Langerin, a novel C-type lectin specific to Langerhans cells, is an endocytic receptor that induces the formation of Birbeck granules

Network of dendritic cells within the muscular layer of the mouse intestine

Dendritic cells (DCs) are located at body surfaces such as the skin, respiratory and genital tracts, and intestine. To further analyze intestinal DCs, we adapted an epidermal sheet separation technique and obtained two intestinal layers, facing the lumen and serosa. Unexpectedly, immunolabeling of the layer toward the serosa revealed a regular, dense, planar network of cells with prominent dendritic morphology within the external muscular layer and with increasing frequency along the length of the intestine. Direct examination of the serosal-disposed layers showed a significant fraction of the DCs to express DEC-205/CD205, CD11c, Langerin/CD207, Fcgamma receptor/CD16/32, CD14, and low levels of activation markers, CD25, CD80, CD86, and CD95. By more sensitive FACS analyses, cells from this layer contained two CD11c(+) populations of CD45(+) CD205(+), CD19(-) leukocytes, MHC II(+) and MHC II(-). When ovalbumin conjugated to an anti-DEC-205 antibody was injected into mice, the conjugate targeted to these DCs, which upon isolation were able to stimulate ovalbumin-specific, CD4(+) and CD8(+) T cell antigen receptor-transgenic T cells. In vivo, these DCs responded to two microbial stimuli, systemic LPS and oral live bacteria, by up-regulating CD80, CD86, DEC-205, and Langerin within 12 h. This network of DCs thus represents a previously unrecognized antigen-presenting cell system in the intestine.

Estrogen selectively promotes the differentiation of dendritic cells with characteristics of Langerhans cells

The steroid hormone estrogen regulates the differentiation, survival, or function of diverse immune cells. Previously, we found that physiological amounts of 17beta-estradiol act via estrogen receptors (ER) to promote the GM-CSF-mediated differentiation of dendritic cells (DC) from murine bone marrow progenitors in ex vivo cultures. Of the two major subsets of CD11c(+) DC that develop in these cultures, estrogen is preferentially required for the differentiation of a CD11b(int)Ly6C(-) population, although it also promotes increased numbers of a CD11b(high)Ly6C(+) population. Although both DC subsets express ERalpha, only the CD11b(high)Ly6C(+) DC express ERbeta, perhaps providing a foundation for the differential regulation of these two DC types by estrogen. The two DC populations exhibit distinct phenotypes in terms of capacity for costimulatory molecule and MHC expression, and Ag internalization, which predict functional differences. The CD11b(int)Ly6C(-) population shows the greatest increase in MHC and CD86 expression after LPS activation. Most notably, the estrogen-dependent CD11b(int)Ly6C(-) DC express langerin (CD207) and contain Birbeck granules characteristic of Langerhans cells. These data show that estrogen promotes a DC population with the unique features of epidermal Langerhans cells and suggest that differentiation of Langerhans cells in vivo will be dependent upon local estrogen levels and ER-mediated signaling events in skin.

Solitary cutaneous dendritic cell tumor in a child: Role of dendritic cell markers for the diagnosis of skin Langerhans cell histiocytosis

We describe a child with a solitary dendritic cell (DC) tumor positive for S-100 protein, CD1a, and HLA-DR with the clinical and histopathologic features of a so-called solitary variant of congenital self-healing Hashimoto-Pritzker reticulohistiocytosis (CSHRH). CSHRH is a spontaneously regressing, benign form of Langerhans cell histiocytosis (LCH) and was thought to be a histiocytosis consisting of precursor Langerhans cells. In our study the tumor cells did not express CD68, indicating that they represent mature DCs. Because of the negative finding for Langerin, it cannot be assessed whether the tumor consists of terminally mature Langerhans cells that have lost Langerin expression upon maturation or of mature dermal DCs. This case demonstrates that the progress in DC biology necessitates reevaluation of our knowledge of LCH to better understand the different variants of the disease. Therefore the literature on CSHRH is reviewed in light of present knowledge on cutaneous DC immunology.

Flk2+ myeloid progenitors are the main source of Langerhans cells

Langerhans cells (LCs) are antigen-presenting cells (APCs) residing in the epidermis that play a major role in skin immunity. Our earlier studies showed that when skin is inflamed LCs are replaced by bone marrow-derived progenitor cells, while during steady-state conditions LCs are able to self-renew in the skin. Identification of the LC progenitors in bone marrow would represent a critical step toward identifying the factors that regulate LC generation as well as their trafficking to the skin. To determine LC lineage origin, we reconstituted lethally irradiated CD45.2 mice with rigorously purified lymphoid and myeloid progenitors from CD45.1 congenic mice. Twenty-four hours later, we exposed the mice to UV light to deplete resident LCs and induce their replacement by progenitors. Reconstitution with common myeloid progenitors (CMPs), common lymphoid progenitors (CLPs), granulocyte-macrophage progenitors (GMPs), or early thymic progenitors led to LC generation within 2 to 3 weeks. CMPs were at least 20 times more efficient at generating LCs than CLPs. LCs from both lineages were derived almost entirely from fetal liver kinase-2+ (Flk-2+) progenitors, displayed typical dendritic-cell (DC) morphology, and showed long-term persistence in the skin. These results indicate that LCs are derived mainly from myeloid progenitors and are dependent on Flt3-ligand for their development.

Human dendritic cell subsets for vaccination

Protective immunity results from the interplay of antigen (Ag)-nonspecific innate immunity and Ag-specific adaptive immunity. The cells and molecules of the innate system employ non-clonal recognition pathways such as lectins and TLRs. B and T lymphocytes of the adaptive immune system employ clonal receptors recognizing Ag or peptides in a highly specific manner. An essential link between innate and adaptive immunity is provided by dendritic cells (DCs). As a component of the innate immune system, DC organize and transfer information from the outside world to the cells of the adaptive immune system. DC can induce such contrasting states as active immune responsiveness or immunological tolerance. Recent years have brought a wealth of information regarding DC biology and pathophysiology that shows the complexity of this cell system. Thus, presentation of antigen by immature (non-activated) DCs leads to tolerance, whereas mature, antigen-loaded DCs are geared towards the launching of antigen-specific immunity. Furthermore, DCs are composed of multiple subsets with distinct functions at the interface of the innate and adaptive immunity. Our increased understanding of DC pathophysiology will permit their rational manipulation for therapy such as vaccination to improve immunity.

