Recruitment of dendritic cells in oral lichen planus

Spontaneous regression of highly immunogenic Molluscum contagiosum virus (MCV)-induced skin lesions is associated with plasmacytoid dendritic cells and IFN-DC infiltration

Molluscum contagiosum virus (MCV) infection induces self-limiting cutaneous lesions in an immunocompetent host that can undergo spontaneous regression preceded by local inflammation. On histology, a large majority of MCV-induced lesions are characterized by islands of hyperplastic epithelium containing infected keratinocytes and surrounded by scarce inflammatory infiltrate. However, spontaneous regression has been associated with the occurrence of a dense inflammatory reaction. By histology and immunohistochemistry, we identified MCV-induced lesions showing a dense inflammatory infiltrate associated with cell death in keratinocytes (inflammatory Molluscum contagiosum (I-MC)). In I-MC, hyperplastic keratinocytes were highly immunogenic as demonstrated by the expression of major histocompatibility complex class I and II molecules. Immune cell infiltration consisted of numerous cytotoxic T cells admixed with natural killer cells and plasmacytoid dendritic cells (PDCs). Accordingly, a type I IFN signature associated with PDC infiltration was demonstrated in both keratinocytes and inflammatory cells. Among the latter, a cell population resembling IFN-DC (CD123(+)CD11c(+)CD16(+)CD14(+)MxA(+)) was identified in proximity to islands of apoptotic keratinocytes. In vitro-generated IFN-DCs expressed a strong cytotoxic signature, as demonstrated by high levels of tumor necrosis factor-related apoptosis-inducing ligand (TRAIL) and Fas ligand (FasL). This study establishes a previously unreported model to underpin the role of innate immune cells in viral immune surveillance.

Accumulation of plasmacytoid DC: Roles in disease pathogenesis and targets for immunotherapy

Plasmacytoid DC (pDC) secrete type I IFN in response to viruses and RNA/DNA/immunocomplexes. Type I IFN confer resistance to viral infections and promote innate and adaptive immune responses. pDC also produce cytokines and chemokines that influence recruitment and function of T cells and differentiation of B cells. Thus, pDC have been implicated both in protective immune responses and in induction of tolerance. In this Viewpoint, we discuss how the recruitment and accumulation of pDC may impact pathogenesis of several diseases and how pDC can be targeted for therapeutic interventions.

Origin and functional heterogeneity of non-lymphoid tissue dendritic cells in mice

Dendritic cells (DCs) have been extensively studied in mice lymphoid organs, but less is known about the origin and the mechanisms that regulate DC development and function in non-lymphoid tissues. Here, we discuss recent evidence establishing the contribution of the DC-restricted lineage to the non-lymphoid tissue DC pool and discuss the mechanisms that control the homeostasis of non-lymphoid tissue DCs. We also review recent results underlining the functional specialization of tissue DCs and discuss the potential implications of these findings in tissue immunity and in the development of novel vaccine strategies.

Langerhans cells and more: langerin-expressing dendritic cell subsets in the skin

Langerhans cells (LCs) are antigen-presenting dendritic cells (DCs) that reside in epithelia. The best studied example is the LC of the epidermis. By electron microscopy, their identifying feature is the unique rod- or tennis racket-shaped Birbeck granule. The phenotypic hallmark is their expression of the C-type lectin receptor langerin/CD207. Langerin, however, is also expressed on a recently discovered population of DC in the dermis and other tissues of the body. These 'dermal langerin(+) dendritic cells' are unrelated to LCs. The complex field of langerin-negative dermal DCs is not dealt with here. In this article, we briefly review the history, ontogeny, and homeostasis of LCs. More emphasis is laid on the discussion of functional properties in vivo. Novel models using genetically engineered mice are contributing tremendously to our understanding of the role of LCs in eliciting adaptive immune responses against pathogens or tumors and in inducing and maintaining tolerance against self antigens and innocuous substances in vivo. Also, innate effector functions are increasingly being recognized. Current activities in this area are reviewed, and possibilities for future exploitation of LC in medicine, e.g. for the improvement of vaccines, are contemplated.

Granzyme B produced by human plasmacytoid dendritic cells suppresses T-cell expansion

Human plasmacytoid dendritic cells (pDCs) are crucially involved in the modulation of adaptive T-cell responses in the course of neoplastic, viral, and autoimmune disorders. In several of these diseases elevated extracellular levels of the serine protease granzyme B (GrB) are observed. Here we demonstrate that human pDCs can be an abundant source of GrB and that such GrB(+) pDCs potently suppress T-cell proliferation in a GrB-dependent, perforin-independent manner, a process reminiscent of regulatory T cells. Moreover, we show that GrB expression is strictly regulated on a transcriptional level involving Janus kinase 1 (JAK1), signal transducer and activator of transcription 3 (STAT3), and STAT5 and that interleukin-3 (IL-3), a cytokine secreted by activated T cells, plays a central role for GrB induction. Moreover, we find that the immunosuppressive cytokine IL-10 enhances, while Toll-like receptor agonists and CD40 ligand strongly inhibit, GrB secretion by pDCs. GrB-secreting pDCs may play a regulatory role for immune evasion of tumors, antiviral immune responses, and autoimmune processes. Our results provide novel information about the complex network of pDC-T-cell interactions and may contribute to an improvement of prophylactic and therapeutic vaccinations.

