Despite tremendous recent advances in our understanding of the molecular and cellular basis of cystic fibrosis (CF), there remains a paradox of why recruited neutrophils fail to eradicate bacterial infections in the airways of individuals with CF. The focus of this chapter is on new research authenticating the CF neutrophil as a key player in disease pathogenesis. Studies specifying intrinsic abnormalities due to a lack of cystic fibrosis transmembrane conductance regulator (CFTR) function, along with reports indicating reprogrammed cell activity secondary to chronic bacterial infection and inflammation, will be discussed.
- cystic fibrosis
- cystic fibrosis transmembrane conductance regulator
- neutrophil function
Cystic fibrosis (CF) is a multi-system disease resulting from mutations in the gene encoding the cystic fibrosis transmembrane conductance regulator (CFTR). In excess of 1900 CF mutations have been identified thus far , leading to misfolding of the CFTR protein and defective chloride (Cl-) transport across cell membranes. CF affects various organs including the pancreas, liver, and intestinal tract, but the most severe complications often occur in the lung. CF related symptoms, although variable among patients, are typically present early in life and increase in severity with age despite aggressive therapeutic intervention. CFTR absence or malfunction causes defective ion transport across the epithelium, reduction in pericillary liquid volume, and persistent mucus hypersecretion. As a consequence, mucus accumulates on the airway surface and leads to chronic bacterial infection, exacerbated airway inflammation, and lung injury. Pulmonary inflammation in the CF setting has been observed as early as infancy and there is evidence of structural lung disease present in children with CF as young as 10 weeks old, with 50%–70% of children presenting with bronchiectasis by 3–5 years [2-6]. Additional studies have shown neutrophil-dominated airway inflammation in children with CF [7, 8], and with increasing age elevated levels of proinflammatory mediators including interleukin (IL)-8 , tumour necrosis factor-alpha (TNF-alpha) , and leukotriene B4 (LTB4)  serve to escalate the chronic neutrophil presence in the pulmonary circulation. Indeed, key studies have demonstrated that neutrophil-released granule proteins, particularly neutrophil elastase (NE), play a crucial pathological role (Figure 1) [12, 13]. In the healthy lung, neutrophils represent approximately 1% of the inflammatory cells; however, they account for 60–70% of the total cell count in CF bronchial lavage fluid [14, 15] and ~25% of CF children were positive for free NE activity in airway samples at 3 months old .
Despite advances in our understanding of the molecular and cellular basis of CF, there persists an enigma as to why recruited neutrophils fail to eradicate bacterial infections in the lung. Support for the hypothesis that a genetic defect gives rise to dysregulated neutrophil responses in CF is shown by a study demonstrating upregulation of genes coding for both chemokines and proteins involved in signal transduction in CF . A recent study has demonstrated that CXC chemokine receptors 1/2 (CXCR1/CXCR2) haplotypes in CF modulate antibacterial neutrophil functions against
The focus of this chapter is on new research authenticating the CF neutrophil as a key player in disease pathogenesis. Studies published in the previous 10 years specifying intrinsic abnormalities due to a lack of CFTR function, along with reports indicating reprogrammed cell activity secondary to chronic bacterial infection and inflammation will be discussed. Our review of the literature was carried out using the MEDLINE database (from 2005 to the year 2015), Google Scholar, and The Cochrane Library databases using several appropriate generic terms.
