Measurement of CD4+ and CD8+ T-Lymphocyte Cytokine Secretion and Gene Expression Changes in p-Phenylenediamine Allergic Patients and Tolerant Individuals

Inflammatory plasma signature of chronic hand eczema: Associations with aetiological and clinical subtypes

BACKGROUND

Chronic hand eczema (CHE) is a highly prevalent, heterogeneous, skin disease that encompasses different aetiological and clinical subtypes. Severe CHE without atopic dermatitis has been associated with systemic inflammation; yet it remains unknown if specific CHE subtypes leave distinct, systemic, molecular signatures.

OBJECTIVES

To characterize the inflammatory plasma signature of different aetiological and clinical CHE subtypes.

METHODS

We assessed expression levels of 266 inflammatory and cardiovascular disease risk plasma proteins as well as filaggrin gene mutation status in 51 well-characterized CHE patients without concomitant atopic dermatitis and 40 healthy controls. Plasma protein expression was compared between aetiological and clinical CHE subgroups and controls both overall and according to clinical CHE severity. Correlation analyses for biomarkers, clinical and self-reported variables were performed.

RESULTS

Very severe, chronic allergic contact dermatitis (ACD) on the hands was associated with a mixed Type 1/Type 2 systemic immune activation as compared with controls. Circulating levels of Type 1/Type 2 inflammatory biomarkers correlated positively with clinical disease severity among CHE patients with ACD. No biomarkers were found, that could discriminate between aetiological subtypes, for example, between ACD and irritant contact dermatitis. Hyperkeratotic CHE showed a distinct, non-atopic dermatitis-like, systemic footprint with upregulation of markers associated with Type 1 inflammation and tumour necrosis factor alpha, but not Type 2 inflammation. Increased levels of CCL19 and CXCL9/10 could discriminate hyperkeratotic CHE from both vesicular and chronic fissured CHE, whereas no difference was found between the latter two subtypes.

CONCLUSION

Profiling of systemic biomarkers showed potential for identifying certain CHE subtypes. Peripheral blood levels of inflammatory biomarkers were associated and correlated with the clinical disease severity of chronic ACD on the hands, underlining that this is a systemic disease. We question whether hyperkeratotic CHE should be classified as eczema.

Regulation of immune response genes in the skin of allergic and clinically tolerant individuals exposed to p-phenylenediamine

BACKGROUND

p-Phenylenediamine (PPD) is a potent contact allergen found in many hair colour products. However, not all individuals develop allergic contact dermatitis (ACD) although they are regularly exposed to PPD. It is unclear whether these asymptomatic individuals are true non-responders to PPD or whether they mount a response to PPD without showing any symptoms.

METHODS

Skin biopsies were collected from 11 asymptomatic hairdressers regularly exposed to PPD and from 10 individuals with known ACD on day 4 after patch testing with 1% PPD in petrolatum and petrolatum exclusively as control. RNA sequencing and confocal microscopy were performed.

RESULTS

T cell activation, inflammation and apoptosis pathways were up-regulated by PPD in both asymptomatic and allergic individuals. Compared to asymptomatic individuals with a negative patch test, individuals with a strong reaction to PPD strongly up-regulated both pro- and anti-inflammatory cytokines genes. Interestingly, PPD treatment induced significant up-regulation of several genes for chemokines, classical type 2 dendritic cell markers and regulatory T cell markers in both asymptomatic and allergic individuals. In addition, apoptosis signalling pathway was activated in both non-responders and allergic individuals.

CONCLUSION

This study demonstrates that there are no true non-responders to PPD but that the immune response elicited by PPD differs between individuals and can lead to either tolerance, subclinical inflammation or allergy.

