Fluorescent Artificial Antigens Revealed Extended Membrane Networks Utilized by Live Dendritic Cells for Antigen Uptake

Increased vesicular dynamics and nanoscale clustering of IL-2 after T cell activation

T cells coordinate intercellular communication through the meticulous regulation of cytokine secretion. Direct visualization of vesicular transport and intracellular distribution of cytokines provides valuable insights into the temporal and spatial mechanisms involved in regulation. Employing Jurkat E6-1 T cells and interleukin-2 (IL-2) as a model system, we investigated vesicular dynamics using single-particle tracking and the nanoscale distribution of intracellular IL-2 in fixed T cells using superresolution microscopy. Live-cell imaging revealed that in vitro activation resulted in increased vesicular dynamics. Direct stochastic optical reconstruction microscopy and 3D structured illumination microscopy revealed nanoscale clustering of IL-2. In vitro activation correlated with spatial accumulation of IL-2 nanoclusters into more pronounced and elongated clusters. These observations provide visual evidence that accelerated vesicular transport and spatial concatenation of IL-2 clusters at the nanoscale may constitute a potential mechanism for modulating cytokine release by Jurkat T cells.

Phalloidin-PAINT: Enhanced quantitative nanoscale imaging of F-actin

We present phalloidin-based points accumulation for imaging in nanoscale topography (phalloidin-PAINT), enabling quantitative superresolution imaging of filamentous actin (F-actin) in the cell body and delicate membrane protrusions. We demonstrate that the intrinsic phalloidin dissociation enables PAINT superresolution microscopy in an imaging buffer containing low concentrations of dye-conjugated phalloidin. We further show enhanced single-molecule labeling by chemically promoting phalloidin dissociation. Two benefits of phalloidin-PAINT are its ability to consistently quantify F-actin at the nanoscale throughout the entire cell and its enhanced preservation of fragile cellular structures. In a proof-of-concept study, we employed phalloidin-PAINT to superresolve F-actin structures in U2OS and dendritic cells (DCs). We demonstrate more consistent F-actin quantification in the cell body and structurally delicate membrane protrusions of DCs compared with direct stochastic optical reconstruction microscopy (dSTORM). Using DC2.4 mouse DCs as the model system, we show F-actin redistribution from podosomes to actin filaments and altered prevalence of F-actin-associated membrane protrusions on the culture glass surface after lipopolysaccharide exposure. The concept of our work opens new possibilities for quantitative protein-specific PAINT using commercially available reagents.

Quantitative Superresolution Imaging of F-Actin in the Cell Body and Cytoskeletal Protrusions Using Phalloidin-Based Single-Molecule Labeling and Localization Microscopy

We present single-molecule labeling and localization microscopy (SMLLM) using dye-conjugated phalloidin to achieve enhanced superresolution imaging of filamentous actin (F-actin). We demonstrate that the intrinsic phalloidin dissociation enables SMLLM in an imaging buffer containing low concentrations of dye-conjugated phalloidin. We further show enhanced single-molecule labeling by chemically promoting phalloidin dissociation. Two benefits of phalloidin-based SMLLM are better preservation of cellular structures sensitive to mechanical and shear forces during standard sample preparation and more consistent F-actin quantification at the nanoscale. In a proof-of-concept study, we employed SMLLM to super-resolve F-actin structures in U2OS and dendritic cells (DCs) and demonstrate more consistent F-actin quantification in the cell body and structurally delicate cytoskeletal proportions, which we termed membrane fibers, of DCs compared to direct stochastic optical reconstruction microscopy (dSTORM). Using DC2.4 mouse dendritic cells as the model system, we show F-actin redistribution from podosomes to actin filaments and altered prevalence of F-actin-associated membrane fibers on the culture glass surface after lipopolysaccharide exposure. While our work demonstrates SMLLM for F-actin, the concept opens new possibilities for protein-specific single-molecule labeling and localization in the same step using commercially available reagents.

