The evolving function of Langerhans cells in adaptive skin immunity

Immunohistochemical Characterization of Langerhans Cells in the Skin of Three Amphibian Species

The amphibian taxon includes three orders that present different morphological characteristics: Anura, Caudata, and Apoda. Their skin has a crucial role: it acts as an immune organ constituting a physical, chemical, immunological, and microbiological barrier to pathogen insult and conducts essential physiological processes. Amphibians have developed specialized features to protect the vulnerable skin barrier, including a glandular network beneath the skin surface that can produce antimicrobial and toxic substances, thus contributing to the defense against pathogens and predators. This study aims to characterize Langerhans cells in the skin of Lithobates catesbeianus (order: Anura; Shaw, 1802), Amphiuma means (order: Caudata; Garden, 1821), and Typhlonectes natans (order: Apoda; Fischer, 1880) with the following antibodies: Langerin/CD207 (c-type lectin), Major Histocompatibility Complex (MHC)II, and Toll-like receptor (TLR)2 (expressed by different types of DCs). Our results showed Langerhans cells positive for Langerin CD/207 in the epidermis of the three species; moreover, some antigen-presenting cells (APCs) in the connective tissue expressed TLR2 and MHCII. The distribution of the Langerhans cells is very similar in the three amphibians examined, despite their different habitats. A greater knowledge of the amphibian immune system could be useful to better understand the phylogeny of vertebrates and to safeguard amphibians from population declines. Furthermore, the similarities between amphibians' and human skin concerning immunological features may be useful in both biology and translational medicine.

Anatomical contacts between sensory neurons and epidermal cells: an unrecognized anatomical network for neuro-immuno-cutaneous crosstalk

Sensory neurons innervating the skin are conventionally thought to be the sole transducers of touch, temperature, pain and itch. However, recent studies have shown that keratinocytes - like Merkel cells - act as sensory transducers, whether for innocuous or noxious mechanical, thermal or chemical stimuli, and communicate with intraepidermal free nerve endings via chemical synaptic contacts. This paradigm shift leads to consideration of the whole epidermis as a sensory epithelium. Sensory neurons additionally function as an efferent system. Through the release of neuropeptides in intimate neuroepidermal contact areas, they contribute to epidermal homeostasis and to the pathogenesis of inflammatory skin diseases. To counteract the dogma regarding neurocutaneous interactions, seen exclusively from the perspective of soluble and spreading mediators, this review highlights the essential contribution of the unrecognized anatomical contacts between sensory neurons and epidermal cells (keratinocytes, melanocytes, Langerhans cells and Merkel cells), which take part in the reciprocal dialogue between the skin, nervous system and immune system.

Langerhans cells are essential components of the angiogenic niche during murine skin repair

Angiogenesis, the growth of new blood vessels from pre-existing vessels, occurs during development, injury repair, and tumorigenesis to deliver oxygen, immune cells, and nutrients to tissues. Defects in angiogenesis occur in cardiovascular and inflammatory diseases, and chronic, non-healing wounds, yet treatment options are limited. Here, we provide a map of the early angiogenic niche by analyzing single-cell RNA sequencing of mouse skin wound healing. Our data implicate Langerhans cells (LCs), phagocytic, skin-resident immune cells, in driving angiogenesis during skin repair. Using lineage-driven reportersw, three-dimensional (3D) microscopy, and mouse genetics, we show that LCs are situated at the endothelial cell leading edge in mouse skin wounds and are necessary for angiogenesis during repair. These data provide additional future avenues for the control of angiogenesis to treat disease and chronic wounds and extend the function of LCs beyond their canonical role in antigen presentation and T cell immunity.

