Elicitation Of Contact Hypersensitivity Research Articles

Contact Hypersensitivity as a Murine Model of Allergic Contact Dermatitis.

Contact hypersensitivity (CHS) is an experimental model of allergic contact dermatitis (ACD) that can be studied in mice. This study aims to present an objective laboratory method that may help to study the CHS reaction in mice, which can be measured and quantified by various tests. To induce CHS, on day "0", mice were sensitized on a previously shaved spot by abdominal skin painting with the hapten 2,4,6-trinitrochlorobenzene (TNCB) in an acetone-ethanol mixture, whereas negative control mice were sham sensitized with vehicle alone-acetone-ethanol mixture. On day "4", the baseline ear thickness was measured with a micrometer prior to the elicitation of CHS (challenge) by painting both ears with diluted TNCB both in the test and control groups. After 24 h, the ear swelling was measured with a micrometer. CHS is an example of a T cell-mediated immune response that causes swelling in inflamed tissue, peaking 24 h after the skin challenge with the same hapten. An increase in ear edema correlated with augmented ear weight, myeloperoxidase (MPO) activity, pro-inflammatory cytokine concentration in the ear extracts, increased thickening of the edematous dermis in the histological examination, and ear vascular permeability. There was also an increase in the concentration of TNP-specific IgG1 antibodies in the sera of the test group when compared with the control mice. Additionally, CHS can be successfully transferred with the CHS-effector cells obtained from donors previously sensitized with TNCB. The CHS-effector cells were administered intravenously into naïve recipient mice, which were subsequently challenged with the same diluted hapten. Ear swelling was measured with a micrometer 24 h later.

Feeding of a fat-enriched diet causes the loss of resistance to contact hypersensitivity.

Low-molecular weight chemicals or metal ions can cause allergic contact dermatitis, an inflammatory skin disease. Mice lacking Toll-like receptors 2 and 4 (TLR2/4 mice) are resistant to contact hypersensitivity (CHS). In the Western population obesity is increasing, which is known to have a proinflammatory impact. The aim of this study was to investigate the impact of a high-fat diet (HFD) on the sensitization and elicitation of CHS. We hypothesized that a proinflammatory micromilieu can be caused by an increase in adipose tissue, which might be sufficient to break the resistance of TLR2/4 mice. Four weeks prior to sensitization, wild-type (wt) or TLR2/4 mice were fed normal chow (NC), control diet (CD), or HFD. The effects on CHS and inflammation were analysed by measuring the ear swelling response, using flow cytometry and enzyme-linked immunosorbent assay. The reaction of wt mice to 2,4,6-trinitro-1-chlorobenzene (TNCB) was increased by HFD. While NC-fed TLR2/4 mice were still resistant to CHS, HFD and, unexpectedly, CD feeding broke the resistance of TLR2/4 mice to TNCB. These experiments suggest that the increased fat content or the different fatty acid composition of the diets increases inflammation and, therefore, the likelihood of developing CHS.

Silencing of PD-L2/B7-DC by Topical Application of Small Interfering RNA Inhibits Elicitation of Contact Hypersensitivity

Abstract PD-L2 is a ligand for the immune checkpoint receptor PD-1, however, its regulatory function is unclear. We previously reported that silencing of CD86 in cutaneous dendritic cells (DCs) by topical siRNA application inhibits the elicitation of contact hypersensitivity (CHS). Here we investigated the effects of topical PD-L2 siRNA application on allergic skin disease. PD-L2 was induced in DCs concurrently with the elevation of MHC class II and CD86 expression. Topical PD-L2 siRNA application inhibited elicitation of CHS by suppressing early proinflammatory cytokine expression and migration of hapten-carrying DCs into lymph nodes. Local injection of neutralizing anti-PD-L2 mAb comparably inhibited CHS. PD-L2 siRNA treatment inhibited the CHS in PD-1/PD-L1 double-knockout mice and in the sensitized T-cell-transferred skin. These results suggest that the effects of PD-L2 silencing are independent of PD-1 but dependent on local memory T cells. Most of the inhibitory effects of PD-L2 and CD86 silencing on CHS were comparable, but PD-L2 siRNA treatment did not inhibit atopic disease-like manifestations and Th2 responses in NC/Nga mice. Our results suggest that PD-L2 in cutaneous DCs acts as a costimulator rather than a regulator. Local PD-L2 silencing by topical siRNA application represents a new therapeutic approach for contact allergy.

