Ly6 family proteins in neutrophil biology

Immunological Feature and Transcriptional Signaling of Ly6C Monocyte Subsets From Transcriptome Analysis in Control and Hyperhomocysteinemic Mice

Background

Murine monocytes (MC) are classified into Ly6C^high and Ly6C^low MC. Ly6C^high MC is the pro-inflammatory subset and the counterpart of human CD14⁺⁺CD16⁺ intermediate MC which contributes to systemic and tissue inflammation in various metabolic disorders, including hyperhomocysteinemia (HHcy). This study aims to explore molecule signaling mediating MC subset differentiation in HHcy and control mice.

Methods

RNA-seq was performed in blood Ly6C^high and Ly6C^low MC sorted by flow cytometry from control and HHcy cystathionine β-synthase gene-deficient (Cbs^-/-) mice. Transcriptome data were analyzed by comparing Ly6C^high vs. Ly6C^low in control mice, Ly6C^high vs. Ly6C^low in Cbs^-/- mice, Cbs^-/- Ly6C^high vs. control Ly6C^high MC and Cbs^-/- Ly6C^low vs. control Ly6C^low MC by using intensive bioinformatic strategies. Significantly differentially expressed (SDE) immunological genes and transcription factor (TF) were selected for functional pathways and transcriptional signaling identification.

Results

A total of 7,928 SDE genes and 46 canonical pathways derived from it were identified. Ly6C^high MC exhibited activated neutrophil degranulation, lysosome, cytokine production/receptor interaction and myeloid cell activation pathways, and Ly6C^low MC presented features of lymphocyte immunity pathways in both mice. Twenty-four potential transcriptional regulatory pathways were identified based on SDE TFs matched with their corresponding SDE immunological genes. Ly6C^high MC presented downregulated co-stimulatory receptors (CD2, GITR, and TIM1) which direct immune cell proliferation, and upregulated co-stimulatory ligands (LIGHT and SEMA4A) which trigger antigen priming and differentiation. Ly6C^high MC expressed higher levels of macrophage (MΦ) markers, whereas, Ly6C^low MC highly expressed lymphocyte markers in both mice. HHcy in Cbs^-/- mice reinforced inflammatory features in Ly6C^high MC by upregulating inflammatory TFs (Ets1 and Tbx21) and strengthened lymphocytes functional adaptation in Ly6C^low MC by increased expression of CD3, DR3, ICOS, and Fos. Finally, we established 3 groups of transcriptional models to describe Ly6C^high to Ly6C^low MC subset differentiation, immune checkpoint regulation, Ly6C^high MC to MΦ subset differentiation and Ly6C^low MC to lymphocyte functional adaptation.

Conclusions

Ly6C^high MC displayed enriched inflammatory pathways and favored to be differentiated into MΦ. Ly6C^low MC manifested activated T-cell signaling pathways and potentially can adapt the function of lymphocytes. HHcy reinforced inflammatory feature in Ly6C^high MC and strengthened lymphocytes functional adaptation in Ly6C^low MC.

Non-radioactive and sensitive tracking of neutrophils towards inflammation using antibody functionalized magnetic particle imaging tracers

White blood cells (WBCs) are a key component of the mammalian immune system and play an essential role in surveillance, defense, and adaptation against foreign pathogens. Apart from their roles in the active combat of infection and the development of adaptive immunity, immune cells are also involved in tumor development and metastasis. Antibody-based therapeutics have been developed to regulate (i.e. selectively activate or inhibit immune function) and harness immune cells to fight malignancy. Alternatively, non-invasive tracking of WBC distribution can diagnose inflammation, infection, fevers of unknown origin (FUOs), and cancer. Magnetic Particle Imaging (MPI) is a non-invasive, non-radioactive, and sensitive medical imaging technique that uses safe superparamagnetic iron oxide nanoparticles (SPIOs) as tracers. MPI has previously been shown to track therapeutic stem cells for over 87 days with a ~200 cell detection limit. In the current work, we utilized antibody-conjugated SPIOs specific to neutrophils for in situ labeling, and non-invasive and radiation-free tracking of these inflammatory cells to sites of infection and inflammation in an in vivo murine model of lipopolysaccharide-induced myositis. MPI showed sensitive detection of inflammation with a contrast-to-noise ratio of ~8-13.

High mRNA expression of LY6 gene family is associated with overall survival outcome in pancreatic ductal adenocarcinoma

Pancreatic cancer ranks one of the worst in overall survival outcome with a 5 year survival rate being less than 10%. Pancreatic cancer faces unique challenges in its diagnosis and treatment, such as the lack of clinically validated biomarkers and the immensely immunosuppressive tumor microenvironment. Recently, the LY6 gene family has received increasing attention for its multi-faceted roles in cancer development, stem cell maintenance, immunomodulation, and association with more aggressive and hard-to-treat cancers. A detailed study of mRNA expression of LY6 gene family and its association with overall survival (OS) outcome in pancreatic cancers is lacking. We used publicly available clinical datasets to analyze the mRNA expression of a set of LY6 genes and its effect on OS outcome in the context of the tumor microenvironment and immunomodulation. We used web-based tools Kaplan-Meier Plotter, cBioPortal, Oncomine and R-programming to analyze copy number alterations, mRNA expression and its association with OS outcome in pancreatic cancer. These analyses demonstrated that high expression of LY6 genes is associated with OS and disease free survival (DFS) outcome. High expression of LY6 genes and their association with OS outcome is dependent on the composition of tumor microenvironment. Considering that LY6 proteins are anchored to the outer cell membrane or secreted, making them readily accessible, these findings highlight the potential of LY6 family members in the future of pancreatic cancer diagnosis and treatment.

Dynamic capillary stalls in reperfused ischemic penumbra contribute to injury: A hyperacute role for neutrophils in persistent traffic jams

Ever since the introduction of thrombolysis and the subsequent expansion of endovascular treatments for acute ischemic stroke, it remains to be identified why the actual outcomes are less favorable despite recanalization. Here, by high spatio-temporal resolution imaging of capillary circulation in mice, we introduce the pathological phenomenon of dynamic flow stalls in cerebral capillaries, occurring persistently in salvageable penumbra after reperfusion. These stalls, which are different from permanent cellular plugs of no-reflow, were temporarily and repetitively occurring in the capillary network, impairing the overall circulation like small focal traffic jams. In vivo microscopy in the ischemic penumbra revealed leukocytes traveling slowly through capillary lumen or getting stuck, while red blood cell flow was being disturbed in the neighboring segments under reperfused conditions. Stall dynamics could be modulated, by injection of an anti-Ly6G antibody specifically targeting neutrophils. Decreased number and duration of stalls were associated with improvement in penumbral blood flow within 2-24 h after reperfusion along with increased capillary oxygenation, decreased cellular damage and improved functional outcome. Thereby, dynamic microcirculatory stall phenomenon can be a contributing factor to ongoing penumbral injury and is a potential hyperacute mechanism adding on previous observations of detrimental effects of activated neutrophils in ischemic stroke.

Intravital Imaging of Pulmonary Immune Response in Inflammation and Infection

Intravital microscopy (IVM) is a unique imaging method providing insights in cellular functions and interactions in real-time, without the need for tissue extraction from the body. IVM of the lungs has specific challenges such as restricted organ accessibility, respiratory movements, and limited penetration depth. Various surgical approaches and microscopic setups have been adapted in order to overcome these challenges. Among others, these include the development of suction stabilized lung windows and the use of more advanced optical techniques. Consequently, lung IVM has uncovered mechanisms of leukocyte recruitment and function in several models of pulmonary inflammation and infection. This review focuses on bacterial pneumonia, aspiration pneumonia, sepsis-induced acute lung Injury, and cystic fibrosis, as examples of lung inflammation and infection. In addition, critical details of intravital imaging techniques of the lungs are discussed.

IL-17C contributes to NTHi-induced inflammation and lung damage in experimental COPD and is present in sputum during acute exacerbations

Neutrophilic inflammation results in loss of lung function in chronic obstructive pulmonary disease (COPD). Gram-negative bacteria, such as nontypeable Haemophilus influenzae (NTHi), trigger acute exacerbations of COPD (AECOPD) and contribute to chronic lung inflammation. The pro-inflammatory cytokine interleukin-17C (IL-17C) is expressed by airway epithelial cells and regulates neutrophilic chemotaxis. Here, we explored the function of IL-17C in NTHi- and cigarette smoke (CS)-induced models of COPD. Neutrophilic inflammation and tissue destruction were decreased in lungs of IL-17C-deficient mice (Il-17c-/-) chronically exposed to NTHi. Numbers of pulmonary neutrophils were decreased in Il-17c-/- mice after acute exposure to the combination of NTHi and CS. However, Il-17c-/- mice were not protected from CS-induced lung inflammation. In a preliminary patient study, we show that IL-17C is present in sputum samples obtained during AECOPD and associates with disease severity. Concentrations of IL-17C were significantly increased during advanced COPD (GOLD III/IV) compared to moderate COPD (GOLD I/II). Concentrations of IL-17A and IL-17E did not associate with disease severity. Our data suggest that IL-17C promotes harmful pulmonary inflammation triggered by bacteria in COPD.

