Antimicrobial activity of HL-60 cells compared to primary blood-derived neutrophils against Staphylococcus aureus

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.

A conserved 3D pattern in a Streptococcus pyogenes M protein immunogen elicits M-type crossreactivity

Coiled coil-forming M proteins of the widespread and potentially deadly bacterial pathogen Streptococcus pyogenes (strep A) are immunodominant targets of opsonizing antibodies. However, antigenic sequence variability of M proteins into >220 M types, as defined by their hypervariable regions (HVRs), is considered to limit M proteins as vaccine immunogens because of type specificity in the antibody response. Surprisingly, a multi-HVR immunogen in clinical vaccine trials was shown to elicit M-type crossreactivity. The basis for this crossreactivity is unknown but may be due in part to antibody recognition of a 3D pattern conserved in many M protein HVRs that confers binding to human complement C4b-binding protein (C4BP). To test this hypothesis, we investigated whether a single M protein immunogen carrying the 3D pattern would elicit crossreactivity against other M types carrying the 3D pattern. We found that a 34-amino acid sequence of S. pyogenes M2 protein bearing the 3D pattern retained full C4BP-binding capacity when fused to a coiled coil-stabilizing sequence from the protein GCN4. We show that this immunogen, called M2G, elicited cross-reactive antibodies against a number of M types that carry the 3D pattern but not against those that lack the 3D pattern. We further show that the M2G antiserum-recognized M proteins displayed natively on the strep A surface and promoted the opsonophagocytic killing of strep A strains expressing these M proteins. As C4BP binding is a conserved virulence trait of strep A, we propose that targeting the 3D pattern may prove advantageous in vaccine design.

Evaluation of the innate immune response of caprine neutrophils against Mycobacterium avium subspecies paratuberculosis in vitro

Neutrophils constitute an essential component of the innate immune response, readily killing most bacteria through phagocytosis, degranulation, and the release of neutrophil extracellular traps (NETs) among other mechanisms. These cells play an unclear role in mycobacterial infections such as Mycobacterium avium subspecies paratuberculosis (Map), the etiological agent of paratuberculosis, and its response is particularly understudied in ruminants. Herein, a wide set of techniques were adapted, or newly developed, to study the in vitro response of caprine neutrophils after Map infection. Immunofluorescence was used to demonstrate, simultaneously, chemotaxis, phagocytosis, degranulation, and NETs. The quantification of neutrophil phagocytic activity against Map at a 1:10 multiplicity of infection (MOI), through flow cytometry, showed values that varied from 4.54 to 5.63% of phagocyting neutrophils. By immunofluorescence, a 73.3 ± 14.5% of the fields showed NETs, and the mean release of DNA, attributable to NETosis, calculated through a fluorometric method, was 16.2 ± 3.5%. In addition, the RNA expression of TGF-β, TNF and IL-1β cytokines, measured through reverse transcription qPCR, was significantly higher in the two latter. Overall, neutrophil response was proportional to the number of bacteria. This work confirms that the simultaneous study of several neutrophil mechanisms, and the combination of different methodologies, are essential to reach a comprehensive understanding of neutrophil response against pathogens, demonstrates that, in vitro, caprine neutrophils display a strong innate response against Map, using their entire repertoire of effector functions, and sets the basis for further in vitro and in vivo studies on the role of neutrophils in paratuberculosis.

A high-throughput cytotoxicity screening platform reveals agr-independent mutations in bacteraemia-associated Staphylococcus aureus that promote intracellular persistence

Staphylococcus aureus infections are associated with high mortality rates. Often considered an extracellular pathogen, S. aureus can persist and replicate within host cells, evading immune responses, and causing host cell death. Classical methods for assessing S. aureus cytotoxicity are limited by testing culture supernatants and endpoint measurements that do not capture the phenotypic diversity of intracellular bacteria. Using a well-established epithelial cell line model, we have developed a platform called InToxSa (intracellular toxicity of S. aureus) to quantify intracellular cytotoxic S. aureus phenotypes. Studying a panel of 387 S. aureus bacteraemia isolates, and combined with comparative, statistical, and functional genomics, our platform identified mutations in S. aureus clinical isolates that reduced bacterial cytotoxicity and promoted intracellular persistence. In addition to numerous convergent mutations in the Agr quorum sensing system, our approach detected mutations in other loci that also impacted cytotoxicity and intracellular persistence. We discovered that clinical mutations in ausA, encoding the aureusimine non-ribosomal peptide synthetase, reduced S. aureus cytotoxicity, and increased intracellular persistence. InToxSa is a versatile, high-throughput cell-based phenomics platform and we showcase its utility by identifying clinically relevant S. aureus pathoadaptive mutations that promote intracellular residency.

