Dendritic cell development: multiple pathways to nature's adjuvants

Cutting edge: conventional CD8 alpha+ dendritic cells are generally involved in priming CTL immunity to viruses

Dendritic cells (DCs) play a central role in initiating immune responses. Despite this, there is little understanding how different DC subsets contribute to immunity to different pathogens. CD8alpha(+) DC have been shown to prime immunity to HSV. Whether this very limited capacity of a single DC subset priming CTL immunity is restricted to HSV infection or is a more general property of anti-viral immunity was examined. Here, we show that the CD8alpha(+) DCs are the principal DC subset that initiates CTL immunity to s.c. infection by influenza virus, HSV, and vaccinia virus. This same subset also dominated immunity after i.v. infection with all three viruses, suggesting a similar involvement in other routes of infection. These data highlight the general role played by CD8alpha(+) DCs in CTL priming to viral infection and raises the possibility that this DC subset is specialized for viral immunity.

Benign fibrous histiocytoma with indeterminate cells and eosinophils: collision, differentiation, or involution?

This report describes the clinicopathologic, immunohistochemical, and ultrastructural features of a benign fibrous histiocytoma of 3 years' duration situated on the posterior right arm of a 17-year-old woman. To our knowledge, this is the first published description of an association between the histologic features of benign fibrous histiocytoma with proliferating dermal dendrocytes and solid clusters of indeterminate cells and inflammatory infiltrate containing numerous eosinophils. Cell type identification was confirmed by immunohistochemical demonstration of positivity of indeterminate cells for CD1a and S-100 protein, by absence of Birbeck granules in electron microscopy study, and by positivity of fibroblast-like cells for factor XIIIa and negativity for CD34. Mitosis or cytologically atypical cells were absent. The MIB1-measured proliferative index of the tumor cells was less than 5% in spindle cells and approximately 15% in indeterminate cells. Possible pathogenic pathways are discussed that could account for divergent differentiation or a combination of neoplasms of different lineages.

DCs as targets for vaccine design

The increasingly stringent requirements laid down by regulatory authorities have brought to an end the largely empirical design of vaccines. Vaccines must now be designed rationally, in order that appropriate immune responses are elicited with few or no side effects. The DC plays a pivotal role in determining the type of immune response that ensues following exposure of the host to an Ag. In this review, we identify some of the features and properties of DCs, and how these properties can be exploited in the design of smart vaccines.

Splenic dendritic cell subsets prime and boost CD8 T cells and are involved in the generation of effector CD8 T cells

The ability of the dendritic cell (DC) subsets, CD8alpha+ and CD8alpha- DCs, to initiate a CD8 T cell response or to activate memory CD8 T cells and generate effector CD8 T cells has been controversial. In this study, we analyse the capacity of splenic DC subsets to induce CD8 T cell responses to a CD8 T cell epitope (pb9) of a malaria antigen. The administration of peptide-pulsed CD8alpha- or CD8alpha+ DCs primes and boosts a primed CD8 T cell response against the malaria epitope. In vitro, depletion of CD11c(+) DCs from mouse splenocytes, immunised with recombinant vaccinia virus Ankara (MVA) expressing pb9 epitope, significantly reduced the generation of pb9-specific IFNgamma producing effector CD8 T cells, indicating that splenic DCs are involved in the development of pb9-specific IFNgamma producing effector cells. Taken together, this result shows that both DC subsets have the ability to prime and boost CD8 T cell responses and are involved in the activation of memory CD8 T cells.

Cutting Edge: A possible role for CD4+ thymic macrophages as professional scavengers of apoptotic thymocytes

A vast majority of thymocytes are eliminated during T cell development by apoptosis. However, apoptotic thymocytes are not usually found in the thymus, indicating that apoptotic thymocytes must be eliminated rapidly by scavengers. Although macrophages and dendritic cells are believed to play such role, little is known about scavengers in the thymus. We found that CD4(+)/CD11b(+)/CD11c(-) cells were present in the thymus and that they expressed costimulatory molecules for T cell selection and possessed Ag-presenting activity. Moreover, these CD4(+)/CD11b(+) cells phagocytosed apoptotic thymocytes much more efficiently than thymic CD4(-)/CD11b(+) cells as well as activated peritoneal macrophages. CD4(+)/CD11b(+) cells became larger along with thymus development, while no such change was observed in CD4(-)/CD11b(+) cells. Finally, engulfed nuclei were frequently found in CD4(+)/CD11b(+) cells. These results strongly suggest that thymic CD4(+)/CD11b(+) cells are major scavengers of apoptotic thymocytes.

Evaluation of Myeloid and Lymphoid Dendritic Cells in Peritoneal Fluid in Women with Non-malignant Ovarian Tumors

PROBLEM

Identification of myeloid and lymphoid dendritic cells (DCs) in peritoneal fluid (PF) and peripheral blood (PB) of patients with ovarian pathology.

METHOD OF STUDY

PF and PB were collected from 60 patients who underwent laparoscopy because of non-malignant ovarian tumors. Mononuclear cells were separated by gradient centrifugation. The cell surface antigens were determined by flow cytometry using monoclonal antibodies.

RESULTS

Both myeloid and lymphoid DCs were detected in PF and PB of women with ovarian tumors. The percentage of myeloid DCs was significantly higher in PF than in PB. The concentration of PF myeloid DCs was the highest (P < 0.05) in patients with dermoid cysts (0.67 x 10(6)/mL PF) in comparison with the other studied groups, excluding patients with normal pelvis.

CONCLUSIONS

Domination of myeloid and not lymphoid cells in PF may support the hypothesis that local PF immune disturbances may play a role in some non-malignant ovarian pathology.

Antigen presentation by murine dendritic cells is nuclear factor-kappa B dependent both in vitro and in vivo

Antigen presentation is a key rate-limiting step in the immune response. Dendritic cells (DCs) have been reported to be the most potent antigen-presenting cells for naïve T cells, but little is known about the biochemical pathways that regulate this function. We here demonstrate that mature murine DC can be infected with adenovirus at high efficiency (>95%) and that an adenovirus transferring the endogenous inhibitor IkappaBalpha blocks nuclear factor-kappa B (NF-kappaB) function in murine DC. This result indicates that antigen presentation in the mixed leucocyte reaction is NF-kappaB dependent, confirming data with human DC in vitro. However, the importance of this finding depends on verifying that this is true also in vivo. Using delayed type hypersensitivity with allogeneic cells, we show that NF-kappaB inhibition had a marked immunosuppressive effect in vivo. These results thus establish NF-kappaB as an effective target for blocking DC antigen presentation and hence inhibiting T-cell-dependent immune responses. This finding has potential implications for the development of therapeutic agents for use in various pathological conditions of the immune system, including allergy and autoimmunity, and also in transplantation.