Lipopolysaccharides of Fusobacterium nucleatum and Porphyromonas gingivalis increase RANKL-expressing neutrophils in air pouches of mice

Increases of neutrophils and osteoclasts are pathological changes of periodontitis. RANKL is an osteoclast differentiation factor. The effect of periodontopathogen LPS on RANKL-expressing neutrophils has not been clarified yet. We evaluated numerical changes of RANKL-expressing neutrophils in air pouches of mice injected with LPSs of Fusobacterium nucleatum and Porphyromonas gingivalis. Mice with air pouches were assigned into saline (C)-, E. coli LPS- (Ec LPS)-, F. nucleatum LPS (Fn LPS)-, P. gingivalis LPS (Pg LPS)-, and Fn LPS and Pg LPS (Fn + Pg LPS)-injected groups. CD11b+Ly6G+ neutrophils and CD11b+Ly6G+RANKL+ neutrophils in blood and air pouch exudates were determined by flow cytometry. In blood, compared to the C group, the Fn LPS group showed increases of CD11b+Ly6G+ neutrophils and CD11b+Ly6G+RANKL+ neutrophils whereas the Pg LPS group showed no significant differences. These increases in the Fn LPS group were not different to those in the Ec LPS group. In exudates, Fn LPS and Pg LPS groups showed increases of CD11b+Ly6G+ neutrophils and CD11b+Ly6G+RANKL+ neutrophils compared to the C group. Increased levels in the Fn LPS group were not different to those in the Ec LPS group, but Pg LPS group was lower than those in the Ec LPS group. In blood and exudates, the Fn + Pg LPS group showed no difference in levels of these neutrophils compared to the Ec LPS group. LPSs of F. nucleatum and P. gingivalis increased RANKL-expressing neutrophils although the degrees of increases were different. These suggest that periodontopathogen LPS can act as a stimulant to increase RANKL-expressing neutrophils.

LY6D-induced macropinocytosis as a survival mechanism of senescent cells

Although senescent cells display various morphological changes including vacuole formation, it is still unclear how these processes are regulated. We have recently identified the gene, lymphocyte antigen 6 complex, locus D (LY6D), to be upregulated specifically in senescent cells. LY6D is a glycosylphosphatidylinositol-anchored cell-surface protein whose function remains unknown. Here, we analyzed the functional relationship between LY6D and the senescence processes. We found that overexpression of LY6D induced vacuole formation and knockdown of LY6D suppressed the senescence-associated vacuole formation. The LY6D-induced vacuoles were derived from macropinocytosis, a distinct form of endocytosis. Furthermore, Src family kinases and Ras were found to be recruited to membrane lipid rafts in an LY6D-dependent manner, and inhibition of their activity impaired the LY6D-induced macropinocytosis. Finally, reduction of senescent-cell survival induced by glutamine deprivation was recovered by albumin supplementation to the culture media in an LY6D-dependent manner. Because macropinocytosis acts as an amino acid supply route, these results suggest that LY6D-mediated macropinocytosis contributes to senescent-cell survival through the incorporation of extracellular nutrients.

Parasitoid wasp venom vesicles (venosomes) enter Drosophila melanogaster lamellocytes through a flotillin/lipid raft-dependent endocytic pathway

Venosomes are extracellular vesicles found in the venom of Leptopilina endoparasitoids wasps, which transport and target virulence factors to impair the parasitoid egg encapsulation by the lamellocytes of their Drosophila melanogaster host larva. Using the co-immunolocalization of fluorescent L. boulardi venosomes and one of the putative-transported virulence factors, LbGAP, with known markers of cellular endocytosis, we show that venosomes endocytosis by lamellocytes is not a process dependent on clathrin or macropinocytosis and internalization seems to bypass the early endosomal compartment Rab5. After internalization, LbGAP colocalizes strongly with flotillin-1 and the GPI-anchored protein Atilla/L1 (a lamellocyte surface marker) suggesting that entry occurs via a flotillin/lipid raft-dependent pathway. Once internalized, venosomes reach all intracellular compartments, including late and recycling endosomes, lysosomes, and the endoplasmic reticulum network. Venosomes therefore enter their target cells by a specific mechanism and the virulence factors are widely distributed in the lamellocytes' compartments to impair their functions.

Expression-based analysis of genes related to single nucleotide polymorphism hits associated with bovine leukemia virus proviral load in Argentinean dairy cattle

In dairy cattle infected with bovine leukemia virus (BLV), the proviral load (PVL) level is directly related to the viral transmission from infected animals to their healthy herdmates. Two contrasting phenotypic groups can be identified when assessing PVL in peripheral blood of infected cows. A large number of reports point to bovine genetic variants (single nucleotide polymorphisms) as one of the key determinants underlying PVL level. However, biological mechanisms driving BLV PVL profiles and infection progression in cattle have not yet been elucidated. In this study, we evaluated whether a set of candidate genes affecting BLV PVL level according to whole genome association studies are differentially expressed in peripheral blood mononuclear cells derived from phenotypically contrasting groups of BLV-infected cows. During a 10-mo-long sampling scheme, 129 Holstein cows were phenotyped measuring anti-BLV antibody levels, PVL quantification, and white blood cell subpopulation counts. Finally, the expression of 8 genes (BOLA-DRB3, PRRC2A, ABT1, TNF, BAG6, BOLA-A, LY6G5B, and IER3) located within the bovine major histocompatibility complex region harboring whole genome association SNP hits was evaluated in 2 phenotypic groups: high PVL (n = 7) and low PVL (n = 8). The log₂ initial fluorescence value (N₀) transformed mean expression values for the ABT1 transcription factor were statistically different in high- and low-PVL groups, showing a higher expression of the ABT1 gene in low-PVL cows. The PRRC2A and IER3 genes had a significant positive (correlation coefficient = 0.61) and negative (correlation coefficient = -0.45) correlation with the lymphocyte counts, respectively. Additionally, the relationships between gene expression values and lymphocyte counts were modeled using linear regressions. Lymphocyte levels in infected cows were better explained (coefficient of determination = 0.56) when fitted a multiple linear regression model using both PRRC2A and IER3 expression values as independent variables. The present study showed evidence of differential gene expression between contrasting BLV infection phenotypes. These genes have not been previously related to BLV pathobiology. This valuable information represents a step forward in understanding the BLV biology and the immune response of naturally infected cows under a commercial milk production system. Efforts to elucidate biological mechanisms leading to BLV infection progression in cows are valuable for BLV control programs. Further studies integrating genotypic data, global transcriptome analysis, and BLV progression phenotypes are needed to better understand the BLV-host interaction.

Neutrophil-to-Lymphocyte Ratio: A Biomarker to Monitor the Immune Status of Astronauts

A comprehensive understanding of spaceflight factors involved in immune dysfunction and the evaluation of biomarkers to assess in-flight astronaut health are essential goals for NASA. An elevated neutrophil-to-lymphocyte ratio (NLR) is a potential biomarker candidate, as leukocyte differentials are altered during spaceflight. In the reduced gravity environment of space, rodents and astronauts displayed elevated NLR and granulocyte-to-lymphocyte ratios (GLR), respectively. To simulate microgravity using two well-established ground-based models, we cultured human whole blood-leukocytes in high-aspect rotating wall vessels (HARV-RWV) and used hindlimb unloaded (HU) mice. Both HARV-RWV simulation of leukocytes and HU-exposed mice showed elevated NLR profiles comparable to spaceflight exposed samples. To assess mechanisms involved, we found the simulated microgravity HARV-RWV model resulted in an imbalance of redox processes and activation of myeloperoxidase-producing inflammatory neutrophils, while antioxidant treatment reversed these effects. In the simulated microgravity HU model, mitochondrial catalase-transgenic mice that have reduced oxidative stress responses showed reduced neutrophil counts, NLR, and a dampened release of selective inflammatory cytokines compared to wildtype HU mice, suggesting simulated microgravity induced oxidative stress responses that triggered inflammation. In brief, both spaceflight and simulated microgravity models caused elevated NLR, indicating this as a potential biomarker for future in-flight immune health monitoring.

Early neutrophil infiltration is critical for inflammation-sensitized hypoxic-ischemic brain injury in newborns

Neutrophils are the most abundant leukocytes and usually the first immune cell-type recruited to a site of infection or tissue damage. In asphyxiated neonates, elevated peripheral neutrophil counts are associated with poorer neurological outcomes. Induced neutropenia provides brain protection in animal models of neonatal hypoxic-ischemic (HI) injury, but the anti-neutrophil serum used in past studies heavily cross-reacts with monocytes, thus complicating the interpretation of results. Here we examined neutrophil influx and extravasation, and used a specific anti-Ly6G antibody for induced neutropenia against lipopolysaccharide (LPS)-pretreated HI injury in murine neonates, a model for inflammation-sensitized hypoxic-ischemic encephalopathy (HIE). As early as 6 h after the LPS/HI insult, the mRNAs for neutrophil-recruiting and mitogenic chemokines ascended in the ipsilateral hemisphere, coinciding with immuno-detection of neutrophils. However, neutrophils mainly resided within blood vessels, exhibiting signs for neutrophil extracellular traps (NETs), before 48 h post-LPS/HI. Prophylactic anti-Ly6G treatment blocked the brain infiltration of neutrophils, but not monocytes or lymphocytes, and markedly decreased LPS/HI-induced pro-inflammatory cytokines, matrix metalloproteinase 9 (MMP-9), and brain tissue loss. In contrast, anti-Ly6G treatment at 4 h post-LPS/HI failed to prevent the influx of neutrophils and brain damage. Together, these results suggest important pathological functions for early-arriving neutrophils in inflammation-sensitized HIE.

