Isolation and function of human dendritic cells

Airway Macrophage and Dendritic Cell Subsets in the Resting Human Lung

Dendritic cells (DCs) and macrophages (MΦs) are antigen-presenting phagocytic cells found in many peripheral tissues of the human body, including the blood, lymph nodes, skin, and lung. They are vital to maintaining steady-state respiration in the human lung based on their ability to clear airways while also directing tolerogenic or inflammatory responses based on specific stimuli. Over the past three decades, studies have determined that there are multiple subsets of these two general cell types that exist in the airways and interstitium. Identifying these numerous subsets has proven challenging, especially with the unique microenvironments present in the lung. Cells found in the vasculature are not the same subsets found in the skin or the lung, as demonstrated by surface marker expression. By transcriptional profiling, these subsets show similarities but also major differences. Primary human lung cells and/ or tissues are difficult to acquire, particularly in a healthy condition. Additionally, surface marker screening and transcriptional profiling are continually identifying new DC and MΦ subsets. While the overall field is moving forward, we emphasize that more attention needs to focus on replicating the steady-state microenvironment of the lung to reveal the physiological functions of these subsets.

Potential autocrine regulation of interleukin-33/ST2 signaling of dendritic cells in allergic inflammation

This study identified a novel phenomenon that dendritic cells (DCs) produced interleukin (IL)-33 via Toll-like receptor (TLR)-mediated innate pathway. Mouse bone marrow-derived DCs were treated with or without microbial pathogens or recombinant murine IL-33. IL-33 mRNA and protein were found to be expressed by DCs and largely induced by several microbial pathogens, highly by lipopolysaccharide (LPS) and flagellin. Using two mouse models of topical challenge by LPS and flagellin and experimental allergic conjunctivitis, IL-33-producing DCs were observed in ocular mucosal surface and the draining cervical lymph nodes in vivo. The increased expression levels of myeloid differentiation primary-response protein 88 (MyD88), nuclear factor (NF)-κB1, NF-κB2, and RelA accompanied by NF-κB p65 nuclear translocation were observed in DCs exposed to flagellin. IL-33 induction by flagellin was significantly blocked by TLR5 antibody or NF-κB inhibitor quinazoline and diminished in DCs from MyD88 knockout mice. IL-33 stimulated the expression of DC maturation markers, CD40 and CD80, and proallergic cytokines and chemokines, OX40L, IL-4, IL-5, IL-13, CCL17 (C-C motif chemokine ligand 17), TNF-α (tumor necrosis factor-α), and IL-1β. This stimulatory effect of IL-33 in DCs was significantly blocked by ST2 antibody or soluble ST2. Our findings demonstrate that DCs produce IL-33 via TLR/NF-κB signaling pathways, suggesting a molecular mechanism by which local allergic inflammatory response may be amplified by DC-produced IL-33 through potential autocrine regulation.

Generation of self-renewing immature dendritic cells from mouse spleen that can take up mycobacteria and present antigens to T cells

Dendritic cells (DC) play a key role in driving the adaptive immune response to Mycobacterium tuberculosis (MTB), the causative pathogen of tuberculosis (TB). However, studying these important yet very sparse immune cells in the context of MTB pathogenesis is severely restricted by the lack of suitable cell lines and the complexity of culturing of DC progenitors, usually obtained from the bone marrow. However, significant advances have been made towards generating long-term DC cultures from various lymphoid tissues. Here, we report the evidence for generating a long-term, self-renewing DC culture from the Balb/c mouse spleen. We demonstrate that these cells, termed IDC-3, have a myeloid DC origin, i.e. they are CD11c(+) CD11b(++) CD8-α(-) F4/80(+/-) and that they also display a phenotype MHC-II(+) CD16/32(++) CD80(+/-) CD86(+) , indicating that they are immature DC. Following incubation with Mycobacterium bovis BCG (Bacillus Calmette Guerin), the IDC-3 efficiently took up bacteria and acquired the morphology of mature DC. Importantly though, when IDC-3 were pre-stimulated with a mycobacterial antigen in vitro, they were able to induce proliferation of T lymphocytes from mice immunized with the same antigen. The T-cell stimulatory potential of IDC-3 was further enhanced when the cells were co-stimulated with an anti-CD40 mAb. We therefore suggest that the IDC-3 culture system could be a useful tool for studying the interaction of DC with mycobacteria.

Isolation of human blood DC subtypes

Human blood dendritic cells (DCs) are a rare, heterogeneous cell population that comprise approximately 1% of circulating peripheral blood mononuclear cells (PBMCs). Their isolation has been confounded by their scarcity and lack of distinguishing markers and their characterisation perplexed by the recent discovery of phenotypic and functionally distinct subsets. Human blood DCs are broadly defined as leukocytes that are HLA-DR positive and lack expression of markers specific for T cell, B cell, NK cell, monocyte and granulocyte lineages. They can be subdivided into the CD11c(-) (CD123(+)CD303(+)CD304(+)) plasmacytoid DC and CD11c(+) myeloid DC, which can be further subdivided into three subsets based on differential expression of CD1c, CD141 and CD16. DC can be isolated from peripheral blood by using an initial density gradient centrifugation step to enrich for mononuclear cells followed by immunomagnetic depletion of cells expressing markers specific for leukocyte lineages and undesired DC subsets. Subsequent flow cytometry-based cell sorting allows the isolation of highly pure individual DC subsets that can then be used for functional studies.

Immunophenotypic identification, enumeration, and characterization of human peripheral blood dendritic cells and dendritic-cell precursors

Study of dendritic cells is complicated by their low frequency and the lack of specific markers for sensitive and specific identification. Furthermore, these cells are not a homogeneous population, but contain a variety of subsets. Flow cytometry has well-established applications for the analysis of cells present at low frequencies; the use of a two-step acquisition procedure increases the number of cells for analysis. This unit presents protocols for the identification and enumeration of dendritic cells and cell subsets in erythrocyte-lysed whole peripheral blood. Special attention is paid to the combinations of reagents used for the identification of all dendritic cells as well as each subset, and on the multiparametric gating strategies for specific analysis.

LF 15-0195 Generates Synergistic Tolerance by Promoting Formation of CD4+CD25+CTLA4+ T Cells

The purpose of the present study was to investigate the influence of 15-deoxyspergualin (LF) on the phenotypes and functions of dendritic cells (DCs) and T cells and to further illustrate the mechanism of LF-inducing immunologic tolerance. DCs from mice were cultured and treated with varying doses of LF at specific time-points. Fluorescence-activated cell sorting (FACS) was used to verify the changes of phenotypes in the cultured DCs labeled with fluorescent antibody. DCs were also used as stimulators in mixed leukocyte reaction to detect their ability to stimulate T-cell proliferation. DCs and T cells, treated with or without LF, were cultured together; phenotypes and cytokine profile of the T cells were identified and assayed by FACS and enzyme-linked immunosorbent assay. LF induced a dose- and time-dependent suppression of maturation of DCs and a dose-dependent suppression of T-cell proliferation in mixed leukocyte reaction when LF-treated DCs were used as stimulators. LF-treated DCs, cultured with naive T cells, could promote the formation of CD4+CD25+CTLA4+ T-cell subtypes and the production of higher levels of interleukin-10. It was suggested that the mechanism of LF-induced tolerance was inhibiting maturation and function of DC and inducing the formation of regulatory T-cell subtype by "suppressor DCs" to achieve a new immune balance.