Sourcing cells for in vitro models of human vascular barriers of inflammation

The vascular system plays a critical role in the progression and resolution of inflammation. The contributions of the vascular endothelium to these processes, however, vary with tissue and disease state. Recently, tissue chip models have emerged as promising tools to understand human disease and for the development of personalized medicine approaches. Inclusion of a vascular component within these platforms is critical for properly evaluating most diseases, but many models to date use "generic" endothelial cells, which can preclude the identification of biomedically meaningful pathways and mechanisms. As the knowledge of vascular heterogeneity and immune cell trafficking throughout the body advances, tissue chip models should also advance to incorporate tissue-specific cells where possible. Here, we discuss the known heterogeneity of leukocyte trafficking in vascular beds of some commonly modeled tissues. We comment on the availability of different tissue-specific cell sources for endothelial cells and pericytes, with a focus on stem cell sources for the full realization of personalized medicine. We discuss sources available for the immune cells needed to model inflammatory processes and the findings of tissue chip models that have used the cells to studying transmigration.

Modulatory Contribution of Oxygenating Hydrogels and Polyhexamethylene Biguanide on the Antimicrobial Potency of Neutrophil-like Cells

Neutrophils are a first line of host defense against infection and utilize a series of oxygen-dependent processes to eliminate pathogens. Research suggests that oxygen availability can improve anti-infective mechanisms by promoting the formation of reactive oxygen species. Also, oxygen can synergistically upregulate the antibacterial properties of certain antibiotics against bacteria by altering their metabolism and causing an increase in the antibiotic uptake of bacteria. Therefore, understanding the effects of oxygen availability, as provided via a biomaterial treatment alone or along with potent antibacterial agents, on neutrophil functions can lead us to the development of new anti-inflammatory and anti-infective approaches. However, the study of neutrophil functions in vitro is often limited by their short life span and nonreproducibility, which suggests the need for cell line-based models as a substitute for primary neutrophils. Here, we took advantage of the differentiated human leukemia-60 cell line (HL-60), as an in vitro neutrophil model, to test the effects of local oxygen and antibacterial delivery by fluorinated methacrylamide chitosan (MACF) hydrogels incorporated with polyhexamethylene biguanide (PHMB) antibacterial agent. Considering the natural modes of neutrophil actions to combat bacteria, we studied the impact of our dual functioning oxygenating-antibacterial platforms on neutrophil phagocytosis and antibacterial properties as well as the formation of neutrophil extracellular traps (NETs) and reactive oxygen species (ROS). Our results demonstrated that supplemental oxygen and antibacterial delivery from MACF-PHMB hydrogel platforms upregulated neutrophil antibacterial properties and ROS production. NET formation by neutrophils upon treatment with MACF and PHMB varied when chemical and biological stimuli were used. Overall, this study presents a model to study immune responses in vitro and lays the foundation for future studies to investigate if similar responses also occur in vivo.

Responses of promyelocytic leukemia HL60 cells as an inflammatory cell lineage model to silica microparticles used to coat blood collection tubes

Background

The preparation of platelet-rich fibrin (PRF) requires glass blood collection tubes, and thus, the shortage or unavailability of such tubes has driven clinicians to search for suitable substitutes, such as silica-coated plastic tubes. However, we have previously demonstrated the cytotoxicity of silica microparticles (MPs) used in plastic tubes to cultured human periosteal cells. To further establish the effects of silica MPs on inflammation, we examined silica MP-induced changes in a human promyelocytic cell model in vitro.