UVA Radiation Impairs Phenotypic and Functional Maturation of Human Dermal Dendritic Cells

There is now strong evidence that the ultraviolet A (UVA) part of the solar spectrum contributes to the development of skin cancers. Its effect on the skin immune system, however, has not been fully investigated. Here, we analyzed the effects of UVA radiation on dermal dendritic cells (DDC), which, in addition, provided further characterization of these cells. Dermal sheets were obtained from normal human skin and irradiated, or not, with UVA at 2 or 12 J per cm2. After a 2 d incubation, the phenotype of emigrant cells was analyzed by double immunostaining and flow cytometry. Results showed that migratory DDC were best characterized by CD1c expression and that only few cells co-expressed the Langerhans cell marker Langerin. Whereas the DC extracted from the dermis displayed an immature phenotype, emigrant DDC showed increased expression of HLA-DR and acquired co-stimulation and maturation markers. We showed here that UVA significantly decreased the number of viable emigrant DDC, a process related to increased apoptosis. Furthermore, UVA irradiation impaired the phenotypic and functional maturation of migrating DDC into potent antigen-presenting cells, in a concentration-dependent manner. The results provide further evidence that UVA are immunosuppressive and suggest an additional mechanism by which solar radiation impairs immune response.

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

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

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

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

Selective expression of vacuolar H+-ATPase subunit d2 by particular subsets of dendritic cells among leukocytes

Dendritic cells (DC) are far more potent to activate T cells than other antigen presenting cells (e.g., macrophages) and distributed to many organs where DC develop to functionally and phenotypically distinctive subsets. To isolate DC-differentially expressed genes, we used a subtractive cDNA cloning (XS52 DC minus J774 macrophages), resulting in the identification of d2 isoform of vacuolar (V) H+-ATPase subunit d. Unlike the ubiquitously expressed isoform (d1), d2 mRNA manifested expression restricted to particular subsets of DC (e.g., skin- and bone marrow-derived DC) among leukocytes and encoded two transcripts (1.6 and 3.0 kb) that differed in the length of the 3'-untranslated region. The d2 protein displayed association with membranes and the localization in lysosomes and antigen-containing endosomes. Interestingly, XS52 DC expressed seven-fold higher V-ATPase proton-pump activity than J774 macrophages and distinguished from the macrophage by high levels of isoforms a1 and a2 expression among V-ATPase subunits. These results indicated that d2 is a new marker for DC and it may, co-operatively with subunit a isoforms, regulate V-ATPase activity.

Migratory Langerhans cells in mouse lymph nodes in steady state and inflammation

Dendritic cells cells induce immunity or-in the steady state-maintain peripheral tolerance. Little is known in that regard about Langerhans cells. Therefore, we investigated migrating Langerhans cells in the steady-state versus inflammation. Increased numbers of Langerhans cells, as determined by immunostaining for Langerin/CD207, appeared in the lymph nodes in response to a contact allergen. Whereas a large proportion of Langerhans cells expressed CD86 in the steady state, CD40, and CD80 were found on a smaller percentage. During inflammation, more CD40(+), CD80(+), CD274/B7-H1/PD-L1(+), and CD273/B7-DC/PD-L2(+) Langerhans cells were found in the lymph nodes, and they expressed higher levels of these molecules. CD275/inducible T cell co-stimulator (ICOS) ligand was not detected. Langerhans cells in the nodes of contact allergen-treated mice produced more IL-12p40/70. This correlated with more interferon-gamma being produced by activated lymph node T cells. Epicutaneous immunization with ovalbumin under inflammatory conditions led to a more vigorous proliferation of antigen-specific CD4 T cells in vitro and in vivo as compared with immunization in the steady state. The latter modality, however did not induce strong CD4 T cell tolerance in this model. Thus, the overall phenotype of Langerhans cells is not an indicator for their immunogenic or tolerogenic potential.

TNF-alpha enhances phenotypic and functional maturation of human epidermal Langerhans cells and induces IL-12 p40 and IP-10/CXCL-10 production

Dendritic cells (DC) play a central role in immunity/tolerance decision, depending on their activation/maturation state. TNF-alpha is largely produced in the skin under inflammatory conditions. However, it still remains to be defined how TNF-alpha modulates the activation status of human LC, the most specialized DC controlling skin immunity. Here, we reported that fresh immature LC, highly purified from healthy human skin and exposed for two days to TNF-alpha under serum-free conditions, expressed up-regulated level of co-stimulatory molecules (CD40, CD54, CD86), maturation markers (CD83, DC-LAMP), CCR7 lymph node homing receptor, and down-regulated Langerin level, in a dose-dependent manner. This mature phenotype is closely associated with enhanced LC allostimulatory capacity. Furthermore, TNF-alpha significantly increased the number of viable LC and decreased their spontaneous apoptosis. More importantly, TNF-alpha induced LC to produce both IFN-gamma-inducible-protein IP-10/CXCL10, a Th1-attracting chemokine and IL-12 p40. Bioactive IL-12 p70 was never detected, even after additional CD40 stimulus. The results implicate LC as an effective target through which TNF-alpha may up- or down-regulate the inflammatory skin reactions.

Reactivity of Langerhans cells in human reconstructed epidermis to known allergens and UV radiation

Epidermal Langerhans cells are the outmost guards of our immune defence system. These cells are directly involved in phenomena such as contact hypersensitivity and UV-induced immunosuppression. Some years ago we succeeded in introducing CD34(+)-derived Langerhans cells into a reconstructed human epidermis. Here we describe their reactivity after topical exposure of the reconstructed epidermis to known allergens, allergen-inducible cytokines, irritants and UV irradiation. Exposure to allergens for 24 h resulted in an activated appearance of the Langerhans cells and in some cases a decrease in their number. Concomitantly, IL-1beta and CD86 mRNA over-expressions were detected in the reconstructed epidermis. A topical treatment with TNF-alpha or IL-1beta revealed that both cytokines induced an activated appearance of the Langerhans cells as early as 4 h following application. Irritants had no effect on the integrated Langerhans cells. Exposure of the reconstructed epidermis to Solar Simulated Radiation caused a dramatic decrease in the number of Langerhans cells and a loss of dendricity in the remaining cells 24 h after irradiation. The topical application of a large spectrum UVA/B filter before irradiation prevented these UV-induced alterations. In our hands, this model provides a promising tool to evaluate the sensitization potential of new compounds and to validate the efficacy of sunscreens to prevent UV-induced immunosuppression.