Understanding the complexities of SARS-CoV2 infection and its immunology: A road to immune-based therapeutics

Emerging infectious diseases always pose a threat to humans along with plant and animal life. SARS-CoV2 is the recently emerged viral infection that originated from Wuhan city of the Republic of China in December 2019. Now, it has become a pandemic. Currently, SARS-CoV2 has infected more than 27.74 million people worldwide, and taken 901,928 human lives. It was named first 'WH 1 Human CoV' and later changed to 2019 novel CoV (2019-nCoV). Scientists have established it as a zoonotic viral disease emerged from Chinese horseshoe bats, which do not develop a severe infection. For example, Rhinolophus Chinese horseshoe bats harboring severe acute respiratory syndrome-related coronavirus (SARSr-CoV) or SARSr-Rh-BatCoV appear healthy and clear the virus within 2-4 months period. The article introduces first the concept of EIDs and some past EIDs, which have affected human life. Next section discusses mysteries regarding SARS-CoV2 origin, its evolution, and human transfer. Third section describes COVID-19 clinical symptoms and factors affecting susceptibility or resistance. The fourth section introduces the SARS-CoV2 entry in the host cell, its replication, and the establishment of productive infection. Section five describes the host's immune response associated with asymptomatic, symptomatic, mild to moderate, and severe COVID-19. The subsequent seventh and eighth sections mention the immune status in COVID-19 convalescent patients and re-emergence of COVID-19 in them. Thereafter, the eighth section describes viral strategies to hijack the host antiviral immune response and generate the "cytokine storm". The ninth section describes about transgenic humane ACE2 (hACE2) receptor expressing mice to study immunity, drugs, and vaccines. The article ends with the development of different immunomodulatory and immunotherapeutics strategies, including vaccines waiting for their approval in humans as prophylaxis or treatment measures.

LY6K promotes glioblastoma tumorigenicity via CAV-1-mediated ERK1/2 signaling enhancement

BACKGROUND

Lymphocyte antigen 6 complex, locus K (LY6K) is a putative oncogene in various cancers. Elevated expression of LY6K is correlated with poor patient prognosis in glioblastoma (GBM). The aim of this study is to advance our understanding of the mechanism by which LY6K contributes to GBM tumor biology.

METHODS

Bioinformatic data mining was used to investigate LY6K expression in relation to GBM clinical outcome. To understand the role of LY6K in GBM, we utilized patient-derived glioma stemlike cells (GSCs) and U87 cells and employed immunoblotting, immunofluorescent staining, radiation treatment, and orthotopic GBM xenograft models.

RESULTS

Our results show that increased expression of LY6K inversely correlates with GBM patient survival. LY6K promotes tumorigenicity in GBM cells both in vitro and in vivo. The mechanism underlying this tumorigenic behavior is enhancement of extracellular signal-regulated kinase 1 and 2 (ERK1/2) signaling. Interestingly, we observed that tumor-promoting LY6K-ERK1/2 signaling is mediated by the interaction of LY6K with caveolin-1, rather than through oncogenic receptor tyrosine kinase-mediated signaling. Moreover, association of LY6K with the cell membrane is crucial for its tumorigenic functions. Finally, DNA methylation maintains LY6K silencing, and hypomethylation of the LY6K promoter increases its expression. In GSCs, ionizing radiation leads to demethylation of the LY6K promoter, thereby increasing LY6K expression and GSC resistance to radiation.

CONCLUSIONS

Our study highlights the importance of the contribution of LY6K to GBM tumor biology and suggests LY6K as a potential membrane target for treating GBM.

TDP-43 mediated blood-brain barrier permeability and leukocyte infiltration promote neurodegeneration in a low-grade systemic inflammation mouse model

BACKGROUND

Neuronal cytoplasmic inclusions containing TAR DNA-binding protein 43 (TDP-43) are a neuropathological feature of several neurodegenerative diseases, including amyotrophic lateral sclerosis (ALS), frontotemporal dementia (FTD), and Alzheimer's Disease (AD). Emerging evidence also indicates that systemic inflammation may be a contributor to the pathology progression of these neurodegenerative diseases.

METHODS

To investigate the role of systemic inflammation in the progression of neuronal TDP-43 pathology, AAV9 particles driven by the UCHL1 promoter were delivered to the frontal cortex of wild-type aged mice via intracranial injections to overexpress TDP-43 or green fluorescent protein (GFP) in corticospinal motor neurons. Animals were then subjected to a low-dose (500 μg/kg) intraperitoneal E. coli lipopolysaccharide (LPS) administration challenge for 2 weeks to mimic a chronically altered low-grade systemic inflammatory state. Mice were then subjected to neurobehavioral studies, followed by biochemical and immunohistochemical analyses of the brain tissue.

RESULTS

In the present study, we report that elevated neuronal TDP-43 levels induced microglial and astrocytic activation in the cortex of injected mice followed by increased RANTES signaling. Moreover, overexpression of TDP-43 exerted abundant mouse immunoglobulin G (IgG), CD3, and CD4+ T cell infiltration as well as endothelial and pericyte activation suggesting increased blood-brain barrier permeability. The BBB permeability in TDP-43 overexpressing brains yielded the frontal cortex vulnerable to the systemic inflammatory response following LPS treatment, leading to marked neutrophil infiltration, neuronal loss, reduced synaptosome-associated protein 25 (SNAP-25) levels, and behavioral impairments in the radial arm water maze (RAWM) task.

CONCLUSIONS

These results reveal a novel role for TDP-43 in BBB permeability and leukocyte recruitment, indicating complex intermolecular interactions between an altered systemic inflammatory state and pathologically prone TDP-43 protein to promote disease progression.

Neutrophil diversity and plasticity in tumour progression and therapy

Neutrophils play a key role in defence against infection and in the activation and regulation of innate and adaptive immunity. In cancer, tumour-associated neutrophils (TANs) have emerged as an important component of the tumour microenvironment. Here, they can exert dual functions. TANs can be part of tumour-promoting inflammation by driving angiogenesis, extracellular matrix remodelling, metastasis and immunosuppression. Conversely, neutrophils can also mediate antitumour responses by direct killing of tumour cells and by participating in cellular networks that mediate antitumour resistance. Neutrophil diversity and plasticity underlie the dual potential of TANs in the tumour microenvironment. Myeloid checkpoints as well as the tumour and tissue contexture shape neutrophil function in response to conventional therapies and immunotherapy. We surmise that neutrophils can provide tools to tailor current immunotherapy strategies and pave the way to myeloid cell-centred therapeutic strategies, which would be complementary to current approaches.

The Impact of Immune Cells on the Skeletal Muscle Microenvironment During Cancer Cachexia

Progressive weight loss combined with skeletal muscle atrophy, termed cachexia, is a common comorbidity associated with cancer that results in adverse consequences for the patient related to decreased chemotherapy responsiveness and increased mortality. Cachexia's complexity has provided a barrier for developing successful therapies to prevent or treat the condition, since a large number of systemic disruptions that can regulate muscle mass are often present. Furthermore, considerable effort has focused on investigating how tumor derived factors and inflammatory mediators directly signal skeletal muscle to disrupt protein turnover regulation. Currently, there is developing appreciation for understanding how cancer alters skeletal muscle's complex microenvironment and the tightly regulated interactions between multiple cell types. Skeletal muscle microenvironment interactions have established functions in muscle response to regeneration from injury, growth, aging, overload-induced hypertrophy, and exercise. This review explores the growing body of evidence for immune cell modulation of the skeletal muscle microenvironment during cancer-induced muscle wasting. Emphasis is placed on the regulatory network that integrates physiological responses between immune cells with other muscle cell types including satellite cells, fibroblast cells, and endothelial cells to regulate myofiber size and plasticity. The overall goal of this review is to provide an understanding of how different cell types that constitute the muscle microenvironment and their signaling mediators contribute to cancer and chemotherapy-induced muscle wasting.

