Elicitation Phase Of Contact Hypersensitivity Research Articles

The junctional adhesion molecule-like protein (JAML) is important for the inflammatory response during contact hypersensitivity.

The junctional adhesion molecule-like protein (JAML) plays important roles in wound healing and activation of epidermal γδ T cells in mice. Whether JAML plays a role in contact hypersensitivity (CHS), the animal model of allergic contact dermatitis (ACD), is not known. To examine the role of JAML in CHS, we used various mouse models of CHS in JAML knockout (KO) and wild-type (WT) mice. Furthermore, the expression of the JAML ligand coxsackievirus and adenovirus receptor (CXADR) on keratinocytes was accessed in vitro and in vivo. JAML KO mice had a diminished inflammatory response during both the sensitization and elicitation phase of CHS and had reduced numbers of CD8+ and CD4+ T cells in the epidermis. Furthermore, interferon γ (IFNγ), interleukin 1β (IL-1β) and CXCL10 production were significantly reduced in JAML KO mice during the elicitation phase. We found that CD8+ T cells express JAML and that JAML is essential for rapid flare-up responses to contact allergens. Finally, we show that keratinocytes up-regulate the JAML ligand CXADR following exposure to contact allergens. Our study is the first to show a central role of JAML in CHS and reveals a potential new target for the treatment of ACD in humans.

006 Conventional dendritic cell 2 as an activator for cytotoxic T lymphocytes in the elicitation phase of murine contact hypersensitivity

Cytotoxic T lymphocyte (CTL) has been found to be activated by cutaneous dendritic cell (DC) in inducible skin-associated lymphoid tissue (iSALT) in a murine contact hypersensitivity (CHS) model. Cutaneous DCs are classified into Langerhans cell (LC), conventional DC1 (cDC1), conventional DC2 (cDC2) and monocyte-derived DC (MoDC); however, which DC subsets activate CTL within iSALT during the elicitation phase of CHS has remained unclear. To clarify this, we used Langerin-diphtheria toxin receptor (DTR), XCR1-DTR and CD301b-DTR mice to deplete LC, cDC1 and cDC2, respectively.

PD-L1 on mast cells suppresses effector CD8+ T-cell activation in the skin in murine contact hypersensitivity

The programmed cell death-1 (PD-1)/programmed death ligand 1 (PD-L1) pathway is known to inhibit the activation of effector CD8+ T cells. However, just how this regulatory pathway is involved in the pathophysiology of CD8+ T-cell-mediated inflammatory skin diseases remains unclear. Our aim was to elucidate the mechanisms by which the PD-1/PD-L1 pathway exerts its regulatory roles in CD8+ T-cell-mediated cutaneous immune responses. PD-L1-deficient (Pdl1-/-) mice were used for the murine contact hypersensitivity model. Inflammatory responses such as IFN-γ production from CD8+ T cells in the skin was evaluated by flow cytometry. Compared with wild-type mice, Pdl1-/- mice exhibited exacerbated ear swelling and increased numbers of IFN-γ+ CD8+ T cells in the skin. Adoptive T-cell transfer experiments revealed the involvement of the PD-1/PD-L1 pathway in the elicitation phase of contact hypersensitivity. Bone marrow chimera experiments showed that PD-L1 on radioresistant cells was responsible for this regulatory pathway. Flow cytometric analysis revealed that among the radioresistant cells in the skin, PD-L1 was most highly expressed on mast cells (MCs) before and after elicitation. Administration of anti-PD-L1 blocking antibody during the elicitation phase significantly enhanced ear swelling responses and increased the number of IFN-γ+CD8+ T cells in the skin of wild-type mice, whereas no significant effects were observed in MC-deficient (WBB6F1/J-KitW/KitW-v/J and C57BL/6-KitW-sh/W-sh) mice. The high level of expression of PD-L1 on human skin MCs was confirmed by database analysis and immunohistochemical analysis. PD-L1 on MCs negatively regulates CD8+ T-cell activation in the skin.

