Hapten application to the skin induces an inflammatory program directing hapten-primed effector CD8 T cell interaction with hapten-presenting endothelial cells

The VCAM1-ApoE pathway directs microglial chemotaxis and alleviates Alzheimer's disease pathology

In Alzheimer's disease (AD), sensome receptor dysfunction impairs microglial danger-associated molecular pattern (DAMP) clearance and exacerbates disease pathology. Although extrinsic signals, including interleukin-33 (IL-33), can restore microglial DAMP clearance, it remains largely unclear how the sensome receptor is regulated and interacts with DAMP during phagocytic clearance. Here, we show that IL-33 induces VCAM1 in microglia, which promotes microglial chemotaxis toward amyloid-beta (Aβ) plaque-associated ApoE, and leads to Aβ clearance. We show that IL-33 stimulates a chemotactic state in microglia, characterized by Aβ-directed migration. Functional screening identified that VCAM1 directs microglial Aβ chemotaxis by sensing Aβ plaque-associated ApoE. Moreover, we found that disrupting VCAM1-ApoE interaction abolishes microglial Aβ chemotaxis, resulting in decreased microglial clearance of Aβ. In patients with AD, higher cerebrospinal fluid levels of soluble VCAM1 were correlated with impaired microglial Aβ chemotaxis. Together, our findings demonstrate that promoting VCAM1-ApoE-dependent microglial functions ameliorates AD pathology.

Contact dermatitis

Contact dermatitis (CD) is among the most common inflammatory dermatological conditions and includes allergic CD, photoallergic CD, irritant CD, photoirritant CD (also called phototoxic CD) and protein CD. Occupational CD can be of any type and is the most prevalent occupational skin disease. Each CD type is characterized by different immunological mechanisms and/or requisite exposures. Clinical manifestations of CD vary widely and multiple subtypes may occur simultaneously. The diagnosis relies on clinical presentation, thorough exposure assessment and evaluation with techniques such as patch testing and skin-prick testing. Management is based on patient education, avoidance strategies of specific substances, and topical treatments; in severe or recalcitrant cases, which can negatively affect the quality of life of patients, systemic medications may be needed.

Regulatory T Cells Prevent Neutrophilic Infiltration of Skin during Contact Hypersensitivity Reactions by Strengthening the Endothelial Barrier

The healing phase of contact hypersensitivity reactions is critically dependent on regulatory T cells (Tregs), but even the early inflammatory phase, that is, 6-24 hours after induction of a contact hypersensitivity reaction, is susceptible to Treg-mediated suppression. To investigate the underlying mechanisms, we injected Tregs before the challenge and analyzed the skin-infiltrating cells as early as 6 hours later. Early on, we found mainly neutrophils in the challenged skin, but only a few T cells. This influx of neutrophils was blocked by the injection of Tregs, indicating that they were able to prevent the first wave of leukocytes, which are responsible for starting an immune reaction. As an underlying mechanism, we identified that Tregs can tighten endothelial junctions by inducing intracellular cAMP, leading to protein kinase A-RhoA‒dependent signaling. This eventually reorganizes endothelial junction proteins, such as Notch3, Nectin 2, Filamin B, and VE-cadherin, all of which contribute to the tightening of the endothelial barrier. In summary, Tregs prevent the leakage of proinflammatory cells from and into the tissue, which establishes a mechanism to downregulate immune reactions.

Galectin-1 Expression in CD8+ T Lymphocytes Controls Inflammation in Contact Hypersensitivity

Allergic contact dermatitis, also known as contact hypersensitivity, is a frequent T-cell‒mediated inflammatory skin disease characterized by red, itchy, swollen, and cracked skin. It is caused by the direct contact with an allergen and/or irritant hapten. Galectin-1 (Gal-1) is a β-galactoside‒binding lectin, which is highly expressed in several types of immune cells. The role of endogenous Gal-1 in contact hypersensitivity is not known. We found that Gal-1‒deficient mice display more sustained and prolonged skin inflammation than wild-type mice after oxazolone treatment. Gal-1‒deficient mice have increased CD8⁺ T cells and neutrophilic infiltration in the skin. After the sensitization phase, Gal-1‒depleted mice showed an increased frequency of central memory CD8⁺ T cells and IFN-γ secretion by CD8⁺ T cells. The absence of Gal-1 does not affect the migration of transferred CD4⁺ and CD8⁺ T cells from the blood to the lymph nodes or to the skin. The depletion of CD4⁺ T lymphocytes as well as adoptive transfer experiments demonstrated that endogenous expression of Gal-1 on CD8⁺ T lymphocytes exerts a major role in the control of contact hypersensitivity model. These data underscore the protective role of endogenous Gal-1 in CD8⁺ but not CD4⁺ T cells in the development of allergic contact dermatitis.