Silencing of PD-L2/B7-DC by Topical Application of Small Interfering RNA Inhibits Elicitation of Contact Hypersensitivity

PD-L2 is a ligand for the immune checkpoint receptor PD-1; however, its regulatory function is unclear. We previously reported that silencing of CD86 in cutaneous dendritic cells by topical application of small interfering RNA (siRNA) inhibits the elicitation of contact hypersensitivity (CHS). Here, we investigated the effects of topical application of PD-L2 siRNA on allergic skin disease. PD-L2 was induced in dendritic cells concurrently with the elevation of major histocompatibility complex class II and CD86 expression. Topical application of PD-L2 siRNA inhibited the elicitation of CHS by suppressing early proinflammatory cytokine expression and migration of hapten-carrying dendritic cells into lymph nodes. Local injection of neutralizing anti-PD-L2 mAb inhibited CHS to the same extent. PD-L2 siRNA treatment inhibited CHS in PD-1/PD-L1 double knockout mice and in the sensitized T-cell-transferred skin. These results suggest that the effects of PD-L2 silencing are independent of PD-1 but dependent on local memory T cells. Most of the inhibitory effects of PD-L2 and CD86 silencing on CHS were comparable, but PD-L2 siRNA treatment did not inhibit atopic disease-like manifestations and T helper type 2 responses in NC/Nga mice. Our results suggest that PD-L2 in cutaneous dendritic cells acts as a costimulator rather than a regulator. Local PD-L2 silencing by topical application of siRNA represents a therapeutic approach for contact allergy.

Antibody Light Chains Dictate the Specificity of Contact Hypersensitivity Effector Cell Suppression Mediated by Exosomes.

Antibody light chains (LCs), formerly considered a waste product of immunoglobulin synthesis, are currently recognized as important players in the activation of the immune response. However, very little is known about the possible immune regulatory functions of LCs. Recently, we reported that hapten-specific LCs coat miRNA-150-carrying exosomes produced by CD8+ suppressor T cells downregulating the contact hypersensitivity (CHS) reaction in an antigen-specific manner, in mice tolerized by intravenous administration of a high dose of hapten-coupled syngeneic erythrocytes. Thus, the current studies aimed at investigating the role of hapten-specific LCs in antigen-specific, exosome-mediated suppression of CHS effector cells. Suppressor T cell-derived exosomes from tolerized B-cell-deficient µMT−/−, NKT-cell-deficient Jα18−/−, and immunoglobulin-deficient JH−/− mice were nonsuppressive, unless supplemented with LCs of specificity strictly respective to the hapten used for sensitization and CHS elicitation in mice. Thus, these observations demonstrate that B1-cell-derived LCs, coating exosomes in vivo and in vitro, actually ensure the specificity of CHS suppression. Our research findings substantially expand current understanding of the newly discovered, suppressor T cell-dependent tolerance mechanism by uncovering the function of antigen-specific LCs in exosome-mediated, cell–cell communication. This express great translational potential in designing nanocarriers for specific targeting of desired cells.

Gene expression profiles in auricle skin as a possible additional endpoint for determination of sensitizers: A multi-endpoint evaluation of the local lymph node assay

