Comparison between photostability of Alexa Fluor 448 and Alexa Fluor 647 with conventional dyes FITC and APC by flow cytometry

Visualization and Characterization of the Brain Regional Heterogeneity of Astrocyte-Astrocyte Structural Interactions by Using Improved Iontophoresis with Dual-Fluorescent Dyes

Astrocytes are morphologically intricate cells and actively modulate the function of the brain. Through numerous fine processes, astrocytes come into contact with neurons, blood vessels, and other glia cells. Emerging evidence has shown that astrocytes exhibit brain regional diversity in their morphology, transcriptome, calcium signaling, and functions. However, little is known about the brain regional heterogeneity of astrocyte-astrocyte structural interaction. So far, the visualization and characterization of the morphological features of adjacent astrocytes have been difficult, and as a result, it is still well-accepted that astrocytes in the adult brain share non-overlapped territory. In contrast, employing an approach that combines viral labeling with dual-fluorescent dyes iontophoresis under brightfield and imaging using confocal microscopy allows for the efficient and specific labeling of adjacent astrocytes, enabling a comprehensive visualization of their fine processes and the degree of their territorial overlap. Our study in the hypothalamic regions of the brain revealed a marked spatial overlap among adjacent astrocytes, which differs from the conventional understanding based on more extensively studied regions, like the hippocampus. Additionally, we revealed the heterogeneity of the astrocyte-neuron ratio across brain regions and conducted an assessment of the photostability and labeling efficiency of fluorescent dyes used for labeling adjacent astrocytes. Our study provides new insights for studying the morphological heterogeneity of astrocytes across the central nervous system.

Tracing Human IgE B Cell Antigen Receptor-Bearing Cells With a Monoclonal Anti-Human IgE Antibody That Specifically Recognizes Non-Receptor-Bound IgE

Up to 30% of the population suffers from immunoglobulin E (IgE)-mediated allergies. Despite current stepwise gating approaches, the unambiguous identification of human IgE-producing cells by flow cytometry and immunohistology remains challenging. This is mainly due to the scarcity of these cells and the fact that IgE is not only expressed in a membrane-bound form on the surface of IgE-producing cells in form of the B cell antigen receptor (BCR), but is more frequently found on various cell types bound to the low and high affinity receptors, CD23 and FcϵRI, respectively. Here we sought to develop a sequential gating strategy for unambiguous detection of cells bearing the IgE BCR on their surface. To that aim we first tested the monoclonal anti-IgE antibody omalizumab for its ability to discriminate between IgE BCR and receptor-bound IgE using cells producing IgE or bearing IgE bound to CD23 as well as basophils exhibiting FcϵRI receptor-bound IgE. Using flow cytometry, we demonstrated that omalizumab recognized IgE producing cells with a high sensitivity of up to 1 IgE+ cell in 1000 human peripheral blood mononuclear cells (PBMCs). These results were confirmed by confocal microscopy both in cell suspensions as well as in nasal polyp tissue sections. Finally, we established a consecutive gating strategy allowing the clear identification of class-switched, allergen-specific IgE+ memory B cells and plasmablasts/plasma cells in human PBMCs. Birch pollen specific IgE+ memory B cells represented on average 0.734% of total CD19+ B cells in allergic patients after allergen exposure. Thus, we developed a new protocol for exclusive staining of non-receptor bound allergen-specific IgE+ B cell subsets in human samples.

Monitoring Intracellular Routing of Internalized Antigens by Immunofluorescence Microscopy

Antigen-presenting cells (APCs), especially macrophages and dendritic cells (DCs), are important for the induction of an adaptive immune response through their phagocytic capacity. APCs internalize extracellular antigens and, dependent on their intracellular localization, antigen-derived peptides are presented on MHC I or MHC II molecules. In context of antigen presentation and T cell activation tracking of internalized antigens is of high interest. In this article, we provide an immunofluorescence protocol and illustrate the analysis of intracellular routing of internalized antigens using the example of the model-antigen ovalbumin (OVA) in bone marrow-derived dendritic cells (BM-DCs). This protocol describes a procedure to stain such cells with an antibody against EEA-1, a marker for early endosomes, which can be easily adapted to other endosome markers, antigen-presenting cells, or antigens.

The hydrophobic C-terminal sequence of transthyretin affects its catalytic kinetics towards amidated neuropeptide Y

Transthyretin (TTR) is a transporter for thyroid hormone and retinol binding protein that has recently been reported to have proteolytic activity against certain substrates, including amidated neuropeptide Y (NPY). However, the proteolytic activity of TTR towards NPY is not fully understood. Here, we used fluorescence-based assays to determine the catalytic kinetics of human TTR towards human amidated NPY. The Michaelis constant (KM) and catalytic efficiency (kcat/KM) of TTR proteolysis were 15.88 ± 0.44 μm and 687 081 ± 35 692 m -1·s-1, respectively. In addition, we demonstrated an effect of the C-terminal sequence of TTR. When the C-terminal sequence of TTR was made more hydrophobic, the KM and kcat/KM changed to 12.87 ± 0.22 μm and 983 755 ± 18 704 m -1·s-1, respectively. Our results may be useful for the development of TTR as a therapeutic agent with low risk of the undesirable symptoms that develop from amidated NPY, and for further improvement of the kcat/KM of TTR.