Intravital imaging - dynamic insights into natural killer T cell biology

invariant Natural Killer T Cells Modulate the Peritoneal Macrophage Response to Polymicrobial Sepsis

INTRODUCTION

A dysregulated immune system is a major driver of the mortality and long-term morbidity from sepsis. With respect to macrophages, it has been shown that phenotypic changes are critical to effector function in response to acute infections, including intra-abdominal sepsis. Invariant natural killer T cells (iNKT cells) have emerged as potential central regulators of the immune response to a variety of infectious insults. Specifically, various iNKT cell:macrophage interactions have been noted across a spectrum of diseases, including acute events such as sepsis. However, the potential for iNKT cells to affect peritoneal macrophages during an abdominal septic event is as yet unknown.

METHODS

Cecal ligation and puncture (CLP) was performed in both wild type (WT) and invariant natural killer T cell knockout (iNKT-/-) mice. 24 h following CLP or sham operation, peritoneal macrophages were collected for analysis. Analysis of macrophage phenotype and function was undertaken to include analysis of bactericidal activity and cytokine or superoxide production.

RESULTS

Within iNKT-/- mice, a greater degree of intraperitoneal macrophages in response to the sepsis was noted. Compared to WT mice, within iNKT-/- mice, CLP did induce an increase in CD86+ and CD206+, but no difference in CD11b+. Unlike WT mice, intra-abdominal sepsis within iNKT-/- mice induced an increase in Ly6C-int (5.2% versus 14.9%; P < 0.05) and a decrease in Ly6C-high on peritoneal macrophages. Unlike phagocytosis, iNKT cells did not affect macrophage bactericidal activity. Although iNKT cells did not affect interleukin-6 production, iNKT cells did affect IL-10 production and both nitrite and superoxide production from peritoneal macrophages.

CONCLUSIONS

The observations indicate that iNKT cells affect specific phenotypic and functional aspects of peritoneal macrophages during polymicrobial sepsis. Given that pharmacologic agents that affect iNKT cell functioning are currently in clinical trial, these findings may have the potential for translation to critically ill surgical patients with abdominal sepsis.

Motility and tumor infiltration are key aspects of invariant natural killer T cell anti-tumor function

Dysfunction of invariant natural killer T (iNKT) cells contributes to immune resistance of tumors. Most mechanistic studies focus on their static functional status before or after activation, not considering motility as an important characteristic for antigen scanning and thus anti-tumor capability. Here we show via intravital imaging, that impaired motility of iNKT cells and their exclusion from tumors both contribute to the diminished anti-tumor iNKT cell response. Mechanistically, CD1d, expressed on macrophages, interferes with tumor infiltration of iNKT cells and iNKT-DC interactions but does not influence their intratumoral motility. VCAM1, expressed by cancer cells, restricts iNKT cell motility and inhibits their antigen scanning and activation by DCs via reducing CDC42 expression. Blocking VCAM1-CD49d signaling improves motility and activation of intratumoral iNKT cells, and consequently augments their anti-tumor function. Interference with macrophage-iNKT cell interactions further enhances the anti-tumor capability of iNKT cells. Thus, our findings provide a direction to enhance the efficacy of iNKT cell-based immunotherapy via motility regulation.

Harnessing cytokine-induced killer cells to accelerate diabetic wound healing: an approach to regulating post-traumatic inflammation

Impaired immunohomeostasis in diabetic wounds prolongs inflammation and cytokine dysfunction, thus, delaying or preventing wound-surface healing. Extensive clinical studies have been conducted on cytokine-induced killer (CIK) cells recently, as they can be easily proliferated using a straightforward, inexpensive protocol. Therefore, the function of CIK cells in regulating inflammatory environments has been drawing attention for clinical management. Throughout the current investigation, we discovered the regenerative capacity of these cells in the challenging environment of wounds that heal poorly due to diabetes. We demonstrated that the intravenous injection of CIK cells can re-establish a proregenerative inflammatory microenvironment, promote vascularization and, ultimately, accelerate skin healing in diabetic mice. The results indicated that CIK cell treatment affects macrophage polarization and restores the function of regenerative cells under hyperglycemic conditions. This novel cellular therapy offers a promising intervention for clinical applications through specific inflammatory regulation functions.