2. The debate on CFTR expression by neutrophils
The year 2015 marks the 26th anniversary of the identification and isolation of the
Up to this point, no connection between abnormal neutrophil function and the expression of CFTR protein in human neutrophils had been made, and whether or not neutrophils express functional CFTR was still the topic of great debate among leading scientists and clinicians [5, 8, 13, 14], with relevance for the development of CFTR-targeting pharmacotherapy. This is emanating from worldwide laboratories equally committed to the pursuit of knowledge on the cause for impaired neutrophil activity in CF and also the potential consequence of the loss of functional CFTR Cl- channels. Indeed, there is still great controversy as to the true nature of dysregulated neutrophil activity in CF and, for example, in 2010, McKeon and colleagues could only detect low levels of
Over the years, a number of reasons for not detecting CFTR protein in neutrophil cell fractions by Western blot analysis have been put forward and include the susceptibility of CFTR protein to degradation, a lack of reliable anti-CFTR antibodies, and also boiling of cell fractions prior to electrophoresis. As these issues were addressed researchers have detected CFTR protein in human neutrophils and have established functional roles for membrane associated CFTR. In line with this concept, in 2006, Painter and colleagues demonstrated the presence of CFTR protein in human neutrophil membrane phagolysosomes by confocal microscopy, and also verified the expression of
3. The role of CFTR in neutrophils: oxygen dependent and independent mechanisms of microbial killing
3.1. Oxygen dependent killing
The focus of this chapter will now turn to studies that have reported impaired neutrophil activity due to a lack of CFTR function. Of major relevance to bacterial killing in CF, reported defective killing of microbes due to conditions that prevail within the vacuole of phagocytosing neutrophils will be discussed. The process of neutrophil mediated bacterial clearance can be divided into two main processes: those that are oxygen independent and those that are oxygen dependent. With regards to oxidative mechanisms of microbial killing, the first indications that oxygen plays a role in the functionality of neutrophils was first discovered by Baldridge and Gerard . By exposing canine neutrophils to bacteria they observed a significant increase in oxygen consumption , and later it was revealed that this increase in oxygen consumption was independent of mitochondrial respiration . Following discovery of the respiratory burst, it was discovered that neutrophils from patients with chronic granulomatous disease (CGD) failed to mount a respiratory burst during phagocytosis and these individuals are characterised by an abnormality of neutrophil function and recurrent life-threatening infections [39, 40]. CGD provides the most definitive evidence for the physiological and clinical importance of the respiratory burst, or alternatively referred to as the NADPH oxidase (nicotinamide adenine dinucleotide phosphate oxidase). Indeed, patients with CGD have played a vital role in understanding the structure and mechanism of the NADPH oxidase (Figure 2). The burst of oxygen consumption upon phagocytosis and the absence of this process in CGD leading to impaired bacterial killing was understood to indicate that the oxygen consumed was converted to antimicrobial oxidants. By exposing neutrophils to opsonised bacteria, Cohen and colleagues demonstrated that 99% of oxygen consumed was converted to superoxide (O2-)  and the requirement of O2- as a precursor to hydrogen peroxide (H2O2) was confirmed . It is not known what concentration of H2O2 is attained within the vacuole, with measurement from 0.01μM  to 100mM estimated, depending on the amount of phagocytosis and the intracellular pH . These oxidants produced by neutrophils may also contribute to lung tissue damage and the shield against oxidant-modulated injury is the extracellular anti-oxidant glutathione; but this is significantly decreased in CF epithelial lining fluid [44-47]. Of major relevance is that CFTR has been linked to extracellular glutathione transport  and in paediatric reports of extremely high levels of protein oxidation have been detected in airway samples .
H2O2 generated during the oxidative burst has limited bactericidal properties and the best-defined function of H2O2 in the antimicrobial activities of neutrophils comes from the function of H2O2 as a substrate for myeloperoxidase (MPO) in the presence of halides (chloride (Cl-)). Neutrophil MPO was initially called verdoperoxidase, and later its name subsequently changed to MPO. It is present in exceptionally high concentrations in neutrophils, with levels estimated to be no less than 5% of the dry weight of the cell. MPO is synthesized and packaged into azurophilic, also referred to as primary granules of neutrophils, during the promyelocyte stage of granulocyte development and is present in mature resting granulocytes.
Mature MPO is a 150 kDa tetramer composed of two glycosylated 59–64 kDa heavy subunits and two unglycosylated 14 kDa light subunits as a pair of protomers linked together by a disulphide bond. When the phagosome containing microorganisms fuses with cytoplasmic granules, MPO, along with the other components of the granules, is released into the vacuole. A role for MPO as a component of the antimicrobial armoury of neutrophils was proposed with the finding that MPO was strongly microbial when combined with H2O2 and a halide [50, 51]. MPO and H2O2 form an enzyme-substrate complex, which oxidises ions to the toxic agent hypohalous acid. Any of the halide ions (I-, Br-, Cl-) can be oxidised with iodide and bromide being more effective than Cl- on a molar basis . It is more likely however that the neutrophil uses Cl- because it is present in high concentration in biological fluids, resulting in the formation of hypochlorous acid (HOCl). There are three proposed means of Cl- transport to the phagosome: extracellular Cl- intake during phagocytosis of a pathogen, stored Cl- within granules released into the phagosome upon vesicle fusion, and passive or active transport of Cl- from the cytosol to the phagosome . Only active or passive transport has been suggested to provide a constant supply of Cl- (Figure 3)  and two Cl- ion channels (ClCs), ClC-3and CFTR have been implicated in the transport of Cl- within the neutrophil and the phagosome [33, 54]. The influx of protons to the phagosomal lumen by V-ATPase has been demonstrated to facilitate the transport of Cl- ions into the phagosome by ClCs including the CFTR  (Figure 3).
