Uncovering the multifaceted roles played by neutrophils in allogeneic hematopoietic stem cell transplantation

Allogeneic hematopoietic stem cell transplantation (alloHSCT) is a life-saving procedure used for the treatment of selected hematological malignancies, inborn errors of metabolism, and bone marrow failures. The role of neutrophils in alloHSCT has been traditionally evaluated only in the context of their ability to act as a first line of defense against infection. However, recent evidence has highlighted neutrophils as key effectors of innate and adaptive immune responses through a wide array of newly discovered functions. Accordingly, neutrophils are emerging as highly versatile cells that are able to acquire different, often opposite, functional capacities depending on the microenvironment and their differentiation status. Herein, we review the current knowledge on the multiple functions that neutrophils exhibit through the different stages of alloHSCT, from the hematopoietic stem cell (HSC) mobilization in the donor to the immunological reconstitution that occurs in the recipient following HSC infusion. We also discuss the influence exerted on neutrophils by the immunosuppressive drugs delivered in the course of alloHSCT as part of graft-versus-host disease (GVHD) prophylaxis. Finally, the potential involvement of neutrophils in alloHSCT-related complications, such as transplant-associated thrombotic microangiopathy (TA-TMA), acute and chronic GVHD, and cytomegalovirus (CMV) reactivation, is also discussed. Based on the data reviewed herein, the role played by neutrophils in alloHSCT is far greater than a simple antimicrobial role. However, much remains to be investigated in terms of the potential functions that neutrophils might exert during a highly complex procedure such as alloHSCT.     

Sputum microbiome profiles identify severe asthma phenotypes of relative stability at 12 to 18 months

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GPR34-mediated sensing of lysophosphatidylserine released by apoptotic neutrophils activates type 3 innate lymphoid cells to mediate tissue repair

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Prednisolone inhibits cytokine-induced adhesive and cytotoxic interactions between endothelial cells and neutrophils in vitro

We assessed whether prednisolone influenced the ability of human polymorphonuclear neutrophils (PMN) to adhere to and cause lysis of human umbilical vein endothelial cells (HUVEC) in vitro (as measured by the release of 51Cr). Pretreatment of the endothelium with IL-1beta or tumour necrosis factor-alpha (TNF-alpha) caused prominent endothelial E-selectin expression and endothelial hyperadhesiveness for neutrophils, as well as PMN-mediated cytotoxicity. All these processes were dose-dependently reduced when prednisolone was added to the assay system. This protective effect remained when HUVEC alone were pretreated with the drug prior to washing and cytokine activation. Likewise, when HUVEC cytotoxicity was induced by the nitric oxide (NO) donor S-nitroso-acetyl-penicillamine (SNAP), prednisolone reduced cell injury significantly. In contrast, prednisolone did not interfere with signalling systems between TNF-alpha-stimulated HUVEC and quiescent PMN such as IL-8 generation and release of cytosolic Ca2 + in the PMN. Thus, in this in vitro model of vasculitis, prednisolone dose-dependently reduced cytokine-induced E-selectin expression and HUVEC hyperadhesiveness for neutrophils, as well as reducing neutrophil-dependent cytotoxicity against HUVEC via NO-dependent steps.     

Granulocyte-macrophage colony-stimulating factor (GM-CSF) but not granulocyte colony-stimulating factor (G-CSF) induces plasma membrane expression of proteinase 3 (PR3) on neutrophils in vitro

The theoretical risk of triggering vasculitis resulting from administration of G-CSF and GM-CSF to patients with anti-neutrophil cytoplasmic antibody (ANCA)-associated vasculitides (AAV), such as Wegener's granulomatosis (WG), who develop agranulocytosis due to cytotoxic therapy, is unknown. Since there is strong evidence that activation of polymorphonuclear neutrophils (PMN) induced by binding of ANCA to PR3 or myeloperoxidase (MPO) expressed on their plasma membrane is involved in the pathogenesis of systemic vasculitides (SV), we studied the surface expression of PR3 and MPO on PMN from healthy donors in response to G-CSF and GM-CSF in vitro by flow cytometric analysis. Increasing doses of G-CSF did not alter PR3 expression on either untreated or tumour necrosis factor-alpha (TNF-alpha)-primed donor PMN significantly. In contrast, GM-CSF significantly increased PR3 membrane expression on both intact PMN and neutrophils primed with TNF-alpha. MPO expression was not significantly altered by either G-CSF or GM-CSF. In summary, these data demonstrate that GM-CSF, but not G-CSF, induces plasma membrane expression of PR3 on PMN in vitro. Since in AAV accessibility of the antigen (PR3 or MPO) to the antibody (ANCA) on the plasma membrane of PMN is thought to be essential for neutrophil activation by ANCA, the results of the present study suggest that administration of GM-CSF to patients with WG with neutropenia implies a definite theoretical risk of deterioration of vasculitis via this mechanism.     

