Overexpression of CD1d by keratinocytes in psoriasis and CD1d-dependent IFN-gamma production by NK-T cells

The role of p38 MAPK in the aetiopathogenesis of psoriasis and psoriatic arthritis

The pathogenetic mechanisms responsible for the induction of immune-mediated disorders, such as psoriasis, remain not well characterized. Molecular signaling pathways are not well described in psoriasis, as well as psoriatic arthritis, which is seen in up to 40% of patients with psoriasis. Signaling pathway defects have long been hypothesized to participate in the pathology of psoriasis, yet their implication in the altered psoriatic gene expression still remains unclear. Emerging data suggest a potential pathogenic role for mitogen activated protein kinases p38 (p38 MAPK) extracellular signal-regulated kinase 1/2 (ERK1/2), and c-Jun N-terminal kinase (JNK) in the development of psoriasis. The data are still limited, though, for psoriatic arthritis. This review discusses the current data suggesting a crucial role for p38 MAPK in the pathogenesis of these disorders.

Lifting the silver flakes: the pathogenesis and management of chronic plaque psoriasis

Psoriasis is a common chronic inflammatory skin condition in which patients suffer from mild to chronic plaque skin plaques. The disease manifests through an excessive inflammatory response in the skin due to complex interactions between different genetic and environmental factors. Psoriasis can affect the physical, emotional, and psychosocial well-being of patients, and currently there is no cure with treatments focusing primarily on the use of anti-inflammatory agents to control disease symptoms. Traditional anti-inflammatory agents can cause immunosuppression and adverse systemic effects. Further understanding of the disease has led to current areas of research aiming at the development of selective molecular targets to suppress the pathogenic immune responses.

UVB-induced skin inflammation and cutaneous tissue injury is dependent on the MHC class I-like protein, CD1d

CD1d is a major histocompatibility complex class 1–like molecule that regulates the function and development of natural killer T (NKT) cells. Previously, we identified a critical role for the CD1d-NKT cell arm of innate immunity in promoting the development of UVB-induced p53 mutations, immune suppression, and skin tumors. Sunburn, an acute inflammatory response to UVB-induced cutaneous tissue injury, represents a clinical marker for non-melanoma skin cancer (NMSC) risk. However, the innate immune mechanisms controlling sunburn development are not considered relevant in NMSC etiology, and remain poorly investigated. Here we found that CD1d knockout (CD1d^−/−) mice resist UVB-induced cutaneous tissue injury and inflammation compared with wild-type (WT) mice. This resistance was coupled with a faster epithelial tissue healing response. In contrast, the skins of UVB-irradiated invariant NKT cell-knockout (Jα18^−/−) and NKT cell–deficient (TCRα^−/−) mice, which express CD1d but are deficient in CD1d-dependent NKT cells, exhibited as much cutaneous tissue injury and inflammation as WT mice. In the absence of NKT cells, CD1d-deficient keratinocytes, dendritic cells, and macrophages exhibited diminished basal and stress-induced levels of pro-inflammatory mediators. Thus, our findings identify an essential role for CD1d in promoting UVB-induced cutaneous tissue injury and inflammation. They also suggest sunburn and NMSC etiologies are immunologically linked.

Invariant natural killer T cells are enriched at the site of cutaneous inflammation in lupus erythematosus

BACKGROUND

Systemic lupus erythematosus (SLE) is associated with a numerical and functional reduction of peripheral blood (PB) invariant natural killer T (iNKT) cells. Limited information exists on the role of iNKT cells in the pathogenesis of lupus erythematosus.

OBJECTIVE

To investigate the frequency and phenotype of iNKT cells in PB and dermal infiltrates from patients with SLE, subacute-cutaneous lupus erythematosus (SCLE) and discoid lupus erythematosus (DLE).

METHODS

PB was obtained from 23 SLE, 6 SCLE, and 11 DLE patients, and from 30 healthy controls. iNKT cell frequency and CCR4/CCR6 surface expression were assessed by flow cytometry. The frequency and phenotype of skin infiltrating Vα24(+)Vβ11(+) iNKT cells were investigated by immunofluorescence in lesional biopsies from 20 patients, unaffected skin from 3 patients, and from 6 healthy controls.

RESULTS

Lupus erythematosus patients displayed significantly lower percentages of circulating CD3(+)6B11(+) iNKT cells compared to healthy controls. Whereas CCR6 expression on iNKT cells was enhanced in active SLE patients regardless of cutaneous involvement compared to healthy controls, CCR4 was exclusively increased in patients with active cutaneous lesions. Furthermore, iNKT cells were significantly enriched in lesional skin of SLE and DLE patients, but not in unaffected skin of lupus patients. The majority of lesional iNKT cells expressed IFN-γ and CCR4.

CONCLUSION

The deficiency in circulating iNKT cells in cutaneous lupus erythematosus is associated with an increase of iNKT cells at the site of cutaneous inflammation. These data underscore the importance of analyzing iNKT cells not only in PB, but also in the target tissues.

CD1d and natural killer T cells in immunity to Mycobacterium tuberculosis

The critical role of peptide antigen-specific T cells in controlling mycobacterial infections is well documented in natural resistance and vaccine-induced immunity against Mycobacterium tuberculosis. However, many other populations of leukocytes contribute to innate and adaptive immunity against mycobacteria. Among these, non-conventional T cells recognizing lipid antigens presented by the CD1 antigen presentation system have attracted particular interest. In this chapter, we review the basic immunobiology and potential antimycobacterial properties of a subset of CD1-restricted T cells that have come to be known as Natural Killer T cells. This group of lipid reactive T cells is notable for its high level of conservation between humans and mice, thus enabling a wide range of highly informative studies in mouse models. As reviewed below, NKT cells appear to have subtle but potentially significant activities in the host response to mycobacteria. Importantly, they also provide a framework for investigations into other types of lipid antigen-specific T cells that may be more abundant in larger mammals such as humans.

