Presentation of exogenous protein antigens by dendritic cells to T cell clones. Intact protein is presented best by immature, epidermal Langerhans cells

Development and maturation of Langerhans cells, spleen and bone marrow dendritic cells in TNF-alpha/lymphotoxin-alpha double-deficient mice

Dendritic cells are key regulators of immunity and tolerance. TNF-alpha has manifold effects on dendritic cells. It is an indispensable ingredient in several dendritic cell generation protocols, especially in the human, and it is included in diverse maturation stimuli for dendritic cells. Mice deficient in various components of the TNF/lymphotoxin system (TNF-alpha, lymphotoxin-alpha and -beta, TNF receptors, combinations thereof) have profound defects in mounting immune responses to infections. The dendritic cell system in these mice has been incompletely studied to date. We therefore investigated dendritic cells from the epidermis (Langerhans cells), spleen and the bone marrow of mice double-deficient in TNF-alpha and lymphotoxin-alpha. We report that dendritic cells in these mice are grossly normal. Langerhans cells, spleen and bone marrow dendritic cells can develop and mature. Their expression of MHC II and CD86 is not impaired, and their T cell-stimulatory as well as antigen-processing capacity is comparable to their normal counterparts. Thus, the described defects in these mice appear to be due the lack of lymph nodes, the disturbed architecture of the spleen, and deranged chemokine production patterns, rather than to a profoundly altered dendritic cell system.

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.

Basic Concepts of Immune Response and Defense Development

The induction of immune responses requires critical interaction between innate parts of the immune system, which respond rapidly and in a relatively nonspecific manner, and other specific parts, which recognize particular epitopes on an antigen. A critical element in this interaction is the role played by dendritic cells (DCs), which represent "professional antigen-presenting cells." DCs endocytose and process antigen to peptide presented on the cell surface in association with major histocompatibility complex (MHC) molecules. This presentation results in interaction with and stimulation of helper T (Th) lymphocytes, which recognize peptide in association with either MHC class II or cytotoxic T (Tc) lymphocytes, which recognize peptide in association with MHC class I. Stimulation of Th lymphocytes produces the growth and differentiation factors (cytokines) essential for the B lymphocytes that have responded to a more intact form of the antigen and that differentiate into antibody-producing cells. The precise interaction between the cells depends on cognate ligand-receptor recognition between the B and Th lymphocytes. DCs also play a direct role with the stimulation of the B lymphocytes. It appears that DC can deliver antigen to the B lymphocytes in a more intact form than the processed form essential for stimulating T lymphocytes, and can release cytokines that assist the differentiation of the B lymphocytes into antibody-producing cells. This close relationship among the three cell types and the cytokines that are produced ensures the precise control and regulation necessary for immune response development.

Molecular cloning and preliminary expression analysis of banded dogfish (Triakis scyllia) CC chemokine cDNAs by use of suppression subtractive hybridization

Suppression subtractive hybridization was carried out by using cDNAs of peripheral white blood cells (PWBCs) of banded dogfish (Triakis scyllia) after phorbol 12-myristate 13-acetate (PMA) stimulation. The Trsc-SCYA107, MIP3alpha1 and MIP3alpha2 clones contained an open reading frame encoding 97, 99 and 97 amino acids, respectively. Comparison of the deduced amino acids showed that the banded dogfish MIP3alpha1 and MIP3alpha2 sequences shared 42.3% and 40.0% identity with human SCYA20, respectively, while the Trsc-SCYA107 sequence shared 50.6, 44.2 and 42.0% identity with the catshark (Scyliorhinus canicula) Scca-SCYA107, rainbow trout (Oncorhynchus mykiss) CK4A and CK4B, respectively. The genomic sequences of banded dogfish Trsc-SCYA107, MIP3alpha1 and MIP3alpha2 contain four exons and three introns, and MIP3alpha1 and MIP3alpha2 shared the same intron/exon organization with that of human. The MIP3alpha1 and MIP3alpha2 genes of lipopolysaccharide (LPS)-unstimulated banded dogfish were expressed in gill, kidney and liver, while Trsc-SCYA107 mRNA was detected in various tissues except for brain. However, the constitutive expression of MIP3alpha2 gene was much lower than the Trsc-SCYA107 and MIP3alpha1 genes. RT-PCR analysis of the Trsc-SCYA107 expression in tissues of LPS-stimulated fish showed enhanced expression at 24 h poststimulation in the gill, heart, leydig, spleen and testes, while the expression of MIP3alpha1 and MIP3alpha2 was not influenced by LPS-stimulation in vivo. Furthermore, a relative increase in the expression of the Trsc-SCYA107 and MIP3alpha2 genes in PWBCs was observed at 1-12 h poststimulation with PMA and LPS, with maximal expression observed at 3 h, while MIP3alpha1 expression was observed at 3-12 h poststimulation only with PMA.

Lymphoid organ dendritic cells: beyond the Langerhans cells paradigm

The immune system has developed mechanisms to detect and initiate responses to a continual barrage of immunological challenges. Dendritic cells (DC), a heterogeneous population of leucocytes, play a major role as immunosurveillance agents. To accomplish this function, DC are equipped with highly efficient mechanisms to detect pathogens, to capture, process and present antigens, and to initiate T-cell responses. These mechanisms are developmentally regulated during the DC life cycle in a process termed 'maturation', which was originally defined using Langerhans cells (LC), a DC type of the epidermis. LC exist in the skin in an immature state dedicated to capturing antigens, and in the subcutaneous lymph nodes in a mature state dedicated to presenting those antigens to T cells. The phenotypic changes undergone by LC during maturation, and the correlation of these changes with tissue localization, have been generally considered a paradigm for all DC. However, studies of the multiple DC types found in the lymphoid organs of mice and humans have revealed that most DC subsets do not follow the life cycle typified by LC. In this review we discuss the limitations of the 'LC paradigm' and suggest that this model should be revised to accommodate the heterogeneity of the DC system. We also discuss the implications of the maturational status of the DC subsets contained in the lymphoid organs for their putative roles in the induction of immune responses and the maintenance of peripheral tolerance.

Migration of antigen presenting cells from periphery to the peritoneum during an inflammatory response: role of chemokines and cytokines

We demonstrate the migration of antigen presenting cells (APCs), macrophages, and dendritic cells from the subcutaneous site to the peritoneum after they have picked up the antigen, using cell tracking dye. The migration of the APCs is more universal as it was also observed after injection of MethA tumor, DH-5alpha cells, and leishmania parasites, in addition to AK-5 tumor cells. Cellular migration is mediated by several chemokines and cytokines that also induce heavy influx of immune cells into the peritoneum. MIP-3beta secreted by the mesothelial cells is involved in the cellular influx into the peritoneum, whereas IL-12 and IFN-gamma produced by the APCs induced activation of immune cells in the peritoneum. Our results suggest an antigen presentation function for the APCs in the peritoneum as studied by lymphoproliferation assays. These studies indicate antigen presentation function of the activated migratory APCs from the distant subcutaneous site to the peritoneum, suggesting it acts as an important lymphoid organ involved in the enhancement of effector cell function.

