Cdc42-mediated MTOC polarization in dendritic cells controls targeted delivery of cytokines at the immune synapse

ALCAM-mediated cDC1 CD8 T cells interactions are suppressed in advanced lung tumors

Conventional type 1 dendritic cells (cDC1) are critical regulators of anti-tumoral T-cell responses. The structure and abundance of intercellular contacts between cDC1 and CD8 T cells in cancer tissues is important to determine the outcome of the T-cell response. However, the molecular determinants controlling the stability of cDC1-CD8 interactions during cancer progression remain poorly investigated. Here, we generated a genetic model of non-small cell lung cancer crossed to a fluorescent cDC1 reporter (KP-XCR1venus) to allow the detection of cDC1-CD8T cell clusters in tumor tissues across tumor stages. We found that cDC1-CD8 clusters are abundant and productive at the early stages of tumor development but progressively diminish in advanced tumors. Transcriptional profiling and flow cytometry identified the adhesion molecule ALCAM/CD166 (Activated Leukocyte Cell Adhesion Molecule, ligand of CD6) as highly expressed by lung cDC1 and significantly downregulated in advanced tumors. Analysis of human datasets indicated that ALCAM is downregulated in non-small cell lung cancer and its expression correlates to better prognosis. Mechanistically, triggering ALCAM on lung cDC1 induces cytoskeletal remodeling and contact formation whereas its blockade prevents T-cell activation. Together, our results indicate that ALCAM is important to stabilize cDC1-CD8 interactions at early tumor stages, while its loss in advanced tumors contributes to immune evasion.

Reprogramming dendritic cells through the immunological synapse: A two-way street

Dendritic cells (DCs) bridge innate and adaptive immunity. Their main function is to present antigens to prime T cells and initiate and shape adaptive responses. Antigen presentation takes place through intimate contacts between the two cells, termed immune synapses (IS). During the formation of IS, information travels towards the T-cell side to induce and tune its activation; but it also travels in reverse via engagement of membrane receptors and within extracellular vesicles transferred to the DC. Such reverse information transfer and its consequences on DC fate have been largely neglected. Here, we review the events and effects of IS-mediated antigen presentation on DCs. In addition, we discuss novel technological advancements that enable monitoring DCs interactions with T lymphocytes, the main effects of DCs undergoing productive IS (postsynaptic DCs, or psDCs), and how reverse information transfer could be harnessed to modulate immune responses for therapeutic intervention.

Role of Rho GTPases in inflammatory bowel disease

Rat sarcoma virus homolog (Rho) guanosine triphosphatases (GTPases) function as "molecular switch" in cellular signaling regulation processes and are associated with the pathogenesis of inflammatory bowel disease (IBD). This chronic intestinal tract inflammation primarily encompasses two diseases: Crohn's disease and ulcerative colitis. The pathogenesis of IBD is complex and considered to include four main factors and their interactions: genetics, intestinal microbiota, immune system, and environment. Recently, several novel pathogenic components have been identified. In addition, potential therapies for IBD targeting Rho GTPases have emerged and proven to be clinically effective. This review mainly focuses on Rho GTPases and their possible mechanisms in IBD pathogenesis. The therapeutic possibility of Rho GTPases is also discussed.

Multiple centrosomes enhance migration and immune cell effector functions of mature dendritic cells

Centrosomes play a crucial role during immune cell interactions and initiation of the immune response. In proliferating cells, centrosome numbers are tightly controlled and generally limited to one in G1 and two prior to mitosis. Defects in regulating centrosome numbers have been associated with cell transformation and tumorigenesis. Here, we report the emergence of extra centrosomes in leukocytes during immune activation. Upon antigen encounter, dendritic cells pass through incomplete mitosis and arrest in the subsequent G1 phase leading to tetraploid cells with accumulated centrosomes. In addition, cell stimulation increases expression of polo-like kinase 2, resulting in diploid cells with two centrosomes in G1-arrested cells. During cell migration, centrosomes tightly cluster and act as functional microtubule-organizing centers allowing for increased persistent locomotion along gradients of chemotactic cues. Moreover, dendritic cells with extra centrosomes display enhanced secretion of inflammatory cytokines and optimized T cell responses. Together, these results demonstrate a previously unappreciated role of extra centrosomes for regular cell and tissue homeostasis.

Podocalyxin Expressed in Antigen Presenting Cells Promotes Interaction With T Cells and Alters Centrosome Translocation to the Contact Site

Podocalyxin (PODXL), a cell surface sialomucin expressed in diverse types of normal and malignant cells, mediates cellular adhesion to extracellular matrix and cell-to-cell interaction. A previous study reported the expression of PODXL protein on monocytes undergoing macrophage differentiation, yet the expression of this molecule in other antigen presenting cells (APCs) and its function in the immune system still remain undetermined. In this study, we report that PODXL is expressed in human monocyte-derived immature dendritic cells at both the mRNA and protein levels. Following dendritric cells maturation using pro-inflammatory stimuli, PODXL expression level decreased substantially. Furthermore, we found that PODXL expression is positively regulated by IL-4 through MEK/ERK and JAK3/STAT6 signaling pathways. Our results revealed a polarized distribution of PODXL during the interaction of APCs with CD4⁺ T cells, partially colocalizing with F-actin. Notably, PODXL overexpression in APCs promoted their interaction with CD4⁺ T cells and CD8⁺ T cells and decreased the expression of MHC-I, MHC-II, and the costimulatory molecule CD86. In addition, PODXL reduced the translocation of CD4⁺ T-cell centrosome toward the APC-contact site. These findings suggest a regulatory role for PODXL expressed by APCs in immune responses, thus representing a potential target for therapeutic blockade in infection and cancer.

Identification of hepatocellular carcinoma-related genes associated with macrophage differentiation based on bioinformatics analyses

Macrophage differentiation is associated with tumorigenesis, including the tumorigenesis of hepatocellular carcinoma (HCC). Herein, we explored the value of macrophage differentiation-associated genes (MDGs) in the prognosis of HCC using data from The Cancer Genome Atlas (TCGA) and the International Cancer Genome Consortium (ICGC) databases. We performed multivariate Cox regression analyses to identify the hub genes affecting HCC patient prognoses. The correlations between hub genes and macrophage differentiation and immune checkpoint inhibitors (PD-1, PD-L1, and CTLA4) were investigated. Finally, the potential mechanism was examined with gene set enrichment analysis (GSEA). In total, seventeen differentially expressed MDGs were obtained after intersecting data from the two databases. Multivariate analysis indicated that CDC42 expression was an independent prognostic indicator in both databases. Furthermore, CDC42 showed a strong correlation with the tumor infiltration levels of immune cells in HCC tissue. Correlation analysis revealed that CDC42 expression was positively associated with M2 macrophage markers and immune checkpoint inhibitors, which indicated that CDC42 expression might be related to M2 macrophage differentiation and HCC cell immune tolerance. Finally, GSEA showed that CDC42 expression was most significantly related to the Wnt signaling pathway. In conclusion, this study showed that CDC42 expression might be an important MDG in HCC and may prove to be a new gene for studying macrophage differentiation in HCC. Abbreviations: HCC: hepatocellular carcinoma; TCGA: The Cancer Genome Atlas; ICGC: International Cancer Genome Consortium; GSEA: gene set enrichment analysis; GO: Gene Ontology; KEGG: Kyoto Encyclopedia of Genes and Genomes; ROC: receiver operating characteristic; K-M: Kaplan-Meier; AUC: the area under the ROC curve; TNM: Tumor size/lymph nodes/distance metastasis.