The Use of In Vitro Systems for Evaluating Immunotoxicity: The Report and Recommendations of an ECVAM Workshop

This is the report of a workshop organised by the European Centre for the Validation of Alternative Methods (ECVAM). ECVAM's main goal, as defined in 1993 by its Scientific Advisory Committee, is to promote the scientific and regulatory acceptance of alternative methods that are of importance to the biosciences and which replace, reduce or refine the use of laboratory animals. One of the first priorities set by ECVAM was the implementation of procedures that would enable it to become well informed about the state-of-the-art of non-animal test development and validation, and the potential for the possible incorporation of alternative tests into regulatory procedures. It was decided that this would be best achieved by the organization of ECVAM workshops on specific topics, at which small groups of invited experts would review the current status of various types of in vitro tests and their potential uses, and make recommendations about the best ways forward (Anonymous, 1994). The workshop on "The use of in vitro systems for evaluating Immunotoxicity" was held at ECVAM (Ispra), Italy, on 24th-26th November 2003. The participants represented academia, national organizations, international regulatory bodies and industry. The aim of the workshop was to review the state-of-the-art in the field of in vitro immunotoxicology, and to develop strategies towards the replacement of in vivo testing. At the end of this report are listed the recommendations that should be considered for prevalidation and validation of relevant and reliable procedures, that could replace the use of animals in chemical and cosmetics toxicity testing.

Serum interleukin-6 levels in response to methotrexate treatment in psoriatic patients

BACKGROUND

Psoriasis is a chronic autoimmune hyperproliferative skin disease. In psoriasis, the cutaneous and systemic overexpression of various proinflammatory cytokines, such as interleukin-6 (IL-6) has been demonstrated. Methotrexate (MTX) has been used in the treatment of psoriasis. The aim of this study is to assess the effect of MTX on serum IL-6 levels and also to find the association between PASI score and IL-6 levels in psoriatic patients during MTX therapy.

METHODS

We recruited 20 control subjects and 22 Psoriasis vulgaris patients for this study. The patients were treated with 7.5mg of methotrexate per week for 12 weeks. Folic acid was given at 5mg once daily except on the day of MTX for 12 weeks. There were 2 dropouts, because of increased liver enzyme levels. Blood samples were collected at three intervals (i.e., Day 0, 6 weeks, 12 weeks) from psoriatic patients and only once from control subjects. PASI score, biochemical and hematological parameters were assessed. Serum IL-6 level was analyzed by using ELISA.

RESULTS

Biochemical and hematological parameters showed no significant changes. Serum IL-6 level and PASI score declined significantly (p<0.001) from Day 0 to 12 weeks of MTX treatment and also showed positive correlation before (r=0.992; p<0.000) and after (r=0.987; p<0.000) treatment with MTX. Out of 4 clinical indices of PASI, only 2 indices namely Infiltration (I) and Desquamation (D) showed positive correlation with IL-6 before and after MTX treatment.

CONCLUSION

The treatment response with MTX in psoriatic patients can be seen both at clinical and molecular levels.

Contact-dependent interference with invariant NKT cell activation by herpes simplex virus-infected cells

Invariant CD1d-restricted NKT (iNKT) cells play important roles in generating protective immune responses against infections. In this study, we have investigated the role of human iNKT cells in HSV-1 infection and their interaction with epidermal keratinocytes. These cells express CD1d and are the primary target of the virus. Keratinocytes loaded with α-galactosyl ceramide (α-GalCer) could stimulate IFN-γ production and CD25 upregulation by iNKT cells. However, both α-GalCer-dependent and cytokine-dependent activation of iNKT cells was impaired after coculture with HSV-1-infected cells. Notably, CD1d downregulation was not observed on infected keratinocytes, which were also found to inhibit TCR-independent iNKT cell activation. Further examination of the cytokine profile of iNKT-keratinocyte cocultures showed inhibition of IFN-γ, IL-5, IL-10, IL-13, and IL-17 secretion but upregulation of IL-4 and TNF-α after the infection. Moreover, cell-to-cell contact between infected keratinocytes and iNKT cells was required for the inhibition of activation, as the cell-free supernatants containing virus did not affect activation. Productive infection of iNKT cells was however not required for the inhibitory effect. After coculture with infected cells, iNKT cells were no longer responsive to further stimulation with α-GalCer-loaded CD1d-expressing cells. We found that exposure to HSV-1-infected cells resulted in impaired TCR signaling downstream of ZAP70. Additionally, infected cells upregulated the expression of the negative T cell regulator, galectin-9; however, blocking experiments indicated that the impairment of iNKT cell responses was independent of galectin-9. Thus, interference with activation of human iNKT cells by HSV-1 may represent a novel immunoevasive strategy used by the virus to avoid immune clearance.

A single intradermal injection of IFN-γ induces an inflammatory state in both non-lesional psoriatic and healthy skin

Psoriasis is a chronic, debilitating, immune-mediated inflammatory skin disease. As IFN-γ is involved in many cellular processes, including activation of dendritic cells (DCs), antigen processing and presentation, cell adhesion and trafficking, and cytokine and chemokine production, IFN-γ-producing Th1 cells were proposed to be integral to the pathogenesis of psoriasis. Recently, IFN-γ was shown to enhance IL-23 and IL-1 production by DCs and subsequently induce Th17 cells, which are important contributors to the inflammatory cascade in psoriatic lesions. To determine whether IFN-γ indeed induces the pathways expressed in psoriatic lesions, a single intradermal injection of IFN-γ was administered to an area of clinically normal, non-lesional (NL) skin of psoriasis patients and biopsies were collected 24 hours later. Although there were no visible changes in the skin, IFN-γ induced many molecular and histological features characteristic of psoriatic lesions. IFN-γ increased a number of differentially expressed genes in the skin, including many chemokines concomitant with an influx of T cells and inflammatory DCs. Furthermore, inflammatory DC products tumor necrosis factor (TNF), inducible nitric oxide synthase, IL-23, and TNF-related apoptosis-inducing ligand were present in IFN-γ-treated skin. Thus, IFN-γ, which is significantly elevated in NL skin compared with healthy skin, appears to be a key pathogenic cytokine that can induce many features of the inflammatory cascade of psoriasis.

A single intradermal injection of IFN-γ induces an inflammatory state in both non-lesional psoriatic and healthy skin

Psoriasis is a chronic, debilitating, immune-mediated inflammatory skin disease. As IFN-γ is involved in many cellular processes, including activation of dendritic cells (DCs), antigen processing and presentation, cell adhesion and trafficking, and cytokine and chemokine production, IFN-γ-producing Th1 cells were proposed to be integral to the pathogenesis of psoriasis. Recently, IFN-γ was shown to enhance IL-23 and IL-1 production by DCs and subsequently induce Th17 cells, which are important contributors to the inflammatory cascade in psoriatic lesions. To determine whether IFN-γ indeed induces the pathways expressed in psoriatic lesions, a single intradermal injection of IFN-γ was administered to an area of clinically normal, non-lesional (NL) skin of psoriasis patients and biopsies were collected 24 hours later. Although there were no visible changes in the skin, IFN-γ induced many molecular and histological features characteristic of psoriatic lesions. IFN-γ increased a number of differentially expressed genes in the skin, including many chemokines concomitant with an influx of T cells and inflammatory DCs. Furthermore, inflammatory DC products tumor necrosis factor (TNF), inducible nitric oxide synthase, IL-23, and TNF-related apoptosis-inducing ligand were present in IFN-γ-treated skin. Thus, IFN-γ, which is significantly elevated in NL skin compared with healthy skin, appears to be a key pathogenic cytokine that can induce many features of the inflammatory cascade of psoriasis.