Emerging Human Coronavirus Infections (SARS, MERS, and COVID-19): Where They Are Leading Us

Coronavirus infections are responsible for mild, moderate, and severe infections in birds and mammals. These were first isolated in humans as causal microorganisms responsible for common cold. The 2002-2003 SARS epidemic caused by SARS-CoV and 2012 MERS epidemic (64 countries affected) caused by MERS-CoV showed their acute and fatal side. These two CoV infections killed thousands of patients infected worldwide. However, WHO has still reported the MERS case in December 2019 in middle-eastern country (Saudi Arabia), indicating the MERS epidemic has not ended completely yet. Although we have not yet understood completely these two CoV epidemics, a third most dangerous and severe CoV infection has been originated in the Wuhan city, Hubei district of China in December 2019. This CoV infection called COVID-19 or SARS-CoV2 infection has now spread to 210 countries and territories around the world. COVID-19 has now been declared a pandemic by the World Health Organization (WHO). It has infected more than 16.69 million people with more than 663,540 deaths across the world. Thus the current manuscript aims to describe all three (SARS, MERS, and COVID-19) in terms of their causal organisms (SARS-CoV, MERS-CoV, and SARS-CoV2), similarities and differences in their clinical symptoms, outcomes, immunology, and immunopathogenesis, and possible future therapeutic approaches.

Mice Deficient in T-bet Form Inducible NO Synthase-Positive Granulomas That Fail to Constrain Salmonella

Clearance of intracellular infections caused by Salmonella Typhimurium (STm) requires IFN-γ and the Th1-associated transcription factor T-bet. Nevertheless, whereas IFN-γ^-/- mice succumb rapidly to STm infections, T-bet^-/- mice do not. In this study, we assess the anatomy of immune responses and the relationship with bacterial localization in the spleens and livers of STm-infected IFN-γ^-/- and T-bet^-/- mice. In IFN-γ^-/- mice, there is deficient granuloma formation and inducible NO synthase (iNOS) induction, increased dissemination of bacteria throughout the organs, and rapid death. The provision of a source of IFN-γ reverses this, coincident with subsequent granuloma formation and substantially extends survival when compared with mice deficient in all sources of IFN-γ. T-bet^-/- mice induce significant levels of IFN-γ^- after challenge. Moreover, T-bet^-/- mice have augmented IL-17 and neutrophil numbers, and neutralizing IL-17 reduces the neutrophilia but does not affect numbers of bacteria detected. Surprisingly, T-bet^-/- mice exhibit surprisingly wild-type-like immune cell organization postinfection, including extensive iNOS⁺ granuloma formation. In wild-type mice, most bacteria are within iNOS⁺ granulomas, but in T-bet^-/- mice, most bacteria are outside these sites. Therefore, Th1 cells act to restrict bacteria within IFN-γ-dependent iNOS⁺ granulomas and prevent dissemination.

Immune cells as tumor drug delivery vehicles

This review article describes the use of immune cells as potential candidates to deliver anti-cancer drugs deep within the tumor microenvironment. First, the rationale of using drug carriers to target tumors and potentially decrease drug-related side effects is discussed. We further explain some of the current limitations when using nanoparticles for this purpose. Next, a comprehensive step-by-step description of the migration cascade of immune cells is provided as well as arguments on why immune cells can be used to address some of the limitations associated with nanoparticle-mediated drug delivery. We then describe the benefits and drawbacks of using red blood cells, platelets, granulocytes, monocytes, macrophages, myeloid-derived suppressor cells, T cells and NK cells for tumor-targeted drug delivery. An additional section discusses the versatility of nanoparticles to load anti-cancer drugs into immune cells. Lastly, we propose increasing the circulatory half-life and development of conditional release strategies as the two main future pillars to improve the efficacy of immune cell-mediated drug delivery to tumors.

The IL-17 receptor IL-17RE mediates polyIC-induced exacerbation of experimental allergic asthma

BACKGROUND

The interleukin 17 receptor E (IL-17RE) is specific for the epithelial cytokine interleukin-17C (IL-17C). Asthma exacerbations are frequently caused by viral infections. Polyinosinic:polycytidylic acid (pIC) mimics viral infections through binding to pattern recognition receptors (e.g. TLR-3). We and others have shown that pIC induces the expression of IL-17C in airway epithelial cells. Using different mouse models, we aimed to investigate the function of IL-17RE in the development of experimental allergic asthma and acute exacerbation thereof.

METHODS

Wild-type (WT) and IL-17RE deficient (Il-17re-/-) mice were sensitized and challenged with OVA to induce allergic airway inflammation. pIC or PBS were applied intranasally when allergic airway inflammation had been established. Pulmonary expression of inflammatory mediators, numbers of inflammatory cells, and airway hyperresponsiveness (AHR) were analyzed.

RESULTS

Ablation of IL-17RE did not affect the development of OVA-induced allergic airway inflammation and AHR. pIC induced inflammation independent of IL-17RE in the absence of allergic airway inflammation. Treatment of mice with pIC exacerbated pulmonary inflammation in sensitized and OVA-challenged mice in an IL-17RE-dependent manner. The pIC-induced expression of cytokines (e.g. keratinocyte-derived chemokine (KC), granulocyte-colony stimulating factor (G-CSF)) and recruitment of neutrophils were decreased in Il-17re-/- mice. pIC-exacerbated AHR was partially decreased in Il-17re-/- mice.

CONCLUSIONS

Our results indicate that IL-17RE mediates virus-triggered exacerbations but does not have a function in the development of allergic lung disease.

The presence of neutrophils causes RANKL expression in periodontal tissue, giving rise to osteoclast formation

BACKGROUNDS AND OBJECTIVE

Increased neutrophil infiltration and osteoclast formation are key characteristics of periodontitis. The effect of these neutrophils on osteoclast formation in periodontitis remains unclear. Therefore, we investigated the effects of neutrophils on osteoclast formation in a neutrophil-deficient mouse model of periodontitis.

METHODS

Anti-Ly6G antibody (Ab) was used for neutrophil depletion in two mouse models: periodontitis and air pouch. In the periodontitis experiments, mice were divided into PBS-administered control (C), control Ab-administered periodontitis (P), and anti-Ly6G Ab-administered periodontitis (P + Ly6G) groups. Periodontitis was induced by ligature of mandibular first molars. In the air pouch experiments, mice were divided into PBS-administered (C), LPS and control Ab-administered (LPS), and LPS and anti-Ly6G Ab-administered (LPS + Ly6G) groups. Neutrophil migration into air pouches was induced by LPS injection. Flow cytometry was used to examine CD11b⁺ Ly6G⁺ neutrophils in the blood of periodontitis mice and CD11b⁺ Ly6G⁺ RANKL⁺ neutrophils in exudates of air pouch mice. In periodontal tissue, Ly6G⁺ neutrophil and RANKL⁺ cell numbers in periodontal ligament and alveolar bone areas were estimated using immunohistochemistry, osteoclast numbers were measured using TRAP assay, and alveolar bone loss was determined by H&E staining.

RESULTS

In blood, CD11b⁺ Ly6G⁺ neutrophils were found in greater percentage in the P group than in the C group on days 3 and 7. However, the percentage of neutrophils was lower in the P + Ly6G group than in the C and P groups. In periodontal tissue, the numbers of Ly6G⁺ neutrophils and RANKL⁺ cells were lower in the P + Ly6G group than in the P group on day 3. Ly6G⁺ neutrophil numbers decreased more in the P + Ly6G group than in the P group on day 7, but RANKL⁺ cell numbers did not decrease in the P + Ly6G group. In exudates, the number of CD11b⁺ Ly6G⁺ RANKL⁺ neutrophils was greater in the LPS group than in the C and LPS + Ly6G groups. On days 3 and 7, the numbers of osteoclasts and alveolar bone loss were greater in periodontal tissue in the P and P + Ly6G groups than in the C group. Interestingly, there were fewer osteoclasts in the P + Ly6G group than in the P group on day 3.

CONCLUSION

Neutrophil deficiency caused a reduction in numbers of both RANKL⁺ cells and osteoclasts in periodontitis-induced tissues only on day 3. Furthermore, in the LPS-injected air pouch model, neutrophil deficiency reduced the influx of RANKL⁺ neutrophils. These findings suggest that the presence of neutrophils induces RANKL expression and could induce osteoclast formation in the early stages of periodontitis.

Site-1 protease ablation in the osterix-lineage in mice results in bone marrow neutrophilia and hematopoietic stem cell alterations

Site-1 protease (S1P) ablation in the osterix-lineage in mice drastically reduces bone development and downregulates bone marrow-derived skeletal stem cells. Here we show that these mice also suffer from spina bifida occulta with a characteristic lack of bone fusion in the posterior neural arches. Molecular analysis of bone marrow-derived non-red blood cell cells, via single-cell RNA-Seq and protein mass spectrometry, demonstrate that these mice have a much-altered bone marrow with a significant increase in neutrophils and Ly6C-expressing leukocytes. The molecular composition of bone marrow neutrophils is also different as they express more and additional members of the stefin A (Stfa) family of proteins. In vitro, recombinant Stfa1 and Stfa2 proteins have the ability to drastically inhibit osteogenic differentiation of bone marrow stromal cells, with no effect on adipogenic differentiation. FACS analysis of hematopoietic stem cells show that despite a decrease in hematopoietic stem cells, S1P ablation results in an increased production of granulocyte-macrophage progenitors, the precursors to neutrophils. These observations indicate that S1P has a role in the lineage specification of hematopoietic stem cells and/or their progenitors for development of a normal hematopoietic niche. Our study designates a fundamental requirement of S1P for maintaining a balanced regenerative capacity of the bone marrow niche.

