520 research outputs found
Differential requirements of MyD88 and TRIF pathways in TLR4-mediated immune responses in murine B cells
LPS stimulates the TLR4/Myeloid differentiation protein-2 (MD-2) complex and promotes a variety ofimmune responses in B cells. TLR4 has two main signaling pathways, MyD88 and Toll/IL-1R (TIR)-domain-containing adaptor-inducing interferon- (TRIF) pathways, but relatively few studies have examinedthese pathways in B cells. In this study, we investigated MyD88- or TRIF-dependent LPS responses inB cells by utilizing their knockout mice. Compared with wild-type (WT) B cells, MyD88−/−B cells weremarkedly impaired in up-regulation of CD86 and proliferation induced by lipid A moiety of LPS. TRIF−/−Bcells were also impaired in these responses compared with WT B cells, but showed better responses thanMyD88−/−B cells. Regarding class switch recombination (CSR) elicited by lipid A plus IL-4, MyD88−/−B cells showed similar patterns of CSR to WT B cells. However, TRIF−/−B cells showed the impaired inthe CSR. Compared with WT and MyD88−/−B cells, TRIF−/−B cells exhibited reduced cell division, fewerIgG1+cells per division, and decreased activation-induced cytidine deaminase (Aicda) mRNA expressionin response to lipid A plus IL-4. Finally, IgG1 production to trinitrophenyl (TNP)-LPS immunization wasimpaired in TRIF−/−mice, while MyD88−/−mice exhibited increased IgG1 production. Thus, MyD88 andTRIF pathways differently regulate TLR4-induced immune responses in B cells
Drastic Change of Magnetic Phase Diagram in Doped Quantum Antiferromagnet TlCuMgCl
TlCuCl is a coupled spin dimer system, which has a singlet ground state
with an excitation gap of = 5.5 T.
TlCuMgCl doped with nonmagnetic Mg ions undergoes
impurity-induced magnetic ordering. Because triplet excitation with a finite
gap still remains, this doped system can also undergo magnetic-field-induced
magnetic ordering. By specific heat measurements and neutron scattering
experiments under a magnetic field, we investigated the phase diagram in
TlCuMgCl with , and found that impurity- and
field-induced ordered phases are the same. The gapped spin liquid state
observed in pure TlCuCl is completely wiped out by the small amount of
doping.Comment: 9 pages, 5 figures, jpsj2 class file, to be published in J. Phy. Soc.
Jpn. Vol.75 No.3 (2006); layout changed, unrelated figure remove
Pressure-Induced Magnetic Quantum Phase Transitions from Gapped Ground State in TlCuCl3
Magnetization maesurements under hydrostatic pressure were performed on an
S=1/2 coupled spin system TlCuCl3 with a gapped ground state under magnetic
field H parallel to the [2,0,1] direction. With increasing applied pressure P,
the gap decreases and closes completely at Pc=0.42 kbar. For P>Pc, TlCuCl3
undergoes antiferromagnetic ordering. A spin-flop transition was observed at
Hsf=0.7T. The spin-flop field is approximately independent of pressure,
although the sublattice magnetization increases with pressure. The gap and Neel
temperature are presented as function is attributed to to the relative
enhancement of the interdimer exchange interactions compared with the
intradimer exchange interaction.Comment: 4pages,3figures To be published in J. Phys. Soc. Jpn. Vol.73 No.1
Few-electron molecular states and their transitions in a single InAs quantum dot molecule
We study electronic configurations in a single pair of vertically coupled
self-assembled InAs quantum dots, holding just a few electrons. By comparing
the experimental data of non-linear single-electron transport spectra in a
magnetic field with many-body calculations, we identify the spin and orbital
configurations to confirm the formation of molecular states by filling both the
quantum mechanically coupled symmetric and anti-symmetric states. Filling of
the anti-symmetric states is less favored with increasing magnetic field, and
this leads to various magnetic field induced transitions in the molecular
states.Comment: 14 pages, 3 figures, Accepted for publication in Phys. Rev. Let
