Biomedical subjects

Marc Michel

Publications and source records attributed to Marc Michel.

14 recordsLinked to original sources

PubMed2026

Affinity-matured B cell responses neutralizing type-I interferons underlie severe viral infections.

Autoantibodies neutralizing type-I interferons (AAN-I-IFNs) emerge as global, common, and strong determinants of a growing number of severe viral diseases. We report that AAN-I-IFNs+ patients with life-threatening COVID-19 pneumonia harbor circulating type-I IFN-specific B cells indistinguishable from patients bearing T cell tolerance defects of genetic origin. This autoimmune response mobilizes a highly diverse and stable circulating B cell response that is detected prior to severe viral infection and acquires high affinity and neutralization potential to type-I IFNs through extended somatic hypermutation. X-ray crystallography and AlphaFold3 structural analysis of hundreds of patient-derived monoclonal antibodies reveals the extended breadth of this response, targeting three major B cell epitopes covering all facets of type-I IFNs. These findings support a model in which a germinal-center-derived memory B cell response directed against type-I IFNs is established before severe viral infection, providing a core mechanism linking T cell tolerance defect to pathogenic AAN-I-IFNs underlying severe viral diseases.

Humans↗

PubMed2007

Psoas abscess: An unusual manifestation of Q fever.

Q fever may lead to serious complications in chronically infected patients. We report two cases of psoas abscess due to Coxiella burnetii associated with lumbar osteomyelitis secondary to an aortic aneurysmal infection. Diagnosis was based on serology, and PCR detected C. burnetii DNA in an abscess sample.

Journal Article↗

PubMed2006

Layer-by-layer self-assembled polyelectrolyte multilayers with embedded liposomes: immobilized submicronic reactors for mineralization.

The development of chemical reactions in nanospaces is of paramount importance for the development of active nanodevices, particularly in nanofluidics. It has been shown in a previous paper that phospholipid vesicles can be incorporated without spontaneous bilayer rupture into poly-L-glutamic acid/poly(allylamine) (PGA/PAH) multilayered polyelectrolyte films. The aim of the present study was to use such a system as an "embedded submicronic reactor" able to trigger precipitation of calcium phosphates within closed spaces through an enzymatic reaction, the enzyme also being encapsulated in the vesicle interior. To this aim, large unilamellar vesicles (LUVs) were produced containing calcium ions as active ions in the mineralization process, spermine as an activator of crystal growth, and alkaline phosphatase as a catalyst to convert phosphate esters into phosphates. After stabilization by adding a layer of poly-(D-lysine), these vesicles were embedded in a (PGA-PAH)n film. A paranitrophenyl phosphate containing solution was then put in contact with this film. It is shown by means of infrared spectroscopy in the attenuated total reflection mode that, consecutively to this contact, calcium phosphates are growing inside the embedded vesicles. By using scanning near-field fluorescence microscopy, it is demonstrated that the alkaline phosphatase enzymes are most probably located inside the vesicles after their embedding. In addition, atomic force microscopy was used to show, after chemical removal of the organic top layer of the film, that the inorganic platelets produced after the precipitation reaction are localized in volumes of similar size and shape as that of the vesicles into which the phosphate ester hydrolysis and subsequent precipitation reaction did occur.

Journal Article↗

PubMed2005

Assessment of a therapeutic strategy for adults with severe autoimmune thrombocytopenic purpura based on a bleeding score rather than platelet count.

BACKGROUND AND OBJECTIVES: The optimal treatment for patients with autoimmune thrombocytopenic purpura (AITP) and a platelet count < or =20x10(9)/L is intravenous immunoglobulin (IVIg) but this treatment is expensive and steroids are a good alternative in less severe cases. Since the occurrence of life-threatening hemorrhage in adult AITP is a rare event, the aim of our study was to validate a therapeutic strategy based on a bleeding score for the short-term management of adults with AITP and a platelet count < or =20x10(9)/L. DESIGN AND METHODS: We developed a method to quantify hemorrhage in adults with AITP. Bleeding severity was graded on a numerical scale based on physical examination. When the bleeding score was < or =8, the patients were treated with steroids alone. For scores >8, patients received IVIg (1 to 2 g/kg) in combination with oral steroids. A good response was defined as the lowering of the initial bleeding score within 2 days after treatment initiation regardless of the platelet count. RESULTS: We applied this strategy for the management of 60 consecutive adults (mean age 48+/-23 years) with AITP and a platelet count < or =20x10(9)/L/L (mean platelet count 6+/-5x10(9)/L/L). Based on this strategy, IVIg was required in only 50% of the patients and no life-threatening bleeding occurred in patients treated with steroids alone. INTERPRETATION AND CONCLUSIONS: A therapeutic strategy based on a bleeding score rather than the platelet count appears to be relevant and safe and is a good IVIg-sparing strategy.