Critical Review of the Evolution of Extracellular Vesicles' Knowledge: From 1946 to Today

Extracellular vesicles (EVs) are a family of particles/vesicles present in blood and body fluids, composed of phospholipid bilayers that carry a variety of molecules that can mediate cell communication, modulating crucial cell processes such as homeostasis, induction/dampening of inflammation, and promotion of repair. Their existence, initially suspected in 1946 and confirmed in 1967, spurred a sharp increase in the number of scientific publications. Paradoxically, the increasing interest for EV content and function progressively reduced the relevance for a precise nomenclature in classifying EVs, therefore leading to a confusing scientific production. The aim of this review was to analyze the evolution of the progress in the knowledge and definition of EVs over the years, with an overview of the methodologies used for the identification of the vesicles, their cell of origin, and the detection of their cargo. The MISEV 2018 guidelines for the proper recognition nomenclature and ways to study EVs are summarized. The review finishes with a “more questions than answers” chapter, in which some of the problems we still face to fully understand the EV function and potential as a diagnostic and therapeutic tool are analyzed.

Cytoskeletal control of the secretory immune synapse

The immune synapse is a very important but often transient site for secretion between immune cells. How secretion is controlled in a coordinated fashion at the synapse is a subject of much investigation. Two key mechanisms are the polarisation of the centrosome and rapid actin dynamics across the immune synapses that form between interacting immune cells. In recent years it has become clear that different immune cells utilise a diversity of immune synapses that modify these mechanisms in order to optimise specialised modes of secretion. Here we describe some of the latest research, focusing on regulation by centrosomal and actin dynamics in a variety of immune cells.

Dynamic Microtubule Arrays in Leukocytes and Their Role in Cell Migration and Immune Synapse Formation

The organization of microtubule arrays in immune cells is critically important for a properly operating immune system. Leukocytes are white blood cells of hematopoietic origin, which exert effector functions of innate and adaptive immune responses. During these processes the microtubule cytoskeleton plays a crucial role for establishing cell polarization and directed migration, targeted secretion of vesicles for T cell activation and cellular cytotoxicity as well as the maintenance of cell integrity. Considering this large spectrum of distinct effector functions, leukocytes require flexible microtubule arrays, which timely and spatially reorganize allowing the cells to accommodate their specific tasks. In contrast to other specialized cell types, which typically nucleate microtubule filaments from non-centrosomal microtubule organizing centers (MTOCs), leukocytes mainly utilize centrosomes for sites of microtubule nucleation. Yet, MTOC localization as well as microtubule organization and dynamics are highly plastic in leukocytes thus allowing the cells to adapt to different environmental constraints. Here we summarize our current knowledge on microtubule organization and dynamics during immune processes and how these microtubule arrays affect immune cell effector functions. We particularly highlight emerging concepts of microtubule involvement during maintenance of cell shape and physical coherence.

Proteostasis in dendritic cells is controlled by the PERK signaling axis independently of ATF4

Differentiated dendritic cells display an unusual activation of the integrated stress response, which is necessary for normal type-I Interferon production and cell migration.

In stressed cells, phosphorylation of eukaryotic initiation factor 2α (eIF2α) controls transcriptome-wide changes in mRNA translation and gene expression known as the integrated stress response. We show here that DCs are characterized by high eIF2α phosphorylation, mostly caused by the activation of the ER kinase PERK (EIF2AK3). Despite high p-eIF2α levels, DCs display active protein synthesis and no signs of a chronic integrated stress response. This biochemical specificity prevents translation arrest and expression of the transcription factor ATF4 during ER-stress induction by the subtilase cytotoxin (SubAB). PERK inactivation, increases globally protein synthesis levels and regulates IFN-β expression, while impairing LPS-stimulated DC migration. Although the loss of PERK activity does not impact DC development, the cross talk existing between actin cytoskeleton dynamics; PERK and eIF2α phosphorylation is likely important to adapt DC homeostasis to the variations imposed by the immune contexts.

Scrib and Dlg1 polarity proteins regulate Ag presentation in human dendritic cells

We recently reported, for the first time, the expression and regulation of the PDZ polarity proteins Scrib and Dlg1 in human APCs, and also described the viral targeting of these proteins by NS1 of influenza A virus in human dendritic cells (DCs). Scrib plays an important role in reactive oxygen species (ROS) production in Mϕs and uropod formation and migration in T cells, while Dlg1 is important for T cell downstream activation after Ag recognition. Nevertheless, the functions of these proteins in human DCs remain unknown. Here, we knocked-down the expression of both Scrib and Dlg1 in human DCs and then evaluated the expression of co-stimulatory molecules and cytokine production during maturation. We demonstrated that Scrib is necessary for adequate CD86 expression, while Dlg1 is important for CD83 up-regulation and IL-6 production upon maturation, suggesting that Scrib and Dlg1 participate in separate pathways in DCs. Additionally, both proteins are required for adequate IL-12 production after maturation. Furthermore, we showed that the inefficient maturation of DCs induced by Scrib or Dlg1 depletion leads to impaired T cell activation. Our results revealed the previously unknown contribution of Scrib and Dlg1 in human DCs pivotal functions, which may be able to impact innate and adaptive immune response.

The Scribble Complex PDZ Proteins in Immune Cell Polarities

hScrib and hDlg belong to the PDZ family of proteins. Since the identification of these highly phylogenetically conserved scaffolds, an increasing amount of experiments has elucidated the roles of hScrib and hDlg in a variety of cell functions. Remarkably, their participation during the establishment of polarity in epithelial cells is well documented. Although the role of both proteins in the immune system is scantly known, it has become a growing field of investigation. Here, we summarize the interactions and functions of hScrib and hDlg1, which participate in diverse functions involving cell polarization in immune cells, and discuss their relevance in the immune cell biology. The fundamental role of hScrib and hDlg1 during the establishment of the immunological synapse, hence T cell activation, and the recently described role of hScrib in reactive oxygen species production in macrophages and of hDlg1 in cytokine production by dendritic cells highlight the importance of both proteins in immune cell biology. The expression of these proteins in other leukocytes can be anticipated and needs to be confirmed. Due to their multiple interaction domains, there is a wide range of possible interactions of hScrib and hDlg1 that remains to be explored in the immune system.