Uptake Quantification of Antigen Carried by Nanoparticles and Its Impact on Carrier Adjuvanticity Evaluation

Nanoparticles have been identified in numerous studies as effective antigen delivery systems that enhance immune responses. However, it remains unclear whether this enhancement is a result of increased antigen uptake when carried by nanoparticles or the adjuvanticity of the nanoparticle carriers. Consequently, it is important to quantify antigen uptake by dendritic cells in a manner that is free from artifacts in order to analyze the immune response when antigens are carried by nanoparticles. In this study, we demonstrated several scenarios (antigens on nanoparticles or inside cells) that are likely to contribute to the generation of artifacts in conventional fluorescence-based quantification. Furthermore, we developed the necessary assay for accurate uptake quantification. PLGA NPs were selected as the model carrier system to deliver EsxB protein (a Staphylococcus aureus antigen) in order to testify to the feasibility of the established method. The results showed that for the same antigen uptake amount, the antigen delivered by PLGA nanoparticles could elicit 3.6 times IL-2 secretion (representative of cellular immune response activation) and 1.5 times IL-12 secretion (representative of DC maturation level) compared with pure antigen feeding. The findings above give direct evidence of the extra adjuvanticity of PLGA nanoparticles, except for their delivery functions. The developed methodology allows for the evaluation of immune cell responses on an antigen uptake basis, thus providing a better understanding of the origin of the adjuvanticity of nanoparticle carriers. Ultimately, this research provides general guidelines for the formulation of nano-vaccines.

Migrasome: a new functional extracellular vesicle

Migrasome is a novel cellular organelle produced during cell migration, and its biogenesis depends on the migration process. It is generated in a variety of cells such as immune cells, metastatic tumor cells, other special functional cells like podocytes and cells in developing organisms. It plays important roles in various fields especially in the information exchange between cells. The discovery of migrasome, as an important supplement to the extracellular vesicle system, provides new mechanisms and targets for comprehending various biological or pathological processes. In this article, we will review the discovery, structure, distribution, detection, biogenesis, and removal of migrasomes and mainly focus on summarizing its biological functions in cell-to-cell communication, homeostatic maintenance, embryonic development and multiple diseases. This review also creates prospects for the possible research directions and clinical applications of migrasomes in the future.

Current Advances in the Biomedical Applications of Quantum Dots: Promises and Challenges

Quantum dots (QDs) are a type of nanoparticle with exceptional photobleaching-resistant fluorescence. They are highly sought after for their potential use in various optical-based biomedical applications. However, there are still concerns regarding the use of quantum dots. As such, much effort has been invested into understanding the mechanisms behind the behaviors of QDs, so as to develop safer and more biocompatible quantum dots. In this mini-review, we provide an update on the recent advancements regarding the use of QDs in various biomedical applications. In addition, we also discuss# the current challenges and limitations in the use of QDs and propose a few areas of interest for future research.

Migrasomes, a new mode of intercellular communication

Migrasomes are newly discovered extracellular vesicles (EVs) that are formed in migrating cells and mediate intercellular communication. However, their size, biological generation, cargo packaging, transport, and effects on recipient cells by migrasomes are different from those of other EVs. In addition to mediating organ morphogenesis during zebrafish gastrulation, discarding damaged mitochondria, and lateral transport of mRNA and proteins, growing evidence has demonstrated that migrasomes mediate a variety of pathological processes. In this review, we summarize the discovery, mechanisms of formation, isolation, identification, and mediation of cellular communication in migrasomes. We discuss migrasome-mediated disease processes, such as osteoclast differentiation, proliferative vitreoretinopathy, tumor cell metastasis by PD-L1 transport, immune cell chemotaxis to the site of infection by chemokines, angiogenesis promotion via angiogenic factors by immune cells, and leukemic cells chemotaxis to the site of mesenchymal stromal cells. Moreover, as new EVs, we propose the potential of migrasomes for disease diagnosis and treatment. Video Abstract.

Research Progress and Direction of Novel Organelle-Migrasomes

Migrasomes are organelles that are similar in structure to pomegranates, up to 3 μm in diameter, and contain small vesicles with a diameter of 50-100 nm. These membranous organelles grow at the intersections or tips of retracting fibers at the back of migrating cells. The process by which cells release migrasomes and their contents outside the cell is called migracytosis. The signal molecules are packaged in the migrasomes and released to the designated location by migrasomes to activate the surrounding cells. Finally, the migrasomes complete the entire process of information transmission. In this sense, migrasomes integrate time, space, and specific chemical information, which are essential for regulating physiological processes such as embryonic development and tumor invasion and migration. In this review, the current research progress of migrasomes, including the discovery of migrasomes and migracytosis, the structure of migrasomes, and the distribution and functions of migrasomes is discussed. The migratory marker protein TSPAN4 is highly expressed in various cancers and is associated with cancer invasion and migration. Therefore, there is still much research space for the pathogenesis of migratory bodies and cancer. This review also makes bold predictions and prospects for the research directions of the combination of migrasomes and clinical applications.