Actin cytoskeleton control of the comings and goings of T lymphocytes.

T lymphocytes are key players of adaptive immune responses. Upon recognition of specific peptides presented by human leukocyte antigen (HLA) molecules on antigen presenting cells (APC), these cells execute subset-related functions such as killing, help and regulation. The ontogeny, the activation and the effector functions of T lymphocytes are all steps of T-lymphocyte life cycle that rely on high motility properties. These cells travel through the organism in a succession of steps, including entry into tissues, interstitial migration, APC scanning, synapse formation and tissue exit. Such ability is possible because of a plastic motility behavior, which is highly controlled in time and space. The molecular basis for the adaptable motility behavior of T lymphocytes is only starting to be unraveled. The scope of this review is to discuss recent data pointing to the key role of regulators of actin cytoskeleton remodeling in tuning distinct aspects of T-lymphocyte motility during their entry, residency and exit from tissues.

Bayesian phylogeographic inferences reveal contrasting colonization dynamics among European groundwater isopods.

The potentially important role of northern microrefugia during postglacial dispersal is challenging the view of southern Europe as a refuge and source area of European biota. In groundwaters, large geographic ranges of presumably good dispersers are increasingly suspected to consist of assemblages of cryptic species with narrow ranges. Moreover, a large species range, even when confirmed by molecular evidence, tells us little about the spatiotemporal dynamics of dispersal. Here, we used phylogenetic inferences, species delineation methods and Bayesian phylogeographic diffusion models to test for the likelihood of postglacial colonization from distant refugia among five morphospecies of Proasellus (Isopoda, Asellidae). All morphospecies except one were monophyletic, but they comprised a total of 15-17 cryptic species. Three cryptic species retained ranges that spanned a distance >650 km, similar to that of the nominal morphospecies. Bayesian diffusion models based on mitochondrial markers revealed considerable spatiotemporal heterogeneity in dispersal rates, suggesting that short-time dispersal windows were instrumental in shaping species ranges. Only one species was found to experience a recent, presumably postglacial, range expansion. The Jura and Alpine foothills probably played a major role in maintaining diversity within Proasellus in northern regions by acting both as diversification hotspots and Pleistocene refugia. Gaining insight into the spatiotemporal heterogeneity of dispersal rates revealed contrasting colonization dynamics among species that were not consistent with a global postglacial colonization of Europe from distant refugia.

Long-term safety and efficacy of lentiviral hematopoietic stem/progenitor cell gene therapy for Wiskott-Aldrich syndrome.

Patients with Wiskott-Aldrich syndrome (WAS) lacking a human leukocyte antigen-matched donor may benefit from gene therapy through the provision of gene-corrected, autologous hematopoietic stem/progenitor cells. Here, we present comprehensive, long-term follow-up results (median follow-up, 7.6 years) (phase I/II trial no. NCT02333760 ) for eight patients with WAS having undergone phase I/II lentiviral vector-based gene therapy trials (nos. NCT01347346 and NCT01347242 ), with a focus on thrombocytopenia and autoimmunity. Primary outcomes of the long-term study were to establish clinical and biological safety, efficacy and tolerability by evaluating the incidence and type of serious adverse events and clinical status and biological parameters including lentiviral genomic integration sites in different cell subpopulations from 3 years to 15 years after gene therapy. Secondary outcomes included monitoring the need for additional treatment and T cell repertoire diversity. An interim analysis shows that the study meets the primary outcome criteria tested given that the gene-corrected cells engrafted stably, and no serious treatment-associated adverse events occurred. Overall, severe infections and eczema resolved. Autoimmune disorders and bleeding episodes were significantly less frequent, despite only partial correction of the platelet compartment. The results suggest that lentiviral gene therapy provides sustained clinical benefits for patients with WAS.

Multi-color magnetic nanoparticle imaging using magnetorelaxometry.