The murine local lymph node assay (LLNA) is widely used to test chemicals to induce skin sensitization. Exposure of mouse auricle skin to a sensitizer results in proliferation of local lymph node T cells, which has been measured by in vivo incorporation of H3-methyl thymidine or 5-bromo-2′-deoxyuridine (BrdU). The stimulation index (SI), the ratio of the mean proliferation in each treated group to that in the concurrent vehicle control group, is frequently used as a regulatory-authorized endpoint for LLNA. However, some non-sensitizing irritants, such as sodium dodecyl sulfate (SDS) or methyl salicylate (MS), have been reported as false-positives by this endpoint. In search of a potential endpoint to enhance the specificity of existing endpoints, we evaluated 3 contact sensitizers; (hexyl cinnamic aldehyde [HCA], oxazolone [OXA], and 2,4-dinitrochlorobenzene [DNCB]), 1 respiratory sensitizer (toluene 2,4-diisocyanate [TDI]), and 2 non-sensitizing irritants (MS and SDS) by several endpoints in LLNA. Each test substance was applied to both ears of female CBA/Ca mice daily for 3 consecutive days. The ears and auricle lymph node cells were analyzed on day 5 for endpoints including the SI value, lymph node cell count, cytokine release from lymph node cells, and histopathological changes and gene expression profiles in auricle skin. The SI values indicated that all the test substances induced significant proliferation of lymph node cells. The lymph node cell counts showed no significant changes by the non-sensitizers assessed. The inflammatory findings of histopathology were similar among the auricle skins treated by sensitizers and irritants. Gene expression profiles of cytokines IFN-γ, IL-4, and IL-17 in auricle skin were similar to the cytokine release profiles in draining lymph node cells. In addition, the gene expression of the chemokine CXCL1 and/or CXCL2 showed that it has the potential to discriminate sensitizers and non-sensitizing irritants. Our results suggest that multi-endpoint analysis in the LLNA leads to a better determination of the sensitizing potential of test substances. We also show that the gene expression of CXCL1 and/or CXCL2, which is involved in elicitation of contact hypersensitivity (CHS), can be a possible additional endpoint for discrimination of sensitizing compounds in LLNA.

A novel population of myeloid-derived Gr-1+ CXCR2+CD11c+Ly6C+cells expressing FasL and perforin is required for contact hypersensitivity responses (CAM4P.150)

Abstract Allergic contact hypersensitivity (CHS) is a CD8 T cell mediated response to hapten skin sensitization and challenge. Hapten-primed CD8 cell infiltration into the skin challenge site during elicitation of CHS requires prior infiltration of Gr-1+ CXCR2+ cells expressing FasL and perforin. This study further characterized these Gr-1+ cells. These cells were purified from harvested bone marrow of hapten sensitized and challenged mice by depletion of CD3+, B220+, NK1+, F4/80+, class II MHC+ and Ly6G+ cells. Flow cytometry analyses indicate >90% of the remaining bone marrow cells are FasL+, CD11c+, Ly6C+, CXCR2+, CCR2+, CX3CR1+ and express perforin and granzyme B. These cells are at low numbers in the bone marrow of naïve mice but increase to peak numbers 2 hrs. after hapten challenge of sensitized WT and Rag-/- mice and T-cell depleted WT mice. Generation of these myeloid cells is inhibited by anti-TNFa mAb. Transfer of these myeloid-derived cells from WT donors restores the absent CHS-response in sensitized gld/perforin-/- mice and induces expression of the T cell chemoattractants CCL1, CCL2, and CCL5 in the skin 3-6 hrs after challenge. These results describe a novel population of myeloid cells expressing FasL and perforin/granzyme B that are generated in the bone marrow following hapten challenge of sensitized mice and are activated to induce expression of the chemoattractants directing hapten-primed T cell infiltration into the hapten challenged skin site to mediate CHS.

