Human hepatic lymph nodes contain normal numbers of mature myeloid dendritic cells but few plasmacytoid dendritic cells

Plasmacytoid dendritic cells in the eye

Plasmacytoid dendritic cells (pDCs) are a unique subpopulation of immune cells, distinct from classical dendritic cells. pDCs are generated in the bone marrow and following development, they typically home to secondary lymphoid tissues. While peripheral tissues are generally devoid of pDCs during steady state, few tissues, including the lung, kidney, vagina, and in particular ocular tissues harbor resident pDCs. pDCs were originally appreciated for their potential to produce large quantities of type I interferons in viral immunity. Subsequent studies have now unraveled their pivotal role in mediating immune responses, in particular in the induction of tolerance. In this review, we summarize our current knowledge on pDCs in ocular tissues in both mice and humans, in particular in the cornea, limbus, conjunctiva, choroid, retina, and lacrimal gland. Further, we will review our current understanding on the significance of pDCs in ameliorating inflammatory responses during herpes simplex virus keratitis, sterile inflammation, and corneal transplantation. Moreover, we describe their novel and pivotal neuroprotective role, their key function in preserving corneal angiogenic privilege, as well as their potential application as a cell-based therapy for ocular diseases.

Dendritic cell subsets and locations

Dendritic cells (DCs) are a unique class of immune cells that act as a bridge between innate and adaptive immunity. The discovery of DCs by Cohen and Steinman in 1973 laid the foundation for DC biology, and the advances in the field identified different versions of DCs with unique properties and functions. DCs originate from hematopoietic stem cells, and their differentiation is modulated by Flt3L. They are professional antigen-presenting cells that patrol the environmental interphase, sites of infection, or infiltrate pathological tissues looking for antigens that can be used to activate effector cells. DCs are critical for the initiation of the cellular and humoral immune response and protection from infectious diseases or tumors. DCs can take up antigens using specialized surface receptors such as endocytosis receptors, phagocytosis receptors, and C type lectin receptors. Moreover, DCs are equipped with an array of extracellular and intracellular pattern recognition receptors for sensing different danger signals. Upon sensing the danger signals, DCs get activated, upregulate costimulatory molecules, produce various cytokines and chemokines, take up antigen and process it and migrate to lymph nodes where they present antigens to both CD8 and CD4 T cells. DCs are classified into different subsets based on an integrated approach considering their surface phenotype, expression of unique and conserved molecules, ontogeny, and functions. They can be broadly classified as conventional DCs consisting of two subsets (DC1 and DC2), plasmacytoid DCs, inflammatory DCs, and Langerhans cells.

Characterization of Antigen-Presenting Cell Subsets in Human Liver-Draining Lymph Nodes

T-cell immunity in the liver is tightly regulated to prevent chronic liver inflammation in response to antigens and toxins derived from food and intestinal bacterial flora. Since the main sites of T cell activation in response to foreign components entering solid tissues are the draining lymph nodes (LN), we aimed to study whether Antigen-Presenting Cell (APC) subsets in human liver lymph-draining LN show features that may contribute to the immunologically tolerant liver environment. Healthy liver LN, iliac LN, spleen and liver perfusates were obtained from multi-organ donors, while diseased liver LN were collected from explanted patient livers. Inguinal LN were obtained from kidney transplant recipients. Mononuclear cells were isolated from fresh tissues, and immunophenotypic and functional characteristics of APC subsets were studied using flowcytometry and in ex vivo cultures. Healthy liver-draining LN contained significantly lower relative numbers of CD1c⁺ conventional dendritic cells (cDC2), plasmacytoid DC (PDC), and CD14⁺CD163⁺DC-SIGN⁺ macrophages (MF) compared to inguinal LN. Compared to spleen, both types of LN contained low relative numbers of CD141^hi cDC1. Both cDC subsets in liver LN showed a more activated/mature immunophenotype than those in inguinal LN, iliacal LN, spleen and liver tissue. Despite their more mature status, cDC2 isolated from hepatic LN displayed similar cytokine production capacity (IL-10, IL-12, and IL-6) and allogeneic T cell stimulatory capacity as their counterparts from spleen. Liver LN from patients with inflammatory liver diseases showed a further reduction of cDC1, but had increased relative numbers of PDC and MF. In steady state conditions human liver LN contain relatively low numbers of cDC2, PDC, and macrophages, and relative numbers of cDC1 in liver LN decline during liver inflammation. The paucity of cDC in liver LN may contribute to immune tolerance in the liver environment.