Dendritic cell-based approaches to cancer immunotherapy

Immunologic approaches to the treatment of malignancies are currently enjoying a resurgence of enthusiasm due to the discovery of tumour-associated antigens and the requirements for stimulating a tumour antigen-specific immune response. The goal of the newer strategies is to stimulate immunity against specific tumour-associated antigens, rather than to broadly, but non-specifically, stimulate the immune system. Since dendritic cells, professional antigen-presenting cells, play a central role in stimulating immune responses in vivo, there is considerable interest in immunising patients with autologous dendritic cells loaded with tumour antigens of interest. Methods for generating large numbers of dendritic cells under clinically-applicable conditions have been developed and it has been shown that they may be loaded with antigen in many different forms including proteins or peptides, RNA or DNA and cellular extracts. Ongoing research is seeking to optimise the purity, antigen loading and maturation of the dendritic cells. Phase I clinical trials have been initiated in order to study the safety and feasibility of immunisations with dendritic cells in humans with various malignancies. Phase II studies will be performed to establish which tumours and clinical scenarios will be most relevant for dendritic cell immunotherapy. Although the commercial applicability of dendritic cell-based immunotherapy has been recognised by the biotechnology industry, commercial availability of dendritic cell vaccines await phase III studies.

Cysteinyl leukotrienes regulate dendritic cell functions in a murine model of asthma

Dendritic cells (DCs) act as APCs in the airway and play a critical role in allergy. Cysteinyl leukotrienes (cysLTs) synthesized from arachidonic acid are primary mediators of immediate asthmatic reaction. The aim of this study was to investigate the effects of cysLTs on Dermatophagoides farinae (Der f)-pulsed mouse myeloid DCs in inducing allergic airway inflammation in vitro and in vivo. Control DC (medium-pulsed), Der f-pulsed DC, cysLT-pulsed DC, Der f- and cysLT-pulsed DC, and Der f-pulsed and cysLT receptor antagonist (LTRA)-treated DC were prepared from murine bone marrow, and the production of cytokines ws compared. Subsequently, these DCs were intranasally instilled into another group of naive mice, followed by intranasal Der f challenge to induce allergic airway inflammation in vivo. Der f-pulsed DC produced significantly higher amounts of IL-10 and IL-12 compared with control DC. Der f- and cysLT-pulsed DC further increased IL-10 production compared with Der f-pulsed DC. In contrast, treatment of Der f-pulsed DC with LTRA increased IL-12 and decreased IL-10. Intranasal instillation of Der f-pulsed DC resulted in airway eosinophilia associated with a significant rise in IL-5 levels in the airway compared with control DC. Pulmonary eosinophilia and excess IL-5 were further enhanced in Der f- and cysLT-pulsed DC-harboring mice. In contrast, Der f-pulsed and LTRA-treated DC significantly inhibited airway eosinophilia, reduced IL-5, and increased IFN-gamma in the airway. Our results suggest that cysLTs play an important role in the development of allergic airway inflammation by regulating the immunomodulatory functions of DCs.

Lineage specificity of gene expression patterns

The hematopoietic system offers many advantages as a model for understanding general aspects of lineage choice and specification. Using oligonucleotide microarrays, we compared gene expression patterns of multiple purified hematopoietic cell populations, including neutrophils, monocytes, macrophages, resting, centrocytic, and centroblastic B lymphocytes, dendritic cells, and hematopoietic stem cells. Some of these cells were studied under both resting and stimulated conditions. We studied the collective behavior of subsets of genes derived from the Biocarta database of functional pathways, hand-tuned groupings of genes into broad functional categories based on the Gene Ontology database, and the metabolic pathways in the Kyoto Encyclopedia of Genes and Genomes database. Principal component analysis revealed strikingly pervasive differences in relative levels of gene expression among cell lineages that involve most of the subsets examined. These results indicate that many processes in these cells behave differently in different lineages. Much of the variation among lineages was captured by the first few principal components. Principal components biplots were found to provide a convenient visual display of the contributions of the various genes within the subsets in lineage discrimination. Moreover, by applying tree-constructing methodologies borrowed from phylogenetics to the expression data from differentiated cells and stem cells, we reconstructed a tree of relationships that resembled the established hematopoietic program of lineage development. Thus, the mRNA expression data implicitly contained information about developmental relationships among cell types.

Regulation of Mite Allergen-pulsed Murine Dendritic Cells by Respiratory Syncytial Virus

Dendritic cells (DCs) are the only antigen-presenting cells that determine T-cell differentiation and play an important role in both allergy and viral infection. Respiratory syncytial virus (RSV) can infect DCs and affect their functions. The aim of this study was to determine the interaction between RSV infection and Dermatophagoides farinae allergen (D. farinae) sensitization on the development of allergy at the DC level. Murine bone marrow-derived DCs were prepared and treated as: control; D. farinae-pulsed DCs (D. farinae-DCs); ultraviolet-inactivated RSV challenged; RSV-infected, D. farinae-pulsed plus ultraviolet-inactivated RSV-challenged; and D. farinae-pulsed plus RSV-infected. In in vitro experiments, we compared the expression of costimulatory molecules and cytokine production between the six groups of DCs. Another group of naive mice were then intranasally inoculated with these DCs, after which intranasal challenge with D. farinae was performed to develop allergic airway inflammation in vivo. In comparison with D. farinae-DCs, D. farinae-pulsed plus RSV-infected DCs showed helper T cell (Th) 1-favored expression of costimulatory molecules and cytokine production. Allergic airway inflammation induced by intranasal instillation of D. farinae-DCs was abrogated when infected with RSV, which was associated with a concomitant suppression of Th2 response in the lung. Our results indicated that RSV suppresses D. farinae-DCs to induce Th2 response both in vitro and in vivo through regulation of expression of surface markers and production of immunoregulatory cytokines.

The evolving role of monoclonal antibodies and dendritic cell therapy in hematologic malignancies

The approach for treatment of hematological cancers had changed in the last decade from non-specific eradication of tumor cells by chemotherapy to more specific strategies by activation of immune system. There are number of potential targets of immune responses in patients with hematological malignancies. Some have been developed like monoclonal antibody therapy and others that have yet to be define like dendritic cell infusion. In this review, we will discuss the evolving role of monoclonal antibody therapy and donor dendritic cell infusion in mounting on immune response in hematological malignancies.

