Engagement of the Fc epsilon RI stimulates the production of IL-16 in Langerhans cell-like dendritic cells

Langerhans cells: Central players in the pathophysiology of atopic dermatitis

Atopic dermatitis (AD) is the most common chronic inflammatory skin disease worldwide. AD is a highly complex disease with different subtypes. Many elements of AD pathophysiology have been described, but if/how they interact with each other or which mechanisms are important in which patients is still unclear. Langerhans cells (LCs) are antigen-presenting cells (APCs) in the epidermis. Depending on the context, they can act either pro- or anti-inflammatory. Many different studies have investigated LCs in the context of AD and found them to be connected to all major mechanisms of AD pathophysiology. As APCs, LCs recruit other immune cells and shape the immune response, especially adaptive immunity via polarization of T cells. As sentinel cells, LCs are primary sensors of the skin microbiome and are important for the decision of immunity versus tolerance. LCs are also involved with the integrity of the skin barrier by influencing tight junctions. Finally, LCs are important cells in the neuro-immune crosstalk in the skin. In this review, we provide an overview about the many different roles of LCs in AD. Understanding LCs might bring us closer to a more complete understanding of this highly complex disease. Potentially, modulating LCs might offer new options for targeted therapies for AD patients.

Immunoglobulin E-Mediated Autoimmunity

The study of autoimmunity mediated by immunoglobulin E (IgE) autoantibodies, which may be termed autoallergy, is in its infancy. It is now recognized that systemic lupus erythematosus, bullous pemphigoid (BP), and chronic urticaria, both spontaneous and inducible, are most likely to be mediated, at least in part, by IgE autoantibodies. The situation in other conditions, such as autoimmune uveitis, rheumatoid arthritis, hyperthyroid Graves’ disease, autoimmune pancreatitis, and even asthma, is far less clear but evidence for autoallergy is accumulating. To be certain of an autoallergic mechanism, it is necessary to identify both IgE autoantibodies and their targets as has been done with the transmembrane protein BP180 and the intracellular protein BP230 in BP and IL-24 in chronic spontaneous urticaria. Also, IgE-targeted therapies, such as anti-IgE, must have been shown to be of benefit to patients as has been done with both of these conditions. This comprehensive review of the literature on IgE-mediated autoallergy focuses on three related questions. What do we know about the prevalence of IgE autoantibodies and their targets in different diseases? What do we know about the relevance of IgE autoantibodies in different diseases? What do we know about the cellular and molecular effects of IgE autoantibodies? In addition to providing answers to these questions, based on a broad review of the literature, we outline the current gaps of knowledge in our understanding of IgE autoantibodies and describe approaches to address them.

Infectious Complications in Atopic Dermatitis

Atopic dermatitis is characterized by the interplay of skin barrier defects with the immune system and skin microbiome that causes patients to be at risk for infectious complications. This article reviews the pathogenesis of atopic dermatitis and the mechanisms through which patients are at risk for infection from bacterial, viral, and fungal pathogens. Although these complications may be managed acutely, prevention of secondary infections depends on a multipronged approach in the maintenance of skin integrity, control of flares, and microbial pathogens.

Regulation of cellular processes by interleukin-16 in homeostasis and cancer

Interleukin-16 (IL-16) is generated as a precursor molecule that is cleaved by caspase-3 to produce a pro-IL-16 molecule that functions as a regulator of T cell growth, and a secreted peptide that functions as a CD4 and/or CD9 ligand for induction of cell motility and activation. IL-16 has been predominantly studied as a contributing factor in the orchestration of an immune response; however, more recently IL-16 bioactivity has been closely associated with the progression of a number of different cancers. While the association between IL-16 plasma levels and tumor progression has been reported for many types of cancer, the mechanism for IL-16 involvement has been partially elucidated for three of the cancer types, cutaneous T cell lymphoma (CTCL), multiple myeloma (MM), and breast cancer. The mechanism for promoting cell growth is different in each of these cancers and involves a sequence mutation in the pro-molecule facilitating decreased p27(KIP1) levels in CTCL; over expression of the secreted IL-16 molecule to induce proliferation in CTCL T cells, and plasma cells in MM; and increased secreted IL-16 acting to recruit CD4+ pro-tumor macrophages in breast cancer. This article will review the cellular process for generating IL-16, the biological activities for both the pro- and secreted forms of the protein, and then the mechanism by which these forms contribute to cancer progression. As a soluble cytokine the ability to reduce or eliminate IL-16 synthesis through siRNA approaches or bioactivity through the use of neutralizing antibody treatment may represent a novel therapeutic approach.

Potential efficacy of imiquimod on immunity-related cytokines in murine skin in vivo and in human Langerhans cells in vitro

INTRODUCTION

Imiquimod, an immune-response modifier, has been proven to be clinically effective in the treatment of viral infections and skin cancers, but its mechanism of action remains poorly understood. This study aimed to assess the effects of imiquimod on the expression of three immunity-related cytokines, TNF-α, IL-1β, and IL-6.

