Primary immune deficiencies with defects in neutrophil function

Isolation methods determine human neutrophil responses after stimulation

Studying neutrophils is challenging due to their limited lifespan, inability to proliferate, and resistance to genetic manipulation. Neutrophils can sense various cues, making them susceptible to activation by blood collection techniques, storage conditions, RBC lysis, and the isolation procedure itself. Here we assessed the impact of the five most used methods for neutrophil isolation on neutrophil yield, purity, activation status and responsiveness. We monitored surface markers, reactive oxygen species production, and DNA release as a surrogate for neutrophil extracellular trap (NET) formation. Our results show that neutrophils isolated by negative immunomagnetic selection and density gradient methods, without RBC lysis, resembled untouched neutrophils in whole blood. They were also less activated and more responsive to milder stimuli in functional assays compared to neutrophils obtained using density gradients requiring RBC lysis. Our study highlights the importance of selecting the appropriate method for studying neutrophils, and underscores the need for standardizing isolation protocols to facilitate neutrophil subset characterization and inter-study comparisons.

Fast and furious: The neutrophil and its armamentarium in health and disease

Neutrophils are powerful effector cells leading the first wave of acute host-protective responses. These innate leukocytes are endowed with oxidative and nonoxidative defence mechanisms, and play well-established roles in fighting invading pathogens. With microbicidal weaponry largely devoid of specificity and an all-too-well recognized toxicity potential, collateral damage may occur in neutrophil-rich diseases. However, emerging evidence suggests that neutrophils are more versatile, heterogeneous, and sophisticated cells than initially thought. At the crossroads of innate and adaptive immunity, neutrophils demonstrate their multifaceted functions in infectious and noninfectious pathologies including cancer, autoinflammation, and autoimmune diseases. Here, we discuss the kinetics of neutrophils and their products of activation from bench to bedside during health and disease, and provide an overview of the versatile functions of neutrophils as key modulators of immune responses and physiological processes. We focus specifically on those activities and concepts that have been validated with primary human cells.

Glycopeptide Antibiotics Impair Neutrophil Effector Functions

INTRODUCTION

Neutrophilic granulocytes represent the first line of defense against microorganisms. Granulocytes phagocytose microorganisms and specifically synthesize oxygen radicals against them, which eventually kills the invaders.

METHODS

Neutrophilic granulocytes were isolated from peripheral blood of healthy volunteer donors. Putative interference of new-generation antibiotics with neutrophil function was tested using a collection of granulocyte-stimulating agents and Amplex™ Red-based plate assay and flow cytometry-based respiratory burst assays. In addition, phagocytosis of E. coli, IL-8 production, bactericidal activity, and CD62L expression of granulocytes were evaluated.

RESULTS

Of note, we found that the two glycopeptide antibiotics dalbavancin and teicoplanin inhibited ROS production upon granulocyte activation via different signaling pathways in a dose-dependent manner. Dalbavancin also blocked the PMA-induced shedding of CD62L. In contrast, the oxazolidinone antibiotics tedizolid and linezolid had no effect on neutrophil function, while the combination of ceftazidime/avibactam dose dependently inhibited the fMLP/Cytochalasin B-induced granulocyte burst in a dose-dependent manner. Additionally, we showed that dalbavancin and teicoplanin as well as sulfametrole/trimethoprim and ceftazidime/avibactam inhibited baseline and PMA-induced IL-8 production by neutrophilic granulocytes. Moreover, dalbavancin impaired the bactericidal activity of neutrophilic granulocytes.

CONCLUSION

We here identified hitherto unknown inhibitory effects of several classes of antibiotics on the effector functions of neutrophilic granulocytes.

Neutrophil intrinsic and extrinsic regulation of NETosis in health and disease

Neutrophil extracellular traps (NETs) evolved to protect the host against microbial infections and are formed by a web-like structure of DNA that is decorated with antimicrobial effectors. Due to their potent inflammatory functions, NETs also cause tissue damage and can favor and/or aggravate inflammatory diseases. This multipronged activity of NETs requires that the induction, release, and degradation of NETs are tightly regulated. Here we describe the key pathways that are intrinsic to neutrophils and regulate NETosis, and we review the most recent findings on how neutrophil extrinsic factors participate in the formation of NETs. In particular, we emphasize how bystander cells contribute to modifying the capacity of neutrophils to undergo NETosis. Finally, we discuss how these neutrophil extrinsic processes can be harnessed to protect the host against the excessive inflammation elicited by uncontrolled NET release.

Bi-fluorescent Staphylococcus aureus infection enables single-cell analysis of intracellular killing in vivo

Techniques for studying the clearance of bacterial infections are critical for advances in understanding disease states, immune cell effector functions, and novel antimicrobial therapeutics. Intracellular killing of Staphylococcus aureus by neutrophils can be monitored using a S. aureus strain stably expressing GFP, a fluorophore that is quenched when exposed to the reactive oxygen species (ROS) present in the phagolysosome. Here, we expand upon this method by developing a bi-fluorescent S. aureus killing assay for use in vivo. Conjugating S. aureus with a stable secondary fluorescent marker enables the separation of infected cell samples into three populations: cells that have not engaged in phagocytosis, cells that have engulfed and killed S. aureus, and cells that have viable internalized S. aureus. We identified ATTO647N-NHS Ester as a favorable dye conjugate for generating bi-fluorescent S. aureus due to its stability over time and invariant signal within the neutrophil phagolysosome. To resolve the in vivo utility of ATTO647N/GFP bi-fluorescent S. aureus, we evaluated neutrophil function in a murine model of chronic granulomatous disease (CGD) known to have impaired clearance of S. aureus infection. Analysis of bronchoalveolar lavage (BAL) from animals subjected to pulmonary infection with bi-fluorescent S. aureus demonstrated differences in neutrophil antimicrobial function consistent with the established phenotype of CGD.

