Interleukin 15-dependent crosstalk between conventional and plasmacytoid dendritic cells is essential for CpG-induced immune activation

The function of interleukin 15 (IL-15) in unmethylated CpG oligodeoxynucleotide (CpG)-induced immune responses remains unknown. Here, in response to CpG, both wild-type and natural killer cell-depleted mice produced IL-12 and became resistant to a lethal dose of Listeria monocytogenes. In contrast, CpG-treated IL-15-deficient mice produced little IL-12 and succumbed to L. monocytogenes. CpG-stimulated conventional dendritic cells (cDCs) were the main producers of both IL-15 and IL-12, but cDCs did not produce IL-12 in the absence of plasmacytoid DCs (pDCs). The cDC-derived IL-15 induced CD40 expression by cDCs. Interaction between CD40 on cDCs and CD40 ligand on pDCs led to IL-12 production by cDCs. Thus, IL-15-dependent crosstalk between cDCs and pDCs is essential for CpG-induced immune activation.

Opposing roles of blood myeloid and plasmacytoid dendritic cells in HIV-1 infection of T cells: transmission facilitation versus replication inhibition

CD11c(+) myeloid dendritic cells (MDCs) and CD11c(-) CD123(+) plasmacytoid DCs (PDCs) have been identified as main human DC subsets. MDCs are professional antigen-presenting cells for T cells, and include Langerhans cells, dermal DCs, and interstitial DCs. They have been associated with HIV-1 capture and sexual transmission, whereas PDCs play an important role in the innate immune responses to different types of viruses, including HIV-1. To compare the influence of MDCs and PDCs on HIV-1 infection of T cells, we isolated donor-matched MDCs and PDCs from peripheral blood, activated them by adding different maturation-inducing compounds, and cocultured them with T cells and HIV-1. We found that MDCs enhance HIV-1 infection through capture of the virus and subsequent transmission to T cells, and that differently matured MDC subsets have different HIV-1 transmission efficiencies. These differences were not due to soluble factors, viral capture differences, or the expression of integrins ICAM-1, -2, -3, or LFA-1. In contrast, regardless of their state of maturation, PDCs inhibit HIV-1 replication in T cells through the secretion of IFNalpha and an additional, unidentified small molecule. This study shows that the 2 main types of DCs have opposing roles in HIV-1 infection of T cells.

Regulatory dendritic cells act as regulators of acute lethal systemic inflammatory response

Bacterial infection triggers host inflammation through the activation of immune cells, leading to the elimination of bacteria. However, the regulatory mechanisms of the host inflammatory response remain unknown. Here we report that a subset of potent tolerogenic dendritic cells (DCs), regulatory DCs (DCregs), control the systemic inflammatory response. Unlike normal DCs, which produced proinflammatory cytokines in response to bacterial lipopolysaccharide (LPS), DCregs produced fewer proinflammatory cytokines and instead preferentially produced interleukin-10 (IL-10), and these events involved the expression of IκBNS and Bcl-3 as well as cyclic AMP (cAMP)-mediated activation of protein kinase A (PKA). In addition, DCregs not only suppressed LPS-induced production of proinflammatory cytokines in macrophages, but also reduced their serum levels in mice. Furthermore, DCregs protected mice against the lethality induced by experimental endotoxemia and bacterial peritonitis. The inhibitory effect of DCregs against inflammatory responses involved the production of IL-10. On the other hand, naturally existing tolerogenic DC subsets producing IL-10, CD11clowCD45RBhigh DCs, also suppressed LPS-induced host inflammatory responses. Thus, a subset of tolerogenic DCs act as potential regulators of the host inflammatory response, and they might have preventive and therapeutic potential for the treatment of systemic as well as local inflammatory diseases.

