The S1P-S1PR Axis in Neurological Disorders-Insights into Current and Future Therapeutic Perspectives.

Sphingosine 1-phosphate (S1P), derived from membrane sphingolipids, is a pleiotropic bioactive lipid mediator capable of evoking complex immune phenomena. Studies have highlighted its importance regarding intracellular signaling cascades as well as membrane-bound S1P receptor (S1PR) engagement in various clinical conditions. In neurological disorders, the S1P-S1PR axis is acknowledged in neurodegenerative, neuroinflammatory, and cerebrovascular disorders. Modulators of S1P signaling have enabled an immense insight into fundamental pathological pathways, which were pivotal in identifying and improving the treatment of human diseases. However, its intricate molecular signaling pathways initiated upon receptor ligation are still poorly elucidated. In this review, the authors highlight the current evidence for S1P signaling in neurodegenerative and neuroinflammatory disorders as well as stroke and present an array of drugs targeting the S1P signaling pathway, which are being tested in clinical trials. Further insights on how the S1P-S1PR axis orchestrates disease initiation, progression, and recovery may hold a remarkable potential regarding therapeutic options in these neurological disorders

A Sphingosine 1-Phosphate Gradient Is Linked to the Cerebral Recruitment of T Helper and Regulatory T Helper Cells during Acute Ischemic Stroke.

Emerging evidence suggests a complex relationship between sphingosine 1-phosphate (S1P) signaling and stroke. Here, we show the kinetics of S1P in the acute phase of ischemic stroke and highlight accompanying changes in immune cells and S1P receptors (S1PR). Using a C57BL/6 mouse model of middle cerebral artery occlusion (MCAO), we assessed S1P concentrations in the brain, plasma, and spleen. We found a steep S1P gradient from the spleen towards the brain. Results obtained by qPCR suggested that cells expressing the S1PR type 1 (S1P1+) were the predominant population deserting the spleen. Here, we report the cerebral recruitment of T helper (TH) and regulatory T (TREG) cells to the ipsilateral hemisphere, which was associated with differential regulation of cerebral S1PR expression patterns in the brain after MCAO. This study provides insight that the S1P-S1PR axis facilitates splenic T cell egress and is linked to the cerebral recruitment of S1PR+ TH and TREG cells. Further insights by which means the S1P-S1PR-axis orchestrates neuronal positioning may offer new therapeutic perspectives after ischemic stroke

Real-time deformability cytometry reveals sequential contraction and expansion during neutrophil priming.

It has become increasingly apparent that the biomechanical properties of neutrophils impact on their trafficking through the circulation and in particularly through the pulmonary capillary bed. The retention of polarized or shape-changed neutrophils in the lungs was recently proposed to contribute to acute respiratory distress syndrome pathogenesis. Accordingly, this study tested the hypothesis that neutrophil priming is coupled to morpho-rheological (MORE) changes capable of altering cell function. We employ real-time deformability cytometry (RT-DC), a recently developed, rapid, and sensitive way to assess the distribution of size, shape, and deformability of thousands of cells within seconds. During RT-DC analysis, neutrophils can be easily identified within anticoagulated "whole blood" due to their unique granularity and size, thus avoiding the need for further isolation techniques, which affect biomechanical cell properties. Hence, RT-DC is uniquely suited to describe the kinetics of MORE cell changes. We reveal that, following activation or priming, neutrophils undergo a short period of cell shrinking and stiffening, followed by a phase of cell expansion and softening. In some contexts, neutrophils ultimately recover their un-primed mechanical phenotype. The mechanism(s) underlying changes in human neutrophil size are shown to be Na+ /H+ antiport-dependent and are predicted to have profound implications for neutrophil movement through the vascular system in health and disease

Immune surveillance and humoral immune responses in kidney transplantation - A look back at T follicular helper cells.

