A nanoscale reorganization of the IL-15 receptor is triggered by NKG2D in a ligand-dependent manner

Spatial statistics of submicron size clusters of activating and inhibitory Natural Killer cell receptors in the resting state regulate early time signal discrimination

Natural Killer (NK) cells are lymphocytes of the innate immunity and sense healthy or diseased target cells with activating and inhibitory NK cell receptor (NKR) molecules expressed on the cell surface. The protection provided by NK cells against viral infections and tumors critically depends on their ability to distinguish healthy cells from diseased target cells that express 100-fold more activating ligands. NK cell signaling and activation depend on integrating opposing signals initiated by activating and inhibitory NKRs interacting with the cognate ligands expressed on target cells. A wide range of imaging experiments have demonstrated aggregation of both activating and inhibitory NKRs in the plasma membrane on submicron scales in resting NK cells. How do these submicron size NKR clusters formed in the resting state affect signal discrimination? Using in silico mechanistic signaling modeling with information theory and published superresolution imaging data for two well-studied human NKRs, activating NKG2D and inhibitory KIR2DL1, we show that early time signal discrimination by NK cells depends on the spatial statistics of these clusters. When NKG2D and KIR2DL1 clusters are disjoint in the resting state, these clusters help NK cells to discriminate between target cells expressing low and high doses of the activating cognate ligand, whereas, when the NKR clusters fully overlap the NK cells are unable to distinguish between healthy and diseased target cells. Therefore, the spatial statistics of submicron scale clusters of activating and inhibitory NKRs at the resting state provides an additional layer of control for signal discrimination in NK cells.

Membrane Fluctuation Model for Understanding the Effect of Receptor Nanoclustering on the Activation of Natural Killer Cells through Biomechanical Feedback

We investigated the role of ligand clustering and density in the activation of natural killer (NK) cells. To that end, we designed reductionist arrays of nanopatterned ligands arranged with different cluster geometries and densities and probed their effects on NK cell activation. We used these arrays as an artificial microenvironment for the stimulation of NK cells and studied the effect of the array geometry on the NK cell immune response. We found that ligand density significantly regulated NK cell activation while ligand clustering had an impact only at a specific density threshold. We also rationalized these findings by introducing a theoretical membrane fluctuation model that considers biomechanical feedback between ligand-receptor bonds and the cell membrane. These findings provide important insight into NK cell mechanobiology, which is fundamentally important and essential for designing immunotherapeutic strategies targeting cancer.

The Power of Three: Nanomaterials for Natural Killer (NK) Cell Immunoengineering Maximize Their Potency if They Exploit Multireceptor Stimulation

Many emerging cancer treatments are immunotherapies that modulate Natural Killer- (NK) or T cell activation, posing a challenge to develop immunoengineering nanomaterials that improve on the performance of molecular reagents. In physiological activation, multiple immunoreceptors signal in consort; however, current biomaterials do not replicate this. Here, NK cells are created for the first time, activating bionanomaterials that stimulate >2 immunoreceptors. Nanoclusters of monoclonal antibodies (mAb), templated by nanoscale graphene oxide sheets (NGO) (≈75 nm size), are exploited. To inform nanoreagent design, a model system of planar substrates with anchored mAb is first investigated. Combining mAb that stimulates three NK cell activating receptors (αNKP46 + αNKG2D + αDNAM-1), activated NK cells act more potently than any single receptor or pair. Applying this insight, an NGO-mAb nanocluster combining three distinct mAb: NGO-mAb(αNKP46 + αNKG2D + αDNAM-1) is created. This construct is potent and outperforms single-receptor-simulating nanoclusters, activating nearly twice as many NK cells as NGO-mAb(αNKP46) at a similar mAb dose or delivering similar activation at 10× lower dosage. Further, NGO-mAb are more potent than planar substrates for both single- and triple-mAb stimulation. These results imply a new concept for immunoengineering biomaterials: both nanoclustering and multi-receptor stimulation should be incorporated for maximum effect.

