Using Imaging Flow Cytometry to Quantify Neutrophil Phagocytosis

Intrapulmonary-administered myeloid derived suppressor cells rescue mice from Pseudomonas aeruginosa infection and promote a regulatory/repair phenotype

Pseudomonas aeruginosa (P.aeruginosa) is a pathogenic opportunistic bacterium, classified as a priority by the WHO for the research of new treatments. As this bacterium is harmful through the inflammation and tissue damage it causes, we investigated the role of Myeloid Derived Suppressor Cells (MDSC) in P.aeruginosa infections and their potential as a therapeutic tool. Using both 'classically' obtained MDSC (through mice bone-marrow differentiation), and a new procedure developed here (using the ER-Hoxb8 hematopoietic cell line), we observed that after administering intra-nasally a lethal dose of P.aeruginosa (PAO1), intra-pulmonary transfer of MDSC, in both prophylactic and therapeutic protocols, markedly improves survival of P.aeruginosa infected animals. Mechanistically, with a sub-lethal dose of P.aeruginosa, we observed that MDSC transfer modulated lung tissue injury, down-regulated inflammatory responses and elicited lung repair. We further showed that WT-PAO1 and MDSC (and their subtypes PMN-MDSC and M-MDSC) could interact directly in vitro and in vivo, and that both PMN- and M-MDSC gene expression (assessed through RNA sequencing) was modulated after in vitro P.aeruginosa infection, and that WT-PAO1 (but not ΔFlic-PAO1) infection led to inhibition of T cell proliferation and promoted epithelial cell wound healing. Furthermore, we showed that the transcription factor Nr4A1 was up-regulated in both PMN- and M-MDSC- infected cells and may be an important mediator in the process. Altogether, we highlight a potential beneficial role of MDSC in P.aeruginosa infection responses and suggest that the unique properties of these cells make them attractive potential new therapeutic tools for patients with acute or chronic inflammatory diseases.

Comparative Effectiveness of Ascorbic Acid vs. Calcium Ascorbate Ingestion on Pharmacokinetic Profiles and Immune Biomarkers in Healthy Adults: A Preliminary Study

BACKGROUND

Previous trials have displayed augmented intracellular vitamin C concentrations in the leukocytes at 24 h after acute supplementation with 1000 mg calcium ascorbate (CA), compared to ascorbic acid (AA).

OBJECTIVE

The primary objective was to evaluate comparative leukocyte vitamin C accumulation kinetics over 32 h following acute 250 mg or 500 mg doses from the two sources. Secondary objectives were to evaluate neutrophil phagocytic function and lymphocyte differentiation between the two sources of vitamin C.

METHODS

Ninety-three healthy females (250 mg, n = 27; 500 mg, n = 24) and males (250 mg, n = 19; 500 mg, n = 23) were assigned to ingest a single dose of CA or AA providing 250 mg or 500 mg of vitamin C in two separate double-blind, randomized crossover trials.

RESULTS

There were no significant differences in the primary or secondary outcomes between the two treatments in the 250 mg low-dose study. Conversely, there was evidence that ingestion of 500 mg of CA increased DHA in plasma, increased neutrophil functionality during the first 8 h of the PK study, promoted increased natural killer cells, and altered weight-adjusted PK profiles, suggesting greater volume distribution and clearance from the blood.

CONCLUSIONS

These findings indicate that 500 mg of CA may promote some immune benefits compared to 500 mg of AA ingestion.

An AI-based imaging flow cytometry approach to study erythrophagocytosis

Erythrophagocytosis is a process consisting of recognition, engulfment and digestion by phagocytes of antibody-coated or damaged erythrocytes. Understanding the dynamics that are behind erythrophagocytosis is fundamental to comprehend this cellular process under specific circumstances. Several techniques have been used to study phagocytosis. Among these, an interesting approach is the use of Imaging Flow Cytometry (IFC) to distinguish internalization and binding of cells or particles. However, this method requires laborious analysis. Here, we introduce a novel approach to analyze the phagocytosis process by combining Artificial Intelligence (AI) with IFC. Our study demonstrates that this approach is highly suitable to study erythrophagocytosis, categorizing internalized, bound and non-bound erythrocytes. Validation experiments showed that our pipeline performs with high accuracy and reproducibility.