It is generally believed that HOCl is the most bactericidal oxidant known to be produced by the neutrophil. Levels of HOCl produced are based on calculations made after phorbol ester stimulation, which results in the secretion of O2- across the membrane to the surrounding supernatant and levels achieved are estimated at 80μM.
Levels produced in the phagocytic vacuole have been estimated using chlorinated fluorescein as a specific marker for HOCl production and by use of this technique it was calculated that 11% of oxygen consumed was converted to HOCl, resulting in 28μM within the phagosome . HOCl is an extremely strong non-radical oxidant and bacterial targets include adenosine triphosphate (ATP)-generating systems , disruption of basement membranes or cell membranes, and fragmentation of proteins . Chloramines are generated indirectly through the reaction of HOCl with amines, but are less reactive than HOCl but much more stable, and are therefore called “long lived oxidants.” Because of the high intracellular concentration of the β-amino acid taurine,
Having described the importance of MPO mediated halogenation for adequate microbial killing, there is also a need to mention that MPO deficiency occurs with a high prevalence and patients are not clinically afflicted by serious bacterial infections , with infections by
3.2. Oxygen independent microbial killing
The presence of an oxygen independent microbial mechanism in neutrophils is demonstrated by the ability of these cells to kill bacteria under anaerobic conditions. Hirsch and colleagues reported that neutrophil lysates killed bacteria and that this effect was due to a substance they called phagocytin . The component responsible for bacterial killing was localized to the cytoplasmic granules which are released into the phagocytic vacuole . Neutrophil-derived microbial molecules are packaged within four distinct subgroups of granules (Figure 4) and are released either into the phagocytic vacuole or to the outside of the cell upon activation. Granule biogenesis follows the granulocyte differentiation pathway. The azurophilic (also referred to as primary) granules first emerge at the stage of the promyelocytes  and contain MPO, the serine proteases neutrophil elastase (NE), cathepsin G and proteinase 3, defensins and bacterial permeability-increasing protein , and are considered as the true microbial compartment mobilized upon phagocytosis. Later in differentiation, at the metamyelocyte stage, specific granules containing lactoferrin , 18 kDa human cathelicidin antimicrobial protein (hCAP-18], and lysozyme emerge , followed by a third population termed the gelatinase granules which predominantly contain gelatinase (matric metalloprotease (MMP)-9 and MMP-2), lysozyme, and leukolysin [74, 75]. A forth type of granule, called the secretory vesicles, appears at the stage of the mature neutrophil. Movement of the cytoplasmic granules following ingestion of bacteria was first observed by Robineaux and Frederic , and by use of chicken leukocytes with their large dense granules, Hirsch observed by phase contrast microscopy, degranulation and release of the granule contents directly into the phagocytic vacuole, by fusion of the granule membrane with the invaginated cell membrane . As for any form of intracellular vesicle transport, degranulation is a tightly regulated process. Small GTPases of the Ras superfamily are known key regulators of cellular events including vesicle transport, cell division, control of cytoskeletal rearrangements, and nuclear assembly. Secondary and tertiary granules are tethered through a small GTPase Rab27a and its effector protein Munc13-4  which interacts with the soluble N-ethylmaleimide association protein receptor (SNARE), a protein complex composed of vesicle-associated membrane proteins (VAMPs) on the vesicle surface and SNAP23 and STX4 on the plasma membrane [79-81]. Once the granule is docked the granule membrane fuses with the plasma membrane enabling release of granule contents. The small GTPase Rac2 has been shown necessary for the release of primary granules  but of interest, a sub-population of Rab27a positive primary granules was also found  with different Rab27a effectors Slp1 and Munc13-4 reported necessary for primary and tertiary granules release, respectively .