Anti-Inflammatory Neutrophil Functions in the Resolution of Inflammation and Tissue Repair

Neutrophils are highly abundant circulating leukocytes that are amongst the first cells to be recruited to sites of infection or sterile injury. Their ability to generate and release powerful cytotoxic products ties with their role in host defence from bacterial and fungal infections. Neutrophilic inflammation is tightly regulated to limit the amount of 'bystander injury' caused. Neutrophils were in the past regarded as short-lived, indiscriminate killers of invading microorganisms. However, this view has changed quite dramatically in recent years. Amongst other insights, neutrophils are now recognised to also have important anti-inflammatory functions that are critical for the resolution of inflammation and return to homeostasis. This minireview focusses on anti-inflammatory neutrophil functions, placing a particular focus on recent findings linked to neutrophil cell death, several types of which may be anti-inflammatory (apoptosis, secondary necrosis, and neutrophil extracellular traps). These are discussed together with features that may further promote the clearance of dead cells by efferocytosis and reprogramming of macrophages to promote resolution and repair.

Preclinical Evaluation of Foamy Virus Vector-Mediated Gene Addition in Human Hematopoietic Stem/Progenitor Cells for Correction of Leukocyte Adhesion Deficiency Type 1

Ex vivo gene therapy procedures targeting hematopoietic stem and progenitor cells (HSPCs) predominantly utilize lentivirus-based vectors for gene transfer. We provide the first pre-clinical evidence of the therapeutic utility of a foamy virus vector (FVV) for the genetic correction of human leukocyte adhesion deficiency type 1 (LAD-1), an inherited primary immunodeficiency resulting from mutation of the β2 integrin common chain, CD18. CD34+ HSPCs isolated from a severely affected LAD-1 patient were transduced under a current good manufacturing practice-compatible protocol with FVV harboring a therapeutic CD18 transgene. LAD-1-associated cellular chemotactic defects were ameliorated in transgene-positive, myeloid-differentiated LAD-1 cells assayed in response to a strong neutrophil chemoattractant in vitro. Xenotransplantation of vector-transduced LAD-1 HSPCs in immunodeficient (NSG) mice resulted in long-term (∼5 months) human cell engraftment within murine bone marrow. Moreover, engrafted LAD-1 myeloid cells displayed in vivo levels of transgene marking previously reported to ameliorate the LAD-1 phenotype in a large animal model of the disease. Vector insertion site analysis revealed a favorable vector integration profile with no overt evidence of genotoxicity. These results coupled with the unique biological features of wild-type foamy virus support the development of FVVs for ex vivo gene therapy of LAD-1.

E-cigarettes and Vaping: A Smoking Cessation Method or Another Smoking Innovation?

The prevalence of using e-cigarettes (vaping) has risen rapidly since its introduction in 2007, mostly among male youth. Although research on the health risks of e-cigarettes is still limited, there is growing evidence of debilitating pulmonary conditions and general immune weakness from e-cigarettes, leading to various infections. Moreover, there are concerns that vaping could be used as a new model of cannabis consumption, increasing cannabis addiction among adolescents. With well-known health risks from traditional smoking, e-cigarettes are viewed as a safe way of smoking, appealing more to youth. Additionally, extensive e-cigarette marketing boosted by the internet and fame has resulted in worries that e-cigarettes can lead to a renormalization of cigarette smoking and can be used as a new method to consume vaporized drugs. Although the concern that e-cigarettes are as harmful as traditional smoking has been raised, youth and most healthcare providers remain relatively unaware. Therefore, this review explored the association between e-cigarettes and traditional smoking. With the introduction of e-cigarettes in the last two decades, the topic is still new and less studied. Therefore, this review will help us understand the topic to better care for e-cigarette smokers and reduce the increasing public health burden from vaping.

Opportunities presented by zebrafish larval models to study neutrophil function in tissues

Appropriate neutrophil function is essential for innate immune defence and to avoid inflammatory pathology. Neutrophils can adapt their responses according to their environment and recently, the existence of multiple distinct neutrophil populations has been confirmed in both health and disease. However, the study of neutrophil functions in their tissue environment has remained challenging, and for instance, the relationship between neutrophil maturity and function is not fully understood. Many neutrophil morphological and functional features are highly conserved between mammals and non-mammalian vertebrates. This enables the use of the transparent and genetically tractable zebrafish larvae to study neutrophil biology. We review data on the development and function of zebrafish larval neutrophils and advances zebrafish have brought to studies of neutrophil biology. In addition, we discuss opportunities and aspects to be considered when using the larval zebrafish model to further enhance our understanding of neutrophil function in health and disease.