Identification of proteases employed by dendritic cells in the processing of protein purified derivative (PPD)

Dendritic cells (DC) are known to present exogenous protein Ag effectively to T cells. In this study we sought to identify the proteases that DC employ during antigen processing. The murine epidermal-derived DC line Xs52, when pulsed with PPD, optimally activated the PPD-reactive Th1 clone LNC.2F1 as well as the Th2 clone LNC.4k1, and this activation was completely blocked by chloroquine pretreatment. These results validate the capacity of XS52 DC to digest PPD into immunogenic peptides inducing antigen specific T cell immune responses. XS52 DC, as well as splenic DC and DCs derived from bone marrow degraded standard substrates for cathepsins B, C, D/E, H, J, and L, tryptase, and chymases, indicating that DC express a variety of protease activities. Treatment of XS52 DC with pepstatin A, an inhibitor of aspartic acid proteases, completely abrogated their capacity to present native PPD, but not trypsin-digested PPD fragments to Th1 and Th2 cell clones. Pepstatin A also inhibited cathepsin D/E activity selectively among the XS52 DC-associated protease activities. On the other hand, inhibitors of serine proteases (dichloroisocoumarin, DCI) or of cystein proteases (E-64) did not impair XS52 DC presentation of PPD, nor did they inhibit cathepsin D/E activity. Finally, all tested DC populations (XS52 DC, splenic DC, and bone marrow-derived DC) constitutively expressed cathepsin D mRNA. These results suggest that DC primarily employ cathepsin D (and perhaps E) to digest PPD into antigenic peptides.

Epicutaneous application of CpG oligodeoxynucleotides with peptide or protein antigen promotes the generation of CTL

Immunostimulatory oligodeoxynucleotides (ODN) are effective adjuvants in the induction of humoral and cellular immune responses when administered parenterally with antigen. The skin has recently become a target organ for the design of non-invasive vaccine technologies. Using ovalbumin (OVA) as a model antigen, we demonstrate that the application of ODN sequences to tape-stripped skin promotes the induction of potent cytotoxic T lymphocyte (CTL) responses to co-administered peptide. Induction of peptide-specific CTL required the presence of CpG motifs within the ODN. CTL afforded tumor protection against a tumor expressing an immunodominant OVA CTL epitope. CTL could also be induced to whole protein administered onto the skin. Differential CpG sequence activity was noted with respect to the induction of CTL to epicutaneous protein with an ODN sequence containing a poly-G motif having an optimal effect. Peptide-specific CTL could be detected in the peripheral blood as early as 6 d after a single immunization. These results highlight the potential of the bare skin as a route for vaccine development and indicate an important role for immunostimulatory ODN as adjuvants to generate functional CTL with the help of the skin immune system.

The linkage of innate to adaptive immunity via maturing dendritic cells in vivo requires CD40 ligation in addition to antigen presentation and CD80/86 costimulation

Dendritic cell (DC) maturation is an innate response that leads to adaptive immunity to coadministered proteins. To begin to identify underlying mechanisms in intact lymphoid tissues, we studied alpha-galactosylceramide. This glycolipid activates innate Valpha14(+) natural killer T cell (NKT) lymphocytes, which drive DC maturation and T cell responses to ovalbumin antigen. Hours after giving glycolipid i.v., tumor necrosis factor (TNF)-alpha and interferon (IFN)-gamma were released primarily by DCs. These cytokines induced rapid surface remodeling of DCs, including increased CD80/86 costimulatory molecules. Surprisingly, DCs from CD40(-/-) and CD40L(-/-) mice did not elicit CD4(+) and CD8(+) T cell immunity, even though the DCs exhibited presented ovalbumin on major histocompatibility complex class I and II products and expressed high levels of CD80/86. Likewise, an injection of TNF-alpha up-regulated CD80/86 on DCs, but CD40 was required for immunity. CD40 was needed for DC interleukin (IL)-12 production, but IL-12p40(-/-) mice generated normal ovalbumin-specific responses. Therefore, the link between innate and adaptive immunity via splenic DCs and innate NKT cells has several components under distinct controls: antigen presentation in the steady state, increases in costimulatory molecules dependent on inflammatory cytokines, and a distinct CD40/CD40L signal that functions together with antigen presentation ("signal one") and costimulation ("signal two") to generate functioning CD4(+) T helper cell 1 and CD8(+) cytolytic T lymphocytes.

Transduction of dendritic cells with recombinant adenovirus encoding HCA661 activates autologous cytotoxic T lymphocytes to target hepatoma cells

Transduction of recombinant adenovirus into dendritic cells (DCs) is a promising new tool for cancer vaccine development. Here, we report that an adenovirus vector carrying hepatocellular carcinoma (HCC) antigen HCA661 and infected into DCs generates T-cell immunity against hepatoma cells. HCA661 is a novel cancer/testis (CT) antigen screened by SEREX from sera of an HCC patient. We constructed a recombinant adenovirus expressing the full-length cDNA of HCA661 gene and then transduced immature DCs, which had been generated with GM-CSF and IL-4 from peripheral blood mononuclear cell of HLA-A2⁺ healthy donors. The resulting adenovirus-transduced DCs differentiated in the presence of monocyte-conditioned medium and poly [I] : poly [C], expressing the surface markers of mature DCs, including CD83, CD80, CD86 and HLA-DR. After maturation, the transduced DCs transcribed HCA661 mRNA and were able to prime the naïve T cells to become cytotoxic T lymphocytes (CTLs). Intracellular flow cytometry and enzyme-linked immunospot assay showed that these CTLs were able to target a hepatoma cell line, HepG2, which is HLA-A2 and HCA661 positive. In summary, we found that this recombinant adenovirus can help to induce DC maturation and these mature DCs can activate T cells to target hepatoma cells. Therefore, this recombinant adenovirus may have potential for use in liver cancer immunotherapy.

T-cell costimulatory capacity of oral and skin epithelial cells in vitro: presence of suppressive activity in supernatants from skin epithelial cell cultures

Oral Langerhans cells (LC) have better T-cell costimulatory capacity than skin LC. In this study factors affecting this capacity have been assessed in a mixed epithelial cell lymphocyte reaction (MELR) assay. Flow cytometry analysis of freshly recovered cells revealed major histocompatibility complex (MHC) class II molecule expression on 7.5% of the oral epithelial cells and 9.7% of the skin epithelial cells. Monoclonal anti class II antibodies significantly reduced the T-cell proliferation in the MELR. Pretreatment of skin epithelial cells with interleukin-1beta, tumour necrosis factor-alpha or interferon (IFN)-gamma did not affect the MELR proliferation, but incubation with IFNgamma significantly suppressed the T-cell response. Transfer of supernatants from cultures of skin epithelial cells and allogeneic T cells to cultures of oral epithelial cells and T cells resulted in a reduced T-cell proliferation while supernatants from oral epithelial cells and T cells did not reduce proliferation. The higher proliferation in cultures of T cells and oral epithelial cells than in cultures containing skin epithelial cells may be due to the presence of a suppressive factor in the skin epithelial cell suspensions.

Langerhans cells utilize CD1a and langerin to efficiently present nonpeptide antigens to T cells

Langerhans cells (LCs) constitute a subset of DCs that initiate immune responses in skin. Using leprosy as a model, we investigated whether expression of CD1a and langerin, an LC-specific C-type lectin, imparts a specific functional role to LCs. LC-like DCs and freshly isolated epidermal LCs presented nonpeptide antigens of Mycobacterium leprae to T cell clones derived from a leprosy patient in a CD1a-restricted and langerin-dependent manner. LC-like DCs were more efficient at CD1a-restricted antigen presentation than monocyte-derived DCs. LCs in leprosy lesions coexpress CD1a and langerin, placing LCs in position to efficiently present a subset of antigens to T cells as part of the host response to human infectious disease.