A blinded in vitro analysis of the intrinsic immunogenicity of hepatotoxic drugs: implications for preclinical risk assessment

In vitro preclinical drug-induced liver injury (DILI) risk assessment relies largely on the use of hepatocytes to measure drug-specific changes in cell function or viability. Unfortunately, this does not provide indications toward the immunogenicity of drugs and/or the likelihood of idiosyncratic reactions in the clinic. This is because the molecular initiating event in immune DILI is an interaction of the drug-derived antigen with MHC proteins and the T-cell receptor. This study utilized immune cells from drug-naïve donors, recently established immune cell coculture systems and blinded compounds with and without DILI liabilities to determine whether these new methods offer an improvement over established assessment methods for the prediction of immune-mediated DILI. Ten blinded test compounds (6 with known DILI liabilities; 4 with lower DILI liabilities) and 5 training compounds, with known T-cell-mediated immune reactions in patients, were investigated. Naïve T-cells were activated with 4/5 of the training compounds (nitroso sulfamethoxazole, vancomycin, Bandrowski's base, and carbamazepine) and clones derived from the priming assays were activated with drug in a dose-dependent manner. The test compounds with DILI liabilities did not stimulate T-cell proliferative responses during dendritic cell-T-cell coculture; however, CD4+ clones displaying reactivity were detected toward 2 compounds (ciprofloxacin and erythromycin) with known liabilities. Drug-responsive T-cells were not detected with the compounds with lower DILI liabilities. This study provides compelling evidence that assessment of intrinsic drug immunogenicity, although complex, can provide valuable information regarding immune liabilities of some compounds prior to clinical studies or when immune reactions are observed in patients.

Association of p-phenylenediamine exposure with alterations of pulmonary function, pruritus and health-related quality of life in hair dye factory workers: a cross-sectional study

P-Phenylenediamine (PPD) is a common component of hair dye, which can cause skin contact allergy and asthma with impaired pulmonary function. However, the adverse effects of occupational exposure to different dose PPD was rarely mentioned. We recruited 124 workers from a hair dye factory to explore the association of occupational PPD exposure on pulmonary function, pruritus and health related quality of life (HRQL). We categorized exposure to PPD into 3 levels: lower exposure group (< 0.00001 mg/m³); middle exposure group (0.00001-0.00033 mg/m³); higher exposure group (0.00033-0.047 mg/m³). The HRQL and subjective pruritus of the workers were assessed by the short form 36 health survey (SF-36) and Visual analogue scale (VAS) of pruritus, respectively. In the high PPD-exposed group, the percentage of FEV1 (FEV1%) was lower in higher exposure group compared with lower exposure group. The FEV1/FVC was also lower in comparison to the higher exposure and middle exposure groups (p < 0.05). PPD levels were negatively correlated with vitality and mental health (p < 0.01). The structural equation model showed the positive effects of PPD on VAS level (β = 0.213, p < 0.001), and indicated partly negtive effects of PPD on total score of SF-36 (β = - 0.465, p = 0.002), respectively. Our results indicate that occupational exposure to PPD might be associated with pulmonary function impairment, poor HRQL, and subjective pruritus of the workers.

In Vitro Monitoring of Human T Cell Responses to Skin Sensitizing Chemicals-A Systematic Review

Background: Chemical allergies are T cell-mediated diseases that often manifest in the skin as allergic contact dermatitis (ACD). To prevent ACD on a public health scale and avoid elicitation reactions at the individual patient level, predictive and diagnostic tests, respectively, are indispensable. Currently, there is no validated in vitro T cell assay available. The main bottlenecks concern the inefficient generation of T cell epitopes and the detection of rare antigen-specific T cells. Methods: Here, we systematically review original experimental research papers describing T cell activation to chemical skin sensitizers. We focus our search on studies published in the PubMed and Scopus databases on non-metallic allergens in the last 20 years. Results: We identified 37 papers, among them 32 (86%) describing antigen-specific human T cell activation to 31 different chemical allergens. The remaining studies measured the general effects of chemical allergens on T cell function (five studies, 14%). Most antigen-specific studies used peripheral blood mononuclear cells (PBMC) as antigen-presenting cells (APC, 75%) and interrogated the blood T cell pool (91%). Depending on the individual chemical properties, T cell epitopes were generated either by direct administration into the culture medium (72%), separate modification of autologous APC (29%) or by use of hapten-modified model proteins (13%). Read-outs were mainly based on proliferation (91%), often combined with cytokine secretion (53%). The analysis of T cell clones offers additional opportunities to elucidate the mechanisms of epitope formation and cross-reactivity (13%). The best researched allergen was p-phenylenediamine (PPD, 12 studies, 38%). For this and some other allergens, stronger immune responses were observed in some allergic patients (15/31 chemicals, 48%), illustrating the in vivo relevance of the identified T cells while detection limits remain challenging in many cases. Interpretation: Our results illustrate current hardships and possible solutions to monitoring T cell responses to individual chemical skin sensitizers. The provided data can guide the further development of T cell assays to unfold their full predictive and diagnostic potential, including cross-reactivity assessments.

