Dynamic Behavior of T Cells and Thymocytes in Lymphoid Organs as Revealed by Two-Photon Microscopy

AbstractThe initial application of two-photon imaging to the study of lymphoid tissues has provided a dramatic glimpse into how cells of the immune system move and interact in their native environments. In this review we summarize what we have learned so far and point out areas for future investigation using this approach

Intravital Imaging Reveals Distinct Dynamics for Natural Killer and CD8+ T Cells during Tumor Regression

SummaryRecognition of NKG2D ligands by natural killer (NK) cells plays an important role during antitumoral responses. To address how NKG2D engagement affects intratumoral NK cell dynamics, we performed intravital microscopy in a Rae-1β-expressing solid tumor. This NKG2D ligand drove NK cell accumulation, activation, and motility within the tumor. NK cells established mainly dynamic contacts with their targets during tumor regression. In sharp contrast, cytotoxic T lymphocytes (CTLs) formed stable contacts in tumors expressing their cognate antigen. Similar behaviors were observed during effector functions in lymph nodes. In vitro, contacts between NK cells and their targets were cytotoxic but did not elicit sustained calcium influx nor adhesion, whereas CTL contact stability was critically dependent on extracellular calcium entry. Altogether, our results offer mechanistic insight into how NK cells and CTLs can exert cytotoxic activity with remarkably different contact dynamics

Manipulating leukocyte interactions in vivo through optogenetic chemokine release.

Light-mediated release of signaling ligands, such as chemoattractants, growth factors, and cytokines is an attractive strategy for investigation and therapeutic targeting of leukocyte communication and immune responses. We introduce a versatile optogenetic method to control ligand secretion, combining UV-conditioned endoplasmic reticulum-to-Golgi trafficking and a furin-processing step. As proof of principle, we achieved light-triggered chemokine secretion and demonstrated that a brief pulse of chemokine release can mediate a rapid flux of leukocyte contacts with target cells in vitro and in vivo. This approach opens new possibilities for dynamic investigation of leukocyte communication in vivo and may confer the potential to control the local release of soluble mediators in the context of immune cell therapies.This work was supported by Institut Pasteur, INSERM, the European Research Council (starting grant LymphocyteContacts) (P.B.), and the Medical Research Council (RG73189) (M.S.)

Dissecting T Cell Contraction In Vivo Using a Genetically Encoded Reporter of Apoptosis

SummaryContraction is a critical phase of immunity whereby the vast majority of effector T cells die by apoptosis, sparing a population of long-lived memory cells. Where, when, and why contraction occurs has been difficult to address directly due in large part to the rapid clearance of apoptotic T cells in vivo. To circumvent this issue, we introduced a genetically encoded reporter for caspase-3 activity into naive T cells to identify cells entering the contraction phase. Using two-photon imaging, we found that caspase-3 activity in T cells was maximal at the peak of the response and was associated with loss of motility followed minutes later by cell death. We demonstrated that contraction is a widespread process occurring uniformly in all organs tested and targeting phenotypically diverse T cells. Importantly, we identified a critical window of time during which antigen encounters act to antagonize T cell apoptosis, supporting a causal link between antigen clearance and T cell contraction. Our results offer insight into a poorly explored phase of immunity and provide a versatile methodology to study apoptosis during the development or function of a variety of immune cells in vivo

Cosmological Large-scale Structures beyond Linear Theory in Modified Gravity

We consider the effect of modified gravity on the growth of large-scale structures at second order in perturbation theory. We show that modified gravity models changing the linear growth rate of fluctuations are also bound to change, although mildly, the mode coupling amplitude in the density and reduced velocity fields. We present explicit formulae which describe this effect. We then focus on models of modified gravity involving a scalar field coupled to matter, in particular chameleons and dilatons, where it is shown that there exists a transition scale around which the existence of an extra scalar degree of freedom induces significant changes in the coupling properties of the cosmic fields. We obtain the amplitude of this effect for realistic dilaton models at the tree-order level for the bispectrum, finding them to be comparable in amplitude to those obtained in the DGP model.Comment: 25 pages, 11 figure