Langerhans cells are strongly reduced in the skin of transgenic mice overexpressing follistatin in the epidermis

Activins are members of the transforming growth factor-beta (TGF-beta) family and are important for skin morphogenesis and wound healing. TGF-beta1 is necessary for the population of the epidermis with Langerhans cells (LC). However, a role for activin in LC biology is not known. To address this question, we analyzed skin from transgenic mice overexpressing the activin antagonist follistatin in the epidermis. Using immunofluorescence, we observed a striking decrease in the number of LC in the epidermis of transgenic mice in comparison to wild-type mice. Nevertheless, these LC expressed normal levels of major histocompatibility complex (MHC)-class II and Langerin/ CD207 in situ. In explant cultures of whole ear skin the number of dendritic cells (DC), which migrated into the culture medium, was reduced. This reduction was even more pronounced in cultures of epidermal sheets. Virtually all emigrated cutaneous DC displayed typical morphology with cytoplasmic "veils", showed translocation of MHC-class II to the surface membrane, and expressed the maturation marker 2A1. Thus, cutaneous DC from transgenic mice seemed to mature normally. These results demonstrate that overexpression of follistatin in the epidermis affects LC trafficking but not maturation and suggest a novel role of the follistatin-binding partner activin in LC biology.

Cutaneous CXCL14 Targets Blood Precursors to Epidermal Niches for Langerhans Cell Differentiation

Dendritic cells (DCs) are major constituents of peripheral tissues, where they control immunity to foreign and self-antigens. The process of continuous DC renewal under homeostatic conditions is largely undefined. Here, we demonstrate that CD14+ DC precursors, either derived from CD34+ hematopoietic progenitor cells or isolated from blood, were attracted by the chemokine CXCL14, which is constitutively produced in healthy skin and other epithelial tissues. In a tissue model we show that human epidermal equivalents profoundly affected CD14+ DC precursors, including their suprabasal positioning and survival as well as their differentiation into Langerhans cell-like cells with potent antigen-presentation functions. Our model assigns unprecedented roles to CXCL14 and epidermal tissue as attractant and niche of differentiation, respectively, in the renewal of Langerhans cells under steady-state conditions.

Augmentation of cutaneous immune responses by ATP gamma S: purinergic agonists define a novel class of immunologic adjuvants

Extracellular nucleotides activate ligand-gated P2XR ion channels and G protein-coupled P2YRs. In this study we report that intradermal administration of ATPgammaS, a hydrolysis-resistant P2 agonist, results in an enhanced contact hypersensitivity response in mice. Furthermore, ATPgammaS enhanced the induction of delayed-type hypersensitivity to a model tumor vaccine in mice and enhanced the Ag-presenting function of Langerhans cells (LCs) in vitro. Exposure of a LC-like cell line to ATPgammaS in the presence of LPS and GM-CSF augmented the induction of I-A, CD80, CD86, IL-1beta, and IL-12 p40 while inhibiting the expression of IL-10, suggesting that the immunostimulatory activities of purinergic agonists in the skin are mediated at least in part by P2Rs on APCs. In this regard, an LC-like cell line was found to express mRNA for P2X(1), P2X(7), P2Y(1), P2Y(2), P2Y(4), P2Y(9), and P2Y(11) receptors. We suggest that ATP, when released after trauma or infection, may act as an endogenous adjuvant to enhance the immune response, and that P2 agonists may augment the efficacy of vaccines.

Recombinant adenovirus type 5 vectors that target DC-SIGN, ChemR23 and alpha(v)beta3 integrin efficiently transduce human dendritic cells and enhance presentation of vectored antigens

Recombinant adenoviruses (rAds) represent a promising system for vaccine delivery but transduce dendritic cells (DC) relatively poorly. To address this concern, we used a biotin-avidin linkage to conjugate rAd vectors to ligands which bind with high affinity to selected receptors on DC (ChemR23, alpha(v)beta3 integrin, and DC-SIGN). The targeted vectors had an enhanced ability to transduce human monocyte-derived DC compared to untargeted virus. In addition, DC transduced with targeted rAd vectors were more efficient at stimulating cytokine production by autologous memory CD8+ T cells, against a vector-encoded antigen. These results expand the range of cell surface receptors that can be used to target rAd5 vectors to DC, and may facilitate future development of rAd-based vaccines.

Dynamics and function of Langerhans cells in vivo: dermal dendritic cells colonize lymph node areas distinct from slower migrating Langerhans cells

Langerhans cells (LCs) are prominent dendritic cells (DCs) in epithelia, but their role in immunity is poorly defined. To track and discriminate LCs from dermal DCs in vivo, we developed knockin mice expressing enhanced green fluorescent protein (EGFP) under the control of the langerin (CD207) gene. By using vital imaging, we showed that most EGFP(+) LCs were sessile under steady-state conditions, whereas skin inflammation induced LC motility and emigration to lymph nodes (LNs). After skin immunization, dermal DCs arrived in LNs first and colonized areas distinct from slower migrating LCs. LCs reaching LNs under steady-state or inflammatory conditions expressed similar levels of costimulatory molecules. Langerin and EGFP were also expressed on thymic DCs and on blood-derived, CD8alpha(+) DCs from all secondary lymphoid organs. By using a similar knockin strategy involving a diphtheria toxin receptor (DTR) fused to EGFP, we demonstrated that LCs were dispensable for triggering hapten-specific T cell effectors through skin immunization.

Histology, Immunohistochemistry and Ultrastructure of the Equine Palatine Tonsil

The palatine tonsils of five young horses formed 10-12 cm elongated follicular structures extending from the root of the tongue on either side to the base of the epiglottis and lateral to the glossoepiglottic fold. The stratified squamous non-keratinized epithelium of the outer surface was modified into crypts as reticular epithelium by heavy infiltration of lymphoid cells from underlying lymphoid follicles. In places, lymphoid tissue reaching almost to the surface and with only one to two cell layers intact was identified as the lymphoepithelium. Langerhans cells with Birbeck granules were interspersed between epithelial cells. Lymphoid tissue organized in lymphoid follicles constituted the parenchyma of the palatine tonsil. CD4-positive cells were more numerous and CD8-positive lymphocytes less numerous compared with their distribution in the lingual tonsil. B cells and macrophages were also more numerous than in the lingual tonsil and lectins showed a different pattern of attachment. M cells were not observed. High endothelial venules with well-developed vesiculo-vacuolar organelle had structural evidence of transendothelial and interendothelial migration of lymphocytes. Striated muscles as seen in the deeper lamina propria mucosae of the lingual tonsil were absent. The immunohistological and ultrastructural characteristics of the equine palatine tonsil are similar to those of humans but differ from those of the lingual tonsil and are consistent with a role as an effector and inductor immunological organ.