MATERIALS AND METHODS

Female BALB/C mice were treated for seven days with topical 1% imiquimod cream; they were then killed and skin samples were snap-frozen. In the in vitro studies, both purified LCs and HaCaT cells were incubated with 5 μg/ml imiquimod for four hours. In all samples, the mRNA levels of TNF-α, IL-1β, and IL-6 were then detected by reverse transcription polymerase chain reaction, and the secretion levels were determined by an enzyme-linked immunosorbent assay.

RESULTS

Imiquimod upregulated the mRNA and protein expression levels of TNF-α, IL-1β, and IL-6 in the skin of imiquimod-treated BALB/C mice and in human LCs, compared with untreated controls (P<0.05). However, there was no significant difference in the expression of these cytokines in imiquimod-treated and untreated HaCaT cells.

CONCLUSIONS

These findings indicate that imiquimod increased the expression of TNF-α, IL-1β, and IL-6 in skin and that the target cell of imiquimod may be the LCs but is unlikely to be the epidermal keratinocytes.

Association between serum IL-16 levels and the degree of sensitization in patients with atopic dermatitis

BACKGROUND

Interleukin (IL)-16 has been characterized as an immunomodulatory cytokine. Besides its chemotactic properties, IL-16 amplifies inflammatory processes and possesses immunoregulatory functions. Our aim was to investigate the association between serum IL-16 levels and the degree of allergic sensitization in patients with atopic dermatitis (AD).

METHODS

The serum level of IL-16 was measured by immunoenzymatic assays. Eosinophil cell count, serum total and specific IgE levels were assessed; prick tests were also carried out. Based on specific IgE levels and prick tests, AD patients were divided into sensitized and nonsensitized subgroups, and correlations among serum IL-16, total IgE levels and eosinophil cell counts were measured in the total patient group and in subgroups.

RESULTS

In the total patient group, significantly higher levels of IL-16 were found in the sera of patients with AD, compared to healthy individuals and patients with psoriasis. A significant correlation was detected between serum levels of IL-16 and total IgE, total IgE and eosinophil counts, but not between IL-16 and eosinophils. When sensitized and nonsensitized subgroups were compared, IL-16 levels showed a significant difference in subgroups that were divided based on specific IgE measurements, but not in those subgroups which were divided based on prick tests. On the other hand, serum total IgE levels showed a significant difference between sensitized and nonsensitized subgroups, assessed by the specific IgE method and also by prick test.

CONCLUSION

Serum IL-16 levels of AD patients correlate to some extent with sensitization. This correlation is not as strong as the correlation between total IgE levels and allergic sensitization.

Fucoidan suppresses IgE production in peripheral blood mononuclear cells from patients with atopic dermatitis

We previously reported that fucoidan, a dietary fiber purified from seaweed, inhibited IgE production in B cells from mice spleen in vitro and ovalbumin-sensitized mice in vivo. In this study, we examined the effect of fucoidan on IgE production in human peripheral blood mononuclear cells (PBMC) in vitro. PBMC, obtained from healthy donors or patients with atopic dermatitis (AD) with high levels of serum IgE, were cultured with IL-4 and anti-CD40 antibody in the presence or absence of fucoidan. Fucoidan significantly reduced IgE production in PBMC without affecting cell proliferation and IFN-γ production. Fucoidan also inhibited immunoglobulin germline transcripts of B cells in PBMC, and decreased the number of IgE-secreting cells. The inhibitory effects of fucoidan were similarly observed for both PBMC from patients with AD and those with healthy donors. Our findings indicate that fucoidan suppresses IgE induction by inhibiting immunoglobulin class-switching to IgE in human B cells, even after the onset of AD.

CD40 ligation during dendritic cell maturation reduces cell death and prevents interleukin-10-induced regression to macrophage-like monocytes

Dendritic cells (DCs) have become popular candidates in cancer vaccination because of their crucial role in inducing T-cell responses. However, clinical studies greatly differ in their protocols for generating DCs and the efficacy in treating established tumors needs to be improved. We systematically analyzed DCs maturated by five different protocols for surface markers, the alloproliferative T-cell response, the DC survival after cytokine deprivation, the stability of surface markers under the influence of interleukin-10 (IL-10) and the DC cytokine secretion pattern. Monocyte-derived DCs were maturated by CD40-ligand (CD40-L), unmethylated cytosine-guanosine dinucleotides-oligodinucleotides (CpG-ODN), an inflammatory cytokine cocktail (ICC), a combination of ICC and CD40-L, or ICC, CD40-L and CpG-ODN. A high co-expression of DC maturation and costimulation markers was found after treatment with ICC plus CD40-L (69.3 +/- 9.6% CD83/CD80 double positive staining) and correlated with a significantly increased cell survival, a high expression of the antiapoptotic factor bcl-(XL), a stable CD83(high)/CD14(low) expression under the influence of IL-10, and a strong alloproliferative T-cell response. In conclusion, our data support the use of maturation protocols containing ICC plus CD40-L in order to generate highly mature, phenotypically stable, cell-death resistant, and T-cell stimulatory DCs for clinical application in cancer patients.