SLAMF7 and IL-6R define distinct cytotoxic versus helper memory CD8+ T cells

The prevailing ‘division of labor’ concept in cellular immunity is that CD8⁺ T cells primarily utilize cytotoxic functions to kill target cells, while CD4⁺ T cells exert helper/inducer functions. Multiple subsets of CD4⁺ memory T cells have been characterized by distinct chemokine receptor expression. Here, we demonstrate that analogous CD8⁺ memory T-cell subsets exist, characterized by identical chemokine receptor expression signatures and controlled by similar generic programs. Among them, Tc2, Tc17 and Tc22 cells, in contrast to Tc1 and Tc17 + 1 cells, express IL-6R but not SLAMF7, completely lack cytotoxicity and instead display helper functions including CD40L expression. CD8⁺ helper T cells exhibit a unique TCR repertoire, express genes related to skin resident memory T cells (T_RM) and are altered in the inflammatory skin disease psoriasis. Our findings reveal that the conventional view of CD4⁺ and CD8⁺ T cell capabilities and functions in human health and disease needs to be revised.

We classically consider the T cell compartment divided into cytotoxic CD8⁺ T cells and multiple, different helper CD4⁺ T cell subsets. Here the authors demonstrate that distinct memory CD8⁺ T cell subsets phenotypically inhabit CD4⁺ T cell like populations including some with helper-like characteristics.

Comorbidities and the impact of atopic dermatitis

OBJECTIVE

Atopic dermatitis (AD) is a chronic pruritic inflammatory skin disease with substantial patient and population burdens. A number of comorbid health problems occur in patients with AD, aside from the cutaneous signs and symptoms. This review summarizes recent developments in the burden and comorbidities of AD.

DATA SOURCES

Literature review.

STUDY SELECTIONS

Nonsystematic.

RESULTS

Different aspects of AD, such as chronic pruritus, psychosocial distress, and inflammation, can lead to anxiety, depression, or suicidality. Atopic dermatitis is associated with and may predispose to higher risk of other atopic disorders, including asthma, hay fever, food allergy, and eosinophilic esophagitis. Persons with AD appear to be at higher risk for infectious and cardiovascular risk.

CONCLUSION

Atopic dermatitis is associated with substantial burden and comorbidities. Identifying AD comorbidities is essential for proper disease management and improving overall patient outcomes.

Gentiana scabra Bunge roots alleviates skin lesions of contact dermatitis in mice

ETHNOPHARMACOLOGICAL RELEVANCE

The roots and rhizomes of Gentiana scabra Bunge in the family Gentianaceae comprise a major herbal medicine for skin diseases caused by wind-heat or dampness-heat in China, Japan and Korea. This treatment can clear away heat and dry dampness and purge fire from the liver and gallbladder.

AIM OF THE STUDY

This study was designed to investigate the therapeutic potential and anti-inflammatory effects of G. scabra, roots and rhizomes.

MATERIALS AND METHODS

Thin layer chromatography (TLC) and high performance liquid chromatography (HPLC) revealed the presence of gentiopicrin in the roots and rhizomes of G. scabra. We then investigated the effects of ethanol extract of G. scabra, roots and rhizomes (EEGS) on skin lesions and thickness, erythema and melanin index, histopathological abnormalities, and cytokine and chemokine production in mice with contact dermatitis (CD) induced by 1-fluoro-2,4-dinitrofluorobenzene (DNFB). Moreover, the effects of EEGS on body weights and spleen body weight ratio were evaluated.