Low-dose ethanol aggravates allergic dermatitis in mice

Alcohol injures dendritic cells and suppresses cellular immunity, while some evidence indicates that drinking alcohol aggravates allergic asthma. This study investigated the effect of low doses of ethanol in enhancing allergic reactions in the skin of mice. Liquid food containing alcohol was administered to conventional NC/Nga mice to induce alcoholic hepatic steatosis, and spontaneous dermatitis was evaluated. BALB/c mice were administered approximately 1 g/kg body weight of ethanol by gavage, and contact hypersensitivity (CHS) or active cutaneous anaphylaxis (ACA) was induced. Spleens were collected 24 h after the elicitation of CHS and mRNA expressions of interferon (IFN)-γ, interleukin (IL)-4, IL-6, IL-10, and IL-18 were measured by quantitative RT-PCR. Alcohol-containing diet exaggerated spontaneous dermatitis in conventional NC/Nga mice and contact hypersensitivity in BALB/c mice. Ethanol administered by gavage for 5 days enhanced contact hypersensitivity in BALB/c mice. Ethanol administration with gavage also enhanced ACA of BALB/c mice. Ethanol did not affect mRNA expression of IFN-γ and IL-4, but did enhance IL-6, IL-10, and IL-18 mRNA expression. Histological evaluation revealed an absence of hepatic steatosis in mice administered ethanol by gavage for 5 days. In ethanol-administered mice, inflamed areas presented as lesions or a local extreme accumulation of mononuclear cells in the epidermis. These findings suggest that ethanol enhances the expression of inflammatory cytokines independently from T helper (Th)1/Th2 cytokine phenotypes, causing abnormalities in the epidermis resulting in exacerbated allergic reactivity.

N‐acetyl‐S‐farnesyl‐l‐cysteine suppresses chemokine production by human dermal microvascular endothelial cells

Isoprenylcysteine (IPC) molecules modulate G-protein-coupled receptor signalling. The archetype of this class is N-acetyl-S-farnesyl-l-cysteine (AFC). Topical application of AFC locally inhibits skin inflammation and elicitation of contact hypersensitivity in vivo. However, the mechanism of these anti-inflammatory effects is not well understood. Dermal microvascular endothelial cells (ECs) are involved in inflammation, in part, by secreting cytokines that recruit inflammatory cells. We have previously shown that the sympathetic nerve cotransmitter adenosine-5'-triphosphate (ATP) and adenosine-5'-O-(3-thio) triphosphate (ATPγS), an ATP analogue that is resistant to hydrolysis, increase secretion of the chemokines CXCL8 (interleukin-8), CCL2 (monocyte chemotactic protein-1) and CXCL1 (growth-regulated oncogene α) by dermal microvascular ECs. Production of these chemokines can also be induced by the exposure to the proinflammatory cytokine TNFα. We have now demonstrated that AFC dose-dependently inhibits ATP-, ATPγS- and TNFα-induced production of CXCL1, CXCL8 and CCL2 by a human dermal microvascular EC line (HMEC-1) in vitro under conditions that do not affect cell viability. Inhibition of ATPγS- or TNFα-stimulated release of these chemokines was associated with reduced mRNA levels. N-acetyl-S-geranyl-l-cysteine, an IPC analogue that is inactive in inhibiting G-protein-coupled signalling, had greatly reduced ability to suppress stimulated chemokine production. AFC may exert its anti-inflammatory effects through the inhibition of chemokine production by stimulated ECs.

Contact Sensitizers Induce Skin Inflammation via ROS Production and Hyaluronic Acid Degradation

BackgroundAllergic contact dermatitis (ACD) represents a severe health problem with increasing worldwide prevalence. It is a T cell-mediated skin disease induced by protein-reactive organic and inorganic chemicals. A key feature of contact allergens is their ability to trigger an innate immune response that leads to skin inflammation. Previous evidence from the mouse contact hypersensitivity (CHS) model suggests a role for endogenous activators of innate immune signaling. Here, we analyzed the role of contact sensitizer induced ROS production and concomitant changes in hyaluronic acid metabolism on CHS responses.Methodology/Principal FindingsWe analyzed in vitro and in vivo ROS production using fluorescent ROS detection reagents. HA fragmentation was determined by gel electrophoresis. The influence of blocking ROS production and HA degradation by antioxidants, hyaluronidase-inhibitor or p38 MAPK inhibitor was analyzed in the murine CHS model. Here, we demonstrate that organic contact sensitizers induce production of reactive oxygen species (ROS) and a concomitant breakdown of the extracellular matrix (ECM) component hyaluronic acid (HA) to pro-inflammatory low molecular weight fragments in the skin. Importantly, inhibition of either ROS-mediated or enzymatic HA breakdown prevents sensitization as well as elicitation of CHS.Conclusions/SignificanceThese data identify an indirect mechanism of contact sensitizer induced innate inflammatory signaling involving the breakdown of the ECM and generation of endogenous danger signals. Our findings suggest a beneficial role for anti-oxidants and hyaluronidase inhibitors in prevention and treatment of ACD.