Neisseria gonorrhoeae scavenges host sialic acid for Siglec-mediated, complement-independent suppression of neutrophil activation

Gonorrhea, caused by the bacterium Neisseria gonorrhoeae (Gc), is characterized by neutrophilic influx to infection sites. Gc has developed mechanisms to resist killing by neutrophils that include modifications to its surface lipooligosaccharide (LOS). One such LOS modification is sialylation: Gc sialylates its terminal LOS sugars with cytidine-5'-monophosphate-N-acetylneuraminic acid, which is scavenged from the host using LOS sialyltransferase (Lst) since Gc cannot make its sialic acid. Sialylation enables sensitive strains of Gc to resist complement-mediated killing in a serum-dependent manner. However, little is known about the contribution of sialylation to complement-independent, direct Gc-neutrophil interactions. In the absence of complement, we found sialylated Gc expressing opacity-associated (Opa) proteins decreased the oxidative burst and granule exocytosis from primary human neutrophils. In addition, sialylated Opa+ Gc survived better than vehicle treated or Δlst Gc when challenged with neutrophils. However, Gc sialylation did not significantly affect Opa-dependent association with or internalization of Gc by neutrophils. Previous studies have implicated sialic acid-binding immunoglobulin-type lectins (Siglecs) in modulating neutrophil interactions with sialylated Gc. Blocking neutrophil Siglecs with antibodies that bind to their extracellular domains eliminated the ability of sialylated Opa+ Gc to suppress the oxidative burst and resist neutrophil killing. These findings highlight a new role for sialylation in Gc evasion of human innate immunity, with implications for the development of vaccines and therapeutics for gonorrhea.

IMPORTANCE

Neisseria gonorrhoeae, the bacterium that causes gonorrhea, is an urgent global health concern due to increasing infection rates, widespread antibiotic resistance, and its ability to thwart protective immune responses. The mechanisms by which Gc subverts protective immune responses remain poorly characterized. One way N. gonorrhoeae evades human immunity is by adding sialic acid that is scavenged from the host onto its lipooligosaccharide, using the sialyltransferase Lst. Here, we found that sialylation enhances N. gonorrhoeae survival from neutrophil assault and inhibits neutrophil activation, independently of the complement system. Our results implicate bacterial binding of sialic acid-binding lectins (Siglecs) on the neutrophil surface, which dampens neutrophil antimicrobial responses. This work identifies a new role for sialylation in protecting N. gonorrhoeae from cellular innate immunity, which can be targeted to enhance the human immune response in gonorrhea.

Deep-learning image analysis for high-throughput screening of opsono-phagocytosis-promoting monoclonal antibodies against Neisseria gonorrhoeae

Antimicrobial resistance (AMR) is nowadays a global health concern as bacterial pathogens are increasingly developing resistance to antibiotics. Monoclonal antibodies (mAbs) represent a powerful tool for addressing AMR thanks to their high specificity for pathogenic bacteria which allows sparing the microbiota, kill bacteria through complement deposition, enhance phagocytosis or inhibit bacterial adhesion to epithelial cells. Here we describe a visual opsono-phagocytosis assay which relies on confocal microscopy to measure the impact of mAbs on phagocytosis of the bacterium Neisseria gonorrhoeae by macrophages. With respect to traditional CFU-based assays, generated images can be automatically analysed by convolutional neural networks. Our results demonstrate that confocal microscopy and deep learning-based analysis allow screening for phagocytosis-promoting mAbs against N. gonorrhoeae, even when mAbs are not purified and are expressed at low concentration. Ultimately, the flexibility of the staining protocol and of the deep-learning approach make the assay suitable for other bacterial species and cell lines where mAb activity needs to be investigated.

