Leukocyte trafficking

Method for in vivo bioluminescence imaging as a valuable strategy for pre-clinical evaluation of leukocyte trafficking as shown here for small molecule α4-integrin antagonists as a promising therapeutic for IBD. Leukocyte trafficking is a therapeutic target in IBD. The integrins α4β7 and α4β1 regulate leukocyte migration into tissues and lymphoid organs. Current strategies rely on biologics, such as mAb, to inhibit leukocyte recruitment. Here we show the in vivo therapeutic effects of a small molecule α4-integrin antagonist (GSK223618A) in a leukocyte-trafficking model and a murine model of colitis. Leukocytes isolated from MLNs of transgenic β-actin-luc+ mice were injected i.v. into recipients with DSS-induced colitis. Recipient mice were orally gavaged with vehicle or an α4-integrin antagonist 1 h pre-adoptive transfer, followed by bioluminescence whole body and ex vivo organ imaging 4 h post-transfer. To confirm its therapeutic effect, the α4-integrin antagonist was given orally ...

Type I natural killer T (NKT) cells are innate-like T lymphocytes that recognize glycolipid antigens presented by the MHC class I-like protein CD1d. Agonistic activation of NKT cells leads to rapid pro-inflammatory and immune modulatory cytokine and chemokine responses. This property of NKT cells, in conjunction with their interactions with antigen-presenting cells, controls downstream innate and adaptive immune responses against cancers and infectious diseases, as well as in several inflammatory disorders. NKT cell properties are acquired during development in the thymus and by interactions with the host microbial consortium in the gut, the nature of which can be influenced by NKT cells. This latter property, together with the role of the host microbiota in cancer therapy, necessitates a new perspective. Hence, this review provides an initial approach to understanding NKT cells from an ecological evolutionary developmental biology (eco-evo-devo) perspective.

Aneurysmal subarachnoid hemorrhage (SAH) is a potentially devastating clinical problem. Despite advances in the diagnosis and treatment of SAH, outcome remains unfavorable. An increased inflammatory state, one that is characterized by enhanced leukocyte trafficking has been reported to contribute to neuronal injury in association with multiple brain insults, including hemorrhagic and ischemic stroke. This study was designed to investigate, in rats, the neuropathologic consequences of heightened leukocyte trafficking following SAH, induced via endovascular perforation of the anterior cerebral artery. Experiments focused on the initial 48 h post-SAH and sought to establish whether blockade of vascular adhesion protein-1 (VAP-1), with LJP-1586, was able to provide dose-dependent neuroprotection. Treatment with LJP-1586 was initiated at 6h post-SAH. An intravital microscopy and closed cranial window system, that permitted examination of temporal patterns of rhodamine-6G-labeled leukocyt...

Inflammatory bowel disease (IBD), encompassing Crohn's disease and ulcerative colitis, is associated with enhanced leukocyte infiltration to the gut, which is directly linked to the clinical aspects of these disorders. Thus, leukocyte trafficking is a major target for IBD therapy. Past and emerging techniques to study leukocyte trafficking bothin vitroandin vivohave expanded our knowledge of the leukocyte migration process and the role of inhibitors. Various strategies have been employed to target chemokine- and integrin-ligand interactions within the multistep adhesion cascade and the S1P/S1PR1 axis in leukocyte migration. Though there is an abundance of preclinical data demonstrating efficacy of leukocyte trafficking inhibitors, many have yet to be confirmed in clinical studies. Vigilance for toxicity and further research is required into this complex and emerging area of IBD therapy.

Cell migration plays important roles in embryonic development and inflammation, and this process is highly regulated to ensure tissue homeostasis. A number of barriers exist to prevent the inappropriate migration of leukocytes into healthy peripheral tissues, including retention of these cells in the inactive state and maintenance of the integrity and charge of the vascular endothelium. However, active signals also are likely to exist that can repulse cells or abolish existing cell migration. One such paradigm exists in the developing nervous system, where neuronal migration is mediated by a balance between chemoattractive and chemorepulsive signals. The ability of the guidance molecule netrin-1 to repulse or abolish attraction of neuronal cells expressing the UNC5b receptor makes it an attractive candidate for the regulation of inflammatory cell migration. Here, we show that netrin-1 is expressed on vascular endothelium, where it is regulated by infection and inflammatory cytokines...