Novel expression of vascular endothelial growth factor receptor (VEGFR)-3 and VEGF-C on corneal dendritic cells

Vascular endothelial growth factor-3 (VEGFR-3) plays a critical role in embryonic cardiovascular development and is thought to be expressed exclusively on the lymphatic endothelium, high endothelial venules, and rarely on adult vascular endothelium. Recent evidence also suggests expression of VEGFR-3 on some tumor-associated macrophages. We have studied the expression of VEGFR-3, its ligand VEGF-C and the co-receptor neuropilin-2, in normal and inflamed corneas and characterized the phenotype and distribution of VEGFR-3(+) cells. Our data demonstrate, for the first time, the expression of VEGFR-3 on corneal dendritic cells (DC) and its up-regulation in inflammation. VEGFR-3(+) DC are CD11c(+)CD45(+)CD11b(+), and are mostly major histocompatibility (MHC) class II(-)CD80(-)CD86(-), indicating immature DC of a monocytic lineage. During inflammation, there is rapid increase in the number of VEGFR-3(+) DC in the cornea associated with heightened membranous expression as compared to a mostly intracellular expression in uninflamed tissue. VEGFR-3(+) DC in normal corneas are VEGF-C(-)neuropilin-2(-), but express VEGF-C in inflammation. Interestingly, similar cells are absent both in the normal and inflamed skin. These data demonstrate, for the first time, the expression of VEGFR-3 and VEGF-C on tissue DC, which implicate a novel potential relationship between lymphangiogenesis and leukocyte trafficking in the eye.

A comparison of the phenotype of dendritic cells derived from discrete Peyer's patch macrophages of non-infected and Toxoplasma gondii infected mice

A comparison of the expression of surface membrane antigens between dendritic cells (DC) derived from Peyer's patch macrophages (DPP-DC) of non-infected and Toxoplasma gondii (T. gondii) infected mice was performed. C57BL/6J mice aged 6-8 weeks of both sexes were infected orally with a 0.5 ml suspension containing 2 x 10(4) bradyzoites of the Beverley strain of T. gondii, sacrificed on day 8 and DC generated using discrete Peyer's patch macrophages (DPP-Mø) as progenitor cells. When a comparison of the expression of surface membrane antigens between the antigen presenting cells (APC) obtained from discrete Peyer's patches of non-infected and T. gondii infected mice was carried out, no significant differences were observed in the macrophage progenitor and DC populations expression of F4/80, DEC-205, CD11c, CD80 (B7-1) and CD34. However, a significant decrease in MHC class II antigen levels and a down regulation of the co-stimulatory molecule CD86 (B7-2) were noted. B7-1 appeared to be the dominant co-stimulatory ligand, whereas B7-2, which was down regulated during T. gondii infection, had a weak expression. Taken together, these results may help clarify the role of DC in the complex network regulating surface membrane antigens, as well as, their capacity for antigen uptake, processing and presentation during toxoplasmosis.

Regulation of MHC class I transport in human dendritic cells and the dendritic-like cell line KG-1

Dendritic cells (DCs) progress through distinct maturational phases; immature DCs capture Ag while mature DCs are optimized for Ag presentation. Proper control of immunity requires regulated compartmentalization of MHC class II molecules. We report that DCs also regulate MHC class I trafficking throughout maturation. Although mature human DCs express high levels of surface MHC class I, immature DCs exhibit lower surface levels while retaining MHC class I-peptide complexes in the Golgi. A cell line, KG-1, behaves similarly. We confirm the similarity of KG-1 to DCs by demonstrating its capacity to present exogenous Ags in an MHC class I-restricted fashion to CD8(+) T cell hybridomas, a phenomenon called cross-presentation. Biochemical characterization of MHC class I trafficking throughout maturation showed that, in early KG-1 dendritic-like cells, surface arrival of MHC class I-peptide complexes is delayed by their retention in the Golgi. In mature dendritic-like cells, these complexes relocate to the surface and their stability increases, concomitant with up-regulation of costimulatory molecules. Maturation induces qualitative changes in the MHC class I-associated peptide repertoire demonstrated by increased thermostability. The differential processing of MHC class I throughout maturation may prevent premature immune activation while promoting T cell responses in lymph nodes to Ags acquired at sites of inflammation.

Mucosal CD8alpha+ DC, with a plasmacytoid phenotype, induce differentiation and support function of T cells with regulatory properties

Repetitive stimulation of naïve T cells by immature splenic dendritic cells (DC) can result in the differentiation of T-cell lines with regulatory properties. In the present study we identified a population of DC in the mucosae that exhibit the plasmacytoid phenotype, secrete interferon-alpha (IFN-alpha) following stimulation with oligodeoxynucleotides containing certain cytosine-phosphate-guanosine (CpG) motifs and can differentiate naïve T cells into cells that exhibit regulatory properties. Although these DC appear to be present in both spleen and mesenteric lymph nodes (MLN), only CpG-matured DC from the MLN (but not the spleen) were able to differentiate naïve T cells into T regulatory 1-like cells with regulatory properties. The activity of these DC failed to sustain robust T-cell proliferation and thereby enhanced the suppressive efficacy of CD4+ CD25+ T regulatory cells. These DC are the major CD8alpha+ DC population in the Peyer's patches (PP). Given their significant presence in mucosal tissue, we propose that these DC may provide a mechanistic basis for the homeostatic regulation in the gut by eliciting regulatory cell suppressor function and poorly supporting T helper cell proliferation at a site of high antigenic stimulation like the intestine.

Peritoneal dialysis solutions inhibit the differentiation and maturation of human monocyte-derived dendritic cells: effect of lactate and glucose-degradation products

Peritoneal dialysis (PD) is a well-established therapy for end-stage renal failure, but its efficiency is limited by recurrent peritonitis. As PD solutions impair local inflammatory responses within the peritoneal cavity, we have analyzed their influence on the in vitro maturation of human monocyte-derived dendritic cells (MDDC). Evaluation of MDDC maturation parameters [expression of adhesion and costimulatory molecules, receptor-mediated endocytosis, allogeneic T cell activation, production of tumor necrosis factor alpha, interleukin (IL)-6 and IL-12 p70, and nuclear factor (NF)-kappaB activation] revealed that currently used PD solutions differentially inhibit the lipopolysaccharide (LPS)-induced maturation of MDDC, an inhibition that correlated with their ability to impair the LPS-stimulated NF-kappaB activation. Evaluation of PD components revealed that sodium lactate and glucose-degradation products impaired the acquisition of maturation parameters and NF-kappaB activation in a dose-dependent manner. Moreover, PD solutions impaired monocyte-MDDC differentiation, inhibiting the acquisition of DC markers such as CD1a and DC-specific intercellular adhesion molecule-3 grabbing nonintegrin (CD209). These findings have important implications for the initiation of immune responses under high lactate conditions, such as those occurring within tumor tissues or after macrophage activation.

Porcine antigen presenting cells produce soluble adjuvants that stimulate B cells within and across the species

Interactions between porcine antigen presenting cells (pAPCs) and host lymphocytes may be important in cellular and humoral rejection of porcine organ xenografts. To investigate the role of pAPCs in the activation of xenogeneic lymphocytes, porcine bone marrow cells were stimulated using porcine GM-CSF with or without porcine IL-4 to generate populations of pAPCs that had phenotypic characteristics of myeloid dendritic cells. These bone marrow-derived pAPCs were weak stimulators of xenogeneic (mouse and human) T cells in vitro but induced primary B-cell proliferation and augmented CD40-induced B-cell proliferation. Inoculation of mice with small numbers of pAPCs resulted in localized expansion of lymph node B cells. The mitogenic effect on xenogeneic B cells could be reproduced by medium in which pAPCs had been cultured, implicating one or more soluble products. In blocking experiments IL-12, IL-6, and IL-10 were found not to contribute to the mitogenic effect of pAPC medium. In contrast, pIFN was found to be capable of augmenting CD40-induced proliferation of xenogeneic B-cell proliferation but did not act as a B-cell mitogen. We conclude that myeloid APCs from the pig produce soluble factors that are capable of acting as primary mitogens for xenogeneic B cells as well as augmenting additional B-cell activating stimuli. This direct interaction between porcine APCs and xenogeneic B cells may serve as an important adjuvant for the stimulation of humoral immunity to porcine xenografts.