Phenotype and function of murine peritoneal cavity macrophage derived-dendritic cells

The accessory activity was reported in murine peritoneal cavity macrophage derived dendritic cells (PEC-DC) in a mixed lymphocyte reaction (MLR). Here we continue the characterization of the generated PEC-DC using the criteria of morphology, phenotype and other accessory function. We have demonstrated that murine peritoneal cavity macrophages can be induced to differentiate in vitro into cells exhibiting typical dendritic cell (DC) morphology, phenotype and function. The proliferative capacity of the progenitors was amplified in the first step of the culture (day 0-7) using a combination of early cytokines: interleukin 4 and granulocyte-macrophage colony-stimulating factor. The second step of the culture started at day 7 with the removal of early growth factors to allow differentiation and final maturation of DC during 2 days of culture with interferon gamma plus either Toxoplasma lysate antigen (TLA) or lipopolysaccharide (LPS), a bacterial agent as a DC maturing agent. The resulting DC population exhibited typical DC morphology and expressed higher levels of MHC class II and the co-stimulatory molecules CD80 and CD86 compared to the untreated peritoneal cells. The generated DC cells efficiently presented soluble protein antigen to CD3(+) spleen T cells.

A novel bulk-culture method for generating mature dendritic cells from mouse bone marrow cells

We established a novel culture method for generating dendritic cells (DC) from mouse bone marrow (BM) cells. Unfractionated bulk BM cells were cultured in the presence of granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) for 5-7 days and a DC population was isolated by gradient centrifugation with 14.5% (w/v) metrizamide. Through this method, 30-40 x 10(6)/mouse DC with 85-95% purity was obtained on day 7; this yield was higher than those of conventional DC generated by Inaba's method either with GM-CSF alone (conventional-GM DC) or GM-CSF and IL-4 (conventional-GM/4 DC). Bulk-cultured DC have a more matured phenotype than both conventional-GM and -GM/4 DC as shown by higher expression of CD86, MHC class II and CD40. Functional analyses reveal that (1) bulk-DC show less ability in endocytosis than conventional-GM DC and are comparable in IL-12 p70 production with conventional-GM and -GM/4 DC. (2) Bulk-DC exhibit stronger stimulatory capacity in allogeneic T-cell proliferation than conventional DC. (3) By using ovalbumin (OVA) and OVA-specific T-cell receptor (TCR) transgenic mice (DO11.10) system, OVA protein-loaded bulk-DC stimulated CD4 T cells of DO11.10 mice more than conventional-GM DC and comparable with conventional-GM/4 DC. (4) Furthermore, OVA peptide-pulsed bulk-DC stimulated CD4 T cells more than conventional-GM and -GM/4 DC. These data indicate that bulk-DC are functionally more mature than conventional DC. Taken together, bulk-culture method is a simple technique for generating functionally mature BM-DC in large quantities and high purity.

Isolation and characterization of rhesus blood dendritic cells using flow cytometry

Recognition of dendritic cells (DCs) as initiators and modulators of immune responses and growing use of rhesus monkeys for the preclinical optimization of vaccine formulations prompted characterization of the phenotype and function of isolated rhesus peripheral blood DCs. We developed a flow cytometric method to directly identify and isolate DCs from rhesus peripheral blood whereby a T cell depleted population negative for CD3, CD14, CD16 and CD20 but positive for CD83 yielded a cell population with surface markers, morphology, and a cytokine profile similar to human myeloid DCs. Rhesus blood DCs were more effective than monocytes and B cells in mixed lymphocyte reactions and in the presentation of recombinant malaria blood stage antigen MSP-1((42)) to autologous T cells. The ability to isolate rhesus blood DC from peripheral blood should be a useful tool for immunological investigations.

Dendritic cell dynamics in the liver and hepatic lymph

Dendritic cells (DC) are bone-marrow-derived cells that function as professional antigen-presenting cells (APC). Liver is an essential organ for a host defense. It not only is armed with a powerful macrophage system but also is constantly surveyed by a heavy traffic of DC and lymphocytes. In case of emergency, such as infection and inflammation, DC traffic in the liver is accelerated. DC in the liver (interstitial DC) capture and process antigens, enter the draining lymph (DC in hepatic lymph) and accumulate in the T-cell area of hepatic lymph nodes (LN). DC in the LN present antigens to T and B cells to initiate immune responses. In accelerated states, DC precursors are recruited to the liver and soon translocate to hepatic lymph. Even mature lymph DC can undergo a blood-lymph translocation from the liver to hepatic LN after i.v. injection into normal rats. Rat Kupffer cells in the hepatic sinusoids are capable of selectively trapping DC from the blood in vivo and in vitro, suggesting involvement of certain adhesion molecules. Kupffer cells presumably elaborate chemokines to attract and trap the recruited DC via selective adhesion, leading to DC extravasation. The accelerated traffic and the presence of blood-lymph translocation would induce rapid and efficient immune responses and thus contribute to the local defense to antigens within liver tissues as well as systemic defense to blood-borne antigens. DC progenitors are also present in the liver, and these may play an important role in tolerance induction in liver transplantation.

Flow cytometric analysis of different adhesion molecules expression on circulating CD14- and CD64- human dendritic cell precursors

Blood dendritic cell precursors (DCps) are identified as mononuclear leukocytes expressing HLA-DR but lacking the characteristic antigens associated with T cells (CD3), NK cells (CD16 and CD56) and B cells (CD 19). Dendritic cell precursors are distinguished from monocytes by their lack of expression of CD64 rather than of CD14. This study investigated whether CD14- DCps differed from CD64-DCps, which were predominantly CD14+, in their expression of five well-characterised adhesion molecules. There were significantly fewer cells expressing CD11b, CD18 and CD29 in the CD64-DCp population compared with CD14- DCps, and this CD64- DCp subpopulation also had a lower expression of CD11b and CD18. Our results suggest that the two DC precursor subpopulations may differ from one another in their binding characteristics to blood vessel walls and to other leukocytes.

Dendritic cells: immunological sentinels with a central role in health and disease

Immunological effector cells must be sensitive to the antigens or environmental signals that indicate that a pathogen is present. To this end, a group of cells known as the professional antigen-presenting cells have the ability to educate T, B and NK cells as to the fingerprints of specific infections. The most adept of these cells are a closely related family termed dendritic cells (DC). A subset of these act as peripheral sentinels, specializing in the uptake, processing and presentation of antigenic material combined with an ability to detect a wide variety of 'danger' signals. These 'danger' or activation signals induce profound changes in dendritic cell physiology, facilitating the efficient stimulation of both adaptive and innate immunity. In the present review, a number of recent advances in the understanding of DC biology are discussed. These advances offer insights into the pathogenesis of a wide variety of diseases and point towards future strategies for immunotherapy.