Peer reviewed: TrueT follicular helper cells comprise a specialized, heterogeneous subset of immune-competent T helper cells capable of influencing B cell responses in lymphoid tissues. In physiology, for example in response to microbial challenges or vaccination, this interaction chiefly results in the production of protecting antibodies and humoral memory. In the context of kidney transplantation, however, immune surveillance provided by T follicular helper cells can take a life of its own despite matching of human leukocyte antigens and employing the latest immunosuppressive regiments. This puts kidney transplant recipients at risk of subclinical and clinical rejection episodes with a potential risk for allograft loss. In this review, the current understanding of immune surveillance provided by T follicular helper cells is briefly described in physiological responses to contrast those pathological responses observed after kidney transplantation. Sensitization of T follicular helper cells with the subsequent emergence of detectable donor-specific human leukocyte antigen antibodies, non-human leukocyte antigen antibodies their implication for kidney transplantation and lessons learnt from other transplantation "settings" with special attention to antibody-mediated rejection will be addressed

An unbiased proteomic approach to identifying cell surface markers in neutrophils

Introduction: Efferocytosis refers to the engulfment of dead cells by phagocytes such as neutrophils and macrophages and culminates in the beneficial removal of inflammatory cargo and auto-reactive material. While many of the mechanisms involved in efferocytosis have been described, the critically important ‘apoptotic-cell-associated molecular patterns’ have yet to be identified. Methods: Human whole blood samples were obtained from healthy volunteers. Neutrophils were isolated and subjected to a temperature shift to facilitate a wave of synchronised apoptosis. The plasma membrane proteome was assessed using tandem-mass-tag liquid chromatography-mass spectrometry (TMT-LC/MS) of apoptotic and time- and donor- matched non-apoptotic neutrophils, which allowed the identification of the plasma membrane proteins expressed or downregulated during apoptosis. In parallel, a method was developed to quantify efferocytosis. Briefly, apoptotic neutrophils or genome-modified neutrophil-like cells overexpressing the proteins identified to be up- regulated on apoptotic neutrophils, were fed to the monocytic cell line THP-1, which had been previously primed with phorbol-12-myristate-13-acetate (PMA) to acquire the functional properties of human macrophages. Efferocytosis was assessed by confocal microscopy and flow cytometry. Results: The late-stage apoptotic neutrophil plasma membrane profile identified several protein targets to be either up- or downregulated. The expression kinetics over time of ‘targets’ were then validated using flow cytometry. TIMD-4, a never previously described protein in (human) neutrophils, is actively up- regulated in preparation for apoptosis, and links to the phagocyte’s recognition and removal abilities of apoptotic cells, suggesting that TIMD-4 is a novel ‘eat me’ signal produced by apoptotic neutrophils. Conclusions: TMT-LC/MS can be successfully used to determine functionally relevant changes in the neutrophil plasma membrane, and has provided novel insights into the processes underlying efferocytosis of human neutrophils.AstraZeneca/MedImmune (RCAG/891) NIHR Cambridge Biomedical Research Centre German Academic Scholarship Foundation (Studienstiftung des deutschen Volkes

What’s happening where when SARS-CoV-2 infects: are TLR7 and MAFB sufficient to explain patient vulnerability?

The present COVID-19 pandemic has revealed that several characteristics render patients especially prone to developing severe COVID-19 disease, i.e., the male sex, obesity, and old age. An explanation for the observed pattern of vulnerability has been proposed which is based on the concept of low sensitivity of the TLR7-signaling pathway at the time of infection as a common denominator of vulnerable patient groups. We will discuss whether the concept of established TLR-tolerance in macrophages and dendritic cells of the obese and elderly prior to infection can explain not only the vulnerability of these two demographic groups towards development of a severe infection with SARS-CoV-2, but also the observed cytokine response in these vulnerable patients, which is skewed towards pro-inflammatory cytokines with a missing interferon signature

The S1P-S1PR Axis in Neurological Disorders-Insights into Current and Future Therapeutic Perspectives.

