Biomedical subjects

Jean-François Nicolas

Publications and source records attributed to Jean-François Nicolas.

At least 19 recordsLinked to original sources

PubMed2006

Clonal origin of the mammalian forebrain from widespread oriented mixing of early regionalized neuroepithelium precursors.

The forebrain is formed by remodeling and growth of the anterior neural plate. This morphogenesis occurs in response to inductive signals during gastrulation and neurulation but is poorly understood at the cellular level. Here, we have used the LaacZ method of single cells labeling to visualize, at E12.5, clones originated at early stages of mouse forebrain development. The largest clones show that single progenitors can give rise to neuroepithelial cells dispersed across the forebrain. A significant fraction of the clones, and even relatively small ones, populated both the diencephalon and the telencephalon, indicating that the clonal separation between diencephalic and telencephalic progenitors is transient and/or partial. However, two groups of large clones, populating either the diencephalon or the telencephalon, dispersed within their respective domains, suggesting an early regionalization between some diencephalic and telencephalic progenitors. Widespread oriented mixing within these territories and then clonal expansion into smaller domains probably follow this initial regionalization. These data are consistent with a model of progressive specification of forebrain domains. We propose that the ordered expansion of early regionalized progenitor pools for the diencephalon and telencephalon could establish a potential link between early inductive signals and forebrain morphogenesis.

Animals↗

PubMed2006

[Epidemiology and pathophysiology of eczemas].

Pathophysiological characteristics of these two types of eczema, both involve antigen specific effector T lymphocytes and down-regulatory CD4+ T cells (Treg). These cells are responsible for the cutaneous inflammatory response through the production of inflammatory cytokines and the destruction of keratinocytes by apoptosis. The main difference between these two types of disease is the nature of the environmental antigen. Indeed, protein allergens are involved in cases of atopic dermatitis whereas non protein chemicals (calles haptens) are responsible for allergic contact dermatitis. The skin lesions of eczema follow the activation of antigen specific T lymphocytes within the skin, leading to the production of inflammatory cytokines and to the destruction of keratinocytes by apoptosis. CD4+ Treg cells are endowed with down-regulatory and tolerogenic functions since they limit the skin inflammation in patients and prevent sensitization and induction of eczema in normal individuals. Eczema should therefore be considered as inflammatory dermatoses caused by the loss of immune tolerance to environmental antigens. Different strategies capable of restoring immune tolerance could avoid eczema outbursts and/or induce prolonged remissions of the disease.

Eczema↗

PubMed2006

CD8+ T cells are effector cells of contact dermatitis to common skin allergens in mice.

Allergic contact dermatitis (ACD) to strong experimental haptens is mediated by specific CD8+ T cells. Here, we show that similar mechanisms occur for weak haptens, which comprise the vast majority of chemicals responsible for human ACD. We used a model of ACD, that is, the contact hypersensitivity reaction, to test for the allergenicity of three weak haptens involved in fragrance allergy. ACD to weak haptens could not be induced in normal mice. In contrast, mice acutely depleted in CD4+ T cells developed a typical ACD reaction to the three weak fragrance allergens that peaked 24 hours after challenge. Priming of CD8+ T cells was observed in draining lymph nodes 5 days after sensitization and development of ACD was associated with the infiltration of activated CD8+ T cells in the challenged skin. CD8+ T cells were effectors of the ACD reaction as in vivo treatment with depleting anti-CD8 mAbs abrogated the ACD responses and as purified CD8+ T cells could adoptively transfer ACD to naive recipients. In conclusion, our data demonstrate a dominant role of CD8+ T cells as initiators of ACD to weak haptens, and suggest that CD8+ T cells may represent potential targets for preventing or treating ACD.

Allergens↗

PubMed2006

[Allergic contact dermatitis: how to re-induce tolerance?].