Dendritic cell biology and the application of dendritic cells to immunotherapy of multiple myeloma

Dendritic cells (DCs) are extremely efficient antigen-presenting cells that are potent stimulators of both B and T cell immune responses. Although DCs are normally present in extremely small numbers in the circulation, recent advances in DC biology have made it possible to generate DCs in culture. DCs can be generated in vitro from various cellular sources including bone marrow, cord blood and peripheral blood. Although culture conditions are extremely diverse, the majority of protocols grow DCs in GM-CSF and either TNF-alpha and/or IL-4. The addition of other growth factors such as SCF and Flt-3 ligand can dramatically enhance DC recovery. It is important to appreciate that DC subsets have been identified. Thus, DC at different stages of maturation, based on phenotype and capacity to capture antigen, can be obtained depending on culture conditions. For clinical applications, DCs can be generated in serum-free media and cryopreserved for future clinical applications. The ability to obtain DCs in numbers suitable for manipulating immune responses has pushed DC-based immunotherapies into the spotlight for treatment of various malignancies, including multiple myeloma, a B cell malignancy that is presently incurable. Although high-dose chemotherapy and transplantation have improved complete remission rates and overall survival in myeloma, immunotherapeutic strategies are needed for the additional cytoreduction needed to achieve a cure. Because DCs specialize in antigen capture and are extremely potent at stimulating T cell responses, they are ideally suited for generating anti-myeloma T cell responses in vivo. Several studies have demonstrated that myeloma protein, also called idiotype (Id), is sufficiently immunogenic and can be used to generate in vivo T cell responses in myeloma patients. Clinical trials using Id-pulsed DCs as a vaccine to treat minimal residual disease or relapsed myeloma are currently underway. Feasibility studies indicate that antigen-pulsed autologous DCs can be used to elicit in vivo Id-specific T cell responses. Additional studies are needed to optimize current DC vaccination protocols and determine clinical benefits associated with this approach. It is hoped that, following conventional therapies, a combination of adoptive immunotherapeutic modalities such as DCs together with myeloma-specific T cells may lead to improved clinical responses in multiple myeloma, and ultimately lead to complete remission and cure.

Extensive characterization of the immunophenotype and pattern of cytokine production by distinct subpopulations of normal human peripheral blood MHC II+/lineage- cells

Dendritic cells (DC) represent the most powerful professional antigen-presenting cells (APC) in the immune system. The aim of the present study was to analyse, on a single-cell basis by multiparametric flow cytometry with simultaneous four-colour staining and a two-step acquisition procedure, the immunophenotypic profile and cytokine production of DC from 67 normal whole peripheral blood (PB) samples. Two clearly different subsets of HLA-II+/lineage- were identified on the basis of their distinct phenotypic characteristics: one DC subset was CD33strong+ and CD123dim+ (0.16 +/- 0.06% of the PB nucleated cells and 55.9 +/- 11. 9% of all PB DC) and the other, CD33dim+ and CD123strong+ (0.12 +/- 0.04% of PB nucleated cells and 44.53 +/- 11.5% of all PB DC). Moreover, the former DC subpopulation clearly showed higher expression of the CD13 myeloid-associated antigen, the CD29 and CD58 adhesion molecules, the CD2, CD5 and CD86 costimulatory molecules, the CD32 IgG receptor and the CD11c complement receptor. In addition, these cells showed stronger HLA-DR and HLA-DQ expression and a higher reactivity for the IL-6 receptor alpha-chain (CD126) and for CD38. In contrast, the CD123strong+/CD33dim+ DC showed a stronger reactivity for the CD4 and CD45RA molecules, whereas they did not express the CD58, CD5, CD11c and CD13 antigens. Regarding cytokine production, our results show that while the CD33strong+/CD123dim+ DC are able to produce significant amounts of inflammatory cytokines, such as IL-1beta (97 +/- 5% of positive cells), IL-6 (96 +/- 1.1% of positive cells), IL-12 (81.5 +/- 15.5% of positive cells) and tumour necrosis factor-alpha (TNF-alpha) (84 +/- 22.1% of positive cells) as well as chemokines such as IL-8 (99 +/- 1% of positive cells), the functional ability of the CD123strong+/CD33dim+ DC subset to produce cytokines under the same conditions was almost null. Our results therefore clearly show the presence of two distinct subsets of DC in normal human PB, which differ not only in their immunophenotype but also in their functionality, as regards cytokine production.

Circulating CD2+ Monocytes Are Dendritic Cells

Low levels of CD2 have been described on subsets of monocytes, macrophages, and dendritic cells. CD2 is expressed on about one-third of circulating monocytes, at levels one-half log lower than on T or NK cells, representing 2–4% of PBMC. FACS analysis of CD2+ and CD2− monocytes revealed no significant difference in the expression of adhesion molecules (CD11a/b/c), class II Ags (HLA-DR, -DQ, -DP), myeloid Ags (CD13, CD14, CD33), or costimulatory molecules (CD80, CD86). Freshly isolated CD2+ and CD2− monocytes were morphologically indistinguishable by phase contrast microscopy. However, scanning electron microscopy revealed large prominent ruffles on CD2+ monocytes in contrast to small knob-like projections on CD2− monocytes. After 2 days of culture, the CD2+ monocytes largely lost CD14 expression and developed distinct dendrites, whereas the CD2− monocytes retained surface CD14 and remained round or oval. Freshly isolated CD2+ monocytes were more potent inducers of the allogeneic MLR and more efficiently induced proliferation of naive T cells in the presence of HIV-1 gp120 than did CD2− monocytes. After culture in the presence of GM/CSF and IL-4, CD2+ monocytes were up to 40-fold more potent than monocyte-derived dendritic cells or CD2− monocytes at inducing allogeneic T cell proliferation. These findings suggest that circulating CD2+ and CD2− monocytes are dendritic cells and the precursors of macrophages, respectively. Thus, dendritic cells are far more abundant in the blood than previously thought, and they and precursors of macrophages exist in the circulation as phenotypically, morphologically, and functionally distinct monocyte populations.

Immunohistochemical localization of CD1a-positive putative dendritic cells in human breast tumours

The presence of a high number of infiltrating CD1a+ cells in malignant neoplasms has been reported to be associated with an improved prognosis, reduced tumour recurrence and fewer metastases. This study identified a population of CD1a+ cells within the lymphoid cell infiltrate in human ductal breast carcinoma (n = 52), which was significantly different from normal breast tissue, in which only two out of nine cases expressed CD1a+ cells (P = 0.0192). In the majority of cases, the infiltrate was low compared with the number of macrophages and T cells present (results not shown). There was no correlation between the number of CD1a+ cells and tumour grade, with all tumour grades expressing similar numbers of infiltrating CD1a+ cells. There was clear evidence, however, that the CD1a+ cells were closely associated with tumour cells. It is likely that CD1a+ cells have a role in antigen capture and presentation in human tumours, and this study documents the density of CD1a+ cells in a large sample of all histological grades of human breast carcinomas.