Induction of dendritic cell maturation by IL-18

IL-18 is a pluripotent proinflammatory cytokine produced primarily by antigen presenting cells involved in numerous aspects of immune regulation most notably on lymphoid cells. The effect of IL-18 stimulation on cells in the myeloid compartment, however, has been poorly studied. Human monocytes did not respond to IL-18. However, the human myelomonocytic cell line KG-1 and monocyte-derived dendritic cells (generated by GM-CSF+IL-4) showed a marked increase in CD83, HLA-DR, and several costimulatory molecules upon stimulation with IL-18. Furthermore, IL-18 decreased pinocytosis of these cells and increased their ability to stimulate alloreactive T cell proliferation, all characteristics of mature dendritic cells. These results suggest that IL-18 is involved in the maturation of myeloid DCs, but not differentiation of monocytes into DCs. The finding that IL-18 is involved in the maturation of dendritic cells is both novel and unexpected and indicates another important role for IL-18 as a key regulator of immune responses.

CCL3/MIP-1αIs a Potent Immunostimulator When Coexpressed with Interleukin-2 or Granulocyte-Macrophage Colony-Stimulating Factor in a Leukemia/Lymphoma Vaccine

Chemokines orchestrate trafficking of immune effector cells during inflammation. Here we demonstrate that chemokines also serve to potentiate effector cell-mediated antineoplastic immune responses in vaccination strategies. As a critical mediator of inflammation, macrophage inflammatory protein 1alpha (CCL3/MIP-1alpha) attracts and stimulates both antigen-presenting and cytotoxic cells. In the A20 leukemia/lymphoma vaccine model, we explored the efficacy of MIP-1alpha in combination with interleukin-2 (IL-2) or granulocyte-macrophage colony-stimulating factor (GM-CSF). After subcutaneous injection of the MIP-1alpha + IL-2 or MIP-1alpha + GM-CSF combination vaccine, focal but pronounced infiltrates of CD4+ and CD8+ T cells were observed at the vaccination sites. In mice with preestablished leukemia/lymphoma, survival is significantly improved in animals treated with MIP-1alpha + GM-CSF- and MIP-1alpha + IL-2-secreting vaccines. Protection is superior in the MIP-1alpha + GM-CSF group, with the effects of MIP-1alpha and GM-CSF being synergistic. In contrast, suppression of lymphoblast proliferation by single-immunogen vaccines secreting MIP-1alpha, GM-CSF, or IL-2 alone does not translate to improved survival. The systemic protective effects afforded by the MIP-1alpha + IL-2 or MIP-1alpha + GM-CSF combination are mediated by different effector cell populations. In the MIP-1alpha + IL-2 group, antineoplastic defense is mediated by CD8+ T and NK cells, whereas in the MIP-1alpha + GM-CSF group CD4+ T cells are involved in addition to CD8+ cytotoxic T cells, underscoring that T cell help is critical for long-term protection. Thus combination of MIP-1alpha with different cytokines recruits different sets of effector cells into a potent antineoplastic immune response.

Epidermal viral immunity induced by CD8alpha+ dendritic cells but not by Langerhans cells

The classical paradigm for dendritic cell function derives from the study of Langerhans cells, which predominate within skin epidermis. After an encounter with foreign agents, Langerhans cells are thought to migrate to draining lymph nodes, where they initiate T cell priming. Contrary to this, we show here that infection of murine epidermis by herpes simplex virus did not result in the priming of virus-specific cytotoxic T lymphocytes by Langerhans cells. Rather, the priming response required a distinct CD8alpha+ dendritic cell subset. Thus, the traditional view of Langerhans cells in epidermal immunity needs to be revisited to accommodate a requirement for other dendritic cells in this response.

A pilot trial of tumor lysate-loaded dendritic cells for the treatment of metastatic renal cell carcinoma

Cultured tumor lysate-loaded dendritic cells (TuLy-DC) have been demonstrated in vitro to stimulate potent immune modulations and generate significant antitumor response. We report the results of a pilot trial of TuLy-DC vaccine for patients with metastatic renal cell carcinoma (mRCC). Fourteen mRCC patients underwent nephrectomy to obtain autologous TuLy prepared by subjecting tumor cells to 3 freeze/thaw cycles. Dendritic cells were generated from peripheral blood CD14+ precursors cultured in the presence of GM-CSF, IL-4, and 10% autologous serum. Patients received one vaccination of TuLy alone as an immunologic control, followed by 3 weekly vaccinations of DC-TuLy injected intradermally in the midaxillary region. Peripheral blood lymphocytes were collected before and after weekly vaccines and were assessed for changes in phenotype, cytotoxicity, and cytokine profile. The TuLy-DC vaccine was successfully prepared and administered to 12 patients, whereas 2 patients did not receive vaccine treatment due to declines in postoperative performance status. The vaccines were well tolerated, with only grade 1 toxicities noted. One patient had a partial response to treatment that did not correspond to any significant change in immunologic profile. This pilot trial demonstrated both the safety and feasibility of reliably preparing a DC-based vaccine for mRCC patients. Our data suggest that autologous TuLy-DC vaccines generate only limited clinical response. Further clinical studies are needed to identify the most potent treatment regimen that can consistently mediate an antitumor immune response in vivo.

Milestones in the research on skin epidermal Langerhans/dendritic cells (LCs/DCs) from the discovery of Paul Langerhans 1868-1989

Almost 100 years elapsed after the discovery of dendritic cells in the human skin epithelium by Paul Langerhans in 1868 until the initiation of research on those cells was reinitiated. The present paper provides the milestones in the research on Langerhans/dendritic cells (LCs/DCs) between 1960 and 1989. This historical review will explain how researchers gradually discovered the role of the bone marrow-derived dendritic cells in the immune response. The paper is an appendix to the manuscript entitled: "Immunological and regulatory functions of uninfected and infected immature and mature subtypes of dendritic cells" (Virus Genes 26: 119-130, 2003).

Immunological and regulatory functions of uninfected and virus infected immature and mature subtypes of dendritic cells--a review

In 1868, dendritic cells (DCs) were discovered in human skin by Paul Langerhans using gold staining. These cells were named Langerhans cells (LCs) after their discoverer who, due to their dendrites, regarded them as neurons. One hundred and eleven years were to pass until it was discovered that in vertebrates these cells originate in the bone marrow as monocytes. In the 1980s, DC research was mostly carried out on DCs that are present in different tissues of mice and humans. These studies revealed that after interaction with foreign antigens, skin LCs/DCs migrate through the lymph vessels to the draining lymph nodes and induce the two arms of the immune response. The isolation of DCs from tissue cell suspensions opened the way to studies on the cells' surface proteins and their ability to stimulate immune responses. During the 1990s, studies revealed the role of DCs in the activation of naive T cells in the lymph nodes and the regulatory properties of DCs in lymph nodes, thymus, gut, and spleen. Part A of the review deals with the DC system of human and mice and immunological and regulatory functions of subsets of DCs in the skin with reference to migrating and stationary DCs, as well as the connection between DCs and the nervous system. Furthermore, the origin of both follicular DCs that are present in lymphoid tissues and thymic DCs are discussed. Part B is devoted to virus infections of DCs with an emphasis on infections caused by human herpes viruses. Part C presents the modulation of DC gene expression in response to the influenza virus. Contemporary research focuses on the role of DCs in the immune systems of vertebrates. Moreover, studies are being conducted on the regulatory functions of DCs by tissue cells in different organs of vertebrates.