Allergic contact dermatitis (ACD) is a skin inflammatory disease mediated by activation of CD8+ cytotoxic T cells specific for haptens in contact with the skin. CD4+ T cells behave as both regulatory and tolerogenic cells since they down-regulate the skin inflammation in patients with ACD (regulation) and prevent the development of eczema (tolerance) in normal individuals. Thus, ACD corresponds to a breakdown of immune tolerance to haptens in contact with the skin. Several regulatory CD4+ T cell subsets (Treg), especially CD4+CD25+ natural Treg cells, are involved in immunological tolerance and regulation to haptens through the production of the immunosuppressive cytokines IL-10 and TGF-beta. Ongoing strategies to re-induce immune tolerance to haptens in patients with eczema include improvement of existing methods of tolerance induction (oral tolerance, low dose tolerance, allergen-specific immunotherapy, UV-induced tolerance) as well as development of new drugs able to activate IL-10 producing Treg cells in vivo. Ongoing and future progress in this area will open up new avenues for treatment of eczema and more generally autoimmune and allergic diseases resulting from a breakdown of tolerance to autoantigens and allergens, respectively.

Allergens↗

PubMed2006

CD8+ cytotoxic T cells induce relapsing colitis in normal mice.

BACKGROUND & AIMS: Most mouse models of IBD have emphasized an effector role of type-1 CD4+ T cells in colitis. The aim of this study was to develop a model of antigen-specific relapsing colitis to investigate the relative contribution of CD4+ and CD8+ effectors. METHODS: Balb/C mice were sensitized and challenged with a suboptimal dose of 2.4 dinitrobenzene sulfonic acid to generate a colonic delayed-type hypersensitivity response. The respective role of CD4+ and CD8+ T cells in the initiation of colitis was analyzed by in vivo monoclonal antibody depletion and cell-transfer experiments. Dynamic and function of the colitogenic effectors were studied by immunohistochemistry, fluorescence-activated cell sorter analysis, enzyme-linked immunospot assay, quantitative polymerase chain reaction, and in vivo CTL assays. RESULTS: Relapsing colitis rapidly occurred only after challenge of previously sensitized mice. Interferon-gamma-producing cytotoxic CD8+ T cells (Tc1) specific for hapten-modified self-proteins were generated in colon-draining lymph nodes on day 5 after sensitization, before the onset of disease. These CD8+ T cells were rapidly recruited upon challenge into colon lamina propria as granzyme B-expressing effectors exerting ex vivo cytotoxicity against syngeneic hapten-modified colonic epithelial cells. Colitis was prevented by in vivo antibody depletion of CD8+, but not of CD4+, T cells and could be induced in naive recipients within 48 hours after transfer of CD8+, but not CD4+, T cells purified from sensitized mice. CONCLUSIONS: Our data show that antigen-specific CD8+ T cells can induce relapsing colitis in normal mice and suggest that the cytolytic function of CD8 Tc1 against epithelial cells may initiate the intestinal inflammatory process.

Animals↗

PubMed2006

Smooth muscle of the dorsal aorta shares a common clonal origin with skeletal muscle of the myotome.

We show that cells of the dorsal aorta, an early blood vessel, and of the myotome, the first skeletal muscle to form within the somite, derive from a common progenitor in the mouse embryo. This conclusion is based on a retrospective clonal analysis, using a nlaacZ reporter targeted to the alpha-cardiac actin gene. A rare intragenic recombination event results in a functional nlacZ sequence, giving rise to clones of beta-galactosidase-positive cells. Periendothelial and vascular smooth muscle cells of the dorsal aorta are the main cell types labelled, demonstrating that these are clonally related to the paraxial mesoderm-derived cells of skeletal muscle. Rare endothelial cells are also seen in some clones. In younger clones, arising from a recent recombination event, myotomal labelling is predominantly in the hypaxial somite, adjacent to labelled smooth muscle cells in the aorta. Analysis of Pax3(GFP/+) embryos shows that these cells are Pax3 negative but GFP positive, with fluorescent cells in the intervening region between the aorta and the somite. This is consistent with the direct migration of smooth muscle precursor cells that had expressed Pax3. These results are discussed in terms of the paraxial mesoderm contribution to the aorta and of the mesoangioblast stem cells that derive from it.

Actins↗

PubMed2006

Pathophysiology of urticaria.