Dendritic Cell-specific Intercellular Adhesion Molecule 3-grabbing Non-integrin (DC-SIGN)-mediated Enhancement of Dengue Virus Infection Is Independent of DC-SIGN Internalization Signals

Dengue virus (DV) is a mosquito-borne flavivirus that causes hemorrhagic fever in humans. In the natural infection, DV is introduced into human skin by an infected mosquito vector where it is believed to target immature dendritic cells (DCs) and Langerhans cells (LCs). We found that DV productively infects DCs but not LCs. We show here that the interactions between DV E protein, the sole mannosylated glycoprotein present on DV particles, and the C-type lectin dendritic cell-specific intercellular adhesion molecule 3-grabbing non-integrin (DC-SIGN) are essential for DV infection of DCs. Binding of mannosylated N-glycans on DV E protein to DC-SIGN triggers a rapid and efficient internalization of the viral glycoprotein. However, we observed that endocytosis-defective DC-SIGN molecules allow efficient DV replication, indicating that DC-SIGN endocytosis is dispensable for the internalization step in DV entry. Together, these results argue in favor of a mechanism by which DC-SIGN enhances DV entry and infection in cis. We propose that DC-SIGN concentrates mosquito-derived DV particles at the cell surface to allow efficient interaction with an as yet unidentified entry factor that is ultimately responsible for DV internalization and pH-dependent fusion into DCs.

Production of large numbers of Langerhans' cells with intraepithelial migration ability in vitro

Langerhans' cells (LCs) are a subset of immature dendritic cells (DCs) and play a key role in the initiation and regulation of immune responses. Functional studies of these cells have been hampered by difficulties in generating a large number of LCs in vitro. We describe a new method to efficiently generate immature DCs exhibiting morphological, immunohistochemical, and ultrastructural features of LCs (CD1a+, Birbeck Granules+, CD207+, E-cadherin+, cutaneous lymphocyte-associated antigen+, and CCR6+) from a limited number of CD34+ cord blood progenitors. This method is based on a two-step procedure consisting of an amplification phase followed by a terminal differentiation induction. The amplification step is initiated with a combination of hematopoietic growth factors (thrombopoietin/stem cell factor/fetal liver tyrosine kinase-3 ligand), cytokines (granulocyte-macrophage colony-stimulating factor, tumor necrosis factor-alpha, and interleukin-4), and 5 ng/ml of transforming growth factor (TGF)-beta1. The differentiation is induced by increasing the concentration of TGF-beta1 to 12.5 ng/ml. These culture conditions were efficient for generating a large number of immature LCs (8.74 x 10(6) +/- 3.2) from 15 x 10(4) CD34+ progenitor cells. In addition, these LCs were shown to be able to infiltrate an in vitro reconstructed epithelium. Because LCs play an important role in the mucosal immunity, this technique could be useful to study their interactions with epithelial pathogenic agents and to perform pharmacological, toxicological, and clinical research.

Glycobiology of Head and Neck Squamous Epithelia and Carcinomas

An impressive variety of regulatory processes including cell adhesion and migration, proliferation, apoptosis and differentiation folding and routing of glycoproteins have been found to be mediated by specific lectin-carbohydrate interactions. This article summarizes the data on glycobiological aspects of differentiation of squamous epithelia in the head and neck region under physiological conditions and in cancer. The possible function of lectins in tumor development and invasiveness is debated. Introduction of labeled endogenous lectins as a tool for the study of functional glycomics at the cellular level in head and neck squamous epithelia and carcinomas enables a complex interpretation of studied data because these lectins are normally occurring in these tissues. The lectinology of Langerhans cells in head and neck squamous epithelia and carcinoma is also mentioned. Finally, the use of the described data in the diagnosis and prospectively in the treatment of head and neck squamous cell carcinoma is shown.

A lack of Birbeck granules in Langerhans cells is associated with a naturally occurring point mutation in the human Langerin gene

A heterozygous mutation in the Langerin gene corresponding to position 837 in the Langerin mRNA was identified in a person deficient in Birbeck granules (BG). This mutation results in an amino acid replacement of tryptophan by arginine at position 264 in the carbohydrate recognition domain of the Langerine protein. Expression of mutated Langerin in human fibroblasts induces tubular-like structures that are negative for BG-specific antibodies and do not resemble the characteristic structural features of BG.

Dendritic cells as therapeutic vaccines against cancer

Mouse studies have shown that the immune system can reject tumours, and the identification of tumour antigens that can be recognized by human T cells has facilitated the development of immunotherapy protocols. Vaccines against cancer aim to induce tumour-specific effector T cells that can reduce the tumour mass, as well as tumour-specific memory T cells that can control tumour relapse. Owing to their capacity to regulate T-cell immunity, dendritic cells are increasingly used as adjuvants for vaccination, and the immunogenicity of antigens delivered by dendritic cells has now been shown in patients with cancer. A better understanding of how dendritic cells regulate immune responses will allow us to better exploit these cells to induce effective antitumour immunity.

Human papillomavirus 16 virus-like particles use heparan sulfates to bind dendritic cells and colocalize with langerin in Langerhans cells

Langerhans cells (LC), the immature dendritic cells (DC) that reside in epithelial tissues are among the first immune cells to encounter human papillomavirus (HPV) and are not activated by HPV virus-like particles (VLPs) in contrast to DC. The notion that the differences in response to HPV VLPs between LC and DC are associated with different types of cell binding and intracellular trafficking has been addressed. Inhibition experiments with heparin and sodium chlorate showed that heparan sulfates are necessary for HPV 16 VLPs to bind to DC but not to LC. Electron microscopy analysis demonstrated a colocalization of HPV 16 VLPs and langerin, which is expressed only by LC. This colocalization was observed on the cell surface but also in cytoplasmic vesicles. As anti-langerin antibodies, HPV 16 VLPs were associated with a faster entry kinetics in LC, as reflected by the fact that VLPs were observed near the nuclear membrane of LC within 10 min whereas more than 60 min were needed in DC. However, no difference between LC and DC was observed for the endocytosis pathway. HPV 16 VLPs entered in both DC and LC by a clathrin-dependent-pathway and were then localized in large cytoplasmic vesicles resembling endosomes.

Histology and Ultrastructure of the Equine Lingual Tonsil. II. Lymphoid Tissue and Associated High Endothelial Venules

The stratified squamous epithelium of the lingual tonsil of five young horses was infiltrated with CD4 and CD8 positive cells, which were very numerous in the crypt reticular epithelium along with macrophages and IgGb and IgA positive cells. Lymphoid follicles of the lamina propria mucosae consisted of a parafollicular area, corona and germinal centre. The parafollicular area was populated by large numbers of CD4 and CD8 positive lymphocytes as well as macrophages, inter-digitating cells, and a few B-lymphocytes. The germinal centre contained mainly IgGb and IgG(T) positive cells, plasma cells and small numbers of follicular dendritic cells, macrophages, CD4, CD8 and IgA positive cells. Some venules in the parafollicular and inter-follicular areas had features characteristic of high endothelial venules with irregular nuclei and cytoplasmic processes on the luminal surface. In addition to the normal cytoplasmic organelles, a novel vesiculo-vacuolar organelle was observed in small clusters toward the lateral, luminal and abluminal surfaces of these high endothelial venules. These vesiculo organelles along with their stomata and diaphragms, communicated with each other and with inter-endothelial clefts forming a structural basis for enhanced permeability and extravasation of macromolecules. The presence of lymphocytes in the high endothelial venules is consistent with transmural and inter-endothelial passage of these cells.

