulation. We conclude by showing how a reconciliation of the two types of models may be possible, perhaps through the regulatory potential of heritable epigenetic mechanisms. This type of reconciliation may open up new avenues for manipulating T cell cytokine expression and redirecting immune responses.

Animals↗
PubMed1999

Educating T cells: early events in the differentiation and commitment of cytokine-producing CD4+ and CD8+ T cells.

T lymphocytes acquire the ability to synthesize cytokines during their primary response to antigen, often giving rise to effector populations with a polarized type 1 or type 2 cytokine profile. However, polarization is not a simple choice between two differentiation pathways. This article reviews the evidence, particularly from single-cell and clonal studies, that polarization is the outcome of a series of stochastic events whose probabilities are determined in part by genetic background and in part by extracellular signals received during activation and clonal expansion. The data suggest that these extracellular signals independently and differentially regulate the probability of expression of each cytokine gene, for example by their effects on clonal expansion and chromatin remodeling, CpG demethylation and transcriptional activation of cytokine genes. Polarization is, therefore, achieved at the population level by altering frequencies of expression among cells with many different expression patterns, rather than by selective differentiation of a discrete subset. Type 1 and type 2 populations progressively lose responsiveness to counter-polarizing stimuli. While the molecular basis of this process is not yet known, the observed persistence of cells with flexible cytokine profiles in some polarized populations suggests that loss of flexibility may also be a probabilistic event.

Animals↗
PubMed1999

Single-cell analysis by RT-PCR reveals differential expression of multiple type 1 and 2 cytokine genes among cells within polarized CD4+ T cell populations.

RT-PCR was used to examine the expression of IFN-gamma, IL-2, IL-4, IL-5, IL-6 and IL-10 mRNAs by single murine CD4+ T cells activated either in a strongly type 1-polarized mixed lymphocyte reaction (MLR) or in the type 2-polarized response to immunization with keyhole limpet hemocyanin (KLH) in alum. The frequencies of expression of each cytokine differed markedly between the two responses, consistent with their polarization at the population level. However, most cells expressed only none to three of the six cytokines assayed, few displayed the canonical type 1 profile and none in either response expressed a full type 2 or type 0 profile. A significant fraction of cells co-expressed IFN-gamma with IL-4 and/or other type 2 cytokines at frequencies that suggested that most of these genes were independently regulated. Collectively, these single-cell expression patterns indicate that polarization at the population level can mask substantial intercellular heterogeneity, and show directly that multiple type 1 and 2 cytokines can be expressed simultaneously in an individual T cell.

Animals↗
PubMed1998

Persistence of donor-reactive CD4+ T cells in liver and spleen of rats tolerant to a liver allograft.

BACKGROUND: In the rat, orthotopic liver transplantation from a DA strain donor to a PVG recipient causes an early rejection response that spontaneously resolves over the following weeks to yield long-lasting, donor-specific tolerance. METHODS: Limiting dilution analysis was used to estimate the frequencies of host CD4+ cells able to proliferate in response to donor antigens in the grafted liver and spleen of recipients during and after tolerance induction. RESULTS: Compared with naive PVG rats, both the frequencies and absolute numbers of donor-reactive host CD4+ cells in the liver and spleen rose significantly during the first week after transplantation and remained elevated for at least 3 months. CONCLUSION: We conclude that the development of tolerance in this model is not associated with deletion of clonogenic donor-reactive CD4+ T cells by clonal exhaustion or any other mechanism.

Animals↗
PubMed1998

Distinct methylation of the interferon gamma (IFN-gamma) and interleukin 3 (IL-3) genes in newly activated primary CD8+ T lymphocytes: regional IFN-gamma promoter demethylation and mRNA expression are heritable in CD44(high)CD8+ T cells.

