NKG2D and its ligands as cytotoxic factors in cutaneous lupus erythematosus.

Cutaneous lupus erythematosus (CLE) is an autoimmune skin disorder that is characterized by an anti-epidermal lymphocytic infiltrate invading the dermo-epidermal junction, causing an interface dermatitis (ID). Pathogenesis of CLE has been linked to activation of innate immunity. NKG2D is an innate immune receptor on NK cells and distinct T-cell populations. The NKG2D ligands MHC class I polypeptide-related sequence A and B (MICA, MICB) have been associated to CLE susceptibility. Our gene microarray analyses of chronic discoid lupus erythematosus (CDLE) skin lesions, separated in epidermal, junctional and dermal skin areas via laser microdissection, revealed a high expression of NKG2D in the lymphocytic infiltrate and led us to further investigate the role of NKG2D in CLE. Pathway analyses showed a strong "interferon (IFN) signature" and vast activation of innate immune response pathways (TLR, RIG-I, cytosolic DNA sensing, JAK/STAT) in CDLE, that expressed the high NKG2D signal. Immunohistochemistry (IHC) confirmed the presence of NKG2D and its ligand MICB in CDLE and subacute cutaneous lupus erythematosus (SCLE) lesions. Finally, HaCaT cells were stimulated with nucleic acids and extracted RNA was sequenced with Illumina HiSeq and showed that stressed keratinocytes express typical NKG2D ligands MICA/B and ULBP2. This study provides first evidence that NKG2D is present in CDLE and SCLE skin lesions and could be relevant for cytotoxicity in IFN-driven skin lesions with upregulated innate immune response pathways present in CLE. It could furthermore play a role in CLE inflammation promoted by keratinocytes under cell stress.

Cognitive distortions in anorexia nervosa and borderline personality disorder.

Thought-shape fusion (TSF) is a cognitive distortion associated with eating disorders (ED). A similar distortion, thought-abandonment fusion (TAbF), is assumed to occur in borderline personality disorder (BPD). In this study the specificity of TSF in participants with anorexia nervosa (AN) and TAbF in participants with BPD was examined. 63 patients completed questionnaires assessing the manifestation of trait-TAbF and trait-TSF, as well as relevant psychopathology. Nonparametric conditional inference trees were used to test for cognitive disorder-specificity. Participants with AN exhibited higher trait-TSF-scores than those with BPD, when participants with BPD and a co-occurring AN were removed. Trait-TSF in participants with AN seemed to be disorder-specific. Participants with BPD and a co-occurring AN had the highest TAbF-scores. The specificity hypothesis could only be partially confirmed for trait-TAbF: while participants with BPD and a co-occurring AN tended to have the highest trait-TAbF scores, high mean values could also be found in participants with AN. The results indicate that TAbF is not specific to BPD, but may also play a role in AN. Both distortions seem to play a role in the maintenance of the respective disorders.

Effectiveness of telephone-based aftercare case management for adult patients with unipolar depression compared to usual care: A randomized controlled trial.

BACKGROUND: Patients with depression often have limited access to outpatient psychotherapy following inpatient treatment. The objective of the study was to evaluate the long-term effectiveness of a telephone-based aftercare case management (ACM) intervention for patients with depression. METHODS: We performed a prospective randomized controlled trial in four psychotherapeutic inpatient care units with N = 199 patients with major depression or dysthymia (F32.x, F33.x, F34.1, according to the ICD-10). The ACM consisted of six phone contacts at two-week intervals performed by trained and certified psychotherapists. The control group received usual care (UC). The primary outcome was depressive symptom severity (BDI-II) at 9-month follow-up, and secondary outcomes were health-related quality of life (SF-8, EQ-5D), self-efficacy (SWE), and the proportion of patients initiating outpatient psychotherapy. Mixed model analyses were conducted to compare improvements between treatment groups. RESULTS: Regarding the primary outcome of symptom severity, the groups did not significantly differ after 3 months (p = .132; ES = -0.23) or at the 9-month follow-up (p = .284; ES = -0.20). No significant differences in health-related quality of life or self-efficacy were found between groups. Patients receiving ACM were more likely to be in outpatient psychotherapy after 3 months (OR: 3.00[1.12-8.07]; p = .029) and 9 months (OR: 4.78 [1.55-14.74]; p = .006) than those receiving UC. CONCLUSIONS: Although telephone-based ACM did not significantly improve symptom severity, it seems to be a valuable approach for overcoming treatment barriers to the clinical pathways of patients with depression regarding their access to outpatient psychotherapy.

