Antigen-pulsed dendritic cells can efficiently induce an antibody response in vivo.

The aim of this study was to develop an immunization procedure avoiding external adjuvant. Data are presented showing that syngeneic dendritic cells (DC), which have been pulsed in vitro with antigen, induce a strong antibody response in mice. By contrast, antigen (Ag)-pulsed low-density B cells, although equally able to induce interleukin 2 secretion by an Ag-specific T cell hybridoma in vitro, only weakly prime the mice in vivo. Moreover, we show that the injection of Ag-pulsed DC induces the synthesis of isotypes similar to the immunoglobulin classes detected after immunization with the same Ag in complete Freund's adjuvant. Importantly, high amounts of IgG2a antibodies are produced, suggesting that T helper type 1 cells are activated. Collectively, these data indicate that DC can initiate a primary humoral response and that they may be used as physiological adjuvant in vivo.     

CD8(+) but not CD8(-) dendritic cells cross-prime cytotoxic T cells in vivo

Bone marrow-derived antigen-presenting cells (APCs) take up cell-associated antigens and present them in the context of major histocompatibility complex (MHC) class I molecules to CD8(+) T cells in a process referred to as cross-priming. Cross-priming is essential for the induction of CD8(+) T cell responses directed towards antigens not expressed in professional APCs. Although in vitro experiments have shown that dendritic cells (DCs) and macrophages are capable of presenting exogenous antigens in association with MHC class I, the cross-presenting cell in vivo has not been identified. We have isolated splenic DCs after in vivo priming with ovalbumin-loaded beta2-microglobulin-deficient splenocytes and show that they indeed present cell-associated antigens in the context of MHC class I molecules. This process is transporter associated with antigen presentation (TAP) dependent, suggesting an endosome to cytosol transport. To determine whether a specific subset of splenic DCs is involved in this cross-presentation, we negatively and positively selected for CD8(-) and CD8(+) DCs. Only the CD8(+), and not the CD8(-), DC subset demonstrates cross-priming ability. FACS((R)) studies after injection of splenocytes loaded with fluorescent beads showed that 1 and 0.6% of the CD8(+) and the CD8(-) DC subsets, respectively, had one or more associated beads. These results indicate that CD8(+) DCs play an important role in the generation of cytotoxic T lymphocyte responses specific for cell-associated antigens.     

Interactions between T helper cells and dendritic cells during the rat mixed lymphocyte reaction

This paper describes the interactions between dendritic cells (DC) and T helper (Th) cells in the rat mixed lymphocyte reaction (MLR). Th blasts that are actively proliferating were generated in a 5 d primary MLR; resting Th memory cells were derived from a 10-12 d MLR. The DC were purified from thoracic duct lymph derived from rats whose mesenteric lymph nodes had been removed. The results show that DC are the major stimulators in the primary MLR and also for the restimulation of Th blasts and Th memory cells. Th blasts rapidly formed large clusters when cultured with DC but not with Ia+ macrophages or B cells. This interaction was not dependent on a major histocompatibility complex (MHC) difference between the T blasts and the DC. Con A-activated T and B blasts also formed clusters when cultured with DC. Th memory cells formed small clusters with DC, but, in a different assay in which clusters are dispersed, we detected an antigen-specific interaction between Th memory cells and DC. The monoclonal antibodies W3/25 (anti-rat CD4) and MRC OX-6 (anti-MHC class II) blocked proliferation in the primary MLR and also inhibited the restimulation of Th memory cells. However, the restimulation of Th blasts in a secondary MLR was only blocked by MRC OX-6. These results suggest that there are different requirements for the restimulation of T blasts than for the activation of primary or memory Th cells. W3/25 and MRC OX-6 did not affect the clustering of T blasts with DC but they both inhibited the antigen-specific binding of Th memory cells to DC. The data suggest that the CD4 (W3/25) antigen is involved in antigen-specific interactions between Th cells and DC.     

