Low-radio-frequency eclipses of the redback pulsar J2215+5135 observed in the image plane with LOFAR.

The eclipses of certain types of binary millisecond pulsars (i.e. 'black widows' and 'redbacks') are often studied using high-time-resolution, 'beamformed' radio observations. However, they may also be detected in images generated from interferometric data. As part of a larger imaging project to characterize the variable and transient sky at radio frequencies <200 MHz, we have blindly detected the redback system PSR J2215+5135 as a variable source of interest with the Low-Frequency Array (LOFAR). Using observations with cadences of two weeks - six months, we find preliminary evidence that the eclipse duration is frequency dependent (∝ν-0.4), such that the pulsar is eclipsed for longer at lower frequencies, in broad agreement with beamformed studies of other similar sources. Furthermore, the detection of the eclipses in imaging data suggests an eclipsing medium that absorbs the pulsed emission, rather than scattering it. Our study is also a demonstration of the prospects of finding pulsars in wide-field imaging surveys with the current generation of low-frequency radio telescopes.

New methods to constrain the radio transient rate: results from a survey of four fields with LOFAR.

We report on the results of a search for radio transients between 115 and 190 MHz with the LOw-Frequency ARray (LOFAR). Four fields have been monitored with cadences between 15 min and several months. A total of 151 images were obtained, giving a total survey area of 2275 deg2. We analysed our data using standard LOFAR tools and searched for radio transients using the LOFAR Transients Pipeline. No credible radio transient candidate has been detected; however, we are able to set upper limits on the surface density of radio transient sources at low radio frequencies. We also show that low-frequency radio surveys are more sensitive to steep-spectrum coherent transient sources than GHz radio surveys. We used two new statistical methods to determine the upper limits on the transient surface density. One is free of assumptions on the flux distribution of the sources, while the other assumes a power-law distribution in flux and sets more stringent constraints on the transient surface density. Both of these methods provide better constraints than the approach used in previous works. The best value for the upper limit we can set for the transient surface density, using the method assuming a power-law flux distribution, is 1.3 × 10-3 deg-2 for transients brighter than 0.3 Jy with a time-scale of 15 min, at a frequency of 150 MHz. We also calculated for the first time upper limits for the transient surface density for transients of different time-scales. We find that the results can differ by orders of magnitude from previously reported, simplified estimates.

Evidence for bidirectional histamine transport by murine hematopoietic progenitor cells.

Murine hematopoietic progenitor cells synthesize substantial amounts of histamine in response to IL-3 or calcium ionophore. They also take up extracellular histamine by an active transport system. In the present study we demonstrate that this system mediates both influx and efflux of histamine. Indeed, MR16155 and thioperamide, the two H3 antagonists which are most effective in inhibiting histamine uptake, likewise diminish the release of preloaded histamine from bone marrow cells. These compounds also inhibit the release of histamine which has been newly synthesized by hematopoietic progenitors in response to IL-3 or calcium ionophore, as assessed by the accumulation of the mediator inside the cells in the presence of the antagonists. The potency of different histamine receptor antagonists as inhibitors of histamine release increases with their capacity to block histamine uptake.

Binding of histamine H3-receptor antagonists to hematopoietic progenitor cells. Evidence for a histamine transporter unrelated to histamine H3 receptors.

Hematopoietic progenitor cells can take up histamine or release IL-3-induced histamine through a bi-directional transport system that is blocked by H3-receptor antagonists. In the present study we demonstrate a correlation between the affinity of various H3-receptor antagonists and their potency as inhibitors of histamine uptake. All compounds that blocked histamine uptake also inhibited IL-3-induced histamine release. Yet, classical H3 receptors are not involved in this biological activity, since highly specific histamine H3-receptor agonists neither alter histamine uptake nor affect the release of endogenous histamine synthesized in response to IL-3. Furthermore, the inhibitory effect of H3-receptor antagonists on histamine uptake was not reversed by the agonists. Unlike H3-receptor antagonists, the agonists did not displace the binding of the labeled antagonist iodoproxyfan.