Neisseria gonorrhoeae scavenges host sialic acid for Siglec-mediated, complement-independent suppression of neutrophil activation

Gonorrhea, caused by the bacterium Neisseria gonorrhoeae (Gc), is characterized by neutrophil influx to infection sites. Gc has developed mechanisms to resist killing by neutrophils that include modifications to its surface lipooligosaccharide (LOS). One such LOS modification is sialylation: Gc sialylates its terminal LOS sugars with cytidine-5'-monophosphate-N-acetylneuraminic acid (CMP-NANA) scavenged from the host using LOS sialyltransferase (Lst), since Gc cannot make its own sialic acid. Sialylation enables sensitive strains of Gc to resist complement-mediated killing in a serum-dependent manner. However, little is known about the contribution of sialylation to complement-independent, direct Gc-neutrophil interactions. In the absence of complement, we found sialylated Gc expressing opacity-associated (Opa) proteins decreased the oxidative burst and granule exocytosis from primary human neutrophils. In addition, sialylated Opa+ Gc survived better than vehicle treated or Δlst Gc when challenged with neutrophils. However, Gc sialylation did not significantly affect Opa-dependent association with or internalization of Gc by neutrophils. Previous studies have implicated sialic acid-binding immunoglobulin-type lectins (Siglecs) in modulating neutrophil interactions with sialylated Gc. Blocking neutrophil Siglecs with antibodies that bind to their extracellular domains eliminated the ability of sialylated Opa+ Gc to suppress oxidative burst and resist neutrophil killing. These findings highlight a new role for sialylation in Gc evasion of human innate immunity, with implications for the development of vaccines and therapeutics for gonorrhea.

Phagocytosis via complement receptor 3 enables microbes to evade killing by neutrophils

CR3 (CD11b/CD18; αmβ2 integrin) is a conserved phagocytic receptor. The active conformation of CR3 binds the iC3b fragment of complement C3 as well as many host and microbial ligands, leading to actin-dependent phagocytosis. There are conflicting reports about how CR3 engagement affects the fate of phagocytosed substrates. Using imaging flow cytometry, we confirmed that binding and internalization of iC3b-opsonized polystyrene beads by primary human neutrophils was CR3-dependent. iC3b-opsonized beads did not stimulate neutrophil reactive oxygen species, and most beads were found in primary granule-negative phagosomes. Similarly, Neisseria gonorrhoeae that does not express phase-variable Opa proteins suppresses neutrophil reactive oxygen species and delays phagolysosome formation. Here, binding and internalization of Opa-deleted (Δopa) N. gonorrhoeae by adherent human neutrophils was inhibited using blocking antibodies against CR3 and by adding neutrophil inhibitory factor, which targets the CD11b I-domain. No detectable C3 was deposited on N. gonorrhoeae in the presence of neutrophils alone. Conversely, overexpressing CD11b in HL-60 promyelocytes enhanced Δopa N. gonorrhoeae phagocytosis, which required the CD11b I-domain. Phagocytosis of N. gonorrhoeae was also inhibited in mouse neutrophils that were CD11b-deficient or treated with anti-CD11b. Phorbol ester treatment upregulated surface CR3 on neutrophils in suspension, enabling CR3-dependent phagocytosis of Δopa N. gonorrhoeae. Neutrophils exposed to Δopa N. gonorrhoeae had limited phosphorylation of Erk1/2, p38, and JNK. Neutrophil phagocytosis of unopsonized Mycobacterium smegmatis, which also resides in immature phagosomes, was CR3-dependent and did not elicit reactive oxygen species. We suggest that CR3-mediated phagocytosis is a silent mode of entry into neutrophils, which is appropriated by diverse pathogens to subvert phagocytic killing.