Increased expression of CC chemokine ligand 18 in extrinsic atopic dermatitis patients

BACKGROUND

Although most patients with atopic dermatitis (AD) show high total and allergen-specific serum immunoglobulin E (IgE) levels, a small subgroup of AD patients have normal total IgE levels and negative serum allergen-specific IgE. This subgroup has been termed 'intrinsic' AD (IAD) as a counterpart to 'extrinsic' AD (EAD). However, the difference of chemokines between IAD and EAD has not yet been evaluated.

OBJECTIVE

We investigated the expression of CC chemokine ligand (CCL) 17, CCL22, and CCL18 in patients with IAD and EAD, which are known to be highly expressed in AD patients.

METHODS

We assessed the protein levels of these chemokines in peripheral blood mononuclear cells (PBMCs), sera and lesional skins. We also evaluated CCL18 mRNA levels in monocytes, Langerhans cell (LC)-like dendritic cells (DCs) and inflammatory dendritic epidermal cell (IDEC)-like DCs from both types of AD patients.

RESULTS

There were no significant differences in CCL17 and CCL22 expression in PBMCs, sera and lesional skins of patients with IAD and EAD. CCL18 expression did not differ in PBMCs, sera and LC-like DCs from the two subgroups, but strong CCL18 expression was observed in lesional skins and IDEC-like DCs in patients with EAD. Lastly, serum CCL18 levels significantly decreased after immunotherapy.

CONCLUSION

This study suggests that the chemokine micromilieu, especially the level of CCL18, is different between EAD and IAD patients. High FcepsilonRI surface-expressing DCs, such as IDEC, were the major source of CCL18, and produced a prominent CCL18 microenvironment in EAD patients compared with IAD patients.

[Omalizumab as a therapeutic option in atopic eczema. Current evidence and potential benefit]

The monoclonal anti-IgE antibody omalizumab is currently approved for the treatment of severe asthma. Randomized controlled trials for the indication atopic eczema have not yet been performed. This paper summarizes the current evidence on the effectiveness of omalizumab in atopic eczema. Using a systematic electronic search strategy, we identified three case series. These suggest that a subgroup of patients with extrinsic atopic eczema but only moderately elevated IgE levels might benefit most from omalizumab treatment. A randomized controlled trial should be performed to clarify the potential benefit of omalizumab for patients with atopic eczema. Additionally, such a study might help us to better understand the role of IgE in the pathogenesis of atopic eczema.

New developments in FcepsilonRI regulation, function and inhibition

The high-affinity Fc receptor for IgE (FcepsilonRI), a multimeric immune receptor, is a crucial structure for IgE-mediated allergic reactions. In recent years, advances have been made in several important areas of the study of FcepsilonRI. The first area relates to FcepsilonRI-mediated biological responses that are antigen independent. The second area encompasses the biological relevance of the distinct signalling pathways that are activated by FcepsilonRI; and the third area relates to the accumulated evidence for the tight control of FcepsilonRI signalling through a broad array of inhibitory mechanisms, which are being developed into promising therapeutic approaches.

IL-16 serum level in children with atopic dermatitis

IL-16 is a natural ligand of CD4 molecules and induces chemotaxis in CD4-expressing cells. It amplifies the inflammatory reaction by stimulating cytokine production in monocytes and activating T-cells. There is evidence that IL-16 plays a role in the pathogenesis of atopic dermatitis, and increased serum levels of IL-16 have been detected in allergic diseases. However, few data are available on IL-16 serum levels in atopic dermatitis. The aim of our study is to measure IL-16 serum levels in childhood atopic dermatitis before and after treatment and to evaluate a possible correlation between IL-16 serum levels and disease severity. IL-16 serum levels were measured by an ELISA approach in 34 children (19 males and 15 females; mean age 6.8 years) with moderate to severe atopic dermatitis, at their first visit and after 3 months of treatment, and in 10 non-atopic healthy controls of the same age group. The severity of atopic dermatitis was measured by SCORAD index. IL-16 serum levels were significantly higher in patients affected by atopic dermatitis than in controls before and after treatment with tacrolimus ointment. No clear correlation was found between IL-16 serum levels and atopic dermatitis severity. IL-16 serum levels are increased in atopic dermatitis but do not seem to correlate with disease severity.

Who is really in control of skin immunity underphysiologicalcircumstances - lymphocytes, dendritic cells or keratinocytes?

Our views of the skin immunity theatre are undergoing constant change. These not only reflect paradigm shifts in general immunology and skin biology, but also have profound clinical implications, which call for strategic changes in dermatological therapy. Nowhere can this be witnessed at a greater level of instructiveness and fascination than when addressing the question posed by this new Controversies feature. Thus, after a very long period of dominance by T cells and Langerhans cells as 'lead actors' on the skin immunity stage, the lowly keratinocyte has recently made an astounding theatrical appearance as a key protagonist of the innate skin immunity system, which may control even acquired skin immune responses. Further enhancing dramatic complexity and tension, the mast cell has entered as an additional actor claiming centre stage, and the epidermal Langerhans cell has slipped in a surprise appearance as the chief agent of immunotolerance. May you, esteemed reader, enjoy the spectacle offered here by selected immunodermatology authorities who double as 'stage managers' pushing their respective favourite actors into the limelight. You get everything you may expect from a good performance - complete with the impresario's overture that lures you into the theatre and sets the stage, competing divas, recently discovered new talents and even the critic's digest while the performance is still ongoing. By the time the curtain drops, you will have reached your own, independent conclusions on how to answer the title question of this play - at least for the time being...