The epidermis as an adjuvant

It is now clear that the epidermis has an active role in local immune responses in the skin. Keratinocytes are involved early in inflammation by providing first-line innate mechanisms and, in addition, can contribute to adaptive immune responses that may be associated with clinical disease. Moreover, keratinocytes are capable of enhancing and shaping the outcome of inflammation in response to stimuli and promoting particular types of immune bias. Through understanding the underlying mechanisms, the role of keratinocytes in disease pathogenesis will be further defined, which is likely to lead to the identification of potential targets for prophylactic or therapeutic intervention.

Glucagon-like peptide-1 (GLP-1) and the regulation of human invariant natural killer T cells: lessons from obesity, diabetes and psoriasis

AIMS/HYPOTHESIS

The innate immune cells, invariant natural killer T cells (iNKT cells), are implicated in the pathogenesis of psoriasis, an inflammatory condition associated with obesity and other metabolic diseases, such as diabetes and dyslipidaemia. We observed an improvement in psoriasis severity in a patient within days of starting treatment with an incretin-mimetic, glucagon-like peptide-1 (GLP-1) receptor agonist. This was independent of change in glycaemic control. We proposed that this unexpected clinical outcome resulted from a direct effect of GLP-1 on iNKT cells.

METHODS

We measured circulating and psoriatic plaque iNKT cell numbers in two patients with type 2 diabetes and psoriasis before and after commencing GLP-1 analogue therapy. In addition, we investigated the in vitro effects of GLP-1 on iNKT cells and looked for a functional GLP-1 receptor on these cells.

RESULTS

The Psoriasis Area and Severity Index improved in both patients following 6 weeks of GLP-1 analogue therapy. This was associated with an alteration in iNKT cell number, with an increased number in the circulation and a decreased number in psoriatic plaques. The GLP-1 receptor was expressed on iNKT cells, and GLP-1 induced a dose-dependent inhibition of iNKT cell cytokine secretion, but not cytolytic degranulation in vitro.

CONCLUSIONS/INTERPRETATION

The clinical effect observed and the direct interaction between GLP-1 and the immune system raise the possibility of therapeutic applications for GLP-1 in inflammatory conditions such as psoriasis.

Alternative spliced CD1d transcripts in human bronchial epithelial cells

CD1d is a MHC I like molecule which presents glycolipid to natural killer T (NKT) cells, a group of cells with diverse but critical immune regulatory functions in the immune system. These cells are required for optimal defence against bacterial, viral, protozoan, and fungal infections, and control of immune-pathology and autoimmune diseases. CD1d is expressed on antigen presenting cells but also found on some non-haematopoietic cells. However, it has not been observed on bronchial epithelium, a site of active host defence in the lungs. Here, we identify for the first time, CD1D mRNA variants and CD1d protein expression on human bronchial epithelial cells, describe six alternatively spliced transcripts of this gene in these cells; and show that these variants are specific to epithelial cells. These findings provide the basis for investigations into a role for CD1d in lung mucosal immunity.

Analysis of granulysin-mediated cytotoxicity in peripheral blood of patients with psoriatic arthritis

The objective of the present study was to investigate possible changes in granulysin (GNLY)-mediated cytotoxicity of peripheral blood lymphocytes in psoriatic arthritis (PsA) patients with respect to different phases of the disease. We prospectively enrolled 25 PsA patients in the active phase, 26 PsA patients in remission and 24 healthy controls. The simultaneous detection of intracellular GNLY and cell surface antigens (CD3 and CD56) was performed with flow cytometry. GNLY apoptotic protein was visualised by immunocytochemistry. Natural killer (NK) cell cytotoxicity was analysed with a cytotoxicity assay against human erythroleukaemia K-562 cells. The percentage of GNLY(+) cells did not differ significantly between PsA patients in the acute phase and those in remission; however, it was always higher than in healthy examinees due to the increased percentage of GNLY(+) cells within T cells, NKT cells, and both, and in the CD56(+dim) and CD56(+bright) NK subsets. The mean fluorescence intensity for GNLY was higher in all lymphocyte subpopulations in the acute phase than in remission and in healthy controls. Accordingly, GNLY-mediated NK cell cytotoxicity against K-562 cells of active phase PsA patients was significantly higher than that in patients in remission or in healthy controls. These findings demonstrated the involvement of GNLY in the worsening of PsA and suggested that GNLY mediated the development of joint lesions.

Regulation of immune responses to HPV infection and during HPV-directed immunotherapy

The recent development of vaccines prophylactic against human papillomavirus (HPV) infection has the potential to reduce the incidence of cervical cancer globally by up to 70% over the next 40 years, if universal immunization is adopted. As these prophylactic vaccines do not alter the natural history of established HPV infection, immunotherapies to treat persistent HPV infection and associated precancers would be of benefit to assist with cervical cancer control. Efforts to develop immuno-therapeutic vaccines have been hampered by the relative non-immunogenicity of HPV infection, by immunoregulatory processes in skin, and by subversion of immune response induction and immune effector functions by papillomavirus proteins. This review describes HPV-specific immune responses induced by viral proteins, their regulation by host and viral factors, and highlights some conclusions from our own recent research.

NK cells and psoriasis

Psoriasis is a chronic condition of the skin characterised by distinctive scaly plaques. The immune system is now thought to play a major role in the development and pathogenesis of psoriasis with immune cells and cytokines influencing keratinocyte function. Keratinocytes in turn, can activate and recruit immune cells leading to a positive feedback loop in disease. Natural Killer (NK) cells are lymphocytes that are best known for killing virally infected and cancer cells. However, evidence is emerging to support a role for NK cells in psoriasis. NK cells are found in the inflammatory infiltrate in psoriatic skin lesions. They can produce a range of inflammatory cytokines, many of which are important in the pathogenesis of psoriasis. Recent genetic studies have identified a range of potential molecules relating to NK cell biology that are known to be important in psoriasis. This paper will discuss the evidence, both cellular and genetic, for NK cell involvement in psoriasis.