Dendritic Cell-Based Therapy Using LY6E Peptide with a Putative Role Against Colorectal Cancer

Introduction

Albeit early stage gastrointestinal (GI) carcinomas have a good prognosis if treated with surgery, diagnosis is often confirmed at a late stage and efficacious drugs are lacking. Recent progress in immune-based therapies has focused on dendritic cells (DCs), aiming to elicit tumor-specific responses by inducing immunological memory. Our previous microarray study indicated that a biomarker, termed lymphocyte antigen-6E (LY6E), is commonly overexpressed in two potentially lethal GI cancers: those of colon and stomach. In this study, we examined the antigenic potency of LY6E in stimulating DCs.

Methods

Following isolation, differentiation, and maturation of mononuclear cells, DCs were pulsed with LY6E peptide, a protein related to major histocompatibility complex (MHC) class I/II. Subsequently, DCs were co-cultured with mouse splenocytes to assess antigen-specific T-cell proliferation. Elucidated cytotoxic T-lymphocyte responses were assessed using subcutaneous colorectal murine tumor models.

Results

Our in vitro results suggest that DCs loaded with LY6E peptide antigen are capable of stimulating and inducing proliferation of murine T-cells. Furthermore, our in vivo results demonstrate that LY6E peptide has a substantial impact on provoking immune responses against induced colon cancer in mice.

Discussion

In conclusion, based on the overexpression of LY6E in colorectal, gastric, and pancreatic cancers, the role of this peptide should be further investigated with a goal of developing new therapies for these challenging diseases.

Mesenchymal stromal cells induce distinct myeloid-derived suppressor cells in inflammation

Mesenchymal stem/stromal cells (MSCs) regulate immunity through myeloid-derived suppressor cells (MDSCs), which are a heterogeneous population of immature myeloid cells with phenotypic and functional diversity. Herein, we identified a distinct subset of MDSCs induced by MSCs in the BM under inflammatory conditions. MSCs directed the differentiation of Ly6Glo BM cells from CD11bhiLy6Chi cells to CD11bmidLy6Cmid cells both in cell contact-independent and -dependent manners upon GM-CSF stimulation in vitro and in mice with experimental autoimmune uveoretinitis (EAU). RNA-Seq indicated that MSC-induced CD11bmidLy6CmidLy6Glo cells had a distinct transcriptome profile from CD11bhiLy6ChiLy6Glo cells. Phenotypic, molecular, and functional analyses showed that CD11bmidLy6CmidLy6Glo cells differed from CD11bhiLy6ChiLy6Glo cells by low expression of MHC class II and costimulatory molecules and proinflammatory cytokines, high production of immunoregulatory molecules, lack of change in response to LPS, and inhibition of T cell proliferation and activation. Consequently, adoptive transfer of MSC-induced CD11bmidLy6CmidLy6Glo cells significantly attenuated the development of EAU in mice. Further mechanistic study revealed that suppression of prostaglandin E2 (PGE2) and HGF secretion in MSCs by siRNA transfection partially reversed the effects of MSCs on MDSC differentiation. Altogether, data demonstrate that MSCs drive the differentiation of BM cells toward CD11bmidLy6CmidLy6Glo MDSCs, in part through HGF and COX-2/PGE2, leading to resolution of ocular autoimmune inflammation.

Single-Cell Transcriptomic Analysis of Tumor-Derived Fibroblasts and Normal Tissue-Resident Fibroblasts Reveals Fibroblast Heterogeneity in Breast Cancer

Cancer-associated fibroblasts (CAFs) are a prominent stromal cell type in solid tumors and molecules secreted by CAFs play an important role in tumor progression and metastasis. CAFs coexist as heterogeneous populations with potentially different biological functions. Although CAFs are a major component of the breast cancer stroma, molecular and phenotypic heterogeneity of CAFs in breast cancer is poorly understood. In this study, we investigated CAF heterogeneity in triple-negative breast cancer (TNBC) using a syngeneic mouse model, BALB/c-derived 4T1 mammary tumors. Using single-cell RNA sequencing (scRNA-seq), we identified six CAF subpopulations in 4T1 tumors including: 1) myofibroblastic CAFs, enriched for α-smooth muscle actin and several other contractile proteins; 2) ‘inflammatory’ CAFs with elevated expression of inflammatory cytokines; and 3) a CAF subpopulation expressing major histocompatibility complex (MHC) class II proteins that are generally expressed in antigen-presenting cells. Comparison of 4T1-derived CAFs to CAFs from pancreatic cancer revealed that these three CAF subpopulations exist in both tumor types. Interestingly, cells with inflammatory and MHC class II-expressing CAF profiles were also detected in normal breast/pancreas tissue, suggesting that these phenotypes are not tumor microenvironment-induced. This work enhances our understanding of CAF heterogeneity, and specifically targeting these CAF subpopulations could be an effective therapeutic approach for treating highly aggressive TNBCs.

CD44 Receptor Mediates Urate Crystal Phagocytosis by Macrophages and Regulates Inflammation in A Murine Peritoneal Model of Acute Gout

Gout is a chronic arthritis caused by the deposition of poorly soluble monosodium urate monohydrate (MSU) crystals in peripheral joints. Resident macrophages initiate inflammation in response to MSU mediated by NF-κB nuclear translocation and NLRP3 inflammasome activation. We investigated the role of CD44, a transmembrane receptor, in mediating MSU phagocytosis by macrophages. We used an antibody that sheds the extracellular domain (ECD) of CD44 to study the role of the receptor and its associated protein phosphatase 2A (PP2A) in macrophage activation. We also studied the significance of CD44 in mediating MSU inflammation in-vivo. Cd44^−/− BMDMs showed reduced MSU phagocytosis, LDH release, IL-1β expression and production compared to Cd44^+/+ BMDMs. Elevated CD44 staining was detected intracellularly and CD44 colocalized with α-tubulin as a result of MSU exposure and ECD-shedding reduced MSU phagocytosis in murine and human macrophages. Anti-CD44 antibody treatment reduced NF-κB p65 subunit nuclear levels, IL-1β expression, pro-IL-1β and IL-8 production in MSU stimulated THP-1 macrophages (p < 0.01). The effect of the antibody was mediated by an enhancement in PP2A activity. CD44 ECD-shedding reduced the conversion of procaspase-1 to active caspase-1, caspase-1 activity and resultant generation of mature IL-1β in macrophages. Neutrophil and monocyte influx and upregulated production of IL-1β was evident in wildtype mice. MSU failed to trigger neutrophil and monocyte recruitment in Cd44^−/− mice and lower IL-1β levels were detected in peritoneal lavages from Cd44^−/− mice (p < 0.01). Anti-CD44 antibody treatment reduced neutrophil and monocyte recruitment and resulted in reduced lavage IL-1β levels in the same model. CD44 plays a biologically significant role in mediating phagocytosis of MSU and downstream inflammation and is a novel target in gout treatment.

Effects of nanoparticle-mediated delivery of pitavastatin on atherosclerotic plaques in ApoE-knockout mice and THP-1-derived macrophages

The treatment of atherosclerosis remains complex. Pitavastatin serves an important role in the prevention and treatment of atherosclerosis. The present study aimed to investigate the effects of nanoparticle (NP)-mediated delivery of pitavastatin into atherosclerotic plaques as a novel treatment method for atherosclerosis. The results of the present study demonstrated that pitavastatin-NP was more effective in attenuating the size of atherosclerotic plaques and enhancing the stability of plaques in vitro compared with pitavastatin alone. In an apolipoprotein E (ApoE)-knockout mouse model of atherosclerosis, a single intravenous injection of fluorescein isothiocyanate-NP resulted in the delivery of NP into atherosclerotic plaques for up to 7 days post-injection. In ApoE-knockout mice and THP-1-derived macrophages, pitavastatin-NP attenuated the development of atherosclerosis, which was associated with regulating lipid metabolism, and inhibited the secretion of inflammatory markers compared with pitavastatin alone. Additionally, the treatment advantages of pitavastatin-NP were independent of lipid lowering. The results demonstrated that pitavastatin-NP administration was more effective in attenuating the development of atherosclerotic plaques compared with systemic administration of pitavastatin.