Plasmacytoid dendritic cells: physiologic roles and pathologic states

Plasmacytoid dendritic cells (PDCs) have perplexed pathologists for decades, undergoing multiple adjustments in nomenclature as their lineage and functions have been characterized. Although PDCs account for less than 0.1% of peripheral blood mononuclear cells, they serve as a principal source of interferon-alpha and are also known as interferon-I producing cells (IPCs). Upon activation in vitro, they can differentiate into dendritic cells, and recent studies have substantiated a potential role in antigen presentation. Thus, PDCs may act as a link between innate and adaptive immunity. Normally found in small quantities in primary and secondary lymphoid organs, PDCs accumulate in a variety of inflammatory conditions, including Kikuchi-Fujimoto lymphadenopathy, hyaline-vascular Castleman disease, and autoimmune diseases, and in certain malignancies such as classical Hodgkin lymphoma and carcinomas. Demonstrating potential for neoplastic transformation reflective of varying stages of maturation, clonal proliferations range from PDC nodules most commonly associated with chronic myelomonocytic leukemia to the rare but highly aggressive malignancy now known as blastic plasmacytoid dendritic cell neoplasm (BPDCN). Formerly called blastic natural killer cell lymphoma or CD4/CD56 hematodermic neoplasm, BPDCN, unlike natural killer cell lymphomas, is not associated with Epstein-Barr virus infection and is generally not curable with treatment regimens for non-Hodgkin lymphomas. In fact, this entity is no longer considered to be a lymphoma and instead represents a unique precursor hematopoietic neoplasm. Acute leukemia therapy regimens may lead to sustained clinical remission of BPDCN, with bone marrow transplantation in first complete remission potentially curative in adult patients.

Lichen planus-like eruptions: an emerging side effect of tumor necrosis factor-alpha antagonists

As tumor necrosis factor (TNF)-alpha inhibitors gain wider use in clinical practice, it is becoming increasingly evident that these potent immunosuppressants can also induce inflammatory reactions. We present two cases of lichen planus-like eruptions after infliximab and adalimumab therapy for psoriasis, and review the literature on this phenomenon. Eleven cases of lichen planus or lichenoid drug eruptions have been previously reported in patients taking TNF-alpha inhibitors, in addition to several cases of psoriasiform eruptions with a lichenoid histology. Because TNF-alpha has been implicated in the pathogenesis of lichen planus, induction of lichenoid reactions by TNF-alpha inhibition is somewhat unexpected. We consider potential immunologic mechanisms, and suggest that TNF-alpha inhibition may precipitate lichenoid reactions through disruption of a delicate balance between TNF-alpha and interferon-alpha in susceptible patients.

Cutaneous distribution of plasmacytoid dendritic cells in lupus erythematosus. Selective tropism at the site of epithelial apoptotic damage

Recent evidences suggest a significant role of Plasmacytoid dendritic cells (PDC) role in the pathogenesis of lupus erythematosus (LE) via production of type I IFN. Taking advantage on the availability of multiple reagents (CD123, BDCA2, and CD2ap) specifically recognizing PDC on fixed tissues, we investigated the occurrence of PDC in a cohort of 74 LE patients. The large majority of LE biopsies (67/74; 90.5%) showed cutaneous infiltration of PDC. PDC were more frequently observed (96.4 vs 72.2) and numerous in cutaneous LE compared to systemic LE (SLE) and correlated with the density of the inflammatory infiltrate (r=0.40; p<0.001). PDC reduction in SLE might be related to a broader tissue distribution of this cellular population, as indicated by their occurrence in kidneys in 11 out of 24 (45.8%) cases studied. The distribution of cutaneous PDC showed two distinct patterns. More commonly, PDC were observed within perivascular inflammatory nodules in the dermis, associated with CD208+ mature DC and T-bet+ cells [D-PDC]. A second component was observed along the dermal-epithelial junction [J-PDC], in association with cytotoxic T-cells in areas of severe epithelial damage. Notably, chemerin reactivity was observed in 64% of LE biopsies on endothelial cells and in the granular layer keratinocytes. Cutaneous PDC in LE strongly produced type I IFN, as indicated by the diffuse MxA expression, and the cytotoxic molecule granzyme B. This study confirms cutaneous PDC infiltration as hallmark of LE. The topographical segregation in D-PDC and J-PDC suggests a novel view of the role of these cells in skin autoimmunity.