Single-cell analysis reveals differences among iNKT cells colonizing peripheral organs and identifies Klf2 as a key gene for iNKT emigration

Invariant natural killer T cell (iNKT) subsets are differentially distributed in various immune organs. However, it remains unclear whether iNKT cells exhibit phenotypical and functional differences in different peripheral organs and how thymic iNKT cells emigrate to peripheral organs. Here, we used single-cell RNA-seq to map iNKT cells from peripheral organs. iNKT1 cells from liver, spleen, and lymph node appear to have distinct phenotypic profiles and functional capabilities. However, iNKT17 transcriptomes were comparable across peripheral organs. In addition, by integrating data with a thymic iNKT cell study, we uncovered a transient population of recent thymic emigrants, a cluster of peripheral iNKT cells with high expression of transcription factor Kruppel-like factor 2 (Klf2). Deletion of Klf2 led to a severe impairment of iNKT differentiation and migration. Our study revealed that iNKT subsets are uniquely distributed in peripheral organs with some inter-local tissue variation, especially for iNKT1 cell, and identified Klf2 as a rheostat for iNKT cell migration and differentiation.

Functional visualization of NK Cell-mediated killing of metastatic single tumor cells

Natural killer (NK) cells lyse invading tumor cells to limit metastatic growth in the lung, but how some cancers evade this host protective mechanism to establish a growing lesion is unknown. Here, we have combined ultra-sensitive bioluminescence imaging with intravital two-photon microscopy involving genetically encoded biosensors to examine this question. NK cells eliminated disseminated tumor cells from the lung within 24 hr of arrival, but not thereafter. Intravital dynamic imaging revealed that 50% of NK-tumor cell encounters lead to tumor cell death in the first 4 hr after tumor cell arrival, but after 24 hr of arrival, nearly 100% of the interactions result in the survival of the tumor cell. During this 24-hr period, the probability of ERK activation in NK cells upon encountering the tumor cells was decreased from 68% to 8%, which correlated with the loss of the activating ligand CD155/PVR/Necl5 from the tumor cell surface. Thus, by quantitatively visualizing, the NK-tumor cell interaction at the early stage of metastasis, we have revealed the crucial parameters of NK cell immune surveillance in the lung.

Multi-Modal Multi-Spectral Intravital Microscopic Imaging of Signaling Dynamics in Real-Time during Tumor-ImmuneInteractions

Intravital microscopic imaging (IVM) allows for the study of interactions between immune cells and tumor cells in a dynamic, physiologically relevant system in vivo. Current IVM strategies primarily use fluorescence imaging; however, with the advances in bioluminescence imaging and the development of new bioluminescent reporters with expanded emission spectra, the applications for bioluminescence are extending to single cell imaging. Herein, we describe a molecular imaging window chamber platform that uniquely combines both bioluminescent and fluorescent genetically encoded reporters, as well as exogenous reporters, providing a powerful multi-plex strategy to study molecular and cellular processes in real-time in intact living systems at single cell resolution all in one system. We demonstrate that our molecular imaging window chamber platform is capable of imaging signaling dynamics in real-time at cellular resolution during tumor progression. Importantly, we expand the utility of IVM by modifying an off-the-shelf commercial system with the addition of bioluminescence imaging achieved by the addition of a CCD camera and demonstrate high quality imaging within the reaches of any biology laboratory.

Intravital imaging of interactions between iNKT and kupffer cells to clear free lipids during steatohepatitis

Rationale: Invariant natural killer T (iNKT) cells and Kupffer cells represent major hepatic populations of innate immune cells. However, their roles in steatohepatitis remain poorly understood. To elucidate their functions in steatohepatitis development, real-time, in vivo analysis is necessary to understand the pathophysiological events in the dynamic interactions between them during diet-induced steatohepatitis.

Methods: We used a steatohepatitis animal model induced by a methionine-choline-deficient (MCD) diet. Multi-photon confocal live imaging and conventional experimental techniques were employed to investigate the hepatic pathological microenvironment of iNKT and Kupffer cells, interactions between them, and the biological effects of these interactions in steatohepatitis.