021 PD-L1 on radio-resistant cells negatively regulates effector CD8+ T-cell activation during the elicitation phase of contact hypersensitivity

021 PD-L1 on radio-resistant cells negatively regulates effector CD8+ T-cell activation during the elicitation phase of contact hypersensitivity

IL-25 enhances TH17 cell–mediated contact dermatitis by promoting IL-1β production by dermal dendritic cells

In addition to thymic stromal lymphopoietin and IL-33, IL-25 is known to induce TH2 cytokine production by various cell types, including TH2 cells, TH9 cells, invariant natural killer T cells, and group 2 innate lymphoid cells, involved in TH2-type immune responses. Because both TH2-type and TH17-type cells/cytokines are crucial for contact hypersensitivity (CHS), IL-25 can contribute to this by enhancing TH2-type immune responses. However, the precise role of IL-25 in the pathogenesis of fluorescein isothiocyanate-induced CHS is poorly understood. We investigated the contribution of IL-25 to CHS using Il25-/- mice. CHS was evaluated by means of measurement of ear skin thickness in mice after fluorescein isothiocyanate painting. Skin dendritic cell (DC) migration, hapten-specific TH cell differentiation, and detection of IL-1β-producing cells were determined by using flow cytometry, ELISA, and immunohistochemistry, respectively. In contrast to thymic stromal lymphopoietin, we found that IL-25 was not essential for skin DC migration or hapten-specific TH cell differentiation in the sensitization phase of CHS. Unexpectedly, mast cell- and non-immune cell-derived IL-25 was important for hapten-specific TH17 cell-mediated rather than TH2 cell-mediated inflammation in the elicitation phase of CHS by enhancing TH17-related, but not TH2-related, cytokines in the skin. In particular, IL-1β produced by dermal DCs in response to IL-25 was crucial for hapten-specific TH17cell activation, contributing to induction of local inflammation in the elicitation phase of CHS. Our results identify a novel IL-25 inflammatory pathway involved in induction of TH17 cell-mediated, but not TH2 cell-mediated, CHS. IL-25 neutralization can be a potential approach for treatment of CHS.

The Role of Interleukin-19 in Contact Hypersensitivity.

Interleukin (IL)-19 is a member of the IL-10 family of interleukins and is an immuno-modulatory cytokine produced by the main macrophages. The gastrointestinal tissues of IL-19 knockout mice show exacerbated experimental colitis mediated by the innate immune system and T cells. There is an increasing focus on the interaction and relationship of IL-19 with the function of T cells. Contact hypersensitivity (CHS) is T cell-mediated cutaneous inflammation. Therefore, we asked whether IL-19 causes CHS. We investigated the immunological role of IL-19 in CHS induced by 1-fluoro-2,4-dinitrofluorobenzene as a hapten. IL-19 was highly expressed in skin exposed to the hapten, and ear swelling was increased in IL-19 knockout mice. The exacerbation of the CHS response in IL-19 knockout mice correlated with increased levels of IL-17 and IL-6, but no alterations were noted in the production of interferon (IFN)γ and IL-4 in the T cells of the lymph nodes. In addition to the effect on T cell response, IL-19 knockout mice increased production of inflammatory cytokines. These results show that IL-19 suppressed hapten-dependent skin inflammation in the elicitation phase of CHS.

317 PD-L1 on radio-resistant cells regulates effector CD8+ T-cell activation during the elicitation phase of contact hypersensitivity

317 PD-L1 on radio-resistant cells regulates effector CD8+ T-cell activation during the elicitation phase of contact hypersensitivity

Neutrophils are required for both the sensitization and elicitation phase of contact hypersensitivity.

Allergic contact dermatitis and its animal model, contact hypersensitivity (CHS), are T cell-mediated inflammatory skin diseases induced by contact allergens. Though numerous cellular and molecular players are known, the mechanism of chemical-induced sensitization remains poorly understood. Here, we identify neutrophils as crucial players in the sensitization phase of CHS. Genetic deficiency of neutrophils caused by myeloid-specific deletion of Mcl-1 or antibody-mediated depletion of neutrophils before sensitization abrogated the CHS response. Neutrophil deficiency reduced contact allergen-induced cytokine production, gelatinase release, and reactive oxygen species production in naive mice. Mast cell deficiency inhibited neutrophil accumulation at the site of sensitization. In turn, neutrophils were required for contact allergen-induced release of further neutrophil-attracting chemokines, migration of DCs to the draining lymph nodes, and priming of allergen-specific T cells. Lymph node cells from mice sensitized in the absence of neutrophils failed to transfer sensitization to naive recipients. Furthermore, no CHS response could be induced when neutrophils were depleted before elicitation or when normally sensitized lymph node cells were transferred to neutrophil-deficient recipients, indicating an additional role for neutrophils in the elicitation phase. Collectively, our data identify neutrophils to be critically involved in both the sensitization and elicitation phase of CHS.