Depletion of Langerhans cells in human papillomavirus type 16-infected skin is associated with E6-mediated down regulation of E-cadherin

Human papillomavirus type 16 (HPV16) is an oncogenic virus that causes persistent infections in cervical epithelium. The chronic nature of HPV16 infections suggests that this virus actively evades the host immune response. Intraepithelial Langerhans cells (LC) are antigen-presenting cells that are critical in T-cell priming in response to viral infections of the skin. Here we show that HPV16 infection is directly associated with a reduction in the numbers of LC in infected epidermis. Adhesion between keratinocytes (KC) and LC, mediated by E-cadherin, is important in the retention of LC in the skin. Cell surface E-cadherin is reduced on HPV16-infected basal KC, and this is directly associated with the reduction in numbers of LC in infected epidermis. Expression of a single viral early protein, HPV16 E6, in KC reduces levels of cell surface E-cadherin thereby interfering with E-cadherin-mediated adhesion. Through this pathway, E6 expression in HPV16-infected KC may limit presentation of viral antigens by LC to the immune system, thus preventing the initiation of a cell-mediated immune response and promoting survival of the virus.

Influenza virus-induced dendritic cell maturation is associated with the induction of strong T cell immunity to a coadministered, normally nonimmunogenic protein

We evaluated the proposal that during microbial infection, dendritic cells (DCs) undergo maturation and present a mixture of peptides derived from the microbe as well as harmless environmental antigens. Mice were exposed to an aerosol of endotoxin free ovalbumin (OVA) in the absence or presence of influenza virus. In its absence, OVA failed to induce B and T cell responses and even tolerized, but with influenza, OVA-specific antibodies and CD8+ cytolytic T lymphocytes developed. With or without infection, OVA was presented selectively in the draining mediastinal lymph nodes, as assessed by the comparable proliferation of infused, CD8+ and CD4+, TCR transgenic T cells. In the absence of influenza, these OVA-specific T cells produced little IL-2, IL-4, IL-10, and IFN-gamma, but with infection, both CD4+ and CD8+ T cells made high levels of IL-2 and IFN-gamma. The OVA plus influenza-treated mice also showed accelerated recovery to a challenge with recombinant vaccinia OVA virus. CD11c+ DCs from the mediastinal lymph nodes of infected mice selectively stimulated both OVA- and influenza-specific T cells and underwent maturation, with higher levels of MHC class II, CD80, and CD86 molecules. The relatively slow (2-3 d) kinetics of maturation correlated closely to the time at which OVA inhalation elicited specific antibodies. Therefore respiratory infection can induce DC maturation and simultaneously B and T cell immunity to an innocuous antigen inhaled concurrently.

Contrasting roles of dendritic cells and B cells in the immune control of Epstein-Barr virus

The human gamma-herpesvirus, Epstein-Barr virus (EBV), has growth-transforming potential in vivo and in vitro. Despite this, most healthy carriers remain free of EBV-associated malignancies because of effective T cell-mediated immune control of the virus. A better understanding of these highly efficient control mechanisms is important in the development of new treatment strategies for EBV-associated malignancies. A rational approach to EBV immunotherapy requires answering two questions about the initiation of the protective EBV-specific immune response. The first question is, what is the antigen-presenting cell responsible for priming EBV specific immunity? Second, which viral antigen is central to protective EBV adaptive immunity seen in healthy carriers of the virus? We provide evidence in this review that dendritic cells rather than EBV-transformed B cells are responsible for orchestrating protective EBV immunity and that the EBV nuclear antigen 1 (EBNA1)-specific CD4+ T cell response probably plays a role in resistance against all types of EBV-associated malignancies in healthy carriers. This implies that EBNA1 targeting to dendritic cells should be a component of vaccine and immunotherapy development against EBV-associated malignancies.

Langerhans cells - dendritic cells of the epidermis

Langerhans cells (LC) are dendritic cells of the epidermis. They are highly specialized leukocytes that serve immunogenic and tolerogenic purposes. Here, we review some aspects of LC biology, emphasizing those areas where LC are or may turn out to be special.

Some interfaces of dendritic cell biology

The field of dendritic cell (DC) biology is robust, with several new approaches to analyze their role in vivo and many newly recognized functions in the control of immunity and tolerance. There also is no shortage of mysteries and challenges. To introduce this volume, I would like to summarize four interfaces of DC research with other lines of investigation and highlight some current issues. One interface is with hematopoiesis. DCs constitute a distinct lineage of white blood cell development with some unique features, such as their origin from both lymphoid and myeloid progenitors, the existence of several distinct subsets, and an important final stage of differentiation termed "maturation," which occurs in response to inflammation and infection, and is pivotal for determining the subsequent immune response. A second interface is with lymphocyte biology. DCs are now known to influence many different classes of lymphocytes (B, NK, NKT) and many types of T cell responses (Th1/Th2, regulatory T cells, peripheral T cell deletion), not just the initial priming or induction of T cell-mediated immunity, which was the first function to be uncovered. DCs are sentinels, controlling many of the afferent or inductive limbs of immune function, alerting the immune system and controlling its early decisions. A third interface is with cell biology. This is a critical discipline to understand at the subcellular and molecular levels the distinct capacities of DCs to handle antigens, to move about the body in a directed way, to bind and activate lymphocytes, and to exert many quality controls on the type of responses, for both tolerance and immunity. A fourth interface is with medicine. Here DCs are providing new approaches to disease pathogenesis and therapy. This interface is perhaps the most demanding, because it requires research with humans. Human research currently is being slowed by the need to deal with many challenges in the design of such studies, and the need to excite, attract and support the young scientists who are essential to move human investigation forward. Nonetheless, DCs are providing new opportunities to study patients and the many clinical conditions that involve the immune system.

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

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

Dendritic cell function in vivo during the steady state: a role in peripheral tolerance

The avoidance of autoimmunity requires mechanisms to actively silence or tolerize self reactive T cells in the periphery. During infection, dendritic cells are not only capturing microbial antigens, but also are processing self antigens from dying cells as well as innocuous environmental proteins. Since the dendritic cells are maturing in response to microbial and other stimuli, peptides will be presented from both noxious and innocuous antigens. Therefore it would be valuable to have mechanisms whereby dendritic cells, prior to infection, establish tolerance to those self and environmental antigens that can be processed upon pathogen encounter. In the steady state, prior to acute infection and inflammation, dendritic cells are in an immature state and not fully differentiated to carry out their known roles as inducers of immunity. These immature cells are not inactive, however. They continuously circulate through tissues and into lymphoid organs, capturing self antigens as well as innocuous environmental proteins. Recent experiments have provided direct evidence that antigen-loaded immature dendritic in vivo silence T cells either by deleting them or by expanding regulatory T cells. In this way, it is proposed that the immune system overcomes at least some of the risk of developing autoimmunity and chronic inflammation. It is proposed that dendritic cells play a major role in defining immunologic self, not only centrally in the thymus but also in the periphery.