Results: We found that iNKT cells were recruited and aggregated into small clusters and interacted dynamically with Kupffer cells in the early stage of steatohepatitis. Most significantly, the iNKT cells in the cluster cleared free lipids released by necrotic hepatocytes and presented a non-classical activation state with high IFN-γ expression. Furthermore, the Kupffer cells in the cell cluster were polarized to type M1. The transcriptome sequencing of iNKT cells showed upregulation of genes related to phagocytosis and lipid processing. Adoptive transfer of iNKT cells to Jα18^-/- mice showed that iNKT and Kupffer cell clusters were essential for balancing the liver and peripheral lipid levels and inhibiting liver fibrosis development.

Conclusions: Our study identified an essential role for dynamic interactions between iNKT cells and Kupffer cells in promoting lipid phagocytosis and clearance by iNKT cells during early liver steatohepatitis. Therefore, modulating iNKT cells is a potential therapeutic strategy for early steatohepatitis.

DAMPs, PAMPs, and LAMPs in Immunity and Sterile Inflammation

Recognizing the importance of leukocyte trafficking in inflammation led to some therapeutic breakthroughs. However, many inflammatory pathologies remain without specific therapy. This review discusses leukocytes in the context of sterile inflammation, a process caused by sterile (non-microbial) molecules, comprising damage-associated molecular patterns (DAMPs). DAMPs bind specific receptors to activate inflammation and start a highly optimized sequence of immune cell recruitment of neutrophils and monocytes to initiate effective tissue repair. When DAMPs are cleared, the recruited leukocytes change from a proinflammatory to a reparative program, a switch that is locally supervised by invariant natural killer T cells. In addition, neutrophils exit the inflammatory site and reverse transmigrate back to the bloodstream. Inflammation persists when the program switch or reverse transmigration fails, or when the coordinated leukocyte effort cannot clear the immunostimulatory molecules. The latter causes inappropriate leukocyte activation, a driver of many pathologies associated with poor lifestyle choices. We discuss lifestyle-associated inflammatory diseases and their corresponding immunostimulatory lifestyle-associated molecular patterns (LAMPs) and distinguish them from DAMPs.

Porcine Invariant Natural Killer T Cells: Functional Profiling and Dynamics in Steady State and Viral Infections

Pigs are important livestock and comprehensive understanding of their immune responses in infections is critical to improve vaccines and therapies. Moreover, similarities between human and swine physiology suggest that pigs are a superior animal model for immunological studies. However, paucity of experimental tools for a systematic analysis of the immune responses in pigs represent a major disadvantage. To evaluate the pig as a biomedical model and additionally expand the knowledge of rare immune cell populations in swine, we established a multicolor flow cytometry analysis platform of surface marker expression and cellular responses for porcine invariant Natural Killer T cells (iNKT). In humans, iNKT cells are among the first line defenders in various tissues, respond to CD1d-restricted antigens and become rapidly activated. Naïve porcine iNKT cells were CD3⁺/CD4⁻/CD8⁺ or CD3⁺/CD4⁻/CD8⁻ and displayed an effector- or memory-like phenotype (CD25⁺/ICOS⁺/CD5^hi/CD45RA⁻/CCR7 ^± /CD27⁺). Based on their expression of the transcription factors T bet and the iNKT cell-specific promyelocytic leukemia zinc finger protein (PLZF), porcine iNKT cells were differentiated into functional subsets. Analogous to human iNKT cells, in vitro stimulation of porcine leukocytes with the CD1d ligand α-galactosylceramide resulted in rapid iNKT cell proliferation, evidenced by an increase in frequency and Ki-67 expression. Moreover, this approach revealed CD25, CD5, ICOS, and the major histocompatibility complex class II (MHC II) as activation markers on porcine iNKT cells. Activated iNKT cells also expressed interferon-γ, upregulated perforin expression, and displayed degranulation. In steady state, iNKT cell frequency was highest in newborn piglets and decreased with age. Upon infection with two viruses of high relevance to swine and humans, iNKT cells expanded. Animals infected with African swine fever virus displayed an increase of iNKT cell frequency in peripheral blood, regional lymph nodes, and lungs. During Influenza A virus infection, iNKT cell percentage increased in blood, lung lymph nodes, and broncho-alveolar lavage. Our in-depth characterization of porcine iNKT cells contributes to a better understanding of porcine immune responses, thereby facilitating the design of innovative interventions against infectious diseases. Moreover, we provide new evidence that endorses the suitability of the pig as a biomedical model for iNKT cell research.