TIGIT can inhibit T cell activation via ligation-induced nanoclusters, independent of CD226 co-stimulation

TIGIT is an inhibitory receptor expressed on lymphocytes and can inhibit T cells by preventing CD226 co-stimulation through interactions in cis or through competition of shared ligands. Whether TIGIT directly delivers cell-intrinsic inhibitory signals in T cells remains unclear. Here we show, by analysing lymphocytes from matched human tumour and peripheral blood samples, that TIGIT and CD226 co-expression is rare on tumour-infiltrating lymphocytes. Using super-resolution microscopy and other techniques, we demonstrate that ligation with CD155 causes TIGIT to reorganise into dense nanoclusters, which coalesce with T cell receptor (TCR)-rich clusters at immune synapses. Functionally, this reduces cytokine secretion in a manner dependent on TIGIT's intracellular ITT-like signalling motif. Thus, we provide evidence that TIGIT directly inhibits lymphocyte activation, acting independently of CD226, requiring intracellular signalling that is proximal to the TCR. Within the subset of tumours where TIGIT-expressing cells do not commonly co-express CD226, this will likely be the dominant mechanism of action.

NKG2D discriminates diverse ligands through selectively mechano-regulated ligand conformational changes

Stimulatory immune receptor NKG2D binds diverse ligands to elicit differential anti-tumor and anti-virus immune responses. Two conflicting degeneracy recognition models based on static crystal structures and in-solution binding affinities have been considered for almost two decades. Whether and how NKG2D recognizes and discriminates diverse ligands still remain unclear. Using live-cell-based single-molecule biomechanical assay, we characterized the in situ binding kinetics of NKG2D interacting with different ligands in the absence or presence of mechanical force. We found that mechanical force application selectively prolonged NKG2D interaction lifetimes with the ligands MICA and MICB, but not with ULBPs, and that force-strengthened binding is much more pronounced for MICA than for other ligands. We also integrated steered molecular dynamics simulations and mutagenesis to reveal force-induced rotational conformational changes of MICA, involving formation of additional hydrogen bonds on its binding interface with NKG2D, impeding MICA dissociation under force. We further provided a kinetic triggering model to reveal that force-dependent affinity determines NKG2D ligand discrimination and its downstream NK cell activation. Together, our results demonstrate that NKG2D has a discrimination power to recognize different ligands, which depends on selective mechanical force-induced ligand conformational changes.

Immobile ligands enhance FcγR-TLR2/1 crosstalk by promoting interface overlap of receptor clusters

Innate immune cells detect pathogens through simultaneous stimulation of multiple receptors, but how cells use the receptor crosstalk to elicit context-appropriate responses is unclear. Here, we reveal that the inflammatory response of macrophages from FcγR-TLR2/1 crosstalk inversely depends on the ligand mobility within a model pathogen membrane. The mechanism is that FcγR and TLR2/1 form separate nanoclusters that interact at their interfaces during crosstalk. Less mobile ligands induce stronger interactions and more overlap between the receptor nanoclusters, leading to enhanced signaling. Different from the prevailing view that immune receptors colocalize to synergize their signaling, our results show that FcγR-TLR2/1 crosstalk occurs through interface interactions between non-colocalizing receptor nanoclusters, which are modulated by ligand mobility. This suggests a mechanism by which innate immune cells could use physical properties of ligands to fine-tune host responses.

Approach to map nanotopography of cell surface receptors

Cells communicate with their environment via surface receptors, but nanoscopic receptor organization with respect to complex cell surface morphology remains unclear. This is mainly due to a lack of accessible, robust and high-resolution methods. Here, we present an approach for mapping the topography of receptors at the cell surface with nanometer precision. The method involves coating glass coverslips with glycine, which preserves the fine membrane morphology while allowing immobilized cells to be positioned close to the optical surface. We developed an advanced and simplified algorithm for the analysis of single-molecule localization data acquired in a biplane detection scheme. These advancements enable direct and quantitative mapping of protein distribution on ruffled plasma membranes with near isotropic 3D nanometer resolution. As demonstrated successfully for CD4 and CD45 receptors, the described workflow is a straightforward quantitative technique to study molecules and their interactions at the complex surface nanomorphology of differentiated metazoan cells.