Identification and expression profiling of a human C-type lectin, structurally homologous to mouse dectin-2

A number of C-type lectins on antigen-presenting cells play an important role in regulating innate immunity. Previously, we identified the mouse C-type lectins (dectin-1, and dectin-2) and human DECTIN-1. To identify human DECTIN-2, we employed degenerative polymerase chain reaction-based cDNA cloning using RNA from human Langerhans cell (LC)-like dendritic cells (DCs). This process yielded a cDNA encoding a C-type lectin with 66.5% amino acid sequence homology to mouse dectin-2, the same gene reported by Kanazawa et al. (J Invest Dermatol 2004: 122: 1522-1524) using the disparate approach of analyzing coding sequences in chromosome 12. Similar to their findings, we found gene expression in lung, spleen, and lymph node. Among resting leukocytes, it was expressed at highest levels by CD14+ monocytes, at lower levels by CD19+ B cells, and not at all by CD4+ T cells. Activation of CD19+ B cells with pokeweed mitogen down-regulated gene expression, whereas expression in CD4+ T cells was induced by Con A. Among our novel findings are an alternatively spliced transcript lacking exon 2, expression in bone marrow and tonsil, expression in CD8+ T cells that is abrogated following activation with phytohemagglutinin, restricted expression to CD1a+ LC within epidermis, and preferential expression by plasmacytoid (rather than myeloid) DC. Finally, we found that treatment with interleukin-4 (IL-4), IL-10, or UVB down regulated gene expression in CD14+ monocytes, whereas granulocyte-macrophage colony-stimulating factor, transforming growth factor-beta1, or tumor necrosis factor-alpha treatment up-regulated it. Our findings may form the basis for understanding the function of human DECTIN-2 in innate immunity.

Recruitment of dendritic cells in oral lichen planus

Using immunohistochemistry the presence of different dendritic cell (DC) subsets was analysed in 16 biopsies from patients with oral lichen planus (OLP). A significant increase of CD1a+/Langerin+ Langerhans cells, DC-SIGN+ DC and CD123+/BDCA2+ plasmacytoid DCs (PDCs) was found in the epithelium and in the stroma of OLP biopsies compared to normal oral mucosa. A proportion of DCs were mature DC-LAMP+ and expressed S100 or CD11c, typically found in the interdigitating DCs of nodal T-cell areas. Double staining revealed that mature DCs co-expressed CCR7, thus indicating the development of a nodal migratory phenotype upon maturation. Significant recruitment of PDCs producing IFN-alpha was demonstrated by the expression of MxA within the lichenoid inflammatory infiltrate and close cell-to-cell contacts between PDCs and mature DCs were observed, with a significant correlation between the numbers of these two populations. Moreover, PDCs were also found to contain Granzyme-B, an associated-cytotoxic granule protein, inducing target cell apoptosis. Taken together, these results suggest that PDCs may promote maturation of DCs and amplify the cytotoxicity of lymphoid cells. Finally, the recruitment of different subtypes of DC, such as Langerhans cells, stromal DC-SIGN+ DCs and PDCs, associated with a significant proportion of mature DCs, acquiring a CCR7+ 'migratory' phenotype, indicate that they may play a pivotal role in the development of the lichenoid inflammatory infiltrate that occurs typically in OLP.

Regulated recruitment of DC-SIGN to cell-cell contact regions during zymosan-induced human dendritic cell aggregation

Zymosan is a beta-glucan, mannan-rich yeast particle widely used to activate the inflammatory response of immune cells. We studied the zymosan-binding potential of human dendritic cells (hDCs) by using specific carbohydrate inhibitors and blocking monoclonal antibodies. We show that DC-specific intercellular adhesion molecule-grabbing nonintegrin (DC-SIGN) is a major nonopsonic recognition receptor for zymosan on hDCs. Indeed, blocking of DC-SIGN inhibited the inflammatory response of DCs to zymosan. We compared the zymosan-binding capacity of hDC-SIGN to that of Dectin-1 and complement receptor 3 (CR3), which are receptors involved in the nonopsonic recognition of these yeast-derived particles. Dectin-1- and DC-SIGN-K562 cells bound to zymosan particles, whereas CR3-K562 cells did not. DC-SIGN and Dectin-1 were also expressed in COS cells to compare their ability to trigger particle internalization in a nonphagocytic cell line. DC-SIGN transfectants were unable to internalize bound particles, indicating that DC-SIGN is primarily involved in recognition but not in particle internalization. Zymosan induced a rapid DC aggregation that was accompanied by a dramatic change of DC-SIGN distribution in the plasma membrane. Under resting conditions, DC-SIGN was diffusely distributed through the cell surface, displaying clusters at the free leading edge. Upon zymosan treatment, DC-SIGN was markedly redistributed to cell-cell contacts, supporting an adhesion role in DC-DC interactions. The mechanism(s) supporting DC-SIGN-mediated intercellular adhesion were further investigated by using DC-SIGN-K562 aggregation. DC-SIGN was highly concentrated at points of cell-cell contact, suggesting a role for enhanced avidity during DC-SIGN-mediated intercellular adhesion.

Ligand recognition by antigen-presenting cell C-type lectin receptors

It is now appreciated that the range of ligands interacting with C-type lectin type receptors on antigen presenting cells includes endogenous self-molecules as well as pathogens and pathogen-derived ligands. Interestingly, not all interactions between these receptors and pathogenic ligands have beneficial outcomes, and it appears that some pathogens have evolved immunoevasive or immunosuppressive activities through receptors such as DC-SIGN. In addition to this, recent data indicate that the well-characterised macrophage mannose receptor is not essential to host defence against fungal pathogens, as previously thought, but has an important role in regulating endogenous glycoprotein clearance. New studies have also demonstrated that different ligand binding and/or sensing receptors collaborate for full and effective immune responses.