Magnetorelaxometry (MRX) is a well-known measurement technique which allows the retrieval of magnetic nanoparticle (MNP) characteristics such as size distribution and clustering behavior. This technique also enables the non-invasive reconstruction of the spatial MNP distribution by solving an inverse problem, referred to as MRX imaging. Although MRX allows the imaging of a broad range of MNP types, little research has been done on imaging different MNP types simultaneously. Biomedical applications can benefit significantly from a measurement technique that allows the separation of the resulting measurement signal into its components originating from different MNP types. In this paper, we present a theoretical procedure and experimental validation to show the feasibility of MRX imaging in reconstructing multiple MNP types simultaneously. Because each particle type has its own characteristic MRX signal, it is possible to take this a priori information into account while solving the inverse problem. This way each particle type's signal can be separated and its spatial distribution reconstructed. By assigning a unique color code and intensity to each particle type's signal, an image can be obtained in which each spatial distribution is depicted in the resulting color and with the intensity measuring the amount of particles of that type, hence the name multi-color MNP imaging. The theoretical procedure is validated by reconstructing six phantoms, with different spatial arrangements of multiple MNP types, using MRX imaging. It is observed that MRX imaging easily allows up to four particle types to be separated simultaneously, meaning their quantitative spatial distributions can be obtained.

How to include the variability of TMS responses in simulations: a speech mapping case study.

When delivered over a specific cortical site, TMS can temporarily disrupt the ongoing process in that area. This allows mapping of speech-related areas for preoperative evaluation purposes. We numerically explore the observed variability of TMS responses during a speech mapping experiment performed with a neuronavigation system. We selected four cases with very small perturbations in coil position and orientation. In one case (E) a naming error occurred, while in the other cases (NEA, B, C) the subject appointed the images as smoothly as without TMS. A realistic anisotropic head model was constructed of the subject from T1-weighted and diffusion-weighted MRI. The induced electric field distributions were computed, associated to the coil parameters retrieved from the neuronavigation system. Finally, the membrane potentials along relevant white matter fibre tracts, extracted from DTI-based tractography, were computed using a compartmental cable equation. While only minor differences could be noticed between the induced electric field distributions of the four cases, computing the corresponding membrane potentials revealed different subsets of tracts were activated. A single tract was activated for all coil positions. Another tract was only triggered for case E. NEA induced action potentials in 13 tracts, while NEB stimulated 11 tracts and NEC one. The calculated results are certainly sensitive to the coil specifications, demonstrating the observed variability in this study. However, even though a tract connecting Broca's with Wernicke's area is only triggered for the error case, further research is needed on other study cases and on refining the neural model with synapses and network connections. Case- and subject-specific modelling that includes both electromagnetic fields and neuronal activity enables demonstration of the variability in TMS experiments and can capture the interaction with complex neural networks.

Toward 2D and 3D imaging of magnetic nanoparticles using EPR measurements.

PURPOSE: Magnetic nanoparticles (MNPs) are an important asset in many biomedical applications. An effective working of these applications requires an accurate knowledge of the spatial MNP distribution. A promising, noninvasive, and sensitive technique to visualize MNP distributions in vivo is electron paramagnetic resonance (EPR). Currently only 1D MNP distributions can be reconstructed. In this paper, the authors propose extending 1D EPR toward 2D and 3D using computer simulations to allow accurate imaging of MNP distributions. METHODS: To find the MNP distribution belonging to EPR measurements, an inverse problem needs to be solved. The solution of this inverse problem highly depends on the stability of the inverse problem. The authors adapt 1D EPR imaging to realize the imaging of multidimensional MNP distributions. Furthermore, the authors introduce partial volume excitation in which only parts of the volume are imaged to increase stability of the inverse solution and to speed up the measurements. The authors simulate EPR measurements of different 2D and 3D MNP distributions and solve the inverse problem. The stability is evaluated by calculating the condition measure and by comparing the actual MNP distribution to the reconstructed MNP distribution. Based on these simulations, the authors define requirements for the EPR system to cope with the added dimensions. Moreover, the authors investigate how EPR measurements should be conducted to improve the stability of the associated inverse problem and to increase reconstruction quality. RESULTS: The approach used in 1D EPR can only be employed for the reconstruction of small volumes in 2D and 3D EPRs due to numerical instability of the inverse solution. The authors performed EPR measurements of increasing cylindrical volumes and evaluated the condition measure. This showed that a reduction of the inherent symmetry in the EPR methodology is necessary. By reducing the symmetry of the EPR setup, quantitative images of larger volumes can be obtained. The authors found that, by selectively exciting parts of the volume, the authors could increase the reconstruction quality even further while reducing the amount of measurements. Additionally, the inverse solution of this activation method degrades slower for increasing volumes. Finally, the methodology was applied to noisy EPR measurements: using the reduced EPR setup's symmetry and the partial activation method, an increase in reconstruction quality of ≈ 80% can be seen with a speedup of the measurements with 10%. CONCLUSIONS: Applying the aforementioned requirements to the EPR setup and stabilizing the EPR measurements showed a tremendous increase in noise robustness, thereby making EPR a valuable method for quantitative imaging of multidimensional MNP distributions.