A super-resolution localisation-based method is shown to map receptor topography in immune cells, which allows quantitative study of molecules and their interactions at the complex surface nanomorphology of cells.

Shedding Structured Light on Molecular Immunity: The Past, Present and Future of Immune Cell Super Resolution Microscopy

In the two decades since the invention of laser-based super resolution microscopy this family of technologies has revolutionised the way life is viewed and understood. Its unparalleled resolution, speed, and accessibility makes super resolution imaging particularly useful in examining the highly complex and dynamic immune system. Here we introduce the super resolution technologies and studies that have already fundamentally changed our understanding of a number of central immunological processes and highlight other immunological puzzles only addressable in super resolution.

Retargeting IL-2 Signaling to NKG2D-Expressing Tumor-Infiltrating Leukocytes Improves Adoptive Transfer Immunotherapy

Ex vivo expansion followed by reinfusion of tumor-infiltrating leukocytes (TILs) has been used successfully for the treatment of multiple malignancies. Most protocols rely on the use of the cytokine IL-2 to expand TILs prior to reinfusion. In addition, TIL administration relies on systemic administration of IL-2 after reinfusion to support transferred cell survival. The use of IL-2, however, can be problematic because of its preferential expansion of regulatory T and myeloid cells as well as its systemic side effects. In this study, we describe the use of a novel IL-2 mutant retargeted to NKG2D rather than the high-affinity IL-2R for TIL-mediated immunotherapy in a murine model of malignant melanoma. We demonstrate that the NKG2D-retargeted IL-2 (called OMCPmutIL-2) preferentially expands TIL-resident CTLs, such as CD8+ T cells, NK cells, and γδT cells, whereas wild-type IL-2 provides a growth advantage for CD4+Foxp3+ T cells as well as myeloid cells. OMCPmutIL-2-expanded CTLs express higher levels of tumor-homing receptors, such as LFA-1, CD49a, and CXCR3, which correlate with TIL localization to the tumor bed after i.v. injection. Consistent with this, OMCPmutIL-2-expanded TILs provided superior tumor control compared with those expanded in wild-type IL-2. Our data demonstrate that adoptive transfer immunotherapy can be improved by rational retargeting of cytokine signaling to NKG2D-expressing CTLs rather than indiscriminate expansion of all TILs.

Gut Bacteria Induce Granzyme B Expression in Human Colonic ILC3s In Vitro in an IL-15-Dependent Manner

Group 3 innate lymphoid cells (ILC3s) in the gut mucosa have long been thought to be noncytotoxic lymphocytes that are critical for homeostasis of intestinal epithelial cells through secretion of IL-22. Recent work using human tonsillar cells demonstrated that ILC3s exposed to exogenous inflammatory cytokines for a long period of time acquired expression of granzyme B, suggesting that under pathological conditions ILC3s may become cytotoxic. We hypothesized that inflammation associated with bacterial exposure might trigger granzyme B expression in gut ILC3s. To test this, we exposed human colon lamina propria mononuclear cells to a panel of enteric bacteria. We found that the Gram-negative commensal and pathogenic bacteria induced granzyme B expression in a subset of ILC3s that were distinct from IL-22-producing ILC3s. A fraction of granzyme B⁺ ILC3s coexpressed the cytolytic protein perforin. Granzyme B expression was mediated, in part, by IL-15 produced upon exposure to bacteria. ILC3s coexpressing all three IL-15R subunits (IL15Rα/β/γ) increased following bacterial stimulation, potentially allowing for cis presentation of IL-15 during bacterial exposure. Additionally, a large frequency of colonic myeloid dendritic cells expressed IL-15Rα, implicating myeloid dendritic cells in trans presentation of IL-15 to ILC3s. Tonsillar ILC3s minimally expressed granzyme B when exposed to the same bacteria or to rIL-15. Overall, these data establish the novel, to our knowledge, finding that human colonic ILC3s can express granzyme B in response to a subset of enteric bacteria through a process mediated by IL-15. These observations raise new questions about the multifunctional role of human gut ILC3s.