Methods

Human promyelocytic HL60 cells were used either without chemical induction or after differentiation induced using phorbol myristate acetate (PMA) or dimethyl sulfoxide. HL60 cells, osteoblastic MG63, and Balb/c mouse cells were treated with silica MPs, and their surface ultrastructure and numbers were examined using a scanning electron microscope and an automated cell counter, respectively. Differentiation markers, such as acid phosphatase, non-specific esterase, and CD11b, were visualized by cytochemical and immunofluorescent staining, and superoxide dismutase (SOD) activity was quantified.

Results

Regardless of SOD activity, silica cytotoxicity was observed in MG63 and Balb/c cells. At sub-toxic doses, silica MPs slightly or moderately upregulated the differentiation markers of the control, PMA-induced monocytic, and dimethyl sulfoxide-induced granulocytic HL60 cells. Although SOD activity was the highest (P < 0.05) in PMA-induced cells, a silica-induced reduction in cell adhesion was observed only in those cells (P < 0.05).

Conclusions

Silica MP contamination of PRF preparations can potentially exacerbate inflammation at implantation sites. Consequently, unless biomedical advantages can be identified, silica-coated plastic blood collection tubes should not be routinely used for PRF preparations.

Immunomodulation: Immunoglobulin Preparations Suppress Hyperinflammation in a COVID-19 Model via FcγRIIA and FcαRI

The rapid spread of SARS-CoV-2 has induced a global pandemic. Severe forms of COVID-19 are characterized by dysregulated immune response and "cytokine storm". The role of IgG and IgM antibodies in COVID-19 pathology is reasonably well studied, whereas IgA is neglected. To improve clinical outcome of patients, immune modulatory drugs appear to be beneficial. Such drugs include intravenous immunoglobulin preparations, which were successfully tested in severe COVID-19 patients. Here we established a versatile in vitro model to study inflammatory as well as anti-inflammatory processes by therapeutic human immunoglobulins. We dissect the inflammatory activation on neutrophil-like HL60 cells, using an immune complex consisting of latex beads coated with spike protein of SARS-CoV-2 and opsonized with specific immunoglobulins from convalescent plasma. Our data clarifies the role of Fc-receptor-dependent phagocytosis via IgA-FcαRI and IgG-FcγR for COVID-19 disease followed by cytokine release. We show that COVID-19 associated inflammation could be reduced by addition of human immunoglobulin preparations (IVIG and trimodulin), while trimodulin elicits stronger immune modulation by more powerful ITAMi signaling. Besides IgG, the IgA component of trimodulin in particular, is of functional relevance for immune modulation in this assay setup, highlighting the need to study IgA mediated immune response.

For Better or for Worse: A Look Into Neutrophils in Traumatic Spinal Cord Injury

Neutrophils are short-lived cells of the innate immune system and the first line of defense at the site of an infection and tissue injury. Pattern recognition receptors on neutrophils recognize pathogen-associated molecular patterns or danger-associated molecular patterns, which recruit them to the destined site. Neutrophils are professional phagocytes with efficient granular constituents that aid in the neutralization of pathogens. In addition to phagocytosis and degranulation, neutrophils are proficient in creating neutrophil extracellular traps (NETs) that immobilize pathogens to prevent their spread. Because of the cytotoxicity of the associated granular proteins within NETs, the microbes can be directly killed once immobilized by the NETs. The role of neutrophils in infection is well studied; however, there is less emphasis placed on the role of neutrophils in tissue injury, such as traumatic spinal cord injury. Upon the initial mechanical injury, the innate immune system is activated in response to the molecules produced by the resident cells of the injured spinal cord initiating the inflammatory cascade. This review provides an overview of the essential role of neutrophils and explores the contribution of neutrophils to the pathologic changes in the injured spinal cord.

Extracellular vesicles from dHL-60 cells as delivery vehicles for diverse therapeutics

Extracellular vesicles (EVs) are membrane-derived heterogeneous vesicles that mediate intercellular communications. They have recently been considered as ideal vehicles for drug-delivery systems, and immune cells are suggested as a potential source for drug-loaded EVs. In this study, we investigated the possibility of neutrophils as a source for drug-loaded EVs. Neutrophil-like differentiated human promyelocytic leukemia cells (dHL-60) produced massive amounts of EVs within 1 h. The dHL-60 cells are also easily loaded with various cargoes such as antibiotics (penicillin), anticancer drug (paclitaxel), chemoattractant (MCP-1), miRNA, and Cas9. The EVs derived from the dHL-60 cells showed efficient incorporation of these cargoes and significant effector functions, such as bactericidal activity, monocyte chemotaxis, and macrophage polarization. Our results suggest that neutrophils or neutrophil-like promyelocytic cells could be an attractive source for drug-delivery EVs.