Therapeutic application of T regulatory cells in composite tissue allotransplantation

With growing number of cases in recent years, composite tissue allotransplantation (CTA) has been improving the quality of life of patient who seeks reconstruction and repair of damaged tissues. Composite tissue allografts are heterogeneous. They are composed of a variety of tissue types, including skin, muscle, vessel, bone, bone marrow, lymph nodes, nerve, and tendon. As a primary target of CTA, skin has high antigenicity with a rich repertoire of resident cells that play pivotal roles in immune surveillance. In this regard, understanding the molecular mechanisms involved in immune rejection in the skin would be essential to achieve successful CTA. Although scientific evidence has proved the necessity of immunosuppressive drugs to prevent rejection of allotransplanted tissues, there remains a lingering dilemma due to the lack of specificity of targeted immunosuppression and risks of side effects. A cumulative body of evidence has demonstrated T regulatory (Treg) cells have critical roles in induction of immune tolerance and immune homeostasis in preclinical and clinical studies. Presently, controlling immune susceptible characteristics of CTA with adoptive transfer of Treg cells is being considered promising and it has drawn great interests. This updated review will focus on a dominant form of Treg cells expressing CD4+CD25+ surface molecules and a forkhead box P3 transcription factor with immune tolerant and immune homeostasis activities. For future application of Treg cells as therapeutics in CTA, molecular and cellular characteristics of CTA and immune rejection, Treg cell development and phenotypes, Treg cell plasticity and stability, immune tolerant functions of Treg cells in CTA in preclinical studies, and protocols for therapeutic application of Treg cells in clinical settings are addressed in this review. Collectively, Treg cell therapy in CTA seems feasible with promising perspectives. However, the extreme high immunogenicity of CTA warrants caution.

Inflammatory features of frontal fibrosing alopecia

INTRODUCTION

Frontal fibrosing alopecia (FFA) is a cicatricial alopecia typically occurring in postmenopausal women. The etiology and pathophysiology of FFA is poorly understood but thought to be immune mediated. This study aims to further explore the extent of fibrosis and the inflammatory microenvironment by characterizing Langerhans cells (LCs), helper T cells, cytotoxic T cells and B cells near hair follicles in FFA.

METHODS

Eleven paraffin-embedded tissues from patients with a clinical and histopathologic diagnosis of FFA were selected for immunohistochemical studies using CD3, CD4, CD8, CD1a and CD20. The lymphocytes and LCs were counted around involved follicles. The CD4/CD8 T-lymphocyte ratios were calculated and compared to the CD4/CD8 T-lymphocyte ratios in uninvolved areas.

RESULTS

On histopathologic review, at least 35% of follicles in each case were affected by the disease with concentric perifollicular fibrosis and a perifollicular lichenoid lymphocytic infiltrate around the infundibuloisthmic portion of the hair follicle. There was an increase of perifollicular LCs (mean of 18, SD of 5.5) and intrafollicular LCs (mean of 14, SD of 4.3) in involved follicles compared to uninvolved follicles (P < .0001). The involved follicles also showed a relative decrease in the CD4/CD8 ratio indicating increased numbers of CD8+ T cells; a finding distinct from the CD4-predominant population in uninvolved follicles (P < .0001).

CONCLUSION

The inflammatory features of FFA show a CD8-biased T-cell infiltrate with increased numbers of LCs in the infundibuloisthmic region. The increased LCs may represent an aberrant immune reaction promoting a CD8+ T-cell response.

Linking immune responses with fibrosis in allergic eye disease

PURPOSE OF REVIEW

Here, we explore an emerging theme in the literature, which is the role of dendritic cells in the causation of fibrosis. To fully appreciate this pathway to disease, we also review the most recent literature regarding dendritic cell biology as it pertains to ocular surface tissues. On the basis of this information, we propose a unifying hypothesis for how dendritic cells may cause conjunctival fibrosis in the allergy setting.

RECENT FINDINGS

Work in models of airway remodeling and liver fibrosis has pointed to a potentially central role for dendritic cells in the pathobiology of fibrosis. Indeed, these cells are recognized as the most potent antigen-presenting cells, and as such activate T lymphocytes that are profibrotic under certain conditions. However, recent findings suggest a more direct role for dendritic cells, which opens up the possibility that a similar pathway may be relevant in the causation of conjunctival fibrosis, particularly in allergic eye disease.