Adenoviral-encoded antigens are presented efficiently by a subset of dendritic cells expressing high levels of alpha(v)beta3 integrins

Dendritic cells (DC) play a central role in antigen presentation and are often targeted by adenoviral (Ad)-based gene therapy. However, DC lack the coxsackie-Ad receptor, and little is known about the process by which they acquire and present Ad-encoded antigens. We examined the expression of alpha(v)beta3 integrins (CD51/CD61) on mouse bone marrow-derived DC (BM-DC) and their susceptibility to transduction by Ad vectors. Less than 10% of BM-DC precursors expressed CD51, but expression increased over time in culture with granulocyte macrophage-colony stimulating factor (GM-CSF)/interleukin (IL)-4. After 7 days, 28 +/- 1.7% of CD11c+ DC expressed high levels of CD51 (CD51(hi)), and the remaining DC expressed low levels of CD51 (CD51(lo)). CD51(hi) CD express higher major histocompatibility complex type 1 (MHC I); however, both of the DC subsets expressed similar levels of MHC II and costimulatory molecules. When exposed to a first-generation Ad vector, transgene expression was restricted to the CD51(hi) DC subset and blocked by soluble peptides expressing an arginine, glycine, aspartic acid (RGD) sequence, confirming the role of integrins in viral entry. Consistent with this, a modified Ad expressing an RGD-binding sequence in its fiber knob (Ad-RGD) transduced the CD51(hi) DC subset with significantly higher efficiency. When BM-DC were transduced with an Ad-expressing ovalbumin (Ad-OVA), the CD51(hi) subset proved superior in activating OT-I (T cell receptor-OVA) T cells. Similar to in vitro effects, systemic administration of GM-CSF/IL-4 increased the expression of CD51 on splenic DC and rendered these cells susceptible to Ad transduction. These results suggest that a limited subset of DC expressing high levels of alpha(v)beta3 integrins is preferentially transduced by Ad vectors and activates CD8+ T cell responses against Ad-encoded antigens.

Suplatast tosilate alters DC1/DC2 balance in peripheral blood in bronchial asthma

Suplatast tosilate is an antiallergic drug that selectively suppresses Th2-cytokine production and inhibits airway hyperresponsiveness and eosinophilic airway inflammation. This drug has been also shown to improve pulmonary function and symptoms in steroid-dependent asthma, resulting in a decrease in doses of inhaled corticosteroid. However, the precise mechanism by which suplatast tosilate exerts an antiasthmatic effect in vivo remains to be known. Our previous study showed the polarization of circulating type 1 dendritic cells (DC1)/type 2 dendritic cells (DC2) balance toward DC2 in asthma, which might be associated with its Th2-dominant immune response. In the present study, we attempted to clarify the effect of suplatast tosilate on DC1/DC2 balance in asthma. Using multicolor flow cytometry, we enumerated circulating DC1 and DC2 before and 8 weeks after treatment with suplatast tosilate in nine patients with asthma. Before the treatment, the patients with asthma had a significant higher percentage of DC2 together with a significant lower ratio of DC1/DC2 compared with normal subjects. Administration of suplatast tosilate significantly decreased the percentage of DC2, but not that of DC1, resulting in a significant raises of the ratio of DC1/DC2. Concomitantly, intracellular cytokine analysis showed that the percentage of IL-4 producing CD4+ T cells was significantly decreased after the treatment. These data suggest that suplatast tosilate normalizes the polarized DC1/DC2 balance toward DC2 in asthma, which may also alter its Th2-dominant Th1/Th2 balance toward Th1.