In vivo reprogramming of UV radiation–induced regulatory T-cell migration to inhibit the elicitation of contact hypersensitivity

Regulatory T (Treg) cells induced by UV radiation (UVR) inhibit only the induction and not the elicitation of contact hypersensitivity (CHS) because they migrate into the lymph nodes but not the skin. The tissue-homing receptor expression and migratory behavior of Treg cells can be altered by means of invitro coincubation with skin-derived antigen-presenting cells. On this invitro treatment, Treg cells migrate into the skin and thus inhibit the elicitation of CHS. We attempted to determine whether Treg cells can be induced by UVR in sensitized mice and manipulated entirely invivo in such a way that they suppress the elicitation of immune responses. Treg cells were induced by applying contact allergens onto UV-exposed skin in wild-type, langerin diphtheria toxin receptor knock-in, or depletion of Treg cell transgenic mice. UVR-induced Treg cells inhibit the elicitation of CHS in sensitized mice when stimulated by means of an antigen-specific boost through the skin. This requires cutaneous antigen-presenting cells that alter the migratory behavior of Treg cells and drive them out of the lymph nodes into the skin. The indication is that antigen-specific Treg cells can be induced in sensitized hosts and manipulated in such a way that they suppress the elicitation of specific immune reactions. Because this is achieved entirely invivo without invasive interventions, our findings might have important implications for strategies aiming to induce and use Treg cells in a therapeutic setting.

Crucial role for human Toll-like receptor 4 in the development of contact allergy to nickel

Allergies to nickel (Ni(2+)) are the most frequent cause of contact hypersensitivity (CHS) in industrialized countries. The efficient development of CHS requires both a T lymphocyte-specific signal and a proinflammatory signal. Here we show that Ni(2+) triggered an inflammatory response by directly activating human Toll-like receptor 4 (TLR4). Ni(2+)-induced TLR4 activation was species-specific, as mouse TLR4 could not generate this response. Studies with mutant TLR4 proteins revealed that the non-conserved histidines 456 and 458 of human TLR4 are required for activation by Ni(2+) but not by the natural ligand lipopolysaccharide. Accordingly, transgenic expression of human TLR4 in TLR4-deficient mice allowed efficient sensitization to Ni(2+) and elicitation of CHS. Our data implicate site-specific human TLR4 inhibition as a potential strategy for therapeutic intervention in CHS that would not affect vital immune responses.

CD22 Expression Mediates the Regulatory Functions of Peritoneal B-1a Cells during the Remission Phase of Contact Hypersensitivity Reactions

Although contact hypersensitivity (CHS) has been considered a prototype of T cell-mediated immune reactions, recently a significant contribution of regulatory B cell subsets in the suppression of CHS has been demonstrated. CD22, one of the sialic acid-binding immunoglobulin-like lectins, is a B cell-specific molecule that negatively regulates BCR signaling. To clarify the roles of B cells in CHS, CHS in CD22(-/-) mice was investigated. CD22(-/-) mice showed delayed recovery from CHS reactions compared with that of wild-type mice. Transfer of wild-type peritoneal B-1a cells reversed the prolonged CHS reaction seen in CD22(-/-) mice, and this was blocked by the simultaneous injection with IL-10 receptor Ab. Although CD22(-/-) peritoneal B-1a cells were capable of producing IL-10 at wild-type levels, i.p. injection of differentially labeled wild-type/CD22(-/-) B cells demonstrated that a smaller number of CD22(-/-) B cells resided in lymphoid organs 5 d after CHS elicitation, suggesting a defect in survival or retention in activated CD22(-/-) peritoneal B-1 cells. Thus, our study reveals a regulatory role for peritoneal B-1a cells in CHS. Two distinct regulatory B cell subsets cooperatively inhibit CHS responses. Although splenic CD1d(hi)CD5(+) B cells have a crucial role in suppressing the acute exacerbating phase of CHS, peritoneal B-1a cells are likely to suppress the late remission phase as "regulatory B cells." CD22 deficiency results in disturbed CHS remission by impaired retention or survival of peritoneal B-1a cells that migrate into lymphoid organs.