Effective electric fields along realistic DTI-based neural trajectories for modelling the stimulation mechanisms of TMS.

In transcranial magnetic stimulation (TMS), an applied alternating magnetic field induces an electric field in the brain that can interact with the neural system. It is generally assumed that this induced electric field is the crucial effect exciting a certain region of the brain. More specifically, it is the component of this field parallel to the neuron's local orientation, the so-called effective electric field, that can initiate neuronal stimulation. Deeper insights on the stimulation mechanisms can be acquired through extensive TMS modelling. Most models study simple representations of neurons with assumed geometries, whereas we embed realistic neural trajectories computed using tractography based on diffusion tensor images. This way of modelling ensures a more accurate spatial distribution of the effective electric field that is in addition patient and case specific. The case study of this paper focuses on the single pulse stimulation of the left primary motor cortex with a standard figure-of-eight coil. Including realistic neural geometry in the model demonstrates the strong and localized variations of the effective electric field between the tracts themselves and along them due to the interplay of factors such as the tract's position and orientation in relation to the TMS coil, the neural trajectory and its course along the white and grey matter interface. Furthermore, the influence of changes in the coil orientation is studied. Investigating the impact of tissue anisotropy confirms that its contribution is not negligible. Moreover, assuming isotropic tissues lead to errors of the same size as rotating or tilting the coil with 10 degrees. In contrast, the model proves to be less sensitive towards the not well-known tissue conductivity values.

[Three-in-one block or femoral nerve block. What should be done and how?]. / Bloc "3 en 1" ou bloc fémoral. Que faut-il faire et comment le faire?

The "3 in 1" block and the femoral nerve block are widely used for lower limb surgery and postoperative analgesia. Whether these blocks are in fact a same regional block with two different names or represent definitively two different blocks remains controversial. A large number of anatomical as well as functional variations of the lumbar plexus have been described and complicate a rational analysis of the spread of local anaesthetics following these blocks. Anatomical, radiological and especially clinical data seem to confirm that these blocks are to be distinguished from one another. Femoral nerve block requires the use of a nerve stimulator and has a high success rate in the territory of the femoral nerve; a spread towards other lumbar nerves, especially the lateral femoral cutaneous nerve, is sometimes observed. The "3 in 1" block is supported by the idea of diffusion within a space that is located after going through two fascial layers. Even in experienced hands, the success predictive value is not high. However, once the "3 in 1" block is well performed, a complete anaesthesia covering the territories of the femoral nerve, the lateral femoral cutaneous nerve, and the obturator nerve occurs. Specific indications of each technique are different: major knee surgery and postoperative analgesia for the "3-in-1" block and leg surgery for femoral nerve block. The best approach for knee arthroscopy remains open for discussion.

[What do French anesthesiologists choose when they are patients themselves?]. / Que choisit l'anesthésiste français quand il est lui-même patient?

To determine whether, as patients, French anaesthesiologists prefer regional anaesthesia, like their North American colleagues, they were all mailed a questionnaire which submitted 2 different scenarios. Scenario A concerned emergency surgery for an open fracture to the right tibia, the patient-cum-anaesthetist having a full stomach. Scenario B was the elective removal of the plate a year later. Response rate was 15% (1,187 answers). For scenario A 89% of physicians preferred regional anaesthesia, while 57% preferred regional anaesthesia for scenario B. Epidural anaesthesia was twice as popular as spinal anaesthesia. Lower limb blocks were only chosen by a minority (A:5%; B:6%). Statistically significant differences were found between selected techniques, according to respondent's age, sex, medical school and type of practice, especially for scenario B. The fear of complications like regurgitation, allergic reaction, or postdural puncture headache seemed to be of less influence in the choice than the experience of the anaesthetist to carry out the anaesthetic in each scenario. It can therefore be concluded that French anaesthesiologists prefer regional anaesthesia for lower limb surgery required for themselves. However, experience of the "operator" with the technique seems to be as important as the technique itself.

[Why choose loco-regional anesthesia for knee surgery?]. / Pourquoi choisir l'anesthésie loco-régionale pour la chirurgie du genou?