Hyperactivated peripheral invariant natural killer T cells correlate with the progression of HBV-relative liver cirrhosis

Invariant NKT (iNKT) cells express markers of both T and NK cells and may produce various cytokines to regulate liver immunity. However, the role of iNKT cells in the progression of HBV-relative liver cirrhosis (HBV-LC) is incompletely understood. Here, we investigated the impact of peripheral iNKT cells on a cohort of patients with HBV-LC. The frequency, number, activation status, apoptosis and proliferation ability of peripheral iNKT cells were detected with flow cytometry. The impact of peripheral iNKT cells on the proliferation of hepatocyte cell line (MIHA) and activation of hepatic stellate cell line (LX-2) was detected with flow cytometry and PCR. In HBV-LC patients, the frequency and absolute number of peripheral iNKT cells significantly reduced, but the expression levels of CD25, interleukin (IL)-4, IL-13 and interferon (IFN)-γ increased. No difference was observed in the proliferation and apoptosis of circulating iNKT cells between patients and healthy controls (HCs). CXCR6 (CD186), known to be closely associated with iNKT cells migration from the periphery to the liver, was highly expressed on peripheral iNKT cells in HBV-LC patients. Furthermore, peripheral iNKT cells had a profound impact on MIHA cell proliferation and LX-2 cell activation through IL-4 or IL-13. Our data suggest that in HBV-LC patients, highly activated peripheral iNKT cells may migrate to the liver and affect hepatocyte cell line (MIHA) proliferation and hepatic stellate cell line (LX-2) activation through the expression of type 2 cytokines, which may result in excessive healing and contributing to the progression of fibrosis toward cirrhosis in liver.

IL-17 production by NKG2D-expressing CD56+ T cells in type 2 diabetes

T cells expressing CD56 (identified as CD3+CD56+) play a potential role in activation or regulation of other immune cells by secreting various cytokines. We hypothesized that these cells expressing the natural group 2, member D (NKG2D) could produce high levels of interleukin (IL)-17 in type 2 diabetes (T2D). CD56 + T cells expressing NKG2D of T2D patients, particularly in poor glycemic control (PC) predominantly produced higher IL-17 compared to the NKG2D negative population. IL-17 production of CD56 + T cells with NKG2D + was positively correlated with the level of HbA1c (N = 22, R² = 0.120 and P =  0.044). Interestingly, CD56+ T cells with NKG2D^Hi of T2D patients had significantly higher IL-17 production than those of CD56 + T cells with NKG2D^Low (P =  0.027) and showed statistically significant with P-value < 0.001 compared to CD56 + T cells with NKG2D^Hi of non-diabetic individuals (ND). In summary, CD56 + T cells expressing NKG2D, especially in the NKG2D^Hi population may be involved in pathogenesis and severity of T2D via IL-17.

Invariant Natural Killer T and Mucosal-Associated Invariant T Cells in Asthmatic Patients

Recent studies have highlighted the heterogeneity of asthma. Distinct patient phenotypes (symptoms, age at onset, atopy, and lung function) may result from different pathogenic mechanisms, including airway inflammation, remodeling, and immune and metabolic pathways in a specific microbial environment. These features, which define the asthma endotype, may have significant consequences for the development and progression of the disease. Asthma is generally associated with Th2 cells, which produce a panel of cytokines (IL-4, IL-5, IL-13) that act in synergy to drive lung inflammatory responses, mucus secretion, IgE production, and fibrosis, causing the characteristic symptoms of asthma. In addition to conventional CD4⁺ T lymphocytes, other T-cell types can produce Th2 or Th17 cytokines rapidly. Promising candidate cells for studies of the mechanisms underlying the pathophysiology of asthma are unconventional T lymphocytes, such as invariant natural killer T (iNKT) and mucosal-associated invariant T (MAIT) cells. This review provides an overview of our current understanding of the impact of iNKT and MAIT cells on asthmatic inflammation, focusing particularly on pediatric asthma.