Specialization, kinetics, and repertoire of type 1 interferon responses by human plasmacytoid predendritic cells

Recent studies suggest plasmacytoid predendritic cells (pDCs) and myeloid dendritic cells (mDCs) have the functional plasticity to produce similar amounts of type 1 interferons (IFNs) and interleukin-12 (IL-12), challenging the concept and existence of DC subsets with distinct function. In this study, we demonstrate that previous studies showed human pDCs produce large amounts of IL-12 because of contaminating mDCs. Using highly purified human DC subsets, we found that although pDCs make 300 times more IFN-alpha than mDCs and mDCs make 13 times more IL-12 p70 than pDCs in response to all the toll-like receptor ligands and CD40 ligands, pDCs rapidly make large amounts of IFN-alpha within the first 12 hours of activation and become refractory to further stimulation. pDCs preferentially expressed the transcriptional factors critical for type 1 IFN, but not for IL-12 transcription, and they dedicated 60% of new transcriptional activity to make 19 type 1 IFN subtypes. This study provides formal proof that the plasticity of DC subsets is limited and that different DC subsets evolve to perform distinct functions in linking innate and adaptive immunity.

HIV-1 selectively infects a subset of nonmaturing BDCA1-positive dendritic cells in human blood

The infection of cultured monocyte-derived dendritic cells (DCs) with HIV-1 involves CD4 and CCR5 receptors, while transmission to T cells is enhanced at least in part by the lectin DC-SIGN/CD209. In the present study, we studied BDCA-1+ myeloid DCs isolated directly from human blood. These cells express CD4 and low levels of CCR5 and CXCR4 coreceptors, but not DC-SIGN. The myeloid DCs replicate two R5 viruses, BaL and YU2, and transfer infection to activated T cells. The virus productively infects a small fraction of the blood DCs that fail to mature in culture, as indicated by the maturation markers CD83 and DC-LAMP/CD208, and the expression of high CD86 and MHC class II, in contrast to many noninfected DCs. A greater proportion of BDCA-1+ DCs are infected when the virus is pseudotyped with the vesicular stomatitis envelope VSV-G (5-15%), as compared with the R5 virus (0.3-3.5%), indicating that HIV-1 coreceptors may limit the susceptibility of DCs to become infected, or the endocytic route of viral entry used by HIV/vesicular stomatitis virus enhances infectivity. When infected and noninfected cells are purified by cell sorting, the former uniformly express HIV p24 gag and are virtually inactive as stimulators of the allogeneic MLR, in contrast to potent stimulation by noninfected DCs from the same cultures. These results point to two roles for a small fraction of blood DCs in HIV-1 pathogenesis: to support productive infection and to evade the direct induction of T cell-mediated immunity.

Renal transplantation reverses functional deficiencies in circulating dendritic cell subsets in chronic renal failure patients

BACKGROUND

Dendritic cell (DC) subsets play critical roles in regulation of innate and adaptive immune responses. These important antigen-presenting cells have not been extensively analyzed in chronic renal failure (CRF), during dialysis, or before and after renal transplantation.

METHODS

The incidence of circulating precursor (pre)-DC subsets relative to total peripheral blood mononuclear cells was analyzed in healthy controls, haemodialysis patients, peritoneal dialysis patients, CRF patients, and renal transplant (RT) recipients. DC subsets were identified and characterized phenotypically by multicolour flow cytometric analysis and purified by immunomagnetic bead isolation respectively. Cytokine production and circulating DC mobilizing cytokines were determined by ELISA.

RESULTS

The incidence of circulating prePDC was reduced in all patients, but the incidence of circulating preMDC was comparable in RT and dialysis patients compared to healthy controls. CRF patients exhibited the lowest incidence of circulating preMDC and prePDC. Immunomagnetic bead-isolated preMDC and prePDC from haemodialysis patients were functionally impaired (reduced expression of surface costimulatory molecules and interleukin-12p70 production following bacterial lipopolysaccharide stimulation, and reduced interferon-alpha production following herpes simplex virus stimulation respectively, compared to healthy controls and RT recipients. Glomerular filtration rate correlated significantly with the incidence of circulating preMDC, but not prePDC.

CONCLUSIONS

Deficiencies in the incidence and function of precursor DC can be reversed with successful renal transplantation achieving normal renal function. However, the finding of reduced incidence of circulating prePDC in the peripheral blood in RT recipients may be of significance in the pathogenesis of infections and malignancies.