RESULTS

Topical application of EEGS alleviated skin lesions such as surface roughness, excoriations and scabs on the skin of CD mice, as well as prevented skin enlargement, and lowered the erythema and melanin index. In addition, EEGS prevented hyperkeratosis, epidermal hyperplasia and immune cell infiltration, and inhibited TNF-α, IFN-γ, IL-6 and MCP-1 production in inflamed tissues. EEGS did not affect changes in body weights and spleen body weight ratio in contrast to dexamethasone.

CONCLUSIONS

These data indicate that the roots and rhizomes of G. scabra can be used as anti-inflammatory agents for CD with relative safety and that its therapeutic mechanisms are related to regulation of pro-inflammatory cytokines such as TNF-α and IFN-γ.

Th9 Cells in Allergic Disease

PURPOSES OF REVIEW

Th9 cells are recognized as a novel subset of effector T helper cells that preferentially produce IL-9. Here, we provide a current update on the reports related to the function of Th9 cells in allergic inflammatory diseases.

RECENT FINDINGS

The effector Th9 cells differentiating from naïve T helper cells have recently been identified. Because of accumulating findings of Th9 cells in many inflammatory diseases, including allergic diseases, diverse functions of Th9 cells in regulating immune responses have been suggested. Related reports indicate multiple sources of IL-9 besides Th9 cells and their association with the pathogenesis of allergic rhinitis, asthma, atopic dermatitis, contact dermatitis, and food allergy. More recently, elements of the epigenetic landscape involving in the regulation of IL-9 by Th9 cells have been identified to be the potential target for allergic inflammation. This review provides the most recent information about Th9 cells and their contribution in airway allergic disease, skin, and food allergy.

The Role and Diagnosis of Allergic Contact Dermatitis in Patients with Atopic Dermatitis

Patients with atopic dermatitis (AD) have increased penetration of allergens, immune dysregulation (including shared cytokine pathways), and frequent use of emollients and topical medications, all of which may predispose toward developing allergic contact dermatitis (ACD). Recent systematic reviews have suggested that ACD is a significant clinical problem in both children and adults with AD. While this remains controversial, ACD remains an important comorbidity and potential exacerbant of AD in clinical practice. Common relevant allergens, include lanolin, neomycin, formaldehyde, sesquiterpene lactone mix, compositae mix, and fragrances that are commonly found in AD patients' personal care products. We herein review the clinical scenarios where patch testing is indicated in AD. In addition, we review the contraindications, preferred patch-testing series, pitfalls, and challenges determining the relevance of positive patch-test reactions in AD patients.

Hypersensitivity reactions due to black henna tattoos and their components: are the clinical pictures related to the immune pathomechanism?

Hypersensitivity to para-phenylenediamine (PPD) and related compounds induced by temporary black henna tattoos has become a serious health problem worldwide. Different patterns of sensitization with various clinical aspects are described in literature due to PPD associated to henna tattoo and these manifestations are likely correlated with the immunological and dermatological pathomechanisms involved. Henna is the Persian name of the plant Lawsonia inermis, Fam. Lythraceae. It is a woody shrub that grow in regions of North Africa, South Asia, India and Sri Lanka. Nowadays it is rather frequent to see temporary "tattoos" performed with henna. To make tattoos darker and long-lasting PPD has been associated to henna in tattoo drawings mixtures, so obtaining "black henna". In these years there has been a rise of contact sensitization to PPD and in medical literature an increased number of cases have been reported on temporary henna tattoo application. Here we review the various clinical patterns related to PPD and henna tattoo, to investigate the possible link between clinic-morphological pictures and the immunological response to PPD and henna. The literature underlines that different clinical manifestations are related to black henna containing PPD, and its derivative products may cause delayed-type as well as immediate-type reactions. Further studies are needed to investigate the relationship between clinical and morphological aspects of PPD contact dermatitis and the T cell subsets predominance.

