Brian E. Anderson

Crystal Structure of Vδ1 T Cell Receptor in Complex with CD1d-Sulfatide Shows MHC-like Recognition of a Self-Lipid by Human γδ T Cells

The nature of the antigens recognized by γδ T cells and their potential recognition of major histocompatibility complex (MHC)-like molecules has remained unclear. Members of the CD1 family of lipid-presenting molecules are suggested ligands for Vδ1 TCR-expressing γδ T cells, the major γδ lymphocyte population in epithelial tissues. We crystallized a Vδ1 TCR in complex with CD1d and the self-lipid sulfatide, revealing the unusual recognition of CD1d by germline Vδ1 residues spanning all complementarity-determining region (CDR) loops, as well as sulfatide recognition separately encoded by nongermline CDR3δ residues. Binding and functional analysis showed that CD1d presenting self-lipids, including sulfatide, was widely recognized by gut Vδ1+ γδ T cells. These findings provide structural demonstration of MHC-like recognition of a self-lipid by γδ T cells and reveal the prevalence of lipid recognition by innate-like T cell populations.

The majority of CD1d-sulfatide-specific T cells in human blood use a semiinvariant Vδ1 TCR

αβ T‐cell lines specific for sulfatide, an abundant myelin glycosphingolipid presented by various CD1 molecules, have been previously derived from PBMCs of patients with demyelinating diseases such as multiple sclerosis (MS) but also from healthy subjects. Using an unbiased tetramer‐based MACS enrichment method to enrich for rare antigen‐specific cells, we confirmed the presence of CD1d‐sulfatide‐specific T cells in all healthy individuals examined. Surprisingly, the great majority of fresh sulfatide‐specific T cells belonged to the γδ lineage. Furthermore, these cells used the Vδ1 TCR variable segment, which is uncommon in the blood but predominates in tissues such as the gut and specifically accumulates in MS lesions. Recombinant Vδ1 TCRs from different individuals were shown to bind recombinant CD1d‐sulfatide complexes in a sulfatide‐specific manner. These results provide the first direct demonstration of MHC‐like‐restricted, antigen‐specific recognition by γδ TCRs. Together with previous reports, they support the notion that human Vδ1 T cells are enriched in CD1‐specific T cells and suggest that the Vδ1 T‐cell population that accumulates in MS lesions might be enriched in CD1‐sulfatide‐specific cells.

Three component time reversal: Focusing vector components using a scalar source

In acoustics, it is known that, for a given response signal at an arbitrary location, reciprocity and time reversal (TR) can be used to focus high levels of acoustic energy at that position. In solid media, elastic waves generally induce different disturbances in three directions. In this paper, both experimental and numerical wave propagation results for solid materials demonstrate the ability to use a scalar source, a three component detector and the reciprocal TR process to selectively focus each of the different vector components, either individually or collectively. The principle is explained from an analytical point of view. The numerical and experimental study demonstrates excellent temporal and spatial focalization. Applications of the selective vector component focusing can be found in damage imaging techniques using both linear or nonlinear ultrasonic waves.

Time Reversal of Continuous-Wave, Steady-State Signals in Elastic Media

Experimental observations of spatial focusing of continuous-wave, steady-state elastic waves in a reverberant elastic cavity using time reversal are reported here. Spatially localized focusing is achieved when multiple channels are employed, while a single channel does not yield such focusing. The amplitude of the energy at the focal location increases as the square of the number of channels used, while the amplitude elsewhere in the medium increases proportionally with the number of channels used. The observation is important in the context of imaging in solid laboratory samples as well as problems involving continuous-wave signals in Earth.

Investigation of the robustness of time reversal acoustics in solid media through the reconstruction of temporally symmetric sources

We investigate some of the limitations of time reversal acoustics (TRA) in solid media with transducers attached to the surface. In particular, we consider the limitations due to the finite size of the transducers and elastic wave propagation. Using a theoretical approach, numerical simulations and validation from laboratory ultrasound experiments, we find that finite size transducers and the existence of longitudinal and shear waves play significant roles in perturbing the time reversal process. Despite these limitations, we show that TRA in solids is very robust, providing the means to reconstruct the main features of the source signal. The analysis of TRA retro-focusing properties in solid specimens is of foremost importance for the development of new non-destructive evaluation techniques.

Energy current imaging method for time reversal in elastic media

An energy current imaging method is presented for use in locating sources of wave energy during the back propagation stage of the time reversal process. During the back propagation phase of an ideal time reversal experiment, wave energy coalesces from all angles of incidence to recreate the source event; after the recreation, wave energy diverges in every direction. An energy current imaging method based on this convergence/divergence behavior has been developed. The energy current imaging method yields a smaller spatial distribution for source reconstruction than is possible with traditional energy imaging methods.

Symmetry-based imaging condition in time reversed acoustics

Introduced in this paper is a new method of determining and investigating focal positions of time reversed elastic wave fields. This method exploits the temporally symmetric nature of time reversed acoustics focused signals as they are akin to the autocorrelation function of the forward propagation received signals. Contrasting this symmetry with the degree of asymmetry at regions away from the focal location provides details about the original source that cannot be retrieved when using other standard imaging conditions.

Experimental implementation of reverse time migration for nondestructive evaluation applications

Reverse time migration (RTM) is a commonly employed imaging technique in seismic applications (e.g., to image reservoirs of oil). Its standard implementation cannot account for multiple scattering/reverberation. For this reason it has not yet found application in nondestructive evaluation (NDE). This paper applies RTM imaging to NDE applications in bounded samples, where reverberation is always present. This paper presents a fully experimental implementation of RTM, whereas in seismic applications, only part of the procedure is done experimentally. A modified RTM imaging condition is able to localize scatterers and locations of disbonding. Experiments are conducted on aluminum samples with controlled scatterers.

Experimentally identifying masked sources applying time reversal with the selective source reduction method

This paper describes a time reversal (TR) method of spatially illuminating a source signal which has been masked by another source signal. This masking occurs as a result of inherent limitations in the traditional TR process. The selective source reduction (SSR) method employs a subtraction technique where one TR focus is selectively reduced to illuminate the masked focus. Experimental results and considerations are presented to demonstrate the SSR method for two elastic wave pulses emitted simultaneously from two spatially separated surficial sources and to examine the limitations of the method. A blind test was conducted to demonstrate that no a priori information about the source(s) is required. Spatial and/or temporal characteristics of multiple close-proximity sources can be resolved with the use of the illumination method. The measurements show that the SSR method’s limitations are chiefly due to imperfect temporal reconstruction of the source function in the time reversed focal signal, which conseq...

Damage imaging in a laminated composite plate using an air-coupled time reversal mirror

We demonstrate the possibility of selectively imaging the features of a barely visible impact damage in a laminated composite plate by using an air-coupled time reversal mirror. The mirror consists of a number of piezoelectric transducers affixed to wedges of power law profiles, which act as unconventional matching layers. The transducers are enclosed in a hollow reverberant cavity with an opening to allow progressive emission of the ultrasonic wave field towards the composite plate. The principle of time reversal is used to focus elastic waves at each point of a scanning grid spanning the surface of the plate, thus allowing localized inspection at each of these points. The proposed device and signal processing removes the need to be in direct contact with the plate and reveals the same features as vibrothermography and more features than a C-scan. More importantly, this device can decouple the features of the defect according to their orientation, by selectively focusing vector components of motion into the object, through air. For instance, a delamination can be imaged in one experiment using out-of-plane focusing, whereas a crack can be imaged in a separate experiment using in-plane focusing. This capability, inherited from the principle of time reversal, cannot be found in conventional air-coupled transducers.