Interleukin (IL)‐39 [IL‐23p19/Epstein–Barr virus‐induced 3 (Ebi3)] induces differentiation/expansion of neutrophils in lupus‐prone mice

Interleukin (IL)‐12 family cytokines play critical roles in autoimmune diseases. Our previous study has shown that IL‐23p19 and Epstein–Barr virus‐induced 3 (Ebi3) form a new IL‐12 family heterodimer, IL‐23p19/Ebi3, termed IL‐39, and knock‐down of p19 or Ebi3 reduced diseases by transferred GL7⁺ B cells in lupus‐prone mice. In the present study, we explore further the possible effect of IL‐39 on murine lupus. We found that IL‐39 in vitro and in vivo induces differentiation and/or expansion of neutrophils. GL7⁺ B cells up‐regulated neutrophils by secreting IL‐39, whereas IL‐39‐deficient GL7⁺ B cells lost the capacity to up‐regulate neutrophils in lupus‐prone mice and homozygous CD19^cre (CD19‐deficient) mice. Finally, we found that IL‐39‐induced neutrophils had a positive feedback on IL‐39 expression in activated B cells by secreting B cell activation factor (BAFF). Taken together, our results suggest that IL‐39 induces differentiation and/or expansion of neutrophils in lupus‐prone mice.     

Early production of IL-17A by γδ T cells in the trachea promotes viral clearance during influenza infection in mice

The innate immune response generated against influenza infection is critical for the inhibition of viral dissemination. The trachea contains different types of innate immune cells that protect the respiratory tract from pathogen invasion. Among them, γδ T cells have the ability to rapidly generate large amounts of pro-inflammatory cytokines to preserve mucosal barrier homeostasis during infection. However, little is known about their role during the early phase of influenza infection in the airways. In this study, we found that, early after infection, γδ T cells are recruited and activated in the trachea and outnumber αβ T cells during the course of the influenza infection that follows. We also showed that the majority of the recruited γδ T cells express the Vγ4 TCR chain and infiltrate in a process that involves the chemokine receptor CXCR3. In addition, we demonstrated that γδ T cells promote the recruitment of protective neutrophils and NK cells to the tracheal mucosa. Altogether, our results highlight the importance of the immune responses mediated by γδ T cells.     

Obesity promotes prolonged ovalbumin‐induced airway inflammation modulating T helper type 1 (Th1), Th2 and Th17 immune responses in BALB/c mice

Clinical and epidemiological studies indicate that obesity affects the development and phenotype of asthma by inducing inflammatory mechanisms in addition to eosinophilic inflammation. The aim of this study was to assess the effect of obesity on allergic airway inflammation and T helper type 2 (Th2) immune responses using an experimental model of asthma in BALB/c mice. Mice fed a high‐fat diet (HFD) for 10 weeks were sensitized and challenged with ovalbumin (OVA), and analyses were performed at 24 and 48 h after the last OVA challenge. Obesity induced an increase of inducible nitric oxide synthase (iNOS)‐expressing macrophages and neutrophils which peaked at 48 h after the last OVA challenge, and was associated with higher levels of interleukin (IL)‐4, IL‐9, IL‐17A, leptin and interferon (IFN)‐γ in the lungs. Higher goblet cell hyperplasia was associated with elevated mast cell influx into the lungs and trachea in the obese allergic mice. In contrast, early eosinophil influx and lower levels of IL‐25, thymic stromal lymphopoietin (TSLP), CCL11 and OVA‐specific immunoglobulin (IgE) were observed in the obese allergic mice in comparison to non‐obese allergic mice. Moreover, obese mice showed higher numbers of mast cells regardless of OVA challenge. These results indicate that obesity affects allergic airway inflammation through mechanisms involving mast cell influx and the release of TSLP and IL‐25, which favoured a delayed immune response with an exacerbated Th1, Th2 and Th17 profile. In this scenario, an intense mixed inflammatory granulocyte influx, classically activated macrophage accumulation and intense mucus production may contribute to a refractory therapeutic response and exacerbate asthma severity.     

Surface-related triggering of the neutrophil respiratory burst. Characterization of the response induced by IgG adsorbed to hydrophilic and hydrophobic glass surfaces

Hydrophilic and hydrophobic glass surfaces precoated with human albumin, fibrinogen, or IgG were investigated with respect to their ability to activate the neutrophil NADPH-oxidase. We found that IgG-coated surfaces induced a substantial and prolonged neutrophil production of reactive oxygen species (ROS). When a hydrophilic surface was used to support protein binding, a somewhat lower neutrophil response (around 35%) was obtained, compared with the response induced by IgG on a hydrophobic surface. The production of ROS was completely eliminated when cytochalasin B was added to the measuring system, suggesting the involvement of the cell cytoskeleton in the activation process. The relation between the intra- and extracellular generation of ROS was further assessed, and we found that most of the ROS produced were released from the cells, in agreement with a model in which the activating surfaces induce a ‘frustrated’ phagocytic response. Serum totally inhibited ‘frustrated’ phagocytosis provided that the IgG molecules were sticking to a hydrophilic surface.