TH9 cells in skin disorders

Interleukin 9 secreting T_H9 cells have been proposed as the latest addition to the family of T helper cell subsets. While a growing body of evidence from animal models points to important roles for these cells in allergic inflammation of the lung, autoinflammation of the gastrointestinal tract, and tumor immunity, their role in skin immunity and skin immunopathology remains poorly defined. Interestingly, studies of T helper cells from healthy humans suggest that T_H9 cells are predominantly skin-homing and skin-resident and that they are involved in protection against extracellular pathogens. Thus, T_H9 cells have entered the stage as potential mediators of cutaneous pathology. However, under which conditions and by which mechanisms these cells contribute to skin immunity and disease still has to be investigated. Here, we review our current understanding of T_H9 cells as skin-tropic T helper cells and their involvement in skin pathology. Further, we discuss open questions with regard to the intricate nature of interleukin 9 producing T helper cells.

In Vitro Priming of Naı̈ve T-cells with p-Phenylenediamine and Bandrowski's Base

p-Phenylenediamine (PPD) is a component of hair dye formulations that is associated with T-cell mediated allergic contact dermatitis. Antigen-specific T-cells from allergic contact dermatitis patients are activated with either PPD or the oxidation product, Bandrowski's base. In nonallergic individuals, T-cells that are activated by Bandrowski's base, but not by PPD, are readily detectable. The aim of the current study was to use an in vitro T-cell priming assay to assess the activation of memory and naı̈ve T-cells from healthy donors with PPD and Bandrowski's base, and to compare these responses to those observed from allergic patients. Both PPD and Bandrowski's base-responsive clones were generated from allergic patients. The majority of Bandrowski's base-responsive clones were CD4+ and displayed a lack of PPD reactivity. In contrast, CD4+ and CD8+ clones displaying PPD reactivity were detected. Approximately 25% of these displayed low levels of reactivity to Bandrowski's base. Clones from the allergic patients secreted a range of cytokines including IFN-γ, Il-13, and Il-22. In healthy donors, Bandrowski's base-specific T-cell proliferative responses and cytokine secretion were detected with both naı̈ve and memory T-cells. T-cell clones generated from the Bandrowski's base-responsive cultures responded to Bandrowski's base but not PPD. PPD-specific naı̈ve and memory T-cell responses were not detected from healthy donors. These data show that Bandrowski's base stimulates pre-existing memory T-cells isolated from healthy donors and primes naı̈ve T-cells when the chemical is bound to autologous dendritic cells. Priming naı̈ve T-cells against PPD failed, suggesting an important individual susceptibility factor is missing from the in vitro T-cell priming assay.

The relative values of CD8+CD25+Foxp3brigh Treg cells correlate with selected lung function parameters in asthma

The study aimed to detect CD8(+)CD25(+)FoxP3(brigh) Tregs and investigate their possible association with selected lung function values. CD8(+)CD25(+)FoxP3(brigh) Tregs were detected by flow cytometry in the peripheral blood of 25 patients with severe asthma (SA), 25 patients with mild-to-moderate asthma (MA), and 25 age-matched healthy donors (NC). The percentages of CD8(+)CD25(+)FoxP3(brigh) Tregs of the patients with severe (3.4 ± 4.55), and mild-to-moderate asthma (7.5 ± 8.15), were markedly lower than those of controls (12.1 ± 13.2). The mean forced expiratory volume in 1 s (FEV1) % predicted value in severe asthma subpopulation was significantly lower (67.05 ± 15.98%) when compared with that of mild-to-moderate asthma subgroup (87.71 ± 16.12%). Interestingly, the percentages of CD8(+)CD25(+)FoxP3(brigh) Tregs correlate with mean peak expiratory flow (PEF)% predicted values in severe (r = 0.7, P <0.01) and mild-to-moderate (r = 0.73, P <0.01) asthma. In contrast, this parameter was positively correlated with FEV1% predicted values in the severe asthmatics only (r = 0.71, P <0.01). In summary, this study establishes a link between the percentage of CD8(+)CD25(+)FoxP3(brigh) Tregs and selected lung function parameters, suggesting that this parameter has potential as a marker for inflammation and airflow obstruction.