Adolescent↗

PubMed2005

Prognostic relevance of large-platelet counts in patients with immune thrombocytopenic purpura.

In this preliminary study, the value of different platelet parameters, measured by the ADVIA120 Analyzer, in predicting the immediate response to intravenous immunoglobulin or intravenous anti-RhoD was assessed in 31 patients with immune thrombocytopenic purpura. The number of large platelets pre-treatment was the only independent predictor of the 24 hour-platelet increase.

Adolescent↗

PubMed2004

Giant liposome microreactors for controlled production of calcium phosphate crystals.

Calcium phosphates are among the most important biominerals in living organisms, where they play both a mechanical and a calcium storage role. Their growth in vivo is under strong biological control, and this process occurs in closed spaces. Our aim in this paper is to describe a microreactor system able to control the mineralization process within closed spaces. To this aim we produce giant liposomes containing calcium ions as active ions in the mineralization process, spermine as an activator of crystal growth, and alkaline phosphatase as a catalyst to convert phosphate esters into phosphates. These phosphate esters are provided in the form of p-nitrophenyl phosphate outside of the liposomes. It is demonstrated that these amphiphilic molecules are able to diffuse through the lipidic container and to be subsequently hydrolyzed under enzymatic catalysis into active phosphate species which interact with the already available calcium and spermine to produce calcium phosphates only in the interior of the liposomes. This opens the route to control the calcium phosphate particle size in biomimetic systems.

Alkaline Phosphatase↗

PubMed2004

Layer by layer self-assembled polyelectrolyte multilayers with embedded phospholipid vesicles.

We describe a method to embed phospholipid vesicles into polyelectrolyte multilayers built up by the alternate deposition of polyanions and polycations. Before deposition, the vesicles are rigidified by polycation adsorption onto their surface avoiding their fusion once deposited on the multilayer surface. The vesicles adsorb to form a compact and "hard" monolayer as imaged by atomic force microscopy. The thickness of the adsorbed vesicle layer, of the order of 250 nm, is very close to the diameter of the vesicles in solution. This work should open the route to the buildup of multilayer films containing phospholipid vesicles that could act as "reservoirs" for drugs or enzymatic nanoreactors.

Adsorption↗

PubMed2004

Autoimmune thrombocytopenic purpura and common variable immunodeficiency: analysis of 21 cases and review of the literature.

To describe the main characteristics and outcome of autoimmune thrombocytopenic purpura (AITP) in patients with common variable immunodeficiency (CVID), we analyzed data from 21 patients and reviewed additional cases from the literature. To be included in this study, patients had to have CVID and a previous history of AITP with a platelet count < or = 50 x 10(9)/L at onset. A complete response to treatment was defined by a platelet count > or = 150 x 10(9)/L, and a partial response by a platelet count >>50 x 10(9)/L with an increase of at least twofold the initial level. The median platelet count at AITP diagnosis was 20 x 10(9)/L (range, 2-50 x 10(9)/L). The median age at AITP diagnosis was 23 years (range, 1-51 yr), whereas the median age at CVID diagnosis was 27 years (range, 10-74 yr). CVID was diagnosed before the onset of AITP in only 4 patients (19%), 3 of whom were being treated with intravenous immunoglobulin (i.v.Ig) replacement therapy. CVID was diagnosed more than 6 months after AITP in 13 cases (62%), and the 2 conditions were diagnosed concomitantly in 4 cases. Eleven patients (52%) had at least 1 autoimmune manifestation other than AITP, among which autoimmune hemolytic anemia (7 cases) and autoimmune neutropenia (5 cases) were preeminent. Seventeen of the 21 patients (80%) received at least 1 treatment for AITP; 13 patients received corticosteroids alone and 7 (54%) achieved at least a partial response; 8 patients received i.v.Ig at 1-2 g/kg alone or in combination with steroids, leading to a short-term response rate of 50%. Four patients underwent a splenectomy (2 complete responses, 2 failures); 2 additional splenectomies were performed for associated autoimmune hemolytic anemia. With a mean follow-up of 5.6 years after the surgical procedure, none of the 6 splenectomized patients had a life-threatening infection. With a median follow-up after AITP onset of 12 years, 13/21 patients (62%) were in treatment-free remission (7 complete responses, 6 partial responses), 7 patients (23%) were in remission while on prednisone < or = 20 mg/day with or without azathioprine, and only 1 patient still had a platelet count <50 x 10(9)/L. Five patients had died at the time of the analysis; none of the deaths was related to a hemorrhage. Severe infections including 3 fatal bacterial infections and 2 opportunistic infections occurred in 6 patients during or after treatment of AITP. In conclusion, AITP, alone or in combination with autoimmune hemolytic anemia (Evans syndrome) and/or autoimmune neutropenia, is frequent in patients with CVID, and is not prevented by i.v.Ig substitutive therapy. Since AITP frequently precedes the diagnosis of CVID, testing for immunoglobulin levels should be performed in every patient diagnosed with AITP. Steroids and splenectomy seem to have the same efficacy as in idiopathic AITP, but the increased risk of severe infections must be taken into consideration.