IL-2基因修饰增强白血病抗原冲击的树突状细胞诱导的抗肿瘤免疫反应

树突状细胞（ｄｅｎｄｒｉｔｉｃｃｅｌｌ,ＤＣ）是目前所知的最有效的激活初始型Ｔ细胞的专职抗原提呈细胞（ａｎｔｉｇｅｎｐｒｅｓｅｎｔｉｎｇｃｅｌｌ,ＡＰＣ）,也是功能最强的ＡＰＣ,在肿瘤免疫治疗中具有独特的地位［１］。Ｐｏｒｇｏｄｏｒ等［２,３］发现用ＭＨＣⅠ类分子限制性抗原多肽冲击致敏从小鼠骨髓诱导的ＤＣ可以在体内诱导产生抗原特异性细胞毒性Ｔ淋巴细胞（ＣＴＬ）,并发现经抗原肽冲击致敏的ＤＣ皮下免疫的小鼠可以产生特异的抗肿瘤效应。ＤｅＭａｔｏｓ等［４］报道用冻融抗原（ｌｙｓａｔｅｓ）冲击的ＤＣ免…     

Cellular kinetics of the intestinal immune response to cholera toxoid in rats

The aims of this study were (a) to find a regime of immunization with cholera toxoid in rats which would establish a high density of antitoxin containing cells (ACC) in the lamina propria of the intestine and (b) to determine the origin of the ACC. The best cellular response was achieved by a single i.p. dose of toxoid in FCA followed by an intraintestinal boost 2 wk later. ACC appeared in the thoracic duct lymph 2 days after boosting, reaching a peak of about 200,000 ACC/h at 3--4 days. This was followed by the appearance of large numbers of ACC in the intestine. The i.p. dose of toxoid by itself gave rise to very few ACC in the gut or thoracic duct lymph, but it had clearly primed the gut immune system for a secondary response. Priming was also achieved by the prolonged oral intake of toxoid. The importance of the intestinal route for boosting was shown by the failure of i.p. challenge to give an ACC response in the intestine after i.p. priming and the small response it provoked after oral priming. ACC among thoracic duct lymphocytes (TDL) and in the lamina propria contained predominantly IgA. Two observations indicated that the major source of the lamina propria ACC was from cells that emerged in the thoracic duct lymph after intraintestinal challenge. Firstly, the establishment of a thoracic duct fistula immediately before challenge prevented the appearance of ACC in the intestine. Secondly, many ACC appeared in the intestine of normal rats after the injection of TDL rich in ACC. Although homing of ACC precursors to the gut was not antigen-dependent, the distribution of ACC in the lamina propria was considerably influenced by the site of the intestinal challenge, the density of ACC being greatest at or distal to the site of injection of toxoid into the lumen of the gut.     

TRANCE, a tumor necrosis factor family member, enhances the longevity and adjuvant properties of dendritic cells in vivo

Mature dendritic cells (DCs) are powerful antigen presenting cells that have the unique capacity to migrate to the T cell zone of draining lymph nodes after subcutaneous injection. Here we report that treatment of antigen-pulsed mature DCs with tumor necrosis factor (TNF)-related activation-induced cytokine (TRANCE), a TNF family member, before immunization enhances their adjuvant capacity and elicits improved T cell priming in vivo, such that both primary and memory T cell immune responses are enhanced. By enumerating migratory DCs in the draining lymph nodes and by studying their function in stimulating naive T cells, we show that one of the underlying mechanisms for enhanced T cell responses is an increase in the number of ex vivo antigen-pulsed DCs that are found in the T cell areas of lymph nodes. These results suggest that the longevity and abundance of mature DCs at the site of T cell priming influence the strength of the DC-initiated T cell immunity in situ. Our findings have the potential to improve DC-based immunotherapy; i.e., the active immunization of humans with autologous DCs that have been pulsed with clinically significant antigens ex vivo.     