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.

IL-17 and IFN-γ Mediate the Elicitation of Contact Hypersensitivity Responses by Different Mechanisms and Both Are Required for Optimal Responses

Hapten-induced contact hypersensitivity (CHS) in the skin is a delayed type cellular immune response that can be mediated by CD8(+) T cells that produce IFN-gamma or IL-17. However, mechanisms for these cytokines in the elicitation of CHS remain to be fully elucidated. In this study, we show that adoptive transfer of CHS with hapten-primed wild-type (WT) CD8(+) T cells is reduced in IFN-gammaR(-/-) or IL-17R(-/-) mice compared with WT controls. The infiltration of granulocytes and macrophages in the hapten challenged skin of IL-17R(-/-) recipients is significantly reduced whereas it is less affected in IFN-gammaR(-/-) recipients although CD8(+) T cell infiltration is inhibited in both recipients. In contrast, the activity of reactive oxidative species is significantly inhibited in IFN-gammaR(-/-) but is less affected in IL-17R(-/-) recipients. Further analysis reveals that the expression of chemokines and cytokines is differentially regulated in the hapten-challenged skin of IFN-gammaR(-/-) or IL-17R(-/-) recipients compared with WT controls. Interestingly, injection of rIL-17 in the skin induces inflammation with a high level of leukocyte infiltration whereas injection of IFN-gamma induces inflammation with a high level of reactive oxidative species. Moreover, neutralization of IL-17 in IFN-gammaR(-/-) or IFN-gamma in IL-17R(-/-) mice further suppresses the adoptive transfer of CHS by hapten-primed WT CD8(+) T cells. The study demonstrates that IFN-gamma and IL-17 mediate the elicitation of CHS by different mechanisms and that both cytokines are required for optimal responses. This outcome improves understanding of pathogenesis and provides new insights into therapeutic strategies for CHS.

Ultraviolet B Suppresses Immunity by Inhibiting Effector and Memory T Cells

Contact hypersensitivity is a T-cell-mediated response to a hapten. Exposing C57BL/6 mice to UV B radiation systemically suppresses both primary and secondary contact hypersensitivity responses. The effects of UVB on in vivo T-cell responses during UVB-induced immunosuppression are unknown. We show here that UVB exposure, before contact sensitization, inhibits the expansion of effector CD4+ and CD8+ T cells in skin-draining lymph nodes and reduces the number of CD4+ and IFN-gamma+ CD8+ T cells infiltrating challenged ear skin. In the absence of UVB, at 10 weeks after initial hapten exposure, the ear skin of sensitized mice was infiltrated by dermal effector memory CD8+ T cells at the site of challenge. However, if mice were previously exposed to UVB, this cell population was absent, suggesting an impaired development of peripheral memory T cells. This finding occurred in the absence of UVB-induced regulatory CD4+ T cells and did not involve prostaglandin E2, suggesting that the importance of these two factors in mediating or initiating UVB-induced immunosuppression is dependent on UVB dose. Together these data indicate that in vivo T-cell responses are prone to immunoregulation by UVB, including a novel effect on both the activated T-cell pool size and the development of memory T cells in peripheral compartments.

Chemokines and Their Receptors as a Target for the Treatment of Contact Hypersensitivity