Targeting Neutrophil β2-Integrins: A Review of Relevant Resources, Tools, and Methods

Neutrophils are important innate immune cells that respond during inflammation and infection. These migratory cells utilize β₂-integrin cell surface receptors to move out of the vasculature into inflamed tissues and to perform various anti-inflammatory responses. Although critical for fighting off infection, neutrophil responses can also become dysregulated and contribute to disease pathophysiology. In order to limit neutrophil-mediated damage, investigators have focused on β₂-integrins as potential therapeutic targets, but so far these strategies have failed in clinical trials. As the field continues to move forward, a better understanding of β₂-integrin function and signaling will aid the design of future therapeutics. Here, we provide a detailed review of resources, tools, experimental methods, and in vivo models that have been and will continue to be utilized to investigate the vitally important cell surface receptors, neutrophil β₂-integrins.

Neisseria gonorrhoeae co-opts C4b-binding protein to enhance complement-independent survival from neutrophils

Neisseria gonorrhoeae (Gc) is a human-specific pathogen that causes the sexually transmitted infection gonorrhea. Gc survives in neutrophil-rich gonorrheal secretions, and recovered bacteria predominantly express phase-variable, surface-expressed opacity-associated (Opa) proteins (Opa+). However, expression of Opa proteins like OpaD decreases Gc survival when exposed to human neutrophils ex vivo. Here, we made the unexpected observation that incubation with normal human serum, which is found in inflamed mucosal secretions, enhances survival of Opa+ Gc from primary human neutrophils. We directly linked this phenomenon to a novel complement-independent function for C4b-binding protein (C4BP). When bound to the bacteria, C4BP was necessary and sufficient to suppress Gc-induced neutrophil reactive oxygen species production and prevent neutrophil phagocytosis of Opa+ Gc. This research identifies for the first time a complement-independent role for C4BP in enhancing the survival of a pathogenic bacterium from phagocytes, thereby revealing how Gc exploits inflammatory conditions to persist at human mucosal surfaces.

Quantitative Analysis of Latex Beads Phagocytosis by Human Macrophages Using Imaging Flow Cytometry with Extended Depth of Field (EDF)

The existing methods of quantitative analysis of phagocytosis are characterized by a number of limitations. The usual method of manually counting phagocytosed objects on photographs obtained by confocal microscopy is very labor-intensive and time-consuming. As well, the resolution of conventional flow cytometry does not allow the fluorescence detection of a large number of phagocytosis objects. Thus, there is a need to combine the rapid analysis by flow cytometry and the visualization capability by confocal microscopy. This is possible due to imaging flow cytometry. However, until now, no protocols have allowed one to quantify phagocytosis at its high intensity. The present paper presents the developed and tested algorithm for assessing the level of phagocytic activity using flow cytometry with visualization and IDEAS software.

Variable Expression of Opa Proteins by Neisseria gonorrhoeae Influences Bacterial Association and Phagocytic Killing by Human Neutrophils

Neisseria gonorrhoeae infection is characterized by local and abundant recruitment of neutrophils. Despite neutrophils' antimicrobial activities, viable N. gonorrhoeae is recovered from infected individuals, leading to the question of how N. gonorrhoeae survives neutrophil attack. One feature impacting N. gonorrhoeae-neutrophil interactions is the phase-variable opacity-associated (Opa) proteins. Most Opa proteins engage human carcinoembryonic antigen-related cell adhesion molecules (CEACAMs) to facilitate bacterial binding and invasion. Neutrophils express two transmembrane CEACAMs, CEACAM1 and the granulocyte-specific CEACAM3. While N. gonorrhoeae isolated from infected individuals is frequently Opa+, expression of OpaD from strain FA1090, which interacts with CEACAMs 1 and 3, is associated with reduced N. gonorrhoeae survival after exposure to human neutrophils. In this study, we hypothesized that the receptor-binding capability of individual Opa proteins impacts bacterial survival in the presence of neutrophils. To test this hypothesis, we introduced opa genes that are constitutively expressed into a derivative of strain FA1090 with all 11 opa genes deleted. The engineered genes encode Opa proteins that bind CEACAM1 and -3, CEACAM1 but not CEACAM3, or neither CEACAM1 nor -3. N. gonorrhoeae expressing CEACAM3-binding Opa proteins survived significantly less well than bacteria expressing other Opa proteins when exposed to primary human neutrophils. The CEACAM3-binding N. gonorrhoeae had significantly greater association with and internalization by neutrophils. However, once internalized, bacteria were similarly killed inside neutrophils, regardless of Opa expression. Furthermore, Opa expression did not significantly impact neutrophil granule mobilization. Our findings indicate that the extent to which Opa proteins mediate nonopsonic binding is the predominant determinant of bacterial survival from neutrophils. IMPORTANCE Neisseria gonorrhoeae, the cause of gonorrhea, is an urgent-threat pathogen due to increasing numbers of infections and increased antibiotic resistance. Many surface components of N. gonorrhoeae are phase variable, including the Opa protein family of adhesins and invasins. While Opa protein expression is selected for in vivo, bacteria expressing some Opa proteins are readily killed by neutrophils, which are recruited to sites of infection. The reason for this discrepancy has remained unresolved. Our work shows that Opa-dependent differences in bacterial survival after exposure to primary human neutrophils correlates with Opa-dependent bacterial binding and phagocytosis. These findings underscore how the ability of N. gonorrhoeae to change Opa expression through phase variation contributes to bacterial resistance to neutrophil clearance.