Characterization of nonlymphoid cells derived from rat peripheral lymph

Mesenteric lymphadenectomy in rats is followed by union of peripheral and central lymphatics, allowing the collection of intestine-derived peripheral lymph cells via the thoracic duct for several days. These cells include a proportion of nonlymphoid cells (NLC) that show irregular and heterogeneous surface morphology including long pseudopodia and veils. They stain variably for nonspecific esterase and acid phosphatase and are ATPase-positive. Their nuclei are irregular and some contain cytoplasmic inclusions, some of which show peroxidase activity and/or contain DNA. NLC have a range of densitites generally lower than that of lymphocytes. Freshly collected NLC express the leukocyte-common antigen (defined by monoclonal antibody MRC Ox 1) and Ia antigens (I-A and I-E subregion products defined by monoclonal antibodies) but they show a relative lack of other surface markers normally found on rat B or T lymphocytes (W3/13, W3/25, MRC Ox 12 (sIg), MRC Ox 19) or rat macrophages (FcR, C’R, mannose R, W3/25). In general NLC are only weakly adherent to glass or plastic. Although a subpopulation of NLC appear to have had a phagocytic past, freshly collected NLC fail to phagocytose a variety of test particles in vitro. NLC also appear incapable of pinocytosis in vitro. This heterogeneity may represent distinct subpopulations of NLC or different stages in the development of a single cell lineage. Direct cannulation of mesenteric lacteals shows that the majority of NLC are derived from the small intestine and their precursors appear to be present both in lamina propria and Peyer's patches. Kinetic studies, following irradiation or intravenous tritiated thymidine, show that the majority of NLC turn over rapidly in the intestine with a modal time of 3-5 d. Studies with bone marrow chimeras show that they are derived from a rapidly dividing precursor present in normal bone marrow. NLC occur at very low frequencies in normal thoracic duct lymph at all times following cannulation. The evidence presented suggests that NLC closely resemble mouse lymphoid dendritic cells. This conclusion is supported by evidence already obtained showing that NLC are potent stimulators of the semi-allogeneic rat primary mixed leukocyte reaction. In addition to the ceils resembling dendritic cells rare monocytoid cells are found in thoracic duct lymph of lymphadenectomized specific pathogen-free rats. The proportion of these cells increases greatly when the animals are conventionally housed. It seems probable that the physiological function of NLC is to act as accessory cells in the lymph nodes to which they normally drain. Methods for enriching NLC and thus facilitating analysis of their functions are discussed.     

Cross-priming of naive CD8 T cells against melanoma antigens using dendritic cells loaded with killed allogeneic melanoma cells

The goal of tumor immunotherapy is to elicit immune responses against autologous tumors. It would be highly desirable that such responses include multiple T cell clones against multiple tumor antigens. This could be obtained using the antigen presenting capacity of dendritic cells (DCs) and cross-priming. That is, one could load the DC with tumor lines of any human histocompatibility leukocyte antigen (HLA) type to elicit T cell responses against the autologous tumor. In this study, we show that human DCs derived from monocytes and loaded with killed melanoma cells prime naive CD45RA(+)CD27(+)CD8(+) T cells against the four shared melanoma antigens: MAGE-3, gp100, tyrosinase, and MART-1. HLA-A201(+) naive T cells primed by DCs loaded with HLA-A201(-) melanoma cells are able to kill several HLA-A201(+) melanoma targets. Cytotoxic T lymphocyte priming towards melanoma antigens is also obtained with cells from metastatic melanoma patients. This demonstration of cross-priming against shared tumor antigens builds the basis for using allogeneic tumor cell lines to deliver tumor antigens to DCs for vaccination protocols.     