Monocyte-derived CD1a+ dendritic cells generated in two different culture systems: immunophenotypic and functional comparison

Previous studies demonstrated that CD1a+ dendritic cells (DCs) could not be prepared ex vivo without using fetal calf serum (FCS). Recently, we developed a method of using heparin to induce differentiation of human monocytes into CD1a+ DCs without using FCS. In order to determine the potential clinical applicability of heparin-induced CD1a+ DCs, we conducted this study to compare both types of CD1a+ DCs, immunophenotypically and functionally. Our results showed that the expression of CD1a on heparin-DCs was lower than that on FCS-DCs. Both types of DCs expressed similar levels of CD11c, HLA-DR, CD40, CD83, CD80 and CD86 before and after lipopolysaccharide stimulation. Immature heparin-DCs and FCS-DCs had similar phagocytic activities. Heparin-DCs consistently secreted higher interleukin-10 (IL-10) and lesser IL-12 than FCS-DCs after activation. Mature heparin-DCs were slightly more active than mature FCS-DCs in stimulating the proliferation of allogeneic CD4+ T cells. Both types of mature CD1a+ DCs primed the naïve CD4+ T cells to produce large amount of interferon-gamma (IFN-gamma). However, naïve CD4+ T cells stimulated with FCS-DCs produced more IFN-gamma, while the naïve CD4+ T cells stimulated with heparin-DCs produced more IL-5. The results indicate that both types of CD1a+ DCs do not have identical function in the priming of CD4+ T cells and have minor difference in immunophenotypes.

Phenotype and function of murine discrete Peyer's patch macrophage derived - dendritic cells

The phenotype and function of peritoneal cavity macrophage-derived dendritic cells (PEC-DC) was previously reported. In this study we have gone further in using our established culture system to generated discrete Peyer's patch dendritic cells (DPP-DC) from murine discrete Peyer's patch macrophages (DPP-Mø), following stimulation with granulocyte macrophage colony stimulating factor (GM-CSF) plus interleukin 4 (IL-4) for 7 days. DPP-Mø from murine small intestines were obtained by mechanical disruption of discrete Peyer's patches (DPP), followed by metrizamide density gradient centrifugation to remove Peyer's patch resident DC and debri, after which an overnight adherent step in tissue culture medium was carried out for macrophage enrichment. Characterization of the generated DPP-DC was carried out using well-established criteria of morphology, expression of membrane antigens and capacity for antigen presentation. Dendritic cells expressed DEC-205, F4/80 and CD34 at high levels, but exhibited very low CD11c levels. They were shown to present soluble protein antigen to CD3(+) spleen T cells. A comparison of the surface antigen expression in the progenitor DPP-Mø population and the generated DPP-DC showed a significant decrease in MHC class II levels and a marked down regulation of the co-stimulatory molecule CD86 (B7-2). High expression of the haemopoietic progenitor marker CD34 indicates that the generated DC, possess a haemopoietic rather than myeloid origin. Taken together, these results may provide a better understanding of the complex network regulating mucosal immune responses.

The transcription factor Spi-B is expressed in plasmacytoid DC precursors and inhibits T-, B-, and NK-cell development

Human plasmacytoid dendritic cells (pDCs), also called type 2 dendritic cell precursors or natural interferon (IFN)-producing cells, represent a cell type with distinctive phenotypic and functional features. They are present in the thymus and probably share a common precursor with T and natural killer (NK) cells. In an effort to identify genes that control pDC development we searched for genes of which the expression is restricted to human pDC using a cDNA subtraction technique with activated monocyte-derived DCs (Mo-DCs) as competitor. We identified the transcription factor Spi-B to be expressed in pDCs but not in Mo-DCs. Spi-B expression in pDCs was maintained on in vitro maturation of pDCs. Spi-B was expressed in early CD34(+)CD38(-) hematopoietic progenitors and in CD34(+)CD1a(-) thymic precursors. Spi-B expression is down-regulated when uncommitted CD34(+)CD1a(-) thymic precursors differentiate into committed CD34(+)CD1a(+) pre-T cells. Overexpression of Spi-B in hematopoietic progenitor cells resulted in inhibition of development of T cells both in vitro and in vivo. In addition, development of progenitor cells into B and NK cells in vitro was also inhibited by Spi-B overexpression. Our results indicate that Spi-B is involved in the control of pDC development by limiting the capacity of progenitor cells to develop into other lymphoid lineages.

Leukemic dendritic cells: potential for therapy and insights towards immune escape by leukemic blasts

Dendritic cells (DCs) are a system of potent antigen-presenting cells (APCs) specialized to initiate primary immune responses. DCs are considered important elements in the induction of specific antitumor cytotoxic effectors. At present, because of potential therapeutic implications, the critical role of DCs in cancer patients is under intensive investigation. Interactions between DCs and acute myeloid leukemia cells represent an attractive model for the study of DC physiology. Moreover, DCs can be a valuable therapeutic tool for the adjuvant treatment of leukemic patients. However, DC subsets in vivo may also be affected by leukemogenesis and may contribute to the escape of leukemia from immune control. The aim of this review is to shed further light on this paradoxical picture where the line between immune tolerance and immune defense is narrow.

Polybrene and interleukin-4: two opposing factors for retroviral transduction of bone-marrow-derived dendritic cells

BACKGROUND

Gene transfer using retroviral transduction offers the advantage of long-term transgene expression in developing strategies that use dendritic cells (DCs) for immunotherapy. The goal of this study was to infect DCs in an immature state in order to take advantage of their proliferating and tolerogenic potential.

METHODS

Immature DCs were generated from murine bone marrow (BM) using either GM-CSF alone or GM-CSF plus IL-4. The cells were transduced directly with retroviral supernatants or by co-culture with the GP + E-86 retroviral packaging cell line in the presence of two different cationic polymers: polybrene and protamine sulfate. Phenotypic and functional characterization of the transduced cells were then performed.

RESULTS

Our results show a low efficiency of retroviral infection of DCs in the presence of polybrene. This cationic polymer was found to be directly cytotoxic to murine DCs and thus favored the growth of contaminating macrophages. This effect was not observed using protamine sulfate. Furthermore, stimulation by IL-4 early in the culture increased DC differentiation, proliferation and transduction. However, we found that DCs generated in GM-CSF plus IL-4 presented a more mature phenotype with an enhanced allogeneic stimulating activity. Finally, we showed that DCs themselves down-regulated transgene expression in the co-cultured packaging cell line in a promoter-dependent manner.

CONCLUSIONS

We have defined optimal conditions to generate and transduce murine BM-derived DCs. This included: the use of protamine sulfate during exposure to retroviral infectious supernatant and the addition of IL-4 at an early stage of the culture. Nevertheless, this cytokine also induced DC maturation. These findings have potential implications in experimental gene therapy.