A canine model of cutaneous late-phase reactions: prednisolone inhibition of cellular and cytokine responses

Immunoglobulin E (IgE)-mediated late-phase reactions can be induced in atopic humans by intradermal injection of relevant allergens or anti-IgE antibodies. The histology of these reactions resembles that of naturally occurring atopic dermatitis. Strikingly similar responses can be induced in dogs, suggesting that a canine model could prove valuable for preclinical investigation of drugs targeting late-phase reactions. This study was designed to characterize the cellular, cytokine and chemokine responses after intradermal anti-IgE injection in untreated and prednisolone-treated dogs. Normal beagles were untreated or treated with prednisolone before intradermal injection of polyclonal rabbit anti-canine IgE or normal rabbit IgG. Biopsies were taken before injection and 6, 24 and 48 hr after injection. Samples were evaluated by histological and immunohistochemical staining, as well as by real-time quantitative polymerase chain reaction analysis. Dermal eosinophil and neutrophil numbers increased dramatically within 6 hr after injection of rabbit anti-canine IgE, and remained moderately elevated at 48 hr. The numbers of CD1c(+) and CD3(+) mononuclear cells were also increased at 6 hr. The real-time quantitative polymerase chain reaction demonstrated marked increases in mRNA expression for interleukin-13 (IL-13), CCL2, CCL5 and CCL17. Levels of mRNA for IL-2, IL-4, IL-6 and IFN-gamma did not change within the limits of detection. Prednisolone administration suppressed the influx of neutrophils, eosinophils, CD1c(+) and CD3(+) cells, as well as expression of IL-13, CCL2, CCL5 and CCL17. These data document the cytokine and chemokine responses to anti-IgE injection in canine skin, and they demonstrate the ability of the model to characterize the anti-inflammatory effects of a known therapeutic agent.

The role of dendritic cell subtypes in the pathophysiology of atopic dermatitis

BACKGROUND

Atopic dermatitis (AD) is an inflammatory, immunologically mediated skin disease characterized by a T helper type 2 cell-predominant phenotype initially with additional acquisition of T helper type 1 cell phenotype during the chronic eczematous phase. Compelling evidence presented here suggests that two types of dendritic cells (DC), myeloid DC (mDC) and plasmacytoid DC (pDC), are important in the pathogenesis of AD.

METHODS

We reviewed the current literature and summarized key information about the role of mDC and pDC in the pathogenesis of AD.

RESULTS

Langerhans cells and inflammatory dendritic epidermal cells, which bear the high-affinity receptor for immunoglobulin E on their cell surface, are hypothesized to contribute to the pathogenesis of AD. pDC, Which play an important role in the defence against viral infections, have also been shown to express high-affinity receptor for immunoglobulin E.

CONCLUSION

Immunoglobulin E receptor-bearing mDC and pDC subtypes in the blood and the skin of patients with AD are of critical immunologic importance in the complex pathophysiologic network of AD. Targeting mDC and pDC subtypes may lead to effective new therapies for the management of AD.

Fc receptors and their role in immune regulation and autoimmunity

The activation threshold of cells in the immune system is often tuned by cell surface molecules. The Fc receptors expressed on various hematopoietic cells constitute critical elements for activating or downmodulating immune responses and combines humoral and cell-mediated immunity. Thus, Fc receptors are the intelligent sensors of the immune status in the individual. However, impaired regulation by Fc receptors will lead to unresponsiveness or hyperreactivity to foreign as well as self-antigens. Murine models for autoimmune disease indicate the indispensable roles of the inhibitory Fc receptor in the suppression of such disorders, whereas activating-type FcRs are crucial for the onset and exacerbation of the disease. The development of many autoimmune diseases in humans may be caused by impairment of the human Fc receptor regulatory system. This review is aimed at providing a current overview of the mechanism of Fc receptor-based immune regulation and the possible scenario of how autoimmune disease might result from their dysfunction.

Modulation of Dendritic Cell Maturation and Function by B Lymphocytes

Investigating the signals that regulate the function of dendritic cells (DC), the sentinels of the immune system, is critical to understanding the role of DC in the regulation of immune responses. Accumulating lines of evidence indicate that in addition to innate stimuli and T cell-derived signals, B lymphocytes exert a profound regulatory effect in vitro and in vivo on the Ag-presenting function of DC. The identification of B cells as a cellular source of cytokines, chemokines, and autoantibodies that are critically involved in the process of maturation, migration, and function of DC provides a rationale for immunotherapeutic intervention of autoimmune and inflammatory conditions by targeting B cells. Conversely, efficient cross-presentation of Ags by DC pulsed with immune complexes provides an alternative approach in the immunotherapy of cancer and infectious diseases.