Spatial distribution of IL4 controls iNKT cell-DC crosstalk in tumors

The spatiotemporal distribution of cytokines orchestrates immune responses in vivo, yet the underlying mechanisms remain to be explored. We showed here that the spatial distribution of interleukin-4 (IL4) in invariant natural killer T (iNKT) cells regulated crosstalk between iNKT cells and dendritic cells (DCs) and controlled iNKT cell-mediated T-helper type 1 (Th1) responses. The persistent polarization of IL4 induced by strong lipid antigens, that is, α-galactosylceramide (αGC), caused IL4 accumulation at the immunological synapse (IS), which promoted the activation of the IL4R-STAT6 (signal transducer and activator of transcription 6) pathway and production of IL12 in DCs, which enhanced interferon-γ (IFNγ) production in iNKT cells. Conversely, the nonpolarized secretion of IL4 induced by Th2 lipid antigens with a short or unsaturated chain was incapable of enhancing this iNKT cell-DC crosstalk and thus shifted the immune response to a Th2-type response. The nonpolarized secretion of IL4 in response to Th2 lipid antigens was caused by the degradation of Cdc42 in iNKT cells. Moreover, reduced Cdc42 expression was observed in tumor-infiltrating iNKT cells, which impaired IL4 polarization and disturbed iNKT cell-DC crosstalk in tumors.

Compartmentalization of dendritic cell and T-cell interactions in the lymph node: Anatomy of T-cell fate decisions

Upon receiving cognate and co-stimulatory priming signals from antigen (Ag)-presenting dendritic cells (DCs) in secondary lymphoid tissues, naïve CD4+ T cells differentiate into distinct effector and memory populations. These alternate cell fate decisions, which ultimately control the T-cell functional attributes, are dictated by programming signals provided by Ag-bearing DCs and by other cells that are present in the microenvironment in which T-cell priming occurs. We know that DCs can be subdivided into multiple populations and that the various DC subsets exhibit differential capacities to initiate development of the different CD4+ T-helper populations. What is less well understood is why different subanatomic regions of secondary lymphoid tissues are colonized by distinct populations of Ag-presenting DCs and how the location of these DCs influences the type of T-cell response that will be generated. Here we review how chemokine receptors and their ligands, which position allergen and nematode-activated DCs within different microdomains of secondary lymphoid tissues, contribute to the establishment of IL-4 committed follicular helper T and type 2 helper cell responses.

Equine Herpesvirus 1 Bridles T Lymphocytes To Reach Its Target Organs

Equine herpesvirus 1 (EHV1) is an ancestral alphaherpesvirus that is related to herpes simplex virus 1 and causes respiratory, reproductive, and neurological disorders in Equidae. EHV1 is indisputably a master at exploiting leukocytes to reach its target organs, accordingly evading the host immunity. However, the role of T lymphocytes in cell-associated viremia remains poorly understood. Here we show that activated T lymphocytes efficiently become infected and support viral replication despite the presence of protective immunity. We demonstrate a restricted expression of viral proteins on the surfaces of infected T cells, which prevents immune recognition. In addition, we indicate a hampered release of progeny, which results in the accumulation of nucleocapsids in the T cell nucleus. Upon engagement with the target endothelium, late viral proteins orchestrate viral synapse formation and viral transfer to the contact cell. Our findings have significant implications for the understanding of EHV1 pathogenesis, which is essential for developing innovative therapies to prevent the devastating clinical symptoms of infection.

Equine herpesvirus 1 (EHV1) replicates in the respiratory epithelium and disseminates through the body via a cell-associated viremia in leukocytes, despite the presence of neutralizing antibodies. “Hijacked” leukocytes, previously identified as monocytic cells and T lymphocytes, transmit EHV1 to endothelial cells of the endometrium or central nervous system, causing reproductive (abortigenic variants) or neurological (neurological variants) disorders. In the present study, we questioned the potential route of EHV1 infection of T lymphocytes and how EHV1 misuses T lymphocytes as a vehicle to reach the endothelium of the target organs in the absence or presence of immune surveillance. Viral replication was evaluated in activated and quiescent primary T lymphocytes, and the results demonstrated increased infection of activated versus quiescent, CD4⁺ versus CD8⁺, and blood- versus lymph node-derived T cells. Moreover, primarily infected respiratory epithelial cells and circulating monocytic cells efficiently transferred virions to T lymphocytes in the presence of neutralizing antibodies. Albeit T-lymphocytes express all classes of viral proteins early in infection, the expression of viral glycoproteins on their cell surface was restricted. In addition, the release of viral progeny was hampered, resulting in the accumulation of viral nucleocapsids in the T cell nucleus. During contact of infected T lymphocytes with endothelial cells, a late viral protein(s) orchestrates T cell polarization and synapse formation, followed by anterograde dynein-mediated transport and transfer of viral progeny to the engaged cell. This represents a sophisticated but efficient immune evasion strategy to allow transfer of progeny virus from T lymphocytes to adjacent target cells. These results demonstrate that T lymphocytes are susceptible to EHV1 infection and that cell-cell contact transmits infectious virus to and from T lymphocytes.

IMPORTANCE Equine herpesvirus 1 (EHV1) is an ancestral alphaherpesvirus that is related to herpes simplex virus 1 and causes respiratory, reproductive, and neurological disorders in Equidae. EHV1 is indisputably a master at exploiting leukocytes to reach its target organs, accordingly evading the host immunity. However, the role of T lymphocytes in cell-associated viremia remains poorly understood. Here we show that activated T lymphocytes efficiently become infected and support viral replication despite the presence of protective immunity. We demonstrate a restricted expression of viral proteins on the surfaces of infected T cells, which prevents immune recognition. In addition, we indicate a hampered release of progeny, which results in the accumulation of nucleocapsids in the T cell nucleus. Upon engagement with the target endothelium, late viral proteins orchestrate viral synapse formation and viral transfer to the contact cell. Our findings have significant implications for the understanding of EHV1 pathogenesis, which is essential for developing innovative therapies to prevent the devastating clinical symptoms of infection.

Immunological Synapse Formation Induces Mitochondrial Clustering and Mitophagy in Dendritic Cells

The immunological synapse (IS) is a superstructure formed during T cell activation at the zone of contact between T cells and dendritic cells (DCs). The IS includes specific molecular components in the T cell and DCs sides that may result in different functionality. Most of the studies on the IS have focused on the T cell side of this structure and, in contrast, the information available on the IS of DCs is sparse. Autophagy is a cellular process involved in the clearance of damaged proteins and organelles via lysosomal degradation. Mitophagy is the selective autophagy of damaged mitochondria. In this study, it is shown that IS formation induces clustering of mitochondria in the IS of DCs and partial depolarization of these organelles. At the IS of the DCs also accumulate autophagy and mitophagy markers, even when the kinase complex mTORC1, an inhibitor of the autophagy, is active. Together the results presented indicate that IS formation induces local clustering of mitochondria and mitophagy, which could be a homeostatic mechanism to control the quality of mitochondria in this region. The data underline the complexity of the regulatory mechanisms operating in the IS of DCs.