SUMMARY

Conjunctival fibrosis is a serious clinical concern and is associated with chronic inflammation of the ocular surface tissue, such as in allergic eye disease. Dendritic cells are required in mediating allergic disease by activating pathologic T lymphocytes. Recent findings pointing to a central role for dendritic cell in fibrosis may, however, mean that these cells could also be contributing directly to conjunctival fibrosis. If so, furthering our understanding of dendritic cells could lead to the identification of novel and more effective therapeutic strategies to treat this disease.

Langerhans cells (CD1a and CD207), dermal dendrocytes (FXIIIa) and plasmacytoid dendritic cells (CD123) in skin lesions of leprosy patients

The clinical course of infection with Mycobacterium leprae varies widely and depends on the pattern of the host immune response. Dendritic cells play an important role in the activation of the innate and adaptive immune system and seem to be essential for the development of the disease. To analyze the presence of epidermal dendritic cells (CD1a and CD207), plasmacytoid dendritic cells (CD123) and dermal dendrocytes (factor XIIIa) in lesion fragments of leprosy patients, skin samples from 30 patients were studied. These samples were submitted to immunohistochemistry against CD1a, CD207, FXIIIa, and CD123. The results showed a larger number of Langerhans cells, detected with the CD1a or CD207 marker, dermal dendrocytes and plasmacytoid dendritic cells in patients with the tuberculoid form. A positive correlation was observed between the Langerhans cell markers CD1a and CD207 in both the tuberculoid and lepromatous forms, and between Langerhans cells and dermal dendrocytes in samples with the tuberculoid form. The present results indicate the existence of a larger number of dendritic cells in patients at the resistant pole of the disease (tuberculoid) and suggest that the different dendritic cells studied play a role, favoring an efficient immune response against infection with M. leprae.

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.

Cutaneous immunopathology of long-standing complex regional pain syndrome

BACKGROUND

Both increased mast cells numbers and raised immune mediator concentrations indicate immune activation in the affected skin of patients with early complex regional pain syndrome (CRPS), but little is known about regional immune cell involvement in late-stage CRPS. The aim of the current study was to determine skin immune cell populations in long-standing CRPS.

METHODS

Using 6-mm skin punch biopsies from CRPS-affected and non-affected tissues, and a combination of chemical and immunofluorescence staining, we examined the density and function of key cell populations including mast cells, epidermal Langerhans cells (LCs) and tissue resident T-cells.

RESULTS

We found no significant differences in either overall immune cell infiltrates, or mast cell density between CRPS-affected and non-affected sub-epidermal tissue sections, contrasting recent findings in early CRPS by other groups. However, CD1a(+) LC densities in the epidermal layer were significantly decreased in affected compared to non-affected CRPS limbs (p < 0.01). T-cell clones isolated from CRPS-affected sub-epidermal tissues displayed a trend towards increased IL-13 production in ELISPOT assays when compared to T-cells isolated from non-affected areas, suggesting a Th2 bias.

CONCLUSIONS

Immune cell abnormalities are maintained in late-stage CRPS disease as manifest by changes in epidermal LC density and tissue resident T-cell phenotype.

Calcitonin gene-related peptide inhibits human immunodeficiency type 1 transmission by Langerhans cells via an autocrine/paracrine feedback mechanism

AIM

Peripheral neurones innervating mucosal epithelia are in direct contact with resident immune cells, including Langerhans cells (LCs). Such neurones secrete the neuropeptide calcitonin gene-related peptide (CGRP) that modulates LCs function. We recently found that CGRP strongly inhibits human immunodeficiency virus type 1 (HIV-1) transmission, by interfering with multiple steps of mucosal LC-mediated HIV-1 transfer, including increased expression of the LC-specific lectin langerin. Herein, we investigated the anti-HIV-1 mechanism of CGRP.