Intrathymic presentation of circulating non-MHC antigens by medullary dendritic cells. An antigen-dependent microenvironment for T cell differentiation

We present evidence for intrathymic presentation of soluble circulating antigens in vivo. Our results show that proteins of different molecular weight enter the mouse thymus rapidly after i.v. injection. The intrathymic presence of antigen was assayed by proliferation of cloned antigen-specific T helper cells, which were cocultured with purified thymic stromal cells; stromal cells were isolated and purified as lymphostromal cell complexes, which preexist in vivo. Antigen presentation copurified with non-adherent medullary dendritic cells (DC) (interdigitating cells). I-A- cortical macrophages forming thymocyte rosettes in vivo and I-A+ cortical epithelial cells forming thymic nurse cells (TNC) in vivo did not act as antigen presenting cells (APC) after antigen pulsing in vivo or in vitro. Thymic APC turn over physiologically and are rapidly replaced (within 2-5 wk) after lethal irradiation by donor bone marrow-derived cells. The frequency of thymocyte-DC interactions in vivo strictly correlates with thymic T cell differentiation, and is independent of the immune status of the animal. Fetal thymic APC seem to be secluded from antigen in the maternal circulation. Thymic DC-ROS probably represent the microenvironment where maturing T cells first encounter non-MHC antigens in the context of self-MHC antigens.     

Functional characteristics of Peyer's patch cells. III. Carrier priming of T cells by antigen feeding

Peyer's patch T cells may serve an important role in the interaction of the host with intraluminal gut antigens. Studies presented in this paper demonstrate that T cells in murine Peyer's patches can be carrier primed for helper function in the induction of an antihapten response by feeding antigen. Carrier priming was assessed by measuring the ability of Peyer's patch cells from mice fed heterologous erythrocytes to enhance an antitrinitrophenyl (TNP) response in vitro when added to normal Peyer's patch cells cultured with TNP coupled to the erythrocyte used for feeding. Priming of T helper cells in Peyer's patches was antigen specific and occurred when erythrocytes were administered orally but not when erythrocytes were injected intravenously or intraperitoneally. Murine Peyer's patches are naturally deficient in a cooperating accessory adherent cell type(s) required for B-cell induction to humoral antibody synthesis in vitro and antigen feeding does not result in significant induction of Peyer's patch B cells to humoral antibody synthesis in vivo. Since Peyer's patch T cells can be carrier-antigen primed for helper function in the absence of B-cell induction to humoral antibody synthesis, these studies may indicate that T-cell priming is less dependent than B-cell induction on cooperating accessory adherent cells.     

Contribution of dendritic cells to stimulation of the murine syngeneic mixed leukocyte reaction

We have studied the proliferative response of unprimed T cells to syngeneic dendritic cells (DC) (syngeneic mixed leukocyte reaction [SMLR]) in cultures of mouse spleen and lymph node. T cells purified by passage over nylon wool contain few DC and exhibits little proliferative activity during several days of culture. Addition of small numbers of purified syngeneic DC induces substantial, dose- dependent, T cell-proliferative responses that peak at day 4-5. B cells purified on anti-Ig-coated plates do not respond to DC at all doses tested. DC culture medium does not induce proliferation, and coculture of DC and T cells is required. Purified mouse B and T lymphocytes stimulate SMLR weakly if at all. Likewise, peritoneal and spleen macrophages are weak or inactive. Therefore, DC are potent and possibly unique primary cells for stimulating the SMLR in mice. sIg- spleen and lymph node cells show extensive background proliferative responses in vitro, and fail to respond to small numbers of purified DC. If the sIg- cells are treated with anti-Ia and complement, or passed over nylon wool, DC are removed and proliferative activity falls. Proliferative activity is restored by adding back DC at levels similar to those present in sIg- cells (1-2%). Thus, DC-dependent, T cell proliferation probably occurs in all spleen and lymph node cultures. As expected from previous work (6), DC are also potent inducers of allogeneic MLR. On a per DC basis, the syngeneic response is 10 times weaker than the allogeneic MLR, and it is not accompanied by the development of cytotoxic lymphocytes. The magnitude of the SMLR was not altered by antigen priming, and DC maintained in isologous rather than fetal calf serum were active stimulators. Therefore, syngeneic stimulation appears to be an intrinsic property of DC, and modification by exogenous agents does not seem to be required. Coculture of DC and T cells results in the development of cell clusters that can be isolated and characterized directly. The clusters account for 10-20% of the viable cells in the culture, but contain greater than 80% of the responding T cells and stimulating DC by morphologic and surface-marker criteria. The efficient physical association of DC and responding T cells implies specific cell-cell recognition. We conclude that the SMLR reflects the ability of T cells, or some subpopulation of T cells, to interact with and proliferate in response to small numbers of DC.     