Approaches to Enhance Natural Killer Cell-Based Immunotherapy for Pediatric Solid Tumors

Treatment of metastatic pediatric solid tumors remain a significant challenge, particularly in relapsed and refractory settings. Standard treatment has included surgical resection, radiation, chemotherapy, and, in the case of neuroblastoma, immunotherapy. Despite such intensive therapy, cancer recurrence is common, and most tumors become refractory to prior therapy, leaving patients with few conventional treatment options. Natural killer (NK) cells are non-major histocompatibility complex (MHC)-restricted lymphocytes that boast several complex killing mechanisms but at an added advantage of not causing graft-versus-host disease, making use of allogeneic NK cells a potential therapeutic option. On top of their killing capacity, NK cells also produce several cytokines and growth factors that act as key regulators of the adaptive immune system, positioning themselves as ideal effector cells for stimulating heavily pretreated immune systems. Despite this promise, clinical efficacy of adoptive NK cell therapy to date has been inconsistent, prompting a detailed understanding of the biological pathways within NK cells that can be leveraged to develop "next generation" NK cell therapies. Here, we review advances in current approaches to optimizing the NK cell antitumor response including combination with other immunotherapies, cytokines, checkpoint inhibition, and engineering NK cells with chimeric antigen receptors (CARs) for the treatment of pediatric solid tumors.

The Role of the Cytoskeleton in Regulating the Natural Killer Cell Immune Response in Health and Disease: From Signaling Dynamics to Function

Natural killer (NK) cells are innate lymphoid cells, which play key roles in elimination of virally infected and malignant cells. The balance between activating and inhibitory signals derived from NK surface receptors govern the NK cell immune response. The cytoskeleton facilitates most NK cell effector functions, such as motility, infiltration, conjugation with target cells, immunological synapse assembly, and cytotoxicity. Though many studies have characterized signaling pathways that promote actin reorganization in immune cells, it is not completely clear how particular cytoskeletal architectures at the immunological synapse promote effector functions, and how cytoskeletal dynamics impact downstream signaling pathways and activation. Moreover, pioneering studies employing advanced imaging techniques have only begun to uncover the architectural complexity dictating the NK cell activation threshold; it is becoming clear that a distinct organization of the cytoskeleton and signaling receptors at the NK immunological synapse plays a decisive role in activation and tolerance. Here, we review the roles of the actin cytoskeleton in NK cells. We focus on how actin dynamics impact cytolytic granule secretion, NK cell motility, and NK cell infiltration through tissues into inflammatory sites. We will also describe the additional cytoskeletal components, non-muscle Myosin II and microtubules that play pivotal roles in NK cell activity. Furthermore, special emphasis will be placed on the role of the cytoskeleton in assembly of immunological synapses, and how mutations or downregulation of cytoskeletal accessory proteins impact NK cell function in health and disease.

Dual-color 3D-dSTORM colocalization and quantification of ROXY1 and RNAPII variants throughout the transcription cycle in root meristem nuclei

To unravel the function of a protein of interest, it is crucial to asses to what extent it associates via direct interactions or by overlapping expression with other proteins. ROXY1, a land plant-specific glutaredoxin, exerts a function in Arabidopsis flower development and interacts with TGA transcription factors in the nucleus. We detected a novel ROXY1 function in the root meristem. Root cells that lack chlorophyll reducing plant-specific background problems that can hamper colocalization 3D microscopy. Thus far, a super-resolution three-dimensional stochastic optical reconstruction microscopy (3D-dSTORM) approach has mainly been applied in animal studies. We established 3D-dSTORM using the roxy1 mutant complemented with green fluorescence protein-ROXY1 and investigated its colocalization with three distinct RNAPII isoforms. To quantify the colocalization results, 3D-dSTORM was coupled with the coordinate-based colocalization method. Interestingly, ROXY1 proteins colocalize with different RNA polymerase II (RNAPII) isoforms that are active at distinct transcription cycle steps. Our colocalization data provide new insights on nuclear glutaredoxin activities suggesting that ROXY1 is not only required in early transcription initiation events via interaction with transcription factors but likely also participates throughout further transcription processes until late termination steps. Furthermore, we showed the applicability of the combined approaches to detect and quantify responses to altered growth conditions, exemplified by analysis of H₂ O₂ treatment, causing a dissociation of ROXY1 and RNAPII isoforms. We envisage that the powerful dual-color 3D-dSTORM/coordinate-based colocalization combination offers plant cell biologists the opportunity to colocalize and quantify root meristem proteins at an increased, unprecedented resolution level <50 nm, which will enable the detection of novel subcellular protein associations and functions.