Finite Number of States, de Sitter Space and Quantum Groups at Roots of Unity

This paper explores the use of a deformation by a root of unity as a tool to build models with a finite number of states for applications to quantum gravity. The initial motivation for this work was cosmological breaking of supersymmetry. We explain why the project was unsuccessful. What is left are some observations on supersymmetry for q-bosons, an analogy between black holes in de Sitter and properties of quantum groups, and an observation on a noncommutative quantum mechanics model with two degrees of freedom, depending on one parameter. When this parameter is positive, the spectrum has a finite number of states; when it is negative or zero, the spectrum has an infinite number of states. This exhibits a desirable feature of quantum physics in de Sitter space, albeit in a very simple, non-gravitational context.Comment: 25 pages, 5 figure

A Role for the Immediate Early Gene Product c-fos in Imprinting T Cells with Short-Term Memory for Signal Summation

T cells often make sequential contacts with multiple DCs in the lymph nodes and are likely to be equipped with mechanisms that allow them to sum up the successive signals received. We found that a period of stimulation as short as two hours could imprint on a T cell a “biochemical memory” of that activation signal that persisted for several hours. This was evidenced by more rapid induction of activation markers and earlier commitment to proliferation upon subsequent stimulation, even when that secondary stimulation occurred hours later. Upregulation of the immediate early gene product c-fos, a component of the AP-1 transcription factor, was maximal by 1–2 hours of stimulation, and protein levels remained elevated for several hours after stimulus withdrawal. Moreover, phosphorylated forms of c-fos that are stable and transcriptionally active persisted for a least a day. Upon brief antigenic stimulation in vivo, we also observed a rapid upregulation of c-fos that could be boosted by subsequent stimulation. Accumulation of phosphorylated c-fos may therefore serve as a biochemical fingerprint of previous suboptimal stimulation, leaving the T cell poised to rapidly resume its activation program upon its next encounter with an antigen-bearing DC

Standardized Whole-Blood Transcriptional Profiling Enables the Deconvolution of Complex Induced Immune Responses

SummarySystems approaches for the study of immune signaling pathways have been traditionally based on purified cells or cultured lines. However, in vivo responses involve the coordinated action of multiple cell types, which interact to establish an inflammatory microenvironment. We employed standardized whole-blood stimulation systems to test the hypothesis that responses to Toll-like receptor ligands or whole microbes can be defined by the transcriptional signatures of key cytokines. We found 44 genes, identified using Support Vector Machine learning, that captured the diversity of complex innate immune responses with improved segregation between distinct stimuli. Furthermore, we used donor variability to identify shared inter-cellular pathways and trace cytokine loops involved in gene expression. This provides strategies for dimension reduction of large datasets and deconvolution of innate immune responses applicable for characterizing immunomodulatory molecules. Moreover, we provide an interactive R-Shiny application with healthy donor reference values for induced inflammatory genes

Autoantibodies against type I IFNs in patients with life-threatening COVID-19

Interindividual clinical variability in the course of severe acute respiratory syndrome coronavirus 2 (SARS-CoV-2) infection is vast. We report that at least 101 of 987 patients with life-threatening coronavirus disease 2019 (COVID-19) pneumonia had neutralizing immunoglobulin G (IgG) autoantibodies (auto-Abs) against interferon-w (IFN-w) (13 patients), against the 13 types of IFN-a (36), or against both (52) at the onset of critical disease; a few also had auto-Abs against the other three type I IFNs. The auto-Abs neutralize the ability of the corresponding type I IFNs to block SARS-CoV-2 infection in vitro. These auto-Abs were not found in 663 individuals with asymptomatic or mild SARS-CoV-2 infection and were present in only 4 of 1227 healthy individuals. Patients with auto-Abs were aged 25 to 87 years and 95 of the 101 were men. A B cell autoimmune phenocopy of inborn errors of type I IFN immunity accounts for life-threatening COVID-19 pneumonia in at least 2.6% of women and 12.5% of men