Gene-modified dendritic cells for use in tumor vaccines

Dendritic cells (DCs) are potent antigen-presenting cells capable of priming activation of naive T cells. Because of their immunostimulatory capacity, immunization with DCs presenting tumor antigens has been proposed as a treatment regimen for cancer. The results from translational research studies and early clinical trials point to the need for improvement of DC-based tumor vaccines before they become a more broadly applicable treatment modality. In this regard, studies suggest that genetic modification of DCs to express tumor antigens and/or immunomodulatory proteins may improve their capacity to promote an antitumor response. Because the DC phenotype is relatively unstable, nonperturbing methods of gene transfer must be employed that do not compromise viability or immunostimulatory capacity. DCs expressing transgenes encoding tumor antigens have been shown to be more potent primers of antitumor immunity both in vitro and in animal models of disease; in some measures of immune priming, gene-modified DCs exceeded their soluble antigen-pulsed counterparts. Cytokine gene modification of DCs has improved their capacity to prime tumor antigen-specific T cell responses and promote antitumor immunity in vivo. Here, we review the current status of gene-modified DCs in both human and murine studies. Although successful results have been obtained to date in experimental systems, we discuss potential problems that have already arisen and may yet be encountered before gene-modified DCs are more widely applicable for use in human clinical trials.     

CpG-matured murine plasmacytoid dendritic cells are capable of in vivo priming of functional CD8 T cell responses to endogenous but not exogenous antigens

Plasmacytoid dendritic cells (PDCs) are a unique leukocyte population capable of secreting high levels of type I interferon (IFN) in response to viruses and bacterial stimuli. In vitro experiments have shown that upon maturation, human and murine PDCs develop into potent immunostimulatory cells; however, their ability to prime an immune response in vivo remains to be addressed. We report that CpG-matured murine PDCs are capable of eliciting in naive mice antigen-specific CTLs against endogenous antigens as well as exogenous peptides, but not against an exogenous antigen. Type I IFN is not required for priming, as injection of CpG-matured PDCs into type I IFN receptor-deficient mice elicits functional CTL responses. Mature PDCs prime CTLs that secrete IFN-gamma and protect mice from a tumor challenge. In contrast, immature PDCs are unable to prime antigen-specific CTLs. However, mice injected with immature PDCs are fully responsive to secondary antigenic challenges, suggesting that PDCs have not induced long-lasting tolerance via anergic or regulatory T cells. Our results underline the heterogeneity and plasticity of different antigen-presenting cells, and reveal an important role of mature PDCs in priming CD8 responses to endogenous antigens, in addition to their previously reported ability to modulate antiviral responses via type I IFN.     

CD40L+ CD4+ memory T cells migrate in a CD62P-dependent fashion into reactive lymph nodes and license dendritic cells for T cell priming

There is growing evidence that the maturation state of dendritic cells (DCs) is a critical parameter determining the balance between tolerance and immunity. We report that mouse CD4⁺ effector memory T (T_EM) cells, but not naive or central memory T cells, constitutively expressed CD40L at levels sufficient to induce DC maturation in vitro and in vivo in the absence of antigenic stimulation. CD4⁺ T_EM cells were excluded from resting lymph nodes but migrated in a CD62P-dependent fashion into reactive lymph nodes that were induced to express CD62P, in a transient or sustained fashion, on high endothelial venules. Trafficking of CD4⁺ T_EM cells into chronic reactive lymph nodes maintained resident DCs in a mature state and promoted naive T cell responses and experimental autoimmune encephalomyelitis (EAE) to antigens administered in the absence of adjuvants. Antibodies to CD62P, which blocked CD4⁺ T_EM cell migration into reactive lymph nodes, inhibited DC maturation, T cell priming, and induction of EAE. These results show that T_EM cells can behave as endogenous adjuvants and suggest a mechanistic link between lymphocyte traffic in lymph nodes and induction of autoimmunity.     