Plasmacytoid dendritic cells in the skin: to sense or not to sense nucleic acids

Plasmacytoid dendritic cells (pDCs) are specialized sensors of viral nucleic acids that initiate protective immunity through the production of type I interferons (IFNs). Normally, pDCs fail to sense host-derived self-nucleic acids but do so when self-nucleic acids form complexes with endogenous antimicrobial peptides produced in damaged skin. Whereas regulated expression of antimicrobial peptides may lead to pDC activation and protective immune responses to skin injury, overexpression of antimicrobial peptides in psoriasis drives excessive sensing of self-nucleic acids by pDCs resulting in IFN-driven autoimmunity. In skin tumors, pDCs are unable to sense self-nucleic acids; however, therapeutic activation of pDCs by synthetic nucleic acids or analogues can be exploited to generate antitumor immunity.

Lichenoid tissue reaction/interface dermatitis: clinical and histological perspectives

A number of uncommon, clinically diverse and poorly understood inflammatory skin diseases are linked by the presence of a set of histopathological elements that have traditionally been referred to as the "lichenoid tissue reaction/interface dermatitis" (LTR/IFD). The prototypic skin disease in this category is lichen planus. However, the LTR/IFD can also be seen in skin disorders associated with systemic illnesses (lupus erythematosus, dermatomyositis), and the skin changes of potentially fatal disorders such as graft-versus-host disease, Stevens-Johnson syndrome, and toxic epidermal necrolysis. It has been traditionally felt that cytotoxic T-lymphocytes represent the final effector cell type for the epidermal basal cell layer injury pattern that is common to LTR/IFD disorders. Recent work has suggested that a number of different LTR/IFD skin disorders share a common inflammatory signaling pathway involving the actions of plasmacytoid dendritic cell-derived IFN-alpha. This signaling pathway appears to amplify cytotoxic T cell injury to the epidermal basal cell compartment. This review will summarize the work implicating this pathway as well as the other cellular and molecular mechanisms that are thought to be responsible for the prototypic LTR/IFD disorder, lichen planus. It is hoped that a better understanding of the immunological commonalities shared by various LTR/IFD disorders will lead to more effective safer treatment options for these illnesses.

Is ethanol consumption beneficial for oral lichen planus?

Oral lichen planus (OLP), one of the most common oral mucosa diseases, is an auto-immune disease characterized histologically by basal keratinocyte damage and interface lymphocyte reaction. Previous studies have proved ethanol consumption can suppress immune system in many aspects, including inhibiting lymphocytes proliferation and their function, modifying antigen-presentation, etc. Pathogenesis of the OLP mainly comprises of antigen-presentation, lymphocytes activation and keratinocyte apoptosis, all of which may be inhibited by ethanol consumption. Thus, we put forth our hypothesis that chronic ethanol consumption may decrease OLP incidence and OLP treatment except the erosive type may benefit from ethanol consumption. In the discussion, we also talk about the extent of ethanol consumption. Still ethanol abuse is not commended, for it may increase incidence of many other diseases, and moderate ethanol consumption may be potentially beneficial for other auto-immune diseases.

Detection of fascin and CCR-7 positive mature dendritic cells in oral lichen planus

BACKGROUND

Dendritic cells (DC) play a crucial role in the pathogenesis of oral lichen planus (OLP) with respect to antigens presented to T cells. We performed immunohistochemical analysis to elucidate the process of activation of DC in OLP.

METHODS

Thirty biopsy specimens were obtained from the patients with OLP. The expressions of CD1a, Langerin, S-100, fascin, chemokine receptor-7 (CCR-7), D2-40, cyclooxygenase-2 (COX-2), and microsomal prostaglandin E synthase-1 (mPGES-1) in DC from OLP and disease free control were investigated using specific antibodies. The distribution and number (1 mm(2)) of DC were assessed in the intra-epithelium and the submucosa specimens. Correlation between the number of DC and epithelium thickness was also determined.

RESULT

Immature DC (Langerin(+), CD1a(+), and S-100(+)) were identified in the epithelia from OLP patients and control, though the numbers of Langerin(+) and CD1a(+) positive cells were decreased in the OLP samples as compared to the control. Mature DC (fascin(+)) were identified in the submucosa specimens, not found in the epithelium from OLP or control. Double immunostaining revealed DC positive for fascin and CCR-7 in the submucosa, which had migrated into D2-40(+) lymph vessels. Furthermore, keratinocytes expressed both Prostaglandin E(2) (PGE(2)) converting enzymes, COX-2, and mPGES-1, indicating PGE(2) synthesis in the epithelial layer of the OLP specimens.

CONCLUSION

Our results indicate that DC change from immature to mature in the epithelium and are then drawn out to the submucosa. We demonstrate that mature DC localized in the submucosa, it consequently migrates into lymph vessels. This maturation process of DC is an important immunopathological feature of OLP.

Evaluation of the profile of the immune cell infiltrate in lichen planus, discoid lupus erythematosus, and chronic dermatitis

AIMS

The term 'interface dermatitis' refers to those dermatoses in which an inflammatory process involves the dermoepidermal junction, with injury and even necrosis of the basal cell keratinocytes. Interface dermatitis can be characterised further as being either vacuolar or lichenoid changes. Immune cell infiltrate is a constant feature in interface dermatitis. In this study, we hypothesised that 'the profile of the immune cell infiltrate varies between lichenoid and vacuolar interface dermatitis'. This investigation tries to test this hypothesis and to characterise immune cells in interface dermatitis.