Role of Lymphoid Structure in Skin Immunity

The skin is the outermost organ of the body and is exposed to many kinds of external pathogens. To manage this, the skin contains multiple types of immune cells. To achieve sufficient induction of cutaneous adaptive immune responses, the antigen presentation/recognition in the skin is an essential process. Recent studies have expanded our knowledge of how T cells survey their cognate antigens in the skin. In addition, the formation of a lymphoid cluster, named inducible skin-associated lymphoid tissue (iSALT), has been reported during skin inflammation. Although iSALT may not be classified as a typical tertiary lymphoid organ, it provides specific antigen presentation sites in the skin. In this article, we provide an overview of the antigen presentation mechanism in the skin, with a focus on the development of iSALT and its function.

Pharmacologic inhibition of hypoxia-inducible factor (HIF)-hydroxylases ameliorates allergic contact dermatitis

BACKGROUND

When an immune cell migrates from the bloodstream to a site of chronic inflammation, it experiences a profound decrease in microenvironmental oxygen levels leading to a state of cellular hypoxia. The hypoxia-inducible factor-1α (HIF-1α) promotes an adaptive transcriptional response to hypoxia and as such is a major regulator of immune cell survival and function. HIF hydroxylases are the family of oxygen-sensing enzymes primarily responsible for conferring oxygen dependence upon the HIF pathway.

METHODS

Using a mouse model of allergic contact dermatitis (ACD), we tested the effects of treatment with the pharmacologic hydroxylase inhibitor DMOG, which mimics hypoxia, on disease development.

RESULTS

Re-exposure of sensitized mice to 2,4-dinitrofluorobenzene (DNFB) elicited inflammation, edema, chemokine synthesis (including CXCL1 and CCL5) and the recruitment of neutrophils and eosinophils. Intraperitoneal or topical application of the pharmacologic hydroxylase inhibitors dymethyloxalylglycine (DMOG) or JNJ1935 attenuated this inflammatory response. Reduced inflammation was associated with diminished recruitment of neutrophils and eosinophils but not lymphocytes. Finally, hydroxylase inhibition reduced cytokine-induced chemokine production in cultured primary keratinocytes through attenuation of the JNK pathway.

CONCLUSION

These data demonstrate that hydroxylase inhibition attenuates the recruitment of neutrophils to inflamed skin through reduction of chemokine production and increased neutrophilic apoptosis. Thus, pharmacologic inhibition of HIF hydroxylases may be an effective new therapeutic approach in allergic skin inflammation.

Epidermal NLRP10 contributes to contact hypersensitivity responses in mice

The nucleotide binding and oligomerization domain-like receptor (NLR) protein NLRP10 is highly expressed in the epidermis and contributes to cell-autonomous responses against invasive bacteria. To investigate the role of NLRP10 in inflammatory responses of the skin we analyzed the effect of full-body and keratinocyte-specific depletion of NLRP10 in croton oil-induced irritant contact dermatitis (ICD) and 1-fluoro-2,4-dinitrobenzene (DNFB)-induced contact hypersensitivity (CHS) in mice. Nlrp10(-/-) mice were phenotypically normal and skin repair after wounding was not affected by lack of NLRP10. Similarly, we did not detect a contribution of NLRP10 to the ICD response induced by croton oil. In contrast, Nlrp10(-/-) mice showed significantly reduced inflammation in the DNFB-induced CHS response as compared to control animals. Microscopic analysis revealed significantly reduced numbers of CD4(+) and CD8(+) T cells in the infiltrates of animals lacking NLRP10 expression after CHS challenge. Epidermis-specific deletion of Nlrp10 by keratin-14 promotor driven Cre-recombinase was sufficient to account for this phenotype, although lymphocyte recruitment seemed to be unaltered in animals lacking NLRP10 expression in keratinocytes. Taken together, we provide evidence that NLRP10 contributes to T-cell-mediated inflammatory responses in the skin and highlight a physiological role of NLRP10 in epidermal keratinocytes.