Characterization of the liver-draining lymph nodes in mice and their role in mounting regional immunity to HBV

The lymphatic system is important in mounting an immune response to foreign antigens and tumors in humans and animal models. The liver produces a large amount of lymph, and its lymphatic system is divided into three major components: the portal, sublobular and superficial lymphatic vessels. Despite the fact that mice are the most commonly used laboratory animals, detailed descriptions of the anatomical location and function of the lymph nodes (LNs) that drain the liver are surprisingly absent. In this study, we found that the portal and celiac LNs adjacent to mouse liver were stained with Evans blue within 5-8 min. Enhanced green fluorescence protein (EGFP)-positive cells from the liver also drained into the two aforementioned LNs. These data indicate that the portal and celiac LNs drain the mouse liver. Lymphadenectomy of the identified liver-draining LNs resulted in hepatitis B virus (HBV) persistence in immunocompetent mice compared with the sham group. In addition, the frequencies of CD8(+) T cells and dendritic cells (DCs) increased significantly in the liver-draining LNs after hydrodynamic injection of HBV plasmid. Liver-draining LN cells in HBV plasmid-injected mice also showed significant antigen-specific proliferation in response to stimulation with recombinant hepatitis B core antigen in vitro. Adoptive transfer of these cells into Rag1(-/-) mice induced a reduction in the serum concentration of hepatitis B surface antigen (HBsAg) compared to liver-draining LN cells in uninjected mice. Altogether our data characterize the liver-draining LNs and provide evidence that the liver-draining LNs induce an anti-HBV-specific immune response responsible for HBV clearance.

Insight into the immunobiology of human skin and functional specialization of skin dendritic cell subsets to innovate intradermal vaccination design

Dendritic cells (DC) are the key initiators and regulators of any immune response which determine the outcome of CD4(+) and CD8(+) T-cell responses. Multiple distinct DC subsets can be distinguished by location, phenotype, and function in the homeostatic and inflamed human skin. The function of steady-state cutaneous DCs or recruited inflammatory DCs is influenced by the surrounding cellular and extracellular skin microenvironment. The skin is an attractive site for vaccination given the extended local network of DCs and the easy access to the skin-draining lymph nodes to generate effector T cells and immunoglobulin-producing B cells for long-term protective immunity. In the context of intradermal vaccination we describe in this review the skin-associated immune system, the characteristics of the different skin DC subsets, the mechanism of antigen uptake and presentation, and how the properties of DCs can be manipulated. This knowledge is critical for the development of intradermal vaccine strategies and supports the concept of intradermal vaccination as a superior route to the conventional intramuscular or subcutaneous methods.

Antigen-presenting cell function in the tolerogenic liver environment

The demands that are imposed on the liver as a result of its function as a metabolic organ that extracts nutrients and clears gut-derived microbial products from the blood are met by a unique microanatomical and immunological environment. The inherent tolerogenicity of the liver and its role in the regulation of innate and adaptive immunity are mediated by parenchymal and non-parenchymal antigen-presenting cells (APCs), cell-autonomous molecular pathways and locally produced factors. Here, we review the central role of liver APCs in the regulation of hepatic immune function and also consider how recent insights may be applied in strategies to target liver tolerance for disease therapy.

Clinicopathologic features of hepatic follicular dendritic cell sarcoma

AIM: To investigate the clinicopathologic features, diagnosis, treatment and prognosis of hepatic follicular dendritic cell sarcoma.