Immunostimulatory Endogenous Nucleic Acids Drive the Lesional Inflammation in Cutaneous Lupus Erythematosus.

Cutaneous lupus erythematosus (CLE) is a photosensitive autoimmune disease characterized by a strong type I IFN-associated inflammation. Keratinocytes are known to determine the interface dermatitis pattern in CLE by production of proinflammatory cytokines in the lower epidermis. These cytokines drive a cytotoxic anti-epithelial immune response resulting in keratinocytic cell death and release of endogenous nucleic acids. We hypothesized that these endogenous nucleic acids (RNA and DNA motifs) have the capacity to activate innate immune pathways in keratinocytes via pathogen recognition receptors. Gene expression analyses showed an excessive activation of innate immune response pathways with strong expression of IFN-regulated cytokines in CLE skin lesions. Cultured keratinocytes produce large amounts of these cytokines in response to stimulation of PRR with endogenous nucleic acids. UV stimulation enhances the immunogenicity of endogenous nucleic acids and induces CLE-like skin lesions in knockout mice lacking the cytosolic DNase TREX1. Our results provide evidence for a pathogenetic role of endogenous nucleic acids in CLE. They are released within the cytotoxic inflammation along the dermo-epidermal junction and have the capacity to drive the CLE-typical inflammation. UV irradiation supports this inflammation by generation of highly immunostimulatory DNA motifs (8-hydroxyguanosine). These findings explain the photosensitivity of patients with lupus and identify pathways of the innate immune system as targets for future therapies.

Ultraviolet light protection by a sunscreen prevents interferon-driven skin inflammation in cutaneous lupus erythematosus.

Irradiation with ultraviolet (UV) light is an important exacerbating factor in cutaneous lupus erythematosus (CLE) and induces various effects in the skin of patients with the disease, such as cell death and inflammation. Recently, we demonstrated the ability of a broad-spectrum sunscreen to prevent UV-induced damage both in patients with CLE and healthy controls (HCs). The aim of this study was to evaluate whether the UV-dependent activation of interferon (IFN)-driven inflammation in CLE can also be prevented by application of the sunscreen. In 20 patients with different subtypes of CLE and 10 HCs, defined areas on the upper back were treated with a broad-spectrum liposomal sunscreen 20 min prior to a combined standardized UVA/UVB irradiation. Immunohistological analyses using antibodies directed against MxA, CD11c, CD123 and CD68 were performed from skin biopsies taken from areas before UV irradiation as well as from sunscreen-treated and sunscreen-untreated areas 24 and 72 h after UV irradiation. The expression of MxA was completely prevented by the sunscreen applied prior to UV irradiation in CLE patients and HCs. Additionally, sunscreen protection significantly diminished the number of the CD11c- and CD123-positive dendritic cells, which are suggested to be a major source of type I/III IFNs, in UV-irradiated skin of patients with CLE. Moreover, the application of the sunscreen prevented the increase in CD68-positive macrophages in both groups 72 h after UV irradiation. The data of this study demonstrate that UV protection reduces lesional tissue damage and inhibits the typical IFN-driven inflammatory response in CLE.

Oxidative damage of DNA confers resistance to cytosolic nuclease TREX1 degradation and potentiates STING-dependent immune sensing.

Immune sensing of DNA is critical for antiviral immunity but can also trigger autoimmune diseases such as lupus erythematosus (LE). Here we have provided evidence for the involvement of a damage-associated DNA modification in the detection of cytosolic DNA. The oxidized base 8-hydroxyguanosine (8-OHG), a marker of oxidative damage in DNA, potentiated cytosolic immune recognition by decreasing its susceptibility to 3' repair exonuclease 1 (TREX1)-mediated degradation. Oxidizative modifications arose physiologically in pathogen DNA during lysosomal reactive oxygen species (ROS) exposure, as well as in neutrophil extracellular trap (NET) DNA during the oxidative burst. 8-OHG was also abundant in UV-exposed skin lesions of LE patients and colocalized with type I interferon (IFN). Injection of oxidized DNA in the skin of lupus-prone mice induced lesions that closely matched respective lesions in patients. Thus, oxidized DNA represents a prototypic damage-associated molecular pattern (DAMP) with important implications for infection, sterile inflammation, and autoimmunity.