A novel role for coinhibitory receptors/checkpoint proteins in the immunopathology of sepsis

Coinhibitory molecules, such as PD-1, CTLA-4, 2B4, and BTLA, are an important new family of mediators in the pathophysiology of severe bacterial and/or fungal infection, as well as the combined insults of shock and sepsis. Further, the expression of these molecules may serve as indicators of the immune status of the septic individual. Using PD-1:PD-L as an example, we discuss in this review how such checkpoint molecules may affect the host response to infection by mediating the balance between effective immune defense and immune-mediated tissue injury. Additionally, we explore how the up-regulation of PD-1 and/or PD-L1 expression on not only adaptive immune cells (e.g., T cells), but also on innate immune cells (e.g., macrophages, monocytes, and neutrophils), as well as nonimmune cells during sepsis and/or shock contributes to functional alterations often with detrimental sequelae.

Program Cell Death Receptor-1-Mediated Invariant Natural Killer T-Cell Control of Peritoneal Macrophage Modulates Survival in Neonatal Sepsis

We have shown that invariant natural killer T (iNKT) cells mediate sepsis-induced end-organ changes and immune responses, including macrophage bacterial phagocytosis, a finding regulated by the check point protein program cell death receptor-1 (PD-1). Furthermore, PD-1 mediates mortality in both adult and neonatal murine sepsis as well as in surgical patients. Given our previous findings, we hypothesize that iNKT cells will also modulate neonatal sepsis survival, and that this effect is regulated in part through PD-1. We utilized a polymicrobial intra-peritoneal cecal slurry (CS) sepsis model in wild type (WT), iNKT^−/− or PD-1^−/− 5–7 day old neonatal pups. Typically, tissues were harvested at 24 h for various bioassays/histology and, in some cases, survival was assessed for up to 7 days. Interestingly, similar to what we recently reported for PD-1^−/− mice following CS, iNKT^−/−-deficient animals exhibit a markedly improved survival vs. WT. Histologically, minor alterations in liver architectural, which were noted in WT pups, were attenuated in both iNKT^−/− and PD-1^−/− pups. Following CS, PECAM-1 expression was unchanged in the WT pups but increased in both iNKT^−/− and PD-1^−/− pups. In WT, following CS the emergence of a Ly6C^low subpopulation was noted among the influxed peritoneal macrophage population. Conversely, within iNKT^−/− pups, there were fewer peritoneal macrophages and a greater percentage of Ly6C^high macrophages. We show not only a key role for iNKT cells in affecting end-organ damage as well as alterations in phagocytes phenotypes in neonatal sepsis but that this iNKT cell mediated effect is driven by the central checkpoint protein PD-1.

Antibody-dependent fragmentation is a newly identified mechanism of cell killing in vivo

The prevailing view is that therapeutic antibodies deplete cells through opsonization and subsequent phagocytosis, complement-dependent lysis or antibody-dependent cellular-cytotoxicity. We used high resolution in vivo imaging to identify a new antibody-dependent cell death pathway where Kupffer cells ripped large fragments off crawling antibody-coated iNKT cells. This antibody-dependent fragmentation process resulted in lethality and depletion of crawling iNKT cells in the liver sinusoids and lung capillaries. iNKT cell depletion was Fcy-receptor dependent and required iNKT cell crawling. Blood, spleen or joint iNKT cells that did not crawl were not depleted. The antibody required high glycosylation for sufficiently strong binding of the iNKT cells to the Fc Receptors on Kupffer cells. Using an acetaminophen overdose model, this approach functionally depleted hepatic iNKT cells and affected the severity of liver injury. This study reveals a new mechanism of antibody-dependent killing in vivo and raises implications for the design of new antibodies for cancer and auto-reactive immune cells.

Effect of PD-1: PD-L1 in Invariant Natural Killer T-Cell Emigration and Chemotaxis Following Sepsis

Invariant natural killer T-cells (iNKT) are a subset of T-cells that play a regulatory role in sepsis. Following cecal ligation and puncture (CLP), iNKT cells emigrate from the liver and into the circulation and peritoneum in a manner dependent upon coinhibitory molecule Programmed Cell Death Receptor 1 (PD-1). We hypothesized that the effect of PD-1 on iNKT-cell emigration was dependent upon the direct PD-1:PD-L1 interaction, and that PD-1 and PD-L1 would play a role in chemotaxis and chemokine receptor expression. Adoptive transfer of Vybrant-labeled wild-type (WT) cells showed the donor iNKT cells migrated from the liver to the peritoneum following CLP, but PD-L1 deficient donor iNKT cells did not. In a chemotaxis assay, WT-iNKT cells chemotaxed to CXCL12, but PD-1 and PD-L1 deficient iNKT cells did not. Using flow cytometry to evaluate chemokine receptor expression, peritoneal iNKT expression of CXCR4 increased following CLP in the WT, PD-1, and PD-L1 deficient animals, and CXCR6 increased in the WT and PD-1 deficient animals. In conclusion here we document that the hepatic emigration of iNKT cells following CLP to the peritoneum appears dependent upon the direct PD-1:PD-L1 interaction; however, although PD-1 and PD-L1 appear to play a role in chemotaxis, this is unlikely a reflection of iNKT-cell chemokine receptor expression changes.

