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Background: Beyond their fundamental role in homeostasis and host defense, neutrophilic granulocytes (neutrophils) are increasingly recognized to contribute to the pathogenesis of malignant tumors. Recently, aging of mature neutrophils in the systemic circulation has been identified to be critical for these immune cells to properly unfold their homeostatic and anti-infectious functional properties. The role of neutrophil aging in cancer remains largely obscure., Methods: Employing advanced in vivo microscopy techniques in different animal models of cancer as well as utilizing pulse-labeling and cell transfer approaches, various ex vivo / in vitro assays, and human data, we sought to define the functional relevance of neutrophil aging in cancer., Results: Here, we show that signals released during early tumor growth accelerate biological aging of circulating neutrophils, hence uncoupling biological from chronological aging of these immune cells. This facilitates the accumulation of highly reactive neutrophils in malignant lesions and endows them with potent protumorigenic functions, thus promoting tumor progression. Counteracting uncoupled biological aging of circulating neutrophils by blocking the chemokine receptor CXCR2 effectively suppressed tumor growth., Conclusions: Our data uncover a self-sustaining mechanism of malignant neoplasms in fostering protumorigenic phenotypic and functional changes in circulating neutrophils. Interference with this aberrant process might therefore provide a novel, already pharmacologically targetable strategy for cancer immunotherapy., Competing Interests: Competing interests: None declared., (© Author(s) (or their employer(s)) 2021. Re-use permitted under CC BY. Published by BMJ.)

Background: The incidence of acute cardiovascular complications is highly time-of-day dependent. However, the mechanisms driving rhythmicity of ischemic vascular events are unknown. Although enhanced numbers of leukocytes have been linked to an increased risk of cardiovascular complications, the role that rhythmic leukocyte adhesion plays in different vascular beds has not been studied., Methods: We evaluated leukocyte recruitment in vivo by using real-time multichannel fluorescence intravital microscopy of a tumor necrosis factor-α-induced acute inflammation model in both murine arterial and venous macrovasculature and microvasculature. These approaches were complemented with genetic, surgical, and pharmacological ablation of sympathetic nerves or adrenergic receptors to assess their relevance for rhythmic leukocyte adhesion. In addition, we genetically targeted the key circadian clock gene Bmal1 (also known as Arntl ) in a lineage-specific manner to dissect the importance of oscillations in leukocytes and components of the vessel wall in this process., Results: In vivo quantitative imaging analyses of acute inflammation revealed a 24-hour rhythm in leukocyte recruitment to arteries and veins of the mouse macrovasculature and microvasculature. Unexpectedly, although in arteries leukocyte adhesion was highest in the morning, it peaked at night in veins. This phase shift was governed by a rhythmic microenvironment and a vessel type-specific oscillatory pattern in the expression of promigratory molecules. Differences in cell adhesion molecules and leukocyte adhesion were ablated when disrupting sympathetic nerves, demonstrating their critical role in this process and the importance of β 2 -adrenergic receptor signaling. Loss of the core clock gene Bmal1 in leukocytes, endothelial cells, or arterial mural cells affected the oscillations in a vessel type-specific manner. Rhythmicity in the intravascular reactivity of adherent leukocytes resulted in increased interactions with platelets in the morning in arteries and in veins at night with a higher predisposition to acute thrombosis at different times as a consequence., Conclusions: Together, our findings point to an important and previously unrecognized role of artery-associated sympathetic innervation in governing rhythmicity in vascular inflammation in both arteries and veins and its potential implications in the occurrence of time-of-day-dependent vessel type-specific thrombotic events.

Under steady-state conditions, aged neutrophils are removed from the circulation in bone marrow, liver, and spleen, thereby maintaining myeloid cell homeostasis. The fate of these aged immune cells under inflammatory conditions, however, remains largely obscure. Here, we demonstrate that in the acute inflammatory response during endotoxemia, aged neutrophils cease returning to the bone marrow and instead rapidly migrate to the site of inflammation. Having arrived in inflamed tissue, aged neutrophils were found to exhibit a higher phagocytic activity as compared with the subsequently recruited nonaged neutrophils. This distinct behavior of aged neutrophils under inflammatory conditions is dependent on specific age-related changes in their molecular repertoire that enable these "experienced" immune cells to instantly translate inflammatory signals into immune responses. In particular, aged neutrophils engage Toll-like receptor-4- and p38 MAPK-dependent pathways to induce conformational changes in β2 integrins that allow these phagocytes to effectively accomplish their mission in the front line of the inflammatory response. Hence, ageing in the circulation might represent a critical process for neutrophils that enables these immune cells to properly unfold their functional properties for host defense., (© 2016 by The American Society of Hematology.)