Encapsulation of hydrophobic allergens into nanoparticles improves the in vitro immunological diagnosis of allergic contact dermatitis

The diagnosis of allergic contact dermatitis (ACD) relies on in vivo patch testing. In vitro immunological assays based on the characterization of circulating allergen-specific memory T cells represent a promising alternative to patch testing. However, their development is hampered by the technical challenge of assessing hydrophobic allergens in serum-based assays. In this study, we show that the encapsulation of fragrance mix 1 (FMI, a mixture of 8 hydrophobic allergens) into poly-ε-caprolactone nanoparticle (NP) vectors: (1) dramatically increases the solubilization of allergens in conventional cell culture media and (2) allows for a robust in vitro reactivation of allergen-specific T cells in large numbers of fragrance allergic patients. Therefore, the encapsulation of hydrophobic allergens into NP vectors opens new avenues to improve the in vitro immunobiological diagnosis of ACD.

FROM THE CLINICAL EDITOR

Allergic Contact Dermatitis (ACD) is a delayed-type hypersensivity reaction prevalent in many individuals. Currently, skin patch testing has been the mainstay for diagnosis clinically. In this study, the authors described an improvement to in vitro immunological assays measuring circulating allergen-specific memory T cells, using nanoparticle vectors. The positive data might provide an exciting alternative to current practice of patch-testing.

A laboratory test based on determination of cytokine profiles: a promising assay to identify exposition to contact allergens and predict the clinical outcome in occupational allergic contact dermatitis

Background

Para-phenylenediamine (PPD) is the main allergen causing adverse reactions to hair dyes and a frequent cause of occupational-related skin sensitization among hairdressers and beauticians. The immunologic mechanism of the disease relies on the production of inflammatory cytokines by allergen-specific T cells, while regulatory T cells are thought to down-modulate the allergic response. This study was aimed at investigating the expression of effector or regulatory cytokines in exposed subjects in order to verify whether different cytokine profiles might predict distinct clinical outcomes. Peripheral blood mononuclear cells (PBMC) from 21 subjects occupationally exposed or not (10) to PPD were kept in short term cultures in the presence of optimized concentrations of NiSO4 × 6H2O or PPD. The production of IFN-γ and IL-10 elicited by antigens were analyzed by the ELISpot assay.

Results

The presence of IFN-γ responses toward PPD was significantly correlated with a positive patch test (P = 0.002) and allergic symptoms, while IL10 responses were invariably found in PPD-exposed but clinically asymptomatic subjects with negative patch testing. We found concordance between the different cytokine profiles and patch test results. No false-positive results were found for the different cytokine profiles induced by PPD, resulting in 100% specificity. The sensitivity of the test was 87.5% (95% CI 65.9-100.0) with an overall test accuracy of 93.3%. Although larger prospective-retrospective studies are necessary to validate the predictive potential of the test, the negative and positive predicted values for PPD in this study were NPV = 87.5% and PPV = 100%, respectively.

Conclusions

These data indicate that distinct cytokine profiles are associated with different clinical manifestations. The test, which is based on a simple and rapid profiling of cytokine responses by T lymphocytes against allergens, has proven to be a promising laboratory tool, useful for both the identification of previous contact with allergens and the etiologic diagnosis of contact allergies as well as capable of predicting the clinical outcome (development of an allergic or tolerant response).

The lymphocyte transformation test in allergic contact dermatitis: New opportunities

Allergic contact dermatitis (ACD) is driven by the activation and proliferation of allergen-specific memory T-lymphocytes and is currently diagnosed by patch testing with a selected panel of chemical allergens. The lymphocyte transformation test (LTT) can be used to monitor ex vivo T-lymphocyte responses to antigens, including contact allergens. The LTT is not viewed as being an alternative to patch testing, but it does seek to reflect experimentally skin sensitization to specific chemicals. The LTT is based on stimulation in vitro of antigen-driven T-lymphocyte proliferation. That is, exposure in culture of primed memory T-lymphocytes to the relevant antigen delivered in an appropriate configuration will provoke a secondary response that reflects the acquisition of skin sensitization. The technical aspects of this test and the utility of the approach for investigation of immune responses to contact allergens in humans are reviewed here, with particular emphasis on further development and refinement of the protocol. An important potential application is that it may provide a basis for characterizing those aspects of T-lymphocyte responses to contact allergens that have the greatest influence on skin sensitizing potency and this will be considered in some detail.