Corrected Super-Resolution Microscopy Enables Nanoscale Imaging of Autofluorescent Lung Macrophages

Observing the cell surface and underlying cytoskeleton at nanoscale resolution using super-resolution microscopy has enabled many insights into cell signaling and function. However, the nanoscale dynamics of tissue-specific immune cells have been relatively little studied. Tissue macrophages, for example, are highly autofluorescent, severely limiting the utility of light microscopy. Here, we report a correction technique to remove autofluorescent noise from stochastic optical reconstruction microscopy (STORM) data sets. Simulations and analysis of experimental data identified a moving median filter as an accurate and robust correction technique, which is widely applicable across challenging biological samples. Here, we used this method to visualize lung macrophages activated through Fc receptors by antibody-coated glass slides. Accurate, nanoscale quantification of macrophage morphology revealed that activation induced the formation of cellular protrusions tipped with MHC class I protein. These data are consistent with a role for lung macrophage protrusions in antigen presentation. Moreover, the tetraspanin protein CD81, known to mark extracellular vesicles, appeared in ring-shaped structures (mean diameter 93 ± 50 nm) at the surface of activated lung macrophages. Thus, a moving median filter correction technique allowed us to quantitatively analyze extracellular secretions and membrane structure in tissue-derived immune cells.

A Review of Super-Resolution Single-Molecule Localization Microscopy Cluster Analysis and Quantification Methods

Single-molecule localization microscopy (SMLM) is a relatively new imaging modality, winning the 2014 Nobel Prize in Chemistry, and considered as one of the key super-resolution techniques. SMLM resolution goes beyond the diffraction limit of light microscopy and achieves resolution on the order of 10-20 nm. SMLM thus enables imaging single molecules and study of the low-level molecular interactions at the subcellular level. In contrast to standard microscopy imaging that produces 2D pixel or 3D voxel grid data, SMLM generates big data of 2D or 3D point clouds with millions of localizations and associated uncertainties. This unprecedented breakthrough in imaging helps researchers employ SMLM in many fields within biology and medicine, such as studying cancerous cells and cell-mediated immunity and accelerating drug discovery. However, SMLM data quantification and interpretation methods have yet to keep pace with the rapid advancement of SMLM imaging. Researchers have been actively exploring new computational methods for SMLM data analysis to extract biosignatures of various biological structures and functions. In this survey, we describe the state-of-the-art clustering methods adopted to analyze and quantify SMLM data and examine the capabilities and shortcomings of the surveyed methods. We classify the methods according to (1) the biological application (i.e., the imaged molecules/structures), (2) the data acquisition (such as imaging modality, dimension, resolution, and number of localizations), and (3) the analysis details (2D versus 3D, field of view versus region of interest, use of machine-learning and multi-scale analysis, biosignature extraction, etc.). We observe that the majority of methods that are based on second-order statistics are sensitive to noise and imaging artifacts, have not been applied to 3D data, do not leverage machine-learning formulations, and are not scalable for big-data analysis. Finally, we summarize state-of-the-art methodology, discuss some key open challenges, and identify future opportunities for better modeling and design of an integrated computational pipeline to address the key challenges.