Contact hypersensitivity (CHS) is an antigen-specific response elicited by exposure to certain low-molecularweight compounds termed haptens, and is the disease often seen clinically. CHS has also been used as a useful model to assess antigen-specific and T cell-dependent immune response. A wide variety of cells are thought to be involved in the pathogenesis of CHS. Keratinocytes and T cells are regarded as important factors, and besides these cells, mast cells, fibroblasts, B cells, macrophages, neutrophils have been demonstrated to be involved. From the studies of gene knockout experiments, it has been gleaned that IL-1β, IL-2, IL-3, IL-4, IL-6, IL-10, IFN-γ, TNF-α are associated with elicitation of CHS. While the roles of these cytokines in CHS have been well elucidated, recent attention has been directed at members of the superfamily of chemoattractant cytokines that are collectively termed chemokines. Both of mouse and human CHS studies showed chemokine genes were sequentially expressed in the elicitation site, suggesting that chemokine-mediated nonimmunological mechanisms precede and corroborate antigen-specific mechanisms during elicitation of CHS. In a mouse CHS study, topical treatment with a corticosteroid drug suppressed completely the infiltrates as well as the ear swelling response. In addition, the up-regulation of gene expressions for chemokines was suppressed by the corticosteroid drug, indicating that the expression of chemokine genes seems to be essential for orientating non-specific skin response to hapten-specific CHS response through the recruitment of inflammatory cells from the circulation into the tissue site. In this review, we discuss the proposed function of chemokines in the pathogenesis of CHS.

The relationships between exposure dose and response in induction and elicitation of contact hypersensitivity in humans

Like all physiological systems, the human immune system exhibits dose-response relationships in its reactions. The strength of sensitization is related to the potency of the immunogen and the dose that reaches the immune system. In skin, as sensitizing dose per unit area (mug cm(-2)) is increased on a log scale, there is a sigmoid dose-response curve for subsequent reactivity. Similarly, the response to elicitation shows a classical sigmoid response to increasing challenge dose, with the dose per unit area again being the determinant. There is a clear inverse correlation between the strength of sensitization and the subsequent dose of antigen to which an individual will respond. This is reflected in the different challenge systems used to diagnose the existence of allergic contact sensitization to a given allergen. The occluded patch test aims to use the highest concentration possible to detect the weakest degrees of allergy, whereas the repeated open application test uses much lower concentrations similar to those encountered in real life, applied repeatedly but without occlusion, to assess clinical relevance. Many authors have attempted to use the lowest concentrations to which rare, highly sensitized individuals can react to define the concentrations which might be free of risk in terms of inducing allergic sensitization. However, it is clear that the dose-response relationships for induction of sensitivity by repeated low-dose exposures must be carefully defined in future studies. This article reviews the dose-response relationships of human contact sensitization.

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.

CD8+ Tc1 and TIL-17 cells mediate allergic contact hypersensitivity by different mechanisms (37.18)

Abstract Allergen induced contact hypersensitivity(CHS) in the skin has been considered to be mediated by CD4+ Th1 and CD8+ Tc1 cells that produce IFN-γ. Our recent studies have demonstrated that CD8+ IL-17 producing T cells (TIL-17) play important roles in the elicitation of CHS. Allergen sensitization induces the development of CD8+ Tc1 and TIL-17 cells that are distinct T cell subpopulations. Here we demonstrate that both CD8+ Tc1 and TIL-17 cells play a role in the elicitation of CHS. However, they mediate inflammatory reactions in the skin by different mechanisms. CHS was reduced but not abolished in mice that were defect in the receptor for IFN-γ (IFN-γR−/−) or IL-17 (IL-17R−/−) compared to wild type controls. Similar results were observed in the adoptive transfer of CHS in the gene knockout mice that were transferred with allergen primed wild type CD8+ T cells. However, neutralization of IL-17 in IFN-γR−/− or IFN-γ in IL-17R−/− recipient mice abrogated the response. It implicates that both IFN-γ and IL-17 signals are involved in the elicitation of CHS and are required for optimal responses. Immunohistochemical analysis indicated that the infiltration of Gr-1+ granulocytes and CD11b+ macrophages in the allergen challenged skin of IL-17R−/− mice was significantly reduced whereas it was slightly affected in IFN-γR−/− mice. Further analysis using real time RT-PCR showed different patterns of chemokines and inflammatory cytokines in the allergen challenged skin of IFN-γR−/− or IL-17R−/− mice. These data indicate that both CD8+ Tc1 and TIL-17 cells take part in the elicitation of CHS and that specific mechanisms orchestrate Tc1 and TIL-17 mediated inflammatory reactions in the skin. The result of current studies may provide new insights into therapeutic strategies for T cell mediated inflammatory disorders.