Differentiation of HL-60 cells in serum-free hematopoietic cell media enhances the production of neutrophil extracellular traps

Neutrophil extracellular traps (NETs) are web-like structures made of chromatin and have been identified to have a role in the host's immune defense. Differentiated human promyelocytic leukemia HL-60 cells (dHL-60) have been used to study the mechanisms of NETs formation, as neutrophils have a short lifespan that limits their use. However, dHL-60 cells are inefficient at generating NETs and therefore are not ideal replacements for neutrophils in studying of NET formation. In the present study, the optimal cell culture conditions and differentiation time that result in the most effective release of NETs from dHL-60 cells upon stimulation were determined. HL-60 cells were cultured in serum (FBS) or serum-free (X-VIVO) medium and differentiated using all-trans retinoic acid (ATRA) or dimethyl sulfoxide (DMSO). dHL-60 cells were stimulated with phorbol 12-myristate 13-acetate (PMA) or Ca²⁺ ionophore (CI). Cell differentiation and apoptosis, as well as the formation of reactive oxygen species (ROS) and citrullinated histone H3 (citH3) were analyzed using flow cytometry. NETs were visualized using fluorescence microscopy and NET quantification was performed using PicoGreen. Induction of HL-60 cells for five days produced the best results in terms of differentiation markers and cell viability. Both ATRA- and DMSO-induced dHL-60 cells were able to release NETs upon PMA and CI stimulation; dHL-60 cells in serum-free medium produced more NETs than those in serum-containing medium. DMSO-dHL-60 (X-VIVO) cells were most efficient at producing NETs and ROS upon stimulation with PMA, while ATRA-dHL-60 (X-VIVO) cells were most efficient at producing NETs and citH3 upon stimulation with CI. It was concluded that DMSO-dHL-60 (X-VIVO) may be a model for the study of ROS-high NETosis and ATRA-dHL-60 (X-VIVO) may be suitable for ROS-low NETosis.

Studying Neutrophil Function in vitro: Cell Models and Environmental Factors

Neutrophils are the most abundant immune cell type in the blood and constitute the first line of defense against invading pathogens. Despite their important role in many diseases, they are challenging to study due to their short life span and the inability to cryopreserve or expand them in vitro. Thus, research into neutrophils has to rely on cells freshly isolated from peripheral blood of human donors, introducing donor-dependent variation in the experimental data. To counteract these problems, researchers tried to develop adequate cell models, such as cell lines. For those functional studies that cannot rely on cell models, a standardization of protocols regarding neutrophil purification and culturing could be a solution. In this review, we provide an overview of the most commonly used models for neutrophil function (HL-60, PLB-985, NB4, Kasumi-1 and induced pluripotent stem cells). In addition, we describe the effects of glucose concentration, pH, oxygen tension and temperature on neutrophil function.

Neutrophil activation by nanomaterials in vitro: comparing strengths and limitations of primary human cells with those of an immortalized (HL-60) cell line

Assessment of nanomaterial (NM) induced inflammatory responses has largely relied on rodent testing via measurement of leukocyte accumulation in target organs. Despite observations that NMs activate neutrophil driven inflammatory responses in vivo, a limited number of studies have investigated neutrophil responses to NMs in vitro. We compared responses between the human neutrophil-like HL-60 cell line and human primary neutrophils following exposure to silver (Ag), zinc oxide (ZnO), copper oxide (CuO) and titanium dioxide (TiO₂) NMs. NM cytotoxicity and neutrophil activation were assessed by measuring cellular metabolic activity, cytokine production, respiratory burst, and release of neutrophil extracellular traps. We observed a similar pattern of response between HL-60 cells and primary neutrophils, however we report that some neutrophil functions are compromised in the cell line. Ag NMs were consistently observed to stimulate neutrophil activation, with CuO NMs inducing similar though weaker responses. TiO₂ NMs did not induce a neutrophil response in either cell type. Interestingly, ZnO NMs readily induced activation of HL-60 cells but did not appear to activate primary cells. Our findings are relevant to the development of a tiered testing strategy for NM hazard assessment which promotes the use of non-rodent models. Whilst we acknowledge that HL-60 cells may not be a perfect substitute for primary cells and require further investigation regarding their ability to predict neutrophil activation, we recommend their use for initial screening of NM-induced inflammation. Primary human neutrophils can then be used for more focused assessments of neutrophil activation before progressing to in vivo models where necessary.