IL-9 regulates allergen-specific Th1 responses in allergic contact dermatitis

The cytokine IL-9, derived primarily from T-helper 9 (Th9) lymphocytes, promotes expansion of the Th2 subset and is implicated in the mechanisms of allergic asthma. We hypothesize that IL-9 also has a role in human allergic contact dermatitis (ACD). To investigate this hypothesis, skin biopsy specimens of positive patch-test sites from non-atopic patients were assayed using quantitative PCR and immunohistochemistry. The cytokines IFN-γ, IL-4, IL-17A, IL-9, and PU.1, a Th9 associated transcription factor, were elevated when compared with paired normal skin. Immunohistochemistry on ACD skin biopsies identified PU.1+ CD3+ and PU.1+ CD4+ cells, consistent with Th9 lymphocytes, in the inflammatory infiltrate. Peripheral blood mononuclear cells from nickel-allergic patients, but not nonallergic controls, show significant IL-9 production in response to nickel. Blocking studies with mAbs to HLA-DR (but not HLA-A, -B, -C) or chloroquine significantly reduced this nickel-specific IL-9 production. In addition, blockade of IL-9 or IL-4 enhanced allergen-specific IFN-γ production. A contact hypersensitivity model using IL-9(-/-) mice shows enhanced Th1 lymphocyte immune responses, when compared with wild-type mice, consistent with our human in vitro data. This study demonstrates that IL-9, through its direct effects on Th1 and ability to promote IL-4 secretion, has a regulatory role for Th1 lymphocytes in ACD.

Idiosyncratic adverse drug reactions: current concepts

Idiosyncratic drug reactions are a significant cause of morbidity and mortality for patients; they also markedly increase the uncertainty of drug development. The major targets are skin, liver, and bone marrow. Clinical characteristics suggest that IDRs are immune mediated, and there is substantive evidence that most, but not all, IDRs are caused by chemically reactive species. However, rigorous mechanistic studies are very difficult to perform, especially in the absence of valid animal models. Models to explain how drugs or reactive metabolites interact with the MHC/T-cell receptor complex include the hapten and P-I models, and most recently it was found that abacavir can interact reversibly with MHC to alter the endogenous peptides that are presented to T cells. The discovery of HLA molecules as important risk factors for some IDRs has also significantly contributed to our understanding of these adverse reactions, but it is not yet clear what fraction of IDRs have a strong HLA dependence. In addition, with the exception of abacavir, most patients who have the HLA that confers a higher IDR risk with a specific drug will not have an IDR when treated with that drug. Interindividual differences in T-cell receptors and other factors also presumably play a role in determining which patients will have an IDR. The immune response represents a delicate balance, and immune tolerance may be the dominant response to a drug that can cause IDRs.

Extra domain A-positive fibronectin-positive feedback loops and their association with cutaneous inflammatory disease

Cutaneous inflammation can show Th1 or Th2 predominance, but the precise mechanisms by which such selectivity is determined are unknown. A recent study has demonstrated that Th1 cells, but not Th2 cells, produce an endogenous ligand for Toll-like receptor (TLR) 4, namely extradomain A+ fibronectin containing extra type III domain A (FnEDA+). As TLR4 stimulation leads to production of proinflammatory cytokines that recruit (via altered endothelial adhesion molecule expression and chemokine production) more Th1/Th17 cells, a positive feedback mechanism for Th1/Th17 inflammation exists. We propose that FnEDA+ positive feedback loops are a potential driver of Th1/Th17 inflammation. Conversely, the inflammatory EDA+ fibronectin loop is negatively regulated in atopic dermatitis, Th2 cytokines actively suppress TLR4 expression of Th1 cytokines, and recruited Th2 cells do not produce FnEDA+. In psoriasis, there are multiple FnEDA+ loops, comprising inflammatory, keratinocyte, and autoimmune loops. In allergic contact dermatitis, a single inflammatory loop operates. In atopic dermatitis, the FnEDA+ loop is actively suppressed by Th2 cytokines, and recruited Th2 cells do not "feedback" FnEDA+. We review endogenous ligands for TLR in relation to inflammatory disease, FnEDA+ function, and the potential role for FnEDA+ in psoriasis, allergic contact dermatitis, and atopic dermatitis.