Immunoglobulin E-bearing antigen-presenting cells in atopic dermatitis

Human antigen-presenting cells (APCs) bind monomeric immunoglobulin E (IgE) via the high-affinity IgE receptor, Fc epsilon RI. Surface expression of this trimeric structure is strongly associated with the atopic status of the donors, and maximal levels are observed on Langerhans cells (LC) and inflammatory dendritic epidermal cells (IDEC) in atopic dermatitis (AD). Although intracellular expression of the Fc epsilon RI alpha-chain is induced by interleukin-4 (IL-4), the upregulation of surface levels on dendritic cells (DC) from atopics is due to enhanced expression of the Fc epsilon RI gamma-chain and stabilization by binding of its ligand IgE. A characteristic function of Fc epsilon RI-bearing APCs is the specific uptake and processing of IgE-bound allergens, which is followed by T-cell stimulation. In AD, DC-mediated presentation of aeroallergens penetrating the epidermis is thought to induce an IgE-mediated, delayed-type hypersensitivity reaction. In addition, different Fc epsilon RI-bearing APC subsets in AD skin might regulate inflammatory processes through the production of Th1/Th2-polarizing signals, proinflammatory cytokines, chemokines, and factors that are involved in the induction of tolerance.

The mode of topical immunomodulators in the immunological network of atopic dermatitis

For a long time, therapeutic strategies of atopic dermatitis (AD) have been dominated by the application of local or systemic steroids or other immunosuppressive agents, which have been limited by their potential for unwanted local or systemic side effects. Recently, the use of a new generation of topical nonsteroidal, immunomodulatory drugs has revolutionized the therapeutic options of this often recalcitrant allergic-inflammatory skin disease. Research work has focused on the identification of the exact mode of action and the immune specificities of the so-called 'topical immunomodulators' (TIMs) such as tacrolimus and pimecrolimus in AD. In addition to the previous findings about the mode of action of TIMs on T cells, other target cells of TIMs such as keratinocytes, mast cells, eosinophils and dendritic cells have been identified recently as potential therapeutic targets. In this overview, we provide a research update about the anti-inflammatory and anti-allergic properties of TIMs on effector cells of AD that may be involved in the complex pathophysiology of AD.

The maturation-dependent production of interleukin-16 is impaired in monocyte-derived dendritic cells from atopic dermatitis patients but is restored by inflammatory cytokines TNF-alpha and IL-1beta

BACKGROUND

Maturation of dendritic cells (DCs) influences important DC functions such as production of cytokines. Recently, DCs were identified as a source of interleukin-16 (IL-16), a chemotactic factor for DCs themselves, CD4+ T cells, and eosinophils. There is evidence that DC-derived IL-16 may contribute to the pathogenesis of atopic dermatitis (AD).

OBJECTIVE

To investigate the production of IL-16 during differentiation of monocytes into DCs in healthy individuals and patients with AD.

METHODS

IL-16 production was investigated by quantitative real-time RT-PCR, intracellular cytokine staining, immunoblotting, and ELISA.

RESULTS

DCs generated from peripheral monocytes by 5-day culture in the presence of IL-4 and granulocyte/macrophage colony-stimulating factor acquired the capability to synthesize, store, and secrete IL-16. Storage and release of IL-16 was further enhanced during final DC maturation induced by additional 3-day culture with tumor necrosis factor-alpha (TNF-alpha) and monocyte-conditioned medium. Maturation, as determined by up-regulation of CD83 and CD86 surface expression, and production of IL-16, but not production of IL-10 and IL-12p40 was impaired in day 8 DCs derived from AD patients compared to those from healthy donors. Stimulation of day 8 DCs from AD patients with TNF-alpha and IL-1beta enhanced the expression of CD83 and CD86 and restored the production of IL-16.

CONCLUSIONS

Signals involved in the activation and maturation of DCs enhance their capacity to produce IL-16. Functional abnormalities present in patients with AD at the monocyte level may account for impaired maturation and IL-16 production of monocyte-derived DCs.

Transforming Growth Factor-β1 Regulates the Expression of the High-Affinity Receptor for IgE on CD34+ Stem Cell-Derived CD1a+ Dendritic Cells In Vitro

It has been reported that monocytes, Langerhans cells (LC) and other dendritic cells (DC) express the high-affinity receptor for IgE (FcepsilonRI) in patients with atopic diseases. These cells may be instrumental in the control of the immune response and the allergic inflammation. In this context, transforming growth factor beta 1 (TGF-beta1) has been highlighted as a key cytokine involved in the mechanisms aimed to orchestrate tolerance and has been suggested as a candidate gene in atopic diseases. In this report, we investigate the putative role of TGF-beta1 in the regulation of FcepsilonRI on cord blood CD34+ stem cell-derived CD1a+ DC (CD34-derived CD1a+ DC). Kinetic experiments show that FcepsilonRI spontaneously appears on the surface of CD1a+ DC, but decreases when exogenous TGF-beta1 is added at high doses (10 ng per mL) or when endogenous TGF-beta1 is neutralized in the culture conditions. In contrast, low-dose TGF-beta1 (0.5 ng per mL) stabilizes surface FcepsilonRI expression on DC. Increasing TGF-beta1 concentrations leads to the generation of LC-like DC showing an augmentation in stimulatory capacity towards allogeneic T cells. In view of these data, a picture emerges that FcepsilonRI+ on DC is finely modified by the TGF-beta1 concentration in the microenvironment and could be of primary relevance in the context of atopic diseases.