The NF-κB regulator Bcl-3 modulates inflammation during contact hypersensitivity reactions in radioresistant cells

Bcl-3 is an atypical member of the IκB family. Bcl-3 functions as a cofactor of p50/NF-κB1 or p52/NF-κB2 homodimers in nuclei, where it modulates NF-κB-regulated transcription in a context-dependent way. Bcl-3 has tumorigenic potential, is critical in host defense of pathogens, and has been reported to ameliorate or exacerbate inflammation, depending on disease model. However, cell-specific functions of Bcl-3 remain largely unknown. Here, we explored the role of Bcl-3 in a contact hypersensitivity (CHS) mouse model, which depends on the interplay between keratinocytes and immune cells. Bcl-3-deficient mice exhibited an exacerbated and prolonged CHS response to oxazolone. Increased inflammation correlated with higher production of chemokines CXCL2, CXCL9, and CXCL10, and consequently increased recruitment of neutrophils and CD8(+) T cells. BM chimera experiments indicated that the ability of Bcl-3 to reduce the CHS response depended on Bcl-3 activity in radioresistant cells. Specific ablation of Bcl-3 in keratinocytes resulted in increased production of CXCL9 and CXCL10 and sustained recruitment of specifically CD8(+) T cells. These findings identify Bcl-3 as a critical player during the later stage of the CHS reaction to limit inflammation via actions in radioresistant cells, including keratinocytes.

Systemic immunogenicity of para-Phenylenediamine and Diphenylcyclopropenone: two potent contact allergy-inducing haptens

p-Phenylenediamine (PPD) and Diphenylcyclopropenone (DPCP) are two potent haptens. Both haptens are known to cause delayed-type hypersensitivity, involving a cytokine response and local infiltration of T-cell subpopulations, resulting in contact dermatitis. We investigated the systemic immune effects of PPD and DPCP, two relatively unexplored skin allergens. The dorsal sides of the ears of BALB/c mice were exposed to PPD or DPCP (0.1% w/v or 0.01% w/v), or vehicle alone. Mice were treated once daily for 3 days (induction period) and subsequently twice per week for 8 weeks. Local and systemic immune responses in the auricular and pancreatic lymph nodes, spleen, liver, serum, and ears were analyzed with cytokine profiling MSD, flow cytometry, and qPCR. Ear swelling increased significantly in mice treated with 1% PPD, 0.01% DPCP or 0.1% DPCP, compared with vehicle treatment, indicating that the mice were sensitized and that there was a local inflammation. Auricular lymph nodes, pancreatic lymph nodes, spleen, and liver showed changes in regulatory T-cell, B-cell, and NKT-cell frequencies, and increased activation of CD8(+) T cells and B cells. Intracellular cytokine profiling revealed an increase in the IFN-γ- and IL-4-positive NKT cells present in the liver following treatment with both haptens. Moreover, we saw a tendency toward a systemic increase in IL-17A. We observed systemic immunological effects of PPD and DPCP. Furthermore, concentrations too low to increase ear thickness and cause clinical symptoms may still prime the immune system. These systemic immunological effects may potentially predispose individuals to certain diseases.

Hapten-induced contact hypersensitivity, autoimmune reactions, and tumor regression: plausibility of mediating antitumor immunity

Haptens are small molecule irritants that bind to proteins and elicit an immune response. Haptens have been commonly used to study allergic contact dermatitis (ACD) using animal contact hypersensitivity (CHS) models. However, extensive research into contact hypersensitivity has offered a confusing and intriguing mechanism of allergic reactions occurring in the skin. The abilities of haptens to induce such reactions have been frequently utilized to study the mechanisms of inflammatory bowel disease (IBD) to induce autoimmune-like responses such as autoimmune hemolytic anemia and to elicit viral wart and tumor regression. Hapten-induced tumor regression has been studied since the mid-1900s and relies on four major concepts: (1) ex vivo haptenation, (2) in situ haptenation, (3) epifocal hapten application, and (4) antigen-hapten conjugate injection. Each of these approaches elicits unique responses in mice and humans. The present review attempts to provide a critical appraisal of the hapten-mediated tumor treatments and offers insights for future development of the field.