Psoriasis: from pathogenesis to novel therapeutic approaches

Psoriasis is one of the commonest chronic inflammatory disorders. Its cause is unknown, but a wealth of studies indicate that the disease results from a complex and dynamic interplay between genetic and environmental factors that trigger an excessive inflammatory response in the skin. Dendritic cells and effector T-cells are central in the development of the psoriastic lesion, and cytokines produced by these cells stimulate keratinocytes to proliferate and increase the migration of inflammatory cells into the skin, promoting epidermal hyperplasia and inflammation. Understanding the immunology of the psoriatic plaque has led to new therapeutic options and novel candidates for immunomodulation, and has changed the ways psoriatic patients are managed.

CD1d expression in paneth cells and rat exocrine pancreas revealed by novel monoclonal antibodies which differentially affect NKT cell activation

Background

CD1d is a nonpolymorphic MHC class I-like molecule which presents nonpeptide ligands, e.g. glycolipids, to NKT cells. These cells are known to have multiple effects on innate and adaptive immune responses and on the development of pathological conditions. In order to analyze CD1d expression and function in the rat, the first rat CD1d-specific monoclonal antibodies (mAbs) were generated.

Methodology/Principal Findings

Two mAbs, WTH-1 and WTH-2, were generated which bound equally well to cell surface-expressed rat and mouse CD1d. Their non-overlapping epitopes were mapped to the CD1d heavy chain. Flow cytometry and immunohistological analyses revealed a nearly identical degree and pattern of CD1d expression for hematopoieitic cells of both species. Notable is also the detection of CD1d protein in mouse and rat Paneth cells as well as the extremely high CD1d expression in acinar exocrine cells of the rat pancreas and the expression of CD4 on rat marginal zone B cells. Both mAbs blocked α-galactosylceramide recognition by primary rat and mouse NKT cells. Interestingly, the two mAbs differed in their impact on the activation of various autoreactive T cell hybridomas, including the XV19.2 hybridoma whose activation was enhanced by the WTH-1 mAb.

Conclusions/Significance

The two novel monoclonal antibodies described in this study, allowed the analysis of CD1d expression and CD1d-restricted T cell responses in the rat for the first time. Moreover, they provided new insights into mechanisms of CD1d-restricted antigen recognition. While CD1d expression by hematopoietic cells of mice and rats was extremely similar, CD1d protein was detected at not yet described sites of non-lymphatic tissues such as the rat exocrine pancreas and Paneth cells. The latter is of special relevance given the recently reported defects of Paneth cells in CD1d^−/− mice, which resulted in an altered composition of the gut flora.

CD1d, a sentinel molecule bridging innate and adaptive immunity, is downregulated by the human papillomavirus (HPV) E5 protein: a possible mechanism for immune evasion by HPV

CD1d and CD1d-restricted natural killer T (NKT) cells serve as a natural bridge between innate and adaptive immune responses to microbes. CD1d downregulation is utilized by a variety of microbes to evade immune detection. We demonstrate here that CD1d is downregulated in human papillomavirus (HPV)-positive cells in vivo and in vitro. CD1d immunoreactivity was strong in HPV-negative normal cervical epithelium but absent in HPV16-positive CIN1 and HPV6-positive condyloma lesions. We used two cell lines for in vitro assay; one was stably CD1d-transfected cells established from an HPV-negative cervical cancer cell line, C33A (C33A/CD1d), and the other was normal human vaginal keratinocyte bearing endogenous CD1d (Vag). Flow cytometry revealed that cell surface CD1d was downregulated in both C33A/CD1d and Vag cells stably transfected with HPV6 E5 and HPV16 E5. Although the steady-state levels of CD1d protein decreased in both E5-expressing cell lines compared to empty retrovirus-infected cells, CD1d mRNA levels were not affected. Confocal microscopy demonstrated that residual CD1d was not trafficked to the E5-expressing cell surface but colocalized with E5 near the endoplasmic reticulum (ER). In the ER, E5 interacted with calnexin, an ER chaperone known to mediate folding of CD1d. CD1d protein levels were rescued by the proteasome inhibitor, MG132, indicating a role for proteasome-mediated degradation in HPV-associated CD1d downregulation. Taken together, our data suggest that E5 targets CD1d to the cytosolic proteolytic pathway by inhibiting calnexin-related CD1d trafficking. Finally, CD1d-mediated production of interleukin-12 from the C33A/CD1d cells was abrogated in both E5-expressing cell lines. Decreased CD1d expression in the presence of HPV E5 may help HPV-infected cells evade protective immunological surveillance.

Inhibition of lipid antigen presentation in dendritic cells by HIV-1 Vpu interference with CD1d recycling from endosomal compartments

Dendritic cells (DCs) play an important role in viral infections both as initiators of immunity and as viral targets. Interaction between DCs and the innate-like CD1d-restricted natural killer T (NKT) cells results in the mutual activation of both cells and the subsequent initiation of cellular immune responses. Here, we show that HIV-1 inhibits the surface expression of CD1d in productively infected DCs and identify this as a novel activity of the HIV-1 vpu gene product. Interestingly, the viral protein U (Vpu) does not enhance constitutive CD1d endocytosis or induce rapid CD1d degradation. Instead, the Vpu protein interacts with CD1d and suppresses its recycling from endosomal compartments to the cell surface by retaining CD1d in early endosomes. This interference with the CD1d antigen presentation pathway strongly inhibits the ability of infected DCs to activate CD1d-restricted NKT cells. Given that the interaction with CD1d-expressing DCs is central to the ability of NKT cells to regulate immunity, these data suggest that interference with the CD1d antigen presentation pathway represents an HIV-1 strategy to evade innate cellular immune responses and imply a role for the innate-like CD1d-restricted NKT cells in the host defense against HIV-1.

Invariant NKT cells in hyperplastic skin induce a local immune suppressive environment by IFN-gamma production

NKT cells can promote or inhibit adaptive immune responses. Cutaneous immunity is tightly regulated by cooperation between innate and adaptive immune processes, but the role of NKT cells in regulating cutaneous immunity is largely unknown. In this study, we show, in a mouse model, that skin-infiltrating CD1d-restricted NKT cells in HPV16-E7 transgenic hyperplastic skin produce IFN-gamma, which can prevent rejection of HPV16-E7-expressing skin grafts. Suppression of graft rejection is associated with the accumulation of CD1d(hi)-expressing CD11c(+)F4/80(hi) myeloid cells in hyperplastic skin. Blockade of CD1d, removal of NKT cells, or local inhibition of IFN-gamma signaling is sufficient to restore immune-mediated graft rejection. Thus, inhibition of NKT cell recruitment or function may enable effective immunity against tumor and viral Ags expressed in epithelial cells.