Intercellular gap of keratinocytes is a migratory pathway for epidermal Langerhans cells

The epidermis is composed of keratinocytes that bind tightly each other. This feature contrasts to the property of the dermis where cellular density is low and filled with extracellular matrix. Therefore, it remains a question how Langerhans cells, a subtype of dendritic cells in the epidermis, migrate within such a “packed” area. Here, we examined the motility of Langerhans cells in the contact hypersensitivity response by means of two-photon microscopy. First, we labeled cellular membrane of keratinocytes with a fluorescent lectin, and revealed that there exist 1-2 nm gaps between adjacent keratinocytes in vivo. In the steady state, and even in the first encounter of hapten (sensitization phase), almost all of Langerin + cells were static and elongated their long dendrites upward through the gaps. In the second encounter of hapten (elicitation phase), however, a subpopulation of Langerin + dendritic cells move downward to the basal layer of epidermis and actively interact with T cells, whereas another population of Langerin + dendritic cells were anchored with upstretched dendrites. Intriguingly, a depletion of Langerin + dendritic cells in elicitation phase resulted in prolonged skin inflammation.Our study has demonstrated that the gaps between keratinocytes provide a migratory pathway for immune cells. It should be essential for the immune cells in the epidermis to migrate in a non-tissue destructive manner. Moreover, we showed that epidermal Langerin + cells are divided into two populations according to their kinetics and morphology, and both or either of them may have a role in termination of inflammation in the elicitation phase of contact hypersensitivity. JSID AbstractsJournal of Dermatological ScienceVol. 69Issue 2Preview Full-Text PDF

Abstract 2471: Immunosuppressive effect of elevated epidermal ornithine decarboxylase activity

Abstract Tumor promoting agents, such as phorbol esters, promote tumorigenesis via induction of inflammation and hyperplasia. However, the immunosuppressive/immunomodulating properties of tumor promoting agents may play a relevant role in tumor promotion as well. Because elevated polyamine biosynthesis is sufficient to promote skin tumorigenesis, we hypothesized that increased activity of epidermal ornithine decarboxylase (ODC), a key regulatory enzyme in polyamine biosynthesis, may suppress the cutaneous immune response in addition to stimulating proliferation. To investigate the role of ODC in the control of cutaneous inflammation, a well-known model of T cell mediated inflammation was used. A contact hypersensitivity (CHS) response was elicited in the ears of both ODC transgenic mice, in which ODC is targeted to the epidermis, and their normal littermates by topical sensitization and challenge with oxazolone. Unlike in normal littermate mice, ear swelling was dramatically reduced in ODC transgenic mice after elicitation of CHS. Flow cytometric and immunohistochemical analyses of the infiltrating immune cells revealed fewer infiltrating immune cells, especially neutrophils, in the elicited ears of ODC transgenic mice. The specific ODC inhibitor, α-difluoromethylornithine, abrogated the suppressive effects of ODC in CHS reactions. Adoptive transfer of sensitized lymphocytes from either ODC transgenic or normal littermate mice to naïve ODC transgenic or wild-type mice indicated that elevated epidermal ODC activity suppress both the sensitization and elicitation phases of CHS. Cytokines are central mediators of immune functions associated with inflammatory reactions. The cytokine profile of ex vivo stimulated lymphocytes isolated from draining lymph nodes showed reduced levels of IL-6 and IL-10 in sensitized and challenged ODC transgenic mice. In vivo labeling of dendritic cells by topical application of fluorescein isothiocyanate (FITC) showed fewer FITC-labeled dendritic cells in the draining lymph nodes of ODC transgenic mice compared to normal littermates. Vascular permeability was assessed using Evans blue extravasation assays during the elicitation phase of CHS. At 24 hours after induction of CHS, there was 45% less plasma extravasation of Evans blue dye into the ear skin of ODC transgenic mice compared to normal littermates. Collectively these data indicate elevated epidermal ODC activity can suppress a number of functions associated with cutaneous inflammatory reactions. In addition to promoting cellular proliferation, the immune suppression mediated by increased epidermal ODC activity may provide an environment conducive to tumor growth. This work was supported by NIH grant CA070739. Citation Format: {Authors}. {Abstract title} [abstract]. In: Proceedings of the 101st Annual Meeting of the American Association for Cancer Research; 2010 Apr 17-21; Washington, DC. Philadelphia (PA): AACR; Cancer Res 2010;70(8 Suppl):Abstract nr 2471.