Prognostic value of tumor-infiltrating dendritic cells expressing CD83 in human breast carcinomas

DCs are the most potent antigen-presenting cells that play a major role in initiating the antitumor immune response. Although the clinical significance of TIDCs has been investigated in a variety of human cancers, few studies have focused on the in situ maturation status of DCs. We have analyzed the maturation-specific significance of TIDCs in the prognosis of patients with breast carcinoma. We evaluated 130 breast carcinomas for the presence of TIDCs using immunohistochemistry with an anti-CD1a antibody for immature DCs and an anti-CD83 antibody for mature DCs. Intratumoral expression of immunosuppressive cytokines was also examined. All samples contained CD1a(+) TIDCs, and 82 (63.1%) samples contained CD83(+) TIDCs. The number of CD83(+) TIDCs was inversely correlated with lymph node metastasis and with tissue expression of VEGF and TGF-beta, whereas the number of CD1a(+) TIDCs was not. Kaplan-Meier analysis (log rank statistics) revealed a significant association of increasing number of CD83(+) TIDCs with longer relapse-free (p = 0.002) and overall (p < 0.001) survival. Furthermore, among patients with lymph node metastasis, the survival rate of those with larger numbers of CD83(+) TIDCs was significantly better than that of patients with fewer CD83(+) TIDCs. Multivariate analysis revealed that CD83(+) TIDCs had independent prognostic relevance in breast carcinomas. The infiltration of tumors by mature DCs expressing CD83 may be of great importance in initiating the primary antitumor immune response and is confirmed as an independent, immunologic prognostic parameter for survival in patients with breast cancer.

p38 Mitogen-activated protein kinase and extracellular signal-regulated kinases play distinct roles in the activation of dendritic cells by two representative haptens, NiCl2 and 2,4-dinitrochlorobenzene

Previous studies have demonstrated that haptens induce several phenotypic and functional changes of dendritic cells in vivo as well as in vitro. Although recently, the crucial role of p38 mitogen-activated protein kinase has been reported in the activation of dendritic cells by haptens, the signal transduction elements involved in each phenotypic and functional changes that occur in the activation of dendritic cells by haptens remain unknown. Therefore, we examined the role of mitogen-activated protein kinases and nuclear factor-kappaB in the signal transduction of dendritic cells stimulated with two representative haptens, i.e., NiCl2 and 2,4-dinitrochlorobenzene. Human monocyte-derived dendritic cells stimulated with 2,4-dinitrochlorobenzene induced the phosphorylation of p38 and stress-activated protein kinase/c-jun N-terminal kinases, whereas NiCl2 induced that of p44/42 extracellular signal-regulated kinases, p38, and stress-activated protein kinase/c-jun N-terminal kinases. In addition, NiCl2 phosphorylated inhibitor kappaB and activated nuclear factor-kappaB. In contrast, primary irritants, e.g., benzalkonium chloride, or sodium lauryl sulfate, did not activate these signal transduction pathways. By using specific inhibitors for extracellular signal-regulated kinases and p38 pathways, PD98059 and SB203580, respectively, we demonstrated that the augmentation of CD86, HLA-DR, and CD83, and the production of interleukin-8 along with its increased mRNA expression by monocyte-derived dendritic cells stimulated with 2,4-dinitrochlorobenzene, and the augmentation of CD83 and the interleukin-12 p40 production by monocyte-derived dendritic cells stimulated with NiCl2, were suppressed by SB203580, whereas PD98059 suppressed the production of interleukin-1beta and tumor necrosis factor-alpha, together with their increased mRNA expression by monocyte-derived dendritic cells treated with NiCl2. On the other hand, in spite of the activation of nuclear factor-kappaB by monocyte-derived dendritic cells stimulated with NiCl2, nuclear factor-kappaB inhibitor did not significantly affect the phenotypic and functional changes in the activation of monocyte-derived dendritic cells. These data indicate that NiCl2 and 2,4-dinitrochlorobenzene stimulate different signal transduction pathways in monocyte-derived dendritic cells, and subsequently induce different phenotypic and functional changes in them.

Oligodeoxynucleotides without CpG motifs work as adjuvant for the induction of Th2 differentiation in a sequence-independent manner

The outcomes of immune responses are regulated by various parameters including how Ags are handled by APCs. In this study, we describe the intrinsic immunomodulatory characteristics of oligodeoxynucleotides (ODNs) that improve the Ag presentation by APCs. ODNs (20-mer) containing CpG motifs induced strong Th1-skewed responses. In contrast, those without CpG motifs enhanced cytokine production by effector Th cells without particular skewing toward Th1 responses or induced the differentiation of unprimed CD4(+) T cells toward Th2 cells. These functional features were prominently envisaged when ODNs were conjugated to the Ag, and were underlain by the facilitated binding of ODN-conjugated Ag to Ia(+) cells. Despite the functional differences between ODNs with CpG motifs and those without CpG motifs, both ODNs bound to Ia(+) cells with similar affinity and kinetics. Immunoenhancing activities of the ODNs were not sequence-dependent; the characteristics, including the facilitation of Ag capture, enhancement of effector Th cell responses, and induction of Th2 cells, were shared by randomly synthesized ODNs conjugated to Ag. This is the first study suggesting that ODNs, independent of the sequences, enhance immune responses through the promoted capture of ODN-conjugated Ag by APCs.

Efficient targeting of protein antigen to the dendritic cell receptor DEC-205 in the steady state leads to antigen presentation on major histocompatibility complex class I products and peripheral CD8+ T cell tolerance

To identify endocytic receptors that allow dendritic cells (DCs) to capture and present antigens on major histocompatibility complex (MHC) class I products in vivo, we evaluated DEC-205, which is abundant on DCs in lymphoid tissues. Ovalbumin (OVA) protein, when chemically coupled to monoclonal alphaDEC-205 antibody, was presented by CD11c+ lymph node DCs, but not by CD11c- cells, to OVA-specific, CD4+ and CD8+ T cells. Receptor-mediated presentation was at least 400 times more efficient than unconjugated OVA and, for MHC class I, the DCs had to express transporter of antigenic peptides (TAP) transporters. When alphaDEC-205:OVA was injected subcutaneously, OVA protein was identified over a 4-48 h period in DCs, primarily in the lymph nodes draining the injection site. In vivo, the OVA protein was selectively presented by DCs to TCR transgenic CD8+ cells, again at least 400 times more effectively than soluble OVA and in a TAP-dependent fashion. Targeting of alphaDEC-205:OVA to DCs in the steady state initially induced 4-7 cycles of T cell division, but the T cells were then deleted and the mice became specifically unresponsive to rechallenge with OVA in complete Freund's adjuvant. In contrast, simultaneous delivery of a DC maturation stimulus via CD40, together with alphaDEC-205:OVA, induced strong immunity. The CD8+ T cells responding in the presence of agonistic alphaCD40 antibody produced large amounts of interleukin 2 and interferon gamma, acquired cytolytic function in vivo, emigrated in large numbers to the lung, and responded vigorously to OVA rechallenge. Therefore, DEC-205 provides an efficient receptor-based mechanism for DCs to process proteins for MHC class I presentation in vivo, leading to tolerance in the steady state and immunity after DC maturation.

