Immunologic properties of purified epidermal Langerhans cells. Distinct requirements for stimulation of unprimed and sensitized T lymphocytes

Differential maturation of murine bone-marrow derived dendritic cells with lipopolysaccharide and tumor necrosis factor-α

Dendritic cells (DCs) play a key role in the interface between the innate and acquired immune systems. In response to both exogenous as well as endogenous signals, DCs undergo a programmed maturation to become an efficient, antigen-presenting cell. Yet little is known regarding the differential responses by endogenous versus exogenous stimuli on DC maturation. In the present report, we have compared the phenotypic, functional, and genome-wide expression responses associated with maturation by bone marrow derived DCs to either an endogenous danger signal, tumor necrosis factor-α (TNF-α), or a microbial product, bacterial lipopolysaccharide (LPS). Examination of the cell surface expression of DCs as well as cytokine production demonstrated that patterns of DC maturation varied dramatically depending upon the stimulus. Whereas LPS was highly effective in terms of inducing phenotypic and functional maturation, TNF-α exposure produced a phenotypically distinct DC. Gene expression patterns in DCs 6 and 24 h after LPS and TNF-α exposure revealed that these activation signals produce fundamentally different genomic responses. Supervised analysis revealed that the expression of 929 probe sets discriminated among the treatment groups, and the patterns of gene expression in TNF-α stimulated DCs were more similar to unstimulated cells at both 6 and 24 h post-stimulation than to LPS-stimulated cells at the same time points. These findings reveal that DCs are capable of a varying phenotypic response to different antigens and endogenous signals.

Calcitonin gene-related peptide: key regulator of cutaneous immunity

Calcitonin gene-related peptide (CGRP) has been viewed as a neuropeptide and vasodilator. However, CGRP is more appropriately thought of as a pleiotropic signalling molecule. Indeed, CGRP has key regulatory functions on immune and inflammatory processes within the skin. CGRP-containing nerves are intimately associated with epidermal Langerhans cells (LCs), and CGRP has profound regulatory effects on Langerhans cell antigen-presenting capability. When LCs are exposed to CGRP in vitro, their ability to present antigen for in vivo priming of naïve mice or elicitation of delayed-type hypersensitivity is inhibited in at least some situations. Administration of CGRP intradermally inhibits acquisition of immunity to Th1-dominant haptens applied to the injected site while augmenting immunity to Th2-dominant haptens, although the cellular targets of activity in these experiments remain unclear. Although CGRP can be a pro-inflammatory agent, several studies have demonstrated that administration of CGRP can inhibit the elicitation of inflammation by inflammatory stimuli in vivo. In this regard, CGRP inhibits the release of certain chemokines by stimulated endothelial cells. This is likely to be physiologically relevant as cutaneous blood vessels are innervated by sensory nerves. Exciting new studies suggest a significant role for CGRP in the pathogenesis of psoriasis and, most strikingly, that CGRP inhibits the ability of LCs to transmit the human immunodeficiency virus 1 to T lymphocytes. A more complete understanding of the role of CGRP in the skin immune system may lead to new and novel approaches for the therapy of immune-mediated skin disorders.

Micronodular thymoma with lymphoid stroma: an immunohistochemical study of the distribution of Langerhans cells and mature dendritic cells in six patients

AIMS

Micronodular thymoma with lymphoid stroma (MNT) is an uncommon variant of thymoma, characterized by multiple small nodules consisting of type A thymoma-like cells, which are separated by abundant B lymphocytes. The aim of the study was to elucidate the pathogenesis of the stromal lymphoid hyperplasia, which is currently unclear.

METHODS AND RESULTS

We retrieved six cases of MNT, and immunohistochemically examined the number and distribution of Langerhans cells (LCs) and mature dendritic cells (DCs), and compared them with those in type A and type AB thymomas. Many LCs were present within the small tumour nests, but LCs were rarely seen in the stroma (75.5/HPF versus 6.1/HPF, P < 0.0001). In contrast, mature DCs were present mainly in the surrounding stroma rather than within the tumour nodules (63.5/HPF versus 6.0/HPF, P < 0.0001), forming clusters with mature T lymphocytes adjacent to lymphoid follicles. In large nodules, as well as in type A and type AB thymomas, a few scattered LCs and DCs were identified. All patients were still alive and well.

CONCLUSIONS

Our results suggest that LCs take up tumour antigens and migrate to the stroma, where they mature and form clusters with T lymphocytes to activate them, resulting in lymphoid follicle formation. The favourable clinical behaviour may be attributable to the immune response induced by LCs.

Nerve-derived transmitters including peptides influence cutaneous immunology

Clinical observations suggest that the nervous and immune systems are closely related. For example, inflammatory skin disorders; such as psoriasis, atopic dermatitis, rosacea and acne; are widely believed to be exacerbated by stress. A growing body of research now suggests that neuropeptides and neurotransmitters serve as a link between these two systems. Neuropeptides and neurotransmitters are released by nerves innervating the skin to influence important actors of the immune system, such as Langerhans cells and mast cells, which are located within close anatomic proximity. Catecholamines and other sympathetic transmitters that are released in response to activation of the sympathetic nervous system are also able to reach the skin and affect immune cells. Neuropeptides appear to direct the outcome of Langerhans cell antigen presentation with regard to the subtypes of Th cells generated and neuropeptides induce the degranulation of mast cells, among other effects. Additionally, endothelial cells, which release many inflammatory mediators and express cell surface molecules that allow leukocytes to exit the bloodstream, appear to be regulated by certain neuropeptides and transmitters. This review focuses on the evidence that products of nerves have important regulatory activities on antigen presentation, mast cell function and endothelial cell biology. These activities are highly likely to have clinical and therapeutic relevance.