Low Zone Tolerance Requires ICAM-1 Expression to Limit Contact Hypersensitivity Elicitation

Painting subsensitizing doses of contact sensitizers on skin (low-dose tolerization) induces antigen (Ag)-specific tolerance, known as low zone tolerance (LZT), which has been experimentally demonstrated by the inhibition of contact hypersensitivity (CHS). Although LZT resulted from the inhibition of the sensitization phase, the effects on the effector/elicitation phase remain unknown. L-selectin and ICAM-1 regulate leukocyte influx into inflamed tissues during the elicitation phase of CHS. LZT was investigated in mice lacking either L-selectin or ICAM-1 to evaluate the roles these leukocyte receptors play in LZT during the elicitation phase. Low-dose tolerization effectively suppressed CHS in wild-type and L-selectin-deficient mice, but not in ICAM-1-deficient mice. Low-dose-tolerized ICAM-1-deficient splenocytes effectively suppressed the elicitation phase in naive wild-type recipients. Sensitized ICAM-1-deficient splenocytes showed normal proliferative responses to the sensitizing Ag and generated normal CHS in wild-type recipients. Thus, ICAM-1 deficiency did not affect sensitization. LZT was associated with a lack of ICAM-1 upregulation after elicitation, suggesting a potentially mechanistic role for ICAM-1. The blockade of IL-10, a possible mediator of LZT, produced by hapten-specific suppressor cells, abrogated LZT and restored ICAM-1 upregulation. These results indicate that low-dose tolerization controls CHS by abrogating ICAM-1 upregulation during the elicitation phase.

CD4 +CD25 + regulatory T cells suppress contact hypersensitivity reactions through a CD39, adenosine-dependent mechanism

Injection of regulatory T (Treg) cells into sensitized mice abrogates the elicitation phase of contact hypersensitivity (CHS) reactions by blocking the adherence of leukocytes to vascular endothelium. We set out to analyze whether adenosine, a suppressive factor recently described as produced by Treg cells, can account for the suppression of the effector T-cell-endothelial cell (EC) interaction. T cells and ECs were cultured in the presence of adenosine, and expression of adhesion molecules and adhesion of T cells to ECs under shear stress were assessed. Furthermore, we injected Treg cells derived from ectonucleotidase-deficient (CD39-/-) mice into sensitized mice and analyzed the sticking and rolling of leukocytes during a CHS response using intravital microscopy. Adenosine or Treg cells, respectively, abrogated the adherence of effector T cells to ECs in vitro. Likewise, injection of adenosine and Treg cells abrogated the ear-swelling reaction, indicating a role of adenosine during Treg cell-induced suppression of CHS responses. As a source for Treg cell-derived adenosine, we identified the ectonucleotidase CD39 because CD39-deficient Treg cells did not prevent adhesion of leukocytes to the endothelium. Furthermore, we show that the impaired adhesion of effector T cells to inflamed endothelium was induced by adenosine-mediated downregulation of expression of E- and P-selectin on the vascular endothelium. Adenosine release by Treg cells is essential to block leukocyte adhesion to endothelium, providing a novel mechanism by which Treg cells mediate immune suppression in vivo.

17.BETA.-Estradiol Enhances Interleukin-18 mRNA Expression after Sensitization of Mice with Contact Hypersensitivity

To clarify the mechanism underlying the enhancing effect of 17β-estradiol (E2) on contact hypersensitivity (CHS) and the expression of interferon (IFN)-γ in mice, the mRNA expression levels of interleukin (IL)-18 were evaluated. Female BALB/c mice aged 3 weeks were ovariectomized, administered 3.2 μg of E2, and sensitized by 50 μl of 3% 4-ethoxymethylene-2-phenyl-2-oxazolin-one (OXA). Seven days later, CHS was elicited by the application of 7.5 μl of 1% OXA on the ear auricles. The auricles, cervical lymph nodes and spleens were excised, and gene expression was evaluated by reverse transcription-polymerase chain reaction. E2 enhanced the expression of IL-18 mRNA in the spleen on the following day and in the ear auricles on days 4 and 7 after sensitization with OXA. The preadministration of an antibody against IL-18 receptor suppressed the CHS and reduced IFN-γ mRNA expression in E2-administered mice. IL-18 was present in the dermis of the ear skin and absent in the epidermis. E2 also enhanced the expression of IFN-γ and IL-18 mRNAs in splenocytes cultured with lipopolysaccharide (LPS). IL-18 protein was detected by flow cytometry in CD4+, CD8+ and NKG2+ lymphocytes among splenocytes cultured with LPS. These results suggest that E2 enhances lymphocyte activation in the sensitization phase of CHS, and that IFN-γ mRNA expression is enhanced in the elicitation phase of CHS.