METHODS

In the presence of CGRP, HIV-1 transfer from LCs to CD4+ T cells was tested with viral clones using either the HIV-1 co-receptor CCR5 (R5) or CXCR4 (X4). Surface expression of CCR5, CXCR4 and langerin was evaluated by flow cytometry. CGRP secretion by LCs was measured with an enzyme immunoassay. Expression of the multimeric CGRP receptor was examined by quantitative real-time RT-PCR and immuno-fluorescent microscopy.

RESULTS

Calcitonin gene-related peptide decreased transfer of HIV-1 R5, but increased that of X4. These opposing effects correlated with decreased CCR5 vs. increased CXCR4 surface expression in LCs. Inhibition of HIV-1 R5 transfer by CGRP involved signal transducer and activator of transcription 4 (STAT4) activation. Both αCGRP and βCGRP were similarly efficient in decreasing HIV-1 R5 transfer and increasing langerin expression. LCs secreted low basal levels of endogenous CGRP, which increased markedly following CGRP treatment. CGRP also increased expression of its cognate receptor in LCs.

CONCLUSION

CGRP engages a positive feedback mechanism that would further enhance its anti-HIV-1 activity. This information might be relevant for the therapeutic use of CGRP as a prophylactic agent against HIV-1.

Regional variations in the histology of porcine skin

Porcine skin is commonly used as a model for human skin injury and as a source material for biologic scaffold materials. Although remarkable similarities between porcine and human skin exist, regional anatomic variations present in human skin are also present in porcine skin. The objective of this study was to evaluate the structure of porcine skin from 11 different anatomic regions in the American Yorkshire crossbreed. Both qualitative and quantitative methods were used, with emphasis on epidermal and dermal thickness, hair follicle density, and collagen and elastin composition and distribution. The results showed that significant regional differences in skin histology exist, particularly with regard to the thickness of the dermis and epidermis and the amount of collagen and elastin within each tissue. Differences were also seen in the distribution of type I and type III collagen within the dermis. Therefore, while porcine skin shares many similarities with human skin, distinct regional differences in composition and morphology exist. This study highlights the importance of appreciating these regional differences to avoid misinterpretation of experimental results when using porcine skin as a human analogue.

The pathophysiological role of dendritic cell subsets in psoriasis

Psoriasis is a chronic inflammatory disorder characterized by an erythematous scaly plaque of the skin and is occasionally accompanied by systemic complications. In the psoriatic lesions, an increased number of cytokine-producing dendritic cells and activated T cells are observed, which indicate that psoriasis is a prototype of an immune-mediated dermatosis. During the last decade, emerging studies demonstrate novel roles for the dendritic cell subsets in the process of disease initiation and maintenance of psoriasis. In addition, recently discovered anti-psoriatic therapies, which specifically target inflammatory cytokines produced by lesional dendritic cells, bring much better clinical improvement compared to conventional treatments. These new therapies implicate the crucial importance of dendritic cells in psoriasis pathogenesis. This review will summarize and discuss the dendritic cell subsets of the human skin and their pathophysiological involvement in psoriasis based on mouse- and patient-oriented studies. [BMB Reports 2014; 47(2): 60-68]

Increased number of Langerhans cells in the epidermis of diabetic foot ulcers correlates with healing outcome