Targeting Gα13-integrin interaction ameliorates systemic inflammation

Systemic inflammation as manifested in sepsis is an excessive, life-threatening inflammatory response to severe bacterial or viral infection or extensive injury. It is also a thrombo-inflammatory condition associated with vascular leakage/hemorrhage and thrombosis that is not effectively treated by current anti-inflammatory or anti-thrombotic drugs. Here, we show that MB2mP6 peptide nanoparticles, targeting the Gα13-mediated integrin "outside-in" signaling in leukocytes and platelets, inhibited both inflammation and thrombosis without causing hemorrhage/vascular leakage. MB2mP6 improved mouse survival when infused immediately or hours after onset of severe sepsis. Furthermore, platelet Gα13 knockout inhibited septic thrombosis whereas leukocyte Gα13 knockout diminished septic inflammation, each moderately improving survival. Dual platelet/leukocyte Gα13 knockout inhibited septic thrombosis and inflammation, further improving survival similar to MB2mP6. These results demonstrate that inflammation and thrombosis independently contribute to poor outcomes and exacerbate each other in systemic inflammation, and reveal a concept of dual anti-inflammatory/anti-thrombotic therapy without exacerbating vascular leakage.

Endocytic Adaptors in Cardiovascular Disease

Endocytosis is the process of actively transporting materials into a cell by membrane engulfment. Traditionally, endocytosis was divided into three forms: phagocytosis (cell eating), pinocytosis (cell drinking), and the more selective receptor-mediated endocytosis (clathrin-mediated endocytosis); however, other important endocytic pathways (e.g., caveolin-dependent endocytosis) contribute to the uptake of extracellular substances. In each, the plasma membrane changes shape to allow the ingestion and internalization of materials, resulting in the formation of an intracellular vesicle. While receptor-mediated endocytosis remains the best understood pathway, mammalian cells utilize each form of endocytosis to respond to their environment. Receptor-mediated endocytosis permits the internalization of cell surface receptors and their ligands through a complex membrane invagination process that is facilitated by clathrin and adaptor proteins. Internalized vesicles containing these receptor-ligand cargoes fuse with early endosomes, which can then be recycled back to the plasma membrane, delivered to other cellular compartments, or destined for degradation by fusing with lysosomes. These intracellular fates are largely determined by the interaction of specific cargoes with adaptor proteins, such as the epsins, disabled-homolog 2 (Dab2), the stonin proteins, epidermal growth factor receptor substrate 15, and adaptor protein 2 (AP-2). In this review, we focus on the role of epsins and Dab2 in controlling these sorting processes in the context of cardiovascular disease. In particular, we will focus on the function of epsins and Dab2 in inflammation, cholesterol metabolism, and their fundamental contribution to atherogenicity.