An advanced culture method for generating large quantities of highly pure dendritic cells from mouse bone marrow

As dendritic cells (DC) are rare populations in all organs, their generation from hematopoietic precursors in large quantities has proven critical to study their biology. From murine bone marrow about 5 x 10(6) cells at 70% purity are obtained per mouse after 8 days of culture with GM-CSF. We have improved this standard method and routinely achieve a 50-fold higher yield, i.e., 1-3 x 10(8) immature and mature DC per mouse at 90-95% purity. The major modifications were: (i) the avoidance of any active depletion of bone marrow cell subpopulations to circumvent loss of precursors, (ii) a lower plating density of bone marrow cells, (iii) a prolonged culture period of 10-12 days, (iv) the reduction of the GM-CSF dose from day 8 or 10 onwards to reduce granulocyte contaminations. The final non-adherent population at day 10-12 constitutes a mixture of immature and mature DC. Further maturation of DC could be induced by high doses of LPS or TNF-alpha for the last 24 h, where 50-70% of the non-adherent fraction represented mature DC with high levels of NLDC-145, CD86 and CD40. This method allows by simple means the generation of high numbers of murine DC with very low B cell or granulocyte contaminations. It will be valuable to study DC biology notably at the molecular level.

Mouse peritoneal cells as a reservoir of late dendritic cell progenitors

Despite the key role played by dendritic cells (DCs) in the physiology of immunity and related diseases, their differentiation pathway has not yet been fully elucidated. In this study we demonstrated that cells obtained from mouse peritoneal cavity lavage can be induced to differentiate in vitro along the dendritic lineage by the addition of optimal concentrations of murine recombinant GMCSF (5OU/ml) for 6 d. At morphological analysis, GM-CSF-treated peritoneal cells appeared loosely adherent to plastic and showed cytoplasmic protrusions and veils typical of DCs. A de novo expression of the DC phenotypic markers MIDC8, DEC205, CD11c and relB with up-regulation of surface MHC-II and complete down-regulation of non-specific esterase (NSE) was also observed in peritoneal cells upon GM-CSF treatment. Functionally, GM-CSF-treated peritoneal cells were highly stimulatory in a mixed lymphocyte reaction, showed a reduced phagocytosis of latex particles and enhanced pinocytic activity. Moreover, tumour necrosis factor (TNF)-alpha (5-10 ng/ml) was able to synergize with GM-CSF in the induction of DC differentiation. On the other hand, when peritoneal cells were induced to differentiate into macrophages by treating in vivo the animals with thioglycollate before peritoneal harvesting, they completely lost the ability to acquire in vitro the dendritic phenotype in response to GM-CSF, either used alone or in combination with TNF-alpha. These results were confirmed by limiting dilution experiments which demonstrated the differentiation of peritoneal cells into DCs at the single cell level. Taken together, these data suggest that resting peritoneal cells in the mouse represent an immature population, capable of further differentiation along either the dendritic or the macrophagic pathway, depending on the type of stimuli they receive.

Optimisation of the conditions for generating human DC initiated antigen specific T lymphocyte lines in vitro

Naive T lymphocytes specific for a given primary antigen occur in low frequencies and require the relevant antigen to be presented by specialist antigen presenting cells (APC), i.e., dendritic cells (DC). For these reasons, the in vitro induction of primary T lymphocyte responses remains a significant technical challenge. We have attempted to improve current strategies for generating in vitro responses by optimising (i) isolation and concomitant activation of DC from peripheral blood, (ii) uptake, processing and presentation of antigen by DC and (iii) antigen driven T lymphocyte proliferation. We established that RPMI 1640 media supplemented with 10% autologous serum resulted in the best yield of CMRF-44+, CD14-, CD19- DC after enrichment over a Nycodenz gradient. Optimal presentation of whole protein and peptide antigen was achieved by addition after the purification of the APC, i.e., at the start of the T lymphocyte proliferation assay. RPMI 1640 supplemented with 10% autologous serum or plasma supported the best antigen driven specific T lymphocyte responses. Using these optimised conditions, we compared the efficacy of PBMC and purified blood DC for priming T lymphocyte responses to the chronic myeloid leukaemia (CML) specific bcr-abl (b3a2) peptide. Peptide specific T lymphocyte responses were generated with both purified DC and whole PBMC, suggesting that T lymphocyte precursor frequency was the limiting factor in these experiments. These results will aid in the generation of human T lymphocyte lines to primary antigens, for in vitro and therapeutic applications.

Type I IFNs Enhance the Terminal Differentiation of Dendritic Cells

This study identifies type I IFNs as activating cytokines in a serum-free system in which human dendritic cells (DC) were generated from CD34+ progenitor cells. After 14 days of culture in GM-CSF, TNF-α, and IL-4, CD34+ progenitors gave rise to a population of large, immature DC expressing CD1a and CD11b but lacking CD14, CD80, CD83, CD86, and CMRF44. During the next 2 wk, this population spontaneously matured into nonadherent, CD1alow/−, CD11blow/−, CD14−, CD80+, CD83+, CD86+, CMRF44+ DC with high allostimulatory activity in the MLR. To examine which factors influenced this maturation, 25 different cytokines or factors were added to the immature DC culture. Only type I IFNs (α or β) accelerated this maturation in a dose-dependent manner, so that after only 3 days the majority of large cells acquired the morphology, phenotype, and function characteristics of mature DC. Furthermore, supernatants from cultures containing spontaneously maturing DC revealed low levels of endogenous IFN production. Because of the similarity of the activation of DC in our culture system with the phenotypic and functional changes observed during Langerhans cells activation and migration in vivo, we investigated the effect of IFN-α on human Langerhans cell migration. IFN-α also activated the migration of human split skin-derived DC, demonstrating that this effect was not limited to DC derived in vitro from hemopoietic progenitor cells. DC activation by type I IFNs represents a novel mechanism of immunomodulation by these cytokines, which could be important during antiviral responses and autoimmune reactions.

Low CD83, but normal MHC class II and costimulatory molecule expression, on spleen dendritic cells from HIV+ patients

Dendritic cells (DCs), which are the most potent antigen-presenting cells for T lymphocytes, are targets for HIV in vitro and in vivo. Antigen presentation by DCs has been suggested to be impaired during HIV infection; however, the extent to which DCs from HIV+ individuals are altered, particularly in lymphoid organs where T cell stimulation takes place, is not clear. To address this question, the levels of expression of functionally important molecules by spleen DCs from HIV+ patients (n = 6), and HIV- organ donors (n = 5) were compared. By rare event analysis of flow cytometry data, spleen DCs from HIV+ patients were not depleted, representing 0.6 +/- 0.4% of spleen mononuclear cells compared with 0.8 +/- 0.5% in HIV- spleens. Fresh HIV+ spleen DCs were MHC II+ and weakly CD86+CD40+, but negative for CD83 and CD80, and hence had a normal phenotype, showing no signs of in vivo activation. After 24 hr of culture, they upregulated the expression of MHC II, CD40, CD80, and CD86 to levels just as high as those on DCs from organ transplant donors. However, cultured DCs from HIV+ spleens showed lower expression of CD83, compared with DCs from HIV- spleens. The biological significance of this observation will be appreciated further when the function of this molecule is better known. These results suggest that putative defects in antigen presentation by DCs from HIV+ patients are not related to the surface expression of MHC II, CD40, CD80, or CD86.