Immunotherapy via dendritic cells

The immune system evolved to protect us from microbes. The antigen (Ag)-nonspecific innate immunity and Ag-specific adaptive immunity synergize to eradicate the invading pathogen through cells, such as dendritic cells (DCZ7) and lymphocytes, and through their effector proteins including antimicrobial peptides, complement, and antibodies. Its intrinsic complexity renders the immune system prone to dysfunction including cancer, autoimmunity, chronic inflammation and allergy. DCs are unique in their capacity to induce and regulate immune responses and are therefore attractive candidates for immunotherapy. However, DCs consist of distinct subsets with common as well as unique functions that lead to distinct types of immune responses. Therefore, understanding DC heterogeneity and their role in immunopathology is critical to design better strategies for immunotherapy. Indeed, what we learn from studying autoimmunity will help us induce strong vaccine specific immunity, either protective, as in the case of microbes, or therapeutic, as in the case of tumors.

FNA diagnosis of primary adult onset lymphocutaneous Langerhans' cell histiocytosis masquerading as deep fungal mycosis

Langerhans' cell histiocytosis (LCH) in its aggressive disseminated form seen most often in children is easily diagnosed by the treating physician. On the contrary, LCH in an adult is localized, extremely rare, and, hence, its diagnosis is missed quite often or underdiagnosed. We describe the troubleshooters encountered in the fine-needle aspiration (FNA) diagnosis of LCH in an adult who presented for 4 years with ulceronodular lesions over the neck, both axillae, and inguinal regions since 4 years of age, which had closely mimicked deep mycosis both clinically and histopathologically.

Disruption of the langerin/CD207 gene abolishes Birbeck granules without a marked loss of Langerhans cell function

Langerin is a C-type lectin expressed by a subset of dendritic leukocytes, the Langerhans cells (LC). Langerin is a cell surface receptor that induces the formation of an LC-specific organelle, the Birbeck granule (BG). We generated a langerin(-/-) mouse on a C57BL/6 background which did not display any macroscopic aberrant development. In the absence of langerin, LC were detected in normal numbers in the epidermis but the cells lacked BG. LC of langerin(-/-) mice did not present other phenotypic alterations compared to wild-type littermates. Functionally, the langerin(-/-) LC were able to capture antigen, to migrate towards skin draining lymph nodes, and to undergo phenotypic maturation. In addition, langerin(-/-) mice were not impaired in their capacity to process native OVA protein for I-A(b)-restricted presentation to CD4(+) T lymphocytes or for H-2K(b)-restricted cross-presentation to CD8(+) T lymphocytes. langerin(-/-) mice inoculated with mannosylated or skin-tropic microorganisms did not display an altered pathogen susceptibility. Finally, chemical mutagenesis resulted in a similar rate of skin tumor development in langerin(-/-) and wild-type mice. Overall, our data indicate that langerin and BG are dispensable for a number of LC functions. The langerin(-/-) C57BL/6 mouse should be a valuable model for further functional exploration of langerin and the role of BG.

Regulation of Antigen Presentation and Cross-Presentation in the Dendritic Cell Network: Facts, Hypothesis, and Immunological Implications

Dendritic cells (DCs) are central to the maintenance of immunological tolerance and the initiation and control of immunity. The antigen-presenting properties of DCs enable them to present a sample of self and foreign proteins, contained within an organism at any given time, to the T-cell repertoire. DCs achieve this communication with T cells by displaying antigenic peptides bound to MHC I and MHC II molecules. Here we review the studies carried out over the past 15 years to characterize these antigen presentation mechanisms, emphasizing their significance in relation to DC function in vivo. The life cycles of different DC populations found in vivo are described. Furthermore, we provide a critical assessment of the studies that examine the mechanisms controlling DC MHC class II antigen presentation, which have often reached contradictory conclusions. Finally, we review findings pertaining to the biological mechanisms that enable DCs to present exogenous antigens on their MHC class I molecules, a process known as cross-presentation. Throughout, we highlight what we consider to be major knowledge gaps in the field and speculate on possible directions for future research.

The dendritic cell-derived protein DC-STAMP is highly conserved and localizes to the endoplasmic reticulum

Recently, we described the molecular identification of dendritic cell-specific TrAnsMembrane protein (DC-STAMP), a multimembrane-spanning protein preferentially expressed by human DC (hDC). In this report, we describe the identification and expression profile of the murine homologue of DC-STAMP (mDC-STAMP) as well as the characterization of the DC-STAMP protein. The results demonstrate that mDC-STAMP is over 90% homologous to hDC-STAMP and is also preferentially expressed by DC in vitro and ex vivo. mDC-STAMP expression is enhanced by interleukin-4 and down-regulated upon DC maturation. Analysis of differently tagged DC-STAMP proteins further demonstrates that hDC-STAMP and mDC-STAMP are glycosylated and primarily localize to an intracellular compartment. Applying confocal microscopy and electron microscopy, we demonstrate that hDC-STAMP localizes to the endoplasmic reticulum (ER) in human embryonic kidney 293 cells as well as hDC transduced with an adenovirus encoding hDC-STAMP-green fluorescent protein fusion protein. These data imply that DC-STAMP may exert its effect in the ER.

Tracking dendritic cells in vivo: insights into DC biology and function

Dendritic cells (DCs) play a vital role in the generation of immune responses, participating both in innate immunity as well as in the initiation of adaptive immunity. However, study of this rare cell population in vivo has been hampered by their low frequency as well as by inadequate means to track antigen-bearing DCs. Our laboratory has developed a novel strategy to genetically tag these DCs in the skin, and to monitor their migration from the periphery to the draining lymph nodes. These studies have provided new insights into the frequency of DC migration, the longevity of DCs in the lymphoid organs, as well as the ability of these DCs to function as antigen-presenting cells. Furthermore, the potential applications of this technique include the ability to evaluate DC function after silencing of specific genes.

Cross-presentation, dendritic cell subsets, and the generation of immunity to cellular antigens

Cross-presentation involves the uptake and processing of exogenous antigens within the major histocompatibility complex (MHC) class I pathway. This process is primarily performed by dendritic cells (DCs), which are not a single cell type but may be divided into several distinct subsets. Those expressing CD8alpha together with CD205, found primarily in the T-cell areas of the spleen and lymph nodes, are the major subset responsible for cross-presenting cellular antigens. This ability is likely to be important for the generation of cytotoxic T-cell immunity to a variety of antigens, particularly those associated with viral infection, tumorigenesis, and DNA vaccination. At present, it is unclear whether the CD8alpha-expressing DC subset captures antigen directly from target cells or obtains it indirectly from intermediary DCs that traffic from peripheral sites. In this review, we examine the molecular basis for cross-presentation, discuss the role of DC subsets, and examine the contribution of this process to immunity, with some emphasis on DNA vaccination.