Combined Effect of Naturally-Derived Biofilm Inhibitors and Differentiated HL-60 Cells in the Prevention of Staphylococcus aureus Biofilm Formation

Nosocomial diseases represent a huge health and economic burden. A significant portion is associated with the use of medical devices, with 80% of these infections being caused by a bacterial biofilm. The insertion of a foreign material usually elicits inflammation, which can result in hampered antimicrobial capacity of the host immunity due to the effort of immune cells being directed to degrade the material. The ineffective clearance by immune cells is a perfect opportunity for bacteria to attach and form a biofilm. In this study, we analyzed the antibiofilm capacity of three naturally derived biofilm inhibitors when combined with immune cells in order to assess their applicability in implantable titanium devices and low-density polyethylene (LDPE) endotracheal tubes. To this end, we used a system based on the coculture of HL-60 cells differentiated into polymorphonuclear leukocytes (PMNs) and Staphylococcus aureus (laboratory and clinical strains) on titanium, as well as LDPE surfaces. Out of the three inhibitors, the one coded DHA1 showed the highest potential to be incorporated into implantable devices, as it displayed a combined activity with the immune cells, preventing bacterial attachment on the titanium and LDPE. The other two inhibitors seemed to also be good candidates for incorporation into LDPE endotracheal tubes.

What Is the Evolutionary Fingerprint in Neutrophil Granulocytes?

Over the years of evolution, thousands of different animal species have evolved. All these species require an immune system to defend themselves against invading pathogens. Nevertheless, the immune systems of different species are obviously counteracting against the same pathogen with different efficiency. Therefore, the question arises if the process that was leading to the clades of vertebrates in the animal kingdom-namely mammals, birds, amphibians, reptiles, and fish-was also leading to different functions of immune cells. One cell type of the innate immune system that is transmigrating as first line of defense in infected tissue and counteracts against pathogens is the neutrophil granulocyte. During the host-pathogen interaction they can undergo phagocytosis, apoptosis, degranulation, and form neutrophil extracellular traps (NETs). In this review, we summarize a wide spectrum of information about neutrophils in humans and animals, with a focus on vertebrates. Special attention is kept on the development, morphology, composition, and functions of these cells, but also on dysfunctions and options for cell culture or storage.

Berberine Maintains the Neutrophil N1 Phenotype to Reverse Cancer Cell Resistance to Doxorubicin

This study explores the contributions of neutrophils to chemotherapeutic resistance and berberine-regulated cancer cell sensitivity to doxorubicin (DOX). In vitro experiments, continuous DOX treatment led to the shift of HL-60 cells to N2 neutrophils and thus induced chemotherapeutic resistance. The combination treatment with DOX and 2 µM berberine resulted in the differentiation of HL-60 cells toward N1 and therefore stimulated HL-60 cell immune clearance. Berberine increased reactive oxygen species (ROS) and decreased autophagy and therefore induced apoptosis in HL-60-N2 cells with morphological changes, but had no effect on cell viability in HL-60-N1 cells. The neutrophil-regulating efficacy of berberine was confirmed in the urethane-induced lung carcinogenic model and H22 liver cancer allograft model. Furthermore, we found that DOX-derived neutrophils had high levels of CD133 and CD309 surface expression, which prevented both chemotherapeutic sensitivity and immune rejection by self-expression of PD-L1 and surface expression of PD-1 receptor on T cells, whereas berberine could downregulate CD133 and CD309 surface expression. Finally, berberine-relevant targets and pathways were evaluated. This study first suggests an important role of berberine in regulating neutrophil phenotypes to maintain cancer cell sensitivity to DOX.

