Quantum Criticality of an Ising-like Spin-1/2 Antiferromagnetic Chain in Transverse Magnetic Field

We report on magnetization, sound velocity, and magnetocaloric-effect measurements of the Ising-like spin-1/2 antiferromagnetic chain system BaCo$_2$V$_2$O$_8$ as a function of temperature down to 1.3 K and applied transverse magnetic field up to 60 T. While across the N\'{e}el temperature of $T_N\sim5$ K anomalies in magnetization and sound velocity confirm the antiferromagnetic ordering transition, at the lowest temperature the field-dependent measurements reveal a sharp softening of sound velocity $v(B)$ and a clear minimum of temperature $T(B)$ at $B^{c,3D}_\perp=21.4$ T, indicating the suppression of the antiferromagnetic order. At higher fields, the $T(B)$ curve shows a broad minimum at $B^c_\perp = 40$ T, accompanied by a broad minimum in the sound velocity and a saturation-like magnetization. These features signal a quantum phase transition which is further characterized by the divergent behavior of the Gr\"{u}neisen parameter $\Gamma_B \propto (B-B^{c}_\perp)^{-1}$. By contrast, around the critical field, the Gr\"{u}neisen parameter converges as temperature decreases, pointing to a quantum critical point of the one-dimensional transverse-field Ising model.Comment: Phys. Rev. Lett., to appea

Probing orbital ordering in LaVO3_{3} epitaxial films by Raman scattering

Single crystals of Mott-Hubbard insulator LaVO3 exhibit spin and orbital ordering along with a structural change below ≈140 K. The occurrence of orbital ordering in epitaxial LaVO3films has, however, been little investigated. By temperature-dependent Raman scatteringspectroscopy, we probed and evidenced the transition to orbital ordering in epitaxial LaVO3film samples fabricated by pulsed-laser deposition. This opens up the possibility to explore the influence of different epitaxial strain (compressive vs. tensile) and of epitaxy-induced distortions of oxygen octahedra on the orbital ordering, in epitaxial perovskite vanadate films

A human coronavirus responsible for the common cold massively kills dendritic cells but not monocytes

Copyright @ 2012, American Society for Microbiology.Human coronaviruses are associated with upper respiratory tract infections that occasionally spread to the lungs and other organs. Although airway epithelial cells represent an important target for infection, the respiratory epithelium is also composed of an elaborate network of dendritic cells (DCs) that are essential sentinels of the immune system, sensing pathogens and presenting foreign antigens to T lymphocytes. In this report, we show that in vitro infection by human coronavirus 229E (HCoV-229E) induces massive cytopathic effects in DCs, including the formation of large syncytia and cell death within only few hours. In contrast, monocytes are much more resistant to infection and cytopathic effects despite similar expression levels of CD13, the membrane receptor for HCoV-229E. While the differentiation of monocytes into DCs in the presence of granulocyte-macrophage colony-stimulating factor and interleukin-4 requires 5 days, only 24 h are sufficient for these cytokines to sensitize monocytes to cell death and cytopathic effects when infected by HCoV-229E. Cell death induced by HCoV-229E is independent of TRAIL, FasL, tumor necrosis factor alpha, and caspase activity, indicating that viral replication is directly responsible for the observed cytopathic effects. The consequence of DC death at the early stage of HCoV-229E infection may have an impact on the early control of viral dissemination and on the establishment of long-lasting immune memory, since people can be reinfected multiple times by HCoV-229E

High viral load of Merkel cell polyomavirus DNA sequences in Langerhans cell sarcoma tissues.

International audienceBACKGROUND: Langerhans cell (LC) sarcoma (LCS) is a high-grade neoplasm with overtly malignant cytologic features and an LC phenotype. We very recently suggested that LC behaves as a reservoir for common dermotropic Merkel cell polyomavirus (MCPyV) and determined the relationship between LC histiocytosis (LCH), which has an underlining oncogenic capacity, and MCPyV as a trigger for a reactive process rather than a neoplastic process. We propose LC to be a reservoir for MCPyV and hypothesize that some LCS subtypes may be related to the MCPyV agent. FINDINGS: We examined seven LCS tissues using multiplex quantitative PCR (Q-PCR) and immunohistochemistry with anti MCPyV large-T (LT) antigen antibody. High viral loads of MCPyV DNA sequences (viral load = relative levels of MCPyV) were detected (0.328-0.772 copies/cell (Merkel cell carcinoma (MCC) = 1.0)) using Q-PCR in 43% (3/7) tissues, but LT antigen expression was not observed (0/7). CONCLUSIONS: Frequent MCPyV-DNA amplification suggests that LCS in some patients may be related to MCPyV infection. Moreover, the higher viral load of LCS (median, 0.453 copies/cell) than low load of LCH (0.003, median of 12 cases) (P < 0.01) may suggest a virally induced tumorigenic process in some LCS. Although the absence of LT antigen expression may indicate a different role for MCPyV in this pathology, some subtypes of LCS may develop in the background of MCPyV-infected LC. To the best of our knowledge, this is the first report on the relationship between MCPyV and LCS. The recent discovery of MCPyV opened new therapeutic avenues for MCC. These data open novel possibilities for therapeutic interventions against LCS

Modified Vaccinia Virus Ankara Exerts Potent Immune Modulatory Activities in a Murine Model

Background: Modified vaccinia virus Ankara (MVA), a highly attenuated strain of vaccinia virus, has been used as vaccine delivery vector in preclinical and clinical studies against infectious diseases and malignancies. Here, we investigated whether an MVA which does not encode any antigen (Ag) could be exploited as adjuvant per se. Methodology/Principal Findings: We showed that dendritic cells infected in vitro with non-recombinant (nr) MVA expressed maturation and activation markers and were able to efficiently present exogenously pulsed Ag to T cells. In contrast to the dominant T helper (Th) 1 biased responses elicited against Ags produced by recombinant MVA vectors, the use of nrMVA as adjuvant for the co-administered soluble Ags resulted in a long lasting mixed Th1/Th2 responses. Conclusions/Significance: These findings open new ways to potentiate and modulate the immune responses to vaccin