Langerhans cells and their role in oral mucosal diseases

Dendritic cells are arguably the most potent antigen-presenting cells and may be the only cells capable of initiating the adaptive immune response. The epithelial residents of dendritic cells are Langerhans cells, which serve as the "sentinels" of the mucosa, altering the immune system not only to pathogen entry but also of tolerance to self antigen and commensal microbes. Oral mucosal Langerhans cells are capable of engaging and internalizing a wide variety of pathogens and have been found responsive to nickel in patients with nickel allergies, oral Candida species, oral lichen planus, lichenoid drug eruptions, graft versus host diseases, periodontal diseases median rhomboid glossitis, human immunodeficiency virus infection, hairy leukoplakia of the tongue, and oral squamous cell carcinoma. Review focuses on the role of antigen-presenting cells in particular Langerhans cells to better understand the mechanisms underlying immune responses. In this review, comprehensive detail about mucosal diseases has been compiled using the PubMed database and through textbooks.

Immunological cells and functions in Gaucher disease

The macrophage (MΦ) has been the focus of causality, research, and therapy of Gaucher disease, but recent evidence casts doubt its solitary role in the disease pathogenesis. The excess of glucosylceramide (GC) in such cells accounts for some of the disease manifestations. Evidence of increased expression of C-C and C-X-C chemokines (i.e., CCL2,CXCL1, CXCL8) in Gaucher disease could be critical for monocyte transformation to inflammatory subsets of macrophages and dendritic cells (DC) as well as neutrophil (PMNs) recruitment to visceral organs. These immune responses could be essential for activation of T- and B-cell subsets, and the induction of numerous cytokines and chemokines that participate in the initiation and propagation of the molecular pathogenesis of Gaucher disease. The association of Gaucher disease with a variety of cellular and humoral immune responses is reviewed here to provide a potential foundation for expanding the complex pathophysiology of Gaucher disease.

An appreciation of Ralph Marvin Steinman (1943–2011)

Ralph Steinman, an editor at the Journal of Experimental Medicine since 1978, shared the 2011 Nobel Prize in Physiology or Medicine for his discovery of dendritic cells (DCs) and their role in immunity. Ralph never knew. He died of pancreatic cancer on September 30, 3 days before the Nobel announcement. Unaware of his death at the time of their announcement, the Nobel Committee made the unprecedented decision that his award would stand. Ralph was the consummate physician-scientist to the end. After his diagnosis, he actively participated in his 4.5 years of treatments, creating experimental therapies using his own DCs in conjunction with the therapies devised by his physicians, all the while traveling, lecturing, and most of all pursuing new investigations in his laboratory. For 38 years—from his discovery of DCs to his Nobel Prize—Ralph pioneered the criteria and methods used to identify, isolate, grow, and study DCs. He and his colleagues demonstrated that DCs are initiators of immunity and regulators of tolerance. In his most recent studies, Ralph was harnessing the specialized features of DCs to design improved vaccines. The following synopsis describes some of his seminal discoveries.

Immune functions of the skin

The skin, the body's largest organ, helps to secure the integrity of the host and, at the same time, allows the individual to communicate with the outside world. This finely tuned balance between protection from harmful pathogens (mostly microorganisms) and bidirectional signal exchange is provided by a network of structural, cellular, and molecular elements that are collectively referred to as the skin barrier. This "gateway" has a physical, chemical, and immunologic component. The role of the latter is to elicit a powerful defense reaction in the case of danger and, at the same time, to prevent such a reaction against innocuous substances. Immune responses originating in the skin are mounted and executed by cells and molecules of the innate or the adaptive immune system. Innate reactions are typically rapid, poorly discriminating, and do not exhibit memory. Adaptive responses, in contrast, show a high degree of specificity as well as memory but need a protracted time for their development. As a consequence, innate and adaptive responses are consecutive events influencing each other. In fact, we now know that the type and magnitude of the innate reactions govern and often determine the quality and quantity of adaptive responses.

Elf3 regulates allergic airway inflammation by controlling dendritic cell-driven T cell differentiation

Elf3 belongs to the Ets family of transcription factors and has been implicated in inflammation. Elf3 is highly expressed in the lungs, and Elf3(-/-) mice are impaired in IL-6 production after intranasal LPS exposure. To identify the role of Elf3 in Th17-driven pulmonary inflammation, we have performed epicutaneous sensitization of Elf3(-/-) mice with OVA followed by airway OVA challenge and have identified Elf3(-/-) mice to be impaired in induction of Th17 response, attributable to impairment of IL-6 production by dendritic cells (DCs). However, increased serum levels of OVA-specific IgG1 and IgE were observed, pointing toward an exaggerated Th2 response. To study Th2 response, we performed i.p. sensitization of Elf3(-/-) mice with OVA and confirmed loss of Elf3 to result in an aggravated Th2 response, characterized by increased generation of IL-4-producing T cells, increased levels of OVA-specific IgE and IgG1 Ab titers, and increased serum levels of Th2 cytokines, together with extensive inflammation and mucus production in airways. Elf3(-/-) DCs were impaired in priming Th1 differentiation, which, in turn, promoted Th2 differentiation. This was mediated by the ability of Elf3(-/-) DCs to undergo hypermaturation but secrete significantly lower levels of IL-12 in response to inflammatory stimuli. The impairment of IL-12 production was due to impairment of IL-12p40 gene induction in Elf3(-/-) DCs in response to inflammatory stimuli. Taken together, our study identifies a novel function of Elf3 in regulating allergic airway inflammation by regulating DC-driven Th1, Th2, and Th17 differentiation.