Inhibition of p21-activated kinase 1 attenuates the cardinal features of asthma through suppressing the lymph node homing of dendritic cells

Dendritic cell (DC) trafficking from lung to the draining mediastinal lymph nodes (MLNs) is a key step for initiation of T cell responses in allergic asthma. In the present study, we investigate the role of DC-mediated airway inflammation after inhibition of p21-activated kinase-1 (PAK1), an effector of Rac and Cdc42 small GTPases, in the allergen-induced mouse models of asthma. Systemic administration of PAK1 specific inhibitor IPA-3 significantly attenuates not only the airway inflammation but also the airway hyperresponsiveness in a mouse model of ovalbumin-induced asthma. Specifically, intratracheal administration of low dosage of IPA-3 consistently decreases not only the airway inflammation but also the DC trafficking from lung to the MLNs. Importantly, intratracheal instillation of IPA-3-treated and ovalbumin-pulsed DCs behaves largely the same as that of either Rac inhibitor-treated and ovalbumin-pulsed DCs or Cdc42 inhibitor-treated and ovalbumin-pulsed DCs in attenuation of the airway inflammation in ovalbumin-challenged mice. Mechanistically, PAK1 is not involved in the maturation, apoptosis, antigen uptake, and T cell activation of cultured DCs, but PAK1 dose lie on the downstream of Rac and Cdc42 to regulate the DC migration toward the chemokine C-C motif chemokine ligand 19. Taken together, this study demonstrates that inhibition of PAK1 attenuates the cardinal features of asthma through suppressing the DC trafficking from lung to the MLN, and that interfere with DC trafficking by a PAK1 inhibitor thus holds great promise for the therapeutic intervention of allergic diseases.

Antigen Presentation by Extracellular Vesicles from Professional Antigen-Presenting Cells

The initiation and maintenance of adaptive immunity require multifaceted modes of communication between different types of immune cells, including direct intercellular contact, secreted soluble signaling molecules, and extracellular vesicles (EVs). EVs can be formed as microvesicles directly pinched off from the plasma membrane or as exosomes secreted by multivesicular endosomes. Membrane receptors guide EVs to specific target cells, allowing directional transfer of specific and complex signaling cues. EVs are released by most, if not all, immune cells. Depending on the type and status of their originating cell, EVs may facilitate the initiation, expansion, maintenance, or silencing of adaptive immune responses. This review focusses on EVs from professional antigen-presenting cells, their demonstrated and speculated roles, and their potential for cancer immunotherapy.

Regulation of T Cell Activation and Differentiation by Extracellular Vesicles and Their Pathogenic Role in Systemic Lupus Erythematosus and Multiple Sclerosis

How autoreactive tissue-infiltrated effector T cells are induced and sustained in autoimmune disease, usually dominated by the Th1 and Th17 subsets, is still largely unknown. In organ-specific autoimmunity, self-reactive T cells initially activated by dendritic cells (DCs) in the lymph nodes migrate and infiltrate into the target tissues where their reactivation by peripheral tissue antigen is a prerequisite for effector cytokine production and tissue destruction. The target tissue microenvironment, as well as the local microenvironment at the immune synapse formed by T cells that encounter cognate antigen presenting cells (APCs) shave recently emerged as critical factors in shaping the differentiation and function of self-reactive effector T cells, providing the signals required for their activation in the form of the self-antigen and cytokine milieu. Moreover, depending on the specific microenvironment, self-reactive effector T cells have the ability to change their phenotype, especially Th17 and regulatory T (Treg) cells, which are characterized by the highest instability. In this context, cell-derived extracellular vesicles, i.e., vesicles carrying cytosolic proteins and nucleic acids protected by a phospholipid bilayer, as well as membrane-associated proteins, with the ability to spread throughout the body by means of biological fluids, are emerging as key mediators in intercellular communications and in the modulation of the microenvironment. In this review, we will discuss recent findings implicating extracellular vesicles (EVs) at different steps of CD4+ T cell differentiation to specific effectors, with a focus on the Th17/Treg balance and its alterations in systemic lupus erythematosus and multiple sclerosis.

Comparative Study of 5'- and 3'-Linked CpG-Antigen Conjugates for the Induction of Cellular Immune Responses

Conjugation of CpG to an antigen induces a stronger immune response compared to that of the mixture. This study compares the in vitro immunostimulatory activity of CpG conjugated via either its 5' or 3' end to the model antigen ovalbumin (OVA). CpG modified with an amine at either the 5' or 3' end was conjugated to OVA via a stable bis-aryl hydrazone bond. Similar levels of CpG conjugation to OVA were observed for both conjugates on the basis of the absorbance at 360 nm for the formation of the bis-aryl hydrazone bond, which determined 2.8 ± 0.3 CpGs linked per OVA. Both the 5' and 3' CpG-OVA conjugates had similar size-exclusion chromatography elution profiles. The immunostimulatory properties of the conjugates were determined by dendritic cells (DCs) and T-cells isolated from mice. The activation of DCs was determined by the upregulation of activation markers CD86 and CD40. T-cells were co-cultured with stimulated DCs, and the immunogenicity was determined by measuring T-cell proliferation and interferon γ production. Both the CpG 5'- and 3'-linked conjugates induced the same level (p > 0.5) of DC activation markers, which were significantly higher than those of the untreated control. Similarly, T-cell assays showed no significant difference (p > 0.5) between the 5' and 3' conjugates with respect to T-cell proliferation and interferon γ production. The 5' and 3' conjugates induced T-cell activation significantly higher than the mixture of CpG and OVA. This study showed that the end at which CpG is conjugated to an antigen has no influence on the generation of a T-cell-based immune response in vitro.

HIV signaling through CD4 and CCR5 activates Rho family GTPases that are required for optimal infection of primary CD4+ T cells

Background

HIV-1 hijacks host cell machinery to ensure successful replication, including cytoskeletal components for intracellular trafficking, nucleoproteins for pre-integration complex import, and the ESCRT pathway for assembly and budding. It is widely appreciated that cellular post-translational modifications (PTMs) regulate protein activity within cells; however, little is known about how PTMs influence HIV replication. Previously, we reported that blocking deacetylation of tubulin using histone deacetylase inhibitors promoted the kinetics and efficiency of early post-entry viral events. To uncover additional PTMs that modulate entry and early post-entry stages in HIV infection, we employed a flow cytometric approach to assess a panel of small molecule inhibitors on viral fusion and LTR promoter-driven gene expression.

Results

While viral fusion was not significantly affected, early post-entry viral events were modulated by drugs targeting multiple processes including histone deacetylation, methylation, and bromodomain inhibition. Most notably, we observed that inhibitors of the Rho GTPase family of cytoskeletal regulators—including RhoA, Cdc42, and Rho-associated kinase signaling pathways—significantly reduced viral infection. Using phosphoproteomics and a biochemical GTPase activation assay, we found that virion-induced signaling via CD4 and CCR5 activated Rho family GTPases including Rac1 and Cdc42 and led to widespread modification of GTPase signaling-associated factors.

Conclusions

Together, these data demonstrate that HIV signaling activates members of the Rho GTPase family of cytoskeletal regulators that are required for optimal HIV infection of primary CD4+ T cells.