Macrophage NOX2 NADPH oxidase maintains alveolar homeostasis in mice

The leukocyte NADPH oxidase 2 (NOX2) plays a key role in pathogen killing and immunoregulation. Genetic defects in NOX2 result in chronic granulomatous disease (CGD), associated with microbial infections and inflammatory disorders, often involving the lung. Alveolar macrophages (AMs) are the predominant immune cell in the airways at steady state, and limiting their activation is important, given the constant exposure to inhaled materials, yet the importance of NOX2 in this process is not well understood. In this study, we showed a previously undescribed role for NOX2 in maintaining lung homeostasis by suppressing AM activation, in CGD mice or mice with selective loss of NOX2 preferentially in macrophages. AMs lacking NOX2 had increased cytokine responses to Toll-like receptor-2 (TLR2) and TLR4 stimulation ex vivo. Moreover, between 4 and 12 week of age, mice with global NOX2 deletion developed an activated CD11bhigh subset of AMs with epigenetic and transcriptional profiles reflecting immune activation compared with WT AMs. The presence of CD11bhigh AMs in CGD mice correlated with an increased number of alveolar neutrophils and proinflammatory cytokines at steady state and increased lung inflammation after insults. Moreover, deletion of NOX2 preferentially in macrophages was sufficient for mice to develop an activated CD11bhigh AM subset and accompanying proinflammatory sequelae. In addition, we showed that the altered resident macrophage transcriptional profile in the absence of NOX2 is tissue specific, as those changes were not seen in resident peritoneal macrophages. Thus, these data demonstrate that the absence of NOX2 in alveolar macrophages leads to their proinflammatory remodeling and dysregulates alveolar homeostasis.

Immune-related adverse events (irAEs) in ankylosing spondylitis (AS) patients treated with interleukin (IL)-17 inhibitors: a systematic review and meta-analysis

BACKGROUND

Ankylosing spondylitis (AS) is a chronic inflammatory rheumatic disease characterized by immune system dysregulation and inflammation in the joints. Interleukin (IL)-17 inhibitors are new biological drugs used to treat AS. In this study, we aimed to assess the risk of immune system-related AEs due to targeting IL-17 or IL-17R.

METHODS

The CENTRAL, PubMed, Scopus, Google Scholar, Clinical Trials Registry, and ICTRP were searched for randomized clinical trials (RCTs) and non-RCTs until February 2021. The risk of irAEs in patients treated with IL-17 inhibitors compared to the placebo or a drug-free control was evaluated. In studies that reported AEs of the IL-17 inhibitors at several different time points, we compared the number of cases/100 patient-year in which irAEs were reported. Subgroup analyses were also performed based on the dose and type of drugs.

RESULTS

Thirteen studies of 1848 AS patients treated by IL-17 inhibitors (secukinumab, ixekizumab, bimekizumab, and netakimab) and 764 participants who received a placebo were included. The risk of some AEs related to immune function in patients under IL-17 inhibitors treatment was significantly higher than that of the placebo group, including infection and infestation (risk difference RD = 0.09, P = 0.02), nasopharyngitis (RD = 0.04, P < 0.001), opportunistic infections (RD = 0.01, P = 0.04), and neutropenia (RD = 0.04, P = 0.03). Besides, the results of the Cochran Q test showed that there were significant differences between the occurrence of some AEs over time, including infection and infestations (p < 0.001, RCTs), upper respiratory tract infections (p < 0.001, non-RCTs), urinary tract infections (p < 0.001, non-RCTs), and diarrhea (p < 0.01, RCTs).

CONCLUSIONS

The most common immune system-related AEs in patients treated with IL-17 inhibitors are mucosal and opportunistic infections.

"Oral Manifestations of Patients with Inherited Defect in Phagocyte Number or Function" a systematic review

INTRODUCTION

Inherited phagocyte defects are one of the subgroups of primary immunodeficiency diseases (PIDs) with various clinical manifestations. As oral manifestations are common at the early ages, oral practitioners can have a special role in the early diagnosis.

MATERIALS AND METHODS

A comprehensive search was conducted in this systematic review study and data of included studies were categorized into four subgroups of phagocyte defects, including congenital neutropenia, defects of motility, defects of respiratory burst, and other non-lymphoid defects.

RESULTS

Among all phagocyte defects, 12 disorders had reported data for oral manifestations in published articles. A total of 987 cases were included in this study. Periodontitis is one of the most common oral manifestations.

CONCLUSION

There is a need to organize better collaboration between medical doctors and dentists to diagnose and treat patients with phagocyte defects. Regular dental visits and professional oral health care are recommended from the time of the first primary teeth eruption in newborns.

The Neutrophil

Neutrophils are immune cells with unusual biological features that furnish potent antimicrobial properties. These cells phagocytose and subsequently kill prokaryotic and eukaryotic organisms very efficiently. Importantly, it is not only their ability to attack microbes within a constrained intracellular compartment that endows neutrophils with antimicrobial function. They can unleash their effectors into the extracellular space, where, even post-mortem, their killing machinery can endure and remain functional. The antimicrobial activity of neutrophils must not be misconstrued as being microbe specific and should be viewed more generally as biotoxic. Outside of fighting infections, neutrophils can harness their noxious machinery in other contexts, like cancer. Inappropriate or dysregulated neutrophil activation damages the host and contributes to autoimmune and inflammatory disease. Here we review a number of topics related to neutrophil biology based on contemporary findings.

The Antimicrobial Activity of Peripheral Blood Neutrophils Is Altered in Patients with Primary Ciliary Dyskinesia

The airways of patients with primary ciliary dyskinesia (PCD) contain persistently elevated neutrophil numbers and CXCL8 levels. Despite their abundance, neutrophils fail to clear the airways from bacterial infections. We investigated whether neutrophil functions are altered in patients with PCD. Neutrophils from patients and healthy controls (HC) were isolated from peripheral blood and exposed to various bacterial stimuli or cytokines. Neutrophils from patients with PCD were less responsive to low levels of fMLF in three different chemotaxis assays (p < 0.05), but expression of the fMLF receptors was unaltered. PCD neutrophils showed normal phagocytic function and expression of adhesion molecules. However, PCD neutrophils produced less reactive oxygen species upon stimulation with bacterial products or cytokines compared to HC neutrophils (p < 0.05). Finally, the capacity to release DNA, as observed during neutrophil extracellular trap formation, seemed to be reduced in patients with PCD compared to HC (p = 0.066). These results suggest that peripheral blood neutrophils from patients with PCD, in contrast to those of patients with cystic fibrosis or COPD, do not show features of over-activation, neither on baseline nor after stimulation. If these findings extend to lung-resident neutrophils, the reduced neutrophil activity could possibly contribute to the recurrent respiratory infections in patients with PCD.