METHODS: The clinical, pathological and immunohistochemical data for three patients with hepatic follicular dendritic cell sarcoma who were treated at our hospital were collected to analyze the clinicopathologic features, diagnosis, treatment and prognosis of the disease. A literature review was also performed to reveal the characteristics of the disease.

RESULTS: All the tumors showed an infiltrative growth pattern. Two tumors were located in the left lobe of the liver, and one in the right lobe. Histopathology revealed co-existence of the components of spindle cell sarcoma and inflammatory cells. Coagulation necrosis was noted in some areas. Immunohistochemically, tumor cells were strongly positive for CD21, CD23, CD35, vimentin, weakly positive for CD45 and EMA, but negative for CK (Pan), CD34, CD117, Dog-1, actin, SMA, caldesmon, desmin, CD10, CD15, CD30, CD1a, ALK, CD68, CD163, HMB45 and S-100. Inflammatory cells were positive for CD20, CD79a, CD2, CD3, CD45RO and CD38. In all three cases, tumor cells were positive for EBER and EBV. A diagnosis of hepatic follicular dendritic cell sarcoma was made.

CONCLUSION: Hepatic follicular dendritic cell sarcoma is a rare tumor with a high degree of malignancy and should be differentiated from interdigitating dendritic cell sarcoma, sarcomatoid hepatocellular carcinoma, inflammatory myofibroblastoma, extra-gastrointestinal stromal tumor, and histiocytosarcoma.

Systemic dendritic cell mobilization associated with administration of FLT3 ligand to SIV- and SHIV-infected macaques

Reports indicate that myeloid and plasmacytoid dendritic cells (mDCs and pDCs), which are key effector cells in host innate immune responses, can be infected with HIV-1 and are reduced in number and function during the chronic phase of HIV disease. Furthermore, it was recently demonstrated that a sustained loss of mDCs and pDCs occurs in SIV-infected macaques. Since loss of functional DC populations might impair innate immune responses to opportunistic microorganisms and neoplastic cells, we explored whether inoculation of naive and SIV- or SHIV-infected pigtailed macaques with the hematopoietic cytokine FLT3-ligand (FLT3-L) would expand the number of mDCs and pDCs in vivo. After the macaques received supraphysiologic doses of FLT3-L, mDCs, pDCs, and monocytes increased up to 45-fold in blood, lymph nodes, and bone marrow (BM), with DC expansion in the BM preceding mobilization in blood and lymphoid tissues. FLT3-L also increased serum levels of IL-12, at least transiently, and elicited higher surface expression of HLA-DR and the activation markers CD25 and CD69 on NK and T cells. During and after treatment of infected animals, APCs increased in number and were activated; however, CD4(+) T cell numbers, virion RNA, and anti-SIV/SHIV antibody titers remained relatively stable, suggesting that FLT3-L might be a safe modality to expand DC populations and provide therapeutic benefit during chronic lentivirus infections.

Dendritic cell populations in colon and mesenteric lymph nodes of patients with Crohn's disease

Dendritic cells (DCs) are key cells in innate and adaptive immune responses that determine the pathophysiology of Crohn's disease. Intestinal DCs migrate from the mucosa into mesenteric lymph nodes (MLNs). A number of different markers are described to define the DC populations. In this study we have identified the phenotype and localization of intestinal and MLN DCs in patients with Crohn's disease and non-IBD patients based on these markers. We used immunohistochemistry to demonstrate that all markers (S-100, CD83, DC-SIGN, BDCA1-4, and CD1a) showed a different staining pattern varying from localization in T-cell areas of lymph follicles around blood vessels or single cells in the lamina propria and in the MLN in the medullary cords and in the subcapsular sinuses around blood vessels and in the T-cell areas. In conclusion, all different DC markers give variable staining patterns so there is no marker for the DC.

