University of Iowa

About: University of Iowa is a education organization based out in Iowa City, Iowa, United States. It is known for research contribution in the topics: Population & Poison control. The organization has 49229 authors who have published 109171 publications receiving 5021465 citations. The organization is also known as: UI & The University of Iowa.

CD4 + T-cell help controls CD8 + T-cell memory via TRAIL-mediated activation-induced cell death

Abstract: The 'help' provided by CD4+ T lymphocytes during the priming of CD8+ T lymphocytes confers a key feature of immune memory: the capacity for autonomous secondary expansion following re-encounter with antigen Once primed in the presence of CD4+ T cells, 'helped' CD8+ T cells acquire the ability to undergo a second round of clonal expansion upon restimulation in the absence of T-cell help 'Helpless' CD8+ T cells that are primed in the absence of CD4+ T cells, in contrast, can mediate effector functions such as cytotoxicity and cytokine secretion upon restimulation, but do not undergo a second round of clonal expansion These disparate responses have features of being 'programmed', that is, guided by signals that are transmitted to naive CD8+ T cells during priming, which encode specific fates for their clonal progeny Here we explore the instructional programme that governs the secondary response of CD8+ T cells and find that helpless cells undergo death by activation-induced cell death upon secondary stimulation This death is mediated by tumour-necrosis factor (TNF)-related apoptosis-inducing ligand (TRAIL) Regulation of Trail expression can therefore account for the role of CD4+ T cells in the generation of CD8+ T cell memory and represents a novel mechanism for controlling adaptive immune responses

Formation of the Isthmus of Panama

Abstract: The formation of the Isthmus of Panama stands as one of the greatest natural events of the Cenozoic, driving profound biotic transformations on land and in the oceans. Some recent studies suggest that the Isthmus formed many millions of years earlier than the widely recognized age of approximately 3 million years ago (Ma), a result that if true would revolutionize our understanding of environmental, ecological, and evolutionary change across the Americas. To bring clarity to the question of when the Isthmus of Panama formed, we provide an exhaustive review and reanalysis of geological, paleontological, and molecular records. These independent lines of evidence converge upon a cohesive narrative of gradually emerging land and constricting seaways, with formation of the Isthmus of Panama sensu stricto around 2.8 Ma. The evidence used to support an older isthmus is inconclusive, and we caution against the uncritical acceptance of an isthmus before the Pliocene.

Adaptive Lasso for sparse high-dimensional regression models

Abstract: We study the asymptotic properties of the adaptive Lasso estimators in sparse, high-dimensional, linear regression models when the number of covariates may increase with the sample size. We consider variable selection using the adap- tive Lasso, where the L1 norms in the penalty are re-weighted by data-dependent weights. We show that, if a reasonable initial estimator is available, under ap- propriate conditions, the adaptive Lasso correctly selects covariates with nonzero coefficients with probability converging to one, and that theestimators of nonzero coefficients have the same asymptotic distribution they would have if the zero co- efficients were known in advance. Thus, the adaptive Lasso hasan oracle property in the sense of Fan and Li (2001) and Fan and Peng (2004). In addition, under a partial orthogonality condition in which the covariates with zero coefficients are weakly correlated with the covariates with nonzero coefficients, marginal regression can be used to obtain the initial estimator. With this initial estimator, the adaptive Lasso has the oracle property even when the number of covariates is much larger than the sample size.