The Enzymatic and Non-Enzymatic Function of Myeloperoxidase (MPO) in Inflammatory Communication

Myeloperoxidase is a signature enzyme of polymorphonuclear neutrophils in mice and humans. Being a component of circulating white blood cells, myeloperoxidase plays multiple roles in various organs and tissues and facilitates their crosstalk. Here, we describe the current knowledge on the tissue- and lineage-specific expression of myeloperoxidase, its well-studied enzymatic activity and incoherently understood non-enzymatic role in various cell types and tissues. Further, we elaborate on Myeloperoxidase (MPO) in the complex context of cardiovascular disease, innate and autoimmune response, development and progression of cancer and neurodegenerative diseases.

Persistent Activation of Innate Immunity in Patients with Primary Antibody Deficiencies

Primary antibody deficiencies (PAD) represent a heterogeneous group of disorders, with common variable immunodeficiency being the most common with clinical significance. The main phenotypic defect resides in the inability of B cells to produce antibodies, and the cornerstone of therapy is immunoglobulin replacement treatment in order to fight infections. However, the management of the other inflammatory manifestations is inadequate, reinforcing the hypothesis that a complex genetic background affecting additional cell populations, such as polymorphonuclear cells (PMN) and monocytes, influences the expression of the clinical phenotype of the disease. In this study, we investigated by flow cytometry in different conditions (resting state, and after isolation and incubation, with and without stimuli) the expression pattern of several markers on PMN and monocytes, indicative of their maturation, capacity for chemotaxis, adhesion, opsonization, migration, and phagocytosis in 25 PAD patients, 12 healthy blood donors, and 4 septic patients. In this context, we also analyzed patients before and after the initiation of replacement treatment, as well as an untreated patient in different clinical conditions. Interestingly, we observed that PAD patients exhibit a chronic activation status of the innate immunity compartment, along with several differences in the expression of activation, maturation, and adhesion markers, with respect to different clinical conditions. Moreover, immunoglobulin replacement treatment had a favorable effect on PMN, as it was expressed by a more mature and less activated phenotype on basal state cells, and an enhanced activation capacity after LPS exposure. Thus, we conclude that PAD patients display a persistent innate immune cell activation, which is probably associated with the chronic inflammatory stress, usually observed in these disorders.

Dissecting Total Plasma and Protein-Specific Glycosylation Profiles in Congenital Disorders of Glycosylation

Protein N-glycosylation is a multifactorial process involved in many biological processes. A broad range of congenital disorders of glycosylation (CDGs) have been described that feature defects in protein N-glycan biosynthesis. Here, we present insights into the disrupted N-glycosylation of various CDG patients exhibiting defects in the transport of nucleotide sugars, Golgi glycosylation or Golgi trafficking. We studied enzymatically released N-glycans of total plasma proteins and affinity purified immunoglobulin G (IgG) from patients and healthy controls using mass spectrometry (MS). The applied method allowed the differentiation of sialic acid linkage isomers via their derivatization. Furthermore, protein-specific glycan profiles were quantified for transferrin and IgG Fc using electrospray ionization MS of intact proteins and glycopeptides, respectively. Next to the previously described glycomic effects, we report unprecedented sialic linkage-specific effects. Defects in proteins involved in Golgi trafficking (COG5-CDG) and CMP-sialic acid transport (SLC35A1-CDG) resulted in lower levels of sialylated structures on plasma proteins as compared to healthy controls. Findings for these specific CDGs include a more pronounced effect for α2,3-sialylation than for α2,6-sialylation. The diverse abnormalities in glycomic features described in this study reflect the broad range of biological mechanisms that influence protein glycosylation.

Bovine viral diarrhea virus compromises Neutrophil's functions in strain dependent manner

Bovine viral diarrhea virus (BVDV) infection is a major problem that results in economically important diseases of the cattle industry worldwide. The two major consequences of this disease are persistent infection and immune dysfunction. A number of studies have been done to determine the underline mechanisms of BVDV-induced immune dysfunction, in particular targeting antigen-presenting cells, T- and B- cells and cytokine gene expression. However, little research has focused Eon the effect of BVDV on neutrophils. Neutrophils are one of the predominant leukocytes circulating in blood and are considered the first line of defense in the innate immune system along with macrophages. Neutrophils not only eliminate the invading bacteria but also activate innate as well as adaptive immune responses. Therefore, compromised neutrophil function would affect both arms of immune system and caused immune suppression. In the current study, we used virus strains from both BVDV-1 and BVDV-2 species. Including a highly virulent non-cytopathic type 2a BVDV (ncp BVDV2a-1373), moderately virulent non-cytopathic type 2a (ncp BVDV2a 28508-5), and a pair of non-cytopathic type 1b BVDV (ncp BVDV1b TGAN) and cytopathic type 1b BVDV (cp BVDV1b TGAC) strain isolated from a case of mucosal disease. The highly virulent ncp BVDV2a-1373 significantly increased neutrophil apoptosis. However, none of the other BVDV strains affected neutrophil viability. All BVDV strains used significantly reduced CD18 and L-selectin expression on neutrophils as well as their oxidative burst and neutrophil extracellular traps (NET) activity. Cp BVDV significantly reduced neutrophil's phagocytic activity but ncp BVDV did not have any effect on it. On the other hand, ncp BVDV significantly increased neutrophil's CD14 expression and chemotactic activity while cp BVDV did not show any effect either on neutrophil's CD14 expression or on chemotactic activity. In conclusion, BVDV affected neutrophils variability and functional activity in strain dependent manner. Results of the current study will further help in understanding the pathophysiology of different BVDV strains.