Mouse CD11c(+) B220(+) Gr1(+) plasmacytoid dendritic cells develop independently of the T-cell lineage

The developmental origin of dendritic cells (DCs) is controversial. In the mouse CD8alpha(+) and CD8alpha(-) DC subsets are often considered to be of lymphoid and myeloid origin respectively, although evidence on this point is conflicting. Very recently a novel CD11c(+) B220(+) DC subset has been identified that appears to be the murine counterpart to interferon alpha (IFNalpha)-producing human plasmacytoid DCs (PDCs). We show here that CD11c(+) B220(+) mouse PDCs, like human PDCs, are present in the thymus and express T lineage markers such as CD8alpha and CD4. However, the intrathymic development of PDCs can be completely dissociated from immature T lineage cells in mixed chimeras established with bone marrow cells from mice deficient for either Notch-1 or T-cell factor 1, two independent mutations that severely block early T-cell development. Our data indicate that thymic PDCs do not arise from a bipotential T/DC precursor.

Lineage plasticity and commitment in T-cell development

The earliest stages of intrathymic T-cell development include not only the acquisition of T-cell characteristics but also programmed loss of potentials for B, natural killer, and dendritic cell development. Evidence from genetics and cell-transfer studies suggests an order and some components of the mechanisms involved in loss of these options, but some of the interpretations conflict. The conflicts can be resolved by a view that postulates overlapping windows of developmental opportunity and individual mechanisms regulating progression along each pathway. This view is consistent with molecular evidence for the expression patterns of positive regulators of non-T developmental pathways, SCL, PU.1 and Id2, in early thymocytes. To some extent, overexpression of such regulators redirects thymocyte development in vitro. Specific commitment functions may normally terminate this developmental plasticity. Both PU.1 overexpression and stimulation of ectopically expressed growth factor receptors can perturb T- and myeloid/dendritic-cell divergence, but only in permissive stages. A cell-line system that approximates DN3-stage thymocytes reveals that PU.1 can alter specification even in a homogeneous population. However, the response of the population to PU.1 is sharply discontinuous. These studies show a critical role for regulatory context in restricting plasticity, which is probably maintained by interacting transcription factor networks.

CD40 ligand and CTLA-4 are reciprocally regulated in the Th1 cell proliferative response sustained by CD8(+) dendritic cells

Subsets of murine dendritic cells (DCs) from the spleen differ in their ability to induce proliferative responses in both primary and secondary CD4(+) T cells. Recent evidence indicates that lymphoid-related CD8(+) DCs fail to provide appropriate signals to freshly isolated secondary CD4(+) T cells to sustain their proliferation in vitro. In the present study, we examined peptide-pulsed CD8(-) and CD8(+) DCs for ability to stimulate Th1 and Th2 cell clones with the same Ag specificity. Defective ability to induce proliferation was selectively shown by CD8(+) DCs presenting Ag to the Th1 clone. The deficiency in CD8(+) DCs was overcome by CD40 triggering before peptide pulsing. When exposed to CD8(+) DCs in the absence of CD40 activation, the Th1 clone expressed low levels of CD40 ligand and high levels of surface CTLA-4. Neutralization of CTLA-4 during the DC/T cell coculture resulted in increased CD40 ligand expression and proliferation of T cells. Remarkably, the activation of CD40 on DCs under conditions that would increase Th1 cell proliferation, also resulted in down-regulation of surface CTLA-4. These results confirm differential effects of CD8(+) and CD8(-) DCs in the stimulation of Ag-primed Th cells. In addition, they suggest that reciprocal regulation of CD40 ligand and CTLA-4 expression occurs in Th1 cells exposed to CD8(+) DCs.

Interdigitating dendritic cell sarcoma of the spleen: report of a case with a review of the literature

Interdigitating dendritic cell sarcoma is an extremely rare neoplasm that mainly occurs in the lymph nodes. We report a case of interdigitating dendritic cell sarcoma arising from the spleen, a previously unreported site for interdigitating dendritic cell sarcoma. An 87-year-old woman, visiting Ashigara Hospital with complaints of palpitation and dyspnea, was found to have pancytopenia and low proteinemia. Abdominal ultrasonography and CT scanning demonstrated severe splenomegaly with heterogeneous enhancement. She received a splenectomy under the clinical diagnosis of a splenic tumor. Grossly, the spleen was markedly enlarged, with confluent massive nodules. Microscopically, the normal architecture was effaced with diffuse proliferation of large pleomorphic cells arrayed in a somewhat sheet-like pattern. Erythrophagocytosis was commonly observed. Immunohistochemical studies showed that the tumor cells were positive for S-100 protein, fascin, vimentin, and CD68, but uniformly negative for CD45, B- and T-cell markers, CD1a, CD30, complement receptors, CD34, Factor VIII, HMB-45, and lysozyme. Ultrastructurally, the tumor cells possessed complex interdigitating cytoplasmic dendritic processes. Birbeck granules were absent. Based on these findings, the present case was diagnosed as interdigitating dendritic cell sarcoma. The patient died of multiple liver metastases 3 months postoperatively.

Dendritic cells: a specialized complex system of antigen presenting cells

The dendritic cell (DC) network is a specialized system for presenting antigen to naive or quiescent T cells, and consequently plays a central role in the induction of T cell and B cell immunity in vivo. Despite considerable achievements in the last ten years, in our understanding of how DC induce and regulate immune responses, much remains to be learned about this complex system of cells. The history and current status of DC termed "directors of the immune system orchestra" is reviewed. The present understanding of DC cell biology, function and use, taking into account their complexity is discussed.

Localized and disseminated histiocytic sarcoma of dendritic cell origin in dogs

Canine histiocytic proliferative disorders include a wide spectrum of diseases characterized by different biologic behaviors. The etiology and pathogenesis of these diseases are largely unknown. The clinicopathologic, morphologic and immunophenotypic characteristics of canine localized and disseminated histiocytic sarcoma were examined in 39 dogs. Rottweilers, Bernese Mountain Dogs, and retrievers were most commonly affected (79%). Localized histiocytic sarcomas (19 dogs) arose from a single site, and metastatic lesions were observed in draining lymph nodes. Predilection sites were subcutis and underlying tissues on extremities, but tumors occurred in other locations, including spleen, lung, brain, nasal cavity, and bone marrow. Disseminated histiocytic sarcomas (20 dogs), a multisystem disease previously described as malignant histiocytosis, primarily affected spleen, lungs, bone marrow, liver, and lymph nodes. Both localized and disseminated canine histiocytic sarcomas were composed of pleomorphic tumor cell populations. CD1+, CD4-, CD11c+, CD11d-, MHC II+, ICAM-1 +, Thy-1 +/- tumor cells were identified in all snap-frozen samples (31 dogs). This phenotype is characteristic for myeloid dendritic antigen-presenting cell lineage. Hence, canine localized and disseminated histiocytic sarcomas are likely myeloid dendritic cell sarcomas. Dendritic antigen-presenting cells are a heterogeneous cell population with regards to their ontogeny, phenotype, function, and localization. The exact sublineage of the proliferating dendritic antigen-presenting cells involved in canine histiocytic sarcomas remains to be determined. Phenotypic analysis of formalin-fixed tissues from eight dogs was limited by available markers. Morphologic features and the phenotype CD18+, CD3-, and CD79a- were the most useful criteria to indicate likely histiocytic origin.