Differential attenuation of β2 integrin-dependent and -independent neutrophil migration by Ly6G ligation

Antibody ligation of the murine neutrophil surface protein Ly6G disrupts neutrophil migration in some contexts but not others. We tested whether this variability reflected divergent dependence of neutrophil migration on β2 integrins, adhesion molecules that interact with Ly6G at the neutrophil surface. In integrin-dependent murine arthritis, Ly6G ligation attenuated joint inflammation, even though mice lacking Ly6G altogether developed arthritis normally. By contrast, Ly6G ligation had no impact on integrin-independent neutrophil migration into inflamed lung. In peritoneum, the role of β2 integrins varied with stimulus, proving dispensable for neutrophil entry in Escherichia coli peritonitis but contributory in interleukin 1 (IL-1)-mediated sterile peritonitis. Correspondingly, Ly6G ligation attenuated only IL-1 peritonitis, disrupting the molecular association between integrins and Ly6G and inducing cell-intrinsic blockade restricted to integrin-dependent migration. Consistent with this observation, Ly6G ligation impaired integrin-mediated postadhesion strengthening for neutrophils arresting on activated cremaster endothelium in vivo. Together, these findings identify selective inhibition of integrin-mediated neutrophil emigration through Ly6G ligation, highlighting the marked site and stimulus specificity of β2 integrin dependence in neutrophil migration.

Role of Neutrophils and Myeloid-Derived Suppressor Cells in Glioma Progression and Treatment Resistance

Recent efforts in brain tumor research have been directed towards the modulation of the immune system for therapeutic interventions. Several human cancers, including gliomas, are infiltrated with immune cell types-including neutrophils and myeloid-derived suppressor cells-that contribute to tumor progression, invasiveness, and treatment resistance. The role of tumor-associated neutrophils and myeloid-derived suppressor cells in cancer biology remains elusive, as these cells can exert a multitude of pro-tumor and antitumor effects. In this review, we provide the current understanding and novel insights on the role of neutrophils and myeloid-derived suppressor cells in glioma progression and treatment resistance, as well as the mechanisms of pleiotropic behaviors in these cells during disease progression, with an emphasis on possible strategies to reprogram these cells towards their antitumor actions.

Deciphering the transcriptomic landscape of tumor-infiltrating CD8 lymphocytes in B16 melanoma tumors with single-cell RNA-Seq

Recent studies have proposed that tumor-specific tumor-infiltrating CD8⁺ T lymphocytes (CD8 TIL) can be classified into two main groups: "exhausted" TILs, characterized by high expression of the inhibitory receptors PD-1 and TIM-3 and lack of transcription factor 1 (Tcf1); and "memory-like" TILs, with self-renewal capacity and co-expressing Tcf1 and PD-1. However, a comprehensive definition of the heterogeneity existing within CD8 TILs has yet to be clearly established. To investigate this heterogeneity at the transcriptomic level, we performed paired single-cell RNA and TCR sequencing of CD8 T cells infiltrating B16 murine melanoma tumors, including cells of known tumor specificity. Unsupervised clustering and gene-signature analysis revealed four distinct CD8 TIL states - exhausted, memory-like, naïve and effector memory-like (EM-like) - and predicted novel markers, including Ly6C for the EM-like cells, that were validated by flow cytometry. Tumor-specific PMEL T cells were predominantly found within the exhausted and memory-like states but also within the EM-like state. Further, T cell receptor sequencing revealed a large clonal expansion of exhausted, memory-like and EM-like cells with partial clonal relatedness between them. Finally, meta-analyses of public bulk and single-cell RNA-seq data suggested that anti-PD-1 treatment induces the expansion of EM-like cells. Our reference map of the transcriptomic landscape of murine CD8 TILs will help interpreting future bulk and single-cell transcriptomic studies and may guide the analysis of CD8IL subpopulations in response to therapeutic interventions.

Small Molecule Binds with Lymphocyte Antigen 6K to Induce Cancer Cell Death

Elevated gene expression of Lymphocyte antigen 6K (LY6K) in cancer cells is associated with poor survival outcomes in multiple different cancer types including cervical, breast, ovarian, lung, and head and neck cancer. Since inhibition of LY6K expression inhibits cancer cell growth, we set out to explore whether pharmacological inhibition of LY6K could produce the same effect. We screened small molecule libraries for direct binding to recombinant LY6K protein in a surface plasmon resonance assay. We found that NSC243928 directly binds to the full-length and mature forms of LY6K and inhibits growth of HeLa cells that express LY6K. NSC243928 did not display binding with LY6D or LY6E. Our data demonstrate a first-time proof of principle study that pharmacological inhibition of LY6K using small molecules in cancer cells is a valid approach to developing targeted therapies against LY6K. This approach will be specifically relevant in hard-to-treat cancers where LY6K is highly expressed, such as cervical, pancreatic, ovarian, head and neck, lung, gastric, and triple-negative breast cancers.

Chemical functionality of multidomain peptide hydrogels governs early host immune response

Multidomain Peptide (MDP) hydrogels are nanofibrous materials with many potential biomedical applications. The peptide sequence design of these materials offers high versatility and allows for the incorporation of various chemical functionalities into the nanofibrous scaffold. It is known that host response to biomaterials is strongly affected by factors such as size, shape, stiffness, and chemistry. However, there is a lack of fundamental understanding of the host response to different MDP hydrogels. In particular, it is unknown what effect the chemical functionality displayed on the nanofiber has on biological activity. Here we evaluated the early inflammatory host response to four MDP hydrogels displaying amines, guanidinium ions, and carboxylates in a subcutaneous injection model. While all the studied peptide materials possess similar nanostructure and physical properties, they trigger markedly different inflammatory responses. These were characterized by immunophenotyping of the cellular infiltrate using multi-color flow cytometry. The negatively-charged peptides elicit minimal inflammation characterized by tissue-resident macrophage infiltration, fast remodeling, and no collagen deposition or blood vessel formation within the implants. In contrast, the positively-charged peptides are highly infiltrated by immune cells, are remodeled at a slower rate, promote angiogenesis, and result in a high degree of collagen deposition. The presence of dynamic cell phenotypes characterizes the inflammation caused by the lysine-based peptide, including inflammatory monocytes, macrophages, and lymphoid cells, which is seen to be resolving over time. The arginine-based hydrogel shows higher inflammatory response with a persistent and significant infiltration of polymorphonuclear myeloid-derived cells, even ten days after implantation. This understanding of the immune response to peptide biomaterials improves our ability to design effective materials and to tailor their use for specific biomedical applications.

Identification of an Early Unipotent Neutrophil Progenitor with Pro-tumoral Activity in Mouse and Human Bone Marrow

Neutrophils are short-lived cells that play important roles in both health and disease. Neutrophils and monocytes originate from the granulocyte monocyte progenitor (GMP) in bone marrow; however, unipotent neutrophil progenitors are not well defined. Here, we use cytometry by time of flight (CyTOF) and single-cell RNA sequencing (scRNA-seq) methodologies to identify a committed unipotent early-stage neutrophil progenitor (NeP) in adult mouse bone marrow. Importantly, we found a similar unipotent NeP (hNeP) in human bone marrow. Both NeP and hNeP generate only neutrophils. NeP and hNeP both significantly increase tumor growth when transferred into murine cancer models, including a humanized mouse model. hNeP are present in the blood of treatment-naive melanoma patients but not of healthy subjects. hNeP can be readily identified by flow cytometry and could be used as a biomarker for early cancer discovery. Understanding the biology of hNeP should allow the development of new therapeutic targets for neutrophil-related diseases, including cancer.

Gr1 makes an unexpected cameo appearance in eosinophils

Discussion of the neutrophil marker Ly6G/Gr1, which is readily detectable on mouse eosinophils, and is expressed in higher levels in the presence of IL-5.

Mouse Models and Tools for the in vivo Study of Neutrophils

Neutrophils are the most abundant leukocytes in human blood and critical actors of the immune system. Many neutrophil functions and facets of their activity in vivo were revealed by studying genetically modified mice or by tracking fluorescent neutrophils in animals using imaging approaches. Assessing the roles of neutrophils can be challenging, especially when exact molecular pathways are questioned or disease states are interrogated that alter normal neutrophil homeostasis. This review discusses the main in vivo models for the study of neutrophils, their advantages and limitations. The side-by-side comparison underlines the necessity to carefully choose the right model(s) to answer a given scientific question, and exhibit caveats that need to be taken into account when designing experimental procedures. Collectively, this review suggests that at least two models should be employed to legitimately conclude on neutrophil functions.

Immunophenotyping monocytes, macrophages and granulocytes in the Pteropodid bat Eonycteris spelaea

Bats are asymptomatic reservoir hosts for several highly pathogenic viruses. Understanding this enigmatic relationship between bats and emerging zoonotic viruses requires tools and approaches which enable the comparative study of bat immune cell populations and their functions. We show that bat genomes have a conservation of immune marker genes which delineate phagocyte populations in humans, while lacking key mouse surface markers such as Ly6C and Ly6G. Cross-reactive antibodies against CD44, CD11b, CD14, MHC II, and CD206 were multiplexed to characterize circulating monocytes, granulocytes, bone-marrow derived macrophages (BMDMs) and lung alveolar macrophages (AMs) in the cave nectar bat Eonycteris spelaea. Transcriptional profiling of bat monocytes and BMDMs identified additional markers – including MARCO, CD68, CD163, CD172α, and CD88 – which can be used to further characterize bat myeloid populations. Bat cells often resembled their human counterparts when comparing immune parameters that are divergent between humans and mice, such as the expression patterns of certain immune cell markers. A genome-wide comparison of immune-related genes also revealed a much closer phylogenetic relationship between bats and humans compared to rodents. Taken together, this study provides a set of tools and a comparative framework which will be important for unravelling viral disease tolerance mechanisms in bats.