Urticaria is dermal edema resulting from vascular dilatation and leakage of fluid into the skin in response to molecules released from mast cells. The major preformed mediator histamine produces a prototypic, short-lived urticaria. However, the clinical spectrum and pattern of lesions indicate that other molecules, including prostaglandins, leukotrienes, cytokines, and chemokines, produced at different times after mast cell activation contribute to the polymorphism of this symptom and the variable evolution of this disease. It is a common practice to distinguish immunological and nonimmunological urticaria. Immunological urticaria is a hypersensitivity reaction mediated by antibodies and/or T-cells that results in mast cell activation. Although immunoglobulin (Ig)E-mediated type I hypersensitivity (HS) was long postulated to be the major immunological pathway associated with mast cell activation, interaction between IgE-bound mast cells and allergens is unlikely to be the mechanism by which urticaria develops in most patients. It is now well established that urticaria may result from the binding of IgG auto-antibodies to IgE and/or to the receptor for IgE molecules on mast cells, thus corresponding to a type II HS reaction. These auto-immune urticarias represent up to 50% of patients with chronic urticaria. Mast cell activation can also result from type III HS through the binding of circulating immune complexes to mast cell-expressing Fc receptors for IgG and IgM. Finally, under certain circumstances, T-cells can induce activation of mast cells, as well as histamine release (type IV HS). Nonimmunological urticarias result from mast cell activation through membrane receptors involved in innate immunity (e.g., complement, Toll-like, cytokine/chemokine, opioid) or by direct toxicity of xenobiotics (haptens, drugs). In conclusion, urticaria may result from different pathophysiological mechanisms that explain the great heterogeneity of clinical symptoms and the variable responses to treatment.

Cell Degranulation↗

PubMed2006

Head-tail patterning of the vertebrate embryo: one, two or many unresolved problems?

When, where and how is the head-tail axis of the embryo set up during development? These are such fundamental and intensely studied questions that one might expect them to have been answered long ago. Not so; we still understand very little about the cellular or molecular mechanisms that lead to the orderly arrangement of body elements along the head-tail axis in vertebrates. In this paper, we outline some of the major outstanding problems and controversies and try to identify some reasons why it has been so difficult to resolve this important issue.

Animals↗

PubMed2005

Defective planar cell polarity in polycystic kidney disease.

Morphogenesis involves coordinated proliferation, differentiation and spatial distribution of cells. We show that lengthening of renal tubules is associated with mitotic orientation of cells along the tubule axis, demonstrating intrinsic planar cell polarization, and we demonstrate that mitotic orientations are significantly distorted in rodent polycystic kidney models. These results suggest that oriented cell division dictates the maintenance of constant tubule diameter during tubular lengthening and that defects in this process trigger renal tubular enlargement and cyst formation.

Animals↗

PubMed2005

Lysophosphatidylcholine is a natural adjuvant that initiates cellular immune responses.

The discovery of new adjuvants that can stimulate the immune response to protein antigens is a major issue for the development of subunit vaccines. Lipoprotein oxidation occurring during the acute phase response (APR) to aggression of the organism, provides signals of danger that are detected by dendritic cells (DC). Among other instructive molecules generated during the APR, lysophosphatidylcholine (LPC) promotes mature DC generation from differentiating human monocytes in vitro. It is shown here that LPC also controls the initiation of an adaptive immune response in vivo. LPC displays adjuvant properties when injected to mice in mixture with various antigens. Immunizations with LPC induced the production of antigen-specific antibodies with an efficiency similar to Alum, the reference adjuvant for human vaccination. Importantly, LPC also induced cytotoxic T cell responses, opening perspectives for vaccine development. Therefore, LPC is a natural adjuvant for the immune system, inducing humoral and cellular immune responses.

Adjuvants, Immunologic↗

PubMed2005

Hair follicle renewal: organization of stem cells in the matrix and the role of stereotyped lineages and behaviors.

Hair follicles (HFs) are renewed via multipotent stem cells located in a reservoir (the bulge); however, little is known about how they generate multi-tissue HFs from a proliferative zone (the matrix). To address this issue, we temporally induced clonal labeling during HF growth. Challenging the prevailing hypothesis, we found that the matrix contains restricted self-renewing stem cells for each inner structure. These cells are located around the dermal papilla forming a germinative layer. They occupy different proximodistal sectors and produce differentiated cells along the matrix radial axis via stereotyped lineages and cell behavior. By contrast, the outer layer of HFs displays a mode of growth involving apoptosis that coordinates the development of outer and inner structures. HF morphology is therefore determined by the organization of cell fates along the proximodistal axis and by cell behavior along the radial (lateral) axis in the matrix. Thus, our studies suggest that fate and behavior are organized by two systems (uncoupled), and this uncoupling may represent a fundamental way to simplify morphogenesis.

Animals↗

PubMed2005

Anopheles mosquito bites activate cutaneous mast cells leading to a local inflammatory response and lymph node hyperplasia.

