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Thierry Martin

Publications and source records attributed to Thierry Martin.

13 recordsLinked to original sources
PubMed2006

Recent developments in X-ray imaging with micrometer spatial resolution.

X-ray detectors for imaging with a spatial resolution in the micrometer and submicrometer range have been developed at synchrotron radiation sources since 1996. The detectors consist of a scintillator, a light microscopy optic and a charge-coupled device (CCD). The scintillator converts part of the X-ray stopped by a material into a visible-light image which is projected onto the CCD by the light optics. A resolution of 0.5 microm FWHM has been achieved using a 1 microm-thick europium-doped Lu3Al5O12 film. The detective quantum efficiency of the detector is mainly limited by the low absorption of X-rays in the thin layer of the scintillator. To increase the absorption, and therefore reduce the exposure time, new scintillators (Lu2O3:Eu3+, Gd2O3:Eu3+, Lu2SiO5:Ce, Gd3Ga5O12:Eu3+, CdWO4) have been investigated. These were fabricated using sol-gel and liquid-phase epitaxy processes. Finally, the first fast microtomography experiment including radiation hardness of the optic is shown. This detector uses a high-intensity white beam with 60 keV effective energy and a fast CCD camera at up to 60 frames s(-1).

Journal Article↗
PubMed2006

Overcoming the hurdle of fluorescent compounds in kinase screening: a case study.

In the field of screening in general and especially in the kinase area, taking into consideration throughput and cost, fluorescence- and luminescence-based assays have been developed as alternatives to radioactivity-based assays. However, fluorescence-based technologies are not devoid of pitfalls. One of the main problems is interference from autofluorescent compounds and the incidence of false-positives as exemplified here with a fluorescence polarization (FP)-based assay. Using the scintillation proximity assay as the in-house standard, we assessed several alternatives to radioactive methods, namely, the amplified luminescent proximity homogeneous assay screen (ALPHAScreen, Perkin-Elmer Life Sciences, Boston, MA), enzyme fragment complementation, FP, and nanofluidics-based fluorescence intensity. Data comparing the sensitivity, robustness, relative sensitivity to autofluorescent compounds, enzyme consumption, and relative costs of each assay for one common kinase are presented. Results obtained seem to favor the nanofluidics mobility shift assay as a method of choice, followed by the direct FP approach, using generic high-molecular-weight phosphate group-binders.

Fluorescence Polarization Immunoassay↗
PubMed2005

Blockade of PI3Kgamma suppresses joint inflammation and damage in mouse models of rheumatoid arthritis.

Phosphoinositide 3-kinases (PI3K) have long been considered promising drug targets for the treatment of inflammatory and autoimmune disorders as well as cancer and cardiovascular diseases. But the lack of specificity, isoform selectivity and poor biopharmaceutical profile of PI3K inhibitors have so far hampered rigorous disease-relevant target validation. Here we describe the identification and development of specific, selective and orally active small-molecule inhibitors of PI3Kgamma (encoded by Pik3cg). We show that Pik3cg(-/-) mice are largely protected in mouse models of rheumatoid arthritis; this protection correlates with defective neutrophil migration, further validating PI3Kgamma as a therapeutic target. We also describe that oral treatment with a PI3Kgamma inhibitor suppresses the progression of joint inflammation and damage in two distinct mouse models of rheumatoid arthritis, reproducing the protective effects shown by Pik3cg(-/-) mice. Our results identify selective PI3Kgamma inhibitors as potential therapeutic molecules for the treatment of chronic inflammatory disorders such as rheumatoid arthritis.

Animals↗
PubMed2005

Autoantigen, innate immunity, and T cells cooperate to break B cell tolerance during bacterial infection.