Hantavirus infection of dendritic cells

Dendritic cells (DCs) play a pivotal role as antigen-presenting cells in the antiviral immune response. Here we show that Hantaan virus (HTNV), which belongs to the Bunyaviridae family (genus Hantavirus) and causes hemorrhagic fever with renal syndrome, productively infects human DCs in vitro. In the course of HTNV infection, DCs did not show any cytopathic effect and viral replication did not induce cell lysis or apoptosis. Furthermore, HTNV did not affect apoptosis-inducing signals that are important for the homeostatic control of mature DCs. In contrast to immunosuppressive viruses, e.g., human cytomegalovirus, HTNV activated immature DCs, resulting in upregulation of major histocompatibility complex (MHC), costimulatory, and adhesion molecules. Intriguingly, strong upregulation of MHC class I molecules and an increased intercellular cell adhesion molecule type 1 expression was also detected on HTNV-infected endothelial cells. In addition, antigen uptake by HTNV-infected DCs was reduced, another characteristic feature of DC maturation. Consistent with these findings, we observed that HTNV-infected DCs stimulated T cells as efficiently as did mature DCs. Finally, infection of DCs with HTNV induced the release of the proinflammatory cytokines tumor necrosis factor alpha and alpha interferon. Taken together, our findings indicate that hantavirus-infected DCs may significantly contribute to hantavirus-associated pathogenesis.

Constitutive presentation of a natural tissue autoantigen exclusively by dendritic cells in the draining lymph node

The major histocompatibility complex (MHC)-dependent presentation of processed tissue-specific self-antigens can contribute to either peripheral (extrathymic) tolerance or the differentiation of autoreactive T cells. Here, we have studied the MHC class II molecule presentation of gastric parietal cell (PC)-specific H(+)/K(+)-ATPase, which induces a destructive autoimmune gastritis in BALB/c mice lacking CD4(+) CD25(+) regulatory T cells. Immunofluorescence microscopy showed physical association of CD11c(+) dendritic cells (DCs) with PCs in the gastric mucosa. H(+)/K(+)-ATPase protein was found within vesicular compartments of a few CD11c(+) DCs only in the draining gastric lymph node (LN) and these antigen-containing DCs increased markedly in number with the onset of tissue destruction in autoimmune animals. Both CD8alpha(hi) and CD8alpha(lo) gastric DCs, but not peripheral or mesenteric DCs, showed evidence of constitutive in vivo processing and presentation of H(+)/K(+)-ATPase. These data provide direct support for a widely held model of local tissue antigen uptake and trafficking by DCs in normal animals and demonstrate that DCs in the draining LN can present a tissue-specific self-antigen under noninflammatory conditions without fully deleting autoreactive T cells or inducing active autoimmunity.

Diversity of receptors binding HIV on dendritic cell subsets

The ability of HIV-1 to use dendritic cells (DCs) for transport and to transfer virus to activated T cells in the lymph node may be crucial in early HIV-1 pathogenesis. We have characterized primary DCs for the receptors involved in viral envelope attachment and observed that C-type lectin receptor (CLR) binding was predominant in skin DCs, whereas binding to emigrating and tonsil DCs was CD4-dependent. No one CLR was solely responsible for envelope binding on all skin DC subsets. DC-SIGN (DC-specific ICAM-3-grabbing nonintegrin) was only expressed by CD14(+)CDla(lo) dermal DCs. The mannose receptor was expressed by CD1a(hi) and CD14(+)CDla(lo) dermal DCs, and langerin was expressed by Langerhans cells. The diversity of CLRs able to bind HIV-1 in skin DCs may reflect their ability to bind a range of microbial glycoproteins.

Dendritic cells, antigen distribution and the initiation of primary immune responses to self and non-self antigens

Immunity or tolerance are determined through the bone marrow-derived, antigen-presenting cells, dendritic cells (DC). Stimulation of lymphocytes by different types of DC, DC at different stages of maturity and DC producing and responding to different growth factors modulate immune responses. Innate receptors for foreign or self antigens provide scope in DC for discrimination between different antigenic stimuli. DC also transfer processed antigens to other DC. We propose that DC do not stimulate responses to antigens in their own environment but only to antigens acquired from other DC, providing a mechanism for discriminating between environmental and non-environmental antigens.

B cells capturing antigen conjugated with CpG oligodeoxynucleotides induce Th1 cells by elaborating IL-12

APCs initiate T cell-mediated immune responses against foreign Ags. Dendritic cells are professional APCs that play unique roles, including Ag-nonspecific capture, priming of naive T cells, and Th1 induction, whereas B cells generally lack these functions. In this study we uncovered novel aspects of murine B cells as APCs using CpG oligodeoxynucleotides (CpG) conjugated with an Ag. B cells served as efficient APCs independently of surface Igs. This characteristic was underlaid by the CpG-mediated Ag uptake and presentation, which were functional only when CpG were covalently conjugated to Ag. The B cells cultured with CpG-conjugated Ag not only enhanced IFN-gamma formation by Th1 cells, but also induced Th1 differentiation from unprimed T cells. These effects paralleled with the increase in the expression of CD40, CD86, and class II molecules on B cells and the coordinated production of IL-12 by the cells. To our knowledge this is the first report revealing that B cells share with dendritic cells common intrinsic characteristics, such as the Ag-nonspecific capture and presentation, and the induction of Th1 differentiation from unprimed T cells.

Cancer immunotherapy with peptide-based vaccines: what have we achieved? Where are we going?

Many human tumor-associated antigens (TAAs) have recently been identified and molecularly characterized. When bound to major histocompatibility complex molecules, TAA peptides are recognized by T cells. Clinical studies have therefore been initiated to assess the therapeutic potential of active immunization or vaccination with TAA peptides in patients with metastatic cancer. So far, only a limited number of TAA peptides, mostly those recognized by CD8(+) T cells in melanoma patients, have been clinically tested. In some clinical trials, partial or complete tumor regression was observed in approximately 10%-30% of patients. No serious side effects have been reported. The clinical responses, however, were often not associated with a detectable T-cell-specific antitumor immune response when patients' T cells were evaluated in ex vivo assays. In this review, we analyze the available human TAA peptides, the potential immunogenicity (i.e., the ability to trigger a tumor-specific T-cell response) of TAA peptides in vitro and ex vivo, and the potential to construct slightly modified forms of TAA peptides that have increased T-cell stimulatory activity. We discuss the available data from clinical trials of TAA peptide-based vaccination (including those that used dendritic cells to present TAA peptides), identify possible reasons for the limited clinical efficacy of these vaccines, and suggest ways to improve the clinical outcome of TAA peptide-based vaccination for cancer patients.

Targeting epidermal Langerhans cells by epidermal powder immunization

Immune reactions to foreign or self-antigens lead to protective immunity and, sometimes, immune disorders such as allergies and autoimmune diseases. Antigen presenting cells (APC) including epidermal Langerhans cells (LCs) play an important role in the course and outcome of the immune reactions. Epidermal powder immunization (EPI) is a technology that offers a tool to manipulate the LCs and the potential to harness the immune reactions towards prevention and treatment of infectious diseases and immune disorders.