A fast and effective determination of the biodistribution and subcellular localization of fluorescent immunoliposomes in freshly excised animal organs

Background

Preclinical research implementing fluorescence-based approaches is inevitable for drug discovery and technology. For example, a variety of contrast agents developed for biomedical imaging are usually evaluated in cell systems and animal models based on their conjugation to fluorescent dyes. Biodistribution studies of excised organs are often performed by macroscopic imaging, whereas the subcellular localization though vital, is often neglected or further validated by histological procedures. Available systems used to define the subcellular biodistribution of contrast agents such as intravital microscopes or ex vivo histological analysis are expensive and not affordable by the majority of researchers, or encompass tedious and time consuming steps that may modify the contrast agents and falsify the results. Thus, affordable and more reliable approaches to study the biodistribution of contrast agents are required. We developed fluorescent immunoliposomes specific for human fibroblast activation protein and murine endoglin, and used macroscopic fluorescence imaging and confocal microscopy to determine their biodistribution and subcellular localization in freshly excised mice organs at different time points post intravenous injection.

Results

Near infrared fluorescence macroscopic imaging revealed key differences in the biodistribution of the respective immunoliposomes at different time points post injection, which correlated to the first-pass effect as well as the binding of the probes to molecular targets within the mice organs. Thus, a higher accumulation and longer retention of the murine endoglin immunoliposomes was seen in the lungs, liver and kidneys than the FAP specific immunoliposomes. Confocal microscopy showed that tissue autofluorescence enables detection of organ morphology and cellular components within freshly excised, non-processed organs, and that fluorescent probes with absorption and emission maxima beyond the tissue autofluorescence range can be easily distinguished. Hence, the endoglin targeting immunoliposomes retained in some organs could be detected in the vascular endothelia cells of the organs.

Conclusions

The underlying work represents a quick, effective and more reliable setup to validate the macroscopic and subcellular biodistribution of contrast agents in freshly excised animal organs. The approach will be highly beneficial to many researchers involved in nanodrug design or in fluorescence-based studies on disease pathogenesis.

Human Invariant NKT Cells Induce IL-1β Secretion by Peripheral Blood Monocytes via a P2X7-Independent Pathway

The cytokine IL-1β plays a central role in inflammatory responses that are initiated by microbial challenges, as well as in those that are due to endogenous processes (often called sterile inflammation). IL-1β secretion that occurs independently of microbial stimulation is typically associated with the presence of endogenous alarmins, such as extracellular ATP (an indicator of cytopathic damage). In this study, we show that IL-2-activated human invariant NKT (iNKT) cells stimulate the secretion of IL-1β protein by human peripheral blood monocytes in a manner that requires neither the presence of microbial compounds nor signaling through the extracellular ATP receptor P2X7 Monocyte IL-1β production was specifically induced by iNKT cells, because similarly activated polyclonal autologous T cells did not have this effect. Secretion of IL-1β protein occurred rapidly (within 3-4 h) and required cell contact between the iNKT cells and monocytes. Similar to IL-1β production induced by TLR stimulation, the iNKT-induced pathway appeared to entail a two-step process involving NF-κB signaling and IL1B gene transcription, as well as assembly of the NLRP3 inflammasome and activation of caspase-1. However, in contrast to the classical inflammasome-mediated pathway of IL-1β production, activation of monocytes via P2X7 was dispensable for iNKT-induced IL-1β secretion, and potassium efflux was not required. Moreover, the iNKT-induced effect involved caspase-8 activity, yet it induced little monocyte death. These results suggest that IL-2-activated human iNKT cells induce monocytes to produce IL-1β through a distinctive pathway that does not require the presence of microbial danger signals or alarmins associated with cytopathic damage.