In vitro culture during retroviral transduction improves thymic repopulation and output after total body irradiation and autologous peripheral blood progenitor cell transplantation in rhesus macaques

Immunodeficiency after peripheral blood progenitor cell (PBPC) transplantation may be influenced by graft composition, underlying disease, and/or pre-treatment. These factors are difficult to study independently in humans. Ex vivo culture and genetic manipulation of PBPC grafts may also affect immune reconstitution, with relevance to gene therapy applications. We directly compared the effects of three clinically relevant autologous graft compositions on immune reconstitution after myeloblative total body irradiation in rhesus macaques, the first time these studies have been performed in a large animal model with direct clinical relevance. Animals received CD34(+) cell dose-matched grafts of either peripheral blood mononuclear cells, purified CD34(+) PBPCs, or purified CD34(+) PBPCs expanded in vitro and retrovirally transduced. We evaluated the reconstitution of T, B, natural killer, dendritic cells, and monocytes in blood and lymph nodes for up to 1 year post-transplantation. Animals receiving selected-transduced CD34(+) cells had the fastest recovery of T-cell numbers, along with the highest T-cell-receptor gene rearrangement excision circles levels, the fewest proliferating Ki-67(+) T-cells in the blood, and the best-preserved thymic architecture. Selected-transduced CD34(+) cells may therefore repopulate the thymus more efficiently and promote a higher output of naïve T-cells. These results have implications for the design of gene therapy trials, as well as for the use of expanded PBPCs for improved T-cell immune reconstitution after transplantation.

Professional type I interferon-producing cells--a unique subpopulation of dendritic cells

Dendritic cells (DC) represent a rare but multifunctional population of cells with the capacity to prime and orchestrate antigen-specific immune responses. Both human and mouse DC are classified to myeloid and plasmacytoid DC (pDC) with distinct functional activities. These DC subsets can be found in the peripheral blood and tissues as resting cells and act as sensors of environmental changes. Activation of DC by various stimuli induces morphological and functional changes and transforms these cells to potent antigen presenting and secretory cells. A newly identified precursor subset of human DC has recently been identified as professional type I interferon producing cells (IPC) with multiple functional activities. Interferon-producing cells, also referred as pDC act as a link between innate and adaptive immunity and possess the capacity to instruct and regulate pathogen- and tumor-specific immune responses. The role of IPC/pDC--partly mediated by type I interferons--has also been demonstrated in the pathogenesis of various diseases and could be used as a target for modulating immune responses.

Interferon-producing killer dendritic cells provide a link between innate and adaptive immunity

Natural killer (NK) cells and dendritic cells (DCs) are, respectively, central components of innate and adaptive immune responses. We describe here a third DC lineage, termed interferon-producing killer DCs (IKDCs), distinct from conventional DCs and plasmacytoid DCs and with the molecular expression profile of both NK cells and DCs. They produce substantial amounts of type I interferons (IFN) and interleukin (IL)-12 or IFN-gamma, depending on activation stimuli. Upon stimulation with CpG oligodeoxynucleotides, ligands for Toll-like receptor (TLR)-9, IKDCs kill typical NK target cells using NK-activating receptors. Their cytolytic capacity subsequently diminishes, associated with the loss of NKG2D receptor (also known as Klrk1) and its adaptors, Dap10 and Dap12. As cytotoxicity is lost, DC-like antigen-presenting activity is gained, associated with upregulation of surface major histocompatibility complex class II (MHC II) and costimulatory molecules, which formally distinguish them from classical NK cells. In vivo, splenic IKDCs preferentially show NK function and, upon systemic infection, migrate to lymph nodes, where they primarily show antigen-presenting cell activity. By virtue of their capacity to kill target cells, followed by antigen presentation, IKDCs provide a link between innate and adaptive immunity.