Aneurysmal subarachnoid hemorrhage (SAH) is a potentially devastating clinical problem. Despite advances in the diagnosis and treatment of SAH, outcome remains unfavorable. An increased inflammatory state, one that is characterized by enhanced leukocyte trafficking has been reported to contribute to neuronal injury in association with multiple brain insults, including hemorrhagic and ischemic stroke. This study was designed to investigate, in rats, the neuropathologic consequences of heightened leukocyte trafficking following SAH, induced via endovascular perforation of the anterior cerebral artery. Experiments focused on the initial 48 h post-SAH and sought to establish whether blockade of vascular adhesion protein-1 (VAP-1), with LJP-1586, was able to provide dose-dependent neuroprotection. Treatment with LJP-1586 was initiated at 6h post-SAH. An intravital microscopy and closed cranial window system, that permitted examination of temporal patterns of rhodamine-6G-labeled leukocyt...

MRL/faslpr mice are affected by a systemic autoimmune disease that results in leukocyte recruitment to a wide range of vascular beds, including the cerebral microvasculature. The mechanisms responsible for the leukocyte trafficking to the brain in these animals are not known. Therefore, the aim of this study was to directly examine the cerebral microvasculature in MRL/faslpr mice and determine the molecular mechanisms responsible for this leukocyte recruitment. Intravital microscopy was used to assess leukocyte-endothelial cell interactions (rolling, adhesion) in the pial microcirculation of MRL+/+ (control) and MRL/faslpr mice at 8, 12, and 16 wk of age. Leukocyte rolling and adhesion were rarely observed in MRL+/+ mice of any age. MRL/faslpr mice displayed similar results at 8 and 12 wk. However, at 16 wk, significant increases in leukocyte rolling and adhesion were observed in these mice. Histological analysis revealed that the interacting cells were exclusively mononuclear. Leuk...

The lung has a unique structure consisting of three functionally different compartments (alveolar, interstitial, and vascular) situated in an extreme proximity. Current methods to localize lung leukocytes using bronchoalveolar lavage and/or lung perfusion have significant limitations for determination of location and phenotype of leukocytes. Here we present a novel method using in vivo antibody labeling to enable accurate compartmental localization/quantification and phenotyping of mouse lung leukocytes. Anesthetized C57BL/6 mice received combined in vivo intravenous and intratracheal labeling with fluorophore-conjugated anti-CD45 antibodies, and lung single-cell suspensions were analyzed by flow cytometry. The combined in vivo intravenous and intratracheal CD45 labeling enabled robust separation of the alveolar, interstitial, and vascular compartments of the lung. In naive mice, the alveolar compartment consisted predominantly of resident alveolar macrophages. The interstitial comp...

Directed cell migration is a prerequisite not only for the development of the central nervous system, but also for topically restricted, appropriate immune responses. This is crucial for host defense and immune surveillance. Attracting environmental cues guiding leukocyte cell traffic are likely to be complemented by repulsive cues, which actively abolish cell migration. One such a paradigm exists in the developing nervous system, where neuronal migration and axonal path finding is balanced by chemoattractive and chemorepulsive cues, such as the neuronal repulsive guidance molecule-A (RGM-A). As expressed at the inflammatory site, the role of RGM-A within the immune response remains unclear. Here we report that RGM-A ( i ) is expressed by epithelium and leukocytes (granulocytes, monocytes, and T/B lymphocytes); ( ii ) inhibits leukocyte migration by contact repulsion and chemorepulsion, depending on dosage, through its receptor neogenin; and ( iii ) suppresses the inflammatory respo...

This article presents a stochastic model of lymphocyte recruitment in inflamed brain microvessels. Recent studies about the inflammatory process of the brain that leads to multiple sclerosis have revealed that lymphocyte extravasation is a sequence of dynamical states, mediated by partially overlapped interactions of different adhesion molecules and activation factors. This study’s model of lymphocyte recruitment is based on process algebras for mobile systems. The biochemical system is modelled as a set of concurrent processes of the biochemical stochastic π-calculus. Processes are driven by suitable probability distributions that quantitatively describe the rates and the times at which reactions to simulations occur. The results of the model reproduce, within the estimated experimental errors, the functional behavior of the data obtained from laboratory measurements.