Development of thymic and splenic dendritic cell populations from different hemopoietic precursors

The antigen-presenting dendritic cells (DCs) found in mouse lymphoid tissues are heterogeneous. Several types of DCs have been identified on the basis of the expression of different surface molecules, including CD4, CD8alpha, and DEC-205. Previous studies by the authors showed that the mouse intrathymic lymphoid-restricted precursors (lin(-)c-kit(+)Thy-1(low)CD4(low)) can produce DCs in the thymus and spleen upon intravenous transfer, suggesting a lymphoid origin of these DCs. In the current study, the potential for DC production by the newly identified bone marrow (BM) common lymphoid precursors (CLPs), common myeloid precursors (CMPs), and committed granulocyte and macrophage precursors was examined. It was found that both the lymphoid and the myeloid precursors had the potential to produce DCs. All the different DC populations identified in mouse thymus and spleen could be produced by all these precursor populations. However, CLPs produced predominantly the CD4(-)CD8alpha(+) DCs, whereas CMPs produced similar numbers of CD4(-)CD8alpha(+) and CD4(+)CD8alpha(-) DCs, although at different peak times. On a per cell basis, the CLPs were more potent than the CMPs at DC production, but this may have been compensated for by an excess of CMPs over CLPs in BM. Overall, this study shows that the expression of CD8alpha does not delineate the hemopoietic precursor origin of DCs, and the nature of the early precursors may bias but does not dictate the phenotype of the DC product.

IL-10 induces CCR6 expression during Langerhans cell development while IL-4 and IFN-gamma suppress it

Immune responses are initiated by dendritic cells (DC) that form a network comprising different populations. In particular, Langerhans cells (LC) appear as a unique population of cells colonizing epithelial surfaces. We have recently shown that macrophage-inflammatory protein-3alpha/CCL20, a chemokine secreted by epithelial cells, induces the selective migration of LC among DC populations. In this study, we investigated the effects of cytokines on the expression of the CCL20 receptor, CCR6, during differentiation of LC. We found that both IL-4 and IFN-gamma blocked the expression of CCR6 and CCL20 responsiveness at different stages of LC development. The effect of IL-4 was reversible and most likely due to the transient blockade of LC differentiation. In contrast, IFN-gamma-induced CCR6 loss was irreversible and was concomitant to the induction of DC maturation. When other cytokines involved in DC and T cell differentiation were tested, we found that IL-10, unlike IL-4 and IFN-gamma, maintained CCR6 expression. The effect of IL-10 was reversible and upon IL-10 withdrawn, CCR6 was lost concomitantly to final LC differentiation. In addition, IL-10 induced the expression of CCR6 and responsiveness to CCL20 in differentiated monocytes that preserve their ability to differentiate into mature DC. Finally, TGF-beta, which induces LC differentiation, did not alter early CCR6 expression, but triggered its irreversible down-regulation, in parallel to terminal LC differentiation. Taken together, these results suggest that the recruitment of LC at epithelial surface might be suppressed during Th1 and Th2 immune responses, and amplified during regulatory immune responses involving IL-10 and TGF-beta.

Molecular cloning of F4/80-like-receptor, a seven-span membrane protein expressed differentially by dendritic cell and monocyte-macrophage subpopulations

A novel dendritic cell (DC) surface molecule termed F4/80-like-receptor (FIRE) has been selected based on its differential expression between DC subsets. The gene encoding FIRE has been cloned and sequenced, and mAbs specific for FIRE have been produced. FIRE is a seven-transmembrane-spanning molecule with two epidermal growth factor-like domains in the extracellular region. It is a novel member of the epidermal growth factor/transmembrane-7 protein subfamily and shows similarity to the macrophage marker F4/80. FIRE is expressed by CD8- DC, but not by CD8+ DC, and it is down-regulated on DC activation. It is expressed by blood monocytes and by some tissue macrophages, but not by most macrophage cell lines or by lymphoid cells. FIRE is a useful marker of myeloid cells with a DC developmental potential.

Extracellular signal-regulated protein kinase signaling pathway negatively regulates the phenotypic and functional maturation of monocyte-derived human dendritic cells

Dendritic cells (DC) are highly specialized antigen-presenting cells that on activation by inflammatory stimuli (eg, tumor necrosis factor alpha [TNF-alpha] and interleukin-1beta [IL-1beta]) or infectious agents (eg, lipopolysaccharide [LPS]), mature and migrate into lymphoid organs. During maturation, DC acquire the capacity to prime and polarize resting naive T lymphocytes. Maturation of monocyte-derived DC (MDDC) is inhibited by the p38 mitogen-activated protein kinase (MAPK) inhibitor SB203580. This study found that in the presence of the mitogen-activated protein kinase kinase 1-extracellular signal-regulated kinase (ERK) inhibitors PD98059 or U0126, TNF-alpha- and LPS-induced phenotypic and functional maturation is enhanced. ERK pathway inhibitors increased expression of major histocompatibility complex and costimulatory molecules; loss of mannose-receptor-mediated endocytic activity; nuclear factor-kappaB DNA-binding activity; release of IL-12 p40; and allogeneic T-cell proliferation induced by LPS or TNF-alpha. Moreover, PD98059 and U0126 enhanced LPS-triggered production of IL-12 p70. In agreement with the effect of ERK inhibitors, maturation of MDDC was delayed in the presence of serum, an effect that was reversed by U0126. These results indicate that the ERK and p38 MAPK signaling pathways differentially regulate maturation of MDDC and suggest that their relative levels of activation might modulate the initial commitment of naive T-helper (Th) cells toward Th1 or Th2 subsets. The findings also suggest that maturation of MDDC might be pharmacologically modified by altering the relative levels of activation of both intracellular signaling routes.

Molecular cloning of a C-type lectin superfamily protein differentially expressed by CD8alpha(-) splenic dendritic cells

Dendritic cells (DC) are potent antigen presenting cells that activate naive T cells. It is becoming increasingly clear that DC are not a homogeneous cell population, but comprise different subpopulations that differ in ontogeny and function. To further the molecular characterisation of DC, we screened for genes that were differentially expressed amongst DC subsets and could therefore give insight into their varying biological functions. Using Representational Difference Analysis (RDA) we identified a gene (CIRE) that is expressed at higher levels in the myeloid-related CD8alpha(-) DC than in the lymphoid-related CD8alpha(+) DC. CIRE is a 238 amino acid type II membrane protein, of approximately 33 kDa in size, whose extracellular region contains a C-type lectin domain. Northern blot analysis revealed that CIRE is almost exclusively expressed in DC and was not detected in organs such as heart, brain, kidney, liver, and thymus. T cells failed to express message for CIRE, whilst B cells expressed very low levels. These data here further substantiated by Northern blot analysis of 18 cell lines of various origins (myeloid, macrophage, B and T cell) where only one cell line, which was of myeloid origin and could give rise to DC, expressed mRNA for CIRE. Semi-quantitative RT-PCR suggested that CIRE is down-regulated upon activation. CIRE shares 57% identity with human DC-SIGN, a molecule that has been shown to be the ligand of ICAM-3 and that is also a receptor that binds HIV and facilitates trans-infection of T cells.

Extinguishing maternal immune responses during pregnancy: implications for immunosuppression

Mammals owe their existence to immunosuppressive processes that prevent fetal rejection in utero. Blocking tryptophan catabolism during murine pregnancy allows maternal T cells to provoke fetal allograft rejection. Cells expressing indoleamine 2,3-dioxygenase (IDO), which catabolizes tryptophan, prevent T cell cycle progression and enhance activation induced T cell death. Here, we discuss the role of cells expressing IDO in regulating maternal T cell immunity during pregnancy and consider whether this mechanism might contribute to immunological discrimination by promoting T cell tolerance in other circumstances.