The advantages and disadvantages of both general and local or regional anaesthesia for knee surgery are presented and the patient characteristics enumerated. Regional anaesthesia reduces the frequency of postoperative thrombo-embolic accidents, diminishes blood-loss and permits good postoperative analgesia. Thus it seems to achieve better results in respect to morbidity and mortality. It requires the patient's consent and acceptance by the surgeons as well as appropriate operating theater management.

[Blocking of the brachial plexus: which technique(s) should be chosen?]. / Bloc du plexus brachial: quelle(s) technique(s) choisir?

Brachial plexus blocks for upper extremity surgery: what are the preferred techniques? Brachial plexus anaesthesia for all types of upper extremity surgical procedures cannot be adequately achieved with a single technique. At least, two approaches are required: above the clavicle, Winnie's interscalene brachial plexus block, using a neurostimulator, has become the standard technique for shoulder surgery. Below the clavicle, midhumerus approach is the most successful approach for elbow, fore arm and hand surgery, especially for outpatient surgery. The best approach for catheter insertion along brachial plexus nerves/trunks remain controversial. The supraclavicular approach using surface landmarks might be the best approach due to its efficacy in achieving complete anaesthesia of the upper extremity and the rarity of secondary displacement of the catheter. Whatever the selected approach(es) to brachial plexus nerves, nerve location it best achieved by neurostimulation and often multiple neurostimulation. Insulated needles are being increasingly used due to accuracy but, currently, there is no general agreement concerning the type of needle bevel to be preferred in regard to both safety and accuracy.

[The neurostimulator in loco-regional anesthesia]. / Neurostimulateur en anesthésie loco-régionale.

The physiological basis of neurostimulation is recalled and its use for the placement of needles for neural blockade described. After an account of available equipment, the author gives his reasons for preferring some of it. Based on experience gained with more than ten thousand cases, a protocol for using neurostimulation to insure close placement of needles to the nerves to be blocked. The advantages and disadvantages of available needles are stated. The indication for the use of neurostimulation in the practice of infiltration anaesthesia are enumerated and its advantages stressed. Finally its limitations and complications are presented.

Reduction of the impact of multiple uncertain conductivity values on EEG dipole source analysis.

It is well known that the uncertain knowledge of the conductivity values of the head tissues has an important impact upon the accuracy of the electroencephalogram source reconstruction. Assuming a certain value of the conductivity often leads to high reconstruction error values when solving the inverse problem. It is possible to quantify the impact of multiple uncertain conductivity values on the localization accuracy. We propose an approach that reduces the impact of these multiple uncertainties on the reconstruction accuracy of the dipole parameters. This paper elaborates the numerical method and shows results of localization accuracy in a five-shell spherical head model. Sensitivity analysis, when considering multiple layers in the head model, shows the different scales of the influence of the various uncertain conductivity values on the potential values. We propose a cost function that reduces the impact of multiple uncertainties of the conductivity value on the electroencephalogram dipole reconstruction and two strategies for selecting potential values on the basis of the sensitivity analysis. Numerical simulations, when considering multiple uncertainties in the model, provide results with higher reconstruction accuracy compared with the case where only a single uncertainty is taken into account.

A DTI-based model for TMS using the independent impedance method with frequency-dependent tissue parameters.

Accurate simulations on detailed realistic head models are necessary to gain a better understanding of the response to transcranial magnetic stimulation (TMS). Hitherto, head models with simplified geometries and constant isotropic material properties are often used, whereas some biological tissues have anisotropic characteristics which vary naturally with frequency. Moreover, most computational methods do not take the tissue permittivity into account. Therefore, we calculate the electromagnetic behaviour due to TMS in a head model with realistic geometry and where realistic dispersive anisotropic tissue properties are incorporated, based on T1-weighted and diffusion-weighted magnetic resonance images. This paper studies the impact of tissue anisotropy, permittivity and frequency dependence, using the anisotropic independent impedance method. The results show that anisotropy yields differences up to 32% and 19% of the maximum induced currents and electric field, respectively. Neglecting the permittivity values leads to a decrease of about 72% and 24% of the maximum currents and field, respectively. Implementing the dispersive effects of biological tissues results in a difference of 6% of the maximum currents. The cerebral voxels show limited sensitivity of the induced electric field to changes in conductivity and permittivity, whereas the field varies approximately linearly with frequency. These findings illustrate the importance of including each of the above parameters in the model and confirm the need for accuracy in the applied patient-specific method, which can be used in computer-assisted TMS.