Differential expression and function of IgA receptors (CD89 and CD71) during maturation of dendritic cells

Dendritic cells (DC) are the most efficient antigen-presenting cells residing in mainly peripheral tissues. Antigen uptake by DC is particularly efficient, being mediated by various receptors such as lectin, scavenger receptors, and Fc receptors (FcRs). Immunoglobulin A (IgA) is part of the first-line immune barrier in mucosae, where DC are numerous. A member of the FcR family, FcalphaRI, is expressed on interstitial DC. We report here that monocyte-derived DC (Mo-DC) express another IgA receptor (IgA-R), the transferrin receptor (TfR), even in the absence of DC proliferation in vitro. Upon incubation with inflammatory cytokines such as tumor necrosis factor alpha and interleukin (IL)-1beta or maturating agents (lipopolysaccharide, CD40 ligand), FcalphaRI and TfR expression on Mo-DC was specifically up-regulated, whereas FcgammaRs and FcepsilonRI expression was down-regulated. Both IgA-Rs were functional, being able to mediate endocytosis by immature and activated Mo-DC. Although FcalphaRI internalized IgA complexes on both types of DC, TfR was only able to mediate IgA complex internalization by immature cells. Cross-linking of FcalphaRI but not of TfR resulted in up-regulation of major histocompatibility complex (MHC) class II/CD86 expression and secretion of IL-10 and IL-12 by immature Mo-DC. Moreover, in activated Mo-DC, cross-linking of FcalphaRI could up-regulated MHC class II/CD86 and triggered IL-10 secretion. Our findings led us to propose that FcalphaRI expressed by interstitial-type DC could play a critical role to sample IgA-recognized antigens and also during DC activation.

Why are dendritic cells important in allergic diseases of the respiratory tract?

Increasing evidence points to the role of antigen-presenting dendritic cells (DC) in regulating adaptive immune responses. DC are especially sensitive to signals derived from microbes, allergens, and the airway tissue microenvironment, can polarize naïve T-cells into either Th1 or Th2 effector cells, and are increasingly recognized as having a central role in the establishment of T-cell memory and tolerance to inhaled antigens. DC form a closely meshed network within the respiratory mucosa and are rapidly recruited from the circulation in response to a variety of proinflammatory stimuli. Studies using animal models have highlighted the role of DC in both initiation and maintenance of allergic airway inflammation. Increased numbers of airway mucosal DC are found in both allergic rhinitis and asthma, and an increasing number of investigators have highlighted important functional differences between DC from atopic and normal individuals. This article reviews recent information on the involvement of DC in the pathogenesis of allergic airway disease and the means by which DC could be exploited as targets for therapy in asthma and allergic rhinitis.

Vaccinia virus pathogenicity in atopic dermatitis is caused by allergen-induced immune response that prevents the antiviral cellular and humoral immunity

Atopic dermatitis (AD) serves as a contraindication for the immunization of AD patients with a live vaccinia virus (VV) vaccine. The antiallergen IgE interacts with the Fc receptors (FcepsilonRI) on dendritic cell (DC) membranes and with allergen molecules. The immunological events that lead to AD disease, the activation of the T-helper 2 (Th2) immune response, the synthesis of the cytokines IL-4, IL-5, IL-13, and the inhibition of the T-helper 1 (Th1) damage the capacity of the host to develop anti-VV cytotoxic cells (CTLs). In the presence of Th2-derived cytokine IL-4 in the AD skin and the synthesis of VV proteins that interfere recruitment of DCs by host cytokines, the VV can cause a generalized infection. Conceptually, new VV recombinants may be needed for human immunization. Such VV recombinants should lack the genes that interfere with the host immune system and express a mutated human IL-4 cytokine gene that will prevent negative regulatory mechanisms. Such improved VV recombinants may be used to express genes from pathogenic viruses.