Indoleamine 2,3-dioxygenase expression in early keratocyte neoplasia of the lower lip correlates to the degree of cell atypia.

Actinic cheilitis (AC) is an early keratocyte neoplasia with inflammation that occurs in the lip vermillion with the potential to develop into invasive squamous cell carcinoma (SCC). The expression of the intracellular enzyme indoleamine 2,3-dioxygenase (IDO) by antigen-presenting cells and/or tumor cells has been described to arrest T cell proliferation by degrading the essential amino acid tryptophan from the environment. The expression of IDO in AC may support cancer progression by inhibiting T cell-mediated rejection responses. The aim of this study was to identify the cellular nature and extent of IDO expression in early keratocye neoplasia of the lower lip (n=25), and to correlate IDO expression to the severity of epithelial atypia (KIN I°- KIN III°) and to the extent of actinic inflammation. The expression of IDO was analyzed together with expression markers for T-cells (CD3), myeloid DCs (S100, CD11c), macrophages (CD68, CD11c), and Langerhans cells (CD1a) by immunohistochemistry and immunofluorescence analysis. Analyses showed that IDO was expressed in myeloid S100(+) CD11c(+) DCs. The expression of IDO correlated significantly with the degree of epithelial atypia (P=0.0005) but not to the extent of inflammation (P=0.4283). Expression of IDO in early atypic skin epithelial conditions might be a predictor to promote carcinogenesis.

Evidence for a pathophysiological role of keratinocyte-derived type III interferon (IFNλ) in cutaneous lupus erythematosus.

Type I IFNs (IFNα/ß) have been shown to have a central role in the pathophysiology of lupus erythematosus (LE). The recently discovered type III IFNs (IFNλ1/IL29, IFNλ2/IL28a, IFNλ3/IL28b) share several functional similarities with type I IFNs, particularly in antiviral immunity. As IFNλs act primarily on epithelial cells, we investigated whether type III IFNs might also have a role in the pathogenesis of cutaneous LE (CLE). Our investigations demonstrate that IFNλ and the IFNλ receptor were strongly expressed in the epidermis of CLE skin lesions and related autoimmune diseases (lichen planus and dermatomyositis). Significantly enhanced IFNλ1 could be measured in the serum of CLE patients with active skin lesions. Functional analyses revealed that human keratinocytes are able to produce high levels of IFNλ1 but only low amounts of IFNα/ß/γ in response to immunostimulatory nuclear acids, suggesting that IFNλ is a major IFN produced by these cells. Exposure of human keratinocytes to IFNλ1 induced the expression of several proinflammatory cytokines, including CXCL9 (CXC-motiv ligand 9), which drive the recruitment of immune cells and are associated with the formation of CLE skin lesions. Our results provide evidence for a role of type III IFNs in not only antiviral immunity but also autoimmune diseases of the skin.

Deconvolution of complex G protein-coupled receptor signaling in live cells using dynamic mass redistribution measurements.

Label-free biosensor technology based on dynamic mass redistribution (DMR) of cellular constituents promises to translate GPCR signaling into complex optical 'fingerprints' in real time in living cells. Here we present a strategy to map cellular mechanisms that define label-free responses, and we compare DMR technology with traditional second-messenger assays that are currently the state of the art in GPCR drug discovery. The holistic nature of DMR measurements enabled us to (i) probe GPCR functionality along all four G-protein signaling pathways, something presently beyond reach of most other assay platforms; (ii) dissect complex GPCR signaling patterns even in primary human cells with unprecedented accuracy; (iii) define heterotrimeric G proteins as triggers for the complex optical fingerprints; and (iv) disclose previously undetected features of GPCR behavior. Our results suggest that DMR technology will have a substantial impact on systems biology and systems pharmacology as well as for the discovery of drugs with novel mechanisms.