When Anopheles mosquitoes probe the skin for blood feeding, they inject saliva in dermal tissue. Mosquito saliva is known to exert various biological activities, but its perception by the immune system and its role in parasite transmission remain poorly understood. In the present study, we report on the cellular changes occurring in the mouse skin and draining lymph nodes after a Anopheles stephensi mosquito bite. We show that mosquito bites induce dermal mast cell degranulation, leading to fluid extravasation and neutrophil influx. This inflammatory response does not occur in mast cell-deficient W/W(v) mice, unless these are reconstituted specifically with mast cells. Mast cell activation caused by A. stephensi mosquito bites is followed by hyperplasia of the draining lymph node due to the accumulation of CD3(+), B220(+), CD11b(+), and CD11c(+) leukocytes. The T cell enrichment of the draining lymph nodes results from their sequestration from the circulation rather than local proliferation. These data demonstrate that mosquito bites and very likely saliva rapidly trigger the immune system, emphasizing the critical contribution of peripheral mast cells in inducing T cell and dendritic cell recruitment within draining lymph nodes, a prerequisite for the elicitation of T and B lymphocyte priming.

Animals↗

PubMed2004

WHIM syndromes with different genetic anomalies are accounted for by impaired CXCR4 desensitization to CXCL12.

The WHIM syndrome is a rare immunodeficiency disorder characterized by warts, hypogammaglobulinemia, infections, and myelokathexis. Dominant heterozygous mutations of the gene encoding CXCR4, a G-protein-coupled receptor with a unique ligand, CXCL12, have been associated with this pathology. We studied patients belonging to 3 different pedigrees. Two siblings inherited a CXCR4 mutation encoding a novel C-terminally truncated receptor. Two unrelated patients were found to bear a wild-type CXCR4 open reading frame. Circulating lymphocytes and neutrophils from all patients displayed similar functional alterations of CXCR4-mediated responses featured by a marked enhancement of G-protein-dependent responses. This phenomenon relies on the refractoriness of CXCR4 to be both desensitized and internalized in response to CXCL12. Therefore, the aberrant dysfunction of the CXCR4-mediated signaling constitutes a common biologic trait of WHIM syndromes with different causative genetic anomalies. Responses to other chemokines, namely CCL4, CCL5, and CCL21, were preserved, suggesting that, in clinical forms associated with a wild-type CXCR4 open reading frame, the genetic anomaly might target an effector with some degree of selectivity for the CXCL12/CXCR4 axis. We propose that the sustained CXCR4 activity in patient cells accounts for the immune-hematologic clinical manifestations and the profusion of warts characteristic of the WHIM syndrome.

Adolescent↗

PubMed2004

[How to understand psoriasis?].

Recent advances in the treatment of psoriasis have led to improve understanding in the pathogenesis of the disease. Skin lesions are scaling erythematous plaques. Although initially considered as a disease of epidermal cells, it is now widely accepted that the epidermal abnormalities, which are characteristic of the disease, are secondary to the development of a skin inflammation. Psoriasis is an autoimmune disease due to the activation in the skin of antigen-specific T cells leading to release of cytokines that results in proliferation of keratinocytes. However, the autoantigen(s) is (are) yet unknown. Several new biological treatments have been developed, which target specific steps in the pathophysiology of the disease.

Cytokines↗

PubMed2004

The clonal origin of myocardial cells in different regions of the embryonic mouse heart.

When and how cells form and pattern the myocardium is a central issue for heart morphogenesis. Many genes are differentially expressed and function in subsets of myocardial cells. However, the lineage relationships between these cells remain poorly understood. To examine this, we have adopted a retrospective approach in the mouse embryo, based on the use of the laacZ reporter gene, targeted to the alpha-cardiac actin locus. This clonal analysis demonstrates the existence of two lineages that segregate early from a common precursor. The primitive left ventricle and the presumptive outflow tract are derived exclusively from a single lineage. Unexpectedly, all other regions of the heart, including the primitive atria, are colonized by both lineages. These results are not consistent with the prespecification of the cardiac tube as a segmented structure. They are discussed in the context of different heart fields and of the evolution of the heart.

Actins↗

PubMed2004

CpG immunostimulatory sequences enhance contact hypersensitivity responses in mice.

