817 research outputs found
Design of lipid nanoparticle delivery agents for multivalent display of recombinant Env trimers in HIV vaccination
Background:
Immunization strategies that elicit antibodies capable of neutralizing diverse strains of the virus will likely be an important part of a successful vaccine against HIV. The envelope trimer is the only neutralizing target on the virus, and strategies to promote durable, high avidity antibody responses against the native intact trimer structure are lacking. We recently developed chemically-crosslinked lipid nanocapsules as carriers of molecular adjuvants and encapsulated or surface-displayed antigens, which promote follicular helper T-cell responses and elicited high-avidity, durable antibody responses to a candidate malaria antigen (Moon et al. Nat. Mater. 10 243 (2011); Moon et al. PNAS 109 1080 (2012)).
Methods:
To apply this system to the delivery of HIV antigens, we developed a strategy to anchor recombinant envelope trimers to the surfaces of these particles under conditions preserving the antigenic integrity of the trimers, allowing multivalent display of these immunogens for immunization. To anchor trimers in their native orientation, gp140 trimers with terminal his-tags were anchored to the surface of lipid nanocapsules via Ni-NTA-functionalized lipids.
Results:
Owing to their significant size (409 kDa) and heavy glycosylation, we found that liquid-ordered and/or gel-phase lipid compositions were required to stably anchor trimers to particle membranes. Trimer-loaded nanocapsules carrying monophosphoryl lipid A elicited durable antibody responses with titers comparable to a Complete Freund’s Adjuvant (CFA)-like emulsion in mice, without the toxic inflammation associated with the latter adjuvant. Further, nanocapsules elicited strong helper T-cell responses associated with a steadily increasing avidity of trimer-binding antibody over 90 days, which was not replicated by other adjuvants.
Conclusion:
These results suggest that nanoparticles displaying HIV trimers in an oriented, multivalent presentation can promote key aspects of the humoral response against Env immunogens.National Institutes of Health (U.S.) (AI095109)Massachusetts Institute of Technology. Ragon Institute of MGH, MIT, and Harvar
Quasi-one-dimensional anisotropic Heisenberg model in a transverse magnetic field
The phase diagram of weakly coupled chains in a transverse magnetic
field is studied using the mean-field approximation for the interchain coupling
and known exact results for an effective one-dimensional model. Results are
applied to the quasi-one-dimensional antiferromagnet and the
value of interchain interaction in this compound is estimated.Comment: 4 pages, 2 figure
The Crab pulsar light curve in the soft gamma ray range: FIGARO II results
The FIGARO II experiment (a large area, balloon borne, crystal scintillator detector working from 0.15 to 4.3 MeV) observed the Crab pulsar on 1990 Jul. 9 for about seven hours. The study of the pulse profile confirms some structures detected with a low significance during the shorter observation of 1986, and adds new important elements to the picture. In particular, between the two main peaks, two secondary peaks appear centered at phase values 0.1 and 0.3, in the energy range 0.38 to 0.49 MeV; in the same energy range, a spectral feature at 0.44 MeV, interpreted as a redshifted positron annihilation line, was observed during the same balloon flight in the phase interval including the second main peak and the neighboring secondary peak. If the phase interval considered is extended to include also the other secondary peak, the significance of the spectral line appears to increase
Hamiltonian formalism of the Landau-Lifschitz equation for a spin chain with full anisotropy
The Hamiltonian formalism of the Landau-Lifschitz equation for a spin chain
with full anisotropy is formulated completely, which constructs a stable base
for further investigations.Comment: 11page
Formfactors and functional form of correlators in the XX spin chain
We present the new expressions for the formfactors of local operators for the
XX - quantum spin chain as a Cauchy determinants. Using the known functional
form of the correlator at large distances we propose the new expression for the
constant for the asymptotics of the correlator as a Cauchy determinant. We
calculate the momentum distribution for the general case of the XXZ spin chain
and point out that it is completely different from the Luttinger model (the
system of fermions). For the XX chain we compare numerically the value of the
lowest formfactor and the expectation value of momentum- zero operators which
is determined by the functional form of the correlator.Comment: LaTex, 18 page
Out of equilibrium correlations in the XY chain
We study the transversal XY spin-spin correlations in the non-equilibrium
steady state constructed in \cite{AP03} and prove their spatial exponential
decay close to equilibrium
Relaxation in the XX quantum chain
We present the results obtained on the magnetisation relaxation properties of
an XX quantum chain in a transverse magnetic field. We first consider an
initial thermal kink-like state where half of the chain is initially
thermalized at a very high temperature while the remaining half, called
the system, is put at a lower temperature . From this initial state, we
derive analytically the Green function associated to the dynamical behaviour of
the transverse magnetisation. Depending on the strength of the magnetic field
and on the temperature of the system, different regimes are obtained for the
magnetic relaxation. In particular, with an initial droplet-like state, that is
a cold subsystem of finite size in contact at both ends with an infinite
temperature environnement, we derive analytically the behaviour of the
time-dependent system magnetisation
Out of equilibrium correlation functions of quantum anisotropic XY models: one-particle excitations
We calculate exactly matrix elements between states that are not eigenstates
of the quantum XY model for general anisotropy. Such quantities therefore
describe non equilibrium properties of the system; the Hamiltonian does not
contain any time dependence. These matrix elements are expressed as a sum of
Pfaffians. For single particle excitations on the ground state the Pfaffians in
the sum simplify to determinants.Comment: 11 pages, no figures; revtex. Minor changes in the text; list of
refs. modifie
Study of Loschmidt Echo for a qubit coupled to an XY-spin chain environment
We study the temporal evolution of a central spin-1/2 (qubit) coupled to the
environment which is chosen to be a spin-1/2 transverse XY spin chain. We
explore the entire phase diagram of the spin-Hamiltonian and investigate the
behavior of Loschmidt echo(LE) close to critical and multicritical point(MCP).
To achieve this, the qubit is coupled to the spin chain through the anisotropy
term as well as one of the interaction terms. Our study reveals that the echo
has a faster decay with the system size (in the short time limit) close to a
MCP and also the scaling obeyed by the quasiperiod of the collapse and revival
of the LE is different in comparison to that close to a QCP. We also show that
even when approached along the gapless critical line, the scaling of the LE is
determined by the MCP where the energy gap shows a faster decay with the system
size. This claim is verified by studying the short-time and also the collapse
and revival behavior of the LE at a quasicritical point on the ferromagnetic
side of the MCP. We also connect our observation to the decoherence of the
central spin.Comment: Accepted for publication in EPJ
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