Topical Application of Cream-emulsified CD86 siRNA Ameliorates Allergic Skin Disease by Targeting Cutaneous Dendritic Cells

Induction of the co-stimulatory molecule CD86 on dendritic cells (DCs) in the peripheral tissues is a critical event in triggering antigen-specific immune responses. In this study, we propose a new small interfering RNA (siRNA)-based therapy using cream-emulsified CD86 siRNA, targeting DCs for murine contact hypersensitivity (CH) and atopic dermatitis (AD)-like disease. Topical application of CD86 siRNA efficiently inhibited CH and markedly decreased the numbers of infiltrating CD86(+) or major histocompatibility complex (MHC) class II(+) cells in murine ear skin. The total number of cells, the percentage of hapten-carrying DCs, and their CD86 expression in the regional lymph nodes (RLNs) also significantly decreased. These results suggest that the silencing of CD86 in local DCs inhibits the recruitment and migration of DCs into the skin and RLNs, respectively, resulting in reduced antigen-specific local inflammation. The therapeutic efficacy of the CD86 siRNA was confirmed in AD-prone NC/Nga mice. Treatment produced marked amelioration in the clinical manifestations of AD and reduced the antigen-specific production of interleukin-4 (IL-4) and serum immunoglobulin E (IgE) and IgG1. Our results suggest that the targeting of cutaneous DCs by CD86 siRNA may be a promising strategy in the treatment of allergic skin disease.

Mast Cells Regulate the Magnitude and the Cytokine Microenvironment of the Contact Hypersensitivity Response

The role that mast cells play during contact hypersensitivity (CS) response is unclear because some studies have shown that mast cell-deficient mice have relatively intact CS responses whereas others have shown opposing results. Mast cells secrete a wide range of immunomodulatory mediators and can potentially influence the type of immune response generated in the skin during CS. Therefore, we examined the type of microenvironment generated during CS in both W/Wv mast cell-deficient and wild-type mice in response to different immunizing doses of hapten (oxazolone). The CS response elicited after low-dose oxazolone was significantly diminished in W/Wv mice compared with wild-type mice. Unexpectedly, the CS response elicited in W/Wv mice immunized with high-dose oxazolone was more severe compared with wild-type mice. In addition, after immunization with high-dose oxazolone, the granulocyte infiltrate in W/Wv mice was increased by twofold compared with wild-type mice. A shift in the cytokine milieu toward the expression of type-1 cytokines as well as a significant increase in the local adhesion of neutrophils and CD4 T cells in the microvasculature of the skin was observed after hapten challenge in W/Wv mice immunized with high-dose oxazolone compared with wild-type mice. These results suggest that mast cells can act as regulators and inducers of the inflammatory response depending on immunizing stimulus strength.

Ultraviolet : A Regulator of Immunity

Humans establish acquired immune systems during the growth, which can sufficiently eliminate pathogen avoiding immune responses to self, such as allergy and autoimmunity. An imbalance of the acquired immune system leads up to immune-mediated disorders. Ultraviolet (UV) exposure helps to establish the normal peripheral tolerance to contact allergen avoiding excessive immune responses. By contrast, UV develops kinds of autoimmune diseases on rare occasions, suggesting that abnormality in the process of UV-induced peripheral tolerance may induce these diseases. To elucidate the mechanism of UV-induced tolerance is possible to provide a new approach for the management of immune diseases. In the current review, focus is on the suggested players of UV-induced tolerance, blocking mechanisms on the elicitation phase of contact hypersensitivity, and the association between UV and autoimmunity. The major impact in basic immunology in this area is the discovery of cell surface marker of regulatory T cells. Therefore, we first discuss about the association of regulatory/suppressor T cells with UV-induced tolerance. Since the elicitation phase depends on cellular influx into the inflammatory sites, which is tightly regulated by adhesion molecules, we also focused on the role of adhesion molecules. Finally, this paper also includes statistical findings concerning the association between UV-radiation and the prevalence of a myositis specific autoantibody. Thus, UV is one of the nice regulators of an immune network and the knowledge of UV-mediated immune regulation will be translated into new therapeutic strategies to human immune-mediated disorders.