Bacterial DNA and synthetic cytidine-phosphate-guanosine-oligodeoxynucleotides (CpG ODN) potently activate dendritic cells (DC) and therefore have been proposed as adjuvants for vaccination strategies. Although CpG ODN are considered as safe adjuvants this study shows that CpG ODN are responsible for enhanced antigen-specific skin inflammatory reactions. We used the murine model of contact hypersensitivity (CHS) to 2,4-dinitrofluorobenzene (DNFB) in which hapten-specific CD8+T cytotoxic 1 cells are effector cells. Subcutaneous injection of CpG ODN, 1 d before sensitization enhanced the CHS response to DNFB and resulted in increased recruitment of CD8+ T cells at the challenge sites, whereas control ODN injection did not have any effect. This effect was local and not systemic as it was only observed when DNFB was applied at the same site as the CpG motifs. CpG ODN-induced enhancement of CHS was due to increased antigen-presenting cell functions of DC since: (i) CpG ODN-injected skin revealed upregulated expression of major histocompatibility complex class II, CD80, and CD86 molecules and (ii) CpG ODN treatment of DNFB-derivatized DC enhanced the intensity of CHS responses after in vivo transfer. Taken together, the results show that CpG ODN may be responsible for immune side-effects such as worsening of T cell-mediated skin diseases.

Adjuvants, Immunologic↗

PubMed2003

CpG content affects gene silencing in mice: evidence from novel transgenes.

BACKGROUND: Transgenes are often engineered using regulatory elements from distantly related genomes. Although correct expression patterns are frequently achieved even in transgenic mice, inappropriate expression, especially with promoters of widely expressed genes, has been reported. DNA methylation has been implicated in the aberrant expression, but the mechanism by which the methylation of a CpG-rich sequence can perturb the functioning of a promoter is unknown. RESULTS: We describe a novel method for analyzing epigenetic controls that allows direct testing of CpGs involvement by using LacZ reporter genes with a CpG content varying from high to zero that are combined with a CpG island-containing promoter of a widely expressed gene - the alpha-subunit of the translation elongation factor 1. Our data revealed that a LacZ transgene with null CpG content abolished the strong transgene repression observed in the somatic tissues of transgenic lines with higher CpG content. Investigation of transgene expression and methylation patterns suggests that during de novo methylation of the genome the CpG island-containing promoter escapes methylation only when combined with the CpG-null transgene. In the other transgenic lines, methylation of the promoter may have led to transcriptional silencing. CONCLUSIONS: We demonstrate that the density of CpG sequences in the transcribed regions of transgenes can have a causal role in repression of transcription. These results show that the mechanism by which CpG islands escape de novo methylation is sensitive to CpG density of adjacent sequences. These findings are of importance for the design of transgenes for controlled expression.

Animals↗

PubMed2003

Innate CD4+CD25+ regulatory T cells are required for oral tolerance and inhibition of CD8+ T cells mediating skin inflammation.

To elucidate the role of CD4+CD25+ regulatory T cells in oral tolerance, we used the model of contact hypersensitivity (CHS) to 2,4-dinitrofluorobenzene (DNFB), which is mediated by CD8+ Tc1 effector cells independently of CD4+ T-cell help. Conversely to normal mice, invariant chain knock-out (KO) (Ii degrees / degrees ) mice, which are deficient in CD4+ T cells, cannot be orally tolerized and develop a chronic hapten-specific CHS response. Transfer of naive CD4+ T cells before hapten gavage into Ii degrees / degrees mice restores oral tolerance by a mechanism independent of interleukin-10 (IL-10) production by CD4+ T cells. That naturally occurring CD4+CD25+ T cells are critical for oral tolerance induction is demonstrated by the finding that (1) transfer of CD4+CD25+ but not CD4+CD25- T cells into Ii degrees / degrees recipients completely prevents the CHS response and skin infiltration by CD8+ T cells, by blocking development of hapten-specific CD8+ T cells; (2) in vivo depletion of CD4+CD25+ cells by antibody treatment in normal mice impairs oral tolerance; and (3) CD4+CD25+ T cells inhibit hapten-specific CD8+ T-cell proliferation and interferon gamma (IFN gamma) production, in vitro. These data show that naturally occurring CD4+CD25+ T cells are instrumental for orally induced tolerance and are key actors for the control of antigen-specific CD8+ T-cell effectors mediating skin inflammation.

Administration, Oral↗