Trioxsalen derivatives with lipoxygenase inhibitory activity

Trioxsalen (TRX) is a 4,5',8-trimethylated psoralen analog presenting interesting biological activities when irradiated with UVA light. A series of TRX derivatives, which where obtained by its chemical modification and incorporation of a variety of unsaturated functions at position 4' of the psoralen ring-system, were evaluated for their antioxidant activity and their inhibitory activity on soybean lipoxygenase (LOX) and lipid peroxidation. The reducing properties of the compounds were evaluated using the 1,1-diphenyl-2-picrylhydrazyl (DPPH) free radical scavenging assay and found to be very low, in the range 0-14%, with the exception of the hydroxamic acid 6 which showed almost identical activity to BHT. TRX derivative 3 significantly inhibited LOX, with IC(50) 9.4 muM. With the exception of TRX, all tested analogs inhibited lipid peroxidation in the range of 35-91%. The most potent compound, namely TRX derivative 3, was studied for its anti-inflammatory activity in vivo on rat paw edema induced by carrageenan, and was found to be of almost identical activity to indomethacin. The results of the biological tests are discussed in terms of structural characteristics.

Skin immune sentinels in health and disease

Human skin and its immune cells provide essential protection of the human body from injury and infection. Recent studies reinforce the importance of keratinocytes as sensors of danger through alert systems such as the inflammasome. In addition, newly identified CD103(+) dendritic cells are strategically positioned for cross-presentation of skin-tropic pathogens and accumulating data highlight a key role of tissue-resident rather than circulating T cells in skin homeostasis and pathology. This Review focuses on recent progress in dissecting the functional role of skin immune cells in skin disease.

IL-18 skews the invariant NKT-cell population via autoreactive activation in atopic eczema

Atopic eczema (AE) is a chronic relapsing inflammatory skin disease where the commensal yeast Malassezia can act as a microbial trigger factor. Malassezia activates human DC to produce IL-18, an innate cytokine that is elevated in serum of AE patients; however, the precise role of IL-18 in human AE etiology is unknown. Herein, we investigated the effect of IL-18 on the human invariant NKT (iNKT) cell compartment in AE. We found that IL-18 was a potent activator of human iNKT-cells and promoted a pro-inflammatory CD1d-dependent response, even in the absence of exogenous ligands. Chronic activation via IL-18 on the other hand was inhibitory and skewed the iNKT-cell pool by selectively suppressing CD4(+) iNKT-cells. This was mimicked in AE patients where the proportion of CD4(+) iNKT-cells was reduced in peripheral blood and coincided with elevated plasma levels of IL-18. Furthermore, a reduced CD4(+) iNKT-cell pool was associated with elevated IgE levels in plasma, and the plasma levels of IL-18 correlated with both total IgE and disease severity in the AE patients. Based on these findings, we propose that IL-18-mediated activation and subsequent dysregulation of the CD1d-restricted iNKT-cells plays a role in the pathogenesis of human AE.

A central role for transcription factor C/EBP-beta in regulating CD1d gene expression in human keratinocytes

CD1d is a nonclassical Ag-presenting molecule that presents glycolipid Ags to NKT cells that are involved in immune defense and tumor rejection. It also plays a role in immunoregulatory functions in the epidermis. The mechanisms controlling the expression of CD1d are not well understood. Therefore, we cloned the CD1d gene promoter and characterized its activities in primary human keratinocytes and other cell lines of epithelial origin. We found that a CCAAT box in the CD1d promoter is required for its expression in keratinocytes. We show here that transcription factor C/EBP-beta binds to the CCAAT box in the CD1d promoter in vitro and in vivo. Consistent with these observations, deletion of the gene encoding for C/EBP-beta caused a loss of CD1d expression. The in vivo regulation of CD1d has significant implications for the pathologic mechanisms of certain immunologic skin diseases in which NKT cells play a role, such as allergic contact dermatitis and psoriasis. Together, these data show a central role for C/EBP-beta in regulating CD1d transcription.

Immunopathogenesis of psoriasis: focus on natural killer T cells

Psoriasis is a common inflammatory skin disease triggered by dysregulated immune response and characterized by hyperproliferation and altered differentiation of keratinocytes. Formation of psoriatic lesions is thought to be elicited by the complex cellular and cytokine network arising from the pathogenic interactions between keratinocytes and components of innate and acquired immune system. Natural killer T (NKT) cells are a heterogenous T-cell lineage that has been implicated in the pathogenesis of various autoimmune diseases including psoriasis. Due to the numerous functions of NKT cells that link innate and adaptive immunity, their role in psoriasis is complex and still elusive. We summarize the currently available literature data on this issue and discuss the possible role of NKT cells in the immunopathogenesis of this autoimmune disease.

Skin immune surveillance by T cells--a new order?

Although studies of the skin have provided fundamental models for innate and adaptive immune surveillance of body surfaces, there remains relatively little understanding of the role that epithelial cells play in sensing infection and/or organ dysfunction, and the pathways available to them to communicate with local and systemic immune cells. In particular, evidence is emerging for a novel stress response initiated by local lymphocytes, rather than dendritic cells, and based on their recognition of epithelial stress-induced antigens. Its consequences are to sustain tissue integrity by providing immunoprotection and novel modes of immunoregulation, whereas its dysregulation may promote body surface immunopathologies.

Natural killer T cells: an unconventional T-cell subset with diverse effector and regulatory functions

Natural killer T (NKT) cells are a unique subset of lymphocytes that express NK cell markers such as CD161 and CD94, as well as a T-cell receptor (TCR) alpha/beta, with a restricted repertoire, which distinguishes them from NK cells, which lack a TCR. In contrast to conventional T-lymphocytes, the TCR of NKT cells does not interact with that of peptide antigens presented by classical major histocompatibility complex-encoded class I or II molecules. Instead, this TCR recognizes glycolipids presented by CD1d, a non-classical antigen-presenting molecule. The rapid response of NKT cells to their cognate antigens is characteristic of an innate immune response, and allows the polarizing cytokines (IFN-gamma and/or IL-4) to regulate adaptive immunity. NKT cells have been found to be critical in the immune response against viral infections and malaria, as well as in tumor immunity, and certain autoimmune diseases. NKT cells have been assessed to represent the "trait d'union" between innate and adaptive immunity. They play an active role in skin diseases, such as contact sensitivity, which have been implicated in UV-induced immunosuppression and psoriasis. Thus, NKT-cells are emerging as an important subset of lymphocytes, with a protective role in host defense and a pathogenic role in certain immune-mediated disease states.

