Trace de cycles d'hystérèse par mesure d'intensité aux rayons X dans le ferroélectrique Mn TO3, (T = Y, Ho, Er, Tm, Yb, Lu). Observation directe des domaines ferroélectriques

If, in the calculation of the diffracted intensities, we write the form factors as f = f₀ + Δf' + iΔf" , we say that there is anomalous scattering. In this case if an X-ray beam falls on a non-centrosymmetric crystal, reflections of the scattering vector H and those of the scattering vector —H can present some important intensity differences. We have applied this principle to the ferroelectric MnTO₃ where T = Y, Ho, Er, Tm, Yb, Lu. Between 0010 and 00[-1][-0] reflections obtained with CuKα radiation, we observe some large intensity difference in the magnitude of 70/100. We use this effect to draw hysteresis loops and plots of « first polarization » in the MnYO₃ crystal. We propose a topographical experiment in order to make a photograph of the ferroelectrics domains in MnYO₃. Finally, we show the necessity of refining the MnTO₃ structure using a crystal composed of a single domain.Si dans le calcul des intensités diffractées par un monocristal on écrit les facteurs de forme f = f₀ + Δf' + iΔf" , on dit qu'il y a dispersion anomale. Dans ce cas si un rayonnement X est envoyé sur un monocristal non centrosymétrique, les réflexions de vecteur de diffusion + H et celles de vecteur de diffusion — H peuvent présenter des différences d'intensités importantes. On applique ceci au ferroélectrique MnTO₃ où T est soit l'yttrium, soit une terre rare appartenant au groupe Ho, Er, Tm, Yb, Lu. Entre les raies 0010 et 00[-1][-0] obtenues avec la radiation CuKα, on met en évidence des différences d'intensité de l'ordre de 70/100. Nous utilisons cet effet pour tracer le cycle d'hystérèse et la courbe de « première polarisation » d'un cristal de MnYO₃. Nous proposons une expérience de topographie pour obtenir une photographie des domaines ferroélectriques sur MnYO₃. Nous montrons enfin le besoin de préciser la structure de MnTO₃ sur un cristal mono-domaine.Lissalde F., Lewy-Bertaut Erwin Félix. Trace de cycles d'hystérèse par mesure d'intensité aux rayons X dans le ferroélectrique Mn TO3, (T = Y, Ho, Er, Tm, Yb, Lu). Observation directe des domaines ferroélectriques. In: Bulletin de la Société française de Minéralogie et de Cristallographie, volume 91, 6, 1968. Réunion annuelle de l'Association Française de Cristallographie, Toulouse, 18-20 mars 1968

ETUDE DES CORRELATIONS DANS LES FERROFLUIDES PAR DIFFUSION CENTRALE ALTERNEE DES RAYONS X SUR LE FAISCEAU SYNCHROTRON

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Are low-density lipoprotein receptor-related protein 1 or non-neutralizing antibodies predictors of FVIII in vivo recovery in haemophilia A patients?

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Circulating FVIII-specific IgG, IgA and IgM memory B cells from haemophilia A patients

International audienceINTRODUCTION:Approximately, 25% of haemophilia A (HA) patients treated by factor VIII (FVIII), develop antibodies, known as inhibitors, neutralizing the activity of infused FVIII. This immune response involves B cells (BC), including FVIII-specific memory B cells (MBC). Production of anti-FVIII antibodies after stimulation of FVIII-specific MBC suggests a role of these cells in the immune response to FVIII. Animal models allowed the study of circulating FVIII-specific cells, however few data are available on HA patients.AIM AND METHODS:In the present study, we simultaneously detected, via ELISpot assay, different isotypes of MBC in the blood of HA patients, after polyclonal activation. Patients included: three with active inhibitors; three with a history of inhibitors; six without any past or active inhibitor.RESULTS:FVIII-specific MBC were detected in peripheral blood of HA patients: (i) patients with active inhibitors (IgG: 4-5.2/10(6) BC; IgA: 2.9-4/10(6) BC) (ii) patients with a past of inhibitors (no IgG BC; IgA: 5-7.5/10(6) BC) (iii) patients without inhibitors (no IgG BC or IgA BC except one patient had two FVIII-specific IgA BC/10(6) BC).CONCLUSION:FVIII-specific IgA MBC were detected in HA patients with past and current immune responses against FVIII and FVIII-specific IgG MBC were found only in those with positive inhibitors. This study shows the possibility to detect and characterize easily and simultaneously the MBC from patient blood and that MBC seem different according to anti-FVIII immune history. It could be a useful tool to study anti-FVIII response and Immune Tolerance Induction cellular mechanisms

Computer-predicted peptides that mimic discontinuous epitopes on the A2 domain of factor VIII

International audienceDevelopment of antibodies (Abs) against factor VIII (FVIII) is a severe complication of haemophilia A treatment. Recent publications suggest that domain specificity of anti-FVIII antibodies, particularly during immune tolerance induction (ITI), might be related to the outcome of the treatment. Obtaining suitable tools for a fine mapping of discontinuous epitopes could thus be helpful. The aim of this study was to map discontinuous epitopes on FVIII A2 domain using a new epitope prediction functionality of the PEPOP bioinformatics tool and a peptide inhibition assay based on the Luminex technology. We predicted, selected and synthesized 40 peptides mimicking discontinuous epitopes on the A2 domain of FVIII. A new inhibition assays using Luminex technology was performed to identify peptides able to inhibit the binding of anti-A2 Abs to A2 domain. We identified two peptides (IFKKLYHVWTKEVG and LYSRRLPKGVKHFD) able to block the binding of anti-A2 allo-antibodies to this domain. The three-dimensional representation of these two peptides on the A2 domain revealed that they are localized on a limited region of A2. We also confirmed that residues 484-508 of the A2 domain define an antigenic site. We suggest that dissection of the antibody response during ITI using synthetic peptide epitopes could provide important information for the management of patients with inhibitors