Elicitation of contact hypersensitivity after repeated suberythemal exposures of humans to solar simulated radiation: number of epidermal Langerhans cells

Ultraviolet radiation suppresses contact hypersensitivity (CHS). The role of epidermal Langerhans cells (LCs, CD1a(+)) in the elicitation phase of CHS is uncertain. To assess the effect of low-doses of solar simulated radiation (SSR) on LC numbers at the CHS elicitation site. 3 groups (each about 30 volunteers) were whole-body irradiated with suberythemal SSR on 2, 10 or 30 consecutive days before sensitization with diphenylcyclopropenone. Another group was not irradiated. Elicitation of CHS took place 3 weeks later with subsequent evaluation by visual scoring and spongiosis grade. CD1a(+) cells in the epidermis from the elicitation site were counted. No difference in CHS intensity between the unirradiated controls and all 3 irradiated groups was found, but a significant negative correlation between the spongiosis grade and the number of SSR exposures was shown. The number of epidermal CD1a(+) cells in the 10- and 30-day groups was reduced compared with the unirradiated group, and the 30-day group had significantly fewer than the 10-day group. Low daily doses of SSR induce suppression of CHS, leading to depletion of LCs at the CHS elicitation site. The effect on the CHS and LCs is cumulative, indicating that photoadaptation for these parameters does not develop over the 30 day irradiation period.

Vascular endothelial growth factor receptor tyrosine kinase inhibitor PTK787/ZK 222584 inhibits both the induction and elicitation phases of contact hypersensitivity

Vascular endothelial growth factor (VEGF) and its endothelial cell receptors (VEGFR) have been shown to be involved in the pathogenesis of the contact hypersensitivity (CHS) reaction. Previous studies have demonstrated that anti-VEGFR-2 antibody significantly suppresses the elicitation phase of CHS but does not affect the induction phase. PTK787/ZK 222584 (1-[4-chloroanilino]-4-[4-pyridylmethyl] phthalazine succinate; PTK/ZK) is a potent inhibitor of VEGFR tyrosine kinases. To test the effect of PTK/ZK on the induction and elicitation phases of CHS separately, we used an established method of CHS assay-sensitization and challenge in BALB/c mice. Either 50 mg/kg/day PTK/ZK or vehicle serving as a control was administered orally in the induction or elicitation phases separately. In the afferent phase, flow cytometry of skin-draining lymph node cells revealed that the migration of Langerhans cells was suppressed in the mice treated with PTK/ZK at sensitization. The degrees of ear swelling at 24 and 48 h were significantly diminished in mice treated with PTK/ZK at sensitization (P < 0.05). In the efferent phase, the degrees of ear swelling at 24 h (P < 0.01) and 48 h (P < 0.05), ear blood flow at 24 and 48 h (P < 0.01), and production of VEGF in the epidermis at 24 h (P < 0.05) were significantly suppressed in mice treated with PTK/ZK at elicitation. These findings and previous demonstrations suggest that both VEGF R-1 and VEGF R-2 are needed during the induction phase, and that VEGFR-2 has a pivotal role in the elicitation phase of the CHS reaction.

Viewpoint 2

Viewpoint 2

A single sub‐erythematous exposure of solar‐simulated radiation on the elicitation phase of contact hypersensitivity induces IL‐10‐producing T‐regulatory cells in human skin

Solar ultraviolet (UV) radiation has hazardous effects on human health that are, in part, associated with its immunosuppressive effects via the induction of interleukin (IL)-10 production. Although IL-10 is produced by both T helper type 2 (Th2) cells and T-regulatory type 1 (Tr1) cells, the relative contribution of either subset in UV radiation-induced immunosuppression has not been established. Here, we show that T cells isolated from non-treated allergic contact dermatitis (ACD) reactions, 48 h following nickel challenge and propagated for 7-10 days in the presence of IL-2, were mainly CD4(+) and produced IL-10, but little interferon-gamma. A single sub-erythematous solar-simulated radiation (SSR) prior to antigen challenge exposure resulted in a clinical attenuation of the intensity of ACD reactions which was associated with a significant increase in both the magnitude of IL-10 production by skin-infiltrating T cells and the frequency of IL-10-producing Tr1 cells. Skin-infiltrating T cells in SSR-exposed, as well as non-exposed, ACD reactions showed a perturbed T-cell receptor (TCR)-Vbeta repertoire, without overexpression of a particular TCR-Vbeta gene product, indicating the presence of high frequencies of nickel non-specific T cells in ACD reactions. These results show that a single sub-erythematous SSR induces immunosuppression via the cutaneous infiltration of IL-10-producing Tr1, and to a lesser extent, Th2 cells.