Sphingosine 1-phosphate (S1P), derived from membrane sphingolipids, is a pleiotropic bioactive lipid mediator capable of evoking complex immune phenomena. Studies have highlighted its importance regarding intracellular signaling cascades as well as membrane-bound S1P receptor (S1PR) engagement in various clinical conditions. In neurological disorders, the S1P-S1PR axis is acknowledged in neurodegenerative, neuroinflammatory, and cerebrovascular disorders. Modulators of S1P signaling have enabled an immense insight into fundamental pathological pathways, which were pivotal in identifying and improving the treatment of human diseases. However, its intricate molecular signaling pathways initiated upon receptor ligation are still poorly elucidated. In this review, the authors highlight the current evidence for S1P signaling in neurodegenerative and neuroinflammatory disorders as well as stroke and present an array of drugs targeting the S1P signaling pathway, which are being tested in clinical trials. Further insights on how the S1P-S1PR axis orchestrates disease initiation, progression, and recovery may hold a remarkable potential regarding therapeutic options in these neurological disorders

The counter-intuitive role of the neutrophil in the acute respiratory distress syndrome.

INTRODUCTION: Neutrophils are the primary effectors of the innate immune system but are profoundly histotoxic cells. The acute respiratory distress syndrome (ARDS) is considered to be a prime example of neutrophil-mediated tissue injury. SOURCES OF DATA: The information presented in this review is acquired from the published neutrophil cell biology literature and the longstanding interest of the senior authors in ARDS pathogenesis and clinical management. AREAS OF AGREEMENT: Investigators in the field would agree that neutrophils accumulate in high abundance in the pulmonary microcirculation, lung interstitium and alveolar airspace of patients with ARDS. ARDS is also associated with systemic neutrophil priming and delayed neutrophil apoptosis and clearance of neutrophils from the lungs. In animal models, reducing circulating neutrophil numbers ameliorates lung injury. AREAS OF CONTROVERSY: Areas of uncertainty include how neutrophils get stuck in the narrow pulmonary capillary network-whether this reflects changes in the mechanical properties of primed neutrophils alone or additional cell adhesion molecules, the role of neutrophil sub-sets or polarization states including pro-angiogenic and low-density neutrophils, whether neutrophil extracellular trap (NET) formation is beneficial (through bacterial capture) or harmful and the potential for neutrophils to participate in inflammatory resolution. The latter may involve the generation of specialized pro-resolving molecules (SPMs) and MMP-9, which is required for adequate matrix processing. GROWING POINTS: Different and possibly stable endotypes of ARDS are increasingly being recognized, yet the relative contribution of the neutrophil to these endotypes is uncertain. There is renewed and intense interest in understanding the complex 'new biology' of the neutrophil, specifically whether this cell might be a valid therapeutic target in ARDS and other neutrophil-driven diseases and developing understanding of ways to enhance the beneficial role of the neutrophil in the resolution phase of ARDS. AREAS TIMELY FOR DEVELOPING RESEARCH: Aside from treatment of the precipitating causes of ARDS, and scrupulous fluid, infection and ventilation management, there are no pharmacological interventions for ARDS; this represents an urgent and unmet need. Therapies aimed at reducing overall neutrophil numbers risk secondary infection; hence better ways are needed to reverse the processes of neutrophil priming activation, hyper-secretion and delayed apoptosis while enhancing the pro-resolution functions of the neutrophil.The research in the authors laboratories is funded by the MRC, British Lung Foundation, Wellcome Trust, NIHR Cambridge Biomedical Research Centre, Gates-Cambridge Scholarship Programme, Addenbrooke’s Charitable Trust, NIH Oxford-Cambridge Scholarship Programme, Cancer Research UK, Wolfson Foundation and non-commercial grants from MedImmune, Bristol Myer Squibs and GlaxoSmithKline

The counter-intuitive role of the neutrophil in the acute respiratory distress syndrome.