A novel dendritic cell subset involved in tumor immunosurveillance

The interferon (IFN)-gamma-induced TRAIL effector mechanism is a vital component of cancer immunosurveillance by natural killer (NK) cells in mice. Here we show that the main source of IFN-gamma is not the conventional NK cell but a subset of B220(+)Ly6C(-) dendritic cells, which are atypical insofar as they express NK cell-surface molecules. Upon contact with a variety of tumor cells that are poorly recognized by NK cells, B220(+)NK1.1(+) dendritic cells secrete high levels of IFN-gamma and mediate TRAIL-dependent lysis of tumor cells. Adoptive transfer of these IFN-producing killer dendritic cells (IKDCs) into tumor-bearing Rag2(-/-)Il2rg(-/-) mice prevented tumor outgrowth, whereas transfer of conventional NK cells did not. In conclusion, we identified IKDCs as pivotal sensors and effectors of the innate antitumor immune response.

Mouse lymphoid tissue contains distinct subsets of langerin/CD207 dendritic cells, only one of which represents epidermal-derived Langerhans cells

Langerin/CD207 is a C-type lectin associated with formation of Birbeck granules (BG) in Langerhans cells (LC). Here, we describe a monoclonal antibody (mAb 205C1) recognizing the extracellular domain of mouse langerin. Cell-surface langerin was detected in all epidermal LC, which presented a uniform phenotype. Two subpopulations of langerin+ cells were identified in peripheral lymph nodes (LN). One population (subset 1) was CD11c(low/+)/CD8alpha(-/low)/CD11b+/CD40+/CD86+. The other population (subset 2) was CD11c(high)/CD8alpha+/CD11b(low), and lacked CD40 and CD86. Only subset 1 was fluorescein 5-isothiocyanate (FITC+) following painting onto epidermis, and the appearance of such FITC+ cells in draining LN was inhibited by pertussis toxin. Mesenteric LN, spleen, and thymus contained only a single population of langerin+ DC, corresponding to peripheral LN subset 2. Unexpectedly, BG were absent from spleen CD8alpha+ DC despite expression of langerin, and these organelles were not induced by mAb 205C1. Collectively, we demonstrate that two langerin+ DC populations (subsets 1 and 2) co-exist in mouse lymphoid tissue. Subset 1 unequivocally identifies epidermal LC-derived DC. The distribution of subset 2 indicates a non-LC origin of these langerin+ cells. These findings should facilitate our understanding of the role played by langerin in lymphoid organ DC subsets.

MyD88-dependent and -independent murine cytomegalovirus sensing for IFN-alpha release and initiation of immune responses in vivo

Antiviral immunity requires early and late mechanisms in which IFN-alpha and IL-12 play major roles. However, the initial events leading to their production remain largely unclear. Given the crucial role of TLR in innate recognition, we investigated their role in antiviral immunity in vivo. Upon murine CMV (MCMV) infection, both MyD88-/- and TLR9-/- mice were more susceptible and presented increased viral loads compared with C57BL/6, TLR2-/-, TLR3-/-, or TLR4-/- mice. However, in terms of resistance to infection, IFN-alpha production and in many other parameters of early inflammatory responses, the MyD88-/- mice showed a more defective response than TLR9-/- mice. In the absence of the TLR9/MyD88 signaling pathway, cytokine production was dramatically impaired with a complete abolition of bioactive IL-12p70 serum release contrasting with a high flexibility for IFN-alpha release, which is initially (36 h) plasmacytoid dendritic cell- and MyD88-dependent, and subsequently (44 h) PDC-, MyD88-independent and, most likely, TLR-independent. NK cells from MCMV-infected MyD88-/- and TLR9-/- mice displayed a severely impaired IFN-gamma production, yet retained enhanced cytotoxic activity. In addition, dendritic cell activation and critical inflammatory cell trafficking toward the liver were still effective. In the long term, except for isotype switching to MCMV-specific IgG1, the establishment of Ab responses was not significantly altered. Thus, our results demonstrate a critical requirement of TLR9 in the process of MCMV sensing to assure rapid antiviral responses, coordinated with other TLR-dependent and -independent events that are sufficient to establish adaptive immunity.