Differential genomic DNA methylation has the potential to influence the development of T cell cytokine production profiles. Therefore, we have conducted a clonal analysis of interferon (IFN)-gamma and interleukin (IL)-3 gene methylation and messenger (m)RNA expression in primary CD8+ T cells during the early stages of activation, growth, and cytokine expression. Despite similar distributions and densities of CpG methylation sites, the IFN-gamma and IL-3 promoters exhibited differential demethylation in the same T cell clone, and heterogeneity between clones. Methylation patterns and mRNA levels were correlated for both genes, but demethylation of the IFN-gamma promoter was widespread across >300 basepairs in clones expressing high levels of IFN-gamma mRNA, whereas demethylation of the IL-3 promoter was confined to specific CpG sites in the same clones. Conversely, the majority of clones expressing low or undetectable levels of IFN-gamma mRNA exhibited symmetrical methylation of four to six of the IFN-gamma promoter CpG sites. Genomic DNA methylation also has the potential to influence the maintenance or stability of T cell cytokine production profiles. Therefore, we also tested the heritability of IFN-gamma gene methylation and mRNA expression in families of clones derived from resting CD44(low)CD8+ T cells or from previously activated CD44(high)CD8+ T cells. The patterns of IFN-gamma gene demethylation and mRNA expression were faithfully inherited in all clones derived from CD44(high) cells, but variable in clones derived from CD44(low) cells. Overall, these findings suggest that differential genomic DNA methylation, including differences among cytokine genes, among individual T cells, and among T cells with different activation histories, is an important feature of cytokine gene expression in primary T cells.

Animals↗
PubMed1998

Helper T cell subsets: heterogeneity, functions and development.

The discovery that the nature of cytokine production by CD4+ T lymphocytes could drastically alter an immune response led to the categorization of distinct helper T cell subsets, most notably Th1 and Th2. Recent evidence suggests that such helper responses are actually quite heterogeneous and ultimately, the course of an immune response depends upon the predominance of particular cytokines. While the factors leading to the production of individual cytokines are not completely defined, it is clear that the nature and dose of antigen, location of antigen challenge, and genetic composition of the individual all play a role in the process. Elucidating the cellular and molecular pathways responsible for helper T cell differentiation will ultimately permit the manipulation of immune responses to pathogens, as well as the development of novel vaccine strategies.

Animals↗
PubMed1998

The CD4+ T-cell response to protein immunization is independent of accompanying IFN-gamma-producing CD8+ T cells.

By virtue of their strong bias towards production of interferon-gamma (IFN-gamma), CD8+ T cells have the potential to promote the development of type 1 immune responses. We have previously shown that the CD4+ T-cell response to immunization with the protein antigen keyhole limpet haemocyanin (KLH) has a mixed interleukin-4 (IL-4)/IFN-gamma production profile. Here we show that this immunization regimen also stimulates accumulation in the draining lymph nodes of CD8+ T cells, which preferentially contain IFN-gamma mRNA ex vivo and secrete IFN-gamma protein in vitro. This provides a model to test whether CD8+ cell-derived IFN-gamma participates in the normal control of the immune response to a non-viable exogenous antigen. To investigate regulation of the anti-KLH response by the CD8+ population or IFN-gamma produced by this or other cell types, mice were administered depleting antibodies. Depletion of CD8+ cells had no effect on the frequency of clonogenic KLH-specific CD4+ T cells, the IL-4/IFN-gamma profiles of their progeny, or the isotype profiles of the serum antibody response to KLH. In contrast, IFN-gamma neutralization diminished cell accumulation in the lymph nodes and reduced both the frequency of KLH-specific CD4+ T cells that gave rise to IFN-gamma-producing clones and serum titres of KLH-specific IgG2a and IgG3. Therefore, despite the potential for cross-regulation, the CD4+ T-cell response to this immunogen is independent of the IFN-gamma-skewed CD8+ response.

Animals↗
PubMed1998

Cytokines: principles and prospects.

Cytokines participate in the induction and effector phases of all immune and inflammatory responses. They are therefore obvious tools and targets for strategies designed to promote, inhibit or redirect these responses. However, the complexity of the cytokine network has hindered the widespread clinical application of many cytokines and it has become clear that a deeper understanding of the normal operation of this system in health and disease is needed for the therapeutic potential of cytokines to be fully realized. This review summarizes some of the principles that are now thought to underlie the diverse functions of the interleukins, interferons, colony-stimulating factors and tumour necrosis factors in immune and inflammatory reactions in vivo. Genetic and structural relationships between these cytokines, the regulation of their synthesis, and the structures and functions of their receptors are outlined. Current knowledge of these parameters suggests ways in which multiple positive and negative regulatory mechanisms are integrated to balance cytokine benefits and harm under physiological conditions and offers new prospects for rational exploitation of this system.

Animals↗