Adolescent↗

PubMed2003

Does Helicobater pylori initiate or perpetuate immune thrombocytopenic purpura?

To determine the prevalence of Helicobacter pylori (H pylori) infection in North American patients with immune thrombocytopenic purpura (ITP) and the effect of H pylori eradication on the platelet count, a prospective study was performed. Seventy-four patients aged 10 years and older (mean age of 41 years) with chronic ITP and a platelet count below 60 x 10(9)/L were enrolled. H pylori infection was found in 22% of patients by means of a breath test and could not be predicted by gastrointestinal symptoms. H pylori-positive patients (52.5 years of age) were older than H pylori-negative patients (38.5 years of age; P =.0035). Fifteen of the 16 H pylori-positive patients were treated and the bacteria was eradicated in 14 (93%). After 3 months, a significant response (platelet count > 50 x 10(9)/L and doubling the initial count) was observed in only one patient. After a median follow-up of 11.5 months, none of the 14 patients had responded. Ten H pylori-negative patients treated with the same regimen also did not increase their platelet counts. In conclusion, unlike several previous reports, this study does not implicate H pylori in the pathogenesis of ITP since the prevalence of H pylori infection was low and eradication of H pylori did not positively influence the course of the ITP.

Adult↗

PubMed2003

Role of the Fcgamma receptor IIA polymorphism in the antiphospholipid syndrome: an international meta-analysis.

OBJECTIVE: To assess the impact of the FcgammaRIIA-R/H131 polymorphism on the risk for antiphospholipid syndrome (APS), both primary and secondary to systemic lupus erythematosus (SLE). METHODS: This international meta-analysis combined data from 9 research teams. FcgammaRIIA-R/H131 genotypes were determined in 481 APS cases (206 with primary APS), 1,420 SLE controls, and 1,655 disease-free controls. Data were combined using fixed-effects and random-effects models. RESULTS: Compared with disease-free controls, the RR genotype was enriched in the entire group of APS cases (odds ratio [OR] 1.65, 95% confidence interval [95% CI] 1.28-2.14); this was driven mostly by patients with secondary APS (OR 1.95, 95% CI 1.45-2.63). The excess of RR homozygotes but not heterozygotes among APS patients suggested a recessive mode of inheritance, rather than the additive model seen for SLE susceptibility, where RR conferred greatest risk, and RH intermediate risk, for SLE. This probably reflected the additional influence of another opposing genetic effect of HH homozygosity on APS predisposition (OR 0.72 for RH versus HH, 95% CI 0.55-0.96). Among SLE patients, those with APS were more frequently HH homozygotes than heterozygotes (OR 0.56 for RH versus HH, 95% CI 0.39-0.81). HH homozygosity also tended to predominate in primary APS compared with secondary APS (OR 0.50 for RR versus HH, 95% CI 0.25-0.99 by fixed-effects model). There was no significant between-study heterogeneity for any of these effects. CONCLUSION: The FcgammaRIIA-R/H131 polymorphism is an important determinant of predisposition to APS, with different influences on SLE and APS susceptibility per se.

Antigens, CD↗

PubMed2003

Intravenous anti-D as a treatment for immune thrombocytopenic purpura (ITP) during pregnancy.