METHODS

Thirty-one interface dermatitis lesions (interface dermatitis group: 19 cases of lichen planus, LP; and 12 cases of discoid lupus erythematosus, DLE) and 20 specimens of normal skin (control group) were examined using immunoperoxidase staining methods. Antibodies targeting histiocytes/dendritic cells (CD68+), T cells (CD3+), B cells (CD20+), T cells with either cytotoxic potential (TIA-1+) or cytotoxic activity (Granzyme-B+) were used to decorate the immune cells. In addition, 16 cases of chronic dermatitis [lichen simplex chronicus (LSC), non-interface dermatitis group] were included to substantiate findings in the interface dermatitis group. The results were scored as mean values of positively stained immune cells.

RESULTS

The numbers of immune cells were significantly high (p < 0.05) in the lesional skin (LP, DLE and LSC) compared with normal skin. The most prevalent cell populations were CD3+ T lymphocytes followed by CD68+ cells. Most of the CD3+ cells were resting (TIA-1+, cytotoxic potential) rather than active T cells (Granzyme-B+, active cytotoxicity). Numeric variations were seen between interface and chronic dermatitis groups with significant increase of the density of immune cells in the interface dermatitis (p < 0.05). We found some variations in the composition and distribution of immune cell infiltrate between LP (lichenoid change) and DLE (vacuolar changes). The mean counts of CD3+ cells were high in LP compared with DLE (p < 0.05). Alternatively, the density of CD20+ cells was high in DLE compared with LP (p < 0.05). High density of CD3+ (perivascular location and dermoepidermal junction, p < 0.05) positively stained cells was found in LP compared with DLE. In contrast, high density of CD20+ (perivascular location and dermoepidermal junction, p < 0.05), TIA-1+ and Granzyme-B+ (perivascular location and dermoepidermal junction, p > 0.05) positively stained cells was observed in DLE compared with LP.

CONCLUSIONS

Here we report some variations in the profile (density and positioning) of the immune cell infiltrate between LP and DLE. These variations include high density of CD68+ cells and CD3+ T lymphocytes in LP and DLE; and the numeric dominance of CD20+ B-lymphocytes in DLE compared with LP. Also, some differences in the density of TIA-1+ and Granzyme-B+ cytotoxic T cells between LP and DLE were observed. Our findings suggest a possible link between the type of these cells and the development of interface dermatitis lesions. The possible ramifications of these findings are open for further investigations.

Intracellular versus extracellular granzyme B in immunity and disease: challenging the dogma

The cytotoxic granzyme B (GrB)/perforin pathway has been traditionally viewed as a primary mechanism that is used by cytotoxic lymphocytes to eliminate allogeneic, virally infected and/or transformed cells. Although originally proposed to have intracellular and extracellular functions, upon the discovery that perforin, in combination with GrB, could induce apoptosis, other potential functions for this protease were, for the most part, disregarded. As there are 5 granzymes in humans and 11 granzymes in mice, many studies used perforin knockout mice as an initial screen to evaluate the role of granzymes in disease. However, in recent years, emerging clinical and biochemical evidence has shown that the latter approach may have overlooked a critical perforin-independent, pathogenic role for these proteases in disease. This review focuses on GrB, the most characterized of the granzyme family, in disease. Long known to be a pro-apoptotic protease expressed by cytotoxic lymphocytes and natural killer cells, it is now accepted that GrB can be expressed in other cell types of immune and nonimmune origin. To the latter, an emerging immune-independent role for GrB has been forwarded due to recent discoveries that GrB may be expressed in nonimmune cells such as smooth muscle cells, keratinocytes, and chondrocytes in certain disease states. Given that GrB retains its activity in the blood, can cleave extracellular matrix, and its levels are often elevated in chronic inflammatory diseases, this protease may be an important contributor to certain pathologies. The implications of sustained elevations of intracellular and extracellular GrB in chronic vascular, dermatological, and neurological diseases, among others, are developing. This review examines, for the first time, the multiple roles of GrB in disease pathogenesis.

Origin, homeostasis and function of Langerhans cells and other langerin-expressing dendritic cells

Langerhans cells (LCs) are a specialized subset of dendritic cells (DCs) that populate the epidermal layer of the skin. Langerin is a lectin that serves as a valuable marker for LCs in mice and humans. In recent years, new mouse models have led to the identification of other langerin(+) DC subsets that are not present in the epidermis, including a subset of DCs that is found in most non-lymphoid tissues. In this Review we describe new developments in the understanding of the biology of LCs and other langerin(+) DCs and discuss the challenges that remain in identifying the role of different DC subsets in tissue immunity.