Human primary dendritic cell subsets differ in their IL-12 release in response to Leishmania major infection.

Immunity against leishmaniasis has primarily been studied in experimental infections of mice. It was shown that infected skin dendritic cells (DC) are critical for the induction of protection against this pathogen, and targeting skin DC in vaccination approaches in mice has proven to be successful. However, little is known about the contribution of human DC subsets from the skin to primary immunity against this pathogen. In this study, we have analysed the interaction between different human DC subsets and Leishmania major. Primary human myeloid and monocyte-derived DC ingested the parasite comparable to that of murine skin DC, and this resulted in DC activation and IL-12 release, a cytokine essential for the induction of Th1/Tc1-dependent protection. Interestingly, both Langerhans cells and plasmacytoid DC did not appear to contribute to protection in humans. Thus, in leishmaniasis, both murine and human data suggest that dermal inflammatory DC appear to be superior in promoting protection.

Type I interferon-associated cytotoxic inflammation in cutaneous lupus erythematosus.

Inappropriate activation of innate immune mechanisms, in particular of the type I interferon (IFN) system, is regarded to play an important role in the pathogenesis of lupus erythematosus (LE). Type I IFN serum levels have been shown to correlate with the disease activity in systemic LE and additionally play a proinflammatory role in the development of LE skin lesions. Recent studies demonstrated a close morphological association between the expression pattern of IFN-inducible chemokines (MxA, CXCL10) and typical histological features of cutaneous LE. These and other studies suggest that a complex network of IFN-associated cytokines, chemokines and adhesion molecules orchestrates and promotes tissue injury observed in LE skin.

Transcriptional profiling identifies an interferon-associated host immune response in invasive squamous cell carcinoma of the skin.

Squamous cell carcinoma (SCC) and basal cell carcinoma (BCC) represent the 2 most common types of nonmelanoma skin cancer. Both derive from keratinocytes but show a distinct biological behavior. Here we present transcriptional profiling data of a large cohort of tumor patients (SCC, n = 42; BCC, n = 114). Differentially expressed genes reflect known features of SCC and BCC including the typical cytokeratin pattern as well as upregulation of characteristic cell proliferation genes. Additionally, we found increased expression of interferon (IFN)-regulated genes (including IFI27, IFI30, Mx1, IRF1 and CXCL9) in SCC, and to a lower extent in BCC. The expression of IFN-regulated genes correlated with the extent of the lesional immune-cell infiltrate. Immunohistological examinations confirmed the expression of IFN-regulated genes in association with a CXCR3+ cytotoxic inflammatory infiltrate on the protein level. Of note, a small subset of SCC samples with low expression of IFN-regulated genes included most organ transplant recipients receiving immunosuppressive medication. Collectively, our findings support the concept that IFN-associated host responses play an important role in tumor immunosurveillance in the skin.

CXCR3 <-> ligand-mediated skin inflammation in cutaneous lichenoid graft-versus-host disease.

BACKGROUND: Lichenoid graft-versus-host disease (liGVHD) histologically shares several common features with other lichenoid dermatoses, such as cutaneous lupus erythematosus and lichen planus (LP), which collectively show a junctional infiltrate of cytotoxic lymphocytes with liquefaction of the basal layer ("interface dermatitis"). Because recent studies have shown a role for type I interferon (IFN)-associated inflammation, including lymphocyte recruitment via CXCR3 <-> ligand interaction in cutaneous lupus erythematosus and LP, we hypothesized that similar mechanisms might also be involved in liGVHD. METHODS: Ten representative lesional skin biopsies taken from patients with different subsets of chronic cutaneous graft versus host disease (GvDH) were recovered from the authors' archives. Eight LP specimens and 5 punch biopsies taken from healthy skin were analyzed for control purposes. Immunohistochemistry was performed to characterize the lesional infiltrate (CD3, CD4, CD8, CD20, CD56, or CD68), to analyze type I IFN signaling (MxA), and to investigate expression of the IFN-inducible chemokines CXCL9 and CXCL10 and their ligand CXCR3. In situ hybridization was performed to visualize IFNalpha expression on the mRNA level. RESULTS: Our analyses revealed striking similarities between the inflammatory pattern seen in LP and liGVHD. Both disorders presented with a predominantly T-cellular inflammation with CD8(+) lymphocytes affecting the basal epidermal layer. The majority of lesional lymphocytes expressed the chemokine receptor CXCR3. The corresponding chemokines CXCL9 and CXCL10 were found in the epidermis and within the inflammatory infiltrate. Analyses of MxA and IFNalpha mRNA expression supported a role for type I IFNs in these conditions. LIMITATIONS: This study was limited by the number of well characterized cases in our archives. In situ hybridization was realizable only in single cases. CONCLUSION: Our results support the hypothesis that CXCR3 <-> ligand-mediated lymphocyte recruitment is involved in cutaneous liGVHD. The fact that CXCL10 was seen in precisely those areas with extensive liquefaction of the basal epidermis supports a role of this chemokine for the development of the typical histologic "interface" pattern.