Tolerogenic dendritic cells and their potential applications

Dendritic cells (DCs) play a pivotal role in regulating the balance between immunity and tolerance of the immune system. Recent advancements in DC biology and techniques for manipulating the function of these cells have shown their immense therapeutic potential for treating a variety of immune disorders. Theoretically, antigen-specific tolerogenic DCs can be generated in vitro and delivered to patients to correct the dysfunctional immune responses that attack their own tissues or over-react to innocuous foreign antigens. However, DCs are a heterogeneous population of cells with differences in cell surface makers, differentiation pathways and functions. Studies are needed to examine which subset of DCs can be used for what type of applications. Furthermore, most of the information on tolerogenic DCs has been obtained from animal models and translational studies are needed to examine how a DC therapeutic strategy can be implemented clinically to modulate immunity.

Early detection of allergic diseases in otorhinolaryngology

Asthmatic diseases have been reported since the ancient world. Hay fever for instance, was described for the first time in the late 18(th) century, and the term "allergy" was introduced about 100 years ago. Today the incidence of allergies is rising; almost one third of the Western population suffers from its side effects. Allergies are some of the most chronic medical complaints, which results in high health expenditures. Therefore, they have a large health and political relevance.Caused by genetic and environmental factors, the group of IgE mediated allergies is large. It consists of e.g. atopic dermatitis, allergic asthma or allergic rhinitis. This paper aims to emphasize the ways of early diagnosis of allergic rhinitis (AR) as AR represents the most important representative of allergic diseases in ENT.

Origin and development of dendritic cells

Dendritic cells (DCs) are specialized antigen-presenting cells and essential mediators of immunity and tolerance. This group of cells is heterogeneous in terms of cell-surface markers, anatomic location, and function. Here, we review the development and function of DCs found in lymphoid and non-lymphoid tissues in the steady state. DC and monocyte lineages originate from a common progenitor, the monocyte and dendritic cell progenitor (MDP). The two cell types diverge when MDPs give rise to monocytes and committed DC progenitors (CDPs) in the bone marrow. CDPs give rise to pre-DCs, which migrate from the bone marrow to lymphoid and non-lymphoid tissues to produce the two major subpopulations of lymphoid tissue DCs and non-lymphoid tissue CD103(+) DCs. Within tissues and during development, DC division and homeostasis are regulated by the hormone Flt3L.

Intestinal dendritic cells and epithelial barrier dysfunction in Crohn's disease

Crohn's disease (CD) is a chronic gastrointestinal inflammatory disorder considered to be the result of an inappropriate and exaggerated mucosal immune reaction to yet undefined triggers from the gut flora in genetically predisposed individuals. This inflammatory phenomenon has been characterized by an adaptive T-cell response in addition to an abnormal function of the innate immune system. Dendritic cells (DCs) are constituents of this innate system, inducing T-cell activation via antigen presentation. In the gut, mucosal DCs are separated from the luminal milieu by a monolayer of cylindrical epithelial cells that forms an anatomical and physiological barrier that controls the normal traffic of antigens between both compartments. An imbalance of colonic and ileal DC distribution in tissues from CD patients as well as functional differences between DCs isolated from normal and diseased intestinal samples have been demonstrated. Moreover, a gut barrier defect in the para- and transepithelial routes in addition to a significant reduction in the intestinal secretion of epithelial products involved in barrier function has been well documented in CD. Therefore, this may expose the diseased mucosa to overwhelming amounts of antigens, resulting in abnormal DC activation and a subsequent imbalance in their distribution. In conclusion, this review provides a summary of relevant progress in CD, intestinal epithelial permeability, and DCs highlighting a potential relationship between increased epithelial permeability and abnormal DC distribution during the pathogenesis of intestinal inflammation.

Targeting tumors with LIGHT to generate metastasis-clearing immunity

Metastatic diseases cause the majority of morbidity and mortality of cancer patients. Established tumors form both physical and immunological barriers to limit immune detection and destruction. Current immunotherapy of vaccination and adoptive transfer shows limited effect at least in part due to the existing barriers in the tumors and depending on the knowledge of tumor antigens. Tumor necrosis factor (TNF) superfamily (TNFSF) member 14 (TNFSF14) LIGHT interacts with stromal cells, dendritic cells (DCs), NK cells, naïve and activated T cells and tumor cells inside the tumor tissues via its two functional receptors, HVEM and lymphotoxin beta receptor (LTbetaR). Targeting tumor tissues with LIGHT leads to augmentation of priming, recruitment, and retention of effector cells at tumor sites, directly or indirectly, to induce strong anti-tumor immunity to inhibit the growth of primary tumors as well as eradicate metastases. Intratumor treatment would break tumor barriers and allow strong immunity against various tumors without defining tumor antigens. This review summarizes recent findings to support that LIGHT is a promising candidate for an effective cancer immunotherapy.

Induction of high expression of CCR7 and high production of IL-12 in human monocyte-derived dendritic cells by a new bacterial component: LCOS 1013

Dendritic cells (DCs) are the most potent antigen presenting cells of the immune system as they can act as initiators, stimulators and regulators of the immune response. Human DCs are most commonly generated for clinical use by in vitro differentiation of monocytes with exogenous cytokines. Here, we investigate the effect of LCOS 1013 on the production of mature Mo-DCs. LCOS 1013 is a new bacterial component from walls of gram(+)Klebsellia pneumoniae bacteria that contain some OmpA glycoproteins. Purified peripheral blood monocytes were cultured for 6 days with IL-4 and GM-CSF in order to obtain immature dendritic cells (Im-MoDCs). On day six, Im-MoDCs were matured with either LCOS 1013, TNF alpha, LPS or CD40-Ligand. LCOS 1013 matured Mo-DCs (LCO-DCs) showed a higher expression of DC-LAMP, CD80, CD83, CD54 and CD40 than TNF alpha, LPS and CD40L matured Mo-DCs. Interestingly, LCO-DCs exhibited high expression of full competent CCR7 and high secretion of IL-12 during their maturation. Functionally, LCO-DCs have equivalent potency to trigger mixed leukocyte reaction and antigen-specific reaction and polarize immune response towards Th1 way. Moreover, we found that LCOS 1013 activates DCs through TLR2. LCOS 1013 represents an attractive therapeutic maturation agent of DCs allowing the production of Mo-DCs with high capacity to migrate and to induced Th1 immune responses.