Immature dendritic cells selectively replicate macrophagetropic (M-tropic) human immunodeficiency virus type 1, while mature cells efficiently transmit both M- and T-tropic virus to T cells

Dendritic cells (DCs) can develop from CD14+ peripheral blood monocytes cultured in granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin 4 (IL-4). By 6 days in culture, the cells have the characteristics of immature DCs and can be further induced to mature by inflammatory stimuli or by monocyte-conditioned medium. After infection with macrophagetropic (M-tropic) human immunodeficiency virus type 1 (HIV-1), monocytes and mature DCs show a block in reverse transcription and only form early transcripts that can be amplified with primers for the R/U5 region. In contrast, immature DCs cultured for 6 or 11 days in GM-CSF and IL-4 complete reverse transcription and show a strong signal when LTR/gag primers are used. Blood monocytes and mature DCs do not replicate HIV-1, whereas immature DCs can be productively infected, but only with M-tropic HIV-1. The virus produced by immature DCs readily infects activated T cells. Although mature DCs do not produce virus, these cells transmit both M- and T-tropic virus to T cells. In the cocultures, both DCs and T cells must express functional chemokine coreceptors for viral replication to occur. Therefore, the developmental stage of DCs can influence the interaction of these cells with HIV-1 and influence the extent to which M-tropic and T-tropic virus can replicate.

Human dendritic cells express functional interleukin-7

Interleukin-7 (IL-7) supports the proliferation of mature T lymphocytes, however, the cellular source of IL-7 for T lymphocyte activation has not been well established. We therefore investigated whether human peripheral blood dendritic cells (DC) produce IL-7 as a contribution towards T lymphocyte activation. Human CMRF-44+/CD14-/CD19- low density DC, purified after overnight tissue culture, contained IL-7 transcripts, detected by direct cell reverse transcription-polymerase chain reaction. Intracytoplasmic staining confirmed IL-7 protein in at least a subpopulation of cultured low density DC. In contrast, resting/immature DC, isolated directly by immunodepletion of lineage marker positive cells, contained no IL-7 mRNA. Thus, the expression of IL-7 by DC follows the pattern described previously for CD80, CD86 and CD40. However, tissue culture of purified resting/immature DC, in contrast to CD80, CD86 and CD40, failed to induce IL-7 transcripts. The functional importance of DC IL-7 expression was demonstrated in an allogeneic mixed leukocyte reaction (MLR). Neutralising mAb to IL-7 significantly inhibited T lymphocyte proliferation when low DC numbers were used, but at higher stimulator numbers, anti-IL-7 mAb failed to inhibit an allogeneic MLR. This suggests, that when DC are in excess, other co-stimulatory pathways can compensate for the lack of IL-7. Addition of IL-7 to a MLR caused a significant increase in the proliferative response stimulated by monocytes and B lymphocytes but not by DC. These data support the concept of an initial phase of antigen uptake by DC followed by the optimisation of DC co-stimulatory potential. The co-stimulatory repertoire expressed, including IL-7, may be regulated by exogenous stimuli, thereby ensuring DC flexibility in mounting a response appropriate to the environmental changes.

High levels of a major histocompatibility complex II-self peptide complex on dendritic cells from the T cell areas of lymph nodes

T lymphocytes recirculate continually through the T cell areas of peripheral lymph nodes. During each passage, the T cells survey the surface of large dendritic cells (DCs), also known as interdigitating cells. However, these DCs have been difficult to release from the lymph node. By emphasizing the use of calcium-free media, as shown by Vremec et al. (Vremec, D., M. Zorbas, R. Scollay, D.J. Saunders, C.F. Ardavin, L. Wu, and K. Shortman. 1992. J. Exp. Med. 176:47-58.), we have been able to release and enrich DCs from the T cell areas. The DCs express the CD11c leukocyte integrin, the DEC-205 multilectin receptor for antigen presentation, the intracellular granule antigens which are recognized by monoclonal antibodies M342, 2A1, and MIDC-8, very high levels of MHC I and MHC II, and abundant accessory molecules such as CD40, CD54, and CD86. When examined with the Y-Ae monoclonal which recognizes complexes formed between I-Ab and a peptide derived from I-Ealpha, the T cell area DCs expressed the highest levels. The enriched DCs also stimulated a T-T hybridoma specific for this MHC II-peptide complex, and the hybridoma underwent apoptosis. Therefore DCs within the T cell areas can be isolated. Because they present very high levels of self peptides, these DCs should be considered in the regulation of self reactivity in the periphery.

Developmental regulation of MHC class II transport in mouse dendritic cells

Dendritic cells (DCs) have the unique capacity to initiate primary and secondary immune responses. They acquire antigens in peripheral tissues and migrate to lymphoid organs where they present processed peptides to T cells. DCs must therefore exist in distinct functional states, an idea that is supported by observations that they downregulate endocytosis and upregulate surface molecules of the class II major histocompatibility complex (MHC) upon maturation. Here we investigate the features of DC maturation by reconstituting the terminal differentiation of mouse DCs in vitro and in situ. We find that early DCs, corresponding to those found in peripheral tissues, exhibit a phenotype in which most class II molecules are intracellular and localized to lysosomes. Upon maturation, these cells give rise to a new intermediate phenotype in which intracellular class II molecules are found in peripheral non-lysosomal vesicles, similar to the specialized CIIV population seen in B cells. The intermediate cells then differentiate into late DCs which express almost all of their class II molecules on the plasma membrane. These variations in class II compartmentalization are accompanied by dramatic alterations in the intracellular transport of the new class II molecules and in antigen presentation. We found that although early DCs could not present antigen immediately after uptake, efficient presentation of the previously internalized antigen occurred after maturation, 24-48 hours later. By regulating class II transport and compartmentalization, DCs are able to delay antigen display, a property crucial to their role in immune surveillance.

Generation of dendritic cells from bone marrow progenitors using GM-CSF, TNF-alpha, and additional cytokines: antagonistic effects of IL-4 and IFN-gamma and selective involvement of TNF-alpha receptor-1

We report the generation of dendritic cells (DC) starting from CD34+ bone marrow (BM) progenitor cells, using a two-stage culture system in which, besides granulocyte-macrophage colony-stimulating factor (GM-CSF) and tumour necrosis factor-alpha (TNF-alpha), stem-cell factor (SCF) was added during the first 5 days, while interleukin-4 (IL-4) and/or interferon-gamma (IFN-gamma) were added during the secondary culture period of 9 days. Addition of IL-4 favoured the outgrowth of CD1a+, HLA-DR+, CD4+, CD40+, CD80+ but CD14- cells with dendritic morphology and strong antigen-presenting capacity. Addition of IFN-gamma selectively induced HLA-DR and CD86 but did not up-regulate CD1a expression or antigen-presenting capacity of the differentiated cells. An antagonism between IL-4 and IFN-gamma could further be confirmed in that, as compared with IL-4 alone, the simultaneous addition of IL-4 and IFN-gamma to GM-CSF plus TNF-alpha during maturation reduced both the phenotypical (CD1a, CD4, CD40) and functional characteristics of DC. Using receptor-specific TNF-alpha mutants, we investigated the relative involvement of TNF-alpha receptors R1 and R2 in the generation of DC. The induction of CD1a and HLA-DR, as well as the increase in allostimulatory capacity were dependent on TNF-R1 triggering, whereas triggering through TNF-R2 had no measurable effect. We conclude first, that the expansion of DC from BM progenitors could most effectively be enhanced in a two-stage culture assay using SCF, GM-CSF, TNF-alpha and IL-4; second, that the effect of TNF-alpha in DC generation involves signalling via the TNF-R1 receptor; and third, that IFN-gamma counteracts some of the effects of IL-4 in DC generation.