Invariant natural killer T cells and immunotherapy of cancer

Invariant CD1d restricted natural killer T (iNKT) cells are regulatory cells that express a canonical TCR-Valpha-chain (Valpha24.Jalpha18 in humans and Valpha14.Jalpha18 in mice) which recognizes glycolipid antigens presented by the monomorphic CD1d molecule. They can secrete a wide variety of both pro-inflammatory and anti-inflammatory cytokines very swiftly upon their activation. Evidence for the significance of iNKT cells in human cancer has been ambiguous. Still, the (pre-)clinical findings reviewed here, provide evidence for a distinct contribution of iNKT cells to natural anti-tumor immune responses in humans. Furthermore, clinical phase I studies that are discussed here have revealed that the infusion of cancer patients with ligand-loaded dendritic cells or cultured iNKT cells is well tolerated. We thus underscore the potential of iNKT cell based immunotherapy in conjunction with established modalities such as surgery and radiotherapy, as adjuvant therapy against carcinomas.

Immunohistochemical analysis of small plaque parapsoriasis: involvement of dendritic cells

Small plaque parapsoriasis (SPP) is one of the cutaneous T-cell lymphoproliferative disorders. The aim of the present study was to show the antigenic profile of a subset of dendritic cells and lymphocytes in SPP in comparison with normal cells to provide data on the role of these two cell types in the pathogenesis of SPP. Skin biopsy specimens of lesions were obtained from 8 patients with SPP. Biopsies of the healthy skin from 9 control individuals were also analyzed. Immunohistochemistry was performed on the frozen tissue sections to reveal binding of anti-HLA Class II, anti-CD1a, anti-CD4, anti-CD8, anti-CD44, anti-CD45, and anti-CD68 monoclonal antibodies. There was a statistically significant increase in the number of CD1a(+), Langerhans cells (LCs), HLA-DR-immunoreactive and, CD1a-positive dermal dendritic cells and CD68(+) macrophages in the SPP group (p=0.008, 0.008, 0.002 and <0.0009, respectively). The number of lymphocytes positive for CD4, CD8 and CD45 was significantly higher than normal in the SPP group (p=0.015, <0.0009 and <0.0009, respectively). Our study demonstrates that both peptide- and lipid-based antigens are involved in the persistent antigenic exposure in SPP. Dendritic cells play a pivotal role in SPP by presenting antigens by both LC and dermal dendritic cells via MHC Class II and CD1a molecules. The CD68(+) macrophages are thought to be involved in the immune response in this pathology as an antigen-presenting cell.

Expression of CD1d and ligand-induced cytokine production are tissue specific in mucosal epithelia of the human lower reproductive tract

Mucosal epithelia of the human lower reproductive tract (vagina, cervix, and penile urethra) are exposed to sexually transmitted microbes, including Chlamydia trachomatis. The in vivo susceptibility of each tissue type to infection with C. trachomatis is quite distinct. CD1d is expressed on the surface of antigen-presenting cells, including mucosal epithelial cells, and interacts specifically with invariant NKT cells. Invariant NKT cells play a role in both innate and adaptive immune responses to microbes. Here we assessed CD1d expression in normal reproductive tissues by using immunohistochemistry. Immortalized epithelial cell lines from the human lower reproductive tract (vagina, endocervix, and penile urethra) were examined for CD1d expression and for ligand-induced cytokine production induced by CD1d cross-linking. CD1d expression in normal tissue was strong in the vagina but weak in the endocervix and penile urethra. Gamma interferon exposure induced CD1d transcription in all of the cell types studied, with the strongest induction in vaginal cells. Flow cytometry revealed cell surface expression of CD1d in vaginal and penile urethral epithelial cells but not in endocervical cells. Ligation of surface-expressed CD1d by monoclonal antibody cross-linking promoted interleukin-12 (IL-12) and IL-15, but not IL-10, production in vaginal and penile urethral cells. No induction was demonstrated in endocervical cells. CD1d-mediated cytokine production in penile urethral cells was abrogated by C. trachomatis infection. Basal deficiency in CD1d-mediated immune responsiveness may result in susceptibility to sexually transmitted agents. Decreased CD1d-mediated signaling may help C. trachomatis evade detection by innate immune cells.

Activation of keratinocyte protein kinase C zeta in psoriasis plaques

PKCzeta (protein kinase C-zeta), a member of protein kinase C family, plays an important role in cell proliferation, differentiation, and apoptosis. It acts as a downstream molecule for TNF-alpha (tumor necrosis factor) signal transduction and also regulates the expression of CD1d, an HLA-class I-like molecule. The interaction of CD1d with natural killer T (NKT) cells has been shown to be important in their Th1 cytokine production in psoriasis. In this study, we examined PKCzeta in psoriasis in order to define its role in the pathogenesis of the disease. We found that T-cell receptor (TCR) V alpha24+ V beta11+ NKT cells and CD1d molecules within psoriatic skin were increased. Moreover, there was an associated increase in PKCzeta mRNA and protein expression with membrane translocation in psoriasis lesions compared to uninvolved skin. Furthermore, cultured keratinocytes exhibited increased PKCzeta activity and membrane translocation upon stimulation by TNF-alpha, a cytokine known to play an important role in the pathogenesis of psoriasis. These results implied that PKCzeta is an important transduction molecule downstream of TNF-alpha signaling and is associated with increased expression of CD1d that may enhance CD1d-NKT cell interactions in psoriasis lesions. This makes PKCzeta a tempting target for possible pharmacological intervention in modifying the downstream effects of TNF-alpha in psoriasis.

The mucosal immune response to laryngopharyngeal reflux

RATIONALE

Laryngopharyngeal reflux (LPR) affects up to 20% of Western populations. Although individual morbidity is usually moderate, treatment costs are high and there are associations with other diseases, including laryngeal cancer. To date, there have been no studies of the mucosal immune response to this common inflammatory disease.

OBJECTIVES

To determine the mucosal immune response to LPR.

METHODS

We performed a prospective immunologic study of laryngeal biopsies from patients with LPR and control subjects (n = 12 and 11, respectively), and of primary laryngeal epithelial cells in vitro.