Dendritic cells: understanding immunogenicity

The impetus for the discovery of dendritic cells in 1972 was to understand immunogenicity, the capacity of an antigenic substance to provoke immunity. During experiments to characterize "accessory" cells that enhanced immunity, we spotted unusual stellate cells in mouse spleen. They had a distinct capacity to form and retract processes or dendrites and were named dendritic cells (DC). DC proved to be different from other cell types and to be peculiarly immunogenic when loaded with antigens. When Langerhans cells were studied, immunogenicity was found to involve two steps: antigen presentation by immature DC and maturation to elicit immunity. Antigen-bearing DC were also immunogenic in vivo and were therefore termed "nature's adjuvants". Several labs then learned to generate large numbers of DC from progenitors, which accelerated DC research. Tolerogenicity via DC, including the control of foxp3(+) suppressor T cells, was recently discovered. Two areas of current research that I find intriguing are to identify mechanisms for antigen uptake and processing, and for the control of different types of immunity and tolerance. These subjects should be studied in vivo with clinically relevant antigens, so that the activities of DC can be better integrated into the prevention and treatment of disease in patients.

Rabbit antithymocyte globulin inhibits monocyte-derived dendritic cells maturation in vitro and polarizes monocyte-derived dendritic cells towards tolerogenic dendritic cells expressing indoleamine 2,3-dioxygenase

BACKGROUND

Rabbit antithymocyte globulin (rATG) is a polyclonal mixture of immunoglobulin (Ig) G. It is used to prevent graft rejection and also graft versus host disease after transplantation. Its effect on lymphocyte function has been widely studied. Dendritic cells are central actors of the immune system. As antigen presenting cells, they are able to initiate, stimulate, and modulate immune responses.

METHODS

In this study, we investigated rATG effects on in vitro differentiation and maturation of monocyte-derived dendritic cells (Mo-DCs).

RESULTS

rATG inhibited maturation of immature Mo-DCs and allowed the generation of dendritic cells expressing ILT-3, CD123, CCR6 but not CCR7 and producing Indoleamine 2,3-dioxygenase mRNA as well as interferon-alpha.

CONCLUSION

rATG polarizes in vitro Mo-DCs towards tolerogenic dendritic cells.

Dendritic cells: translating innate to adaptive immunity

The innate immune system provides many ways to quickly resist infection. The two best-studied defenses in dendritic cells (DCs) are the production of protective cytokines-like interleukin (IL)-12 and type I interferons-and the activation and expansion of innate lymphocytes. IL-12 and type I interferons influence distinct steps in the adaptive immune response of lymphocytes, including the polarization of T-helper type 1 (Th1) CD4+ T cells, the development of cytolytic T cells and memory, and the antibody response. DCs have many other innate features that do not by themselves provide innate resistance but are critical for the induction of adaptive immunity. We have emphasized three intricate and innate properties of DCs that account for their sentinel and sensor roles in the immune system: (1) special mechanisms for antigen capture and processing, (2) the capacity to migrate to defined sites in lymphoid organs, especially the T cell areas, to initiate immunity, and (3) their rapid differentiation or maturation in response to a variety of stimuli ranging from Toll-like receptor (TLR) ligands to many other nonmicrobial factors such as cytokines, innate lymphocytes, and immune complexes. The combination of innate defenses and innate physiological properties allows DCs to serve as a major link between innate and adaptive immunity. DCs and their subsets contribute to many subjects that are ripe for study including memory, B cell responses, mucosal immunity, tolerance, and vaccine design. DC biology should continue to be helpful in understanding pathogenesis and protection in the setting of prevalent clinical problems.

Dendritic cells in a mature age

A common view supposes that dendritic cells (DCs) exist in two basic functional states: immature DCs induce tolerance to self, whereas mature DCs induce immunity to foreign antigens. However, the term 'mature' is often used not only functionally to designate immunogenic DCs but also as a phenotypic description of DCs expressing high levels of MHC, adhesion and co-stimulatory molecules. The recent realization that DCs can express such markers under non-immunogenic conditions raises the question of whether the two connotations of the term 'mature' should continue to be used interchangeably. Here, I discuss the origins of the maturation model and how terminology is evolving to better accommodate our current understanding of the function of DCs.

The class 6 semaphorin SEMA6A is induced by interferon-gamma and defines an activation status of langerhans cells observed in pathological situations

Originally implicated in axon guidance, semaphorins represent a large family of molecules that are now known to be expressed in the immune system. Among different semaphorins tested by reverse transcriptase-polymerase chain reaction in human immune cells, the expression of class 6 transmembrane semaphorin SEMA6A was restricted to dendritic cells (DCs). Using in-house generated monoclonal antibodies, SEMA6A expression appeared further restricted to Langerhans cells (LCs). In vivo, SEMA6A mRNA was expressed in freshly isolated skin LCs but SEMA6A protein was not detectable on normal skin and tonsillar epithelium. Of interest, SEMA6A protein was strongly expressed on skin and bone LCs and on LCs in draining lymph nodes from patients with LC histiocytosis or dermatopathic lymphadenitis, respectively, representing two inflammatory conditions in which LCs display an immature DC-LAMP(low), CD83(low), and CCR7+ phenotype. SEMA6A expression was low in resting LCs generated in vitro and was enhanced by interferon (IFN)-gamma but not by interleukin-4, interleukin-10, IFN-alpha/beta, or lipopolysaccharide. Most IFN-gamma-induced SEMA6A-positive cells remained immature with low CD83 and DC-LAMP/CD208 expression, but they expressed CCR7 and responded to macrophage inflammatory protein-3beta (MIP-3beta/CCL19). The expression of SEMA6A, for which the ligand and function remain unknown, may therefore identify an alternative IFN-gamma-dependent activation status of LCs in vivo.