CCR7 Is Critically Important for Migration of Dendritic Cells in Intestinal Lamina Propria to Mesenteric Lymph Nodes

Although dendritic cells (DCs) located in the small intestinal lamina propria (LP-DCs) migrate to mesenteric lymph nodes (MLNs) constitutively, it is unclear which chemokines regulate their trafficking to MLNs. In this study we report that LP-DCs in unperturbed mice require CCR7 to migrate to MLNs. In vitro, LP-DCs expressing CCR7 migrated toward CCL21, although the LP-DCs appeared morphologically and phenotypically immature. In MLNs, DCs bearing the unique LP-DC phenotype (CD11chighCD8alphaintCD11blowalphaLlowbeta7high and CD11chighCD8alpha-CD11bhighalphaLlowbeta7high) were abundant in wild-type mice, but were markedly fewer in CCL19-, CCL21-Ser-deficient plt/plt mice and were almost absent in CCR7-deficient mice, indicating the critical importance of CCR7 in LP-DC trafficking to MLNs. Interestingly, CCR7+ DCs in MLNs with the unique LP-DC phenotype had numerous vacuoles containing cellular debris in the cytoplasm, although MLN-DCs themselves were poorly phagocytic, suggesting that the debris was derived from the LP, where the LP-DCs ingested apoptotic intestinal epithelial cells (IECs). Consistent with this, LP-DCs ingested IECs vigorously in vitro. By presenting IEC-associated Ag, the LP-DCs also induce T cells to produce IL-4 and IL-10. Collectively, these results strongly suggest that LP-DCs with unique immunomodulatory activities migrate to MLNs in a CCR7-dependent manner to engage in the presentation of IEC-associated Ags acquired in the LP.

Ins and Outs of Dendritic Cells

Dendritic cells (DC) are professional antigen-presenting cells which are strategically positioned at the boundaries between the inner and the outside world, in this way bridging innate and adaptive immunity. DC can initiate T cell responses against microbial pathogens and tumors due to their capacity to stimulate naïve T cells. The development of DC occurs in distinct stages. DC precursors develop in the bone marrow and home to a large variety of tissues. Immature DC capture antigen (Ag) and, following proinflammatory signals, migrate to the lymphoid organs where, after maturation, they present captured Ag to naïve T cells, thereby inducing differentiation of naïve T cells into effector T cells. An important cognate event in the development of cell-mediated immunity is the interaction between CD40 and CD40 ligand. Ligation of CD40 on DC by its ligand results in maturation of the DC. In addition to CD40 ligand (expressed by activated Th cells), inflammatory cytokines, bacterial components or Ag-Ab immune complexes can induce maturation of DC. Maturation of DC is crucial for the priming of efficient T cell responses and is characterized by a decreased Ag processing capacity, an increased cell surface expression of MHC and costimulatory molecules, and rearrangement of cytoskeleton, adhesion molecules, and cytokine receptors. Mature DC migrate from peripheral tissues to secondary lymphoid organs, where T cell priming occurs. DC are not only critical in initiating T cell immunity, they also play a role in the induction of T cell tolerance and the regulation of the type of T cell response that is induced. Here we give an overview of the dendritic cell system.

Upon viral exposure, myeloid and plasmacytoid dendritic cells produce 3 waves of distinct chemokines to recruit immune effectors

Host response to viral infection involves distinct effectors of innate and adaptive immunity, whose mobilization needs to be coordinated to ensure protection. Here we show that influenza virus triggers, in human blood dendritic-cell (DC) subsets (ie, plasmacytoid and myeloid DCs), a coordinated chemokine (CK) secretion program with 3 successive waves. The first one, occurring at early time points (2 to 4 hours), includes CKs potentially attracting effector cells such as neutrophils, cytotoxic T cells, and natural killer (NK) cells (CXCL16, CXCL1, CXCL2, and CXCL3). The second one occurs within 8 to 12 hours and includes CKs attracting effector memory T cells (CXCL8, CCL3, CCL4, CCL5, CXCL9, CXCL10, and CXCL11). The third wave, which occurs after 24 to 48 hours, when DCs have reached the lymphoid organs, includes CCL19, CCL22, and CXCL13, which attract naive T and B lymphocytes. Thus, human blood DC subsets carry a common program of CK production, which allows for a coordinated attraction of the different immune effectors in response to viral infection.

