154 research outputs found
Lipid specificity of the immune effector perforin
Perforin is a pore forming protein used by cytotoxic T lymphocytes to remove cancerous or virus-infected cells during immune response. During the response, the lymphocyte membrane becomes refractory to perforin function by accumulating densely ordered lipid rafts and externalizing negatively charged lipid species. The dense membrane packing lowers the capacity of perforin to bind, and negatively charged lipids scavenge any residual protein before pore formation. Using atomic force microscopy on model membrane systems, we here provide insight into the molecular basis of perforin lipid specificity
Human PrimPol is a highly error-prone polymerase regulated by single-stranded DNA binding proteins
PrimPol is a recently identified polymerase involved in eukaryotic DNA damage tolerance, employed in both re-priming and translesion synthesis mechanisms to bypass nuclear and mitochondrial DNA lesions. In this report, we investigate how the enzymatic activities of human PrimPol are regulated. We show that, unlike other TLS polymerases, PrimPol is not stimulated by PCNA and does not interact with it in vivo. We identify that PrimPol interacts with both of the major single-strand binding proteins, RPA and mtSSB in vivo. Using NMR spectroscopy, we characterize the domains responsible for the PrimPol-RPA interaction, revealing that PrimPol binds directly to the N-terminal domain of RPA70. In contrast to the established role of SSBs in stimulating replicative polymerases, we find that SSBs significantly limit the primase and polymerase activities of PrimPol. To identify the requirement for this regulation, we employed two forward mutation assays to characterize PrimPol's replication fidelity. We find that PrimPol is a mutagenic polymerase, with a unique error specificity that is highly biased towards insertion-deletion errors. Given the error-prone disposition of PrimPol, we propose a mechanism whereby SSBs greatly restrict the contribution of this enzyme to DNA replication at stalled forks, thus reducing the mutagenic potential of PrimPol during genome replication
Galaxy Clusters Selected with the Sunyaev-Zel'dovich Effect from 2008 South Pole Telescope Observations
We present a detection-significance-limited catalog of 21 Sunyaev-Zel'dovich
selected galaxy clusters. These clusters, along with 1 unconfirmed candidate,
were identified in 178 deg^2 of sky surveyed in 2008 by the South Pole
Telescope to a depth of 18 uK-arcmin at 150 GHz. Optical imaging from the
Blanco Cosmology Survey (BCS) and Magellan telescopes provided photometric (and
in some cases spectroscopic) redshift estimates, with catalog redshifts ranging
from z=0.15 to z>1, with a median z = 0.74. Of the 21 confirmed galaxy
clusters, three were previously identified as Abell clusters, three were
presented as SPT discoveries in Staniszewski et al, 2009, and three were first
identified in a recent analysis of BCS data by Menanteau et al, 2010; the
remaining 12 clusters are presented for the first time in this work. Simulated
observations of the SPT fields predict the sample to be nearly 100% complete
above a mass threshold of M_200 ~ 5x10^14 M_sun/h at z = 0.6. This completeness
threshold pushes to lower mass with increasing redshift, dropping to ~4x10^14
M_sun/h at z=1. The size and redshift distribution of this catalog are in good
agreement with expectations based on our current understanding of galaxy
clusters and cosmology. In combination with other cosmological probes, we use
the cluster catalog to improve estimates of cosmological parameters. Assuming a
standard spatially flat wCDM cosmological model, the addition of our catalog to
the WMAP 7-year analysis yields sigma_8 = 0.81 +- 0.09 and w = -1.07 +- 0.29, a
~50% improvement in precision on both parameters over WMAP7 alone.Comment: 19 pages, 9 figures, 4 appendice
Trans-endocytosis of CD80 and CD86:a molecular basis for the cell-extrinsic function of CTLA-4
Cytotoxic T lymphocyte antigen 4 (CTLA-4) is an essential negative regulator of T cell immune responses whose mechanism of action is the subject of debate. CTLA-4 shares two ligands (CD80 and CD86) with a stimulatory receptor, CD28. Here, we show that CTLA-4 can capture its ligands from opposing cells by a process of trans-endocytosis. After removal, these costimulatory ligands are degraded inside CTLA-4-expressing cells, resulting in impaired costimulation via CD28. Acquisition of CD86 from antigen-presenting cells is stimulated by T cell receptor engagement and observed in vitro and in vivo. These data reveal a mechanism of immune regulation in which CTLA-4 acts as an effector molecule to inhibit CD28 costimulation by the cell-extrinsic depletion of ligands, accounting for many of the known features of the CD28-CTLA-4 system
Weak lensing, dark matter and dark energy
Weak gravitational lensing is rapidly becoming one of the principal probes of
dark matter and dark energy in the universe. In this brief review we outline
how weak lensing helps determine the structure of dark matter halos, measure
the expansion rate of the universe, and distinguish between modified gravity
and dark energy explanations for the acceleration of the universe. We also
discuss requirements on the control of systematic errors so that the
systematics do not appreciably degrade the power of weak lensing as a
cosmological probe.Comment: Invited review article for the GRG special issue on gravitational
lensing (P. Jetzer, Y. Mellier and V. Perlick Eds.). V3: subsection on
three-point function and some references added. Matches the published versio
Evidence for the accelerated expansion of the Universe from weak lensing tomography with COSMOS
We present a tomographic cosmological weak lensing analysis of the HST COSMOS
