Regulatory mechanisms in cross-presentation <i>in vivo</i>

Dendritic cells can present exogenous antigen to CD8 T cells using a mechanism termed cross-presentation. This mechanism is important for immune responses against tumors, viruses, intracellular pathogens and autoantigens expressed in peripheral tissues. However, the physiological mechanisms that regulate cross-presentation in vivo in particular the endocytosis mechanisms involved in this process are not well understood. The first aim of this study was to elucidate the role of the mannose receptor (MR), a C-type lectin in cross-presentation. MR deficient mice showed reduced uptake of soluble OVA and diminished activation of CD8 T cells. This was due to the reduced cross-presentation ability of DCs in MR deficient mice, as the MR was only present in the cross-presenting CD8α+ DCs. As opposed to soluble OVA, the cell-associated form of this model antigen did not use the MR to enter the cross-presentation pathways. These data provide first formal evidences that a particular antigen uptake receptor, here the MR can specifically introduce antigen into the cross-presentation pathway. Furthermore, they identify this receptor as a further marker of cross-presenting DCs. The second aim of the present study was to identify the mechanisms by which soluble antigens are transported from the peripheral organs to draining LNs for subsequent cross-presentation. Proteins smaller than the molecular weight of albumin, such as soluble OVA theoretically may pass the kidney glomerular filter and be concentrated in the tubular compartment. It appeared possible that this physiological process might increase the availability of antigen for the cross-presenting APC. Therefore the kidney - renal lymph node (rLN) system was choosen to investigate antigen transport from organ to draining LN. Several lines of independent evidence indicated that soluble OVA was concentrated in the kidney DCs but was transported in a cell-independent fashion to DC resident in the rLN. Further studies showed that these DCs tolerized specific T cells. This tolerization was independent from steady-state migration of kidney DC to draining LN. These findings identify the rLN as a unique site where antigen is rapidly enriched for T cell activation; provided it is small enough to pass the glomerular filter. This mechanism may contribute avoiding unwanted immune responses against innocuous circulating antigens, for example self-serum or food proteins. In conclusion the present study revealed new in vivo mechanisms in regulating cross-presentation of soluble molecules such as antigen uptake via MR and antigen presentation occurring in the kidney – renal LN system

Large Extracellular Vesicles: Have We Found the Holy Grail of Inflammation?

The terms microparticles (MPs) and microvesicles (MVs) refer to large extracellular vesicles (EVs) generated from a broad spectrum of cells upon its activation or death by apoptosis. The unique surface antigens of MPs/MVs allow for the identification of their cellular origin as well as its functional characterization. Two basic aspects of MP/MV functions in physiology and pathological conditions are widely considered. Firstly, it has become evident that large EVs have strong procoagulant properties. Secondly, experimental and clinical studies have shown that MPs/MVs play a crucial role in the pathophysiology of inflammation-associated disorders. A cardinal feature of these disorders is an enhanced generation of platelets-, endothelial-, and leukocyte-derived EVs. Nevertheless, anti-inflammatory effects of miscellaneous EV types have also been described, which provided important new insights into the large EV-inflammation axis. Advances in understanding the biology of MPs/MVs have led to the preparation of this review article aimed at discussing the association between large EVs and inflammation, depending on their cellular origin

Basic requirements for the formation of an intellectual analytical decisionmaking system

The article examines the basic requirements for the content of an intellectual analytical system for making management decisions taking into account the chosen management model of the organization. Shown aspects of control for each model management

Macrophage death following influenza vaccination initiates the inflammatory response that promotes dendritic cell function in the draining lymph node

The mechanism by which inflammation influences the adaptive response to vaccines is not fully understood. Here, we examine the role of lymph node macrophages (LNMs) in the induction of the cytokine storm triggered by inactivated influenza virus vaccine. Following vaccination, LNMs undergo inflammasome-independent necrosis-like death that is reliant on MyD88 and Toll-like receptor 7 (TLR7) expression and releases pre-stored interleukin-1α (IL-1α). Furthermore, activated medullary macrophages produce interferon-β (IFN-β) that induces the autocrine secretion of IL-1α. We also found that macrophage depletion promotes lymph node-resident dendritic cell (LNDC) relocation and affects the capacity of CD11b+ LNDCs to capture virus and express co-stimulatory molecules. Inhibition of the IL-1α-induced inflammatory cascade reduced B cell responses, while co-administration of recombinant IL-1α increased the humoral response. Stimulation of the IL-1α inflammatory pathway might therefore represent a strategy to enhance antigen presentation by LNDCs and improve the humoral response against influenza vaccines

Lymph node fibroblastic reticular cells directly present peripheral tissue antigen under steady-state and inflammatory conditions