Electronic supplementary material

The online version of this article (doi:10.1186/s12977-017-0328-7) contains supplementary material, which is available to authorized users.

Secretion from Myeloid Cells: Secretory Lysosomes

Many cells of the myeloid lineage use an unusual secretory organelle to deliver their effector mechanisms. In these cells, the lysosomal compartment is often modified not only to fulfill the degradative functions of a lysosome but also as a mechanism for secreting additional proteins that are found in the lysosomes of each specialized cell type. These extra proteins vary from one cell type to another according to the specialized function of the cell. For example, mast cells package histamine; cytotoxic T cells express perforin; azurophilic granules in neutrophils express antimicrobial peptides, and platelets von Willebrand factor. Upon release, these very different proteins can trigger inflammation, cell lysis, microbial death, and clotting, respectively, and hence deliver the very different effector mechanisms of these different myeloid cells.

Origins of the cytolytic synapse

Cytotoxic T lymphocytes (CTLs) kill virus-infected and tumour cells with remarkable specificity. Upon recognition, CTLs form a cytolytic immune synapse with their target cell, and marked reorganization of both the actin and the microtubule cytoskeletons brings the centrosome up to the plasma membrane to the point of T cell receptor signalling. Secretory granules move towards the centrosome and are delivered to this focal point of secretion. Such centrosomal docking at the plasma membrane also occurs during ciliogenesis; indeed, striking similarities exist between the cytolytic synapse and the primary cilium that throw light on the possible origins of immune synapses.

ERK1 as a Therapeutic Target for Dendritic Cell Vaccination against High-Grade Gliomas

Glioma regression requires the recruitment of potent antitumor immune cells into the tumor microenvironment. Dendritic cells (DC) play a role in immune responses to these tumors. The fact that DC vaccines do not effectively combat high-grade gliomas, however, suggests that DCs need to be genetically modified specifically to promote their migration to tumor relevant sites. Previously, we identified extracellular signal-regulated kinase (ERK1) as a regulator of DC immunogenicity and brain autoimmunity. In the current study, we made use of modern magnetic resonance methods to study the role of ERK1 in regulating DC migration and tumor progression in a model of high-grade glioma. We found that ERK1-deficient mice are more resistant to the development of gliomas, and tumor growth in these mice is accompanied by a higher infiltration of leukocytes. ERK1-deficient DCs exhibit an increase in migration that is associated with sustained Cdc42 activation and increased expression of actin-associated cytoskeleton-organizing proteins. We also demonstrated that ERK1 deletion potentiates DC vaccination and provides a survival advantage in high-grade gliomas. Considering the therapeutic significance of these results, we propose ERK1-deleted DC vaccines as an additional means of eradicating resilient tumor cells and preventing tumor recurrence. Mol Cancer Ther; 15(8); 1975-87. ©2016 AACR.

The SNARE VAMP7 Regulates Exocytic Trafficking of Interleukin-12 in Dendritic Cells

Interleukin-12 (IL-12), produced by dendritic cells in response to activation, is central to pathogen eradication and tumor rejection. The trafficking pathways controlling spatial distribution and intracellular transport of IL-12 vesicles to the cell surface are still unknown. Here, we show that intracellular IL-12 localizes in late endocytic vesicles marked by the SNARE VAMP7. Dendritic cells (DCs) from VAMP7-deficient mice are partially impaired in the multidirectional release of IL-12. Upon encounter with antigen-specific T cells, IL-12-containing vesicles rapidly redistribute at the immune synapse and release IL-12 in a process entirely dependent on VAMP7 expression. Consistently, acquisition of effector functions is reduced in T cells stimulated by VAMP7-null DCs. These results provide insights into IL-12 intracellular trafficking pathways and show that VAMP7-mediated release of IL-12 at the immune synapse is a mechanism to transmit innate signals to T cells.

•

Intracellular trafficking of IL-12 in dendritic cells is mediated by the SNARE VAMP7

•

VAMP7 is required for optimal secretion of IL-12 in the extracellular space

•

IL-12/VAMP7⁺ vesicles gather at the immune synapse

•

VAMP7 controls synaptic release of IL-12 and IFN-γ production in T cells

The Dendritic Cell Synapse: A Life Dedicated to T Cell Activation

T-cell activation within immunological synapses is a complex process whereby different types of signals are transmitted from antigen-presenting cells to T cells. The molecular strategies developed by T cells to interpret and integrate these signals have been systematically dissected in recent years and are now in large part understood. On the other side of the immune synapse, dendritic cells (DCs) participate actively in synapse formation and maintenance by remodeling of membrane receptors and intracellular content. However, the details of such changes have been only partially characterized. The DCs actin cytoskeleton has been one of the first systems to be identified as playing an important role in T-cell priming and some of the underlying mechanisms have been elucidated. Similarly, the DCs microtubule cytoskeleton undergoes major spatial changes during synapse formation that favor polarization of the DCs subcellular space toward the interacting T cell. Recently, we have begun to investigate the trafficking machinery that controls polarized delivery of endosomal vesicles at the DC–T immune synapse with the aim of understanding the functional relevance of polarized secretion of soluble factors during T-cell priming. Here, we will review the current knowledge of events occurring in DCs during synapse formation and discuss the open questions that still remain unanswered.

Induction of CD4(+) Regulatory and Polarized Effector/helper T Cells by Dendritic Cells

Dendritic cells (DCs) are considered to play major roles during the induction of T cell immune responses as well as the maintenance of T cell tolerance. Naive CD4(+) T cells have been shown to respond with high plasticity to signals inducing their polarization into effector/helper or regulatory T cells. Data obtained from in vitro generated bone-marrow (BM)-derived DCs as well as genetic mouse models revealed an important but not exclusive role of DCs in shaping CD4(+) T cell responses. Besides the specialization of some conventional DC subsets for the induction of polarized immunity, also the maturation stage, activation of specialized transcription factors and the cytokine production of DCs have major impact on CD4(+) T cells. Since in vitro generated BM-DCs show a high diversity to shape CD4(+) T cells and their high similarity to monocyte-derived DCs in vivo, this review reports data mainly on BM-DCs in this process and only touches the roles of transcription factors or of DC subsets, which have been discussed elsewhere. Here, recent findings on 1) the conversion of naive into anergic and further into Foxp3(-) regulatory T cells (Treg) by immature DCs, 2) the role of RelB in steady state migratory DCs (ssmDCs) for conversion of naive T cells into Foxp3(+) Treg, 3) the DC maturation signature for polarized Th2 cell induction and 4) the DC source of IL-12 for Th1 induction are discussed.

Cdc42-dependent actin dynamics controls maturation and secretory activity of dendritic cells

Cdc42 control of actin dynamics keeps DCs in an immature state, and loss of Cdc42 activity facilitates secretion and rapid up-regulation of intracellular molecules to the cell surface, which shows that Cdc42 contributes to DC immunogenicity by regulating the DC actin cytoskeleton.