Although the neutrophil possesses an armoury of anti-microbial proteins and peptides, individual components have been shown to exert microbial effects. For example, NE has long been regarded as the major antibacterial protein and mice made homozygous for a disrupted NE gene have demonstrated impaired resistance to
Examples of proteins stored in specific (secondary) and gelatinase (tertiary) granules include human lactoferrin and MMPs. Lactoferrin is a major component of the specific granules and is active against a variety of pathogens . This protein binds to bacteria through its highly positively charged
In spite of their original role in host defence, NE and proteinase 3 have been strongly implicated in the pulmonary pathology of CF. Indeed it has been shown that NE is the main mediator of proteolysis (Figure 1) but can also cause up-regulation of expression of other proteases including MMPs and cathepsins and as a result it has been proposed that neutralisation of NE activity is central to reducing the overall protease burden . In line with this thought, NE has the ability to degrade structural proteins in the lung including elastin, collagen, and fibronectin and to promote IL-8 production by bronchial epithelial cells , to degrade antimicrobial peptides , and to degrade antiproteases including alpha-1 antitrypsin, SLPI , and elafin  leading to a protease/antiprotease imbalance . Moreover, it has been shown that the process of primary granule release by CF neutrophils appears altered, as greater levels of NE  and MPO  were recorded in the extracellular fluids post stimulation with either CF airway samples, TNF-alpha and IL-8, or serum-opsonised particles. Of importance, altered cytosolic pH regulation in CF neutrophils has been demonstrated [102, 103], which could in turn influence the process of degranulation. In further support of increased primary granule release by CF neutrophils, MPO and NE levels have been reported to be present at significantly increased levels in airway samples from patients with CF compared to controls [49, 104]. Moreover, levels of NE degranulation were not significantly altered following intravenous antibiotic treatment of patients with CF, indicating continued dysregulation of neutrophil activity even with clinical improvement . While the mechanism for excessive primary granule release by CF neutrophils has not been fully investigated [104, 106], new research on the cause of reduced secondary and tertiary granule release has recently been revealed . Contrary to increased release of secondary and tertiary granules by neutrophils of individuals with airway disease linked to alpha-1 antitrypsin deficiency (AATD) , evidence was presented indicating that abnormal CFTR function contributes to impaired neutrophil killing in CF due to inadequate Rab27a activation, which regulates the release of antimicrobial proteins from secondary and tertiary granules. In this study reduced degranulation of lactoferrin of secondary granules and MMP-9 of tertiary granules from patients with CF compared to healthy control cells was observed, an effect mirrored in healthy control cells post CFTR inhibition. Collectively results revealed that CFTR inhibition or dysfunction reduces cytosolic Mg2+ levels resulting in impaired Rab27a activity, ultimately reducing the CF neutrophils ability to kill bacterial pathogens .
4. The involvement of CFTR in neutrophil adherence leading to migration
Before describing the process leading to neutrophil adhesion, it is important to stress the complexity of studying neutrophil adhesion and migration. Blood neutrophils isolated from patients with CF are chronically exposed to pro-inflammatory cytokines, including LTB4 and IL-8, and pathogenic particles including fMLP (formyl-methionyl-leucyl-phenylalanine) and LPS, resulting in these cells being in a constant primed state. Therefore, independent of the expression of CFTR protein, neutrophils in CF may illustrate enhanced cell adherence and migration. To circumvent this dilemma and to eliminate the potential for bias towards inflammatory versus altered neutrophil adhesion due to a lack of CFTR function, an approach taken by researchers is to include neutrophils isolated from inflammatory control patients. For example, in 1998, Russell and colleagues demonstrated that L-selectin shedding is altered in patients with CF resulting in increased neutrophil adhesion in response to IL-8 and fMLP . This paper reported that non-CF bronchiectasis patients did not possess alterations in L-selectin shedding, suggesting that the defect in L-selectin shedding is CF specific and could be a result of defective CFTR rather than the inflammatory status of the individual . Indeed, CFTR expression in human neutrophils has provoked the idea that altered neutrophil migration and adhesion in CF could be caused by an intrinsic defect. Counteracting this concept however, Pohl
Circulating neutrophils generally adhere and migrate in response to pro-inflammatory mediators including TNF-alpha and pathogenic components including N-formyl peptides produced by bacteria. Lipid mediators involved in neutrophil adhesion and chemotaxis include LTB4 [109, 110], with significantly increased levels quantified in sputum of patients with CF . The chemokine IL-8 is the main neutrophil chemo-attractant involved in CF lung neutrophil infiltration , and increased levels of IL-8 have been detected in bronchial lavage fluid and sputum of patients with CF . IL-8 is produced by a number of cells, including fibroblasts , epithelial cells , and by neutrophils themselves . Interestingly, neutrophils isolated from children with CF demonstrate increased migration to IL-8 , and also release significantly increased levels of the chemokine when compared to the blood neutrophils of the same donor, suggesting that the environment that the cell is found triggers disproportionate release of IL-8 .