IL-15 and CD155 expression regulate LAT expression in murine DNAM1+ NK cells, enhancing their effectors functions

NK cells are innate immune cells characterized by their ability to spontaneously lyse tumor and virally infected cells. We have recently demonstrated that IL-15-sufficient DC regulate NK cell effector functions in mice. Here, we established that among ITAM-proximal signaling molecules, the expression levels of the scaffold molecule Linker for Activation of T cells (LAT) and its transcription factor ELF-1 were reduced 4 days after in vivo depletion of DC. Addition of IL-15, a cytokine presented by DC to NK cells, regulates LAT expression in NK cells with a significant effect on the DNAM1⁺ subset compared to DNAM1^- cells. We also found that LAT expression is regulated via interaction of the DNAM1 receptor with its ligand CD155 in both immature and mature NK cells, independently of NK cell education. Finally, we found that LAT expression within DNAM1⁺ NK cells might be responsible for enhanced calcium mobilization following the triggering of activating receptors on NK cells. Altogether, we found that LAT expression is tightly regulated in DNAM1⁺ NK cells, via interaction(s) with DC, which express CD155 and IL-15, resulting in rapid activation of the DNAM1⁺ subset during activating receptor triggering.

Recent Advances in Molecular Mechanisms of the NKG2D Pathway in Hepatocellular Carcinoma

Hepatocellular carcinoma is a common malignant tumor with high mortality. Its malignant proliferation, invasion, and metastasis are closely related to the cellular immune function of the patients. NKG2D is a key activated and type II membrane protein molecule expressed on the surface of almost all NK cells. The human NKG2D gene is 270 kb long, located at 12p12.3-p13.1, and contains 10 exons and 9 introns. The three-dimensional structure of the NKG2D monomeric protein contains two alpha-helices, two beta-lamellae, and four disulfide bonds, and its' signal of activation is transmitted mainly by the adaptor protein (DAP). NKG2D ligands, including MICA, MICB, and ULBPs, can be widely expressed in hepatoma cells. After a combination of NKG2D and DAP10 in the form of homologous two polymers, the YxxM motif in the cytoplasm is phosphorylated and then signaling pathways are also gradually activated, such as PI3K, PLCγ2, JNK-cJunN, and others. Activated NK cells can enhance the sensitivity to hepatoma cells and specifically dissolve by releasing a variety of cytokines (TNF-α and IFN-γ), perforin, and high expression of FasL, CD16, and TRAIL. NK cells may specifically bind to the over-expressed MICA, MICB, and ULBPs of hepatocellular carcinoma cells through the surface activating receptor NKG2D, which can help to accurately identify hepatoma, play a critical role in anti-hepatoma via the pathway of cytotoxic effects, and obviously delay the poor progress of hepatocellular carcinoma.

Genetic diversity affects the nanoscale membrane organization and signaling of natural killer cell receptors

Genetic diversity in human natural killer (NK) cell receptors is linked to resistance and susceptibility to many diseases. Here, we tested the effect of this diversity on the nanoscale organization of killer cell immunoglobulin-like receptors (KIRs). Using superresolution microscopy, we found that inhibitory KIRs encoded by different genes and alleles were organized differently at the surface of primary human NK cells. KIRs that were found at low abundance assembled into smaller clusters than those formed by KIRs that were more highly abundant, and at low abundance, there was a greater proportion of KIRs in clusters. Upon receptor triggering, a structured interface called the immune synapse assembles, which facilitates signal integration and controls NK cell responses. Here, triggering of low-abundance receptors resulted in less phosphorylation of the downstream phosphatase SHP-1 but more phosphorylation of the adaptor protein Crk than did triggering of high-abundance receptors. In cells with greater KIR abundance, SHP-1 dephosphorylated Crk, which potentiated NK cell spreading during activation. Thus, genetic variation modulates both the abundance and nanoscale organization of inhibitory KIRs. That is, as well as the number of receptors at the cell surface varying with genotype, the way in which these receptors are organized in the membrane also varies. Essentially, a change in the average surface abundance of a protein at the cell surface is a coarse descriptor entwined with changes in local nanoscale clustering. Together, our data indicate that genetic diversity in inhibitory KIRs affects membrane-proximal signaling and, unexpectedly, the formation of activating immune synapses.