This pilot study assessed the safety and efficacy of intravenous anti-D in eight Rh(D)-positive women with immune thrombocytopenic purpura (ITP) during the second and third trimesters of pregnancy. The median pretreatment platelet count was 28 x 109/l. The patients received one to seven anti-D infusions at a mean dose of 62.7 micro g/kg, and the response rate to anti-D was 75%. A haemoglobin decrease of > 2.0 g/dl occurred only once. Fetal hydrops was not identified by ultrasonography. The direct antiglobulin test was positive in three out of seven Rh+ newborns, none of whom was anaemic or jaundiced. Anti-D is effective and appears to be safe for both mother and fetus.

Adult↗

PubMed2003

Fulminant hepatitis after infliximab in a patient with hepatitis B virus treated for an adult onset still's disease.

Infliximab, a chimeric anti-tumor necrosis factor-alpha monoclonal antibody, has been demonstrated to be efficient and safe in patients with active rheumatoid arthritis and in the management of severe bouts of Crohn's disease. However, the safety of infliximab has not been evaluated in patients infected with hepatitis B virus. We report the case of a 28-year-old woman, with a positive hepatitis B virus surface antigen, who developed fulminant hepatitis 2 weeks after receiving a second infliximab infusion for a refractory adult onset Still's disease.

Adult↗

PubMed2002

Autoimmune thrombocytopenic Purpura and Helicobacter pylori infection.

BACKGROUND: The mechanisms triggering the production of platelet autoantibodies in autoimmune thrombocytopenic purpura (AITP) are poorly understood. Recently, marked improvements in platelet counts have been reported in patients with AITP and concurrent Helicobacter pylori infection after eradication of H pylori by a standard antibiotic regimen. We looked for an association between H pylori infection and AITP in adults. METHODS: Fifty-one adults of white French origin, negative for human immunodeficiency virus (mean +/- SD age, 40 +/- 19.8 years), with AITP and a platelet count of less than 50 x 10(3)/microL at onset were included. Thirty-five consecutive nonthrombocytopenic patients (mean +/- SD age, 43 +/- 22 years) of the same origin and with unknown H pylori status served as control subjects. Antibodies against H pylori were detected by means of an agglutination method in both patients and control subjects. Sex ratio, mean age, hemorrhagic manifestations, response to corticosteroid therapy, and final outcome were compared in H pylori-negative and H pylori-positive patients with AITP. To test for a possible molecular mimicry mechanism, we also used an immunoblot assay to look for specific H pylori antibodies in platelet eluates from 3 H pylori-positive patients with AITP. RESULTS: Seroprevalence of H pylori in patients with AITP (15 [29%]) was not significatively different from that in control subjects (10 [29%]). The H pylori-positive and H pylori-negative patients with AITP did not differ in main characteristics at AITP onset, response rate to corticosteroids, and final outcome. None of the 3 patients investigated had H pylori antibodies in platelet eluates. CONCLUSION: Although the role of H pylori in a subgroup of patients with AITP cannot be excluded, we found no evidence of an association between H pylori infection and AITP.

Adult↗

PubMed2002

Platelet autoantibodies and lupus-associated thrombocytopenia.

To characterize the antigenic targets of anti-platelet antibodies (APA) found in systemic lupus erythematosus (SLE)-associated thrombocytopenia, 48 patients with immune thrombocytopenia and SLE were compared with 20 patients with SLE who had never been thrombocytopenic. Both cases and controls were tested for circulating APA by an indirect platelet suspension immunofluorescence assay (PSIIFT) and by indirect monoclonal antibody specific immobilization of platelet antigens (MAIPA). A direct platelet suspension immunofluorescence assay (PSIFT) was also used for antibodies bound to platelets in vivo in thrombocytopenic patients; 13 of them with high titres of platelets-bound APA were investigated by direct and indirect MAIPA and platelet eluate analysis. Circulating APA were detected by PSIIFT in 88% of cases and 55% of controls (P = 0.0066) and platelet-bound antibodies were detected by PSIFT in 90% of cases. Indirect MAIPA detected specific APA (mainly directed against GpIIbIIIa) in 36% of cases and only 5% of the controls (P = 0.0076). Nine out of the 13 fully investigated thrombocytopenic patients (69%) had a positive direct MAIPA and/or APA detected in platelet eluates. In conclusion, the production of specific anti-platelet autoantibodies, mainly directed against GpIIb/IIIa, and their binding to platelet membrane plays an important role in the pathogenesis of SLE-associated thrombocytopenia.

Adult↗