Chronic psychological stress suppresses contact hypersensitivity: potential roles of dysregulated cell trafficking and decreased IFN-γ production

Increasing evidence shows that psychological stress can have dramatic impacts on the immune system, particularly the cutaneous immune response in dermatological disorders. While there have been many studies examining the impact of acute psychological stress on contact hypersensitivity there are relatively few studies concerning the impact of chronic psychological stress. Furthermore, the local immunological mechanisms by which chronic psychological stress impacts contact hypersensitivity still remain to be explored. Here we show that restraint-induced chronic psychological stress stimulates activation of the hypothalamus-pituitary-adrenal axis and delays weight gain in female BALB/c mice. We observed that chronic psychological stress reduces the cutaneous immune response as evidence by reduced ear swelling. This correlated with a significant decrease in the inflammatory cell infiltrate. On the other hand, chronic psychological stress does not influence T cell proliferation, activation, or sensitivity to corticosterone but does increase CD4(+) and CD8(+) T cell percentages in draining lymph nodes during a contact hypersensitivity reaction. Chronic psychological stress induces a decrease in overall circulating white blood cells, lymphocytes, and monocytes during a contact hypersensitivity reaction suggesting extravasation from the circulation. Finally, we found markedly reduced local IFN-γ production in chronically stressed animals. Based on these findings we propose that chronic psychological stress reduces contact hypersensitivity due to dysregulated cell trafficking and reduced production of IFN-γ.

Immunomics in Skin Cancer - Improvement in Diagnosis, Prognosis and Therapy Monitoring

This review will focus on the elements of the skin’s immune system, immune cells and/or non-immune cells that support immune mechanisms, molecules with immune origin and/or immune functions that are involved in skin carcinogenesis. All these immune elements are compulsory in the development of skin tumors and/or sustainability of the neoplastic process. In this light, recent data gathered in this review will acknowledge all immune elements that contribute to skin tumorigenesis; moreover, they can serve as immune biomarkers. These immune markers can contribute to the diagnostic improvement, prognosis forecast, therapy monitoring, and even personalized therapeutical approach in skin cancer. Immune processes that sustain tumorigenesis in non-melanoma and melanoma skin cancers are described in the framework of recent data.

CD8 T cells regulate allergic contact dermatitis by modulating CCR2-dependent TNF/iNOS-expressing Ly6C+ CD11b+ monocytic cells

Monocytes and their derived cells have critical roles in inflammation and immune defense. However, their function in skin diseases such as allergic contact dermatitis remains poorly defined. Using a model of contact hypersensitivity (CHS) toward 2,4-dinitrochlorobenzene, we show that Ly6C+ CD11b+ monocytic cells participate in the pathophysiology of CHS and their accumulation is regulated by effector CD8 T cells. These Ly6C+ CD11b+ monocytic cells are the primary contributors of tumor necrosis factor-α (TNF-α) and inducible nitric oxide synthase (iNOS) and derive from Ly6C(hi)CCR2+ monocytes, as they were absent in non-inflamed skin and accumulate as a consequence of inflammation in a C-C chemokine receptor type 2 (CCR2)-dependent manner. Importantly, CCR2(-/-) mice, or wild-type mice depleted of monocytes via clodronate liposomes, display a marked decrease in TNF-α and iNOS expression accompanied by attenuated skin inflammation. Using transgenic mice and antibody depletion, we show that effector CD8 T cells regulate the accumulation of Ly6C+ CD11b+ monocytic cells through IL-17 and activate them for TNF-α and iNOS through IFN-γ. CD8 T cell-derived IFN-γ was also critical for the accumulation of the major histocompatibility complex II-expressing Ly6C+ CD11b+ subset, which expressed intermediate levels of CD11c and costimulatory molecules. Taken together, our findings provide further insight into the pathophysiology of allergic contact dermatitis by showing that CD8 T cells regulate the inflammatory cascade through TNF/iNOS-expressing Ly6C+ CD11b+ monocytic cells.