Determining macrophage versus neutrophil contributions to innate immunity using larval zebrafish

The specific roles of the two major innate immune cell types – neutrophils and macrophages – in response to infection and sterile inflammation are areas of great interest. The larval zebrafish model of innate immunity, and the imaging capabilities it provides, is a source of new research and discoveries in this field. Multiple methods have been developed in larval zebrafish to specifically deplete functional macrophages or neutrophils. Each of these has pros and cons, as well as caveats, that often make it difficult to directly compare results from different studies. The purpose of this Review is to (1) explore the pros, cons and caveats of each of these immune cell-depleted models; (2) highlight and place into a broader context recent key findings on the specific functions of innate immune cells using these models; and (3) explore future directions in which immune cell depletion methods are being expanded.

Summary: Macrophages and neutrophils are distinct innate immune cells with diverse roles in diverse inflammatory contexts. Recent research in larval zebrafish using cell-specific depletion methods has revealed new insights into these cells' functions.

Myeloid loss of Beclin 1 promotes PD-L1hi precursor B cell lymphoma development

Beclin 1 (Becn1) is a key molecule in the autophagy pathway and has been implicated in cancer development. Due to the embryonic lethality of homozygous Becn1-deficient mice, the precise mechanisms and cell type-specific roles of Becn1 in regulating inflammation and cancer immunity remain elusive. Here, we report that myeloid-deficient Becn1 (Becn1ΔM) mice developed neutrophilia, were hypersusceptible to LPS-induced septic shock, and had a high risk of developing spontaneous precursor B cell (pre-B cell) lymphoma with elevated expression of immunosuppressive molecules programmed death ligand 1 (PD-L1) and IL-10. Becn1 deficiency resulted in the stabilization of MEKK3 and aberrant p38 activation in neutrophils, and mediated neutrophil-B cell interaction through Cxcl9/Cxcr3 chemotaxis. Neutrophil-B cell interplay further led to the activation of IL-21/STAT3/IRF1 and CD40L/ERK signaling and PD-L1 expression; therefore, it suppressed CD8+ T cell function. Ablation of p38 in Becn1ΔM mice prevented neutrophil inflammation and B cell tumorigenesis. Importantly, the low expression of Becn1 in human neutrophils was significantly correlated with the PD-L1 levels in pre-B acute lymphoblastic lymphoma (ALL) patients. Our findings have identified myeloid Becn1 as a key regulator of cancer immunity and therapeutic target for pre-B cell lymphomas.

Relating GPI-Anchored Ly6 Proteins uPAR and CD59 to Viral Infection

The Ly6 (lymphocyte antigen-6)/uPAR (urokinase-type plasminogen activator receptor) superfamily protein is a group of molecules that share limited sequence homology but conserved three-fingered structures. Despite diverse cellular functions, such as in regulating host immunity, cell adhesion, and migration, the physiological roles of these factors in vivo remain poorly characterized. Notably, increasing research has focused on the interplays between Ly6/uPAR proteins and viral pathogens, the results of which have provided new insight into viral entry and virus-host interactions. While LY6E (lymphocyte antigen 6 family member E), one key member of the Ly6E/uPAR-family proteins, has been extensively studied, other members have not been well characterized. Here, we summarize current knowledge of Ly6/uPAR proteins related to viral infection, with a focus on uPAR and CD59. Our goal is to provide an up-to-date view of the Ly6/uPAR-family proteins and associated virus-host interaction and viral pathogenesis.

Frontline Science: Cytokine-mediated developmental phenotype of mouse eosinophils: IL-5-associated expression of the Ly6G/Gr1 surface Ag

Eosinophils have broad and extensive immunomodulatory capacity; recent studies have focused on the roles of distinct eosinophil subsets in specific tissue microenvironments. Ly6G is a GPI-linked leukocyte surface Ag understood primarily as a marker of mouse neutrophils, although its full function is not known. Here, we show that Ly6G/Gr1, detected by mAbs 1A8 (anti-Ly6G) and RB6-8C5 (anti-Gr1), is detected prominently on a significant fraction of eosinophils from mouse bone marrow and bone marrow-derived culture, with fractions expressing this Ag increasing in IL-5-enriched microenvironments. Among our findings, we identified SiglecF⁺ Gr1⁺ eosinophils in bone marrow from naïve, allergen-challenged and IL-5 transgenic mice; SiglecF⁺ Gr1⁺ eosinophils were also prominent ex vivo in bone marrow-derived eosinophils (bmEos) in IL-5-enriched culture. Reducing the IL-5 concentration 20-fold had no impact on the rate of generation of SiglecF⁺ bmEos but did result in a marked increase in the Gr1^- fraction (from 17.4 ± 2% to 30 ± 2.3%, ***P < 0.005). Reducing the IL-5 concentration also enhanced chemotaxis; SiglecF⁺ Gr1^- bmEos were considerably more responsive to eotaxin-1 than were their SiglecF⁺ Gr1⁺ counterparts. These results suggest that (i) IL-5 regulates the expression of Ly6G/Gr1, either directly or indirectly, in cells of the eosinophil lineage, (ii) eosinophils generated in response to high concentrations of IL-5 can be distinguished from those generated under homeostatic conditions by expression of the Ly6G/Gr1 cell surface Ag, and (iii) expression of Ly6G/Gr1 may have an impact on function, directly or indirectly, including the potential to undergo chemotaxis in response to eotaxin-1.

Genetic Lineage Tracing of Sca-1+ Cells Reveals Endothelial but Not Myogenic Contribution to the Murine Heart

BACKGROUND

The adult mammalian heart displays a cardiomyocyte turnover rate of ≈1%/y throughout postnatal life and after injuries such as myocardial infarction (MI), but the question of which cell types drive this low level of new cardiomyocyte formation remains contentious. Cardiac-resident stem cells marked by stem cell antigen-1 (Sca-1, gene name Ly6a) have been proposed as an important source of cardiomyocyte renewal. However, the in vivo contribution of endogenous Sca-1⁺ cells to the heart at baseline or after MI has not been investigated.

METHODS

Here we generated Ly6a gene-targeted mice containing either a constitutive or an inducible Cre recombinase to perform genetic lineage tracing of Sca-1⁺ cells in vivo.

RESULTS

We observed that the contribution of endogenous Sca-1⁺ cells to the cardiomyocyte population in the heart was <0.005% throughout all of cardiac development, with aging, or after MI. In contrast, Sca-1⁺ cells abundantly contributed to the cardiac vasculature in mice during physiological growth and in the post-MI heart during cardiac remodeling. Specifically, Sca-1 lineage-traced endothelial cells expanded postnatally in the mouse heart after birth and into adulthood. Moreover, pulse labeling of Sca-1⁺ cells with an inducible Ly6a-MerCreMer allele also revealed a preferential expansion of Sca-1 lineage-traced endothelial cells after MI injury in the mouse.

CONCLUSIONS

Cardiac-resident Sca-1⁺ cells are not significant contributors to cardiomyocyte renewal in vivo. However, cardiac Sca-1⁺ cells represent a subset of vascular endothelial cells that expand postnatally with enhanced responsiveness to pathological stress in vivo.

Ly6C+ Inflammatory Monocyte Differentiation Partially Mediates Hyperhomocysteinemia-Induced Vascular Dysfunction in Type 2 Diabetic db/db Mice

OBJECTIVE

Hyperhomocysteinemia (HHcy) is a potent risk factor for diabetic cardiovascular diseases. We have previously reported that hyperhomocysteinemia potentiates type 1 diabetes mellitus-induced inflammatory monocyte differentiation, vascular dysfunction, and atherosclerosis. However, the effects of hyperhomocysteinemia on vascular inflammation in type 2 diabetes mellitus (T2DM) and the underlying mechanism are unknown. Approach and Results: Here, we demonstrate that hyperhomocysteinemia was induced by a high methionine diet in control mice (homocysteine 129 µmol/L), which was further worsened in T2DM db/db mice (homocysteine 180 µmol/L) with aggravated insulin intolerance. Hyperhomocysteinemia potentiated T2DM-induced mononuclear cell, monocyte, inflammatory monocyte (CD11b+Ly6C+), and M1 macrophage differentiation in periphery and aorta, which were rescued by folic acid-based homocysteine-lowering therapy. Moreover, hyperhomocysteinemia exacerbated T2DM-impaired endothelial-dependent aortic relaxation to acetylcholine. Finally, transfusion of bone marrow cells depleted for Ly6C by Ly6c shRNA transduction improved insulin intolerance and endothelial-dependent aortic relaxation in hyperhomocysteinemia+T2DM mice.

CONCLUSIONS

Hyperhomocysteinemia potentiated systemic and vessel wall inflammation and vascular dysfunction partially via inflammatory monocyte subset induction in T2DM. Inflammatory monocyte may be a novel therapeutic target for insulin resistance, inflammation, and cardiovascular complications in hyperhomocysteinemia+T2DM.