Host defense peptides in the oral cavity and the lung: similarities and differences

Peptides with broad-spectrum antimicrobial activity are found in the mucosal surfaces at many sites in the body, including the airway, the oral cavity, and the digestive tract. Based on their in vitro antimicrobial and other immunomodulatory activities, these host defense peptides have been proposed to play an important role in the innate defense against pathogenic microbial colonization. The genes that encode these peptides are up-regulated by pathogens, further supporting their role in innate immune defense. However, the differences in the local microbial environments between the generally sterile airway and the highly colonized oral cavity suggest a more complex role for these peptides in innate immunity. For example, beta-defensin genes are induced in the airway by all bacteria and Toll-like receptor (TLR) agonists primarily through an NF-kappaB-mediated pathway. In contrast, the same genes are induced in the gingival epithelium by only a subset of bacteria and TLR ligands, via different pathways. Furthermore, the environments into which the peptides are secreted--specifically saliva, gingival crevicular fluid, and airway surface fluid--differ greatly and can effect their respective activities in host defense. In this review, we examine the differences and similarities between host defense peptides in the oral cavity and the airway, to gain a better understanding of their contributions to immunity.

Activin A induces Langerhans cell differentiation in vitro and in human skin explants

Langerhans cells (LC) represent a well characterized subset of dendritic cells located in the epidermis of skin and mucosae. In vivo, they originate from resident and blood-borne precursors in the presence of keratinocyte-derived TGFbeta. In vitro, LC can be generated from monocytes in the presence of GM-CSF, IL-4 and TGFbeta. However, the signals that induce LC during an inflammatory reaction are not fully investigated. Here we report that Activin A, a TGFbeta family member induced by pro-inflammatory cytokines and involved in skin morphogenesis and wound healing, induces the differentiation of human monocytes into LC in the absence of TGFbeta. Activin A-induced LC are Langerin+, Birbeck granules+, E-cadherin+, CLA+ and CCR6+ and possess typical APC functions. In human skin explants, intradermal injection of Activin A increased the number of CD1a+ and Langerin+ cells in both the epidermis and dermis by promoting the differentiation of resident precursor cells. High levels of Activin A were present in the upper epidermal layers and in the dermis of Lichen Planus biopsies in association with a marked infiltration of CD1a+ and Langerin+ cells. This study reports that Activin A induces the differentiation of circulating CD14+ cells into LC. Since Activin A is abundantly produced during inflammatory conditions which are also characterized by increased numbers of LC, we propose that this cytokine represents a new pathway, alternative to TGFbeta, responsible for LC differentiation during inflammatory/autoimmune conditions.

The immune privilege of the oral mucosa

Despite high bacterial colonization and frequent allergen contact, acute inflammatory and allergic reactions are rarely seen in the oral mucosa. Therefore we assert that immune tolerance predominates at this site and antigen presenting cells, such as dendritic cells and different T cell subtypes, serve as key players in oral mucosal tolerance induction. In this article we describe the mechanisms that lead to tolerance induced in the oral mucosa and how they differ from tolerance induced in the lower gastrointestinal tract. Furthermore we discuss ways in which novel nonparenteral approaches for immune intervention, such as allergen-specific immunotherapy applied by way of the sublingual route, might be improved to target the tolerogenic properties of the sophisticated oral mucosal immune network.

Novel markers of normal and neoplastic human plasmacytoid dendritic cells

Plasmacytoid dendritic cells (pDCs) are involved in innate immunity (eg, by secreting interferons) and also give rise to CD4+CD56+ hematodermic neoplasms. We report extensive characterization of human pDCs in routine tissue samples, documenting the expression of 19 immunohistologic markers, including signaling molecules (eg, BLNK), transcription factors (eg, ICSBP/IRF8 and PU.1), and Toll-like receptors (TLR7, TLR9). Many of these molecules are expressed in other cell types (principally B cells), but the adaptor protein CD2AP was essentially restricted to pDCs, and is therefore a novel immunohistologic marker for use in tissue biopsies. We found little evidence for activation-associated morphologic or phenotypic changes in conditions where pDCs are greatly increased (eg, Kikuchi disease). Most of the molecules were retained in the majority of pDC neoplasms, and 3 (BCL11A, CD2AP, and ICSBP/IRF8) were also commonly negative in leukemia cutis (acute myeloid leukemia in the skin), a tumor that may mimic pDC neoplasia. In summary, we have documented a range of molecules (notably those associated with B cells) expressed by pDCs in tissues and peripheral blood (where pDCs were detectable in cytospins at a frequency of <1% of mononuclear cells) and also defined potential new markers (in particular CD2AP) for the diagnosis of pDC tumors.