Cell division cycle 42 (Cdc42) is a member of the Rho guanosine triphosphatase family and has pivotal functions in actin organization, cell migration, and proliferation. To further study the molecular mechanisms of dendritic cell (DC) regulation by Cdc42, we used Cdc42-deficient DCs. Cdc42 deficiency renders DCs phenotypically mature as they up-regulate the co-stimulatory molecule CD86 from intracellular storages to the cell surface. Cdc42 knockout DCs also accumulate high amounts of invariant chain–major histocompatibility complex (MHC) class II complexes at the cell surface, which cannot efficiently present peptide antigens (Ag’s) for priming of Ag-specific CD4 T cells. Proteome analyses showed a significant reduction in lysosomal MHC class II–processing proteins, such as cathepsins, which are lost from DCs by enhanced secretion. As these effects on DCs can be mimicked by chemical actin disruption, our results propose that Cdc42 control of actin dynamics keeps DCs in an immature state, and cessation of Cdc42 activity during DC maturation facilitates secretion as well as rapid up-regulation of intracellular molecules to the cell surface.

TCR Signal Strength Alters T-DC Activation and Interaction Times and Directs the Outcome of Differentiation

The ability of CD4+ T cells to differentiate into effector subsets underpins their ability to shape the immune response and mediate host protection. During T cell receptor-induced activation of CD4+ T cells, both the quality and quantity of specific activatory peptide/MHC ligands have been shown to control the polarization of naive CD4+ T cells in addition to co-stimulatory and cytokine-based signals. Recently, advances in two--photon microscopy and tetramer-based cell tracking methods have allowed investigators to greatly extend the study of the role of TCR signaling in effector differentiation under in vivo conditions. In this review, we consider data from recent in vivo studies analyzing the role of TCR signal strength in controlling the outcome of CD4+ T cell differentiation and discuss the role of TCR in controlling the critical nature of CD4+ T cell interactions with dendritic cells during activation. We further propose a model whereby TCR signal strength controls the temporal aspects of T-DC interactions and the implications for this in mediating the downstream signaling events, which influence the transcriptional and epigenetic regulation of effector differentiation.

Control of Homeostasis and Dendritic Cell Survival by the GTPase RhoA

Tissues accommodate defined numbers of dendritic cells (DCs) in highly specific niches where different intrinsic and environmental stimuli control DC life span and numbers. DC homeostasis in tissues is important, because experimental changes in DC numbers influence immunity and tolerance toward various immune catastrophes and inflammation. However, the precise molecular mechanisms regulating DC life span and homeostasis are unclear. We report that the GTPase RhoA controls homeostatic proliferation, cytokinesis, survival, and turnover of cDCs. Deletion of RhoA strongly decreased the numbers of CD11b(-)CD8(+) and CD11b(+)Esam(hi) DC subsets, whereas CD11b(+)Esam(lo) DCs were not affected in conditional RhoA-deficient mice. Proteome analyses revealed a defective prosurvival pathway via PI3K/protein kinase B (Akt1)/Bcl-2-associated death promoter in the absence of RhoA. Taken together, our findings identify RhoA as a central regulator of DC homeostasis, and its deletion decreases DC numbers below critical thresholds for immune protection and homeostasis, causing aberrant compensatory DC proliferation.

Human Immunodeficiencies Related to Defective APC/T Cell Interaction

The primary event for initiating adaptive immune responses is the encounter between T lymphocytes and antigen presenting cells (APCs) in the T cell area of secondary lymphoid organs and the formation of highly organized intercellular junctions referred to as immune synapses (IS). In vivo live-cell imaging of APC-T cell interactions combined to functional studies unveiled that T cell fate is dictated, in large part, by the stability of the initial contact. Immune cell interaction is equally important during delivery of T cell help to B cells and for the killing of target cells by cytotoxic T cells and NK cells. The critical role of contact dynamics and synapse stability on the immune response is well illustrated by human immune deficiencies in which disease pathogenesis is linked to altered adhesion or defective cross-talk between the synaptic partners. The Wiskott-Aldrich syndrome (WAS) is a severe primary immunodeficiency caused by mutations in the Wiskott-Aldrich syndrome protein (WASp), a scaffold that promotes actin polymerization and links TCR stimulation to T cell activation. Absence or mutations in WASp affects intercellular APC-T cell communications by interfering with multiple mechanisms on both sides of the IS. The warts, hypogammaglobulinemia, infections, and myelokathexis (WHIM) syndrome is caused by mutations in CXCR4, a chemokine receptor that in mutant form leads to impairment of APC-T cell interactions. Present evidences suggest that other recently characterized primary immune deficiencies caused by mutation in genes linked to actin cytoskeletal reorganization, such as WIP and DOCK8, may also depend on altered synapse stability. Here, we will discuss in details the mechanisms of disturbed APC-T cell interactions in WAS and WHIM. Moreover, we will summarize the evidence pointing to a compromised conjugate formation in WIP, DOCK8, and X-linked lymphoproliferative syndrome.

Communication, the centrosome and the immunological synapse

Recent findings on the behaviour of the centrosome at the immunological synapse suggest a critical role for centrosome polarization in controlling the communication between immune cells required to generate an effective immune response. The features observed at the immunological synapse show parallels to centrosome (basal body) polarization seen in cilia and flagella, and the cellular communication that is now known to occur at all of these sites.

Molecular mechanisms and functional implications of polarized actin remodeling at the T cell immunological synapse

Transient,specialized cell-cell interactions play a central role in leukocyte function by enabling specific intercellular communication in the context of a highly dynamic systems level response. The dramatic structural changes required for the formation of these contacts are driven by rapid and precise cytoskeletal remodeling events. In recent years, the immunological synapse that forms between a T lymphocyte and its antigen-presenting target cell has emerged as an important model system for understanding immune cell interactions. In this review, we discuss how regulators of the cortical actin cytoskeleton control synaptic architecture and in this way specify T cell function.

T-cell-receptor-dependent signal intensity dominantly controls CD4(+) T cell polarization In Vivo

Polarization of effector CD4(+) T cells can be influenced by both antigen-specific signals and by pathogen- or adjuvant-induced cytokines, with current models attributing a dominant role to the latter. Here we have examined the relationship between these factors in shaping cell-mediated immunity by using intravital imaging of CD4(+) T cell interactions with dendritic cells (DCs) exposed to polarizing adjuvants. These studies revealed a close correspondence between strength of T cell receptor (TCR)-dependent signaling and T helper 1 (Th1) versus Th2 cell fate, with antigen concentration dominating over adjuvant in controlling T cell polarity. Consistent with this finding, at a fixed antigen concentration, adjuvants inducing Th1 cells operated by affecting DC costimulation that amplified TCR signaling. TCR signal strength controlled downstream cytokine receptor expression, linking the two components in a hierarchical fashion. These data reveal how quantitative integration of antigen display and costimulation regulates downstream checkpoints responsible for cytokine-mediated control of effector differentiation.