Mice Deficient in NOX2 Display Severe Thymic Atrophy, Lymphopenia, and Reduced Lymphopoiesis in a Zymosan-Induced Model of Systemic Inflammation

Patients with chronic granulomatous disease (CGD) who have mutated phagocyte NADPH oxidase are susceptible to infections due to reduced reactive oxygen species production and exhibit autoimmune and inflammatory diseases in the absence of evident infection. Neutrophils and macrophages have been extensively studied since phagocyte NADPH oxidase is mainly found only in them, while the impact of its deficiency on lymphocyte cellularity is less well characterized. We showed herein a zymosan-induced systemic inflammation model that CGD mice deficient in the phagocyte NADPH oxidase gp91phox subunit (NOX2) exhibited more severe thymic atrophy associated with peripheral blood and splenic lymphopenia and reduced lymphopoiesis in the bone marrow in comparison with the wild-type mice. Conversely, the zymosan-exposed CGD mice suffered from more remarkable neutrophilic lung inflammation, circulating and splenic neutrophilia, and enhanced granulopoiesis compared with those in zymosan-exposed wild-type mice. Overall, this study provided evidence that NOX2 deficiency exhibits severe thymic atrophy and lymphopenia concomitant with enhanced neutrophilic inflammation in a zymosan-induced systemic inflammation model.

Neutrophil Extracellular Traps in Host Defense

Neutrophils are produced in the bone marrow and then patrol blood vessels from which they can be rapidly recruited to a site of infection. Neutrophils bind, engulf, and efficiently kill invading microbes via a suite of defense mechanisms. Diverse extracellular and intracellular microbes induce neutrophils to extrude neutrophil extracellular traps (NETs) through the process of NETosis. Here, we review the signaling mechanisms and cell biology underpinning the key NETosis pathways during infection and the antimicrobial functions of NETs in host defense.

Type III IFNs: Beyond antiviral protection

The unexpected discovery of a novel family of antiviral mediators, type III IFNs or IFN-λs, challenged the widely accepted primacy of type I IFNs in antiviral immunity, and it is now well recognized that the IFN-λ-based antiviral system plays a major role in antiviral protection of epithelial barriers. The recent characterization of previously unknown IFN-λ-mediated activities has prompted further reassessment of the role of type I IFNs in innate and adaptive immune and inflammatory responses. Since type I and type III IFNs are co-produced in response to a variety of stimuli, it is likely that many physiological processes are simultaneously and coordinately regulated by these cytokines in pathological conditions, and likely at steady state, as baseline expression of both IFN types is maintained by microbiota. In this review, we discuss emerging differences in the production and signaling of type I and type III IFNs, and summarize results of recent studies describing the involvement of type III IFNs in anti-bacterial and anti-fungal, as well as antiviral, defenses.

Neutrophil Defects and Diagnosis Disorders of Neutrophil Function: An Overview

Primary disorders of neutrophil function result from impairment in neutrophil responses that are critical for host defense. This chapter summarizes inherited disorders of neutrophils that cause defects in neutrophil adhesion, migration, and oxidative killing. These include the leukocyte adhesion deficiencies, actin defects and other disorders of chemotaxis, hyperimmunoglobulin E syndrome, Chédiak-Higashi Syndrome, neutrophil specific granule deficiency, chronic granulomatous disease, and myeloperoxidase deficiency. Diagnostic tests and treatment approaches are also summarized for each neutrophil disorder.

The Sweet-Side of Leukocytes: Galectins as Master Regulators of Neutrophil Function

Among responders to microbial invasion, neutrophils represent one of the earliest and perhaps most important factors that contribute to initial host defense. Effective neutrophil immunity requires their rapid mobilization to the site of infection, which requires efficient extravasation, activation, chemotaxis, phagocytosis, and eventual killing of potential microbial pathogens. Following pathogen elimination, neutrophils must be eliminated to prevent additional host injury and subsequent exacerbation of the inflammatory response. Galectins, expressed in nearly every tissue and regulated by unique sensitivity to oxidative and proteolytic inactivation, appear to influence nearly every aspect of neutrophil function. In this review, we will examine the impact of galectins on neutrophils, with a particular focus on the unique biochemical traits that allow galectin family members to spatially and temporally regulate neutrophil function.

Lymphatic Migration of Immune Cells

Lymphatic vessels collect interstitial fluid that has extravasated from blood vessels and return it to the circulatory system. Another important function of the lymphatic network is to facilitate immune cell migration and antigen transport from the periphery to draining lymph nodes. This migration plays a crucial role in immune surveillance, initiation of immune responses and tolerance. Here we discuss the significance and mechanisms of lymphatic migration of innate and adaptive immune cells in homeostasis, inflammation and cancer.

