Optical precursors in transparent media

We theoretically study the linear propagation of a stepwise pulse through a dilute dispersive medium when the frequency of the optical carrier coincides with the center of a natural or electromagnetically induced transparency window of the medium (slow-light systems). We obtain fully analytical expressions of the entirety of the step response and show that, for parameters representative of real experiments, Sommerfeld-Brillouin precursors, main field and second precursors "postcursors" can be distinctly observed, all with amplitudes comparable to that of the incident step. This behavior strongly contrasts with that of the systems generally considered up to now

Slow light in saturable absorbers

In connection with the experiments recently achieved on doped crystals, biological samples, doped optical fibers and semiconductor heterostructures, we revisit the theory of the propagation of a pulse-modulated light in a saturable absorber. Explicit analytical expressions of the transmitted pulse are obtained, enabling us to determine the parameters optimizing the time-delay of the transmitted pulse with respect to the incident pulse. We finally compare the maximum fractional delay or figure of merit so attainable to those which have been actually demonstrated in the experiments

Reconstitution of huPBL-NSG Mice with Donor-Matched Dendritic Cells Enables Antigen-Specific T-cell Activation

Humanized mouse models provide a unique opportunity to study human immune cells in vivo, but traditional models have been limited to the evaluation of non-specific T-cell interactions due to the absence of antigen-presenting cells. In this study, immunodeficient NOD/SCID/IL2r-γnull (NSG) mice were engrafted with human peripheral blood lymphocytes alone or in combination with donor-matched monocyte-derived dendritic cells (DC) to determine whether antigen-specific T-cell activation could be reconstituted. Over a period of 3 weeks, transferred peripheral blood lymphocytes reconstituted the spleen and peripheral blood of recipient mice with predominantly human CD45-positive lymphocytes. Animals exhibited a relatively normal CD4/CD8 ratio (average 1.63:1) as well as reconstitution of CD3/CD56 (averaging 17.8%) and CD20 subsets (averaging 4.0%). Animals reconstituted with donor-matched CD11c+ DC also demonstrated a CD11c+ population within their spleen, representing 0.27% to 0.43% of the recovered human cells with concurrent expression of HLA-DR, CD40, and CD86. When immunized with adenovirus, either as free replication-incompetent vector (AdV) or as vector-transduced DC (DC/AdV), there was activation and expansion of AdV-specific T-cells, an increase in Th1 cytokines in serum, and skewing of T-cells toward an effector/memory phenotype. T-cells recovered from animals challenged with AdV in vivo proliferated and secreted a Th1-profile of cytokines in response to DC/AdV challenge in vitro. Our results suggest that engrafting NSG mice with a combination of lymphocytes and donor-matched DC can reconstitute antigen responsiveness and allow the in vivo assessment of human immune response to viruses, vaccines, and other immune challenges