Neutrophils migrate in a multistep process consisting of rolling, tight binding, diapedesis, and migration. Initially, E-selectin and P-selectin are upregulated on the epithelium cell surface, and reversibly bind to L-selectin found on the neutrophil cell surface. In turn, L-selectin is shed from the neutrophil membrane resulting in up-regulation of integrins LFA-1 (CD11a/CD18) and MAC-1 (CD11b/CD18) which can both bind to ICAM-1 on the epithelium. Research studies have demonstrated that activation of integrins is in part mediated by IL-8 , and this is particularly relevant in CF as studies involving infants and children have demonstrated increased expression of IL-8 and ICAM-1, possibly indicating intrinsic inflammatory changes at a very early stage in disease progression supporting cell adhesion [119, 120]. This latter study is reinforced by data indicating that CF neutrophils show higher migratory responsiveness to IL-8  supporting elevated numbers of neutrophils migrating to the airways. Moreover, neutrophil activation results in increased cytosolic Ca2+ levels triggering activation of calpain, a calcium dependent protease. Calpain has been demonstrated to liberate adhesion molecules CD11b and CD18, facilitating cell adhesion through the tight binding of integrins to epithelium cell surfaces . Of major importance, studies have shown that CF neutrophils possess increased calpain activity, affecting cleavage of the cholesterol transporter caveolin-1, thereby modulating cholesterol trafficking to the plasma membrane . Interestingly, and of major relevance to CF, Solomkin
5. The involvement of CFTR in neutrophil apoptosis
Timely and effective neutrophil programmed cell death is essential for the resolution of inflammation [124, 125] and abnormal neutrophil apoptosis is associated with decreased antimicrobial defences , incomplete microbial clearance, and sustained inflammation [127, 128]. Three different pathways are involved in the regulation of apoptosis and particular attention will be given to signalling pathways that are relevant to the neutrophil as it has been recognised that neutrophils have unique mechanisms of cell death due to their short half-life and phagocytic activity (Figure 5). Essential to the regulation and execution of apoptosis are the caspases, a family of cytosolic proteases or cysteine-dependent aspartate-directed proteases, involved in all three pathways. The first pathway described is the mitochondrial or intrinsic pathway. This pathway responds to physical and chemical stress signals, including growth factor withdrawal, DNA damage, and endoplasmic stress, and is transduced by members of the Bcl-2 family, which ultimately trigger the mitochondrial outer membrane permeabilisation (MOMP). As a result, several pro-apoptotic mitochondrial proteins, the most important being cytochrome C, are released into the cytosol. Subsequently cytochrome C, apoptotic protease activating factor-1 (Apaf-1) and caspase-9 form the apoptosome [129-131], this results in the activation of caspase-9 which thereafter activates caspase-3 and initiates the execution of apoptosis. In addition, caspase-8 can cleave Bid into truncated Bid (TBid), which ultimately triggers MOMP, thus providing a link from the intrinsic pathway to the extrinsic pathway.
The second pathway, the extrinsic or external death receptor pathway, is activated in response to extracellular signals such as FasL and TNF-alpha and is mediated by the binding of these members of the tumour necrosis factor family to death receptors on the cell surface (e.g., Fas, TNFR). The binding of the FasL and TNF-alpha to its cognate receptor results in the multimerisation of the death receptor and the formation of the death inducing signal complex (DISC), containing multiple adaptor molecules such as the Fas associated death domain (FADD) or TNF-R1-associated death domain (FADD) or TNF-R1-associtaed death domain (TRADD). The respective adaptor death domain then interacts with caspase-8 [132, 133], which in turn leads to the autolytic activation from pro-caspase-8 to caspase-8. After activation and release of its active subunit (p18), caspase-8 then activates caspase-3, which finally executes apoptosis by releasing caspase-activated DNase (CAD) from its inhibitor (ICAD) with DNA fragmentation as a consequence . The third pathway is the ER stress pathway. This pathway is thought to involve the activation of caspases, increase in cytosolic calcium and pro-apoptotic transcription factors in response to stress signals such as hypoxia, accumulation of unfolded protein, and alteration in calcium homeostasis within the ER [135, 136].