Inflammatory consequences of inherited disorders affecting neutrophil function

Primary immunodeficiencies affecting the function of neutrophils and other phagocytic leukocytes are notable for an increased susceptibility to bacterial and fungal infections as a result of impaired leukocyte recruitment, ingestion, and/or killing of microbes. The underlying molecular defects can also impact other innate immune responses to infectious and inflammatory stimuli, leading to inflammatory and autoimmune complications that are not always directly related to infection. This review will provide an update on congenital disorders affecting neutrophil function in which a combination of host defense and inflammatory complications are prominent, including nicotinamide dinucleotide phosphate oxidase defects in chronic granulomatous disease and β2 integrin defects in leukocyte adhesion deficiency.

Interferon Lambda's New Role as Regulator of Neutrophil Function

Neutrophils are increasingly appreciated as multifaceted regulators of innate immunity and inflammation. Historically, these important innate cells have been considered suicidal phagocytes with a primary role in the destruction of extracellular pathogens. Recent studies have significantly altered this simplistic view of neutrophils and have instead presented extensive evidence for a complex role for neutrophils in the control of diverse inflammatory conditions. It is now appreciated that neutrophils are crucial not only for efficient clearance of various pathogens but also in the development and control of inflammatory states such as autoimmunity, cancer, and tissue repair. Mounting evidence also suggests that neutrophils are capable of differential activation giving rise to distinctly polarized cells with diverse effector functions. Interferon lambda (IFN-λ) (also known as type III IFN) has emerged as an unexpected regulator of neutrophil function. IFN-λs are the newest members of the IFN family of antiviral cytokines and although initial studies suggested identical biological activities to type I IFNs, it is now apparent that type III IFN has distinct functions in vivo. In this article, I summarize recent evidence linking type III IFNs to the regulation and potential tailoring of neutrophil responses. These exciting observations might have important implications for the development of IFN-λs as novel therapeutic cytokines for the treatment of a diversity of inflammatory states where neutrophils are crucial players.

The roles of NADPH oxidase in modulating neutrophil effector responses

Neutrophils are phagocytic innate immune cells essential for killing bacteria via activation of a wide variety of effector responses and generation of large amounts of reactive oxygen species (ROS). Majority of the ROS in neutrophils is generated by activation of the superoxide-generating enzyme nicotinamide adenine dinucleotide phosphate (NADPH) oxidase. Independent of their anti-microbial function, NADPH oxidase-derived ROS have emerged as key regulators of host immune responses and neutrophilic inflammation. Data from patients with inherited defects in the NADPH oxidase subunit alleles that ablate its enzyme function as well as mouse models demonstrate profound dysregulation of host inflammatory responses, neutrophil hyper-activation and tissue damage in response to microbial ligands or tissue trauma. A large body of literature now demonstrates how oxidants function as essential signaling molecules that are essential for the regulation of neutrophil responses during priming, degranulation, neutrophil extracellular trap formation, and apoptosis, independent of their role in microbial killing. In this review we summarize how NADPH oxidase-derived oxidants modulate neutrophil function in a cell intrinsic manner and regulate host inflammatory responses. In addition, we summarize studies that have elucidated possible roles of oxidants in neutrophilic responses within the oral mucosa and periodontal disease.

Enhanced Immunoaffinity Purification of Human Neutrophil Flavocytochrome B for Structure Determination by Electron Microscopy

Determination of the structure of human neutrophil (PMN) flavocytochrome b (Cytb) is a necessary step for the understanding of the structure-function essentials of NADPH oxidase activity. This understanding is crucial for structure-driven therapeutic approaches addressing control of inflammation and infection. Our work on purification and sample preparation of Cytb has facilitated progress toward the goal of structure determination. Here we describe exploiting immunoaffinity purification of Cytb for initial examination of its size and shape by a combination of classical and cryoelectron microscopic (EM) methods. For these evaluations, we used conventional negative-stain transmission electron microscopy (TEM) to examine both detergent-solubilized Cytb as single particles and Cytb in phosphatidylcholine reconstituted membrane vesicles as densely packed random, partially ordered, and subcrystalline arrays. In preliminary trials, we also examined single particles by cryoelectron microscopy (cryoEM) methods. We conclude that Cytb in detergent and reconstituted in membrane is a relatively compact, symmetrical protein of about 100 Å in maximum dimension. The negative stain, preliminary cryoEM, and crude molecular models suggest that the protein is probably a heterotetramer of two p22^phox and gp91^phox subunits in both detergent micelles and membrane vesicles. This exploratory study also suggests that high-resolution 2D electron microscopic approaches may be accessible to human material collected from single donors.

Constitutive activation of WASp in X-linked neutropenia renders neutrophils hyperactive

Congenital neutropenia is characterized by low absolute neutrophil numbers in blood, leading to recurrent bacterial infections, and patients often require life-long granulocyte CSF (G-CSF) support. X-linked neutropenia (XLN) is caused by gain-of-function mutations in the actin regulator Wiskott-Aldrich syndrome protein (WASp). To understand the pathophysiology in XLN and the role of WASp in neutrophils, we here examined XLN patients and 2 XLN mouse models. XLN patients had reduced myelopoiesis and extremely low blood neutrophil number. However, their neutrophils had a hyperactive phenotype and were present in normal numbers in XLN patient saliva. Murine XLN neutrophils were hyperactivated, with increased actin dynamics and migration into tissues. We provide molecular evidence that the hyperactivity of XLN neutrophils is caused by WASp in a constitutively open conformation due to contingent phosphorylation of the critical tyrosine-293 and plasma membrane localization. This renders WASp activity less dependent on regulation by PI3K. Our data show that the amplitude of WASp activity inside a cell could be enhanced by cell-surface receptor signaling even in the context in which WASp is already in an active conformation. Moreover, these data categorize XLN as an atypical congenital neutropenia in which constitutive activation of WASp in tissue neutrophils compensates for reduced myelopoiesis.