Role of Th17 cells in skin inflammation of allergic contact dermatitis

Extending the classical concept considering an imbalance exclusively of T helper(h) 1 and Th2 cells on the bottom of many inflammatory diseases, Th17 cells were recently described. Today, there is sufficient experimental evidence to classify psoriasis and allergic contact dermatitis (ACD) amongst other inflammatory skin disorders as IL-17 associated diseases. In several human studies, T-cell-clones could be isolated from eczema biopsies, and high IL-17 levels were observed after challenge with allergen. In the last years, the phenotype of these IL-17 releasing T cells was in the focus of discussion. It has been suggested that Th17 could be identified by expression of retinoic acid receptor-related orphan receptor (ROR)C (humans) or RORγt (mice) and IL-17, accompanied by the absence of IFN-γ and IL-22. In cells from skin biopsies, contact allergens elevate IL-17A, IL-23, and RORC within the subset of Th cells. The indications for a participation of Th17 in the development of ACD are supported by data from IL-17 deficient mice with reduced contact hypersensitivity (CHS) reactions that could be restored after transplantation of wild type CD4⁺ T cells. In addition to Th17 cells, subpopulations of CD8⁺ T cells and regulatory T cells are further sources of IL-17 that play important roles in ACD as well. Finally, the results from Th17 cell research allow today identification of different skin diseases by a specific profile of signature cytokines from Th cells that can be used as a future diagnostic tool.

Cannabinoid 1 receptors in keratinocytes modulate proinflammatory chemokine secretion and attenuate contact allergic inflammation

Epidermal keratinocytes (KCs) and cannabinoid (CB) receptors both participate in the regulation of inflammatory responses in a mouse model for allergic contact dermatitis, the contact hypersensitivity (CHS) response to the obligate sensitizer 2,4-dinitrofluorobenzene. In this study, we investigated the cellular and molecular mechanisms how CB1 receptors attenuate CHS responses to 2,4-dinitrofluorobenzene. We used a conditional gene-targeting approach to identify the relative contribution of CB1 receptors on epidermal KCs for the control of CHS responses. To determine the underlying cellular and molecular mechanisms that regulate inflammatory responses in the effector phase of CHS, we performed further investigations on inflamed ear tissue and primary KC cultures using morphologic, molecular, and immunologic methods. Mice with a KC-specific deletion of CB1 receptors developed increased and prolonged CHS responses. These were associated with enhanced reactive epidermal acanthosis and inflammatory KC hyperproliferation in the effector phase of CHS. In vitro, primary cultures of CB1 receptor-deficient KC released increased amounts of CXCL10 and CCL8 after stimulation with IFN-γ compared with controls. In vivo, contact allergic ear tissue of CB1 receptor-deficient KCs showed enhanced expression of CXCL10 and CCL8 compared with controls. Further investigations established CCL8 as a proinflammatory chemokine regulated by CB1 receptors that promotes immune cell recruitment to allergen-challenged skin. Taken together, these results demonstrate that CB1 receptors are functionally expressed by KCs in vivo and help to limit the secretion of proinflammatory chemokines that regulate T cell-dependent inflammation in the effector phase of CHS.

Decorin potentiates interferon-γ activity in a model of allergic inflammation

The proteoglycan decorin modulates leukocyte recruitment during delayed-type hypersensitivity responses. Decorin-deficient (Dcn(-/-)) mice show reduced edema formation during the first 24 h with a concurrent attenuated recruitment of CD8(+) leukocytes in the inflamed Dcn(-/-) ears. The aim of this study was to elucidate the molecular pathways affected by the loss of decorin. In vivo, reduced numbers of CD8(+) cells in Dcn(-/-) ears correlated with a reduced interferon-γ (Ifn-γ) and CXCL-10 expression. In vitro, Dcn(-/-) lymphocytes displayed an increased adhesion to brain microvascular (bEnd.3) endothelial cells. Decorin treatment of bEnd.3 increased Icam1 and down-regulated Vcam1 expression after TNF-α stimulation. However, Dcn(-/-) and wild-type lymphocytes produced IFN-γ after activation with CD3ε. Upon incubation with decorin, endothelial cells and fibroblasts responded differently to IFN-γ and TNF-α; CCL2 in bEnd.3 cells was more prominently up-regulated by TNF-α compared with IFN-γ. Notably, both factors were more potent in the presence of decorin. Compared with TNF-α, IFN-γ treatment induced significantly more CXCL-10, and both factors increased synthesis of CXCL-10 in the presence of decorin. The response to IFN-γ was similar in Dcn(-/-) and wild-type fibroblasts, an additional source of CXCL-10. However, addition of decorin yielded significantly more CXCL-10. Notably, decorin increased the stability of IFN-γ in vitro and potentiated IFN-γ-induced activation of STAT-1. Furthermore, only dermatan sulfate influenced IFN-γ signaling by significantly increasing CXCL-10 expression in contrast to decorin protein core alone. Our data demonstrate that decorin modulates delayed-type hypersensitivity responses by augmenting the induction of downstream effector cytokines of IFN-γ and TNF-α, thereby influencing the recruitment of CD8(+) lymphocytes into the inflamed tissue.