Dendritic cells, the liver, and transplantation

Interstitial liver dendritic cells (DCs) exhibit phenotypic diversity and functional plasticity. They play important roles in both innate and adaptive immunity. Their comparatively low inherent T cell stimulatory ability and the outcome of their interactions with CD4(+) and CD8(+) T cells, as well as with natural killer (NK) T cells and NK cells within the liver, may contribute to regulation of hepatic inflammatory responses and liver allograft outcome. Liver DCs migrate in the steady state and after liver transplantation to secondary lymphoid tissues, where the outcome of their interaction with antigen-specific T cells determines the balance between tolerance and immunity. Systemic and local environmental factors that are modulated by ischemia-reperfusion injury, liver regeneration, microbial infection, and malignancy influence hepatic DC migration, maturation, and function. Current research in DC biology is providing new insights into the role of these important antigen-presenting cells in the complex events that affect liver transplant outcome.

Dendritic cells are significantly reduced in non-Hodgkin's lymphoma and express less CCR7 and CD62L

Despite the lack of tumor control, infiltration of immune cells has been demonstrated for several malignancies including non-Hodgkin's lymphoma. Since dendritic cells play a pivotal role in the initiation and control of the immune response, the frequency and phenotype of recently described sub-types of dendritic cells in non-Hodgkin's lymphoma were characterized. Myeloid and plasmacytoid dendritic cells were analysed in 55 non-Hodgkin's lymphoma and 33 reactive lymph nodes by flow cytometry and immunohistochemistry. Overall frequency of dendritic cells in reactive lymph nodes was higher than in non-Hodgkin's lymphoma while the pDC/mDCs ratio was comparable. The low frequency of dendritic cells in infiltrated lymph nodes was confirmed by immunohistochemistry; however, no significant difference in the distribution within lymphoid and tumor tissue was detected. For further characterization of the dendritic cells in non-Hodgkin's lymphoma, the expressions of adhesion molecules, costimulatory molecules, chemokine receptors and activation markers were assessed. Interestingly, a significantly decreased expression of CD62L and CCR7, receptors necessary for homing to lymph nodes, was identified in dendritic cells in non-Hodgkin's lymphoma, potentially explaining the lack of these cells. Taken together, dendritic cells are phenotypically altered and reduced in number in NHL, potentially contributing to the loss of tumor control in these patients.

Impairment of circulating myeloid dendritic cells in immunosuppressed liver transplant recipients

The aim of the present study was to elucidate the impact of liver transplantation (LTX) on myeloid dendritic cell (MDC) homeostasis. We observed a threefold reduction of circulating CD1c(+) MDC immediately after LTX (n = 16; P < 0.01), and normalization between 3 and 12 months after LTX. This decline was not due to recruitment of MDC into the liver graft, as numbers of MDC in post-LTX liver graft biopsies were not increased compared to pre-LTX biopsies (n = 7). Moreover, no change in chemokine receptor expression on circulating MDC was observed, suggesting that their homing properties were not altered. Normalization of circulating MDC was associated with withdrawal of corticosteroid therapy, and not with changes in calcineurin inhibitor intake, indicating that corticosteroids are responsible for the observed changes in numbers of circulating MDC. During high-dose corticosteroid treatment early after LTX, circulating MDC showed a lowered maturation status with decreased expression of human leucocyte antigen D-related (HLA-DR) and CD86 compared to pre-LTX values (P < 0.01). However, when MDC from blood of LTX recipients were matured ex vivo, they up-regulated HLA-DR and co-stimulatory molecules to a comparable extent as MDC from healthy individuals. In addition, ex vivo matured MDC from both groups had equal allogeneic T cell stimulatory capacity. In conclusion, during the first months after LTX numbers and maturational status of circulating MDC are impaired significantly, probably due to a suppressive effect of corticosteroids on MDC. However, corticosteroid therapy does not imprint MDC with an intrinsic resistance to maturation stimuli.

Cytokines and chronic liver disease

From an immunological point of view, the healthy liver has been usually associated with the phenomenon of tolerance. A microenvironment of regulatory cytokines produced by liver Kuppfer cells and liver sinusoidal endothelial cells has contributed, together with resident dendritic cells, to generate a tolerogenic environment in this tissue. In this review we discussed the intrahepatic responses to different sorts of liver injury, such as hepatotrophic viruses, alcohol or putative self-antigens. In each case we analyzed the impact of different cytokines in the clinical outcome of the different pathological situations.