In vitro studies suggest that leukocytes locomote in an ameboid fashion independently of pericellular proteolysis. Whether this motility pattern applies for leukocyte migration in inflamed tissue is still unknown. In vivo microscopy on the inflamed mouse cremaster muscle revealed that blockade of serine proteases or of matrix metalloproteinases (MMPs) significantly reduces intravascular accumulation and transmigration of neutrophils. Using a novel in vivo chemotaxis assay, perivenular microinjection of inflammatory mediators induced directional interstitial migration of neutrophils. Blockade of actin polymerization, but not of actomyosin contraction abolished neutrophil interstitial locomotion. Multiphoton laser scanning in vivo microscopy showed that the density of the interstitial collagen network increases in inflamed tissue, thereby providing physical guidance to infiltrating neutrophils. Although neutrophils locomote through the interstitium without pericellular collagen degradation, inhibition of MMPs, but not of serine proteases, diminished their polarization and interstitial locomotion. In this context, blockade of MMPs was found to modulate expression of adhesion/signaling molecules on neutrophils. Collectively, our data indicate that serine proteases are critical for neutrophil extravasation, whereas these enzymes are dispensable for neutrophil extravascular locomotion. By contrast, neutrophil interstitial migration strictly relies on actin polymerization and does not require the pericellular degradation of collagen fibers but is modulated by MMPs.

Effective immune responses require the directed migration of leukocytes from the vasculature to the site of injury or infection. How immune cells “find” their site of extravasation remains largely obscure. Here, we identified a previously unrecognized role of platelets as pathfinders guiding leukocytes to their exit points in the microvasculature: upon onset of inflammation, circulating platelets were found to immediately adhere at distinct sites in venular microvessels enabling these cellular blood components to capture neutrophils and, in turn, inflammatory monocytes via CD40-CD40L-dependent interactions. In this cellular crosstalk, ligation of PSGL-1 by P-selectin leads to ERK1/2 MAPK-dependent conformational changes of leukocyte integrins, which promote the successive extravasation of neutrophils and monocytes to the perivascular tissue. Conversely, blockade of this cellular partnership resulted in misguided, inefficient leukocyte responses. Our experimental data uncover a platelet-directed, spatiotemporally organized, multicellular crosstalk that is essential for effective trafficking of leukocytes to the site of inflammation. [ABSTRACT FROM AUTHOR]

It has been suggested that engineered nanomaterials (ENM), once arrived in the circulation, may affect the cardiovascular system. The aim of thisin vivostudy was to screen major cardiovascular effects of acute systemic administration of a panel of five nanomaterials, TiO2anatase (NM-101), TiO2rutile (NM-104), ZnO (NM-110), SiO2(NM-200) and Ag (NM-300). Mice were anesthetized and the ENM were injected at a dose of 1 mg/kg via a catheter placed in the left femoral artery. Hemodynamic parameters were determined by invasive measurement of blood pressure and non-invasive measurement of heart rate. Ten minutes after injection of the ENM, the formation of light/dye-induced thrombi was assessed in the cremasteric microcirculation by intravital microscopy. In addition, the numbers of rolling, firmly adherent and transmigrated leukocytes were recorded in postcapillary cremasteric venules over a time period of 120 min after injection of ENM by intravital microscopy. The systemic administration of a single dose of the ENM tested did not dramatically alter hemodynamic parameters or affect early steps of leukocyte recruitment. However, the presence of circulating TiO2anatase, but not of TiO2rutile, SiO2, ZnO or Ag nanoparticles, significantly accelerated thrombus formation in the murine microcirculation. Moreover, TiO2anatase but not TiO2rutile nanoparticles increased murine platelet aggregationin vitro. Taken together, only one of the five systemically administered ENM, TiO2anatase, affected hemostasis, whereas none of the ENM tested in this screening study dramatically modulated hemodynamic parameters or early steps of leukocyte recruitment. [ABSTRACT FROM PUBLISHER]

The alkaloid narciclasine has been characterized extensively as an anticancer compound. Accumulating evidence suggests that narciclasine has anti-inflammatory potential; however, the underlying mechanism remains poorly understood. We hypothesized that narciclasine affects the activation of endothelial cells (ECs), a hallmark of inflammatory processes, which is a prerequisite for leukocyte-EC interaction. Thus, we aimed to investigate narciclasine's action on this process in vivo and to analyze the underlying mechanisms in vitro. In a murine peritonitis model, narciclasine reduced leukocyte infiltration, proinflammatory cytokine expression, and inflammation-associated abdominal pain. Moreover, narciclasine decreased rolling and blocked adhesion and transmigration of leukocytes in vivo. In cultured ECs, narciclasine inhibited the expression of cell adhesion molecules intercellular adhesion molecule-1, vascular cell adhesion molecule-1, and E-selectin and blocked crucial steps of the NF-κB activation cascade: NF-κB promotor activity, p65 nuclear translocation, inhibitor of κB α (IκBα) phosphorylation and degradation, and IκBα kinase β and TGF-β-activated kinase 1 phosphorylation. Interestingly, these effects were based on the narciclasine-triggered loss of TNF receptor 1 (TNFR1). Our study highlights narciclasine as an interesting anti-inflammatory compound that effectively inhibits the interaction of leukocytes with ECs by blocking endothelial activation processes. Most importantly, we showed that the observed inhibitory action of narciclasine on TNF-triggered signaling pathways is based on the loss of TNFR1. [ABSTRACT FROM AUTHOR]