Nanoscale reorganizations of histone-like nucleoid structuring proteins in Escherichia coli are caused by silver nanoparticles

Silver nanoparticles (AgNPs) and ions (Ag⁺) have recently gained broad attention due to their antimicrobial effects against bacteria and other microbes. In this work, we demonstrate the use of super-resolution fluorescence microscopy for investigating and quantifying the antimicrobial effect of AgNPs at the molecular level. We found that subjecting Escherichia coli (E. coli) bacteria to AgNPs led to nanoscale reorganization of histone-like nucleoid structuring (H-NS) proteins, an essential nucleoid associated protein in bacteria. We observed that H-NS proteins formed denser and larger clusters at the center of the bacteria after exposure to AgNPs. We quantified the spatial reorganizations of H-NS proteins by examining the changes of various spatial parameters, including the inter-molecular distances and molecular densities. Clustering analysis based on Voronoi-tessellation were also performed to characterize the change of H-NS proteins' clustering behavior. We found that AgNP-treatment led to an increase in the fraction of H-NS proteins forming clusters. Similar effects were observed for bacteria exposed to Ag⁺ ions, suggesting that the release of Ag⁺ ions plays an important role in the toxicity of AgNPs. On the other hand, we observed that AgNPs with two surface coatings showed difference in the nanoscale reorganization of H-NS proteins, indicating that particle-specific effects also contribute to the antimicrobial activities of AgNPs. Our results suggested that H-NS proteins were significantly affected by AgNPs and Ag⁺ ions, which has been overlooked previously. In addition, we examined the dynamic motion of AgNPs that were attached to the surface of bacteria. We expect that the current methodology can be readily applied to broadly and quantitatively study the spatial reorganization of biological macromolecules at the scale of nanometers caused by metal nanoparticles, which are expected to shed new light on the antimicrobial mechanism of metal nanoparticles.

Data analysis to modeling to building theory in NK cell biology and beyond: How can computational modeling contribute?

The use of mathematical and computational tools in investigating Natural Killer (NK) cell biology and in general the immune system has increased steadily in the last few decades. However, unlike the physical sciences, there is a persistent ambivalence, which however is increasingly diminishing, in the biology community toward appreciating the utility of quantitative tools in addressing questions of biological importance. We survey some of the recent developments in the application of quantitative approaches for investigating different problems in NK cell biology and evaluate opportunities and challenges of using quantitative methods in providing biological insights in NK cell biology.

Antigen Receptor Function in the Context of the Nanoscale Organization of the B Cell Membrane

The B cell antigen receptor (BCR) plays a central role in the self/nonself selection of B lymphocytes and in their activation by cognate antigen during the clonal selection process. It was long thought that most cell surface receptors, including the BCR, were freely diffusing and randomly distributed. Since the advent of superresolution techniques, it has become clear that the plasma membrane is compartmentalized and highly organized at the nanometer scale. Hence, a complete understanding of the precise conformation and activation mechanism of the BCR must take into account the organization of the B cell plasma membrane. We review here the recent literature on the nanoscale organization of the lymphocyte membrane and discuss how this new information influences our view of the conformational changes that the BCR undergoes during activation.

What we talk about when we talk about nanoclusters

Superresolution microscopy results have sparked the idea that many membrane proteins are not randomly distributed across the plasma membrane but are instead arranged in nanoclusters. Frequently, these new results seemed to confirm older data based on biochemical and electron microscopy experiments. Recently, however, it was recognized that multiple countings of the very same fluorescently labeled protein molecule can be easily confused with true protein clusters. Various strategies have been developed, which are intended to solve the problem of discriminating true protein clusters from imaging artifacts. We believe that there is currently no perfect algorithm for this problem; instead, different approaches have different strengths and weaknesses. In this review, we discuss single molecule localization microscopy in view of its ability to detect nanoclusters of membrane proteins. To capture the different views on nanoclustering, we chose an unconventional style for this article: we placed its scientific content in the setting of a fictive conference, where five researchers from different fields discuss the problem of detecting and quantifying nanoclusters. Using this style, we feel that the different approaches common for different research areas can be well illustrated. Similarities to a short story by Raymond Carver are not unintentional.

