Modulation of neutrophil recruitment and function is crucial for targeting inflammatory cells to sites of infection to combat invading pathogens while, at the same time, limiting host tissue injury ...or autoimmunity. The underlying mechanisms regulating recruitment of neutrophils, 1 of the most abundant inflammatory cells, have gained increasing interest over the years. The previously described classical recruitment cascade of leukocytes has been extended to include capturing, rolling, adhesion, crawling, and transmigration, as well as a reverse-transmigration step that is crucial for balancing immune defense and control of remote organ endothelial leakage. Current developments in the field emphasize the importance of cellular interplay, tissue environmental cues, circadian rhythmicity, detection of neutrophil phenotypes, differential chemokine sensing, and contribution of distinct signaling components to receptor activation and integrin conformations. The use of therapeutics modulating neutrophil activation responses, as well as mutations causing dysfunctional neutrophil receptors and impaired signaling cascades, have been defined in translational animal models. Human correlates of such mutations result in increased susceptibility to infections or organ damage. This review focuses on current advances in the understanding of the regulation of neutrophil recruitment and functionality and translational implications of current discoveries in the field with a focus on acute inflammation and sepsis.
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Neutrophils and neutrophil-like cells are the major pathogen-fighting immune cells in organisms ranging from slime molds to mammals. Central to their function is their ability to be recruited to ...sites of infection, to recognize and phagocytose microbes, and then to kill pathogens through a combination of cytotoxic mechanisms. These include the production of reactive oxygen species, the release of antimicrobial peptides, and the recently discovered expulsion of their nuclear contents to form neutrophil extracellular traps. Here we discuss these primordial neutrophil functions, which also play key roles in tissue injury, by providing details of neutrophil cytotoxic functions and congenital disorders of neutrophils. In addition, we present more recent evidence that interactions between neutrophils and adaptive immune cells establish a feed-forward mechanism that amplifies pathologic inflammation. These newly appreciated contributions of neutrophils are described in the setting of several inflammatory and autoimmune diseases.
Integrins are the principal cell adhesion receptors that mediate leukocyte migration and activation in the immune system. These receptors signal bidirectionally through the plasma membrane in ...pathways referred to as inside-out and outside-in signaling. Each of these pathways is mediated by conformational changes in the integrin structure. Such changes allow high-affinity binding of the receptor with counter-adhesion molecules on the vascular endothelium or extracellular matrix and lead to association of the cytoplasmic tails of the integrins with intracellular signaling molecules. Leukocyte functional responses resulting from outside-in signaling include migration, proliferation, cytokine secretion, and degranulation. Here, we review the key signaling events that occur in the inside-out versus outside-in pathways, highlighting recent advances in our understanding of how integrins are activated by a variety of stimuli and how they mediate a diverse array of cellular responses.
Neutrophils are recruited from the blood to sites of sterile inflammation, where they are involved in wound healing but can also cause tissue damage. During sterile inflammation, necrotic cells ...release pro-inflammatory molecules including formylated peptides. However, the signaling pathway triggered by formylated peptides to integrin activation and leukocyte recruitment is unknown. By using spinning-disk confocal intravital microscopy, we examined the molecular mechanisms of leukocyte recruitment to sites of focal hepatic necrosis in vivo. We demonstrated that the Bruton’s tyrosine kinase (Btk) was required for multiple Mac-1 activation events involved in neutrophil recruitment and functions during sterile inflammation triggered by fMLF. The Src family kinase Hck, Wiskott-Aldrich-syndrome protein, and phospholipase Cγ2 were also involved in this pathway required for fMLF-triggered Mac-1 activation and neutrophil recruitment. Thus, we have identified a neutrophil Btk signalosome that is involved in a signaling pathway triggered by formylated peptides leading to the selective activation of Mac-1 and neutrophil recruitment during sterile inflammation.
•Btk is required for neutrophil recruitment during sterile inflammation•Btk is required for selective fMLF-triggered Mac-1, but not LFA-1, activation•Hck, WASp, and PLCγ2 are key signaling molecules in the fMLF-triggered pathway•Btk is required for integrin-mediated outside-in signaling and FcRγ-mediated functions
The β2-integrin Mac-1 is crucial for neutrophil recruitment during sterile inflammation. Zarbock and colleagues demonstrate that the Btk signalosome—consisting of Hck, Btk, WASp, and Plcγ2—is indispensible for Mac-1-dependent functions.