Detection of the characteristic pion-decay signature in supernova remnants.

Cosmic rays are particles (mostly protons) accelerated to relativistic speeds. Despite wide agreement that supernova remnants (SNRs) are the sources of galactic cosmic rays, unequivocal evidence for the acceleration of protons in these objects is still lacking. When accelerated protons encounter interstellar material, they produce neutral pions, which in turn decay into gamma rays. This offers a compelling way to detect the acceleration sites of protons. The identification of pion-decay gamma rays has been difficult because high-energy electrons also produce gamma rays via bremsstrahlung and inverse Compton scattering. We detected the characteristic pion-decay feature in the gamma-ray spectra of two SNRs, IC 443 and W44, with the Fermi Large Area Telescope. This detection provides direct evidence that cosmic-ray protons are accelerated in SNRs.

Periodic emission from the gamma-ray binary 1FGL J1018.6-5856.

Gamma-ray binaries are stellar systems containing a neutron star or black hole, with gamma-ray emission produced by an interaction between the components. These systems are rare, even though binary evolution models predict dozens in our Galaxy. A search for gamma-ray binaries with the Fermi Large Area Telescope (LAT) shows that 1FGL J1018.6-5856 exhibits intensity and spectral modulation with a 16.6-day period. We identified a variable x-ray counterpart, which shows a sharp maximum coinciding with maximum gamma-ray emission, as well as an O6V((f)) star optical counterpart and a radio counterpart that is also apparently modulated on the orbital period. 1FGL J1018.6-5856 is thus a gamma-ray binary, and its detection suggests the presence of other fainter binaries in the Galaxy.

Gamma-ray emission concurrent with the nova in the symbiotic binary V407 Cygni.

Novae are thermonuclear explosions on a white dwarf surface fueled by mass accreted from a companion star. Current physical models posit that shocked expanding gas from the nova shell can produce x-ray emission, but emission at higher energies has not been widely expected. Here, we report the Fermi Large Area Telescope detection of variable gamma-ray emission (0.1 to 10 billion electron volts) from the recently detected optical nova of the symbiotic star V407 Cygni. We propose that the material of the nova shell interacts with the dense ambient medium of the red giant primary and that particles can be accelerated effectively to produce pi(0) decay gamma-rays from proton-proton interactions. Emission involving inverse Compton scattering of the red giant radiation is also considered and is not ruled out.

Modulated high-energy gamma-ray emission from the microquasar Cygnus X-3.

Microquasars are accreting black holes or neutron stars in binary systems with associated relativistic jets. Despite their frequent outburst activity, they have never been unambiguously detected emitting high-energy gamma rays. The Fermi Large Area Telescope (LAT) has detected a variable high-energy source coinciding with the position of the x-ray binary and microquasar Cygnus X-3. Its identification with Cygnus X-3 is secured by the detection of its orbital period in gamma rays, as well as the correlation of the LAT flux with radio emission from the relativistic jets of Cygnus X-3. The gamma-ray emission probably originates from within the binary system, opening new areas in which to study the formation of relativistic jets.

Evidence for histamine uptake by murine hematopoietic progenitors.

Based on previous evidence for a role of exogenous and endogenous histamine, we have examined whether this amine can effectively interact with hematopoietic progenitors. We show that tritiated histamine is retained preferentially by bone marrow cells as compared with peritoneal, thymic or spleen cells. Cells interacting with histamine copurify with progenitors in the low density bone marrow fraction. Among this cell population, 5% are labeled as assessed by autoradiography. The characteristics of histamine retention by these cells are consistent with active uptake rather than binding to a known receptor since (a) it is almost completely abrogated at 4 degrees C, by sodium azide or chloroquine, (b) histamine is internalized, and (c) relatively high concentrations of classical receptor antagonists are required to inhibit histamine retention by bone marrow cells.

Absence of CD43 fails to alter T cell development and responsiveness.