Plasmacytoid dendritic cells from human lung cancer draining lymph nodes induce Tc1 responses

Dendritic cells (DC) resident in draining lymph nodes (LN) of patients with lung cancer are proposed to have a critical role in stimulating anti-tumor immunity. CpG oligodeoxynucleotides are undergoing clinical trials in patients with lung cancer and are likely to target plasmacytoid-DC. The present study, therefore, investigated the capacity of plasmacytoid-DC from human lung cancer draining LN to respond to CpG for activation of T cell responses relevant to anti-tumor immunity. The phenotype of DC was examined by flow cytometry, and cytokine production by cytometric bead array (CBA) and ELISA. Plasmacytoid-DC, purified by cell sorting, were immature but expressed the toll-like receptor, TLR9. Plasmacytoid-DC responded to the CpG oligodeoxynucleotide, CpG 2216, by production of the proinflammatory cytokines, IFN-alpha and IL-6. DC were cocultured with normal, allogeneic T cells, and cytokine production determined by CBA and immunophenotyping. CpG 2216 enhanced IFN-gamma production and induced intracellular production of IFN-gamma by CD8(+) and CD4(+), granzyme B by CD8(+), and IL-2 by CD4(+) T cells, respectively. Ligation of CD40 on plasmacytoid-DC combined with exposure to CpG 2216 also strongly enhanced IFN-gamma production. There was no significant difference between the responses of plasmacytoid-DC from patients with lung cancer and patients with benign carcinoid tumors with no pathologic LN involvement. These results indicate that plasmacytoid DC from the draining LN of patients with lung cancer effectively induce Tc1 immunity and could, therefore, represent a novel and attractive target for immunotherapeutic intervention.

Aberrant composition of the dendritic cell population in hepatic lymph nodes of patients with hepatocellular carcinoma

Patients with hepatocellular carcinoma (HCC) are characterized by a weak T-cell response to their tumor, and chronic carriers of hepatitis B virus or hepatitis C virus have a poor T-cell response against the virus. These inadequate T-cell responses may be due to insufficient activation of the T cells by dendritic cells (DCs). Because lymph nodes (LNs) are the primary site of antigen-specific T-cell activation, we hypothesized that hepatic LNs of patients with HCC and/or chronic viral hepatitis might have aberrant compositions of their DC populations. To address this hypothesis, we enumerated mature myeloid DCs (MDCs) and plasmacytoid DCs (PDCs) in hepatic LNs by quantitative immunohistochemistry. Patients with HCC and chronic viral hepatitis and patients with chronic viral hepatitis without HCC were compared with patients with liver inflammation of nonviral etiology and with organ donors with healthy livers. The numbers of PDCs and mature MDCs in hepatic LNs of patients with chronic viral hepatitis did not differ from those of patients with liver inflammation of nonviral etiology nor from individuals with healthy livers. However, hepatic LNs of patients with HBV or HCV infection complicated by HCC showed a 1.5-fold reduction in numbers of mature MDCs and a 4-fold increase in numbers of PDCs in their T-cell areas compared with those of patients with viral hepatitis only (P <.01). In conclusion, patients with HCC have an aberrant composition of the DC population in their hepatic LNs. This may be one of the causes of the inadequate T-cell response against HCC in these patients.