Autoantibody production during infections is considered to result from nonspecific activation of low-affinity autoreactive B cells. Whether this can lead to autoimmune disease remains uncertain. We show that chronic infection by Borrelia burgdorferi of Tg animals expressing human rheumatoid factor (RF) B cells (of low or intermediate affinities) in the absence or in the constitutive presence of the autoantigen (represented here by chimeric IgG with human constant region) breaks their state of immunological ignorance, leading to the production of RFs. Surprisingly, this production was more pronounced in intermediate-affinity RF Tg mice co-expressing the autoantigen. This overproduction was mediated by immune complexes and involved synergistic signaling between the B cell receptor and Toll-like receptors and T cell help. These findings indicate that chronic infection can activate autoreactive B cells with significant affinity and creates conditions that can drive them to differentiate into memory cells. Such cells may have some physiological yet undetermined role, but in autoimmune-prone individuals, this scenario may initiate autoimmunity.

Animals↗
PubMed2004

Pathogenic antiphospholipid antibody: an antigen-selected needle in a haystack.

Antiphospholipid antibodies represent a heterogeneous group of autoantibodies directed against anionic phospholipids (PLs) usually linked to protein cofactors. Their presence during the antiphospholipid syndrome is associated with risks of thrombosis and fetal losses. Among 5 randomly selected monoclonal antiphospholipid antibodies, all originating from a single patient suffering from this autoimmune disease, only 1 induced fetal losses when passively injected into pregnant mice. Its antiphospholipid activity was dependent on annexin A5, and its variable regions contained mainly 3 replacement mutations. To clarify the role of these mutations in the pathogenicity of the antibody, they were in vitro reverted to the germ line configuration. The resulting "germ line" antibody reacted with multiple self-antigens and only partially lost its reactivity against PLs, but it was no more dependent on annexin A5 and, more importantly, was no more pathogenic. This study illustrates that the in vivo antigen-driven maturation process of natural autoreactive B cells can be responsible for pathogenicity.

Adult↗
PubMed2003

Memory B cells producing somatically mutated antiphospholipid antibodies are present in healthy individuals.

Antiphospholipid antibodies (aPLs) are associated with thrombosis and recurrent abortions during autoimmune pathologies, but they are also produced in healthy individuals and during infectious diseases. To analyze the possible links between physiologic and pathologic aPLs, it is of importance to characterize normal aPL production. We took advantage of the known tropism of Epstein-Barr virus (EBV) for B cells in general, and memory B cells in particular, during primary infectious mononucleosis (IMN) in 3 patients to get access to anticardiolipin (aCL)-producing B cells. Flow cytometry analysis of these cells showed that, depending on the patient, 10% to 60% of immunoglobulin M (IgM) aCL-producing B cells express the CD27 marker of memory B cells. Single cell sorting of aCL B cells, followed by single cell reverse transcription-polymerase chain reaction (RT-PCR) amplification of their immunoglobulin variable region genes, showed that some of these cells produce mutated forms of aCL antibodies, confirming their memory B-cell origin. Considering that, during primary IMN, EBV infects and expands already pre-existing memory B cells, we conclude that healthy individuals have a discrete pool of aCL memory cells able to produce mutated forms of antibodies. The implications of this new information are discussed in light of different hypotheses regarding the origin of aCL.

Adolescent↗
PubMed2003

Cirrhosis and bleeding: the need for very early management.

BACKGROUND/AIMS: Retrospective studies suggest that the prognosis of patients with cirrhosis and variceal hemorrhage has improved in more recent decades. In a prospective cohort study in which the choice of prophylactic therapy was left to each practitioner, we followed cirrhotic patients with medium/large varices to determine factors predictive of bleeding and death. METHODS: Three hundred fourteen patients with grades 2 or 3 esophageal varices (Child A and B/C: 218 and 96) were enrolled. One hundred seventy-three patients had no previous history of variceal bleeding. Only 245 patients (100% of patients with prior variceal hemorrhage, 61% of patients without prior hemorrhage) were receiving some form of prophylactic therapy. The median follow-up was 18 months. RESULTS: There were 76 bleeding events and 14 related deaths (18%); nine of these deaths occurred within 24 h of bleeding onset (two at home, two during hospital transfer, and five in hospital, a mean of 2.5 h after onset; six involved Child C patients). Twenty-five deaths were not due to bleeding but were closely related to cirrhosis. In a Cox model, the presence of tense ascites (relative risk 3.4, 95% confidence interval, CI 2.5-5.9) and a prior history of hemorrhage (relative risk 4.4, 95% CI 2.6-7.5) were independent predictors of variceal hemorrhage. In patients without a prior history of bleeding, bleeding risk was higher with more prolonged prothrombin time and lower when patients were receiving propranolol. CONCLUSIONS: Despite the advent of effective drugs and endoscopic therapy for variceal bleeding, about a quarter of deaths occur very early after bleeding onset, confirming the need for rapid specific management.