Langerhans cells (LCs) are a specialized subset of epidermal dendritic cells. They represent one of the first cells of immunologic barrier and play an important role during the inflammatory phase of acute wound healing. Despite considerable progress in our understanding of the immunopathology of diabetes mellitus and its associated comorbidities such as diabetic foot ulcers (DFUs), considerable gaps in our knowledge exist. In this study, we utilized the human ex vivo wound model and confirmed the increased epidermal LCs at wound edges during early phases of wound healing. Next, we aimed to determine differences in quantity of LCs between normal human and diabetic foot skin and to learn if the presence of LCs correlates with the healing outcome in DFUs. We utilized immunofluorescence to detect CD207+ LCs in specimens from normal and diabetic foot skin and DFU wound edges. Specimens from DFUs were collected at the initial visit and 4 weeks later at the time when the healing outcome was determined. DFUs that decreased in size by >50 % were considered to be healing, while DFUs with a size reduction of <50 % were considered non-healing. Quantitative assessment of LCs showed a higher number of LCs in healing when compared to non-healing DFU's. Our findings provide evidence that LCs are present in higher number in diabetic feet than normal foot skin. Healing DFUs show a higher number of LCs compared to non-healing DFUs. These findings indicate that the epidermal immune barrier plays an important role in the DFU healing outcome and may offer new therapeutic avenues targeting LC in non-healing DFUs.

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.

Role of Th17 cells in skin inflammation of allergic contact dermatitis

Extending the classical concept considering an imbalance exclusively of T helper(h) 1 and Th2 cells on the bottom of many inflammatory diseases, Th17 cells were recently described. Today, there is sufficient experimental evidence to classify psoriasis and allergic contact dermatitis (ACD) amongst other inflammatory skin disorders as IL-17 associated diseases. In several human studies, T-cell-clones could be isolated from eczema biopsies, and high IL-17 levels were observed after challenge with allergen. In the last years, the phenotype of these IL-17 releasing T cells was in the focus of discussion. It has been suggested that Th17 could be identified by expression of retinoic acid receptor-related orphan receptor (ROR)C (humans) or RORγt (mice) and IL-17, accompanied by the absence of IFN-γ and IL-22. In cells from skin biopsies, contact allergens elevate IL-17A, IL-23, and RORC within the subset of Th cells. The indications for a participation of Th17 in the development of ACD are supported by data from IL-17 deficient mice with reduced contact hypersensitivity (CHS) reactions that could be restored after transplantation of wild type CD4⁺ T cells. In addition to Th17 cells, subpopulations of CD8⁺ T cells and regulatory T cells are further sources of IL-17 that play important roles in ACD as well. Finally, the results from Th17 cell research allow today identification of different skin diseases by a specific profile of signature cytokines from Th cells that can be used as a future diagnostic tool.

Dendritic cells and the assessment in vitro of skin sensitizing potential

It is now well established that dendritic cells (DC) play pivotal roles in the initiation and orchestration of adaptive immune responses, including cutaneous immune responses to chemical allergens that drive the acquisition of skin sensitization. It is not unexpected, therefore, that a large number, and wide variety, of proposed approaches for the identification of skin sensitizing chemicals in vitro are based upon the use of cultured DC or DC-like cells. The use of DC in this context is legitimate. However, with our rapidly increasing understanding of the diversity of cutaneous DC with respect to both phenotype and function, it is timely now to review briefly the potential limitations and interpretive difficulties that are associated with the use of DC-based assays. Among the important considerations are the fact that chemical-induced changes in the characteristics and function of cultured DC will not necessarily reflect accurately the events that that support the development of skin sensitization in vivo. In addition, most DC-based assays are predicated on a view that cutaneous DC have as their primary function the initiation of adaptive immune responses. However, it is now appreciated that cutaneous DC, and in particular epidermal Langerhans cells (LC), may also play important immunoregulatory roles that serve to limit and contain skin immune responses. Notwithstanding these considerations there is reason to believe that at least some in vitro DC-based assays are of value, and indeed some are currently the subject of a formal validation process. However, it is appropriate that such assays are configured and interpreted carefully, and with an appreciation of the complexity of DC biology.