The role of dendritic cell subtypes in the pathophysiology of atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is an inflammatory, immunologically mediated skin disease characterized by a T helper type 2 cell-predominant phenotype initially with additional acquisition of T helper type 1 cell phenotype during the chronic eczematous phase. Compelling evidence presented here suggests that two types of dendritic cells (DC), myeloid DC (mDC) and plasmacytoid DC (pDC), are important in the pathogenesis of AD.

METHODS

We reviewed the current literature and summarized key information about the role of mDC and pDC in the pathogenesis of AD.

RESULTS

Langerhans cells and inflammatory dendritic epidermal cells, which bear the high-affinity receptor for immunoglobulin E on their cell surface, are hypothesized to contribute to the pathogenesis of AD. pDC, Which play an important role in the defence against viral infections, have also been shown to express high-affinity receptor for immunoglobulin E.

CONCLUSION

Immunoglobulin E receptor-bearing mDC and pDC subtypes in the blood and the skin of patients with AD are of critical immunologic importance in the complex pathophysiologic network of AD. Targeting mDC and pDC subtypes may lead to effective new therapies for the management of AD.

Human dendritic cells: potent antigen-presenting cells at the crossroads of innate and adaptive immunity

Dendritic cells (DCs) are specialized, bone marrow-derived leukocytes that are critical to the development of immunity. Investigators have emphasized the role of DCs in initiating adaptive or acquired MHC-restricted, Ag-specific T cell responses. More recent evidence supports important roles for DCs in the onset of innate immunity and peripheral tolerance. Progress in the generation of DCs from defined hemopoietic precursors in vitro has revealed the heterogeneity of these APCs and their attendant divisions of labor. This review will address these developments in an attempt to integrate the activities of different DCs in coordinating innate and adaptive immunity.

Identification of bovine dendritic cell phenotype from bovine peripheral blood

Dendritic cells (DCs) are professional antigen presenting cells, which initiate primary immune responses and also play an important role in the generation of peripheral tolerance. There is no reliable method established for the isolation of bovine peripheral blood DCs, and furthermore, the phenotypes and the functions of bovine DCs are still not fully clear. In the present study, we have attempted to identify bovine peripheral blood DCs by negative-selection. In bovine peripheral blood mononuclear cells (PBMC), we have newly characterized the phenotype of DCs, which is CD11c+/CD172a+. These cells display features of myeloid type DCs. In the thymic medulla, CD11c+/CD172a+ cells were also present and CD1+/CD172a+ cells were additionally detected as a population of DCs. The data suggest that one of the bovine DCs phenotypes from PBMC is derived from myeloid lineages lacking a CD1 molecule, which then drift to several tissues, and that they then may express a CD1 molecule upon their functional differentiation.

T cell priming by tissue-derived dendritic cells: New insights from recent murine studies

Dendritic cells (DCs) act as sentinels in peripheral tissues, continuously scavenging for antigens in their immediate surroundings. Their involvement in T cell responses is generally thought to consist of a linear progression of events, starting with capture of antigen in peripheral tissues such as the skin followed by migration to draining lymphoid organs and MHC-restricted presentation of antigen-derived peptide to induce T cell priming. The role of tissue-derived DCs in the direct priming of immune responses has lately been challenged. It now appears that, at least in some instances, a non-migratory subtype of DCs in the secondary lymphoid tissue presents tissue-derived antigen to T cells. Here, we review recent developments in research on DC function in the priming of immune responses.