Inherited CARD9 Deficiency: Invasive Disease Caused by Ascomycete Fungi in Previously Healthy Children and Adults

Autosomal recessive CARD9 deficiency underlies life-threatening, invasive fungal infections in otherwise healthy individuals normally resistant to other infectious agents. In less than 10 years, 58 patients from 39 kindreds have been reported in 14 countries from four continents. The patients are homozygous (n = 49; 31 kindreds) or compound heterozygous (n = 9; 8 kindreds) for 22 different CARD9 mutations. Six mutations are recurrent, probably due to founder effects. Paradoxically, none of the mutant alleles has been experimentally demonstrated to be loss-of-function. CARD9 is expressed principally in myeloid cells, downstream from C-type lectin receptors that can recognize fungal components. Patients with CARD9 deficiency present impaired cytokine and chemokine production by macrophages, dendritic cells, and peripheral blood mononuclear cells and defective killing of some fungi by neutrophils in vitro. Neutrophil recruitment to sites of infection is impaired in vivo. The proportion of Th17 cells is low in most, but not all, patients tested. Up to 52 patients suffering from invasive fungal diseases (IFD) have been reported, with ages at onset of 3.5 to 52 years. Twenty of these patients also displayed superficial fungal infections. Six patients had only mucocutaneous candidiasis or superficial dermatophytosis at their last follow-up visit, at the age of 19 to 50 years. Remarkably, for 50 of the 52 patients with IFD, a single fungus was involved; only two patients had IFDs due to two different fungi. IFD recurred in 44 of 45 patients who responded to treatment, and a different fungal infection occurred in the remaining patient. Ten patients died from IFD, between the ages of 12 and 39 years, whereas another patient died at the age of 91 years, from an unrelated cause. At the most recent scheduled follow-up visit, 81% of the patients were still alive and aged from 6.5 to 75 years. Strikingly, all the causal fungi belonged to the phylum Ascomycota: commensal Candida and saprophytic Trychophyton, Aspergillus, Phialophora, Exophiala, Corynesprora, Aureobasidium, and Ochroconis. Human CARD9 is essential for protective systemic immunity to a subset of fungi from this phylum but seems to be otherwise redundant. Previously healthy patients with unexplained invasive fungal infection, at any age, should be tested for inherited CARD9 deficiency.

KEY POINTS

• Inherited CARD9 deficiency (OMIM #212050) is an AR PID due to mutations that may be present in a homozygous or compound heterozygous state. • CARD9 is expressed principally in myeloid cells and transduces signals downstream from CLR activation by fungal ligands. • Endogenous mutant CARD9 levels differ between alleles (from full-length normal protein to an absence of normal protein). • The functional impacts of CARD9 mutations involve impaired cytokine production in response to fungal ligands, impaired neutrophil killing and/or recruitment to infection sites, and defects of Th17 immunity. • The key clinical manifestations in patients are fungal infections, including CMC, invasive (in the CNS in particular) Candida infections, extensive/deep dermatophytosis, subcutaneous and invasive phaeohyphomycosis, and extrapulmonary aspergillosis. • The clinical penetrance of CARD9 deficiency is complete, but penetrance is incomplete for each of the fungi concerned. • Age at onset is highly heterogeneous, ranging from childhood to adulthood for the same fungal disease. • All patients with unexplained IFD should be tested for CARD9 mutations. Familial screening and genetic counseling should be proposed. • The treatment of patients with CARD9 mutations is empirical and based on antifungal therapies and the surgical removal of fungal masses. Patients with persistent/relapsing Candida infections of the CNS could be considered for adjuvant GM-CSF/G-CSF therapy. The potential value of HSCT for CARD9-deficient patients remains unclear.

Lessons learned from the study of human inborn errors of innate immunity

Innate immunity contributes to host defense through all cell types and relies on their shared germline genetic background, whereas adaptive immunity operates through only 3 main cell types, αβ T cells, γδ T cells, and B cells, and relies on their somatic genetic diversification of antigen-specific responses. Human inborn errors of innate immunity often underlie infectious diseases. The range and nature of infections depend on the mutated gene, the deleteriousness of the mutation, and other ill-defined factors. Most known inborn errors of innate immunity to infection disrupt the development or function of leukocytes other than T and B cells, but a growing number of inborn errors affect cells other than circulating and tissue leukocytes. Here we review inborn errors of innate immunity that have been recently discovered or clarified. We highlight the immunologic implications of these errors.

Laminar Flow-based Assays to Investigate Leukocyte Recruitment on Cultured Vascular Cells and Adherent Platelets

The recruitment of leukocytes upon injury or inflammation to sites of injury or tissue damage has been investigated during recent decades and has resulted in the concept of the leukocyte adhesion cascade. However, the exact molecular mechanisms involved in leukocyte recruitment have not yet been fully identified. Since leukocyte recruitment remains an important subject in the field of infection, inflammation, and (auto-) immune research, we present a straightforward laminar flow-based assay to study underlying mechanisms of the adhesion, de-adhesion, and transmigration of leukocytes under venous and arterial flow regimes. The in vitro assay can be used to study the molecular mechanisms that underlie the interactions between leukocytes and their cellular partners in different models of vascular inflammation. This protocol describes a laminar flow-based assay using a parallel-flow chamber and an inverted phase contrast microscope connected to a camera to study the interactions of leukocytes and endothelial cells or platelets, which can be visualized and recorded then analyzed offline. Endothelial cells, platelets, or leukocytes can be pretreated with inhibitors or antibodies to determine the role of specific molecules during this process. Shear conditions, i.e. arterial or venous shear stress, can be easily adapted by the viscosity and flow rate of the perfused fluids and the height of the channel.