A novel role for Notch ligand Delta-1 as a regulator of human Langerhans cell development from blood monocytes

Human Langerhans cells (LCs) are of hematopoietic origin, but cytokine regulation of their development is not fully understood. Notch ligand Delta-1 is expressed in a proportion of the skin. Granulocyte-macrophage colony-stimulating factor (GM-CSF) and transforming growth factor-beta1 (TGF-beta1) are also secreted in the skin. We report here that Delta-1, in concert with GM-CSF and TGF-beta1, induces the differentiation of human CD14(+) blood monocytes into cells that express LC markers: CD1a, Langerin, cutaneous lymphocyte-associated antigen, CC chemokine receptor 6, E-cadherin, and Birbeck granules. The resulting cells display phagocytic activity and chemotaxis to macrophage inflammatory protein-1alpha (MIP-1alpha). In response to CD40 ligand and tumor necrosis factor alpha, the cells acquire a mature phenotype of dendritic cells that is characterized by up-regulation of human leukocyte antigen (HLA)-ABC, HLA-DR, CD80, CD86, CD40, and CD54 and appearance of CD83. These cells in turn show chemotaxis toward MIP-1beta and elicit activation of CD8(+) T cells and T helper cell type 1 polarization of CD4(+) T cells. Thus, blood monocytes can give rise to LCs upon exposure to the skin cytokine environment consisting of Delta-1, GM-CSF, and TGF-beta1, which may be, in part, relevant to the development of human epidermal LCs. Our results extend the functional scope of Notch ligand delta-1 in human hematopoiesis.

Effects of UVB on fascin expression in dendritic cells and Langerhans cells

BACKGROUND

Fascin is an actin-binding protein that regulates the rearrangement of cytoskeletal elements and their interactions with the cell membrane. Previous studies have indicated that fascin expression is enhanced in DC upon maturation and plays a critical role in T cell activation. Ultraviolet irradiation exerts immunosuppressive effects.

OBJECTIVE

We examined the effects of UVB irradiation on the interaction of DC/LC with T cells through fascin.

METHOD

Murine bone marrow-derived DC (BM-DC) were induced by recombinant murine GM-CSF and LPS, and UVB irradiation was applied prior to supplementation with LPS. I-A(+) cells (Langerhans cells (LC)) in the epidermal cell suspensions were exposed to UVB irradiation at the beginning of the 24-h culture. BM-DC and LC were analysed by immunohistochemical staining and flow cytometric analyses. To evaluate the effects of UVB irradiation on DC-T cell binding, we examined the clustering of BM-DC with allogeneic CD4(+) T cells under a confocal microscope.

RESULTS

Fascin expression in BM-DC and LC was decreased by UVB irradiation. Furthermore, UVB irradiation reduced the ability of BM-DC to cluster with allogeneic CD4(+) T cells. Polarization of fascin and filamentous actin (F-actin) at the point of contact of BM-DC with T cells was also disturbed by UVB irradiation.

CONCLUSION

These results suggest that the suppression of fascin expression by UVB irradiation down-regulates the rearrangement of the cytoskeleton and, thereby, antigen presentation in DC/LC.

Characterization of the systemic loss of dendritic cells in murine lymph nodes during polymicrobial sepsis

Dendritic cells (DCs) play a key role in critical illness and are depleted in spleens from septic patients and mice. To date, few studies have characterized the systemic effect of sepsis on DC populations in lymphoid tissues. We analyzed the phenotype of DCs and Th cells present in the local (mesenteric) and distant (inguinal and popliteal) lymph nodes of mice with induced polymicrobial sepsis (cecal ligation and puncture). Flow cytometry and immunohistochemical staining demonstrated that there was a significant local (mesenteric nodes) and partial systemic (inguinal, but not popliteal nodes) loss of DCs from lymph nodes in septic mice, and that this process was associated with increased apoptosis. This sepsis-induced loss of DCs occurred after CD3(+)CD4(+) T cell activation and loss in the lymph nodes, and the loss of DCs was not preceded by any sustained increase in their maturation status. In addition, there was no preferential loss of either mature/activated (MHCII(high)/CD86(high)) or immature (MHCII(low)/CD86(low)) DCs during sepsis. However, there was a preferential loss of CD8(+) DCs in the local and distant lymph nodes. The loss of DCs in lymphoid tissue, particularly CD8(+) lymphoid-derived DCs, may contribute to the alterations in acquired immune status that frequently accompany sepsis.

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.

Sepsis and the dendritic cell

Sepsis is a syndrome of significant morbidity and mortality. Unlike the advances made in other diseases processes, improvements in outcome from sepsis, severe sepsis, and septic shock have been modest. Current research has altered our understanding of sepsis pathogenesis such that present models and definitions are still evolving. One relatively novel cell type, the dendritic cell, is the subject of much current investigation in sepsis. Although our present understanding of dendritic cell biology is incomplete, growing evidence supports the importance of this antigen-presenting cell in the normal and maladaptive responses to microbial invasion and tissue injury. A better understanding of this cell's basic biology as well as its potential as a therapeutic target will undoubtedly play increasing roles in the development of new strategies for the treatment of the septic patient.

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.