Allergic contact dermatitis: xenoinflammation of the skin

Many xenobiotic chemicals cause sterile inflammation. This xenoinflammation is often induced by protein reactive contact allergens resulting in allergic contact dermatitis (ACD). Recent findings reveal that these chemicals mimick infection by triggering innate immune responses via pattern recognition receptors (PRRs) and endogenous danger signals. The emerging cellular responses in ACD are mediated by various innate effector cells. Here, an important role for mast cells has now been recognized. Eventually, chemical specific T cells such as CD8+ and CD4+ Tc1/Th1 as well as Tc17/Th17 cells are activated. Langerhans cells may serve a tolerogenic function. The mechanisms of tolerance induction by ultraviolet irradiation or by very low doses of contact allergen are now understood in much greater detail.

Neutrophil expression of Fas ligand and perforin directs effector CD8 T cell infiltration into antigen-challenged skin

Contact hypersensitivity (CHS) is a T cell response to hapten skin challenge of sensitized individuals proposed to be mediated by hapten-primed CD8 cytolytic T cells. Effector CD8 T cell recruitment into hapten challenge sites to elicit CHS requires prior CXCL1- and CXCL2-mediated neutrophil infiltration into the site. We investigated whether neutrophil activities directing hapten-primed CD8 T cell skin infiltration in response to 2,4-dinitro-1-fluorobenzene (DNFB) required Fas ligand (FasL) and perforin expression. Although DNFB sensitization of gld/perforin-/- mice induced hapten-specific CD8 T cells producing IFN-γ and IL-17, these T cells did not infiltrate the DNFB challenge site to elicit CHS but did infiltrate the challenge site and elicit CHS when transferred to hapten-challenged naive wild-type recipients. Hapten-primed wild-type CD8 T cells, however, did not elicit CHS when transferred to naive gld/perforin-/- recipients. Wild-type bone marrow neutrophils expressed FasL and perforin, and when transferred to sensitized gld/perforin-/- mice, they restored hapten-primed CD8 T cell infiltration into the challenge site and CHS. The FasL/perforin-mediated activity of wild-type neutrophils induced the expression of T cell chemoattractants, CCL1, CCL2, and CCL5, within the hapten-challenged skin. These results indicate FasL/perforin-independent functions of hapten-primed CD8 T cells in CHS and identify new functions for neutrophils in regulating effector CD8 T cell recruitment and immune responses in the skin.

IL-1 receptor signaling is required at multiple stages of sensitization and elicitation of the contact hypersensitivity response

Contact hypersensitivity (CHS) is a CD8 T cell-mediated response to hapten skin sensitization and challenge. The points at which IL-1R signaling is required during this complex, multistep immune response have not been clearly delineated. The role of IL-1R signaling during 2, 4 dinitro-1-fluorobenezene (DNFB) sensitization to induce hapten-specific CD8 effector T cells and in the trafficking of the effector T cells to the DNFB challenge site to elicit the response were investigated using IL-1R deficient mice. DNFB-sensitized IL-1R(-/-) mice had low CHS responses to hapten challenge that were caused in part by marked decreases in hapten-specific CD8 T cell development to IL-17- and IFN-γ-producing cells during sensitization. Hapten-primed wild type CD8 T cell transfer to naive IL-1R(-/-) mice did not result in T cell activation in response to hapten challenge, indicating a need for IL-1R signaling for the localization or activation, or both, of the CD8 T cells at the challenge site. Decreased CD8 T cell priming in sensitized IL-1R(-/-) mice was associated with marked decreases in hapten-presenting dendritic cell migration from the sensitized skin to draining lymph nodes. Transfer of hapten-presenting dendritic cells from wild type donors to naive IL-1R(-/-) mice resulted in decreased numbers of the dendritic cells in the draining lymph nodes and decreased priming of hapten-specific CD8 T cells compared with dendritic cell transfer to naive wild type recipients. These results indicate that IL-1R signaling is required at multiple steps during the course of sensitization and challenge to elicit CHS.