Since the first example of conditional gene targeting in mice in 1994, the use of Cre recombinase and loxP flanked sequences has become an invaluable technique to generate tissue and temporal ...specific gene knockouts. The number of mouse strains expressing floxed-gene sequences, and tissue-specific or temporal-specific Cre-recombinase that have been reported in the literature has grown exponentially. However, increased use of this technology has highlighted several problems that can impact the interpretation of any phenotype observed in these mouse models. In particular, accurate knowledge of the specificity of Cre expression in each strain is critical in order to make conclusions about the role of specific cell types in the phenotypes observed. Cre-mediated deletion specificity and efficiency have been described in many different ways in the literature, making direct comparisons between these Cre strains impossible. Here we report crossing thirteen different myeloid-Cre mouse strains to ROSA-EYFP reporter mice and assaying YFP expression in a variety of naïve unstimulated hematopoietic cells, in parallel. By focusing on myeloid subsets, we directly compare the relative efficiency and specificity of myeloid deletion in these strains under steady-state conditions.
•Review of available myeloid-Cre deleting mouse strains•Parallel analysis of Cre activity in hematopoietic cells of thirteen myeloid-Cre mouse strains.•EYFP-ROSA reporter mice used to assay Cre activity.
Polymorphonuclear neutrophils (PMNs) are increasingly recognized to influence solid tumor development, but why their effects are so context dependent and even frequently divergent remains poorly ...understood. Using an autochthonous mouse model of uterine cancer and the administration of respiratory hyperoxia as a means to improve tumor oxygenation, we provide in vivo evidence that hypoxia is a potent determinant of tumor-associated PMN phenotypes and direct PMN-tumor cell interactions. Upon relief of tumor hypoxia, PMNs were recruited less intensely to the tumor-bearing uterus, but the recruited cells much more effectively killed tumor cells, an activity our data moreover suggested was mediated via their production of NADPH oxidase-derived reactive oxygen species and MMP-9. Simultaneously, their ability to promote tumor cell proliferation, which appeared to be mediated via their production of neutrophil elastase, was rendered less effective. Relieving tumor hypoxia thus greatly improved net PMN-dependent tumor control, leading to a massive reduction in tumor burden. Remarkably, this outcome was T cell independent. Together, these findings identify key hypoxia-regulated molecular mechanisms through which PMNs directly induce tumor cell death and proliferation in vivo and suggest that the contrasting properties of PMNs in different tumor settings may in part reflect the effects of hypoxia on direct PMN-tumor cell interactions.
Shp1 function in myeloid cells Abram, Clare L.; Lowell, Clifford A.
Journal of leukocyte biology,
September 2017, Volume:
102, Issue:
3
Journal Article
Peer reviewed
Open access
Review on the role of Shp1, and how myeloid‐specific dysregulation may contribute to disease.
The motheaten mouse was first described in 1975 as a model of systemic inflammation and autoimmunity, as ...a result of immune system dysregulation. The phenotype was later ascribed to mutations in the cytoplasmic tyrosine phosphatase Shp1. This phosphatase is expressed widely throughout the hematopoietic system and has been shown to impact a multitude of cell signaling pathways. The determination of which cell types contribute to the different aspects of the phenotype caused by global Shp1 loss or mutation and which pathways within these cell types are regulated by Shp1 is important to further our understanding of immune system regulation. In this review, we focus on the role of Shp1 in myeloid cells and how its dysregulation affects immune function, which can impact human disease.
Dectin-1 is a pattern recognition receptor that is important for innate immune responses against fungi in humans and mice. Dectin-1 binds to β-glucans in fungal cell walls and triggers phagocytosis, ...production of reactive oxygen by the NADPH oxidase, and inflammatory cytokine production which all contribute to host immune responses against fungi. Although the autophagy pathway was originally characterized for its role in the formation of double-membrane compartments engulfing cytosolic organelles and debris, recent studies have suggested that components of the autophagy pathway may also participate in traditional phagocytosis. In this study, we show that Dectin-1 signaling in macrophages and bone marrow-derived dendritic cells triggers formation of LC3II, a major component of the autophagy machinery. Further, Dectin-1 directs the recruitment of LC3II to phagosomes, and this requires Syk, activation of reactive oxygen production by the NADPH oxidase, and ATG5. Using LC3-deficient dendritic cells we show that whereas LC3 recruitment to phagosomes is not important for triggering phagocytosis, killing or Dectin-1-mediated inflammatory cytokine production, it facilitates recruitment of MHC class II molecules to phagosomes and promotes presentation of fungal-derived antigens to CD4 T cells.
Background: Dectin-1 is a phagocytic receptor important for host immune responses to fungal infections.
Results: Dectin-1 signaling directs LC3 to phagosomes leading to increased MHC class II recruitment and increased presentation of fungal-derived antigens.
Conclusion: Dectin-1 signaling enhances the efficiency of MHC class II presentation of fungal-derived antigens.
Significance: Dectin-1 signaling can influence how phagosomal contents are handled.
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