[Flow cytometry in the diagnosis of hemophagocytic lymphohistiocytosis in a case with fatal outcome]

Hemophagocytic lymphohistiocytosis is a multisystem inflammation, generated by the uncontrolled and excessive activation of cytotoxic T lymphocytes and natural killer cells. Severe immunodeficiency and generalized macrophage activation can often be detected in the background of this life threatening disorder. It is classified as a primary immunodeficiency. Functional abnormalities of the perforin protein or defects in granule secretory mechanisms are caused by gene mutations in most cases. Diagnostic criteria of hemophagocytic lymphohistiocytosis are the following: fever, splenomegaly, cytopenias affecting at least two of the 3 lineages in peripheral blood, hypertriglyceridemia and hyperferritinemia, elevated serum level of soluble interleukin-2 receptor (sCD25), hypofibrinogenemia, hemophagocytosis in bone marrow and decreased cytotoxic T cell and natural killer cell activity. In this case report the authors summarize the utility of functional flow cytometry in the diagnosis of hemophagocytic lymphohistiocytosis. Using flow cytometry, elevated intracellular perforin content, decreased killing activity of cytotoxic T cells and natural killer cells, and impaired cell surface expression of CD107a (LAMP1 protein) from in vitro stimulated blood lymphocytes were detected. Abnormal secretion of perforin was also demonstrated. Genetic testing revealed mutation of the MUNC 13-4 gene, which confirmed the base of the abnormal flow cytometric findings. This case report demonstrates the value of functional flow cytometry in the rapid diagnosis of genetically determined hemophagocytic lymphohistiocytosis, a condition in which early diagnosis is critical for optimal management. The authors emphasize the significance of functional flow cytometry in the differential diagnosis of immunodeficiencies.

Identification of cinnabarinic acid as a novel endogenous aryl hydrocarbon receptor ligand that drives IL-22 production

The aryl hydrocarbon receptor (AHR) binds to environmental toxicants including synthetic halogenated aromatic hydrocarbons and is involved in a diverse array of biological processes. Recently, the AHR was shown to control host immunity by affecting the balance between inflammatory T cells that produce IL-17 (Th17) and IL-22 versus regulatory T cells (Treg) involved in tolerance. While environmental AHR ligands can mediate this effect, endogenous ligands are likely to be more relevant in host immune responses. We investigated downstream metabolites of tryptophan as potential AHR ligands because (1) tryptophan metabolites have been implicated in regulating the balance between Th17 and Treg cells and (2) many of the AHR ligands identified thus far are derivatives of tryptophan. We characterized the ability of tryptophan metabolites to bind and activate the AHR and to increase IL-22 production in human T cells. We report that the tryptophan metabolite, cinnabarinic acid (CA), is an AHR ligand that stimulates the differentiation of human and mouse T cells producing IL-22. We compare the IL-22-stimulating activity of CA to that of other tryptophan metabolites and define stimulation conditions that lead to CA production from immune cells. Our findings link tryptophan metabolism to AHR activation and define a novel endogenous AHR agonist with potentially broad biological functions.

Auditory hair cell centrioles undergo confined Brownian motion throughout the developmental migration of the kinocilium

Planar polarization of the forming hair bundle, the mechanosensory antenna of auditory hair cells, depends on the poorly characterized center-to-edge displacement of a primary cilium, the kinocilium, at their apical surface. Taking advantage of the gradient of hair cell differentiation along the cochlea, we reconstituted a map of the kinocilia displacements in the mouse embryonic cochlea. We then developed a cochlear organotypic culture and video-microscopy approach to monitor the movements of the kinocilium basal body (mother centriole) and its daughter centriole, which we analyzed using particle tracking and modeling. We found that both hair cell centrioles undergo confined Brownian movements around their equilibrium positions, under the apparent constraint of a radial restoring force of ∼0.1 pN. This magnitude depended little on centriole position, suggesting nonlinear interactions with constraining, presumably cytoskeletal elements. The only dynamic change observed during the period of kinocilium migration was a doubling of the centrioles' confinement area taking place early in the process. It emerges from these static and dynamic observations that kinocilia migrate gradually in parallel with the organization of hair cells into rows during cochlear neuroepithelium extension. Analysis of the confined motion of hair cell centrioles under normal and pathological conditions should help determine which structures contribute to the restoring force exerting on them.

Human immunodeficiency syndromes affecting human natural killer cell cytolytic activity

Natural killer (NK) cells are lymphocytes of the innate immune system that secrete cytokines upon activation and mediate the killing of tumor cells and virus-infected cells, especially those that escape the adaptive T cell response caused by the down regulation of MHC-I. The induction of cytotoxicity requires that NK cells contact target cells through adhesion receptors, and initiate activation signaling leading to increased adhesion and accumulation of F-actin at the NK cell cytotoxic synapse. Concurrently, lytic granules undergo minus-end directed movement and accumulate at the microtubule-organizing center through the interaction with microtubule motor proteins, followed by polarization of the lethal cargo toward the target cell. Ultimately, myosin-dependent movement of the lytic granules toward the NK cell plasma membrane through F-actin channels, along with soluble N-ethylmaleimide-sensitive factor attachment protein receptor-dependent fusion, promotes the release of the lytic granule contents into the cleft between the NK cell and target cell resulting in target cell killing. Herein, we will discuss several disease-causing mutations in primary immunodeficiency syndromes and how they impact NK cell-mediated killing by disrupting distinct steps of this tightly regulated process.

Macrophage cytokines: involvement in immunity and infectious diseases

The evolution of macrophages has made them primordial for both development and immunity. Their functions range from the shaping of body plans to the ingestion and elimination of apoptotic cells and pathogens. Cytokines are small soluble proteins that confer instructions and mediate communication among immune and non-immune cells. A portfolio of cytokines is central to the role of macrophages as sentries of the innate immune system that mediate the transition from innate to adaptive immunity. In concert with other mediators, cytokines bias the fate of macrophages into a spectrum of inflammation-promoting "classically activated," to anti-inflammatory or "alternatively activated" macrophages. Deregulated cytokine secretion is implicated in several disease states ranging from chronic inflammation to allergy. Macrophages release cytokines via a series of beautifully orchestrated pathways that are spatiotemporally regulated. At the molecular level, these exocytic cytokine secretion pathways are coordinated by multi-protein complexes that guide cytokines from their point of synthesis to their ports of exit into the extracellular milieu. These trafficking proteins, many of which were discovered in yeast and commemorated in the 2013 Nobel Prize in Physiology or Medicine, coordinate the organelle fusion steps that are responsible for cytokine release. This review discusses the functions of cytokines secreted by macrophages, and summarizes what is known about their release mechanisms. This information will be used to delve into how selected pathogens subvert cytokine release for their own survival.