The role of antigen presenting cells at distinct anatomic sites: they accelerate and they slow down allergies

It has been repeatedly demonstrated that allergic reactions are driven by the continuous flow of antigen uptake and presentation processes, which are perpetuated mainly by dendritic cells (DC). The ability of allergens to cause allergic inflammation is contingent upon the presence of an immunological milieu and microenvironment that either privileges Th2 responses or prohibits these reactions by the induction of contraregulatory anti-inflammatory activities of the immune system. In the light of recent developments it appears that DC have to manage two opposing tasks: on the one hand they can favor pro-inflammatory reactions and actively induce a T-cell response, yet on the other hand they serve an important function as 'silencers' in the immune system by sending out anti-inflammatory, tolerance inducing signals. This unique capacity of DC has opened several exciting possibilities for a role of DC in both - accelerating and slowing down allergic reactions. It is therefore a challenge to understand in which way DC subtypes located at distinct anatomic sites with frequent allergen exposure, such as the skin, the nasal mucosa, the respiratory tree or the mucosa of the intestinal tract can have an impact on mechanisms involved in tolerance induction or effective immunity.

Association of allergic contact dermatitis with a promoter polymorphism in the IL16 gene

BACKGROUND

There is evidence that IL-16, a cytokine that induces chemotactic responses in CD4(+) T cells, eosinophils, and dendritic cells, plays an important role during different types of cutaneous inflammatory responses, including allergic contact dermatitis (ACD) and atopic dermatitis (AD).

OBJECTIVES

We sought to test for association between a promoter polymorphism in the IL16 gene (T to C transition at position -295) and ACD and AD, respectively.

METHODS

IL16 -295 genotypes were determined in samples from 2 separate case-control studies with white individuals. The first study included healthy individuals (n = 310) and patients with ACD (n = 86). These patients were polysensitized as defined by a contact sensitization to para-substituted aryl compounds and at least one other structurally unrelated allergen. The second study comprised healthy subjects (n = 214) and patients with AD (n = 94).

RESULTS

IL16 -295 genotypes were differently distributed among polysensitized and healthy control subjects (P =.0021). In particular, the IL16 -295*C/C genotype was overrepresented among polysensitized individuals (7.0% vs 1.0% in the control group; odds ratio, 7.68; 95% CI, 1.59-48.12). In contrast, there was no evidence for an association between the IL16 -295 polymorphism and AD.

CONCLUSION

The IL16 -295 promoter polymorphism might influence susceptibility to contact allergy.

FcepsilonRI-FcgammaRII coaggregation inhibits IL-16 production from human Langerhans-like dendritic cells

Langerhans-like dendritic cells (LLDC) express the high-affinity IgE receptor FcepsilonRI form that lacks the beta-chain, and may play an important role in allergic inflammation via production of IL-16. Secretion of mediators by human mast cells and basophils is mediated through FcepsilonRI and is decreased by coaggregating these receptors to the low-affinity IgG receptor, FcgammaRII. We used a recently described human Ig fusion protein (GE2), which is composed of key portions of the human gamma1 and the human epsilon heavy chains, to investigate its ability to inhibit IL-16 production from FcepsilonRI-positive Langerhans-like dendritic cells through coaggregation of FcgammaRII and FcepsilonRI. Unstimulated LLDC-derived from CD14-positive monocytes from atopic donors were shown to express FcgammaRII, an ITIM-containing receptor, but not FcepsilonRI or FcgammaRIII which are activating (ITAM) receptors. When passively sensitized with antigen-specific, human IgE and then challenged with antigen, LLDC were stimulated to produce IL-16. However, when FcepsilonRI and FcgammaRII were coaggregated with GE2, IL-16 production was significantly inhibited. Exposure of LLDCs to GE2 alone did not induce IL-16 production. Our results further extend our studies demonstrating the ability of GE2 to inhibit FcepsilonRI-mediated responses through coaggregation with FcgammaRIIB and at the same time show that human LDCC can be modulated in a fashion similar to mast cells and basophils.

Airway dendritic cells: co-ordinators of immunological homeostasis and immunity in the respiratory tract

The large quantities and complex mixtures of antigens encountered daily at airway mucosal and alveolar surfaces pose a major challenge to maintenance of immunological homeostasis in the respiratory tract. Amongst this myriad of antigens, the immune system must discriminate between innocuous components that can be tolerated by the host and potentially life-threatening pathogens that require a rapid immune response. Dendritic cells (DC) represent the principal cell type at these sites capable of processing antigens and delivering signals that initiate tolerogenic or immunogenic immune responses. This review will discuss the role of DC at the "front-line" of immune surveillance and homeostasis within the respiratory tract and their role in the pathogenesis of respiratory disease.

Unraveling the mission of FcepsilonRI on antigen-presenting cells

A decade ago, the discovery of the high-affinity receptor for IgE (FcepsilonRI) on epidermal Langerhans cells documented the end of the dogma that FcepsilonRI is only expressed on effector cells of anaphylaxis. Since then, the functional significance of this receptor on antigen-presenting cells (APCs) has been an area of intense research work. Scientists have focused on a better understanding of the molecular structure, regulation, and role of FcepsilonRI on APCs in the human immune system. Insights into the cellular events linked to the activation of APCs on ligation of FcepsilonRI by IgE and allergens might provide the basis for new aspects in the pathophysiology of allergic diseases and the design of future diagnostic and therapeutic strategies. This review is dedicated to the 10th anniversary of the discovery of FcepsilonRI on APCs and describes the numerous areas of research in this field.