Regulation of Dendritic Cell Function by NK Cells: Mechanisms Underlying the Synergism in the Combination Therapy of IL-12 and 4-1BB Activation

The interactions between NK cells and dendritic cells (DCs) have been previously demonstrated in vitro. In this report, the in vivo cross-regulation between NK cells and DCs was studied in tumor-bearing mice treated with adenoviral vector expressing IL-12 and agonistic anti-4-1BB Abs. NK cells are essential for both tumor rejection and CTL development in the combination therapy (IL-12 plus anti-4-1BB). The numbers and functional activities of both NK cells and DCs in tumor-infiltrating leukocytes were synergistically increased in the IL-12 plus anti-4-1BB-treated mice compared with treatment with either reagent alone. NK depletion in vivo resulted in a significant decrease in the number of DCs in tumor-infiltrating leukocytes, strongly suggesting that NK cells are involved in the activation and expansion of DCs. The mechanism by which IL-12-activated NK cells regulate DC functions is, in part, mediated through the secretion of IFN-gamma that leads to the up-regulation of 4-1BB by DCs. Furthermore, 4-1BB activation in conjunction with IL-12 gene delivery increased tumor infiltration of green fluorescence protein-labeled DCs and enhanced their MHC class II expression. The activation of DCs by NK cells and the subsequent development of antitumoral CTL responses facilitated by 4-1BB-activated DCs may account for the synergistic effects observed in the combination therapy in comparison to adenoviral vector expressing IL-12 or anti-4-1BB treatment alone.

IN VIVO-MOBILIZED KIDNEY DENDRITIC CELLS ARE FUNCTIONALLY IMMATURE, SUBVERT ALLOREACTIVE T-CELL RESPONSES, AND PROLONG ORGAN ALLOGRAFT SURVIVAL1

BACKGROUND

Migratory antigen-presenting cells resident in kidneys may have tolerogenic potential. Difficulties inherent in their isolation have limited their characterization. The authors examined the phenotype and function of murine kidney dendritic cells (DC) mobilized in vivo by systemic administration of fms-like tyrosine 3 kinase ligand (Flt3L).

METHODS

Monoclonal antibody staining was used to characterize DC subsets in situ, immediately after their isolation, and after lipopolysaccharide stimulation. Cytokine and CC chemokine receptor (CCR) gene expression was analyzed by RNase protection assay. Mixed leukocyte reactions were performed to assess DC allostimulatory ability and also the function of putative T-regulatory cells. In vivo DC trafficking was monitored by fluorescence imaging of dye-labeled cells and the influence of renal DC on vascularized heart allograft survival was determined.

RESULTS

Flt3L induced a marked increase both in CD11cCD8alpha and in CD11cCD8alpha DC within the renal cortex and medulla. Rarer, CD11cB220 (precursor plasmacytoid) DC were also detected. Bulk freshly isolated DC exhibited no interleukin (IL)-12p35 mRNA, low surface co-stimulatory molecule expression, and CCR transcripts, consistent with immaturity. They elicited only weak allogeneic T-cell proliferative responses, and repeated stimulation induced CD4CD25 IL-10 T cells. In vivo, the freshly isolated DC failed to prime T cells of naive allogeneic hosts for anti-donor cytotoxic T-cell responses. When infused systemically, 1 week before organ transplantation, they prolonged graft survival without immunosuppressive therapy.

CONCLUSIONS

Hematopoietin-mobilized renal DC are functionally immature and exhibit tolerogenic potential. Mobilization of DC within kidneys is likely to affect their antigen-handling capacity, immunogenicity, and tolerogenic ability.

Human dendritic cells express neuronal Eph receptor tyrosine kinases: role of EphA2 in regulating adhesion to fibronectin

Eph receptor tyrosine kinases and their ligands, the ephrins, have been primarily described in the nervous system for their roles in axon guidance, development, and cell intermingling. Here we address whether Eph receptors may also regulate dendritic cell (DC) trafficking. Reverse transcription-polymerase chain reaction (RT-PCR) analysis showed that DCs derived from CD34+ progenitors, but not from monocytes, expressed several receptors, in particular EphA2, EphA4, EphA7, EphB1, and EphB3 mRNA. EphB3 was specifically expressed by Langerhans cells, and EphA2 and EphA7 were expressed by both Langerhans- and interstitial-type DCs. EphA and EphB protein expression on DCs generated in vitro was confirmed by staining with ephrin-A3-Fc and ephrin-B3-Fc fusion proteins that bind to different Eph members, in particular EphA2 and EphB3. Immunostaining with anti-EphA2 antibodies demonstrated the expression of EphA2 by immature DCs and by skin Langerhans cells isolated ex vivo. Interestingly, ephrin expression was detected in epidermal keratinocytes and also in DCs. Adhesion of CD34+-derived DCs to fibronectin, but not to poly-l-lysine, was increased in the presence of ephrin-A3-Fc, a ligand of EphA2, through a beta1 integrin activation pathway. As such, EphA2/ephrin-A3 interactions may play a role in the localization and network of Langerhans cells in the epithelium and in the regulation of their trafficking.

Tolerogenic dendritic cells

Dendritic cells (DCs) have several functions in innate and adaptive immunity. In addition, there is increasing evidence that DCs in situ induce antigen-specific unresponsiveness or tolerance in central lymphoid organs and in the periphery. In the thymus DCs generate tolerance by deleting self-reactive T cells. In peripheral lymphoid organs DCs also induce tolerance to antigens captured by receptors that mediate efficient uptake of proteins and dying cells. Uptake by these receptors leads to the constitutive presentation of antigens on major histocompatibility complex (MHC) class I and II products. In the steady state the targeting of DC antigen capture receptors with low doses of antigens leads to deletion of the corresponding T cells and unresponsiveness to antigenic rechallenge with strong adjuvants. In contrast, if a stimulus for DC maturation is coadministered with the antigen, the mice develop immunity, including interferon-gamma-secreting effector T cells and memory T cells. There is also new evidence that DCs can contribute to the expansion and differentiation of T cells that regulate or suppress other immune T cells. One possibility is that distinct developmental stages and subsets of DCs and T cells can account for the different pathways to peripheral tolerance, such as deletion or suppression. We suggest that several clinical situations, including autoimmunity and certain infectious diseases, can be influenced by the antigen-specific tolerogenic role of DCs.