Stromal mesenteric lymph node cells are essential for the generation of gut-homing T cells in vivo

T cells primed in the gut-draining mesenteric lymph nodes (mLN) are imprinted to express α4β7-integrin and chemokine receptor CCR9, thereby enabling lymphocytes to migrate to the small intestine. In vitro activation by intestinal dendritic cells (DC) or addition of retinoic acid (RA) is sufficient to instruct expression of these gut-homing molecules. We report that in vivo stroma cells, but not DC, allow the mLN to induce the generation of gut tropism. Peripheral LN (pLN) transplanted into the gut mesenteries fail to support the generation of gut-homing T cells, even though gut-derived DC enter the transplants and prime T cells. DC that fail to induce α4β7-integrin and CCR9 in vitro readily induce these factors in vivo upon injection into mLN afferent lymphatics. Moreover, uniquely mesenteric but not pLN stroma cells express high levels of RA-producing enzymes and support induction of CCR9 on activated T cells in vitro. These results demonstrate a hitherto unrecognized contribution of stromal cell delivered signals, including RA, on the imprinting of tissue tropism in vivo.     

Oral tolerance originates in the intestinal immune system and relies on antigen carriage by dendritic cells

Oral tolerance induction is a key feature of intestinal immunity, generating systemic nonresponsiveness to ingested antigens. In this study, we report that orally applied soluble antigens are exclusively recognized in the intestinal immune system, particularly in the mesenteric lymph nodes. Consequently, the initiation of oral tolerance is impeded by mesenteric lymphadenectomy. Small bowel transplantation reveals that mesenteric lymph nodes require afferent lymph to accomplish the recognition of orally applied antigens. Finally, oral tolerance cannot be induced in CCR7-deficient mice that display impaired migration of dendritic cells from the intestine to the mesenteric lymph nodes, suggesting that immunologically relevant antigen is transported in a cell-bound fashion. These results demonstrate that antigen transport via afferent lymphatics into the draining mesenteric lymph nodes is obligatory for oral tolerance induction, inspiring new therapeutic strategies to exploit oral tolerance induction for the prevention and treatment of autoimmune diseases.     

Mechanisms involved in radiation enhancement of intratumoral dendritic cell therapy

We have previously reported that local tumor irradiation, without inducing cell death, can augment the therapeutic efficacy of intratumoral (IT) dendritic cell (DC) vaccination. This study examined potential mechanisms underlying radiation enhancement of IT DC therapy in this setting. Even though ionizing radiation did not mediate tumor cell killing, bone marrow-derived DCs acquired in vitro tumor antigens from irradiated D5 murine melanoma cells more efficiently than from untreated cells. This radiation-enhanced loading of DCs did not induce DC maturation, but was associated with improved cross-priming of T cells both in vitro and in vivo. Furthermore, in vivo pulsing of DCs with irradiated versus untreated tumor cells resulted in superior presentation of tumor antigens to T cells. In addition, tumor irradiation facilitated homing of IT administered DCs to the draining lymph node, possibly by down-regulating CCL21 expression within the tumor mass. Studies of the tumor microenvironment in irradiated versus untreated tumors did not reveal significant inflammatory changes. Moreover, radiation did not promote accumulation of CD4 or CD8 effector T cells within solid tumors. Our results indicate that, without inducing cytotoxicity, tumor irradiation can enhance the ability of DCs to capture tumor antigens, migrate to the draining lymph node, and present processed antigens to T cells. These findings may prove useful in designing future strategies for human cancer immunotherapy.     