Leukocyte transendothelial migration is crucial for innate immunity and inflammation. Upon tissue damage or infection, leukocytes exit blood vessels by adhering to and probing vascular endothelial cells (VECs), breaching endothelial cell-cell junctions, and transmigrating across the endothelium. Transendothelial migration is a critical rate-limiting step in this process. Thus, leukocytes must quickly identify the most efficient route through VEC monolayers to facilitate a prompt innate immune response. Biomechanics play a decisive role in transendothelial migration, which involves intimate physical contact and force transmission between the leukocytes and the VECs. While quantifying these forces is still challenging, recent advances in imaging, microfabrication, and computation now make it possible to study how cellular forces regulate VEC monolayer integrity, enable efficient pathfinding, and drive leukocyte transmigration. Here we review these recent advances, paying particular at...

Appropriate regulation of IL-17 production in the host can mean the difference between effective control of pathogens and uncontrolled inflammation that causes tissue damage. Investigation of conventional CD4 T cells (Th17 cells) has yielded invaluable insights into IL-17 function and its regulation. More recently, we and others reported production of IL-17 from innate αβ+ T cell populations, which was shown to occur primarily via IL-23R signaling through the transcription factor STAT-3. In our current study, we identify promyelocytic leukemia zinc finger (PLZF)-expressing iNKT, CD4/CD8, and CD4/CD8 (DN) αβ+T cells, which produce IL-17 in response to TCR and IL-1 receptor ligation independently of STAT-3 signaling. Notably, this noncanonical pathway of IL-17 production may be important in mucosal defense and is by itself sufficient to control pathogenic infection at the ocular surface.

Method for in vivo bioluminescence imaging as a valuable strategy for pre-clinical evaluation of leukocyte trafficking as shown here for small molecule α4-integrin antagonists as a promising therapeutic for IBD. Leukocyte trafficking is a therapeutic target in IBD. The integrins α4β7 and α4β1 regulate leukocyte migration into tissues and lymphoid organs. Current strategies rely on biologics, such as mAb, to inhibit leukocyte recruitment. Here we show the in vivo therapeutic effects of a small molecule α4-integrin antagonist (GSK223618A) in a leukocyte-trafficking model and a murine model of colitis. Leukocytes isolated from MLNs of transgenic β-actin-luc+ mice were injected i.v. into recipients with DSS-induced colitis. Recipient mice were orally gavaged with vehicle or an α4-integrin antagonist 1 h pre-adoptive transfer, followed by bioluminescence whole body and ex vivo organ imaging 4 h post-transfer. To confirm its therapeutic effect, the α4-integrin antagonist was given orally ...

Septic encephalopathy (SE) is a critical factor determining sepsis mortality. Vascular inflammation is known to be involved in SE, but the molecular events that lead to the development of encephalopathy remain unclear. Using time-lapse in vivo two-photon laser scanning microscopy, we provide the first direct evidence that cecal ligation and puncture in septic mice induces microglial trafficking to sites adjacent to leukocyte adhesion on inflamed cerebral microvessels. Our data further demonstrate that septic injury increased the chemokine CXCL1 level in brain endothelial cells by activating endothelial P2RX7 and eventually enhanced the binding of Mac-1 (CD11b/CD18)-expressing leukocytes to endothelial ICAM-1. In turn, leukocyte adhesion upregulated endothelial CX3CL1, thereby triggering microglia trafficking to the injured site. The sepsis-induced increase in endothelial CX3CL1 was abolished in CD18 hypomorphic mutant mice. Inhibition of the P2RX7 pathway not only decreased endothel...

Chemokines are small molecular weight peptides responsible for adhesion, activation, and recruitment of leukocytes into tissues. Leukocytes are thought to influence follicular atresia, ovulation, and luteal function. Many studies in recent years have focused attention on the characterization of leukocyte populations within the ovary, the importance of leukocyte-ovarian cell interactions, and more recently, the mechanisms of ovarian leukocyte recruitment. Information about the role of chemokines and leukocyte trafficking (chemotaxis) during ovarian function is important to understanding paracrine-autocrine relationships shared between reproductive and immune systems. Recent advances regarding chemokine expression and leukocyte accumulation within the ovulatory follicle and the corpus luteum are the subject of this mini-review.

Invariant natural killer T (iNKT) cells are innate-like lymphocytes with unique signaling requirements for their development and differentiation. In this issue of JEM, Raynor et al. (https://doi.org/10.1084/jem.20191157) report that the Hippo signaling pathway controls the maturation and effector differentiation of iNKT cells by modulating cellular metabolism.