Human NK Cells Lyse Th2-Polarizing Dendritic Cells via NKp30 and DNAM-1

Cross-talk between NK cells and dendritic cells (DCs) is important in Th1 immune responses, including antitumor immunity and responses to infections. DCs also play a crucial role in polarizing Th2 immunity, but the impact of NK cell-DC interactions in this context remains unknown. In this study, we stimulated human monocyte-derived DCs in vitro with different pathogen-associated molecules: LPS or polyinosinic-polycytidylic acid, which polarize a Th1 response, or soluble egg Ag from the helminth worm Schistosoma mansoni, a potent Th2-inducing Ag. Th2-polarizing DCs were functionally distinguishable from Th1-polarizing DCs, and both showed distinct morphology and dynamics from immature DCs. We then assessed the outcome of autologous NK cells interacting with these differently stimulated DCs. Confocal microscopy showed polarization of the NK cell microtubule organizing center and accumulation of LFA-1 at contacts between NK cells and immature or Th2-polarizing DCs but not Th1-polarizing DCs, indicative of the assembly of an activating immune synapse. Autologous NK cells lysed immature DCs but not DCs treated with LPS or polyinosinic-polycytidylic acid as reported previously. In this study, we demonstrated that NK cells also degranulated in the presence of Th2-polarizing DCs. Moreover, time-lapse live-cell microscopy showed that DCs that had internalized fluorescently labeled soluble egg Ag were efficiently lysed. Ab blockade of NK cell-activating receptors NKp30 or DNAM-1 abrogated NK cell lysis of Th2-polarizing DCs. Thus, these data indicate a previously unrecognized role of NK cell cytotoxicity and NK cell-activating receptors NKp30 and DNAM-1 in restricting the pool of DCs involved in Th2 immune responses.

NKG2D Ligands-Critical Targets for Cancer Immune Escape and Therapy

DNA damage, oncogene activation and excessive proliferation, chromatin modulations or oxidative stress are all important hallmarks of cancer. Interestingly, all of these abnormalities also induce a cellular stress response. By upregulating “stress-induced ligands,” damaged or transformed cells can be recognized by immune cells and cleared. The human genome encodes eight functional “stress-induced ligands”: MICA, MICB, and ULBP1-6. All of them are recognized by a single receptor, NKG2D, which is expressed on natural killer (NK) cells, cytotoxic T cells and other T cell subsets. The NKG2D ligand/NKG2D-axis is well-recognized as an important mediator of anti-tumor activity; however, patient data about the role of NKG2D ligands in immune surveillance and escape appears conflicting. As these ligands are often actively transcribed, tumor cells are urged to manipulate the expression of these ligands on post-transcriptional or post-translational level. Although our knowledge on the regulation of NKG2D ligand expression remains fragmentary, research of the past years revealed multiple cellular mechanisms that are adopted by tumor cells to reduce the expression of “stress-induced ligands” and therefore escape immune recognition. Here, we review the post-transcriptional and post-translational mechanisms by which NKG2D ligands are modulated in cancer cells and their impact on patient prognosis.We discuss controversies and approaches to apply our understanding of the NKG2D ligand/NKG2D-axis for cancer therapy.

The Paradoxical Role of NKG2D in Cancer Immunity

The activating receptor NKG2D and its ligands are recognized as a potent immune axis that controls tumor growth and microbial infections. With regards to cancer surveillance, various studies have demonstrated the antitumor function mediated by NKG2D on natural killer cells and on conventional and unconventional T cells. The use of NKG2D-deficient mice established the importance of NKG2D in delaying tumor development in transgenic mouse models of cancer. However, we recently demonstrated an unexpected, flip side to this coin, the ability for NKG2D to contribute to tumor growth in a model of inflammation-driven liver cancer. With a focus on the liver, here, we review current knowledge of NKG2D-mediated tumor surveillance and discuss evidence supporting a dual role for NKG2D in cancer immunity. We postulate that in certain advanced cancers, expression of ligands for NKG2D can drive cancer progression rather than rejection. We propose that the nature of the microenvironment within and surrounding tumors impacts the outcome of NKG2D activation. In a form of autoimmune attack, NKG2D promotes tissue damage, mostly in the inflamed tissue adjacent to the tumor, facilitating tumor progression while being ineffective at rejecting transformed cells in the tumor bed.