HLA-DR1–Restricted bcr-abl (b3a2)-Specific CD4+ T Lymphocytes Respond to Dendritic Cells Pulsed With b3a2 Peptide and Antigen-Presenting Cells Exposed to b3a2 Containing Cell Lysates

Chronic myeloid leukemia (CML) is characterized by a specific translocation of the c-abl oncogene on chromosome 9 to the break point cluster region (bcr) on chromosome 22, t(9; 22) (q34; q11). This translocation results in the expression of a 210-kD bcr-abl protein fusion gene product. The juxtaposition of the bcr and abl genes produces a novel junctional amino acid sequence, which may be presented by antigen-presenting cells and recognized specifically by human T lymphocytes. We have generated a CD4+ T lymphocyte line (NG-1) which recognizes the peptide epitope (GFKQSSKALQR) in association with HLA-DRβ1*0101-02. A comparison of antigen-presenting cells showed that CMRF-44+ blood dendritic cell presented a 12mer b3a2 peptide effectively. The b3a2 peptide was able to generate specific primary T-lymphocyte responses in other HLA-DR1 donors. We also show that bcr-abl, b3a2 peptide-specific T-lymphocyte lines proliferate in response to bcr-abl b3a2 containing cell lysates (K562 or CML PBMC derived) but not control (including b2a2 CML PBMC) lysates.

Generation of dendritic cells in vitro from peripheral blood mononuclear cells with granulocyte-macrophage-colony-stimulating factor, interleukin-4, and tumor necrosis factor-alpha for use in cancer immunotherapy

OBJECTIVE

The purpose of the study was to characterize the requirements in terms of precursors, developmental pathways, and media for the generation of large numbers of mature dendritic cells (DC) under conditions acceptable for use in adjuvant, active immunotherapy strategies for surgically treated malignancies.

SUMMARY BACKGROUND DATA

Although limited previously by the small numbers accessible, DC-based immunotherapies for malignancy have become more realistic with the development of methods for efficiently generating larger numbers of DC from peripheral blood mononuclear cells (PBMC) in vitro, but these methods rely on clinically unacceptable culture conditions (such as inclusion of fetal bovine serum), necessitating the development of methods for generating functionally equivalent DC in serum-free conditions.

METHODS

Plastic-adherent PBMC (from healthy donors and patients with cancer) were incubated for 7 days with granulocyte-macrophage-colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) with and without tumor necrosis factor-alpha (TNF-alpha) in fetal bovine serum-containing and serum-free media and were analyzed by Wright's stain for morphology, flow cytometry for phenotype, and mixed lymphocyte reaction for allostimulatory function.

RESULTS

Growth in either serum-containing or serum-free media supplemented with GM-CSF and IL-4 yielded a similarly heterogeneous population of cells, 6% to 10% of which had the morphology (large cells with thin projections), immunophenotype (including CD83+), and function of mature DC. Tumor necrosis factor-alpha significantly augmented the number of these mature DC, whereas preculture depletion of CD14+ PBMC virtually eliminated them.

CONCLUSIONS

Generation of mature DC in the authors' serum-free clinically applicable conditions is similar to serum-containing conditions and requires CD14+ precursors, differentiation through a CD14-CD83- immature stage under the influence of GM-CSF and IL-4, and maturation into a CD83+ DC under the influence of TNF-alpha.

HLA-DR1–Restricted bcr-abl (b3a2)-Specific CD4+ T Lymphocytes Respond to Dendritic Cells Pulsed With b3a2 Peptide and Antigen-Presenting Cells Exposed to b3a2 Containing Cell Lysates

Chronic myeloid leukemia (CML) is characterized by a specific translocation of the c-abl oncogene on chromosome 9 to the break point cluster region (bcr) on chromosome 22, t(9; 22) (q34; q11). This translocation results in the expression of a 210-kD bcr-abl protein fusion gene product. The juxtaposition of the bcr and abl genes produces a novel junctional amino acid sequence, which may be presented by antigen-presenting cells and recognized specifically by human T lymphocytes. We have generated a CD4+ T lymphocyte line (NG-1) which recognizes the peptide epitope (GFKQSSKALQR) in association with HLA-DRβ1*0101-02. A comparison of antigen-presenting cells showed that CMRF-44+ blood dendritic cell presented a 12mer b3a2 peptide effectively. The b3a2 peptide was able to generate specific primary T-lymphocyte responses in other HLA-DR1 donors. We also show that bcr-abl, b3a2 peptide-specific T-lymphocyte lines proliferate in response to bcr-abl b3a2 containing cell lysates (K562 or CML PBMC derived) but not control (including b2a2 CML PBMC) lysates.

Dendritic cells: therapeutic potentials

Dendritic cells (DCs) are leukocytes that are specialized to capture antigens and initiate T-cell-mediated immune responses. After capture of antigens, DCs, then in an immature stage, leave their tissue of residence and migrate through the lymph/blood into secondary lymphoid organs where they differentiate into mature cells. Because DCs can prime animals in the absence of any other adjuvant, they have been termed 'nature's adjuvant'. Large numbers of DCs can now be generated from circulating monocytes or from CD34 hematopoietic progenitors in response to GM-CSF in combination with either IL4 or TNF alpha. In mice, tumor antigen loaded DCs have been shown to prevent the development of tumors and even to induce the regression of established tumors. DCs therapy represents a very promising approach to the treatment of cancer and infectious diseases. Early studies indicate the existence of DC populations that can induce tolerance and may prove useful in organ transplantation.

Isolation of Human Blood Dendritic Cells Using the CMRF-44 Monoclonal Antibody: Implications for Studies on Antigen-Presenting Cell Function and Immunotherapy

Dendritic cells (DC) are potent antigen-presenting cells (APC) with the capacity to stimulate a primary T lymphocyte immune response and are therefore of interest for potential immunotherapeutic applications. Freshly isolated DC or DC precursors may be preferable for studies of antigen uptake and the potential control of APC costimulator activity. In this report, we report that the monoclonal antibody CMRF-44 can be used to detect early DC differentiation. The majority of DC circulating in blood do not express any known DC lineage specific markers, but can be identified by CMRF-44 labeling after a brief period of in vitro culture. The sequential acquisition of DC activation antigens allows the identification of two stages of DC maturation/activation. Cytokines, especially granulocyte-macrophage colony-stimulating factor (GM-CSF ) and tumor necrosis factor (TNF )α, enhance both phases of this process, whereas CD40-ligand trimer preferentially enhances the final DC maturation to a fully mature, activated phenotype. DC positively selected using CMRF-44 possess potent allostimulatory activity and are efficient at the uptake, processing, and presentation of soluble antigens for both primary and secondary immune responses. CMRF-44+ DC are also more potent than other APC types at restimulation of a chronic myeloid leukemia peptide specific T-cell clone. The use of a purified population of freshly isolated DC may be advantageous in attempts to initiate, maintain, and direct immune responses for immunotherapeutic applications.