Competent dendritic cells derived from CD34+ progenitors express CMRF-44 antigen early in the differentiation pathway

Differentiation of CD34(+) haematopoietic stem cells into functional dendritic cells (DC) was investigated using the mAb CMRF-44 and other mAb against DC-associated markers. GM-CSF mobilized peripheral blood stem cells were obtained from healthy donors by leukapheresis. CD34(+) cells were purified using CD34(+)-positive selection,and subsequent immunomagnetic depletion of CD14 and CD2 cells. CD34(+) cells were cultured in medium supplemented with one or more of GM-CSF,TNF-alpha, IL-4 or IL-6. CMRF-44 Ag expression was monitored by flow cytometry, and DC function by allogeneic MLR and tetanus toxoid(TT) presentation assays. CD34(+) cells quickly acquired the CMRF-44 Ag when cultured in the presence of TNF-alpha. By day 3, more than 50% of the cells were double-positive for CD34 and CMRF-44. CD34 expression was gradually lost, so that by day 9, the majority of the cells were CD34(-)/CMRF-44(+).GM-CSF and TNF-alpha also induced CD40 expression, and up-regulation of CD54 and MHC class II on CD34(+) cells; their expression was correlated to the CMRF-44 Ag. Day 3 CD34(+)/CMRF-44(+) cells,but not CD34(+)/CMRF-44(-) cells, become potent APC when cultured further with GM-CSF plus TNF-alpha. These CMRF-44(+) cells were potent inducers of Th1-type immune response in the primary allogeneic MLR and present TT to autologous CD4(+) T cells. TNF-alpha alone is sufficient to induce CMRF-44 expression on CD34(+) cells, but in combination with GM-CSF expands the CMRF-44(+) population. CMRF-44 expression correlates with DC function and may be a useful early marker for commitment of CD34(+) cells to the DC differentiation pathway.

Identification and expression of mouse Langerin (CD207) in dendritic cells

We have cloned the mouse homologue of human Langerin (h-Langerin), a type II transmembrane protein with a single external C-type lectin domain. Mouse Langerin (m-Langerin) displays 65 and 74% homologies in total amino acid and lectin domains with those of h-Langerin. The cognate mouse and rat genes were assigned to chromosome 6D1-D2 and chromosome 4q33 distal-q34.1 proximal respectively, syntenic to the h-Langerin gene on chromosome 2p13. With RT-PCR, m-Langerin transcripts were as expected detected in MHC class II+, but not MHC class II-, cells from epidermis and the expression level was reduced by culture. However, m-Langerin transcripts were also expressed in spleen, lymph nodes (LN), thymus, liver, lung and even heart, but not gut-associated lymphoid tissues. In single-cell lymphoid suspensions, m-Langerin transcripts were mainly detected in the CD11c+ dendritic cells (DC), especially the CD11blow/CD8high fraction of spleen and LN. DC generated from bone marrow precursors by granulocyte macrophage colony stimulating factor (GM-CSF) expressed m-Langerin, but this was shut down during maturation with CD40 ligand or lipopolysaccharide. DC derived from blood monocytes by GM-CSF + IL-4 lacked m-Langerin unless the cultures were supplemented with transforming growth factor (TGF)-beta1. Unexpectedly, significant amounts of m-Langerin transcripts were detected in skin and LN of TGF-beta1-deficient mice, although in much lower amounts than littermate controls. Recombinant m-Langerin could form multimers and bind to mannan-agarose. These findings indicate that Langerin expression is regulated at several levels: by TGF-beta1, DC subsets, DC maturation and the tissue environment.

Preferential infection of immature dendritic cells and B cells by mouse mammary tumor virus

Until now it was thought that the retrovirus mouse mammary tumor virus preferentially infects B cells, which thereafter proliferate and differentiate due to superantigen-mediated T cell help. We describe in this study that dendritic cells are infectable at levels comparable to B cells in the first days after virus injection. Moreover, IgM knockout mice have chronically deleted superantigen-reactive T cells after MMTV injection, indicating that superantigen presentation by dendritic cells is sufficient for T cell deletion. In both subsets initially only few cells were infected, but there was an exponential increase in numbers of infected B cells due to superantigen-mediated T cell help, explaining that at the peak of the response infection is almost exclusively found in B cells. The level of infection in vivo was below 1 in 1000 dendritic cells or B cells. Infection levels in freshly isolated dendritic cells from spleen, Langerhans cells from skin, or bone marrow-derived dendritic cells were compared in an in vitro infection assay. Immature dendritic cells such as Langerhans cells or bone marrow-derived dendritic cells were infected 10- to 30-fold more efficiently than mature splenic dendritic cells. Bone marrow-derived dendritic cells carrying an endogenous mouse mammary tumor virus superantigen were highly efficient at inducing a superantigen response in vivo. These results highlight the importance of professional APC and efficient T cell priming for the establishment of a persistent infection by mouse mammary tumor virus.

Avoiding horror autotoxicus: the importance of dendritic cells in peripheral T cell tolerance

The immune system generally avoids horror autotoxicus or autoimmunity, an attack against the body's own constituents. This avoidance requires that self-reactive T cells be actively silenced or tolerized. We propose that dendritic cells (DCs) play a critical role in establishing tolerance, especially in the periphery, after functioning T cells have been produced in the thymus. In the steady state, meaning in the absence of acute infection and inflammation, DCs are in an immature state and not fully differentiated to carry out their known roles as inducers of immunity. Nevertheless, immature DCs continuously circulate through tissues and into lymphoid organs, capturing self antigens as well as innocuous environmental proteins. Recent experiments have provided direct evidence that antigen-loaded immature DCs silence T cells either by deleting them or by expanding regulatory T cells. This capacity of DCs to induce peripheral tolerance can work in two opposing ways in the context of infection. In acute infection, a beneficial effect should occur. The immune system would overcome the risk of developing autoimmunity and chronic inflammation if, before infection, tolerance were induced to innocuous environmental proteins as well as self antigens captured from dying infected cells. For chronic or persistent pathogens, a second but dire potential could take place. Continuous presentation of a pathogen by immature DCs, HIV-1 for example, may lead to tolerance and active evasion of protective immunity. The function of DCs in defining immunologic self provides a new focus for the study of autoimmunity and chronic immune-based diseases.

Defect of protective immunity to Schistosoma mansoni infection in Mongolian gerbils involves limited recruitment of dendritic cells in the vaccinated skin

In Mongolian gerbils, Meriones unguiculatus, the attenuated Schistosoma mansoni vaccine, is known to induce marginal or no resistance to a homologous infection. To clarify the base of defective acquisition of the resistance, we have focused on the induction phase of protective immunity to S. mansoni, i.e. cellular responses in the skin and skin-draining lymph nodes (SLN). Percutaneous exposure to normal or ultraviolet (18mJ/cm2)-attenuated cercariae induced comparable increases in SLN leucocyte counts, in contrast to other attenuated schistosome vaccine models in rodents where attenuated parasites induce more notable increases in SLN leucocyte counts than normal ones. Using serial sections, it was demonstrated that greater numbers of attenuated larvae remained for a longer period in the exposed skin than normal ones. Correlated with cellular responses in the SLN, attenuated and normal schistosomes elicited a comparable degree of response of epidermal Langerhans' cells/putative dermal dendritic cells that were visualized by immunohistochemistry using a monoclonal antibody to a gerbil major histocompatibility complex class II molecule (HUSM-M.g.30). It is speculated that in Mongolian gerbils limited recruitment of dendritic cells around attenuated S. mansoni larvae, at least partially, contribute to defective induction of protective immunity by the attenuated vaccine.