Oral diseases associated with hepatitis C virus infection. Part 2: lichen planus and other diseases

Some of the most frequent extrahepatic manifestations of hepatitis C virus (HCV) infection involve the oral region predominantly or exclusively. Part 2 of this review discusses the current evidences regarding the association of lichen planus (LP) and other diseases frequently involving the oral cavity with HCV. Epidemiological data suggest that LP may be significantly associated with HCV infections especially in southern Europe and Japan but not in northern Europe. These geographical differences are possibly influenced by immunogenetic factors, the duration of the HCV infection and the design of the published studies. Because of the fact that most of the studies published are retrospective, it is impossible to establish whether the HCV exposure occurred earlier to or after the onset of disease and more prospective studies are clearly warranted. As the virus may replicate in the skin and oral mucosa and HCV-specific T lymphocytes can be found in the oral mucosa of patients with chronic hepatitis C and LP, HCV may be implicated in the pathogenesis of LP. However, little attention has been paid to the variable effect of therapy with interferon-alpha (IFN-alpha), with or without ribavirin for LP. Conversely, it is unlikely that other oral diseases such as oral carcinoma, pemphigus and Behcet disease are triggered by HCV.

Gene Expression Profiling of Lichen Planus Reflects CXCL9+-Mediated Inflammation and Distinguishes this Disease from Atopic Dermatitis and Psoriasis

Here, we present data of a gene expression profiling approach to apply the diagnostic value and pathological significance of this method in different inflammatory skin diseases, using whole skin biopsies. Initially, SAGE was performed to identify frequent tags differentially expressed in various skin diseases. On the basis of these results, a new skin pathology-oriented PIQOR microarray was designed. Lichen planus (LP) was chosen as a model disease to evaluate this system. Controls included healthy skin, atopic dermatitis (AD), and psoriasis (Pso). Gene expression analyses using the topic-defined microarray followed by unclassified clustering was able to discriminate LP from AD and Pso. Genes significantly expressed in LP included type I IFN inducible genes and a specific chemokine expression pattern. The CXCR3 ligand, CXCL9, was the most significant marker for LP. In situ hybridization and immunohistochemistry confirmed the results and revealed that keratinocytes are type I IFN producers in LP skin lesions. Our results show that gene expression profiling using a skin-specific microarray is a reliable method to identify patients with LP in the chosen context and reflect recent models concerning the pathogenesis of this disease. Gene expression profiling might complement the diagnostic spectrum in dermatology and may provide new pathogenetic insights.

Indoleamine 2,3-dioxygenase (IDO): the antagonist of type I interferon-driven skin inflammation?

Recent studies have provided evidence that a type I interferon (IFN)-driven immune response might play an important role in the pathogenesis of lichen planus (LP), an inflammatory disorder of the skin of unclear etiology. Plasmacytoid dendritic cells in affected skin from LP have been proposed to produce IFN-alpha/beta locally, which leads to the expression of IFN-inducible chemokines such as IP10/CXCL10 in the epidermis. This chemokine recruits chemokine receptor CXCR3-expressing T-lymphocytes into the skin via CXCR3/IP10 interactions. Indoleamine 2,3-dioxygenase (IDO), which degrades tryptophan and suppresses T-cell proliferation, is induced by IFNs and other inflammatory cytokines. We show that type I IFN-mediated skin disorders, such as LP, strongly express IDO in lesional skin. This expression closely correlates to the expression of the highly specific type I IFN marker MxA. We further demonstrate that the IDO+ cells in LP are large myeloid CD11c+S100+CD68(-) dendritic cells. Accordingly, CD11c+ antigen-presenting cells significantly up-regulate IDO gene expression and intracellular IDO protein expression after stimulation with IFN-alpha in vitro. These findings reveal that both proinflammatory and counterregulatory mechanisms are operative in cutaneous lesions of LP. We propose that the balance of these mechanisms may be involved in the pathogenesis of this disorder.

Alteration of the expression of CD44 [corrected] isoforms in oral epithelia and saliva from patients with oral lichen planus

Oral lichen planus (OLP) is a chronic inflammatory mucosal disease that cell-mediated immunological mechanisms are involved in pathogenesis. The objective of this study was to investigate the expression of CD44 isoforms including CD44s, CD44v5, and CD44v6 in biopsy specimens and saliva from OLP patients. Thirty-one OLP patients and 30 healthy subjects were enrolled in this study. Immunohistochemical methods were used to detect the expression of CD44 isoforms in oral epithelia, and enzyme-linked immunosorbent assay (ELISA) was performed to measure levels of salivary CD44 isoforms. Our results demonstrated that expression of CD44v6 in oral epithelia from OLP patients was significantly decreased in comparison to controls (p = 0.021). Levels of salivary CD44s and CD44v5 from OLP patients were significantly higher than those from controls (p = 0.007 and p = 0.002, respectively). In summary, our findings provided additional evidence that the pathological stress, such as chronic inflammation, altered the expression of CD44 isoforms in oral epithelia and saliva of OLP patients.

Langerin-expressing and CD83-expressing cells in oral lichen planus lesions

OBJECTIVE

Dendritic Langerhans cells (LCs) have been attributed a role in the pathogenesis of lichen planus as autoantigen-presenting cells initiating expansion of autoreactive T cells. Langerin and CD83, which are cell molecules expressed on LCs, are associated with antigen presentation. The present study examined expression of Langerin and CD83 molecules on LCs in patients with oral lichen planus (OLP).