Lymph node stromal cells (LNSCs) can induce potent, antigen-specific T cell tolerance under steady-state conditions. Although expression of various peripheral tissue–restricted antigens (PTAs) and presentation to naive CD8+ T cells has been demonstrated, the stromal subsets responsible have not been identified. We report that fibroblastic reticular cells (FRCs), which reside in the T cell zone of the LN, ectopically express and directly present a model PTA to naive T cells, inducing their proliferation. However, we found that no single LNSC subset was responsible for PTA expression; rather, each subset had its own characteristic antigen display. Studies to date have concentrated on PTA presentation under steady-state conditions; however, because LNs are frequently inflammatory sites, we assessed whether inflammation altered stromal cell–T cell interactions. Strikingly, FRCs showed reduced stimulation of T cells after Toll-like receptor 3 ligation. We also characterize an LNSC subset expressing the highest levels of autoimmune regulator, which responds potently to bystander inflammation by up-regulating PTA expression. Collectively, these data show that diverse stromal cell types have evolved to constitutively express PTAs, and that exposure to viral products alters the interaction between T cells and LNSCs

Lymphoid Organ-Resident Dendritic Cells Exhibit Unique Transcriptional Fingerprints Based on Subset and Site

Lymphoid organ-resident DC subsets are thought to play unique roles in determining the fate of T cell responses. Recent studies focusing on a single lymphoid organ identified molecular pathways that are differentially operative in each DC subset and led to the assumption that a given DC subset would more or less exhibit the same genomic and functional profiles throughout the body. Whether the local milieu in different anatomical sites can also influence the transcriptome of DC subsets has remained largely unexplored. Here, we interrogated the transcriptional relationships between lymphoid organ-resident DC subsets from spleen, gut- and skin-draining lymph nodes, and thymus of C57BL/6 mice. For this purpose, major resident DC subsets including CD4 and CD8 DCs were sorted at high purity and gene expression profiles were compared using microarray analysis. This investigation revealed that lymphoid organ-resident DC subsets exhibit divergent genomic programs across lymphoid organs. Interestingly, we also found that transcriptional and biochemical properties of a given DC subset can differ between lymphoid organs for lymphoid organ-resident DC subsets, but not plasmacytoid DCs, suggesting that determinants of the tissue milieu program resident DCs for essential site-specific functions

Regulated release of nitric oxide by nonhematopoietic stroma controls expansion of the activated T cell pool in lymph nodes

Fibroblastic reticular cells (FRCs) and lymphatic endothelial cells (LECs) are nonhematopoietic stromal cells of lymphoid organs. They influence the migration and homeostasis of naive T cells; however, their influence on activated T cells remains undescribed. Here we report that FRCs and LECs inhibited T cell proliferation through a tightly regulated mechanism dependent on nitric oxide synthase 2 (NOS2). Expression of NOS2 and production of nitric oxide paralleled the activation of T cells and required a tripartite synergism of interferon-γ, tumor necrosis factor and direct contact with activated T cells. Notably, in vivo expression of NOS2 by FRCs and LECs regulated the size of the activated T cell pool. Our study elucidates an as-yet-unrecognized role for the lymph node stromal niche in controlling T cell responses

The role of lymphatic endothelial cells in liver injury and tumor development

Lymphatics and lymphatic endothelial cells (LECs) possess multiple immunological functions besides affecting immune cell migration such as inhibiting T cell proliferation and antigen presentation by dendritic cells. Moreover, they control the trans-endothelial transport of multiple molecules and antigens. Emerging evidence suggests their active involvements in immunoregulation, tumor and metastases formation. In the liver, increased lymphangiogenesis, specifically at the portal area has been associated with multiple liver diseases in particular primary biliary cirrhosis, idiopathic portal hypertension, and liver malignancies. Nevertheless, the exact role and contribution of LECs to liver diseases are poorly understood. The review summarizes the current understanding of LECs in liver diseases

The Contribution of Non-Professional Antigen-Presenting Cells to Immunity and Tolerance in the Liver

The liver represents a unique organ biased toward a tolerogenic milieu. Due to its anatomical location, it is constantly exposed to microbial and food-derived antigens from the gut and thus equipped with a complex cellular network that ensures dampening T-cell responses. Within this cellular network, parenchymal cells (hepatocytes), non-parenchymal cells (liver sinusoidal endothelial cells and hepatic stellate cells), and immune cells contribute directly or indirectly to this process. Despite this refractory bias, the liver is capable of mounting efficient T-cell responses. How the various antigen-presenting cell (APC) populations contribute to this process and how they handle danger signals determine the outcome of the generated immune responses. Importantly, liver mounted responses convey consequences not only for the local but also to systemic immunity. Here, we discuss various aspects of antigen presentation and its consequences by the non-professional APCs in the liver microenvironment