MEASUREMENTS AND MAIN RESULTS

Quantitative multiple-color immunofluorescence, using antibodies for lymphocytes (CD4, CD8, CD3, CD79, CD161), granulocytes (CD68, EMBP), monocytic cells (CD68, major histocompatibility complex [MHC] class II), and classical and nonclassical MHC (I, II, beta(2)-microglobulin, CD1d). Univariate and multivariate analysis and colocalization measurements were applied. There was an increase in percentage area of mucosal CD8(+) cells in the epithelium (P < 0.005), whereas other leukocyte and granulocyte antigens were unchanged. Although epithelial MHC class I and II expression was unchanged by reflux, expression of the nonclassical MHC molecule CD1d increased (P < 0.05, luminal layers). In vitro, laryngeal epithelial cells constitutively expressed CD1d. CD1d and MHC I expression were inversely related in all subjects, in a pattern which appears to be unique to the upper airway. Colocalization of natural killer T (NKT) cells with CD1d increased in patients (P < 0.01).

CONCLUSIONS

These data indicate a role for the CD1d-NKT cell axis in response to LPR in humans. This represents a useful target for novel diagnostics and treatments in this common condition.

Immunopathogenesis of psoriasis

Investigations into the cause and treatment of psoriasis remain at the forefront of basic and applied clinical research efforts around the world. The purpose for this review is to provide an up-to-date synopsis of recent progress in ten sections exploring the immunological and inflammatory basis for psoriasis. Given the breadth of this topic in investigative skin biology and frequent paradigm shifts, it should not be surprising that the bibliography contains more than 150 references; many of which have been published in the last 5 years. Whereas considerable progress has been made into the immunopathogenesis of psoriasis, many fundamentally important questions remain regarding the role of cells located in both epidermal and dermal compartments. Attempts to characterize various animal models of psoriasis, delineation of the mechanism of action for biological agents, and consideration of molecular links between skin inflammation and various extracutaneous comorbidities are likely to continue challenging investigators and clinicians for many years to come.

Acute upregulation of an NKG2D ligand promotes rapid reorganization of a local immune compartment with pleiotropic effects on carcinogenesis

The self-encoded ligands MICA (human) and Rae-1 (mouse) for the cytotoxic lymphocyte activating receptor NKG2D are highly expressed in carcinomas and inflammatory lesions and have been linked to immunosurveillance and graft rejection. However, whether NKG2D ligands have an intrinsic ability to acutely regulate tissue-associated immune compartments is not known. Here we show that epidermis-specific upregulation of Rae-1 induced rapid, coincident and reversible changes in the organization of tissue-resident V(gamma)5V(delta)1 TCRgammadelta+ intraepithelial T cells and Langerhans cells, swiftly followed by epithelial infiltration by unconventional alphabeta T cells. Whereas local V(gamma)5V(delta)1+ T cells limited carcinogenesis, Langerhans cells unexpectedly promoted it. These results provide unique insight into the early phases of tissue immunosurveillance and indicate that acute changes in NKG2D ligands may alone initiate a rapid, multifaceted immunosurveillance response in vivo.

Human natural killer T cells infiltrate into the skin at elicitation sites of allergic contact dermatitis

The purpose of this study is to identify invariant natural killer T cells (NKT cells) in cellular infiltrate of human allergic contact dermatitis (ACD) skin challenge sites. Skin biopsy specimens were taken from positive patch test reactions from 10 different patients (9 different allergens) and studied by immunochemistry, real-time PCR, nested PCR, and in situ hybridization to identify NKT cells and the cytokines associated with this cell type. Invariant NKT cells were identified in all the 10 skin biopsy specimens studied, ranging from 1.72 to 33% of the cellular infiltrate. These NKT cells were activated in all cases, as they expressed cytokine transcripts for IFN-gamma and IL-4. Invariant NKT cells are present in ACD, regardless of the allergen that triggers the reaction, and are in an activated state. We conclude that innate immunity plays a role in late phases of type IV hypersensitivity reactions and may be responding to self-lipids released during allergic inflammation. These data complement the previous work by other investigators that suggest that NKT cells are important in the early cellular response during primary immune responses to allergens. Herein, it is demonstrated that NKT cells are constantly present during the late elicitation phase of human type IV hypersensitivity reactions.

Antigen biochips verify and extend the scope of antibody detection in Lyme borreliosis

The antibody response of serum IgM and IgG of patients with neuroborreliosis and erythema migrans of Lyme borreliosis (LB) was examined against a 41-kDa flagellar antigen and an 8-mer synthetic OspC8 peptide (VAESPKKP) derived from the C-terminus of outer surface protein C (OspC) from Borrelia garinii. We developed a streptavidin-modified biochip-based immunodiagnosis and compared it with conventional methods such as enzyme-linked immunosorbent assay (ELISA) and Western blot (WB). The diagnostic sensitivity of the coated biochips was demonstrated to be identical, and the results of conventional assays such as ELISA and WB were confirmed. Flagellar antigens lead to better diagnosis because of a higher discriminative value. By contrast, OspC8, a peptide derived from the outer surface antigen, is less sensitive to identify immunity in LB. The inferior antigenicity of OspC8 may be due to epitope masking. Overall, this system is open to simultaneously analyze a larger family of peptides differing in length. Thus, an array approach is generally more advantageous to extend the pattern of antigens to be tested for antigenicity in LB. Serial analysis during ongoing disease may be valuable to learn more about the course of the disease and intermittent reactivation of infection. Protein biochip as a potential substitution of ELISA and WB method offers the opportunity to study serum immunity in a multiplicity of patients simultaneously.

Immunopathogenesis of psoriasis

Psoriasis is a chronic skin disease that affects about 1.5% of the Caucasian population and is characterized by typical macroscopic and microscopic skin alterations. Psoriatic lesions are sharply demarcated, red and slightly raised lesions with silver-whitish scales. The microscopic alterations of psoriatic plaques include an infiltration of immune cells in the dermis and epidermis, a dilatation and an increase in the number of blood vessels in the upper dermis, and a massively thickened epidermis with atypical keratinocyte differentiation. It is considered a fact that the immune system plays an important role in the pathogenesis of psoriasis. Since the early 1990s, it has been assumed that T1 cells play the dominant role in the initiation and maintenance of psoriasis. However, the profound success of anti-tumor necrosis factor-alpha therapy, when compared with T-cell depletion therapies, should provoke us to critically re-evaluate the current hypothesis for psoriasis pathogenesis. Recently made discoveries regarding other T-cell populations such as Th17 and regulatory T cells, dendritic cells, macrophages, the keratinocyte signal transduction and novel cytokines including interleukin (IL)-22, IL-23 and IL-20, let us postulate that the pathogenesis of psoriasis consists of distinct subsequent stages, in each of them different cell types playing a dominant role. Our model helps to explain the varied effectiveness of the currently tested immune modulating therapies and may enable the prediction of the success of future therapies.