Survey. Applying our lensing-optimized data reduction, principal component
interpolation for the ACS PSF, and improved modelling of charge-transfer
inefficiency, we measure a lensing signal which is consistent with pure
gravitational modes and no significant shape systematics. We carefully estimate
the statistical uncertainty from simulated COSMOS-like fields obtained from
ray-tracing through the Millennium Simulation. We test our pipeline on
simulated space-based data, recalibrate non-linear power spectrum corrections
using the ray-tracing, employ photometric redshifts to reduce potential
contamination by intrinsic galaxy alignments, and marginalize over systematic
uncertainties. We find that the lensing signal scales with redshift as expected
from General Relativity for a concordance LCDM cosmology, including the full
cross-correlations between different redshift bins. For a flat LCDM cosmology,
we measure sigma_8(Omega_m/0.3)^0.51=0.75+-0.08 from lensing, in perfect
agreement with WMAP-5, yielding joint constraints Omega_m=0.266+0.025-0.023,
sigma_8=0.802+0.028-0.029 (all 68% conf.). Dropping the assumption of flatness
and using HST Key Project and BBN priors only, we find a negative deceleration
parameter q_0 at 94.3% conf. from the tomographic lensing analysis, providing
independent evidence for the accelerated expansion of the Universe. For a flat
wCDM cosmology and prior w in [-2,0], we obtain w<-0.41 (90% conf.). Our dark
energy constraints are still relatively weak solely due to the limited area of
COSMOS. However, they provide an important demonstration for the usefulness of
tomographic weak lensing measurements from space. (abridged)Comment: 26 pages, 25 figures, matches version accepted for publication by
Astronomy and Astrophysic
A simple parametric model for spherical galaxy clusters
We present an analytic parametric model to describe the baryonic and dark
matter distributions in clusters of galaxies with spherical symmetry. It is
assumed that the dark matter density follows a Navarro, Frenk and White (NFW)
profile and that the gas pressure is described by a generalised NFW (GNFW)
profile. By further demanding hydrostatic equilibrium and that the gas fraction
is small throughout the cluster, one obtains unique functional forms, dependent
on basic cluster parameters, for the radial profiles of all the properties of
interest in the cluster. We show these profiles are consistent both with
numerical simulations and multi-wavelength observations of clusters. We also
use our model to analyse six simulated SZ clusters as well as A611 SZ data from
the Arcminute Microkelvin Imager (AMI). In each case, we derive the radial
profile of the enclosed total mass and the gas pressure and show that the
results are in good agreement with our model prediction.Comment: 10 pages, 3 table, 17 figure
Neonatal CD8 T-cell Hierarchy Is Distinct from Adults and Is Influenced by Intrinsic T cell Properties in Respiratory Syncytial Virus Infected Mice
Following respiratory syncytial virus infection of adult CB6F1 hybrid mice, a predictable CD8+ T cell epitope hierarchy is established with a strongly dominant response to a Kd-restricted peptide (SYIGSINNI) from the M2 protein. The response to KdM282-90 is ∼5-fold higher than the response to a subdominant epitope from the M protein (NAITNAKII, DbM187-195). After infection of neonatal mice, a distinctly different epitope hierarchy emerges with codominant responses to KdM282-90 and DbM187-195. Adoptive transfer of naïve CD8+ T cells from adults into congenic neonates prior to infection indicates that intrinsic CD8+ T cell factors contribute to age-related differences in hierarchy. Epitope-specific precursor frequency differs between adults and neonates and influences, but does not predict the hierarchy following infection. Additionally, dominance of KdM282-90 –specific cells does not correlate with TdT activity. Epitope-specific Vβ repertoire usage is more restricted and functional avidity is lower in neonatal mice. The neonatal pattern of codominance changes after infection at 10 days of age, and rapidly shifts to the adult pattern of extreme KdM282- 90 -dominance. Thus, the functional properties of T cells are selectively modified by developmental factors in an epitope-specific and age-dependent manner
Signaling Signatures and Functional Properties of Anti-Human CD28 Superagonistic Antibodies
Superagonistic CD28 antibodies (CD28SAs) activate T lymphocytes without concomitant perturbation of the TCR/CD3-complex. In rodents these reagents induce the preferential expansion of regulatory T cells and can be used for the treatment of autoimmune diseases. Unexpectedly, the humanized CD28 superagonist TGN1412 caused severe and life threatening adverse effects during a recently conducted phase I clinical trail. The underlying molecular mechanisms are as yet unclear. We show that TGN1412 as well as the commercially available CD28 superagonist ANC28.1 induce a delayed but extremely sustained calcium response in human naïve and memory CD4+ T cells but not in cynomolgus T lymphocytes. The sustained Ca++-signal was associated with the activation of multiple intracellular signaling pathways and together these events culminated in the rapid de novo synthesis of high amounts of pro-inflammatory cytokines, most notably IFN-γ and TNF-α. Importantly, sustained transmembranous calcium flux, activation of Src-kinases as well as activation of PI3K were found to be absolutely required for CD28SA-mediated production of IFN-γ and IL-2. Collectively, our data suggest a molecular basis for the severe side effects caused by TGN1412 and impinge upon the relevance of non-human primates as preclinical models for reagents that are supposed to modify the function of human T cells
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