Fetal liver myelopoiesis occurs through distinct, prospectively isolatable progenitor subsets

Hematopoietic fate maps in the developing mouse embryo remain imprecise. Definitive, adult-type hematopoiesis first appears in the fetal liver, then progresses to the spleen and bone marrow. Clonogenic common lymphoid progenitors and clonogenic common myeloid progenitors (CMPs) in adult mouse bone marrow that give rise to all lymphoid and myeloid lineages, respectively, have recently been identified. Here it is shown that myelopoiesis in the fetal liver similarly proceeds through a CMP equivalent. Fetal liver CMPs give rise to megakaryocyte-erythrocyte-restricted progenitors (MEPs) and granulocyte-monocyte-restricted progenitors (GMPs) that can also be prospectively isolated by cell surface phenotype. MEPs and GMPs generate mutually exclusive cell types in clonogenic colony assays and in transplantation experiments, suggesting that the lineage restriction observed within each progenitor subset is absolute under normal conditions. Purified progenitor populations were used to analyze expression profiles of various hematopoiesis-related genes. Expression patterns closely matched those of the adult counterpart populations. These results suggest that adult hematopoietic hierarchies are determined early in the development of the definitive immune system and suggest that the molecular mechanisms underlying cell fate decisions within the myeloerythroid lineages are conserved from embryo to adult. (Blood. 2001;98:627-635)

Dendritic cells (DCs) in rheumatoid arthritis (RA): progenitor cells and soluble factors contained in RA synovial fluid yield a subset of myeloid DCs that preferentially activate Th1 inflammatory-type responses

There is evidence that mature dendritic cells (DCs) present in the rheumatoid arthritis (RA) joint mediate immunopathology in RA. In this study, we indicate that early myeloid progenitors for DCs and DC growth factors existing in RA synovial fluid (SF) are also likely participants in the RA disease process. A fraction of cells lacking markers associated with mature DCs or DC precursors and enriched in CD34(negative) myeloid progenitors was isolated from RA SF. These cells proliferated extensively when cultured in vitro with cytokines that promote the growth of myeloid DCs (GM-CSF/TNF/stem cell factor/IL-4) and, to a lesser degree, when cultured with monocyte/granulocyte-restricted growth factors (M-CSF/GM-CSF). Mature DCs derived from RA SF progenitors with CD14-DC cytokines known to be prevalent in the inflamed RA joint (GM-CSF/TNF/stem cell factor/IL-13) were potent stimulators of allogeneic T cells and inflammatory-type Th1 responses and included CD14-DC subtypes. Cell-free RA SF facilitated DC maturation from myeloid progenitors, providing direct evidence that the inflamed RA joint environment instructs DC growth. Enhanced development of CD14-derived DCs was correlated with the presence of soluble TNFR (p55), raising the possibility that soluble TNFR also regulate CD14-derived DC growth in vivo. SF from patients with osteoarthritis contained neither myeloid DC progenitors nor DC growth factors. The existence of DC progenitors and myeloid DC growth factors in RA SF supports the concept that RA SF may be a reservoir for joint-associated DCs and reveals a compelling mechanism for the amplification and perpetuation of DC-driven responses in the RA joint, including inflammatory-type Th1 responses.

The dendritic cell populations of mouse lymph nodes

The dendritic cells (DC) of mouse lymph nodes (LN) were isolated, analyzed for surface markers, and compared with those of spleen. Low to moderate staining of LN DC for CD4 and low staining for CD8 was shown to be attributable to pickup of these markers from T cells. Excluding this artifact, five LN DC subsets could be delineated. They included the three populations found in spleen (CD4(+)8(-)DEC-205(-), CD4(-)8(-)DEC-205(-), CD4(-)8(+)DEC-205(+)), although the CD4-expressing DC were of low incidence. LN DC included two additional populations, characterized by relatively low expression of CD8 but moderate or high expression of DEC-205. Both appeared among the DC migrating out of skin into LN, but only one was restricted to skin-draining LN and was identified as the mature form of epidermal Langerhans cells (LC). The putative LC-derived DC displayed the following properties: large size; high levels of class II MHC, which persisted to some extent even in CIITA null mice; expression of very high levels of DEC-205 and of CD40; expression of many myeloid surface markers; and no expression of CD4 and only low to moderate expression of CD8. The putative LC-derived DC among skin emigrants and in LN also showed strong intracellular staining of langerin.

Dendritic cell potentials of early lymphoid and myeloid progenitors

It has been proposed that there are at least 2 classes of dendritic cells (DCs), CD8alpha(+) DCs derived from the lymphoid lineage and CD8alpha(-) DCs derived from the myeloid lineage. Here, the abilities of lymphoid- and myeloid-restricted progenitors to generate DCs are compared, and their overall contributions to the DC compartment are evaluated. It has previously been shown that primitive myeloid-committed progenitors (common myeloid progenitors [CMPs]) are efficient precursors of both CD8alpha(+) and CD8alpha(-) DCs in vivo. Here it is shown that the earliest lymphoid-committed progenitors (common lymphoid progenitors [CLPs]) and CMPs and their progeny granulocyte-macrophage progenitors (GMPs) can give rise to functional DCs in vitro and in vivo. CLPs are more efficient in generating DCs than their T-lineage descendants, the early thymocyte progenitors and pro-T cells, and CMPs are more efficient DC precursors than the descendant GMPs, whereas pro-B cells and megakaryocyte-erythrocyte progenitors are incapable of generating DCs. Thus, DC developmental potential is preserved during T- but not B-lymphoid differentiation from CLP and during granulocyte-macrophage but not megakaryocyte-erythrocyte development from CMP. In vivo reconstitution experiments show that CLPs and CMPs can reconstitute CD8alpha(+) and CD8alpha(-) DCs with similar efficiency on a per cell basis. However, CMPs are 10-fold more numerous than CLPs, suggesting that at steady state, CLPs provide only a minority of splenic DCs and approximately half the DCs in thymus, whereas most DCs, including CD8alpha(+) and CD8alpha(-) subtypes, are of myeloid origin. (Blood. 2001;97:3333-3341)

Dendritic cell development from common myeloid progenitors

Dendritic cells (DCs) are professional antigen-presenting cells which both initiate adaptive immune responses and control tolerance to self-antigens. It has been suggested that these different effects on responder cells depend on subsets of DCs arising from either myeloid or lymphoid hematopoietic origins. In this model, CD8 alpha+ Mac-1- DCs are supposed to be of lymphoid while CD8 alpha- Mac-1+ DCs are supposed to be of myeloid origin. Here we summarize our findings that both CD8 alpha+ and CD8 alpha- DCs can arise from clonogenic common myeloid progenitors (CMPs) in both thymus and spleen. Therefore CD8 alpha expression DCs does not indicate a lymphoid origin and differences among CD8 alpha+ and CD8 alpha- DCs might rather reflect maturation status than ontogeny. On the basis of transplantation studies, it seems likely that most of the DCs in secondary lymphoid organs and a substantial fraction of thymic DCs are myeloid-derived.