MATERIAL AND METHODS

Biopsies were obtained from seven patients with OLP. Oral mucosa from seven healthy subjects served as controls. Monoclonal antibodies (mAbs) were used in standard immunohistochemical procedures to visualize CD1a-, Langerin-, and CD83-molecule-expressing cells.

RESULTS

CD1a+ and Langerin+ cells were found in significantly higher frequencies in OLP epithelium compared with healthy oral epithelium (p<0.01 and p<0.05, respectively); however, the frequency of CD83+ cells did not differ (p>0.05). The connective tissue in OLP lesions showed significantly higher frequencies of CD1a+, Langerin+, and CD83+ cells compared with healthy connective tissue (p<0.01, p<0.01, and p<0.05). CD1a+ and Langerin+ cells in OLP and healthy epithelium had a dendritic morphology.

CONCLUSIONS

The study shows increased numbers of CD1a- and Langerin-expressing LCs in OLP compared with healthy controls. In the connective tissue, CD83+ cells with dendritic morphology were localized to regions of lymphocyte clusters. The presence of CD83+ dendritic cells in areas of lymphocyte clusters in the connective tissue of OLP lesions indicates the possibility of ongoing autoantigen presentation.

Tumoricidal activity of TLR7/8-activated inflammatory dendritic cells

Imiquimod (IMQ), a synthetic agonist to Toll-like receptor (TLR) 7, is being successfully used for the treatment of certain skin neoplasms, but the exact mechanisms by which this compound induces tumor regression are not yet understood. While treating basal cell carcinoma (BCC) patients with topical IMQ, we detected, by immunohistochemistry, sizable numbers of both myeloid dendritic cells (mDCs) and plasmacytoid DCs (pDCs) within the inflammatory infiltrate. Surprisingly, peritumoral mDCs stained positive for perforin and granzyme B, whereas infiltrating pDCs expressed tumor necrosis factor–related apoptosis-inducing ligand (TRAIL). The biological relevance of this observation can be deduced from our further findings that peripheral blood–derived CD11c⁺ mDCs acquired antiperforin and anti–granzyme B reactivity upon TLR7/8 stimulation and could use these molecules to effectively lyse major histocompatibility complex (MHC) class I^lo cancer cell lines. The same activation protocol led pDCs to kill MHC class I–bearing Jurkat cells in a TRAIL-dependent fashion. While suggesting that mDCs and pDCs are directly involved in the IMQ-induced destruction of BCC lesions, our data also add a new facet to the functional spectrum of DCs, ascribing to them a major role not only in the initiation but also in the effector phase of the immune response.

Lichen planus remission is associated with a decrease of human herpes virus type 7 protein expression in plasmacytoid dendritic cells

The cause of lichen planus is still unknown. Previously we showed human herpes virus 7 (HHV-7) DNA and proteins in lesional lichen planus skin, and significantly less in non-lesional lichen planus, psoriasis or healthy skin. Remarkably, lesional lichen planus skin was infiltrated with plasmacytoid dendritic cells. If HHV-7 is associated with lichen planus, then HHV-7 replication would reduce upon lichen planus remission. HHV-7 DNA detection was performed by nested PCR and HHV-7 protein by immunohistochemistry on lesional skin biopsies from lichen planus patients before treatment and after remission. Biopsies were obtained from lichen planus lesions before treatment (n = 18 patients) and after remission (n = 13). Before treatment 61% biopsies contained HHV-7 DNA versus 8% after remission (P = 0.01). HHV-7-protein positive cell numbers diminished significantly after remission in both dermis and epidermis. Expression of HHV-7 was mainly detected in BDCA-2 positive plasmacytoid dendritic cells rather than CD-3 positive lymphocytes. HHV-7 replicates in plasmacytoid dendritic cells in lesional lichen planus skin and diminishes after remission. This study further supports our hypothesis that HHV-7 is associated with lichen planus pathogenesis.

Alterated integrin expression in lichen planopilaris

BACKGROUND

Lichen planopilaris (LPP) is an inflammatory disease characterized by a lymphomononuclear infiltrate surrounding the isthmus and infundibulum of the hair follicle of the scalp, that evolves into atrophic/scarring alopecia. In the active phase of the disease hairs are easily plucked with anagen-like hair-roots. In this study we focused on the expression of integrins and basement membrane components of the hair follicle in active LPP lesions.

METHODS

Scalp biopsies were taken in 10 patients with LPP and in 5 normal controls. Using monoclonal antibodies against alpha3beta1 and alpha6beta4 integrins we showed the expression of these integrins and of the basement membrane components of the hair follicle in active LPP lesions and in healthy scalp skin.

RESULTS

In the LPP involved areas, alpha3beta1 was distributed in a pericellular pattern, the alpha6 subunit was present with a basolateral distribution while the beta4 subunit showed discontinuous expression at the basal pole and occasionally, basolateral staining of the hair follicle.

CONCLUSION

An altered distribution of the integrins in active LPP lesions can explain the phenomenon of easy pulling-out of the hair with a "gelatinous" root-sheath.