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.

The interaction of immunodeficiency viruses with dendritic cells

Dendritic cells (DCs) can influence HIV-1 and SIV pathogenesis and protective mechanisms at several levels. First, HIV-1 productively infects select populations of DCs in culture, particularly immature DCs derived from blood monocytes and skin (Langerhans cells). However, there exist only a few instances in which HIV-1- or SIV-infected DCs have been identified in vivo in tissue sections. Second, different types of DCs reliably sequester and transmit infectious HIV-1 and SIV in culture, setting up a productive infection in T cells interacting with the DCs. This stimulation of infection in T cells may explain the observation that CD4+ T lymphocytes are the principal cell type observed to be infected with HIV-1 in lymphoid tissues in vivo. DCs express a C-type lectin, DC-SIGN/CD209, that functions to bind HIV-1 (and other infectious agents) and transmit virus to T cells. When transfected into the THP-1 cell line, the cytosolic domain of DC-SIGN is needed for HIV-1 sequestration and transmission. However, DCs lacking DC-SIGN (Langerhans cells) or expressing very low levels of DC-SIGN (rhesus macaque monocyte-derived DCs) may use additional molecules to bind and transmit immunodeficiency viruses to T cells. Third, DCs are efficient antigen-presenting cells for HIV-1 and SIV antigens. Infection with several recombinant viral vectors as well as attenuated virus is followed by antigen presentation to CD4+ and CD8+ T cells. An intriguing pathway that is well developed in DCs is the exogenous pathway for nonreplicating viral antigens to be presented on class I MHC products. This should allow DCs to stimulate CD8+ T cells after uptake of antibody-coated HIV-1 and dying infected T cells. It has been proposed that DCs, in addition to expanding effector helper and killer T cells, induce tolerance through T cell deletion and suppressor T cell formation, but this must be evaluated directly. Fourth, DCs are likely to be valuable in improving vaccine design. Increasing DC uptake of a vaccine, as well as increasing their numbers and maturation, should enhance efficacy. However, DCs can also capture antigens from other cells that are initially transduced with a DNA vaccine or a recombinant viral vector. The interaction of HIV-1 and SIV with DCs is therefore intricate but pertinent to understanding how these viruses disrupt immune function and elicit immune responses.

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.

Prostaglandin E2-EP4 signaling initiates skin immune responses by promoting migration and maturation of Langerhans cells

Antigen-specific immune responses in the skin are initiated by antigen uptake into Langerhans cells and the subsequent migration of these cells to draining lymph nodes. Although prostaglandin E2 (PGE2) is produced substantially in skin exposed to antigen, its role remains unclear. Here we show that although Langerhans cells express all four PGE receptor subtypes, their migration to regional lymph nodes was decreased only in EP4-deficient (Ptger4-/-) mice and in wild-type mice treated with an EP4 antagonist. An EP4 agonist promoted the migration of Langerhans cells, increased their expression of costimulatory molecules and enhanced their ability to stimulate T cells in the mixed lymphocyte reaction in vitro. Contact hypersensitivity to antigen was impaired in Ptger4-/- mice and in wild-type mice treated with the EP4 antagonist during sensitization. PGE2-EP4 signaling thus facilitates initiation of skin immune responses by promoting the migration and maturation of Langerhans cells.

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.

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.

Dysfunctional and short-lived subsets in monocyte-derived dendritic cells from patients with advanced cancer

Dendritic cells (DCs) are antigen-presenting cells specialized for the induction of the primary T-cell response. Tumor immunotherapy using DCs loaded with tumor antigens is under way for patients with several types of advanced malignancies. In this study, DC-like cells (Mo-DCs) were generated from peripheral blood monocytes with granulocyte-macrophage colony-stimulating factor and interleukin-4. The antigen-presenting abilities, including capture of apoptotic tumor cells, IL-12 secretion, expression of antigen-presentation-related molecules (HLA-ABC, HLA-DR, and CD80), and mixed leukocyte reaction, of Mo-DCs from 37 patients with advanced cancer (pMo-DCs) were compared to those of 20 healthy volunteers (hMo-DCs). Seven days after the initial culture, no significant difference was found in either the number or the size of Mo-DC-forming colonies between the two groups. However, most of the antigen-presenting abilities of pMo-DCs were weaker than those of hMo-DCs on day 7. On day 14, both number and size of colonies were significantly decreased in pMo-DCs but not in hMo-DCs. Interestingly, the antigen-presenting abilities of the remaining pMo-DCs gradually strengthened with time and by day 14 no significant difference was observed between pMo-DCs and hMo-DCs. These results indicate that pMo-DCs contain dysfunctional and short-lived Mo-DC subsets.