Genetic elimination of CD43 has been associated with increased T cell adhesiveness and T cell hyperresponsiveness to mitogens and alloantigens. Therefore, we investigated whether T cell development was perturbed in CD43-deficient mice by breeding CD43(null) mice with male Ag (Hy)-specific TCR-transgenic mice. Neither positive nor negative thymic selection of male Ag-specific T cells were affected by CD43 status. Furthermore, we did not observe a substantial or consistent hyperresponsive pattern in HY-CD43(null) lymph node cells compared with littermate HY-CD43(+/-) lymph node cells upon analysis of in vitro T cell stimulation with male Ag or mitogen. These observations challenged original conclusions associating absence of CD43 with T cell hyperresponsiveness and led us to re-examine this association. Reported phenotypes of CD43(null) mice have been based on mice with a mixed 129xC57BL/6 genetic background. To exclude a possible influence of genetic background differences among individual mice we analyzed CD43(null) littermates that had been back-bred onto the C57BL/6 background for seven to eight generations. We found that CD43(+) and CD43(null) littermates with the C57BL/6 background exhibited no differences in response to mitogen or alloantigen, thereby establishing that T cell hyperresponsiveness is not a general correlate of CD43 absence.

Murine hematopoietic progenitors are capable of both histamine synthesis and uptake.

We examined various murine hematopoietic cell populations for their capacity to interact with radiolabeled histamine. Only bone marrow cells (BMC) retained substantial amounts of radioactivity, in contrast to thymus, spleen, and peritoneal cells. The characteristics of this interaction are consistent with histamine uptake rather than receptor binding. Indeed, this process is temperature and sodium dependent and reduced by various metabolic inhibitors. Furthermore, the effect of antagonists or agonists of the H1, H2, and H3 receptor subtypes is not in accordance with the involvement of either of these receptors in histamine binding. The target cells of histamine copurify with hematopoietic progenitors in the low-density BM population. They are most enriched in the subset sorted from the blast cell window on the basis of high rhodamine retention. This fraction contains on the average 80% to 90% immature cells and is highly enriched for several clonogenic progenitor subsets. Sixty percent of the Rh-bright cells are labeled by 3H-histamine, as assessed by autoradiography, suggesting that a variety of immature cells participates in this phenomenon. Furthermore, in all sorting procedures used here, the cells capable of histamine uptake coenrich with those producing histamine in response to interleukin-3, indicating at least a partial identity between these cells.

In vivo overexpression of Core2 N-acetylglucosaminyltransferase prevents repopulation of the bone marrow with colony forming cells but fails to affect normal T cell development.

UDP-GlcNAc:Galbet1 --> 3GalNAc-R beta1 --> 6N-acetylglucosaminyltransferase (Core2 N-acetyl-glucosaminyltransferase, C2GnT; EC 2.4.1.102) forms beta1 --> 6N-acetyl-glucosaminyl linkages in O-glycoproteins and creates branches for the addition of N-acetyl-lactosamine antennae. Changes in C2GnT activity have been associated with immune disorders, malignancies, and T-cell ontogeny. In this study, we used SCID (severe combined immune deficiency) mice to determine the effects of C2GnT overexpression on hemopoiesis, and in particular, on thymocyte development. BALB/c bone marrow cells transfected with C2GnT using the retroviral murine stem cell vector were used to repopulate SCID mice. Mice were analysed 3 weeks to 3 months after bone marrow transfer. Elevated levels of C2GnT activity in bone marrow, spleen, and thymus from mice repopulated with C2GnT transfected bone marrow cells indicated that C2GnT was overexpressed in recipient mice. In C2GnT repopulated mice, up to 50% of T cells showed an increase in CD43 130-kDa expression, compared with T cells from control animals, indicative of an elevated C2GnT activity in these cells. Furthermore, T-cell subset numbers appeared to be normal, suggesting that C2GnT overexpression did not alter T-cell ontogeny. Interestingly, C2GnT overexpression negatively affected the repopulation of myeloid cells. Only insignificant numbers of interleukin-3/granulocyte-macrophage colony stimulating factor (IL-3/GM-CSF) responsive bone marrow cells were found to be retrovirally transfected in C2GnT repopulated mice, whereas up to 50% of IL-3/GM-CSF responsive bone marrow cells were found to be retrovirally transfected in corresponding controls. These data indicate that in vivo overexpression of C2GnT negatively interferes with the myeloid differentiation pathway but does not affect T-cell development.