Inhibition of tumour necrosis factor-? secretion from EpiDermTMtissues by a novel small molecule, UTL-5d

BACKGROUND

UTL-5d [N-(4-chlorophenyl)-3-carboxyamidyl-5-methylisoxazole] is a small-molecule tumour necrosis factor (TNF)-alpha modulator being investigated for its potential in several immune-mediated diseases, including psoriasis.

OBJECTIVES

We aimed to determine whether UTL-5d represents a potential antipsoriasis agent.

METHODS

Firstly, a keratinocyte cell-based study was used to study the inhibition of TNF-alpha and gene suppression by UTL-5d in vitro. Secondly, a multilayered human epidermis tissue model, consisting of normal human-derived epidermal keratinocytes, was used to study the dose-dependent reduction of TNF-alpha by UTL-5d as well as the feasibility of using UTL-5d in a lotion formulation.

RESULTS

The cell-based study showed that UTL-5d significantly reduced TNF-alpha secretion from keratinocytes (68% reduction at 17 mug mL(-1)) and suppressed JAK3 and MAP3K2 genes by 70% and 40%, respectively. In the human epidermis tissue model, reduction of TNF-alpha by UTL-5d appeared to be dose dependent (8.35-33.4 microg mL(-1)); UTL-5d also reduced cell death induced by ultraviolet (UV) B. Tissues treated by UTL-5d in a preliminary lotion formulation showed significant reduction of TNF-alpha induced by UVB.

CONCLUSIONS

Our results indicate that UTL-5d may be worthy of further investigation for its potential as a topical agent for psoriasis.

Do immune responses to inhaled skin flakes modulate the expression of allergic disease?

We examine the nature of the immune responses to inhaled skin particles and query whether early exposure could play a role in providing protection against the development of allergic disease. Currently, the main hypothesis used to explain environmental modulation of allergic diseases, the 'hygiene hypothesis', is linked exclusively to microbial exposures acting upon the innate immune system. However, many of the exposures sustaining this hypothesis also involve co-exposure to skin flakes from humans or animals. Such skin flakes contain a complex mixture of antigens, glycolipids and small peptides that may induce immune responses. Should these responses prove relevant to the modulation of allergic diseases, it provides new opportunities to better understand the epidemic of allergic disease and to develop new interventions for its prevention.

Expression of the chemokine receptor CCR5 in psoriasis and results of a randomized placebo controlled trial with a CCR5 inhibitor

Several reports have indicated that the chemokine receptor CCR5 and its ligands, especially CCL5 (formerly known as RANTES), may play a role in the pathogenesis of psoriasis. The purpose of this investigation was to examine the expression of CCR5 and its ligands in chronic plaque psoriasis and to evaluate the clinical and immunohistochemical effect of a CCR5 receptor inhibitor. Immunohistochemical analysis showed low but significant increased total numbers of CCR5 positive cells in epidermis and dermis of lesional skin in comparison to non-lesional skin. However, relative expression of CCR5 proportional to the cells observed revealed that the difference between lesional and non-lesional skin was only statistically significant in the epidermis for CD3 positive cells and in the dermis for CD68 positive cells. Quantification of mRNA by reverse transcriptase-polymerase chain reaction only showed an increased expression of CCL5 (RANTES) in lesional skin. A randomized placebo-controlled clinical trial in 32 psoriasis patients revealed no significant clinical effect and no changes at the immunohistochemical level comparing patients treated with placebo or a CCR5 inhibitor SCH351125. We conclude that although CCR5 expression is increased in psoriatic lesions, this receptor does not play a crucial role in the pathogenesis of psoriasis.

CD1 expression on antigen-presenting cells

CD1 proteins present self and microbial glycolipids to CD 1-restricted T cells, or in the case of CD1d, to NKT cells. The CD1 family in humans consists of group I proteins CDla, CDlb, CDlc, and CDle and the group II protein CDld. Rodents express only CDld, but as CD1d is broadly expressed and traffics to all endosomal compartments, this single CD1 family member is thereby able to acquire antigens in many subcellular compartments. A complete understanding of the CD 1 family requires an appreciation of which cells express CD1 and how CD1 contributes to the unique function of each cell type. While group I CD 1 expression is limited to thymocytes and professional APCs, CD1d has a wider tissue distribution and can be found on many nonhematopoietic cells. The expression and regulation of CD1 are presented here with particular emphasis on the function of CD1 in thymocytes, B cells, monocytes and macrophages, dendritic cells (DCs), and intestinal epithelial cells (IECs). Altered expression of CD 1 in cancer, autoimmunity, and infectious disease is well documented, and the implication of CD 1 expression in these diseases is discussed.

In vitro modulation of TLR-2, CD1d and IL-10 by adapalene on normal human skin and acne inflammatory lesions

The anti-inflammatory mechanisms of adapalene, a synthetic retinoid used for the treatment of acne patients, are partially understood. They seem particularly related to the modulation of the non-specific immunity. Recent studies have shown that Toll-like receptor (TLR)-2 expression, a receptor of the innate immune system, was increased in acne lesions and could play an essential role in acne-linked inflammation. The aim of our study was to investigate the new mechanisms of the anti-inflammatory activity of adapalene in vitro, and more specifically the modulatory effect of adapalene on the expression of TLR-2, CD1d, a cell surface glycoprotein that plays a role as antigen-presenting molecules and is responsible for the development of cutaneous inflammation, and also on the expression and the secretion of the anti-inflammatory interleukin (IL)-10 cytokine. Both explants of normal human skin and explants of acne patients were incubated with adapalene (10(-7) or 10(-6) M) or the control medium for 24 h. Evaluation of epidermal expression by immunohistochemistry showed a decreased expression of TLR-2 and IL-10 in explants of normal skin and explants of acne with adapalene. On the contrary, adapalene increased CD1d expression in explants of acne patients. Thus, adapalene can modulate the epidermal immune system by increasing the CD1d expression and by decreasing the IL-10 expression by keratinocytes. Moreover, these modulations could increase the interactions between dendritic cells and T lymphocytes and could strengthen the antimicrobial activity against Propionibacterium acnes. The decreased expression of TLR-2 by the keratinocytes can contribute to explain the anti-inflammatory activity of adapalene observed in clinical practice.