In the neutrophil the enzymatic activity of active caspase-3, -7, and -9 can be selectively inhibited by X-linked inhibitor of apoptosis (XIAP), a member of the conserved inhibitor of apoptosis (IAP) family of proteins . Moreover, there are a number of key distinguishing features of neutrophil apoptosis. Firstly, the prominent role of the Bcl-2 homologue, Mcl-1, as a survival protein is central to the neutrophil’s ability to undergo rapid apoptosis and may therefore limit the neutrophil’s lifespan .
Mcl-1 is an unusual bcl-2 protein and can be rapidly turned over in the proteasome giving it a short half-life (2h) in the cell and is in contrast to the essential pro-apoptotic bcl-2 homologues, which are known to persist in the cell beyond 12 h. A critical excess of pro- over anti-apoptotic homologues decides the fate of the neutrophil and this eventually leads to loss of mitochondrial membrane potential and the progression of apoptosis . Secondly, the involvement of reactive oxygen species (ROS) is very specific to neutrophil apoptosis. The observation that neutrophils isolated from CGD patients which are known to be NADPH oxidase defective display a significant delayed spontaneous cell death relative to that of neutrophils from healthy donors is important . This suggests that activation of the NADPH oxidase, with consequent production of ROS, is involved in spontaneous apoptosis and in regulating the programmed cell death of neutrophils during phagocytosis.
In contrast to the reported accelerated apoptosis in neutrophils from patients with airways disease associated with AATD , prolonged neutrophil survival has been reported in people with CF independent of infectious state and mutation type . In support of this concept, Moriceau
6. The effect of CFTR mutation targeted therapy on neutrophil function
There can be no doubt that our grasp and understanding of the complex physiology of CFTR protein function has progressed majorly and permitted the development of exciting new treatments designed to target the basic defects of CF. Along with this, continuing improvements in clinical care have allowed improved outcomes for patients with CF including reduced morbidity and preserved lung function. As CFTR has been shown to be an integral membrane channel on neutrophils, the influence of new CFTR therapeutics on neutrophil function is an area of intense interest.
Class I mutations are thought to affect 5% of the CF population in Western society and in this class of
A second area of immense interest is the therapeutic use of aminoglycosides (e.g., gentamycin) and ataluren to cause read through of premature stop codons thereby allowing translation to continue to the end of transcription [148, 149]. Ataluren (PTC 124) is under investigation for its use and role in targeting premature stop codons. This compound has the potential to allow processing of premature stop codons, resulting in the production of normal length and functional CFTR, with insertion at the cell surface. Its beneficial effects have been proven with analysis of nasal chloride transport. The phase III trial in 238 patients with CF failed to achieve its primary end point (improvement in FEV1) at 48 weeks, except in a small subgroup of patients not on concomitant nebulised aminoglycoside treatment .
Class II (e.g.,
Use of this therapy involved a well-designed randomized, double blind, placebo-controlled trial. The study subjects had at least one
Of relevance to the circulating neutrophil and as
A plethora of studies on neutrophil function in CF have been performed and demonstrate alterations in cellular activities including impaired microbial uptake [156, 157], defective intracellular kinase activation , cellular inactivation , and increased oxidant formation [106, 159]. Furthermore, an additional area of intense research has focused on persistent mammalian target of rapamycin (mTOR) and cyclic AMP response element binding protein (CREB) pathway activation in CF airway neutrophils , with more recent data suggesting that neutrophils express augmented cell surface nutrient transporter expression and glucose uptake, consistent with metabolic adaptation . As the CF neutrophil may shape the inflammatory response and influence patient outcome, further research investigating the CF neutrophil is required. In addition, a promising development in the treatment of airway inflammation involves the correction of CFTR dysfunction. If CFTR dysfunction is corrected at a very early age, it is possible that neutrophil induced inflammation involving impaired trafficking, delayed apoptosis, impaired degranulation, and bacterial killing may be significantly curtailed.
We would like to thank the U.S. Cystic Fibrosis Foundation and Science Foundation Ireland under the Research Frontiers Programme (11/RFP/BMT/3094) and the Program for Research in Third Level Institutes administered by the Higher Education Authority in Ireland for support.