Neutrophils to the ROScue: Mechanisms of NADPH Oxidase Activation and Bacterial Resistance

Reactive oxygen species (ROS) generated by NADPH oxidase play an important role in antimicrobial host defense and inflammation. Their deficiency in humans results in recurrent and severe bacterial infections, while their unregulated release leads to pathology from excessive inflammation. The release of high concentrations of ROS aids in clearance of invading bacteria. Localization of ROS release to phagosomes containing pathogens limits tissue damage. Host immune cells, like neutrophils, also known as PMNs, will release large amounts of ROS at the site of infection following the activation of surface receptors. The binding of ligands to G-protein-coupled receptors (GPCRs), toll-like receptors, and cytokine receptors can prime PMNs for a more robust response if additional signals are encountered. Meanwhile, activation of Fc and integrin directly induces high levels of ROS production. Additionally, GPCRs that bind to the bacterial-peptide analog fMLP, a neutrophil chemoattractant, can both prime cells and trigger low levels of ROS production. Engagement of these receptors initiates intracellular signaling pathways, resulting in activation of downstream effector proteins, assembly of the NADPH oxidase complex, and ultimately, the production of ROS by this complex. Within PMNs, ROS released by the NADPH oxidase complex can activate granular proteases and induce the formation of neutrophil extracellular traps (NETs). Additionally, ROS can cross the membranes of bacterial pathogens and damage their nucleic acids, proteins, and cell membranes. Consequently, in order to establish infections, bacterial pathogens employ various strategies to prevent restriction by PMN-derived ROS or downstream consequences of ROS production. Some pathogens are able to directly prevent the oxidative burst of phagocytes using secreted effector proteins or toxins that interfere with translocation of the NADPH oxidase complex or signaling pathways needed for its activation. Nonetheless, these pathogens often rely on repair and detoxifying proteins in addition to these secreted effectors and toxins in order to resist mammalian sources of ROS. This suggests that pathogens have both intrinsic and extrinsic mechanisms to avoid restriction by PMN-derived ROS. Here, we review mechanisms of oxidative burst in PMNs in response to bacterial infections, as well as the mechanisms by which bacterial pathogens thwart restriction by ROS to survive under conditions of oxidative stress.

Cellular and Molecular Defects Underlying Invasive Fungal Infections-Revelations from Endemic Mycoses

The global burden of fungal diseases has been increasing, as a result of the expanding number of susceptible individuals including people living with human immunodeficiency virus (HIV), hematopoietic stem cell or organ transplant recipients, patients with malignancies or immunological conditions receiving immunosuppressive treatment, premature neonates, and the elderly. Opportunistic fungal pathogens such as Aspergillus, Candida, Cryptococcus, Rhizopus, and Pneumocystis jiroveci are distributed worldwide and constitute the majority of invasive fungal infections (IFIs). Dimorphic fungi such as Histoplasma capsulatum, Coccidioides spp., Paracoccidioides spp., Blastomyces dermatiditis, Sporothrix schenckii, Talaromyces (Penicillium) marneffei, and Emmonsia spp. are geographically restricted to their respective habitats and cause endemic mycoses. Disseminated histoplasmosis, coccidioidomycosis, and T. marneffei infection are recognized as acquired immunodeficiency syndrome (AIDS)-defining conditions, while the rest also cause high rate of morbidities and mortalities in patients with HIV infection and other immunocompromised conditions. In the past decade, a growing number of monogenic immunodeficiency disorders causing increased susceptibility to fungal infections have been discovered. In particular, defects of the IL-12/IFN-γ pathway and T-helper 17-mediated response are associated with increased susceptibility to endemic mycoses. In this review, we put together the various forms of endemic mycoses on the map and take a journey around the world to examine how cellular and molecular defects of the immune system predispose to invasive endemic fungal infections, including primary immunodeficiencies, individuals with autoantibodies against interferon-γ, and those receiving biologic response modifiers. Though rare, these conditions provide importance insights to host defense mechanisms against endemic fungi, which can only be appreciated in unique climatic and geographical regions.

Interactions between Neutrophils and Pseudomonas aeruginosa in Cystic Fibrosis

Cystic fibrosis (CF) affects 70,000 patients worldwide. Morbidity and mortality in CF is largely caused by lung complications due to the triad of impaired mucociliary clearance, microbial infections and chronic inflammation. Cystic fibrosis airway inflammation is mediated by robust infiltration of polymorphonuclear neutrophil granulocytes (PMNs, neutrophils). Neutrophils are not capable of clearing lung infections and contribute to tissue damage by releasing their dangerous cargo. Pseudomonas aeruginosa is an opportunistic pathogen causing infections in immunocompromised individuals. P. aeruginosa is a main respiratory pathogen in CF infecting most patients. Although PMNs are key to attack and clear P. aeruginosa in immunocompetent individuals, PMNs fail to do so in CF. Understanding why neutrophils cannot clear P. aeruginosa in CF is essential to design novel therapies. This review provides an overview of the antimicrobial mechanisms by which PMNs attack and eliminate P. aeruginosa. It also summarizes current advances in our understanding of why PMNs are incapable of clearing P. aeruginosa and how this bacterium adapts to and resists PMN-mediated killing in the airways of CF patients chronically infected with P. aeruginosa.