The use of dendritic cells in cancer therapy

Although the immune system evolved to protect the host from infection, what fires the popular imagination is its potential to recognise and destroy cancer. The immune system can generate potent cytotoxicity (eg transplant rejection), but can these mechanisms be harnessed for therapeutic benefit in patients with cancer? The discovery of an ever-increasing array of tumour antigens shows clearly that the targets exist. The challenge lies in generating a sufficiently potent response towards them. Central to the processes of antigen recognition, processing, and presentation to the immune system are dendritic cells. Understanding of the relation between these and the cellular immune response is crucial to elucidation of how to manipulate immune responses. The past 20 years have witnessed a dramatic expansion in this understanding and led to the first early-phase clinical trials of dendritic cells for the treatment of cancer. These studies have established the safety and feasibility of this approach and have produced encouraging evidence of therapeutic efficacy. This paper reviews the biology of dendritic cells and their use in clinical trials, as well as highlighting issues for future trial design.

Dendritic cell modulation by 1alpha,25 dihydroxyvitamin D3 and its analogs: a vitamin D receptor-dependent pathway that promotes a persistent state of immaturity in vitro and in vivo

Dendritic cells (DCs) play a central role in regulating immune activation and responses to self. DC maturation is central to the outcome of antigen presentation to T cells. Maturation of DCs is inhibited by physiological levels of 1alpha,25 dihydroxyvitamin D(3) [1alpha,25(OH)(2)D(3)] and a related analog, 1alpha,25(OH)(2)-16-ene-23-yne-26,27-hexafluoro-19-nor-vitamin D(3) (D(3) analog). Conditioning of bone marrow cultures with 10(-10) M D(3) analog resulted in accumulation of immature DCs with reduced IL-12 secretion and without induction of transforming growth factor beta1. These DCs retained an immature phenotype after withdrawal of D(3) analog and exhibited blunted responses to maturing stimuli (CD40 ligation, macrophage products, or lipopolysaccharide). Resistance to maturation depended on the presence of the 1alpha,25(OH)(2)D(3) receptor (VDR). In an in vivo model of DC-mediated antigen-specific sensitization, D(3) analog-conditioned DCs failed to sensitize and, instead, promoted prolonged survival of subsequent skin grafts expressing the same antigen. To investigate the physiologic significance of 1alpha,25(OH)(2)D(3)/VDR-mediated modulation of DC maturity we analyzed DC populations from mice lacking VDR. Compared with wild-type animals, VDR-deficient mice had hypertrophy of subcutaneous lymph nodes and an increase in mature DCs in lymph nodes but not spleen. We conclude that 1alpha,25(OH)(2)D(3)/VDR mediates physiologically relevant inhibition of DC maturity that is resistant to maturational stimuli and modulates antigen-specific immune responses in vivo.

Effective antigen presentation by dendritic cells is NF-kappaB dependent: coordinate regulation of MHC, co-stimulatory molecules and cytokines

Antigen presentation is a key rate-limiting step in the immune response. Dendritic cells (DC) are the most potent antigen-presenting cells for naive T cells, due to their high expression of MHC and co-stimulatory molecules, but little is known about the biochemical pathways that regulate this function. We here demonstrate that monocyte-derived mature DC can be infected with adenovirus at high efficiency (>95%) and that this procedure can be used to dissect out which pathways are essential for inducing DC antigen presentation to naive T cells. Using adenoviral transfer of the endogenous inhibitor of NF-kappaB, IkappaBalpha, we show that DC antigen presentation is NF-kappaB dependent. The mechanism for this is that NF-kappaB is essential for three aspects of antigen-presenting function: blocking NF-kappaB coordinately down-regulates HLA class II, co-stimulatory molecules like CD80, CD86 and CD40, and immuno-stimulatory cytokines like IL-12 and tumor necrosis factor-alpha. In contrast adhesion molecules are up-regulated after infection with the adenovirus transferring IkappaBalpha, indicating that NF-kappaB also regulates the duration of T cell-DC interaction. These results establish NF-kappaB as an effective target for blocking DC antigen presentation and inhibiting T cell-dependent immune responses, and this finding has potential implications for the development of therapeutic agents for use in allergy, autoimmunity and transplantation.

Unique functions of CD11b+, CD8 alpha+, and double-negative Peyer's patch dendritic cells

We have recently demonstrated the presence of three populations of dendritic cells (DC) in the murine Peyer's patch. CD11b(+)/CD8alpha(-) (myeloid) DCs are localized in the subepithelial dome, CD11b(-)/CD8alpha(+) (lymphoid) DCs in the interfollicular regions, and CD11b(-)/CD8alpha(-) (double-negative; DN) DCs at both sites. We now describe the presence of a novel population of intraepithelial DN DCs within the follicle-associated epithelium and demonstrate a predominance of DN DCs only in mucosal lymphoid tissues. Furthermore, we demonstrate that all DC subpopulations maintain their surface phenotype upon maturation in vitro, and secrete a distinct pattern of cytokines upon exposure to T cell and microbial stimuli. Only myeloid DCs from the PP produce high levels of IL-10 upon stimulation with soluble CD40 ligand(-) trimer, or Staphylococcus aureus and IFN-gamma. In contrast, lymphoid and DN, but not myeloid DCs, produce IL-12p70 following microbial stimulation, whereas no DC subset produces IL-12p70 in response to CD40 ligand trimer. Finally, we show that myeloid DCs from the PP are particularly capable of priming naive T cells to secrete high levels of IL-4 and IL-10, when compared with those from nonmucosal sites, while lymphoid and DN DCs from all tissues prime for IFN-gamma production. These findings thus suggest that DC subsets within mucosal tissues have unique immune inductive capacities.

Murine dendritic cells derived from myeloid progenitors of the thymus are unable to produce bioactive IL-12p70

Dendritic cells (DC) are present at low density in the thymus where they mediate negative selection of self-reactive thymocytes. Previous reports suggest that thymic DC (TDC) are a single population of lymphoid-related DC. In this study, we documented the presence in the adult mouse thymus of an additional population of TDC exhibiting a myeloid phenotype (CD11c(+) CD8alpha(-) CD11b(+)). This population, which can be purified, represented approximately 20% of the total TDC and differs from the population of lymphoid TDC (CD11c(+) CD8(+) CD11b(-)) by its incapacity to produce IL-12p70 under double stimulation by LPS and anti-CD40. Furthermore, using an original culture system allowing expansion of DC from myeloid progenitors, we demonstrated that DC exhibiting a similar myeloid phenotype can be derived from a common DC/macrophage progenitor resident in the adult mouse thymus. We found that, in contrast with myeloid splenic DC expanded in the same conditions, these cultured TDC were unable to produce IL-12p70 under double stimulation by LPS and anti-CD40 or LPS and IFN-gamma. Thus, our results suggest that 1) adult mouse thymus contains at least two phenotypically and functionally distinct populations of DC; and 2) cultured myeloid DC derived from thymus and spleen differ by their ability to produce IL-12p70. The mechanisms underlying the differences in IL-12-secreting capacities of the cultured splenic and thymic DC are under current investigation.