DC-SIGN and DC-SIGNR interact with the glycoprotein of Marburg virus and the S protein of severe acute respiratory syndrome coronavirus

The lectins DC-SIGN and DC-SIGNR can augment viral infection; however, the range of pathogens interacting with these attachment factors is incompletely defined. Here we show that DC-SIGN and DC-SIGNR enhance infection mediated by the glycoprotein (GP) of Marburg virus (MARV) and the S protein of severe acute respiratory syndrome coronavirus and might promote viral dissemination. SIGNR1, a murine DC-SIGN homologue, also enhanced infection driven by MARV and Ebola virus GP and could be targeted to assess the role of attachment factors in filovirus infection in vivo.

A quantitative study of epidermal Langerhans cells in cutaneous leishmaniasis caused by Leishmania tropica

OBJECTIVE

The purpose of this study was to characterize the number and distribution of epidermal Langerhans cells in different clinical forms of dry-type cutaneous leishmaniasis (CL).

METHODS

Sixteen cases of dry-type cutaneous leishmaniasis caused by Leishmania tropica were studied. These cases were classified clinically as five cases of acute leishmaniasis with indurated papules, nodules and plaques with central crust formation and duration < 2 years, six cases of lupoid leishmaniasis with characteristic papules around previous scars of cutaneous leishmaniasis with duration > 2 years, and five cases of chronic nonlupoid type with nonhealing lesions of duration > 2 years. Paraffin-embedded blocks were stained with hematoxylin and eosin (H&E) and stained immunohistochemically for CD1a.

RESULTS

The number of Langerhans cells per millimeter length of epidermis was increased in acute cases compared to chronic and lupoid cases.

CONCLUSIONS

Lesions of acute leishmaniasis contain the greatest amounts of antigen for presentation, so Langerhans cells increase in number and in trafficking to present antigens derived from Leishman bodies to the cellular immune system. In chronic leishmaniasis, the Langerhans cell population is reduced, perhaps because of exhaustion of the source of Langerhans cells, or because of reduced response to modified antigen.

Langerin (CD207) staining in normal pediatric tissues, reactive lymph nodes, and childhood histiocytic disorders

Langerin is a recently identified lectin for which antibodies can be used as immunohistochemical markers of Langerhans cells (LCs). We describe the distribution of staining in autopsy pediatric tissues, dermatopathic and other reactive lymph nodes, and childhood histiocytic lesions using the 12D6 antibody (Novocastra). We also correlate CD1a (antibody O1O) staining to these factors. Langerin on epidermal LCs has a coarsely granular cell membrane and a cytoplasmic staining pattern that is always associated with CD1a expression. All 6 skin samples had Langerin(+)/CD1a(+) LCs within the epidermis. Six of 8 thymuses showed single scattered dendritic-shaped cells in the medulla and rare cells within Hassall corpuscles that coexpressed Langerin and CD1a. Cortical thymocytes were CD1a(+)/Langerin(-). Four of 8 livers examined showed a sinusoidal lining pattern of Langerin+/CD1a(-). All 15 autopsy lymph nodes showed a similarly strong Langerin(+)/CD1a(-) sinus pattern of staining on fixed tissue elements, mostly in medullary sinuses. All 12 dermatopathic lymph nodes showed accumulation of Langerin(+)/CD1a(+) cells in the pale paracortical nodules. All 24 instances of LC histiocytosis (LCH) were Langerin(+)/CD1a(+). All 12 non-LCH histiocytic disorders are negative for Langerin in the histiocytes of interest. We conclude that Langerin is coexpressed with CD1a on LCs and LCH. Lymph node sinuses and hepatic sinusoids show Langerin(+)/CD1a(-) cells, indicating that, when used alone to confirm LCH infiltration, the 12D6 antibody should be used with caution. At other sites, its diagnostic accuracy is similar to that of CD1a.

Toll-like receptor control of the adaptive immune responses

Recognition of microbial infection and initiation of host defense responses is controlled by multiple mechanisms. Toll-like receptors (TLRs) have recently emerged as a key component of the innate immune system that detect microbial infection and trigger antimicrobial host defense responses. TLRs activate multiple steps in the inflammatory reactions that help to eliminate the invading pathogens and coordinate systemic defenses. In addition, TLRs control multiple dendritic cell functions and activate signals that are critically involved in the initiation of adaptive immune responses. Recent studies have provided important clues about the mechanisms of TLR-mediated control of adaptive immunity orchestrated by dendritic cell populations in distinct anatomical locations.

HIV-1 gp120 binding to dendritic cell receptors mobilize the virus to the lymph nodes, but the induced IL-4 synthesis by FcepsilonRI+ hematopoietic cells damages the adaptive immunity--a review, hypothesis, and implications

HIV-1 is equipped with the envelope gp160 glycoprotein for interaction with Langerhans cells (LCs) and dendritic cells (DCs), the members of the innate immune system, which confront the virus at the portal of virus entry in the human body. These cells are equipped with receptors by which they bind and endocytose the virus. The gp120 glycoprotein is used for binding to CD4 receptor and CCR5 co-receptor of T helper 2 (Th2) cells and the virions shed gp120 is able to induce FcepsilonRI+ hematopoietic cells to produce IL-4, which inactivate the host adaptive immune response. The properties of gp120s various functional domains are analyzed together with the regulatory viral proteins, which are involved in the damage to T and B cells during HIV-1 replication. The interaction of HIV-1 virions through their gp120 with LCs and DCs at the portal of virus entry will be discussed. A hypothesis will be presented that the understanding of the role of the different functional domains of gp120 in the life cycle of the virus and during AIDS will help in the design of approaches to prevent and abrogate HIV-1 infection and AIDS.

Sequence and expression of C-type lectin receptors in Atlantic salmon (Salmo salar)

The diverse receptors of the C-type lectin superfamily play key roles in innate immunity. In mammals, cell surface receptors with C-type lectin domains are involved in pathogen recognition and in immune response, and in some cases are exploited by pathogens to gain entry into cells. This study reports on sequence and expression analysis of three paralogous group II C-type lectins from the teleost fish Atlantic salmon (Salmo salar). Each of the receptors showed similarity to immune-relevant mammalian receptors in terms of amino acid sequence and overall organization within the C-type lectin-like domain (CTLD). Two of the three have cytoplasmic motifs consistent with the immunoreceptor tyrosine-based activation motifs (ITAM), which are known to modulate downstream functions in leukocytes. All three C-type lectin receptors were expressed in multiple tissues of healthy fish, including peripheral blood leukocytes and salmon head kidney cells (SHK-1). Each receptor was up-regulated in salmon liver in response to infection by Aeromonas salmonicida and one receptor was substantially up-regulated in cultured SHK-1 cells in response to lipopolysaccharide (LPS). Putative binding sites for the CAAT-enhancer-binding protein (C/EBP) family of transcription factors in the regulatory regions of these C-type lectin genes may mediate their response to bacteria and LPS in salmon leukocytes. The identification of these types of receptors in distinct populations of cells within the immune system will provide important markers for identifying and categorizing the state of differentiation or activation of these cells and lead to further understanding of the interaction between the salmon host and multiple pathogens.