Innate immunity and resistance to tolerogenesis in allotransplantation

The development of immunosuppressive drugs to control adaptive immune responses has led to the success of transplantation as a therapy for end-stage organ failure. However, these agents are largely ineffective in suppressing components of the innate immune system. This distinction has gained in clinical significance as mounting evidence now indicates that innate immune responses play important roles in the acute and chronic rejection of whole organ allografts. For instance, whereas clinical interest in natural killer (NK) cells was once largely confined to the field of bone marrow transplantation, recent findings suggest that these cells can also participate in the acute rejection of cardiac allografts and prevent tolerance induction. Stimulation of Toll-like receptors (TLRs), another important component of innate immunity, by endogenous ligands released in response to ischemia/reperfusion is now known to cause an inflammatory milieu favorable to graft rejection and abrogation of tolerance. Emerging data suggest that activation of complement is linked to acute rejection and interferes with tolerance. In summary, the conventional wisdom that the innate immune system is of little importance in whole organ transplantation is no longer tenable. The addition of strategies that target TLRs, NK cells, complement, and other components of the innate immune system will be necessary to eventually achieve long-term tolerance to human allograft recipients.

Novel immune-modulator identified by a rapid, functional screen of the parapoxvirus ovis (Orf virus) genome

Background

The success of new sequencing technologies and informatic methods for identifying genes has made establishing gene product function a critical rate limiting step in progressing the molecular sciences. We present a method to functionally mine genomes for useful activities in vivo, using an unusual property of a member of the poxvirus family to demonstrate this screening approach.

Results

The genome of Parapoxvirus ovis (Orf virus) was sequenced, annotated, and then used to PCR-amplify its open-reading-frames. Employing a cloning-independent protocol, a viral expression-library was rapidly built and arrayed into sub-library pools. These were directly delivered into mice as expressible cassettes and assayed for an immune-modulating activity associated with parapoxvirus infection. The product of the B2L gene, a homolog of vaccinia F13L, was identified as the factor eliciting immune cell accumulation at sites of skin inoculation. Administration of purified B2 protein also elicited immune cell accumulation activity, and additionally was found to serve as an adjuvant for antigen-specific responses. Co-delivery of the B2L gene with an influenza gene-vaccine significantly improved protection in mice. Furthermore, delivery of the B2L expression construct, without antigen, non-specifically reduced tumor growth in murine models of cancer.

Conclusion

A streamlined, functional approach to genome-wide screening of a biological activity in vivo is presented. Its application to screening in mice for an immune activity elicited by the pathogen genome of Parapoxvirus ovis yielded a novel immunomodulator. In this inverted discovery method, it was possible to identify the adjuvant responsible for a function of interest prior to a mechanistic study of the adjuvant. The non-specific immune activity of this modulator, B2, is similar to that associated with administration of inactivated particles to a host or to a live viral infection. Administration of B2 may provide the opportunity to significantly impact host immunity while being itself only weakly recognized. The functional genomics method used to pinpoint B2 within an ORFeome may be more broadly applicable to screening for other biological activities in an animal.

Antigen presenting cells in a non-mammalian model system, the chicken

The chicken has a different repertoire of tissues, cells and genes of the immune response compared to mammals, yet generally survives infection with viral, bacterial, protozoal and fungal pathogens, and also worms and ectoparasites, just like mammals. Poultry are also probably the most heavily vaccinated group of farmed animals. Antigen presentation to the adaptive immune response therefore obviously normally occurs efficiently in birds. Although comparatively much is known about macrophages and B cells in the chicken, there is as yet little work on the other, professional, antigen-presenting cells, the dendritic cells (DC). Birds also have at least two other sets of phagocytic cells, heterophils and thrombocytes, which may also have the ability to present antigen. Here we review the current state of knowledge about antigen presenting cells in the chicken, concentrating mainly on recent advances in our knowledge of DC.