Monoclonal antibody 2C5 specifically targets neutrophil extracellular traps

Neutrophils can release DNA and granular cytoplasmic proteins that form smooth filaments of stacked nucleosomes (NS). These structures, called neutrophil extracellular traps (NETs), are involved in multiple pathological processes, and NET formation and removal are clinically significant. The monoclonal antibody 2C5 has strong specificity toward intact NS but not to individual NS components, indicating that 2C5 could potentially target NS in NETs. In this study, NETs were generated in vitro using neutrophils and HL-60 cells differentiated into granulocyte-like cells. The specificity of 2C5 toward NETs was evaluated by ELISA, which showed that it binds to NETs with the specificity similar to that for purified nucleohistone substrate. Immunofluorescence showed that 2C5 stains NETs in both static and perfused microfluidic cell cultures, even after NET compaction. Modification of liposomes with 2C5 dramatically enhanced liposome association with NETs. Our results suggest that 2C5 could be used to identify and visualize NETs and serve as a ligand for NET-targeted diagnostics and therapies.

A map of gene expression in neutrophil-like cell lines

BACKGROUND

Human neutrophils are central players in innate immunity, a major component of inflammatory responses, and a leading model for cell motility and chemotaxis. However, primary neutrophils are short-lived, limiting their experimental usefulness in the laboratory. Thus, human myeloid cell lines have been characterized for their ability to undergo neutrophil-like differentiation in vitro. The HL-60 cell line and its PLB-985 sub-line are commonly used to model human neutrophil behavior, but how closely gene expression in differentiated cells resembles that of primary neutrophils has remained unclear.

RESULTS

In this study, we compared the effectiveness of differentiation protocols and used RNA sequencing (RNA-seq) to compare the transcriptomes of HL-60 and PLB-985 cells with published data for human and mouse primary neutrophils. Among commonly used differentiation protocols for neutrophil-like cell lines, addition of dimethyl sulfoxide (DMSO) gave the best combination of cell viability and expression of markers for differentiation. However, combining DMSO with the serum-free-supplement Nutridoma resulted in increased chemotactic response, phagocytic activity, oxidative burst and cell surface expression of the neutrophil markers FPR1 and CD11b without a cost in viability. RNA-seq analysis of HL-60 and PLB-985 cells before and after differentiation showed that differentiation broadly increases the similarity in gene expression between the cell lines and primary neutrophils. Furthermore, the gene expression pattern of the differentiated cell lines correlated slightly better with that of human neutrophils than the mouse neutrophil pattern did. Finally, we created a publicly available gene expression database that is searchable by gene name and protein domain content, where users can compare gene expression in HL-60, PLB-985 and primary human and mouse neutrophils.

CONCLUSIONS

Our study verifies that a DMSO-based differentiation protocol for HL-60 and PLB-985 cell lines gives superior differentiation and cell viability relative to other common protocols, and indicates that addition of Nutridoma may be preferable for studies of chemotaxis, phagocytosis, or oxidative burst. Our neutrophil gene expression database will be a valuable tool to identify similarities and differences in gene expression between the cell lines and primary neutrophils, to compare expression levels for genes of interest, and to improve the design of tools for genetic perturbations.

Neutrophils mediate HIV-specific antibody-dependent phagocytosis and ADCC

There is growing evidence to support the role of Fc-mediated effector functions, such as Antibody-Dependent Cellular cytotoxicity (ADCC) and Antibody-Dependent Phagocytosis (ADP) in the protection and control of HIV. The RV144 trial and other recent HIV vaccine studies have highlighted the importance of ADCC responses in protection against HIV. The role of neutrophils, the most abundant leukocyte in the blood, has not been thoroughly evaluated for Fc-mediated effector functions to HIV. We optimized HIV-specific neutrophil ADCC and Antibody-Dependent Neutrophil Phagocytosis (ADNP) assays using freshly isolated primary human neutrophils from blood. We also developed methods to study ADP using the neutrophil-like HL-60 cell line. We found that neutrophils mediate both HIV-specific ADP and ADCC responses. In vitro, neutrophil-mediated ADCC responses peaked at 4 h, much faster than primary NK cell or monocyte-mediated responses. We detected a wide range of responses in the ADNP, HL-60 mediated ADP and ADCC across a cohort of 41 viremic antiretroviral therapy naïve HIV positive subjects. HL-60 and Neutrophil-mediated ADP and ADCC responses correlated well with each other, suggesting that they measure overlapping functions. The ADNP and HL-60 ADP inversely correlated with HIV viral load, suggesting that these antibody-mediated neutrophil-based assays should prove useful in dissecting HIV-specific immunity.