Isolation of Human Blood Dendritic Cells Using the CMRF-44 Monoclonal Antibody: Implications for Studies on Antigen-Presenting Cell Function and Immunotherapy

Dendritic cells (DC) are potent antigen-presenting cells (APC) with the capacity to stimulate a primary T lymphocyte immune response and are therefore of interest for potential immunotherapeutic applications. Freshly isolated DC or DC precursors may be preferable for studies of antigen uptake and the potential control of APC costimulator activity. In this report, we report that the monoclonal antibody CMRF-44 can be used to detect early DC differentiation. The majority of DC circulating in blood do not express any known DC lineage specific markers, but can be identified by CMRF-44 labeling after a brief period of in vitro culture. The sequential acquisition of DC activation antigens allows the identification of two stages of DC maturation/activation. Cytokines, especially granulocyte-macrophage colony-stimulating factor (GM-CSF ) and tumor necrosis factor (TNF )α, enhance both phases of this process, whereas CD40-ligand trimer preferentially enhances the final DC maturation to a fully mature, activated phenotype. DC positively selected using CMRF-44 possess potent allostimulatory activity and are efficient at the uptake, processing, and presentation of soluble antigens for both primary and secondary immune responses. CMRF-44+ DC are also more potent than other APC types at restimulation of a chronic myeloid leukemia peptide specific T-cell clone. The use of a purified population of freshly isolated DC may be advantageous in attempts to initiate, maintain, and direct immune responses for immunotherapeutic applications.

Dendritic cells in the T-cell areas of lymphoid organs

Substantial numbers of dendritic cells (DCs) are found in the T-cell areas of peripheral lymphoid organs such as the spleen, lymph node and Peyer's patch. By electron microscopy these DCs (also called interdigitating cells) form a network through which T-cells continually recirculate. The cytological features of DCs in the T-cell areas, as well as a number of markers detected with monoclonal antibodies, are similar to mature DCs that develop from other sites such as skin and bone marrow. Some markers that are expressed in abundance are: MHC II and the associated invariant chain, accessory molecules such as CD40 and CD86, a multilectin receptor for antigen presentation called DEC-205, the integrin CD11c, several antigens within the endocytic system that are detected by monoclonal antibodies but are as yet uncharacterized at the molecular level, and, in the human system, molecules termed S100b, CD83 and p55. DCs in the periphery can pick up antigens and migrate to the T-cell areas to initiate immunity. However, there are new observations that DCs within the T-cell areas also express high levels of self-antigens and functional fas-ligand capable of inducing CD4+ T-cell death. We speculate that there are at least 2 sets of DCs in the T-cell areas, a migratory myeloid pathway that brings in antigens from the periphery and induces immunity, and a more resident lymphoid pathway that presents self-antigens and maintains tolerance.

Role of dendritic cells in immunopathogenesis of human immunodeficiency virus infection

The role of dendritic cells (DC) in the pathogenesis of human immunodeficiency virus (HIV) disease has been a subject of considerable interest for several years. Initial studies focused on the infection, dysfunction, and depletion of DC in HIV-infected individuals. More recent studies have begun to identify the functional role of DC in the initiation and propagation of viral replication in T cells in HIV-infected individuals. This review discusses recent data regarding the role of DC in HIV disease with the aim of delineating basic immunopathogenic principles of infection and the development of therapeutic strategies.

Mannose receptor mediated antigen uptake and presentation in human dendritic cells

In an immature state, dendritic cells (DC) can capture antigen via at least two mechanisms. First, DC use macropinocytosis for continuous uptake of large amounts of soluble antigens. Second, they express high levels of mannose receptor that can mediate internalization of glycosylated ligands. We found that dendritic cells can present mannosylated antigen 100-1000 fold more efficiently than non-mannosylated antigen. Immunocytochemistry as well as subcellular fractionation demonstrated that the mannose receptor and MHC class II molecules were located in distinct subcellular compartments. These results demonstrate that the mannose receptor endows DC with a high capacity to present glycosylated antigens at very low concentrations.

Human dendritic cells handling of binding, uptake and degradation of free and IgG-immune complexed dinitrophenylated human serum albumin in vitro

The handling of free and IgG-complexed dinitrophenylated human serum albumin (DNP-HSA) by human dendritic cells (DC) cultured with granulocyte-macrophage colony-stimulating factor (GM-CSF) and interleukin-4 (IL-4) was studied. It has been shown that the amount of uncomplexed or IgG-complexed antigen required by DC to start an immune response is low compared with other antigen-presenting cells. We therefore examined whether such efficient presentation of immune complexes is due to an enhanced Fc gamma RII-mediated endocytosis or to a specialized and efficient antigen handling, i.e., macropinocytosis. The Fc gamma RII expression was found to be heterogeneous on the GM-CSF- and IL-4-cultured DC, i.e. it ranges from low to high expression. The handling of antigen and immune complexes revealed, that the level of binding and uptake of IgG-DNP-HSA complexes by in vitro expanded DC is low compared with free antigen. Uncomplexed DNP-HSA is probably handled either by endocytosis via receptors being more abundant and/or efficient than the Fc gamma RII or via non-receptor-mediated endocytosis. The binding and uptake of IgG-complexed DNP-HSA was blocked by anti-Fc gamma RII antibody, indicating the specificity of the interaction.

Expression and function of CD80 and CD86 costimulator molecules on synovial dendritic cells in chronic arthritis

OBJECTIVE

To examine CD86 expression on dendritic cells isolated from the synovial fluid (SFDC) of patients with chronic arthritis, and to determine the importance of both CD80 and CD86 molecules in SFDC-T lymphocyte interactions.

METHODS

CD86 messenger RNA (mRNA) and surface expression were analyzed in SFDC using reverse transcriptase-polymerase chain reaction and flow cytometry, respectively. The costimulator activity of the SFDC CD80 and CD86 molecules was determined by allogeneic mixed lymphocyte reaction (MLR). CD80 and CD86 induction on SFDC during in vitro culture was also examined.

RESULTS

Fresh SFDC either lacked or showed very weak surface expression of CD86 molecules (as shown previously for CD80), yet contained CD86 mRNA. CD80 antibodies minimally inhibited an allogeneic MLR, whereas CD86 antibodies and CTLA-4 Ig showed significant inhibition. Both CD80 and CD86 molecules were inconsistently induced on SFDC following culture in either media, interferon-gamma, or granulocyte-macrophage colony-stimulating factor.

CONCLUSION

SFDC may be defective antigen-presenting cells in vivo. The ability of CD80 and CD86 molecules to be induced and become functional on SFDC in vitro implies the presence of a negative regulatory compound(s) in the synovial environment.