Carbon nanotube scaffolds instruct human dendritic cells: modulating immune responses by contacts at the nanoscale

Nanomaterials interact with cells and modify their function and biology. Manufacturing this ability can provide tissue-engineering scaffolds with nanostructures able to influence tissue growth and performance. Carbon nanotube compatibility with biomolecules motivated ongoing interest in the development of biosensors and devices including such materials. More recently, carbon nanotubes have been applied in several areas of nerve tissue engineering to study cell behavior or to instruct the growth and organization of neural networks. To gather further knowledge on the true potential of future constructs, in particular to assess their immune-modulatory action, we evaluate carbon nanotubes interactions with human dendritic cells (DCs). DCs are professional antigen-presenting cells and their behavior can predict immune responses triggered by adhesion-dependent signaling. Here, we incorporate DC cultures to carbon nanotubes and we show by phenotype, microscopy, and transcriptional analysis that in vitro differentiated and activated DCs show when interfaced to carbon nanotubes a lower immunogenic profile.

The microglial activation state regulates migration and roles of matrix-dissolving enzymes for invasion

Background

Microglial cells are highly mobile under many circumstances and, after central nervous system (CNS) damage, they must contend with the dense extracellular matrix (ECM) in order to reach their target sites. In response to damage or disease, microglia undergo complex activation processes that can be modulated by environmental cues and culminate in either detrimental or beneficial outcomes. Thus, there is considerable interest in comparing their pro-inflammatory (‘classical’ activation) and resolving ‘alternative’ activation states. Almost nothing is known about how these activation states affect the ability of microglia to migrate and degrade ECM, or the enzymes used for substrate degradation. This is the subject of the present study.

Methods

Primary cultured rat microglial cells were exposed to lipopolysaccharide (LPS) to evoke classical activation or IL4 to evoke alternative activation. High-resolution microscopy was used to monitor changes in cell morphology and aspects of the cytoskeleton. We quantified migration in a scratch-wound assay and through open filter holes, and invasion through Matrigel™. A panel of inhibitors was used to analyze contributions of different matrix-degrading enzymes to migration and invasion, and quantitative real-time reverse transcriptase PCR (qRT-PCR) was used to assess changes in their expression.

Results

Vinculin- and F-actin-rich lamellae were prominent in untreated and IL4-treated microglia (but not after LPS). IL4 increased the migratory capacity of microglia but eliminated the preferential anterior nuclear-centrosomal axis polarity and location of the microtubule organizing center (MTOC). Microglia degraded fibronectin, regardless of treatment, but LPS-treated cells were relatively immobile and IL4-treated cells invaded much more effectively through Matrigel™. For invasion, untreated microglia primarily used cysteine proteases, but IL4-treated cells used a wider range of enzymes (cysteine proteases, cathepsin S and K, heparanase, and matrix metalloproteases). Untreated microglia expressed MMP2, MMP12, heparanase, and four cathepsins (B, K, L1, and S). Each activation stimulus upregulated a different subset of enzymes. IL4 increased MMP2 and cathepsins S and K; whereas LPS increased MMP9, MMP12, MMP14 (MT1-MMP), heparanase, and cathepsin L1.

Conclusions

Microglial cells migrate during CNS development and after CNS damage or disease. Thus, there are broad implications of the finding that classically and alternatively activated microglia differ in morphology, cytoskeleton, migratory and invasive capacity, and in the usage of ECM-degrading enzymes.

Dedicator of cytokinesis 8 interacts with talin and Wiskott-Aldrich syndrome protein to regulate NK cell cytotoxicity

Recently, patients with mutations in DOCK8 have been reported to have a combined immunodeficiency characterized by cutaneous viral infections and allergies. NK cells represent a first-line defense against viral infections, suggesting that DOCK8 might participate in NK cell function. In this study, we demonstrate that DOCK8-suppressed human NK cells showed defects in natural cytotoxicity as well as specific activating receptor-mediated NK cytotoxicity. Additionally, compared with control NK cells, NK cells depleted of DOCK8 showed defective conjugate formation, along with decreased polarization of LFA-1, F-actin, and cytolytic granules toward the cytotoxic synapse. Using a proteomic approach, we found that DOCK8 exists in a macromolecular complex with the Wiskott-Aldrich syndrome protein, an actin nucleation-promoting factor activated by CDC42, as well as talin, which is required for integrin-mediated adhesion. Taken together, our results demonstrate an important role for DOCK8 in NK cell effector function and provide important new mechanistic insight into how DOCK8 regulates F-actin and integrin-mediated adhesion in immune cells.

The transcription factor NFAT exhibits signal memory during serial T cell interactions with antigen-presenting cells

Interactions with antigen-presenting cells (APCs) interrupt T cell migration through tissues and trigger signaling pathways that converge on the activation of transcriptional regulators, including nuclear factor of activated T cells (NFAT), which control T cell function and differentiation. Both stable and unstable modes of cognate T cell-APC interactions have been observed in vivo, but the functional significance of unstable, serial contacts has remained unclear. Here we used multiphoton intravital microscopy in lymph nodes and tumors to show that while NFAT nuclear import was fast (t(1/2 max)∼1 min), nuclear export was slow (t(1/2)∼20 min) in T cells. During delayed export, nuclear NFAT constituted a short-term imprint of transient TCR signals and remained transcriptionally active for the T cell tolerance gene Egr2, but not for the effector gene Ifng, which required continuous TCR triggering for expression. This provides a potential mechanistic basis for the observation that a predominance of unstable APC interactions correlates with the induction of T cell tolerance.

How the immune system talks to itself: the varied role of synapses

Using an elaborately evolved language of cytokines and chemokines as well as cell-cell interactions, the different components of the immune system communicate with each other and orchestrate a response (or wind one down). Immunological synapses are a key feature of the system in the ways in which they can facilitate and direct these responses. Studies analyzing the structure of an immune synapse as it forms between two cells have provided insight into how the stability and kinetics of this interaction ultimately affect the sensitivity, potency, and magnitude of a given response. Furthermore, we have gained an appreciation of how the immunological synapse provides directionality and contextual cues for downstream signaling and cellular decision-making. In this review, we discuss how using a variety of techniques, developed over the last decade, have allowed us to visualize and quantify key aspects of the dynamic synaptic interface and have furthered our understanding of their function. We describe some of the many characteristics of the immunological synapse that make it a vital part of intercellular communication and some of the questions that remain to be answered.

Cytokine secretion by CD4+ T cells at the immunological synapse requires Cdc42-dependent local actin remodeling but not microtubule organizing center polarity

Cytokine secretion by T lymphocytes plays a central role in mounting adaptive immune responses. However, little is known about how newly synthesized cytokines, once produced, are routed within T cells and about the mechanisms involved in regulating their secretions. In this study, we investigated the role of cytoskeleton remodeling at the immunological synapse (IS) in cytokine secretion. We show that a key regulator of cytoskeleton remodeling, the Rho GTPase Cdc42, controls IFN-γ secretion by primary human CD4+ T lymphocytes. Surprisingly, microtubule organizing center polarity at the IS, which does not depend on Cdc42, is not required for cytokine secretion by T lymphocytes, whereas microtubule polymerization is required. In contrast, actin remodeling at the IS, which depends on Cdc42, controls the formation of the polymerized actin ring at the IS, the dynamic concentration of IFN-γ-containing vesicles inside this ring, and the secretion of these vesicles. These results reveal a previously unidentified role of Cdc42-dependent actin remodeling in cytokine exocytosis at the IS.