Immune tolerance after delivery of dying cells to dendritic cells in situ

Peripheral immune tolerance is believed to be induced by the processing and presentation of self-tissues that die during physiologic tissue turnover. To examine the mechanism that mediates tolerance, we injected mice with dying syngeneic TAP(-/-) splenocytes loaded with small amounts of the protein antigen, ovalbumin (OVA). After ingestion and presentation of cell-associated OVA by the CD8(+) subset of dendritic cells in situ, large numbers of antigen-reactive, CD8(+) T cell receptor (TCR) transgenic T lymphocytes were driven into cell cycle, but then the T cells were deleted. The animals were also tolerant to challenge with OVA in complete Freund's adjuvant. An agonistic anti-CD40 monoclonal antibody was then administered together with the OVA-loaded splenocytes, so that the dendritic cells in the recipient mice would mature. In contrast to observations made in the steady state, the antigen-reactive T cells expanded in numbers for 1-2 wk and produced large amounts of interleukin 2 and interferon gamma, while the animals retained responsiveness to antigen rechallenge. The specific tolerance that develops when dendritic cells process self tissues in the steady state should prevent or reduce the development of autoimmunity when dying cells are subsequently processed during infection.

Accumulation of immature Langerhans cells in human lymph nodes draining chronically inflamed skin

The coordinated migration and maturation of dendritic cells (DCs) such as intraepithelial Langerhans cells (LCs) is considered critical for T cell priming in response to inflammation in the periphery. However, little is known about the role of inflammatory mediators for LC maturation and recruitment to lymph nodes in vivo. Here we show in human dermatopathic lymphadenitis (DL), which features an expanded population of LCs in one draining lymph node associated with inflammatory lesions in its tributary skin area, that the Langerin/CD207(+) LCs constitute a predominant population of immature DCs, which express CD1a, and CD68, but not CD83, CD86, and DC-lysosomal-associated membrane protein (LAMP)/CD208. Using LC-type cells generated in vitro in the presence of transforming growth factor (TGF)-beta1, we further found that tumor necrosis factor (TNF)-alpha, as a prototype proinflammatory factor, and a variety of inflammatory stimuli and bacterial products, increase Langerin expression and Langerin dependent Birbeck granules formation in cell which nevertheless lack costimulatory molecules, DC-LAMP/CD208 and potent T cell stimulatory activity but express CCR7 and respond to the lymph node homing chemokines CCL19 and CCL21. This indicates that LC migration and maturation can be independently regulated events. We suggest that during DL, inflammatory stimuli in the skin increase the migration of LCs to the lymph node but without associated maturation. Immature LCs might regulate immune responses during chronic inflammation.

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.

Comparison of the accessory activity of murine peritoneal cavity macrophage derived dendritic cells and peritoneal cavity macrophages in a mixed lymphocyte reaction

A detailed comparison of the accessory cell activities was carried out among murine peritoneal cavity macrophages (PEC-Mphi), peritonea] cavity macrophages stimulated with granulocyte-macrophage colony stimulating factor (GM-CSF) plus interleukin 4 (IL-4), the most popular cytokine combination widely used to generate dendritic cells (DC) and peritoneal cavity macrophage-derived DC (PEC-DC) using a two-way mixed lymphocyte reaction (MLR). All the cell types used efficiently induced statistically significant naïve T cell proliferation at all culture time points and responder:stimulator ratios used. However, marked differences were noted in the magnitude of the proliferative responses. These variations may be attributed to the intensity of expression of MHC class II glycoproteins, as well as the actual numbers of MHC class II+ cells.

An automated method for the quantification of immunostained human Langerhans cells

Allergic contact dermatitis is a frequent and increasing health problem. For ethical reasons, the current animal tests used to screen for contact sensitizers should be replaced by in vitro alternatives. Contact sensitizers have been shown to accelerate Langerhans cell (LC) migration from human organotypic skin explant cultures (hOSECs) more rapidly than non-sensitizers and it has been proposed that the hOSEC model could be used to screen for sensitizers. However, chemically induced decreases in epidermal LC numbers need to be accurately quantified if the alterations in epidermal LC numbers are to form the basis of an alternative system for screening contact sensitizers in vitro. As manual counting of LCs is labour intensive and subject to intra- and inter-personal variation we developed an image analysis routine, using the Leica QWin image analysis software, to quantify LCs in situ using immunohistochemically stained skin sections. LCs can be identified using antibodies against the membrane molecule CD1a or the Lag antibody, which recognises cytoplasmic Birbeck granules. Quantification of epidermal LC number using the image analysis software had a much lower inter-person variation than when the same specimens were counted manually, using both the anti-Lag and CD1a antibodies. The software-aided quantification of epidermal LCs provides an accurate method for measuring chemically-induced changes in LC numbers.

Expression of the actin-bundling protein fascin in cultured human dendritic cells correlates with dendritic morphology and cell differentiation

Dendritic cells are key players of the immune system as they efficiently induce primary immune responses by activating naive T cells. We generated human dendritic cells from CD14+ blood precursors and investigated expression of the actin-bundling protein fascin during maturation by western blotting, immunofluorescence, and cytofluorometry. Cells obtained by culture of CD14+ blood precursors in the presence of granulocyte-macrophage colony-stimulating factor and interleukin-4, which were only weakly positive for the maturation marker CD83, expressed low amounts of fascin. Addition of a cytokine cocktail including tumor necrosis factor alpha, interleukin-1beta, interleukin-6, and prostaglandin E2 induced maturation of the cells and enhanced fascin expression in parallel with CD83 expression. Isolated mature CD83+ cells displayed especially high fascin levels on western blots, as did gated CD83+ dendritic cells in cytofluorometry. Dendritic cells generated from CD34+ blood precursors expressed high levels of fascin as well. Confocal microscopy revealed that location of fascin within the cell was restricted to the area of the submembranous actin cytoskeleton and to the dendritic processes. Suppression experiments using antisense constructs of fascin hint at a retarded morphologic maturation of dendritic cells, supporting the view that fascin expression is pivotal for dendrite formation. Our data suggest that fascin could serve as a marker molecule to monitor the maturation state of in vitro generated dendritic cells for use in clinical trials.