Heterophilic antibodies leading to falsely positive D-dimer concentration in an adolescent.

Background: We present the case of a 15-year-old adolescent with suspected pulmonary embolism and repeatedly elevated D-dimer levels.

Key Clinical Question: We aim to determine the cause for elevated D-dimer levels in a patient without venous thromboembolism.

Clinical Approach: When the D-dimer measurement was repeated with different assays, D-dimer levels were within the normal reference interval.

Vaccination against galectin-1 promotes cytotoxic T-cell infiltration in melanoma and reduces tumor burden.

Galectin-1 (Gal1) is a glycan-binding protein that promotes tumor progression by several distinct mechanisms. Through direct binding to vascular endothelial growth factor (VEGF)-receptor 2, Gal1 is able to induce VEGF-like signaling, which contributes to tumor angiogenesis. Furthermore, several studies have demonstrated an immunosuppressive function of Gal1 through effects on both effector and regulatory T cells.

Interleukin-6 secretion is limited by self-signaling in endosomes.

Cells producing cytokines often express the receptor for the same cytokine, which makes them prone to autocrine signaling. How cytokine release and signaling are regulated in the same cell is not understood. In this study, we demonstrate that signaling by exogenous and self-synthesized inflammatory cytokine interleukin-6 (IL-6) within endosomal compartments acts as a cellular brake that limits the synthesis of IL-6.

Endosomal and Phagosomal SNAREs.

The soluble N-ethylmaleimide-sensitive factor attachment protein receptor (SNARE) protein family is of vital importance for organelle communication. The complexing of cognate SNARE members present in both the donor and target organellar membranes drives the membrane fusion required for intracellular transport. In the endocytic route, SNARE proteins mediate trafficking between endosomes and phagosomes with other endosomes, lysosomes, the Golgi apparatus, the plasma membrane, and the endoplasmic reticulum.

Secretory vesicles of immune cells contain only a limited number of interleukin 6 molecules.

Immune cells communicate by releasing large quantities of cytokines. Although the mechanisms of cytokine secretion are increasingly understood, quantitative knowledge of the number of cytokines per vesicle is still lacking. Here, we measured with quantitative microscopy the release rate of vesicles potentially carrying interleukin-6 (IL-6) in human dendritic cells.

Visualizing Intracellular SNARE Trafficking by Fluorescence Lifetime Imaging Microscopy.

Soluble N-ethylmaleimide sensitive fusion protein (NSF) attachment protein receptor (SNARE) proteins are key for membrane trafficking, as they catalyze membrane fusion within eukaryotic cells. The SNARE protein family consists of about 36 different members. Specific intracellular transport routes are catalyzed by specific sets of 3 or 4 SNARE proteins that thereby contribute to the specificity and fidelity of membrane trafficking.

VAMP8-mediated NOX2 recruitment to endosomes is necessary for antigen release.

Cross-presentation of foreign antigen in major histocompatibility complex (MHC) class I by dendritic cells (DCs) requires activation of the NADPH-oxidase NOX2 complex. We recently showed that NOX2 is recruited to phagosomes by the SNARE protein VAMP8 where NOX2-produced reactive oxygen species (ROS) cause lipid oxidation and membrane disruption, promoting antigen translocation into the cytosol for cross-presentation. In this study, we extend these findings by showing that VAMP8 is also involved in NOX2 trafficking to endosomes.

Fluorescence Lifetime Imaging Microscopy reveals rerouting of SNARE trafficking driving dendritic cell activation.

SNARE proteins play a crucial role in intracellular trafficking by catalyzing membrane fusion, but assigning SNAREs to specific intracellular transport routes is challenging with current techniques. We developed a novel Förster resonance energy transfer-fluorescence lifetime imaging microscopy (FRET-FLIM)-based technique allowing visualization of real-time local interactions of fluorescently tagged SNARE proteins in live cells. We used FRET-FLIM to delineate the trafficking steps underlying the release of the inflammatory cytokine interleukin-6 (IL-6) from human blood-derived dendritic cells.

SWAP70 is a universal GEF-like adaptor for tethering actin to phagosomes.

We recently identified a key role for SWAP70 as the tethering factor stabilizing F-actin filaments on the surface of phagosomes in human dendritic cells by interacting both with Rho-family GTPases and the lipid phosphatidylinositol (3,4)-bisphosphate. In this study, we aimed to investigate whether this role of SWAP70 was general among immune phagocytes. Our data reveal that SWAP70 is recruited to early phagosomes of macrophages and dendritic cells from both human and mouse.

Lipid peroxidation causes endosomal antigen release for cross-presentation.

Dendritic cells (DCs) present foreign antigen in major histocompatibility complex (MHC) class I molecules to cytotoxic T cells in a process called cross-presentation. An important step in this process is the release of antigen from the lumen of endosomes into the cytosol, but the mechanism of this step is still unclear. In this study, we show that reactive oxygen species (ROS) produced by the NADPH-oxidase complex NOX2 cause lipid peroxidation, a membrane disrupting chain-reaction, which in turn results in antigen leakage from endosomes.

The dendritic cell side of the immunological synapse.

Immune responses are initiated by the interactions between antigen-presenting cells (APCs), such as dendritic cells (DCs), with responder cells, such as T cells, via a tight cellular contact interface called the immunological synapse. The immunological synapse is a highly organized subcellular structure that provides a platform for the presentation of antigen in major histocompatibility class I and II complexes (MHC class I and II) on the surface of the APC to receptors on the surface of the responder cells. In T cells, these contacts lead to highly polarized membrane trafficking that results in the local release of lytic granules and in the delivery and recycling of T cell receptors at the immunological synapse.