The role of chemerin in the colocalization of NK and dendritic cell subsets into inflamed tissues

Chemerin is a chemotactic agonist recently identified as the ligand of ChemR23, a serpentine receptor expressed by mononuclear phagocytes and dendritic cells (DCs). This study shows that blood CD56(low)CD16(+) natural killer (NK) cells selectively express functional ChemR23 and that this receptor is coexpressed with CXCR1, the CXCL8 receptor, and the KIR receptors. In vitro culturing of NK cells with IL-2 or IL-15 induced a delayed and time-dependent down-regulation of ChemR23 that was associated with the inhibition of NK cell migration to chemerin. Biopsies obtained from patients with oral lichen planus presented an infiltration of CD94(+)CD3(-)CD56(+) NK cells that coexpressed ChemR23. The same biopsies were infiltrated by myeloid, DC-SIGN(+) and plasmacytoid, CD123(+)BDCA2(+), ChemR23(+) dendritic cells that were occasionally associated with NK cells. In the same histologic sections, chemerin was expressed by inflamed dermal endothelium. These findings propose a role for the ChemR23/chemerin axis in the recruitment of blood NK cells and strongly implicate chemerin as a key factor for the colocalization of NK cells and DC subsets in pathologic peripheral tissues.

Type I interferon-associated cytotoxic inflammation in lichen planus

INTRODUCTION

Lichen planus (LP) is an inflammatory autoimmune skin disease of unknown origin. Evidence has accumulated that autoreactive cytotoxic CD8(+) T lymphocytes cause destruction of keratinocytes. Recent studies suggested that type I interferons (IFNs) play a central role in cytotoxic skin inflammation by increasing the expression of IP10/CXCR10 and recruiting effector cells via CXCR3. Here, we investigated whether type I IFNs are also involved in the pathogenesis of LP.

PATIENTS AND METHODS

Skin biopsies of altogether 17 donors (seven LP and 10 healthy controls) were analyzed by immunohistochemistry using monoclonal antibodies against CD3, CD4, CD8, CD20, CD68, CXCR3, granzyme B, IP10/CXCL10, CD123, and the MxA protein, which is specifically induced by type I IFNs.

RESULTS

Our analysis revealed a significant expression of the MxA protein in all LP skin biopsies, indicating involvement of type I IFNs. Expression of MxA was closely associated with the recruitment of CXCR3(+) and granzyme B(+) lymphocytes, indicating a Th1-biased cytotoxic immune response. Strong expression of the CXCR3 ligand, the interferon-inducible protein IP10/CXCL10, links type I IFN expression and recruitment of CXCR3(+) lymphocytes. Plasmacytoid dendritic cells (pDCs) appear to be a major source of type I IFNs in LP.

DISCUSSION

Our observations support the hypothesis that lesional type I IFNs produced by pDCs plays an important role in chronic cytotoxic inflammation of LP by recruiting cytotoxic effector lymphocytes via IP10/CXCR3 interactions.

Dendritic cells at the oral mucosal interface

The mucosal lining of the respiratory and digestive systems contains the largest and most complex immune system in the body, but surprisingly little is known of the immune system that serves the oral mucosa. This review focuses on dendritic cells, particularly powerful arbiters of immunity, in response to antigens of microbial or tumor origin, but also of tolerance to self-antigens and commensal microbes. Although first discovered in 1868, the epidermal dendritic Langerhans cells remained enigmatic for over a century, until they were identified as the most peripheral outpost of the immune system. Investigators' ability to isolate, enrich, and culture dendritic cells has led to an explosion in the field. Presented herein is a review of dendritic cell history, ontogeny, function, and phenotype, and the role of different dendritic cell subsets in the oral mucosa and its diseases. Particular emphasis is placed on the mechanisms of recognition and capture of microbes by dendritic cells. Also emphasized is how dendritic cells may regulate immunity/tolerance in response to oral microbes.

Expression profile of chemokines and chemokine receptors in epithelial cell layers of oral lichen planus

BACKGROUND

To understand the immunopathological features of oral lichen planus (OLP), we analyzed the expression of chemokines in the epithelial cell layers.

METHODS

Epithelia from OLP or healthy gingiva were collected by laser microdissection. The chemokine and chemokine receptor expressions in the epithelia were analyzed by DNA microarray.

RESULTS

High levels of MIP-3alpha/LARC/CCL20 and its receptor CCR6 were expressed in the lesional epithelia. Furthermore, DC-CK1/CCL18, ELC/CCL19, SDF-1/CXCL12 and CXCR4 expressions were also increased. Immunohistologial analysis showed that high numbers of Langerhans cells (LCs) were present in the epithelia of OLP. Lesional epithelia also expressed high levels of the ligands specific for CXCR3 (e.g. MIG/CXCL9, IP-10/CXCL10 and I-TAC/CXCL11) and CCR5 (e.g. RANTES/CCL5).

CONCLUSIONS

Infiltration of LCs is orchestrated by CCR6. Further, LCs residing in the lesional epithelia may be a mature phenotype. Moreover, infiltration of T cells in OLP could be mediated by signaling pathways through CXCR3 and CCR5.