INTRODUCTION: Neutrophils are the primary effectors of the innate immune system but are profoundly histotoxic cells. The acute respiratory distress syndrome (ARDS) is considered to be a prime example of neutrophil-mediated tissue injury. SOURCES OF DATA: The information presented in this review is acquired from the published neutrophil cell biology literature and the longstanding interest of the senior authors in ARDS pathogenesis and clinical management. AREAS OF AGREEMENT: Investigators in the field would agree that neutrophils accumulate in high abundance in the pulmonary microcirculation, lung interstitium and alveolar airspace of patients with ARDS. ARDS is also associated with systemic neutrophil priming and delayed neutrophil apoptosis and clearance of neutrophils from the lungs. In animal models, reducing circulating neutrophil numbers ameliorates lung injury. AREAS OF CONTROVERSY: Areas of uncertainty include how neutrophils get stuck in the narrow pulmonary capillary network-whether this reflects changes in the mechanical properties of primed neutrophils alone or additional cell adhesion molecules, the role of neutrophil sub-sets or polarization states including pro-angiogenic and low-density neutrophils, whether neutrophil extracellular trap (NET) formation is beneficial (through bacterial capture) or harmful and the potential for neutrophils to participate in inflammatory resolution. The latter may involve the generation of specialized pro-resolving molecules (SPMs) and MMP-9, which is required for adequate matrix processing. GROWING POINTS: Different and possibly stable endotypes of ARDS are increasingly being recognized, yet the relative contribution of the neutrophil to these endotypes is uncertain. There is renewed and intense interest in understanding the complex 'new biology' of the neutrophil, specifically whether this cell might be a valid therapeutic target in ARDS and other neutrophil-driven diseases and developing understanding of ways to enhance the beneficial role of the neutrophil in the resolution phase of ARDS. AREAS TIMELY FOR DEVELOPING RESEARCH: Aside from treatment of the precipitating causes of ARDS, and scrupulous fluid, infection and ventilation management, there are no pharmacological interventions for ARDS; this represents an urgent and unmet need. Therapies aimed at reducing overall neutrophil numbers risk secondary infection; hence better ways are needed to reverse the processes of neutrophil priming activation, hyper-secretion and delayed apoptosis while enhancing the pro-resolution functions of the neutrophil.The research in the authors laboratories is funded by the MRC, British Lung Foundation, Wellcome Trust, NIHR Cambridge Biomedical Research Centre, Gates-Cambridge Scholarship Programme, Addenbrooke’s Charitable Trust, NIH Oxford-Cambridge Scholarship Programme, Cancer Research UK, Wolfson Foundation and non-commercial grants from MedImmune, Bristol Myer Squibs and GlaxoSmithKline

Regulation of ICAM-1 in human neutrophils.

Intercellular cell adhesion molecule 1 (ICAM-1) is a cell surface glycoprotein with a vital role in the immune response to pathogens. The expression pattern of ICAM-1 is wide-ranging, encompassing endothelial cells, epithelial cells and neutrophils. Recent work has characterized the role of ICAM-1 in murine neutrophils, but the function of human neutrophil ICAM-1 is incompletely understood. Herein, we investigated the expression and role of ICAMs in human neutrophils in vitro and in vivo. Our findings show clear expression of ICAM-1, -3 and -4 on peripheral blood-derived neutrophils and demonstrate that the pathogen-associated molecular pattern (PAMP) lipoteichoic acid (LTA) is an inducer of ICAM-1 expression in vitro. In vivo, neutrophils obtained from the pleural cavity of patients with a parapneumonic effusion display enhanced expression of ICAM-1 compared to peripheral blood- and oral cavity-derived neutrophils. Moreover, migration of peripheral blood-derived neutrophils across endothelial cells can upregulate neutrophil ICAM-1 expression. These findings indicate that PAMPs and/or cytokines, alongside transmigration, enhance neutrophil ICAM-1 expression at sites of inflammation. Mechanistically we observed that ICAM-1high neutrophils display elevated S. aureus phagocytic capacity. However, unlike murine neutrophils, ICAM-1 intracellular signaling in human neutrophils was not essential for phagocytosis of S. aureus and reactive oxygen species (ROS) generation. Taken together, these results have important implications for the regulation of neutrophil-mediated pathogen clearance