Gene expression profiling of lichen planus reflects CXCL9+-mediated inflammation and distinguishes this disease from atopic dermatitis and psoriasis.

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

Dendritic cell-derived IL-12p40 homodimer contributes to susceptibility in cutaneous leishmaniasis in BALB/c mice.

Protection against Leishmania major in resistant C57BL/6 mice is mediated by Th1 cells, whereas susceptibility in BALB/c mice is the result of Th2 development. IL-12 release by L. major-infected dendritic cells (DC) is critically involved in differentiation of Th1 cells. Previously, we reported that strain differences in the production of DC-derived factors, e.g., IL-1alphabeta, are in part responsible for disparate disease outcome. In the present study, we analyzed the release of IL-12 from DC in more detail. Stimulated DC from C57BL/6 and BALB/c mice released comparable amounts of IL-12p40 and p70. In the absence of IL-4, BALB/c DC produced significantly more IL-12p40 than C57BL/6 DC. Detailed analyses by Western blot and ELISA revealed that one-tenth of IL-12p40 detected in DC supernatants was released as the IL-12 antagonist IL-12p40 homodimer (IL-12p80). BALB/c DC released approximately 2-fold more IL-12p80 than C57BL/6 DC both in vitro and in vivo. Local injection of IL-12p80 during the first 3 days after infection resulted in increased lesion volumes for several weeks in both L. major-infected BALB/c or C57BL/6 mice, in higher lesional parasite burdens, and decreased Th1-cytokine production. Finally, IL-12p40-transgenic C57BL/6 mice characterized by overexpression of p40 showed increased levels of serum IL-12p80 and enhanced disease susceptibility. Thus, in addition to IL-1alphabeta, strain-dependent differences in the release of other DC-derived factors such as IL-12p80 may influence genetically determined disease outcome.

CXCR3-mediated recruitment of cytotoxic lymphocytes in lupus erythematosus profundus.

BACKGROUND: Lupus erythematosus profundus (LEP) is a rare variant lupus erythematosus with unclear etiology characterized by lobular panniculitis. Recently, we observed a case of LEP involving the lower right eyelid. Our immunohistological analyses of lesional skin biopsies revealed a type I IFN signature in the context of cytotoxic lobular panniculitis. OBJECTIVE: Since type I IFNs have been shown to be involved in other cutaneous LE subtypes, especially in chronic discoid LE, we hypothesized that a type I IFN driven immune response might play an important role in the pathogenesis of LEP. METHODS: In addition to the above case, 9 skin biopsies taken from 5 patients with LEP were analyzed for a type I interferon signature by immunohistochemistry. Furthermore, 8 skin biopsies taken from patients with active chronic discoid LE and 5 biopsies of healthy skin were included for control purposes. The inflammatory infiltrate was characterized using monoclonal antibodies specific for CD3, CD4, CD8, CD20, CD68, and CD123. Subsequently, we analyzed the expression the type I IFN Marker MxA, the cytotoxic molecules granzyme B and Tia1, the chemokine receptor CXCR3 and its ligand, the interferon inducible protein IP10/CXCL10. RESULTS: LEP skin lesions were characterized by a lobular panniculitis, dominated by cytotoxic CXCR3(+) lymphocytes. Strong MxA expression indicated extensive type I IFN production within the fat lobules. Numerous plasmacytoid dendritic cells appear to be the major source of type I IFNs. Lesional expression of IP10 links the type I IFN production and recruitment of CXCR3(+) lymphocytes. LIMITATIONS: The study was based on histological and immunohistological analyses in a limited number of patients, due to the rareness of the investigated disease. CONCLUSION: Our results demonstrate a type I IFN driven immune response in active LEP skin lesions. We suggest that this type I IFN driven inflammation is responsible for the recruitment of CXCR3(+) lymphocytes into fat lobules and enhance their cytotoxic capacity.

