Illuminating the Landscape of In Vivo Immunity Insights from Dynamic In Situ Imaging of Secondary Lymphoid Tissues

AbstractA central feature of the immune system is the migratory behavior of its cellular components. Thus, fully understanding the generation and maintenance of immune responses must include consideration of how hematopoietic cells home to, interact within, and exit from secondary lymphoid organs as well as peripheral tissues. Recent advances in in situ imaging techniques now permit direct observation of these events in their physiologic settings with high spatiotemporal resolution. This review summarizes progress in this area of investigation from a lymphocentric perspective. We highlight controversies, point out key unanswered questions, and briefly outline what we believe are some of the near-term directions that in situ microscopic analysis of the immune system will take

Dynamic imaging of dendritic cell extension into the small bowel lumen in response to epithelial cell TLR engagement

Cells lining the gastrointestinal tract serve as both a barrier to and a pathway for infectious agent entry. Dendritic cells (DCs) present in the lamina propria under the columnar villus epithelium of the small bowel extend processes across this epithelium and capture bacteria, but previous studies provided limited information on the nature of the stimuli, receptors, and signaling events involved in promoting this phenomenon. Here, we use immunohistochemical as well as dynamic explant and intravital two-photon imaging to investigate this issue. Analysis of CD11c–enhanced green fluorescent protein (EGFP) or major histocompatibility complex CII-EGFP mice revealed that the number of trans-epithelial DC extensions, many with an unusual “balloon” shape, varies along the length of the small bowel. High numbers of such extensions were found in the proximal jejunum, but only a few were present in the terminal ileum. The extensions in the terminal ileum markedly increased upon the introduction of invasive or noninvasive Salmonella organisms, and chimeric mouse studies revealed the key role of MyD88-dependent Toll-like receptor (TLR) signaling by nonhematopoietic (epithelial) elements in the DC extension response. Collectively, these findings support a model in which epithelial cell TLR signaling upon exposure to microbial stimuli induces active DC sampling of the gut lumen at sites distant from organized lymphoid tissues

In Vivo Cross-Priming of MHC Class I–Restricted Antigens Requires the TAP Transporter

AbstractRecent in vitro evidence suggests two alternative mechanisms by which bone marrow–derived APCs may process exogenous antigens for presentation to CTL in vivo, a phenomenon termed cross-priming. Although in vitro studies have suggested that both TAP-dependent and TAP-independent pathways exist, we have now demonstrated an absolute requirement for a functional TAP for cross-priming to occur in vivo. Bone marrow chimeras reconstituted with marrow from TAP-defective donors develop functional CD8+ CTL, but have APCs with disrupted TAP function. In such chimeras, in vivo priming of naive CTL was observed when antigen was targeted to the ER in a TAP-independent fashion, but cross-priming could not be demonstrated. These results support the TAP-dependent mechanism of cross-priming

Natural killer cell behavior in lymph nodes revealed by static and real-time imaging

Natural killer (NK) cells promote dendritic cell (DC) maturation and influence T cell differentiation in vitro. To better understand the nature of the putative interactions among these cells in vivo during the early phases of an adaptive immune response, we have used immunohistochemical analysis and dynamic intravital imaging to study NK cell localization and behavior in lymph nodes (LNs) in the steady state and shortly after infection with Leishmania major. In the LNs of naive mice, NK cells reside in the medulla and the paracortex, where they closely associate with DCs. In contrast to T cells, intravital microscopy revealed that NK cells in the superficial regions of LNs were slowly motile and maintained their interactions with DCs over extended times in the presence or absence of immune-activating signals. L. major induced NK cells to secrete interferon-γ and to be recruited to the paracortex, where concomitant CD4 T cell activation occurred. Therefore, NK cells form a reactive but low mobile network in a strategic area of the LN where they can receive inflammatory signals, interact with DCs, and regulate colocalized T cell responses

Precision luminosity measurement in proton-proton collisions at root S=13 TeV in 2015 and 2016 at CMS

The measurement of the luminosity recorded by the CMS detector installed at LHC interaction point 5, using proton-proton collisions at root S = 13 TeV in 2015 and 2016, is reported. The absolute luminosity scale is measured for individual bunch crossings using beam-separation scans (the van der Meer method), with a relative precision of 1.3 and 1.0% in 2015 and 2016, respectively. The dominant sources of uncertainty are related to residual differences between the measured beam positions and the ones provided by the operational settings of the LHC magnets, the factorizability of the proton bunch spatial density functions in the coordinates transverse to the beam direction, and the modeling of the effect of electromagnetic interactions among protons in the colliding bunches. When applying the van der Meer calibration to the entire run periods, the integrated luminosities when CMS was fully operational are 2.27 and 36.3 fb(-1) in 2015 and 2016, with a relative precision of 1.6 and 1.2%, respectively. These are among the most precise luminosity measurements at bunched-beam hadron colliders.Peer reviewe

Measurement of inclusive and differential cross sections for single top quark production in association with a W boson in proton-proton collisions at s \sqrt{s} = 13 TeV

International audienceMeasurements of the inclusive and normalised differential cross sections are presented for the production of single top quarks in association with a W boson in proton-proton collisions at a centre-of-mass energy of 13 TeV. The data used were recorded with the CMS detector at the LHC during 2016–2018, and correspond to an integrated luminosity of 138 fb$^{−1}$. Events containing one electron and one muon in the final state are analysed. For the inclusive measurement, a multivariate discriminant, exploiting the kinematic properties of the events is used to separate the signal from the dominant $\textrm{t}\overline{\textrm{t}}$ background. A cross section of $79.2\pm 0.9{\left(\textrm{stat}\right)}_{-8.0}^{+7.7}\left(\textrm{syst}\right)\pm 1.2\left(\textrm{lumi}\right)$ pb is obtained, consistent with the predictions of the standard model. For the differential measurements, a fiducial region is defined according to the detector acceptance, and the requirement of exactly one jet coming from the fragmentation of a bottom quark. The resulting distributions are unfolded to particle level and agree with the predictions at next-to-leading order in perturbative quantum chromodynamics.[graphic not available: see fulltext