Small Vessels Are a Big Problem in Neurodegeneration and Neuroprotection

The cerebral microcirculation holds a critical position to match the high metabolic demand by neuronal activity. Functionally, microcirculation is virtually inseparable from other nervous system cells under both physiological and pathological conditions. For successful bench-to-bedside translation of neuroprotection research, the role of microcirculation in acute and chronic neurodegenerative disorders appears to be under-recognized, which may have contributed to clinical trial failures with some neuroprotectants. Increasing data over the last decade suggest that microcirculatory impairments such as endothelial or pericyte dysfunction, morphological irregularities in capillaries or frequent dynamic stalls in blood cell flux resulting in excessive heterogeneity in capillary transit may significantly compromise tissue oxygen availability. We now know that ischemia-induced persistent abnormalities in capillary flow negatively impact restoration of reperfusion after recanalization of occluded cerebral arteries. Similarly, microcirculatory impairments can accompany or even precede neural loss in animal models of several neurodegenerative disorders including Alzheimer's disease. Macrovessels are relatively easy to evaluate with radiological or experimental imaging methods but they cannot faithfully reflect the downstream microcirculatory disturbances, which may be quite heterogeneous across the tissue at microscopic scale and/or happen fast and transiently. The complexity and size of the elements of microcirculation, therefore, require utilization of cutting-edge imaging techniques with high spatiotemporal resolution as well as multidisciplinary team effort to disclose microvascular-neurodegenerative connection and to test treatment approaches to advance the field. Developments in two photon microscopy, ultrafast ultrasound, and optical coherence tomography provide valuable experimental tools to reveal those microscopic events with high resolution. Here, we review the up-to-date advances in understanding of the primary microcirculatory abnormalities that can result in neurodegenerative processes and the combined neurovascular protection approaches that can prevent acute as well as chronic neurodegeneration.

IL-17C-mediated innate inflammation decreases the response to PD-1 blockade in a model of Kras-driven lung cancer

Chronic obstructive pulmonary disease (COPD) is associated with neutrophilic lung inflammation and CD8 T cell exhaustion and is an important risk factor for the development of non-small cell lung cancer (NSCLC). The clinical response to programmed cell death-1 (PD-1) blockade in NSCLC patients is variable and likely affected by a coexisting COPD. The pro-inflammatory cytokine interleukin-17C (IL-17C) promotes lung inflammation and is present in human lung tumors. Here, we used a Kras-driven lung cancer model to examine the function of IL-17C in inflammation-promoted tumor growth. Genetic ablation of Il-17c resulted in a decreased recruitment of inflammatory cells into the tumor microenvironment, a decreased expression of tumor-promoting cytokines (e.g. interleukin-6 (IL-6)), and a reduced tumor proliferation in the presence of Haemophilus influenzae- (NTHi) induced COPD-like lung inflammation. Chronic COPD-like inflammation was associated with the expression of PD-1 in CD8 lymphocytes and the membrane expression of the programmed death ligand (PD-L1) independent of IL-17C. Tumor growth was decreased in Il-17c deficient mice but not in wildtype mice after anti-PD-1 treatment. Our results suggest that strategies targeting innate immune mechanisms, such as blocking of IL-17C, may improve the response to anti-PD-1 treatment in lung cancer patients.

Two-photon intravital imaging of leukocyte migration during inflammation in the respiratory system

Two-photon intravital imaging is a powerful method by which researchers are able to directly observe biological phenomena in live organisms. Researchers in various biomedical research fields have applied two-photon imaging to a variety of target organs by utilizing this technology’s ability to penetrate to significant depths with minimal phototoxicity. The mouse respiratory system in inflammation models is a good example, as two-photon intravital imaging can provide insights as to how the immune system is activated in response to inflammation within the respiratory system. Inflammation models can be generated via influenza viral, bacterial, or lipopolysaccharide injection. To exteriorize the lungs or trachea, thoracotomy or tracheotomy is performed, respectively; the appropriate combination of inflammation induction and organ exposure is selected depending on the study purpose. On the other hand, visualizing the movement of leukocytes is also an important component; to this end, immune cell populations of interest are either labeled via the genetic attachment of fluorescent proteins or stained with antibodies or dyes. With the proper selection of methods at each step, twophoton intravital imaging can yield visual evidence regarding immune responses to inflammation.

CD27, CD201, FLT3, CD48, and CD150 cell surface staining identifies long-term mouse hematopoietic stem cells in immunodeficient non-obese diabetic severe combined immune deficient-derived strains

Staining for CD27 and CD201 (endothelial protein C receptor) has been recently suggested as an alternative to stem cell antigen-1 (Sca1) to identify hematopoietic stem cells in inbred mouse strains with low or nil expression of SCA1. However, whether staining for CD27 and CD201 is compatible with low fms-like tyrosine kinase 3 (FLT3) expression and the "SLAM" code defined by CD48 and CD150 to identify mouse long-term reconstituting hematopoietic stem cells has not been established. We compared the C57BL/6 strain, which expresses a high level of SCA1 on hematopoietic stem cells to non-obese diabetic severe combined immune deficient NOD.CB17-prkdc ^scid/Sz (NOD-scid) mice and NOD.CB17-prkdc ^scid il2rg ^tm1Wj1/Sz (NSG) mice which both express low to negative levels of SCA1 on hematopoietic stem cells. We demonstrate that hematopoietic stem cells are enriched within the linage-negative C-KIT⁺ CD27⁺ CD201⁺ FLT3^- CD48-CD150⁺ population in serial dilution long-term competitive transplantation assays. We also make the novel observation that CD48 expression is up-regulated in Lin^- KIT⁺ progenitors from NOD-scid and NSG strains, which otherwise have very few cells expressing the CD48 ligand CD244. Finally, we report that unlike hematopoietic stem cells, SCA1 expression is similar on bone marrow endothelial and mesenchymal progenitor cells in C57BL/6, NOD-scid and NSG mice. In conclusion, we propose that the combination of Lineage, KIT, CD27, CD201, FLT3, CD48, and CD150 antigens can be used to identify long-term reconstituting hematopoietic stem cells from mouse strains expressing low levels of SCA1 on hematopoietic cells.

Lens Epithelial Cells Initiate an Inflammatory Response Following Cataract Surgery

Purpose

Lens epithelial cell (LEC) conversion to myofibroblast is responsible for fibrotic cataract surgery complications including posterior capsular opacification. While transforming growth factor beta (TGFβ) signaling is important, the mechanisms by which the TGFβ pathway is activated post cataract surgery (PCS) are not well understood.

Methods

RNA-seq was performed on LECs obtained from a mouse cataract surgery model at the time of surgery and 24 hours later. Bioinformatic analysis was performed with iPathwayGuide. Expression dynamics were determined by immunofluorescence.

Results

The LEC transcriptome is massively altered by 24 hours PCS. The differentially expressed genes included those important for lens biology, and fibrotic markers. However, the most dramatic changes were in the expression of genes regulating the innate immune response, with the top three altered genes exhibiting greater than 1000-fold upregulation. Immunolocalization revealed that CXCL1, S100a9, CSF3, COX-2, CCL2, LCN2, and HMOX1 protein levels upregulate in LECs between 1 hour and 6 hours PCS and peak at 24 hours PCS, while their levels sharply attenuate by 3 days PCS. This massive upregulation of known inflammatory mediators precedes the infiltration of neutrophils into the eye at 18 hours PCS, the upregulation of canonical TGFβ signaling at 48 hours PCS, and the infiltration of macrophages at 3 days PCS.

Conclusions

These data demonstrate that LECs produce proinflammatory cytokines immediately following lens injury that could drive postsurgical flare, and suggest that inflammation may be a major player in the onset of lens-associated fibrotic disease PCS.

Emerging Role of Lymphocyte Antigen-6 Family of Genes in Cancer and Immune Cells

Stem Cell Antigen-1 (Sca-1/Ly6A) was the first identified member of the Lymphocyte antigen-6 (Ly6) gene family. Sca-1 serves as a marker of cancer stem cells and tissue resident stem cells in mice. The Sca-1 gene is located on mouse chromosome 15. While a direct homolog of Sca-1 in humans is missing, human chromosome 8—the syntenic region to mouse chromosome 15—harbors several genes containing the characteristic domain known as LU domain. The function of the LU domain in human LY6 gene family is not yet defined. The LY6 gene family proteins are present on human chromosome 6, 8, 11, and 19. The most interesting of these genes are located on chromosome 8q24.3, a frequently amplified locus in human cancer. Human LY6 genes represent novel biomarkers for poor cancer prognosis and are required for cancer progression in addition to playing an important role in immune escape. Although the mechanism associated with these phenotype is not yet clear, it is timely to review the current literature in order to address the critical need for future advancements in this field. This review will summarize recent findings which describe the role of human LY6 genes—LY6D, LY6E, LY6H, LY6K, PSCA, LYPD2, SLURP1, GML, GPIHBP1, and LYNX1; and their orthologs in mice at chromosome 15.