Adrenergic beta-Antagonists↗
PubMed2002

B cell positive selection by soluble self-antigen.

It is well established that autoreactive B cells undergo negative selection. This stands in paradox with the high frequency of so-called natural autoreactive B cells producing low affinity polyreactive autoantibodies with recurrent specificities, suggesting that these B cells are selected on the basis of their autoreactivity. We previously described two transgenic mouse lines (with and without IgD) producing a human natural autoantibody (nAAb) that binds ssDNA and human Fcgamma. In the absence of human IgG, nAAb-transgenic B cells develop normally. By crossing these mice with animals expressing knockin chimeric IgG with the human Fcgamma, we now show that the constitutive expression of chimeric IgG promotes the increase of nAAb-expressing B cells. This positive selection is critically dependent on the presence of IgD, occurs in the spleen, and concerns all mature B cell subsets, with a relative preferential enrichment of marginal zone B cells. These data support the view that soluble self-Ags can result in positive clonal selection.

Animals↗
PubMed2002

A role for membrane IgD in the tolerance of pathological human rheumatoid factor B cells.

Under non-autoimmune conditions, rheumatoid factor (RF) B cells coexist peacefully with their antigen (IgG), or can be transiently activated during secondary immune responses because they can present xenoantigens to specific T cells captured in immune complex form. Such a situation should lead to affinity maturation of RF B cells and potentially dangerous production of high-affinity RF. We used two lines of transgenic mice expressing a somatically mutated pathological human RF in presence (IgM and IgD) or in absence (IgM only) of surface IgD, and confirm that RF B cell tolerance can result from an antigen-induced specific, but incomplete, deletion of naive RF B cells after antigen encounter. This deletion mainly concerns immature, transitional B cells. On the contrary, mature, IgM- and IgD-expressing RF B cells are resistant to such a deletion. These IgM and IgD RF B cells are functional and activable through both B cell receptor dependent (anti-IgM) and independent (LPS) pathways, but they are not fully responsive to human IgG either in vivo or in vitro. Taken together, these results suggest that another mechanism could be involved in the silencing of mature naive IgM and IgD RF B cells.

Animals↗
PubMedDate not supplied

T-cell receptor Vbeta gene usage in CSF lymphocytes in X-linked adrenoleukodystrophy.

X-linked adrenoleukodystrophy (ALD) is a peroxisomal disorder with impaired very-long-chain fatty acid (VLCFA) metabolism that produces a neurological disease with significant variability of clinical phenotypes even within kindred. The two most common forms are the cerebral form (CALD) with an important inflammatory reaction at the active edge of demyelinating lesions, resembling some aspects of multiple sclerosis pathology, and adrenomyeloneuropathy (AMN), which involves the spinal cord and in which the inflammatory reaction is mild or absent. One hypothesis is that the phenotypic variability is related to T cell-mediated immune mechanisms playing a primary role in the demyelinating pathogenic process of CALD. The present study aims to test the hypothesis that CSF of patients with the CALD form contains highly restricted T cell populations. The variable regions of the T cell receptor beta chains (TCR Vbeta) were studied in CSF from 29 ALD patients with different phenotypes. RNA was extracted and cDNA synthesized from CSF lymphocytes; TCR Vbeta gene segments were amplified from the cDNA by polymerase chain reaction (PCR) using 20 family-specific primers. PCR products were analyzed by Southern blot. Some amplified Vbeta products were sequenced. The majority of ALD patients (21/29), whatever their phenotype, exhibited oligoclonal T cell expansion. However the overexpression of some TCR Vbeta families was heterogeneous among the different patients without any preponderance of specific Vbeta families or any clustering according to clinical phenotype. In particular a dominant TCR Vbeta utilization was not found in patients with CALD.

Adrenoleukodystrophy↗