Impaired Th1 responses in mice deficient in Epstein-Barr virus-induced gene 3 and challenged with physiological doses of Leishmania major.

Protection against Leishmania major is dependent on IL-12 release from L. major-infected dendritic cells (DC) that induce IFN-gamma-producing Th1/Tc1 cells. IL-27, a novel member of the IL-12 family, is a heterodimer composed of p28 and IL-12p40-related Epstein-Barr virus-induced gene 3 (EBI3), and was shown to be produced by DC. In this study, we utilized EBI3-deficient mice to investigate the role of IL-27 in leishmaniasis using physiological low-dose infections that mimic natural transmissions. Lesions in EBI3(-/-) mice were significantly larger between weeks 3 and 10 post infection, reaching up to approximately threefold increased lesion volumes compared to wild types. In parallel, dermal lesions of EBI3(-/-) mice contained greater parasite numbers, reaching a peak load that was 2-log higher than in C57BL/6 mice. However, lesions in EBI3(-/-) and wild-type mice resolved after 12 weeks. At early time points, the antigen-specific cytokine response in EBI3(-/-) lymph nodes showed increased levels of IL-4, IL-10 and IL-13 and decreased IFN-gamma production. IL-27 production was restricted to the DC population, since the majority of EBI3 expression in lymph nodes of infected mice was found in CD11c(+) cells. In conclusion, our data show that DC-derived IL-27 is critical for the timely initiation of efficient anti-parasite Th1 immunity early in infections.

Coupling of contact sensitizers to thiol groups is a key event for the activation of monocytes and monocyte-derived dendritic cells.

Strong contact sensitizers are able to induce distinct signal transduction mechanisms in antigen-presenting cells by coupling to cell proteins. The predominant target structures of haptens are thought to be thiol and amino groups in cysteine and lysine residues. We studied whether coupling of small reactive chemicals to thiol or amino groups might be responsible for the activation of monocytes and mature monocyte-derived dendritic cells. Human peripheral blood mononuclear cells were stimulated in vitro with subtoxic concentrations of the strong haptens 5-chloro-2-methylisothiazolinone plus 2-methylisothiazolinone and 2, 4, 6-trinitrochlorobenzene, the thiol-reactive reagents N-hydroxymaleimide and N-ethylmaleimide, as well as the amino-reactive compounds sulfosuccinimidyl acetate and 2-iminothiolane. Flow cytometric quantification of tyrosine phosphorylation in CD14+ monocytes showed that 5-chloro-2-methylisothiazolinone plus 2-methylisothiazolinone, 2, 4, 6-trinitrochlorobenzene, N-hydroxymaleimide, and N-ethylmaleimide but not sulfosuccinimidyl acetate and 2-iminothiolane strongly induced this process. Tyrosine phosphorylation induced by 5-chloro-2-methylisothiazolinone plus 2-methylisothiazolinone and 2, 4, 6-trinitrochlorobenzene was completely prevented in the presence of cysteine but not lysine, suggesting a competitive mechanism between cysteine and sulfhydryl groups of cell proteins. Using the mouse ear swelling test N-hydroxymaleimide could be classified as a significant contact allergen in comparison to 2, 4, 6-trinitrochlorobenzene, whereas no sensitizing potential became apparent for sulfosuccinimidyl acetate and 2-iminothiolane. Western blot analysis on monocytes and mature monocyte-derived dendritic cells confirmed the flow cytometric data for tyrosine phosphorylation and demonstrated a selective capacity of haptens and thiol-reactive compounds to activate ERK1/2 mitogen-activated protein kinase. Our data show that strong affinity of a small reactive chemical toward thiol groups is important for the activation of monocytes and monocyte-derived dendritic cells and can support the process of sensitization.