Agonists of peroxisome proliferator-activated receptor gamma inhibit cell growth in malignant melanoma

Peroxisome proliferator-activated receptor gamma is a member of the nuclear receptor superfamily involved in adipocyte differentiation and glucose homeostasis. There is evidence that peroxisome proliferator-activated receptor gamma may also act as a tumor suppressor. Here, we demonstrate expression of peroxisome proliferator-activated receptor gamma in benign melanocytic naevi, different variants of primary cutaneous melanomas, and melanoma metastases. Peroxisome proliferator-activated receptor gamma protein and peroxisome proliferator-activated receptor gamma1 mRNA were also detected in human melanoma cell lines. The peroxisome proliferator-activated receptor gamma specific agonists 15-deoxy-Delta12,14-prostaglandin J2, troglitazone, and rosiglitazone dose-dependently inhibited cell proliferation in four melanoma cell lines, whereas a specific agonist of peroxisome proliferator-activated receptor alpha had no such effect. At a concentration of 50 microM rosiglitazone, the most potent peroxisome proliferator-activated receptor gamma agonist tested suppressed cell growth by approximately 90%. Apoptosis could be induced in melanoma cell lines by incubation with tumor-necrosis-factor-related apoptosis-inducing ligand. In contrast, the growth inhibitory effect of peroxisome proliferator-activated receptor gamma activation was independent of apoptosis and seemed to occur primarily through induction of cell cycle arrest. Our data indicate that melanoma cell growth may be modulated through peroxisome proliferator-activated receptor gamma.

Circulating interleukin 16 (IL-16) in children with atopic/eczema dermatitis syndrome (AEDS): a novel serological marker of disease activity

BACKGROUND

Chemokines play a central role in atopic eczema/dermatitis syndrome (AEDS). Interleukin 16 (IL-16) has been described as a main cytokine involved in CD4+ cell recruitment during inflammation. Recently the influx of CD4+ lymphocytes has been related to the up-regulation of IL-16 in AEDS skin lesions. Circulating beta-chemokines (Eotaxin and RANTES) and IL-16 were investigated in children with AEDS to correlate their presence with the severity of the disease. We also measured serum levels of soluble CD30 (sCD30), a marker of Th2 immune responses related to AEDS disease activity.

METHODS

Serum levels of eotaxin, RANTES, IL-16 and sCD30 were measured by immunoenzymatic assay in paediatric patients with pure AEDS (pAEDS, n = 39); the severity of the disease was graded by SCORAD. Fifteen children with AEDS in presence of respiratory allergy (AEDS+A), 15 with allergic asthma (A) and 20 age-matched healthy donors were investigated as control groups.

RESULTS

When compared to normals, high amounts of Eotaxin and IL-16 were detected in sera of pAEDS (P = 0.002; P < 0.0001), AEDS+A (P = 0.02; P = 0.01) and A patients (P = 0.004; P = 0.03) with respect to normals. Serum levels of RANTES were also elevated in pAEDS patients, significantly higher than normals (P = 0.009), whereas no statistically significant differences could be detected between pAEDS and AEDS+A or A groups. IL-16 was progressively increased in the different stages of pAEDS, with a positive correlation between IL-16 and both SCORAD and sCD30 (P < 0.0001).

CONCLUSION

We suggest that IL-16 could serve as a useful marker of disease activity in childhood pAEDS.

Evidence for a role of Langerhans cell-derived IL-16 in atopic dermatitis

BACKGROUND

The factors controlling infiltration of inflammatory cells into atopic dermatitis (AD) lesions remain to be fully explored. Recently, epidermal cells in lesional AD were reported to contain increased messenger (m)RNA levels of IL-16, a cytokine that induces chemotactic responses in CD4(+)T cells, monocytes, and eosinophils.

OBJECTIVES

We sought to determine the expression of IL-16 in epidermal cells in normal skin and skin from AD lesions and to investigate whether Langerhans cell (LC)-derived IL-16 may contribute to the initiation of atopic eczema.

METHODS

The cutaneous expression of IL-16 was investigated by in situ hybridization and immunohistochemistry. Expression of IL-16 was also investigated in freshly isolated LCs and in keratinocytes by intracellular cytokine staining, quantitative real-time RT-PCR, and ELISA.

RESULTS

Low levels of IL-16 mRNA, but no stored IL-16 protein, were detected in keratinocytes and LCs isolated from normal skin. Synthesis, storage, and secretion of IL-16 could be induced in LCs, but not keratinocytes, by activation with phorbol ester and ionomycin. In normal skin (n = 10) neither keratinocytes nor LCs expressed IL-16. In contrast, IL-16 was contained in approximately 40% of CD1a(+)LCs in patients with active AD (n = 16). IL-16 expression in LCs in patients with AD correlated with the number of infiltrating CD4(+)cells (r =.72, P =.0017) and was completely downregulated parallel to the clinical response of AD lesions to topical treatment with FK506.

CONCLUSION

LC-derived IL-16 may participate in the recruitment and activation of inflammatory cells in AD.