Differential roles of migratory and resident DCs in T cell priming after mucosal or skin HSV-1 infection

Although mucosal surfaces represent the main portal of entry for pathogens, the mechanism of antigen presentation by dendritic cells (DCs) that patrol various mucosal tissues remains unclear. Instead, much effort has focused on the understanding of initiation of immune responses generated against antigens delivered by injection. We examined the contributions of migratory versus lymph node–resident DC populations in antigen presentation to CD4 and CD8 T cells after needle injection, epicutaneous infection, or vaginal mucosal herpes simplex virus (HSV) 1 infection. We show that upon needle injection, HSV-1 became lymph-borne and was rapidly presented by lymph node–resident DCs to CD4 and CD8 T cells. In contrast, after vaginal HSV-1 infection, antigens were largely presented by tissue-derived migrant DCs with delayed kinetics. In addition, migrant DCs made more frequent contact with HSV-specific T cells after vaginal infection compared with epicutaneous infection. Thus, both migrant and resident DCs play an important role in priming CD8 and CD4 T cell responses, and their relative importance depends on the mode of infection in vivo.     

The biology and clinical applications of dendritic cells

Dendritic cells (DC) have an essential role in the induction of immune responses to antigen by naive T cells. As 'professional' antigen-presenting cells they are specialized to take up, process and present soluble antigens in complexes with either class I or class II MHC molecules. They are present in only trace numbers in most tissues and in a relatively immature state but, in the presence of inflammatory signals, they rapidly take up foreign antigens and undergo maturation into potent antigen-presenting cells that migrate to secondary lymphoid tissue where they initiate an immune response. It is now possible to expand populations of DC in vitro both from primitive haemopoietic progenitors as well as from more mature peripheral blood mononuclear cells. This has shed light on many developmental aspects of DC biology and furthered our knowledge of the mechanisms of antigen processing and presentation. It is clear that there is more than one pathway of DC differentiation and that some DC may actually induce immunological unresponsiveness — a possible mechanism for tolerance to self-antigens. For clinicians the most exciting prospect is of their use as cellular adjuvants to generate beneficial responses to antigens of low immunogenicity such as tumour antigens. This review outlines aspects of human DC development and the way in which a greater understanding of their biology may lead to promising clinical applications.     

Freshly isolated Peyer's patch, but not spleen, dendritic cells produce interleukin 10 and induce the differentiation of T helper type 2 cells.

Orally administered antigens often generate immune responses that are distinct from those injected systemically. The role of antigen-presenting cells in determining the type of T helper cell response induced at mucosal versus systemic sites is unclear. Here we examine the phenotypic and functional differences between dendritic cells (DCs) freshly isolated from Peyer's patches (PP) and spleen (SP). Surface phenotypic analysis of CD11c(+) DC populations revealed that PP DCs expressed higher levels of major histocompatibility complex class II molecules, but similar levels of costimulatory molecules and adhesion molecules compared with SP DCs. Freshly isolated, flow cytometrically sorted 98-100% pure CD11c(+) DC populations from PP and SP were compared for their ability to stimulate naive T cells. First, PP DCs were found to be much more potent in stimulating allogeneic T cell proliferation compared with SP DCs. Second, by using naive T cells from ovalbumin peptide-specific T cell receptor transgenic mice, these ex vivo DCs derived from PP, but not from SP, were found to prime for the production of interleukin (IL)-4 and IL-10 (Th2 cytokines). In addition, PP DCs were found to prime T cells for the production of much lower levels of interferon (IFN)-gamma (Th1) compared with SP DCs. The presence of neutralizing antibody against IL-10 in the priming culture dramatically enhanced IFN-gamma production by T cells stimulated with PP DCs. Furthermore, stimulation of freshly isolated PP DCs via the CD40 molecule resulted in secretion of high levels of IL-10, whereas the same stimulus induced no IL-10 secretion from SP DCs. These results suggest that DCs residing in different tissues are capable of inducing distinct immune responses and that this may be related to the distinct cytokines produced by the DCs from these tissues.