Differential effect of CD8(+) and CD8(-) dendritic cells in the stimulation of secondary CD4(+) T cells

Dendritic cells (DC), in their role in initiation of the adaptive immune response, have been extensively studied for their capacity to interact and stimulate naive T cells. Subsets of mature murine DC isolated directly from the spleen have been shown to differ in their ability to induce proliferative responses in both primary CD4(+) and primary CD8(+) T cells; the myeloid-related CD8alpha(-) DC induce a more intense or prolonged proliferation of naive T cells than do the lymphoid-related DC bearing CD8alpha despite similar expression of MHC and co-stimulatory molecules. Here we examine the interaction of these DC subpopulations with T cells already in the activated or memory state which are known to have greater sensitivity to antigen stimulation and bear receptors with increased capacity for signal transduction. We show that influenza virus-specific CD4(+) T cell clones and splenic T cells from peptide-primed animals proliferated in response to antigen presented by separated splenic CD8(-) DC. In contrast, these T cells showed only weak, if any, proliferation in response to CD8(+) DC despite observable cluster formation in the cultures. The differential between the two DC types in inducing proliferation was even more pronounced than previously seen with primary T cells and did not reflect differential longevity of the DC in culture, altered response kinetics or deviation from IL-2 to IL-4 induction with CD8(+) DC, but was related to the levels of IL-2 induced. The deficiency in the CD8(+) DC was not overcome by using infectious virus rather than synthetic peptide as the antigen source. These results show that lymphoid-related CD8(+) splenic DC, despite their mature phenotype, fail to provide appropriate signals to secondary CD4(+) T cells to sustain their proliferation.

2,3,7,8-Tetrachlorodibenzo-p-dioxin affects the number and function of murine splenic dendritic cells and their expression of accessory molecules

Primary T cell-mediated immune responses are highly susceptible to suppression by 2,3,7,8-tetrachlorodibenzo-p-dioxin (TCDD) exposure, yet direct effects of TCDD on T cells have been difficult to demonstrate. Since the activation of naive T cells has been shown to be initiated primarily by dendritic cells (DC), these cells represent a potential target for TCDD immunotoxicity. In this report, we have examined the influence of TCDD exposure on splenic DC phenotype and function in the absence of antigenic stimulation. Results showed that DC from TCDD-treated mice expressed higher levels of several accessory molecules including ICAM-1, CD24, B7-2, and CD40, whereas the expression of LFA-1 was significantly reduced. These effects were dose-dependent and persisted for at least 14 days after exposure. The effects were also dependent upon the aryl hydrocarbon receptor (AhR), as similar effects were observed in AhR+/+ C57Bl/6 and Balb/c mice but not in AhR-/- mice. When DC from TCDD-treated mice were cultured with allogeneic T cells, the proliferative response and production of IL-2 and IFN-gamma by the T cells were increased. Production of IL-12 by the DC was likewise enhanced in comparison to cells from vehicle-treated mice. Interestingly, however, the number of DC recovered from TCDD-treated mice was significantly decreased. Taken together, these results suggest that, in the absence of antigen, TCDD provides an activation stimulus to DC that may lead to their premature deletion. Since the survival of DC has been shown to influence the strength and duration of the immune response, these results suggest a possible novel mechanism for TCDD-induced immune suppression.

Migration of dendritic cells into lymphatics-the Langerhans cell example: routes, regulation, and relevance

Dendritic cells are leukocytes of bone marrow origin. They are central to the control of the immune response. Dendritic cells are highly specialized in processing and presenting antigens (microbes, proteins) to helper T lymphocytes. Thereby, they critically regulate further downstream processes such as the development of cytotoxic T lymphocytes, the production of antibodies by B lymphocytes, or the activation of macrophages. A new field of dendritic cell biology is the study of their potential role in inducing peripheral tolerance. The immunogenic/tolerogenic potential of dendritic cells is increasingly being utilized in immunotherapy, particularly for the elicitation of antitumor responses. One very important specialization of dendritic cells is their outstanding capacity to migrate from sites of antigen uptake to lymphoid organs. Much has been learned about this process from studying one particular type of dendritic cell, namely, the Langerhans cell of the epidermis. Therefore, the migratory properties of Langerhans cells are reviewed. Knowledge about this "prototype dendritic cell" may help researchers to understand migration of other types of dendritic cells.

Dendritic cell migration controlled by alpha 1b-adrenergic receptors

Dendritic cells (DC) bring Ags into lymphoid organs via lymphatic vessels. In this study, we investigated the possibility that the sympathetic neurotransmitter norepinephrine (NE) influences DC migration. Murine epidermal Langerhans cells mobilization is enhanced by systemic treatment with the alpha(2)-adrenergic antagonist yohimbine and inhibited by local treatment with the specific alpha(1)-adrenergic antagonist prazosin (PRA). Consistently, NE enhances spontaneous emigration of DC from ear skin explants, and PRA inhibits this effect. In addition, local treatment with PRA during sensitization with FITC inhibits the contact hypersensitivity response 6 days later. In vitro, bone marrow-derived immature, but not CD40-stimulated mature DC migrate in response to NE, and this effect is neutralized by PRA. NE seems to exert both a chemotactic and chemokinetic activity on immature DC. Coherently, immature, but not mature DC, express mRNA coding for the alpha(1b)-adrenergic receptor subtype. Inactivation of this adrenergic receptor by the specific and irreversible antagonist chloroethylclonidine hinders the migration of injected DC from the footpad to regional lymph nodes. Thus, besides regulating lymph flow, the sympathetic innervation of lymphatic vessels may participate in directing DC migration from the site of inflammation to regional lymph nodes. Alternatively, the chemokinetic activity of NE may enhance the ability of DC to sample local Ags, and hence increase the number of DC migrating to the draining lymph nodes. This finding might improve our understanding of the biological basis of skin diseases and allergic reactions, and opens new pharmacological possibilities to modulate the immune response.

The development, maturation, and turnover rate of mouse spleen dendritic cell populations

Three distinct subtypes of dendritic cells (DC) are present in mouse spleen, separable as CD4(-)8alpha(-), CD4(+)8alpha(-), and CD4(-)8alpha(+) DC. We have tested whether these represent stages of development or activation within one DC lineage, or whether they represent separate DC lineages. All three DC subtypes appear relatively mature by many criteria, but all retain a capacity to phagocytose particulate material in vivo. Although further maturation or activation could be induced by bacterially derived stimuli, phagocytic capacity was retained, and no DC subtype was converted to the other. Continuous elimination of CD4(+)8(-) DC by Ab depletion had no effect on the levels of the other DC subtypes. Bromodeoxyuridine labeling experiments indicated that all three DC subtypes have a rapid turnover (half-life, 1.5-2.9 days) in the spleen, with none being the precursor of another. The three DC subtypes showed different kinetics of development from bone marrow precursors. The CD8alpha(+) spleen DC, apparently the most mature, displayed an extremely rapid turnover based on bromodeoxyuridine uptake and the fastest generation from bone marrow precursors. In conclusion, the three splenic DC subtypes behave as rapidly turning over products of three independent developmental streams.

Development of CD8alpha-positive dendritic cells from a common myeloid progenitor

Dendritic cells (DCs) are critical in both initiating adaptive immune responses and maintaining tolerance to self antigens. These apparently contradictory roles have been suggested to depend on different subsets of DCs that arise from either myeloid or lymphoid hematopoietic origins, respectively. Although DC expression of CD8alpha is attributed to a lymphoid origin, here we show that both CD8alpha+ and CD8alpha- DCs can arise from clonogenic common myeloid progenitors in both thymus and spleen. Thus, expression of CD8alpha is not indicative of a lymphoid origin, and phenotypic and functional differences among DC subsets are likely to reflect maturation status rather than ontogeny.