[Rapid prototyping and bone reconstruction]. / Prototypage rapide et reconstruction osseuse.

The authors describe the main techniques for rapid prototyping used in the medical field, with particular emphasis on Laser stereolithography. They describe the basics of the technique as well as the procedures they currently use to construct anatomic specimens from scanned images. For more than 10 years, the targets of researchers in the field of bone reconstruction in craniofacial surgery have been: to design a system to acquire data directly from CT-scans, to optimize modelling, processing and materials, to verify the possibility of producing prefabricated prostheses with data from preoperative models (22 cases). The target of integrating this technique into therapeutic protocols has been reached. The current trend in research is to produce prostheses from biocompatible materials directly from CT scan data by Laser stereolithography.

IL-2, -4, and -15 differentially regulate O-glycan branching and P-selectin ligand formation in activated CD8 T cells.

The glycosyltransferase core 2 beta1-6 N-acetylglucosaminyl transferase (C2GnT1 or C2GlcNAcT1) is responsible for formation of branched structures on O-glycans present on cell surface glycoproteins. The O-glycan branch created by C2GnT1 is physiologically important insofar as only this structure can be extended and modified to yield P-selectin ligands that promote initial interactions between extravasating lymphocytes and endothelia. In mature T cells, C2GnT1 activity is thought to be induced as an intrinsic consequence of T cell activation. Through analysis of C2GnT1-dependent epitopes on CD43 and CD45RB we have found that in activated CD8(+) T cells expression of C2GnT1 was dependent upon exposure to specific cytokines rather than being induced as a direct consequence of activation. Activated CD8(+) cells became receptive to strong induction of C2GnT1 expression and P-selectin ligand expression in response to IL-2, moderate induction by IL-15, and minimal induction in response to IL-4. Our observations clarify the relationship between T cell activation and C2GnT1 expression, demonstrate the differential impact of distinct cytokines on expression of C2GnT1 activity and P-selectin ligand, and reinforce the concept that the cytokine milieu subsequent to activation can influence adhesion systems that dictate lymphocyte homing properties.

The Distance to the Soft Gamma Repeater SGR 1627-41.

We report millimeter observations of the line of sight to the recently discovered soft gamma repeater SGR 1627-41, which has been tentatively associated with the supernova remnant (SNR) G337.0-0.1. Among the eight molecular clouds along the line of sight to SGR 1627-41, we show that SNR G337.0-0.1 is probably interacting with one of the most massive giant molecular clouds (GMCs) in the Galaxy, at a distance of 11 kpc from the Sun. Based on the high extinction to the persistent X-ray counterpart of SGR 1627-41, we present evidence for an association of this new soft gamma repeater (SGR) with the SNR G337.0-0.1; they both appear to be located on the near side of the GMC. This is the second SGR located near an extraordinarily massive GMC. We suggest that SGR 1627-41 is a neutron star with a high transverse velocity ( approximately 1000 km s-1) escaping the young ( approximately 5000 yr) SNR G337.0-0.1.

Large-scale, decelerating, relativistic x-ray jets from the microquasar XTE J1550-564.

We have detected, at x-ray and radio wavelengths, large-scale moving jets from the microquasar XTE J1550-564. Plasma ejected from near the black hole traveled at relativistic velocities for at least 4 years. We present direct evidence for gradual deceleration in a relativistic jet. The broadband spectrum of the jets is consistent with synchrotron emission from high-energy (up to 10 tera-electron volts) particles that were accelerated in the shock waves formed within the relativistic ejecta or by the interaction of the jets with the interstellar medium. XTE J1550-564 offers a rare opportunity to study the dynamical evolution of relativistic jets on time scales inaccessible for active galactic nuclei jets, with implications for our understanding of relativistic jets from Galactic x-ray binaries and active galactic nuclei.