Characterization of human liver dendritic cells in liver grafts and perfusates

It is generally accepted that donor myeloid dendritic cells (MDC) are the main instigators of acute rejection after organ transplantation. The aim of the present study was to characterize MDC in human donor livers using liver grafts and perfusates as a source. Perfusates were collected during ex vivo vascular perfusion of liver grafts pretransplantation. MDC, visualized in wedge biopsies by immunohistochemistry with anti-BDCA-1 monoclonal antibody (mAb), were predominantly observed in the portal fields. Liver MDC, isolated from liver wedge biopsies, had an immature phenotype with a low expression of CD80 and CD83. Perfusates were collected from 20 grafts; perfusate mononuclear cells (MNC) contained 1.5% (range, 0.3-6.6%) MDC with a viability of 97 +/- 2%. Perfusates were a rich source of hepatic MDC since 0.9 x 10(6) (range, 0.11-4.5 x 10(6)) MDC detached from donor livers during vascular perfusion pretransplantation. Perfusate MDC were used to further characterize hepatic MDC. Perfusate MDC expressed less DC-LAMP (P = 0.000), CD80 (P = 0.000), CD86 (P = 0.003), and CCR7 (P = 0.014) than mature hepatic lymph node (LN) MDC, and similar CD86 (P = 0.140) and CCR7 (P = 0.262) as and more DC-LAMP (P = 0.007) and CD80 (P = 0.002) than immature blood MDC. Perfusate MDC differed from blood MDC in producing significantly higher amounts of interleukin (IL)-10 in response to lipopolysaccharide (LPS), and in being able to stimulate allogeneic T-cell proliferation. In conclusion, human donor livers contain exclusively immature MDC that detach in high numbers from the liver graft during pretransplantation perfusion. These viable MDC have the capacity to stimulate allogeneic T-cells, and thus may represent a major player in the induction of acute rejection.

Immunomagnetic selection of functional dendritic cells from human lymph nodes

It was investigated whether positive immunomagnetic selection with two novel DC-specific mAb allowed purification of functional myeloid dendritic cells (MDC) and plasmacytoid dendritic cells (PDC) from the human lymph nodes (LN). The results were compared with enrichment of DC by low-density Nycodenz gradient centrifugation followed by immunomagnetic depletion of residual B- and T-cells (Nycodenz method). MDC were selected from inguinal LN cell suspensions using CD1c mAb and PDC using anti-BDCA-4 mAb. Immunomagnetic selection with anti-CD1c mAb yielded highly pure MDC preparations (90 +/- 3% MDC; n = 7), provided that the B-cells were thoroughly depleted by using CD19 magnetic beads and Large Depletion (LD) columns prior to selection of MDC. The purified MDC comprised both mature and immature cells and were functional, secreting large amounts of cytokines upon stimulation and strongly stimulating allogeneic T-cell proliferation. Immunomagnetic selection with anti-BDCA-4 mAb enriched PDC 70-fold to a purity of 59 +/- 26% (n = 8). The contamination consisted mainly of BDCA-4(+) T- and NK-cells. The previously used Nycodenz method yielded mixtures of MDC and PDC, not allowing functional studies of MDC and PDC separately. In conclusion, positive immunomagnetic selection with CD1c mAb from human LN cell suspensions yields almost pure MDC preparations, which are, in contrast to those obtained by the Nycodenz method, not contaminated with PDC. Moreover, these MDC are functionally intact. Selection with anti-BDCA-4 mAb does enrich PDC from human LN, but the resulting preparations are contaminated with T- and NK-cells.

Human liver myeloid dendritic cells maturate in vivo into effector DC with a poor allogeneic T-cell stimulatory capacity

We hypothesized that the relatively low immunogenicity of liver grafts might be related to a special maturation program of hepatic myeloid dendritic cells (MDC), yielding relatively immature effector MDC with weak allogeneic T-cell stimulatory capacity. To investigate whether maturation of human liver-derived MDC in vivo differs from maturation of MDC at another anatomical location, we compared the immunophenotypes and allogeneic T-cell stimulatory capacity of MDC from hepatic with those from inguinal lymph nodes (LN). MDC were purified by immunomagnetic selection from hepatic LN obtained from multi-organ donors (n = 8) and from inguinal LN of kidney transplant recipients (n = 7). MDC from hepatic LN had a significantly reduced capacity to stimulate allogeneic T-cell proliferation compared to MDC from inguinal LN. However, this was not due to an immaturity, since MDC from hepatic LN had significantly higher expressions of HLA-DR, CD80, and CD86 compared to MDC from inguinal LN. Hepatic MDC maturate in vivo to a mature type of effector MDC with relatively poor allogeneic T-cell stimulatory capacity.