Detection of Chlamydophila pneumoniae in dendritic cells in atherosclerotic lesions

Dendritic cells (DCs) populate atherosclerotic lesions and might be involved in the regulation of immune reactions in atherosclerosis. The present work was undertaken to examine a possible association of DCs with Chlamydophila pneumoniae in human atherosclerotic plaques obtained by endarterectomy. C. pneumoniae was identified in 17 of 60 (28%) atherosclerotic plaques by a combination of immunohistochemistry and polymerase chain reaction (PCR). Double immunohistochemistry identified the presence of C. pneumoniae within S100(+) DCs that were localised predominantly in the deep layer of the intima under the necrotic core. Quantitative analysis showed that there were no differences in the numbers of DCs between C. pneumoniae(+) and C. pneumoniae(-) groups of atherosclerotic specimens. There were also no differences in the expression of Lag-antigen and HLA-DR by DCs between the groups of specimens. Markers of DC activation CD80 and CD86 were absent from both groups of specimens. Flow cytometry analysis of the effects of C. pneumoniae infection on immature monocyte-derived DCs in vitro showed no changes in the expression of CD1a, MHC class II, CD80 and CD86. The results of this study demonstrate that C. pneumoniae might infect DCs within the atherosclerotic intima but whether the presence of C. pneumoniae in DCs affects the intensity of immune reactions in atherosclerosis needs further clarification.

Transforming Growth Factor-β1 Regulates the Expression of the High-Affinity Receptor for IgE on CD34+ Stem Cell-Derived CD1a+ Dendritic Cells In Vitro

It has been reported that monocytes, Langerhans cells (LC) and other dendritic cells (DC) express the high-affinity receptor for IgE (FcepsilonRI) in patients with atopic diseases. These cells may be instrumental in the control of the immune response and the allergic inflammation. In this context, transforming growth factor beta 1 (TGF-beta1) has been highlighted as a key cytokine involved in the mechanisms aimed to orchestrate tolerance and has been suggested as a candidate gene in atopic diseases. In this report, we investigate the putative role of TGF-beta1 in the regulation of FcepsilonRI on cord blood CD34+ stem cell-derived CD1a+ DC (CD34-derived CD1a+ DC). Kinetic experiments show that FcepsilonRI spontaneously appears on the surface of CD1a+ DC, but decreases when exogenous TGF-beta1 is added at high doses (10 ng per mL) or when endogenous TGF-beta1 is neutralized in the culture conditions. In contrast, low-dose TGF-beta1 (0.5 ng per mL) stabilizes surface FcepsilonRI expression on DC. Increasing TGF-beta1 concentrations leads to the generation of LC-like DC showing an augmentation in stimulatory capacity towards allogeneic T cells. In view of these data, a picture emerges that FcepsilonRI+ on DC is finely modified by the TGF-beta1 concentration in the microenvironment and could be of primary relevance in the context of atopic diseases.

Mature human Langerhans cells derived from CD34+ hematopoietic progenitors stimulate greater cytolytic T lymphocyte activity in the absence of bioactive IL-12p70, by either single peptide presentation or cross-priming, than do dermal-interstitial or monocyte-derived dendritic cells

The emerging heterogeneity of dendritic cells (DCs) mirrors their increasingly recognized division of labor at myriad control points in innate and acquired cellular immunity. We separately generated blood monocyte-derived DCs (moDCs), as well as Langerhans cells (LCs) and dermal-interstitial DCs (DDC-IDCs) from CD34(+) hematopoietic progenitor cells. Differential expression of CD11b, CD52, CD91, and the CD1 isoforms proved useful in distinguishing these three DC types. All mature DCs uniformly expressed comparable levels of HLA-DR, CD83, CD80, and CD86, and were potent stimulators of allogeneic T cells after exposure either to recombinant human CD40L trimer or a combination of inflammatory cytokines with PGE(2). moDCs, however, required 0.5-1 log greater numbers than LCs or DDC-IDCs to stimulate comparable T cell proliferation. Only moDCs secreted the bioactive heterodimer IL-12p70, and moDCs phagocytosed significantly more dying tumor cells than did either LCs or DDC-IDCs. LCs nevertheless proved superior to moDCs and DDC-IDCs in stimulating CTL against a recall viral Ag by presenting passively loaded peptide or against tumor Ag by cross-priming autologous CD8(+) T cells. LCs also secreted significantly more IL-15 than did either moDCs or DDC-IDCs, which is especially important to the generation of CTL. These findings merit further comparisons in clinical trials designed to determine the physiologic relevance of these distinctions in activity between LCs and other DCs.

Human epidermal Langerhans cells differ from monocyte-derived Langerhans cells in CD80 expression and in secretion of IL-12 after CD40 cross-linking

Langerhans cells (LCs) represent an immature population of myeloid dendritic cells (DCs). As a result of their unique Birbeck granules (BGs), langerin expression, and heterogeneous maturation process, they differ from other immature DCs. Monocyte-derived LCs (MoLCs) mimic epidermal LCs. MoLCs with characteristic BGs are generated by culturing blood-derived monocytes with granulocyte macrophage-colony stimulating factor, interleukin (IL)-4, and transforming growth factor-beta1. Here, we compare maturation-induced antigen expression and cytokine release of LCs with MoLCs. To achieve comparable cell populations, LCs and MoLCs were isolated by CD1c cell sorting, resulting in high purity. In unstimulated cells, CD40 was expressed at equal levels. After stimulation with CD40 ligand (CD40L), LCs and MoLCs acquired CD83 and increased CD86. High CD80 expression was exclusively detected in CD1c-sorted MoLCs. Human leukocyte antigen-DR and CD54 expression was found in all cell populations, however, at different intensities. CD40 triggering increased the potency of LCs and MoLCs to stimulate CD4+ T cell proliferation. Activated MoLCs released IL-12p70 and simultaneously, anti-inflammatory IL-10. The application of the Toll-like receptor ligands peptidoglycan, flagellin, and in particular, lipopolysaccharide (LPS) increased the corelease of these cytokines. LCs secreted IL-10 at a comparable level with MoLCs but failed to produce high amounts of IL-12p70 after application of danger signals. These data indicate that MoLCs as well as LCs display no maturation arrest concerning CD83 and CD86 expression. In difference to MoLCs, LCs resisted activation by CD40L and LPS in terms of IL-12 production. This shows that natural and generated LCs share similar features but differ in relevant functions.