Nuclear fragmentation and DNA degradation during programmed cell death in petals of morning glory (Ipomoea nil)
We studied DNA degradation and nuclear fragmentation during programmed cell death (PCD) in petals of Ipomoea nil (L.) Roth flowers. The DNA degradation, as observed on agarose gels, showed a large increase. Using DAPI, which stains DNA, and flow cytometry for DAPI fluorescence, we found that the number of DNA masses per petal at least doubled. This indicated chromatin fragmentation, either inside or outside the nucleus. Staining with the cationic lipophilic fluoroprobe DiOC6 indicated that each DNA mass had an external membrane. Fluorescence microscopy of the nuclei and DNA masses revealed an initial decrease in diameter together with chromatin condensation. The diameters of these condensed nuclei were about 70% of original. Two populations of nuclear diameter, one with an average diameter about half of the other, were observed at initial stages of nuclear fragmentation. The diameter of the DNA masses then gradually decreased further. The smallest observed DNA masses had a diameter less than 10% of that of the original nucleus. Cycloheximide treatment arrested the cytometrically determined changes in DNA fluorescence, indicating protein synthesis requirement. Ethylene inhibitors (AVG and 1-MCP) had no effect on the cytometrically determined DNA changes, suggesting that these processes are not controlled by endogenous ethylene
Impurity-Induced Antiferromagnetic Ordering in the Spin Gap System TlCuCl_3
The magnetization measurements have been performed on the doped spin gap
system TlCu_{1-x}Mg_xCl_3 with x <= 0.025. The parent compound TlCuCl_3 is a
three-dimensional coupled spin dimer system with the excitation gap Delta/k_B =
7.7 K. The impurity-induced antiferromagnetic ordering was clearly observed.
The easy axis lies in the (0,1,0) plane. It was found that the transition
temperature increases with increasing Mg^{2+} concentration x, while the
spin-flop transition field is almost independent of x. The magnetization curve
suggests that the impurity-induced antiferromagnetic ordering coexists with the
spin gap for x <= 0.017.Comment: 5 pages, 6 figures, revtex styl
Magnetization plateaus in weakly coupled dimer spin system
I study a spin system consisting of strongly coupled dimers which are in turn
weakly coupled in a plane by zigzag interactions. The model can be viewed as
the strong-coupling limit of a two-dimensional zigzag chain structure typical,
e.g., for the -planes of KCuCl_3. It is shown that the magnetization
curve in this model has plateaus at 1/3 and 2/3 of the saturation
magnetization, and an additional plateau at 1/2 can appear in a certain range
of the model parameters; the critical fields are calculated perturbatively. It
is argued that for the three-dimensional lattice structure of the KCuCl_3
family the plateaus at 1/4 and 3/4 of the saturation can be favored in a
similar way, which might be relevant to the recent experiments on NH_4CuCl_3 by
Shiramura et al., J. Phys. Soc. Jpn. {\bf 67}, 1548 (1998).Comment: serious changes in Sect. II,III, final version to appear in PR
Neutron Diffraction Study of the Pressure-Induced Magnetic Ordering in the Spin Gap System TlCuCl
Neutron elastic scattering measurements have been performed under the
hydrostatic pressure in order to investigate the spin structure of the
pressure-induced magnetic ordering in the spin gap system TlCuCl. Below the
ordering temperature K for the hydrostatic pressure
GPa, magnetic Bragg reflections were observed at the reciprocal lattice points
{\mib Q}=(h, 0, l) with integer and odd , which are equivalent to
those points with the lowest magnetic excitation energy at ambient pressure.
This indicates that the spin gap closes due to the applied pressure. The spin
structure of the pressure-induced magnetic ordered state for GPa was
determined.Comment: 4 pages, 3 figures, 3 eps files, jpsj2.cls styl
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