Porphyromonas gingivalis-dendritic cell interactions: consequences for coronary artery disease

An estimated 80 million US adults have one or more types of cardiovascular diseases. Atherosclerosis is the single most important contributor to cardiovascular diseases; however, only 50% of atherosclerosis patients have currently identified risk factors. Chronic periodontitis, a common inflammatory disease, is linked to an increased cardiovascular risk. Dendritic cells (DCs) are potent antigen presenting cells that infiltrate arterial walls and may destabilize atherosclerotic plaques in cardiovascular disease. While the source of these DCs in atherosclerotic plaques is presently unclear, we propose that dermal DCs from peripheral inflamed sites such as CP tissues are a potential source. This review will examine the role of the opportunistic oral pathogen Porphyromonas gingivalis in invading DCs and stimulating their mobilization and misdirection through the bloodstream. Based on our published observations, combined with some new data, as well as a focused review of the literature we will propose a model for how P. gingivalis may exploit DCs to gain access to systemic circulation and contribute to coronary artery disease. Our published evidence supports a significant role for P. gingivalis in subverting normal DC function, promoting a semimature, highly migratory, and immunosuppressive DC phenotype that contributes to the inflammatory development of atherosclerosis and, eventually, plaque rupture.

Chemical allergy: translating biology into hazard characterization

The induction by chemicals of allergic sensitization and allergic disease is an important and challenging branch of toxicology. Skin sensitization resulting in allergic contact dermatitis represents the most common manifestation of immunotoxicity in humans, and many hundreds of chemicals have been implicated as skin sensitizers. There are far fewer chemicals that have been shown to cause sensitization of the respiratory tract and asthma, but the issue is no less important because hazard identification remains a significant challenge, and occupational asthma can be fatal. In all areas of chemical allergy, there have been, and remain still, intriguing challenges where progress has required a close and productive alignment between immunology, toxicology, and clinical medicine. What the authors have sought to do here is to exemplify, within the framework of chemical allergy, how an investment in fundamental research and an improved understanding of relevant biological and biochemical mechanisms can pay important dividends in driving new innovations in hazard identification, hazard characterization, and risk assessment. Here we will consider in turn three specific areas of research in chemical allergy: (1) the role of epidermal Langerhans cells in the development of skin sensitization, (2) T lymphocytes and skin sensitization, and (3) sensitization of the respiratory tract. In each area, the aim is to identify what has been achieved and how that progress has impacted on the development of new approaches to toxicological evaluation. Success has been patchy, and there is still much to be achieved, but the journey has been fascinating and there have been some very important developments. The conclusion drawn is that continued investment in research, if coupled with an appetite for translating the fruits of that research into imaginative new tools for toxicology, should continue to better equip us for tackling the important challenges that remain to be addressed.

Langerhans cells are not required for graft-versus-host disease

Graft-versus-host disease (GVHD) is initiated and maintained by antigen-presenting cells (APCs) that prime alloreactive donor T cells. APCs are therefore attractive targets for GVHD prevention and treatment. APCs are diverse in phenotype and function, making understanding how APC subsets contribute to GVHD necessary for the development of APC-targeted therapies. Langerhans cells (LCs) have been shown to be sufficient to initiate skin GVHD in a major histocompatibility complex-mismatched model; however, their role when other host APC subsets are intact is unknown. To address this question, we used mice genetically engineered to be deficient in LCs by virtue of expression of diphtheria toxin A under the control of a BAC (bacterial artificial chromosome) transgenic hu-man Langerin locus. Neither CD8- nor CD4-mediated GVHD was diminished in recipients lacking LCs. Similarly, CD8- and CD4-mediated GVHD, including that in the skin, was unaffected if bone marrow came from donors that could not generate LCs, even though donor LCs engrafted in control mice. Engraftment of donor LCs after irradiation in wild-type hosts required donor T cells, with immunofluorescence revealing patches of donor and residual host LCs. Surprisingly, donor LC engraftment in Langerin-diphtheria toxin A (DTA) transgenic hosts was independent of donor T cells, suggesting that a Langerin(+) cell regulates repopulation of the LC compartment.