CD40 ligand deficiency causes functional defects of peripheral neutrophils that are improved by exogenous IFN-γ

BACKGROUND

Patients with X-linked hyper-IgM syndrome caused by CD40 ligand (CD40L) deficiency often present with episodic, cyclic, or chronic neutropenia, suggesting abnormal neutrophil development in the absence of CD40L-CD40 interaction. However, even when not neutropenic and despite immunoglobulin replacement therapy, CD40L-deficient patients are susceptible to life-threatening infections caused by opportunistic pathogens, suggesting impaired phagocyte function and the need for novel therapeutic approaches.

OBJECTIVES

We sought to analyze whether peripheral neutrophils from CD40L-deficient patients display functional defects and to explore the in vitro effects of recombinant human IFN-γ (rhIFN-γ) on neutrophil function.

METHODS

We investigated the microbicidal activity, respiratory burst, and transcriptome profile of neutrophils from CD40L-deficient patients. In addition, we evaluated whether the lack of CD40L in mice also affects neutrophil function.

RESULTS

Neutrophils from CD40L-deficient patients exhibited defective respiratory burst and microbicidal activity, which were improved in vitro by rhIFN-γ but not soluble CD40L. Moreover, neutrophils from patients showed reduced CD16 protein expression and a dysregulated transcriptome suggestive of impaired differentiation. Similar to CD40L-deficient patients, CD40L knockout mice were found to have impaired neutrophil responses. In parallel, we demonstrated that soluble CD40L induces the promyelocytic cell line HL-60 to proliferate and mature by regulating the expression of genes of the same Gene Ontology categories (eg, cell differentiation) when compared with those dysregulated in peripheral blood neutrophils from CD40L-deficient patients.

CONCLUSION

Our data suggest a nonredundant role of CD40L-CD40 interaction in neutrophil development and function that could be improved in vitro by rhIFN-γ, indicating a potential novel therapeutic application for this cytokine.

The influence of agents differentiating HL-60 cells toward granulocyte-like cells on their ability to release neutrophil extracellular traps

Studies on neutrophil extracellular traps (NETs) are challenging as neutrophils live shortly and easily become activated. Thus, availability of a cell line model closely resembling the functions of peripheral blood neutrophils would be advantageous. Our purpose was to find a compound that most effectively differentiates human promyelocytic leukemia (HL-60) cells toward granulocyte-like cells able to release NETs. HL-60 cells were differentiated with all-trans retinoic acid (ATRA), dimethyl sulfoxide (DMSO) or dimethylformamide (DMF) and stimulated with phorbol 12-myristate 13-acetate (PMA) or calcium ionophore A23187 (CI). Cell differentiation, phagocytosis and calcium influx were analyzed by flow cytometry. Reactive oxygen species production and NETs release were measured fluorometrically and analyzed microscopically. LC3-II accumulation and histone 3 citrullination were analyzed by western blot. ATRA most effectively differentiated HL-60 cells toward granulocyte-like cells. ATRA-dHL-60 cells released NETs only upon PMA stimulation, DMSO-dHL-60 cells only post CI stimulation, while DMF-dHL-60 cells formed NETs in response to both stimuli. Oxidative burst was induced in ATRA-, DMSO- and DMF-dHL-60 cells post PMA stimulation and only in DMF-dHL-60 cells post CI stimulation. Increased histone 3 citrullination was observed in stimulated DMSO- and DMF-, but not in ATRA-dHL-60 cells. The calcium influx was diminished in ATRA-dHL-60 cells. Significant increase in autophagosomes formation was observed only in PMA-stimulated DMF-dHL-60 cells. Phagocytic index was higher in ATRA-dHL-60 cells than in control, DMSO- and DMF-dHL-60 cells. We conclude that ATRA, DMSO and DMF differentiate HL-60 in different mechanisms. DMF is the best stimulus for HL-60 cell differentiation for NETs studies.