Enhanced contact hypersensitivity in human monocyte chemoattractant protein-1 transgenic mouse

Monocyte chemoattractant protein (MCP)-1 is a chemotactic cytokine for monocytes, memoryT cells and dendritic cells (DC). However, the precise role of MCP-1 in a variety of immunological responses remains unclear. In the present study, we analyzed contact hypersensitivity (CHS) using human MCP-1 transgenic mice (hMCP-1Tgm) that constitutively produce high levels of hMCP-1 in the sera. Following 2,4-dinitrofluorobenzene (DNFB) sensitization, enhancement of CHS was demonstrated in Tgm as compared with that in non-Tgm. Anti-hMCP-1 antibodies significantly inhibited the CHS in Tgm. A prominent accumulation of B7-1+I-Ad+ Langerhans' cells (LC) bearing haptens was detected in draining lymph nodes (DLN) of Tgm 24 h after DNFB or fluorescein isothiocyanate (FITC) sensitization. Similar results were obtained with BALB/c mice administrated recombinant (r) hMCP-1. Langerhans' cells (LC) in the epidermal sheets of Tgm increased in size and expressed high levels of I-Ad and B7-1 12 h after FITC application compared with those of non-Tgm. After 18 h, the number of LC in the epidermis was reduced in Tgm. It was also shown that the B7-1 expression on LC of BALB/c mice was augmented after culture with rhMCP-1. These findings demonstrate that MCP-1 not only accelerates LC migration from epidermis into the DLN after sensitization with haptens but also up-regulates the I-Ad and B7-1 expressions, which results in the enhanced T cell activation and CHS.

Bipartite regulation of different components of the MHC class I antigen-processing machinery during dendritic cell maturation

Dendritic cells (DC) are professional antigen-presenting cells (APC) which proceed from immature to a mature stage during their final differentiation. Immature DC are highly effective in terms of antigen uptake and processing, whereas mature DC become potent immunostimulatory cells. Until now, the expression profiles of the major components of the MHC class I antigen-processing machinery (APM) during DC development have not been well characterized. In this study, the mRNA and protein expression levels of the IFN-gamma inducible proteasome subunits, of the proteasome activators PA28, and of key components required for peptide transport and MHC class I-peptide complex assembly have been evaluated in immature and mature stages of human monocyte-derived DC using semiquantitative RT-PCR and Western blot analyses. The IFN-gamma-responsive immunoproteasome subunits LMP2, LMP7 and MECL1 are up-regulated in immature DC, whereas the other components of the MHC class I presentation machinery, such as PA28, TAP, tapasin, and HLA heavy and light chains, were found to be more abundant in mature DC. These findings support the hypothesis that immature DC produced by the differentiation of monocytes in response to IL-4 and granulocyte macrophage colony stimulating factor first increase their capacity to capture antigens and process them into peptides, thereby switching from housekeeping to immunoproteasomes, while mature DC rather up-regulate the components required for peptide translocation and MHC class I-peptide complex formation, and thus specialize in antigen presentation. Our results establish that MHC class I, like MHC class II surface expression, is markedly regulated during DC development and maturation.

Activation through CD40 ligation induces functional Fas ligand expression by Langerhans cells

Langerhans cells (LC) are professional antigen-presenting cells of dendritic cell (DC) lineage and are critical for the induction of primary immune responses in skin. Following antigenic stimulation, LC migrate to regional lymph nodes and induce antigen-specific activation of T cells. After primary expansion, the majority of T cells undergo Fas/Fas ligand (FasL)-mediated apoptotic cell death, thereby suppressing their excessive expansion. Although recent investigations have indicated an immunoregulatory function for DC, whether LC could be involved in Fas/FasL-mediated suppression of activated T cells is still unclear. In this study, we found that LC express FasL after activation triggered through CD40 molecules on their surface, but not by stimulation with LPS or IFN-gamma. The functional significance of FasL expression by LC was demonstrated using two different assays for apoptosis induced in Jurkat cells. The apoptosis in Jurkat cells was completely blocked by anti-FasL blocking antibody, suggesting a Fas/FasL-mediated mechanism. These results indicate a new feedback mechanism to down-regulate T cell activation by LC through the interaction of the TNF receptor/ligand superfamily, CD40/CD40L and Fas/FasL.

Bitter-sweet symphony: defining the role of dendritic cell gp120 receptors in HIV infection

BACKGROUND

Dendritic cells (DC) are believed to be one of the first cell types infected during HIV transmission. Recently a single C-type lectin receptor (CLR), DC-SIGN, has been reported to be the predominant receptor on monocyte derived DC (MDDC) rather than CD4. The role of other CLRs in HIV binding and HIV binding by CLRs on other types of DC in vivo is largely unknown.

OBJECTIVES AND STUDY DESIGN

Review HIV binding to DC populations, both in vitro and in vivo, in light of the immense interest of a recently re-identified CLR called DC-SIGN.

RESULTS AND CONCLUSIONS

From recent work, it is clear that immature MDDC have a complex pattern of HIV gp120 binding. In contrast to other cell types gp120 has the potential to bind to several receptors on DC including CD4 and several types of C type lectin receptor, not just exclusively DC-SIGN. Given the diverse types of DC in vivo future work will need to focus on defining the receptors for HIV binding to these different cell types. Mucosal transmission of HIV in vivo targets immature sessile DCs, including Langerhans cells which lack DC-SIGN. The role of CLRs and DC-SIGN in such transmission remains to be defined.

Novel roles of CpG oligodeoxynucleotides as a leader for the sampling and presentation of CpG-tagged antigen by dendritic cells

Oligodeoxynucleotides containing CpG motifs have been highlighted as potent Th1 activators. We previously reported that Ag and CpG, when conjugated together, synergistically promoted the Ag-specific Th1 development and inhibited the Th2-mediated airway eosinophilia. In this study, we examined the mechanisms underlying the synergism of the covalent conjugation. The CpG-OVA conjugate enhanced the Th1 activation and development. These characteristic features of the conjugate could not be ascribed to the polymerization of OVA, but mirrored the augmented binding of the CpG-tagged Ag to dendritic cells (DCs) in a CpG-guided manner, because phycobiliprotein, R-PE, conjugated to CpG stained a higher proportion of DCs with higher intensity than the mixture. R-PE fluorescence was emitted from cytoplasmic portions of the DCs, which simultaneously expressed costimulatory molecules and IL-12. The CpG-conjugated R-PE trafficking described above actually served as a potent Ag. These results indicate that CpG conjugated to Ag exhibit novel joint properties as promoters of Ag uptake and DC activators, thereby potentiating the ability of DCs to generate Th1 cells. The DNA-mediated promotion of Ag uptake would be advantageous for evoking host immune responses against invading microorganisms.

In vivo-matured Langerhans cells continue to take up and process native proteins unlike in vitro-matured counterparts

We have been able to identify the cell subset derived from Langerhans cells in the total dendritic cell population of the peripheral lymph node and hence to follow their trafficking under normal physiological conditions as well as upon skin irritation. As expected, the rapid mobilization of Langerhans cells triggered by inflammatory signals into the draining lymph node correlated with an up-regulation of costimulatory molecules and with an enhanced immunostimulatory capacity. Surprisingly, however, these cells, instead of shutting down, maintain the capacity to capture and process protein Ags during the couple of days they stay alive in stark contrast to in vitro-matured dendritic cells.