Groalpha-mediated recruitment of neutrophils is required for elicitation of contact hypersensitivity

Exploring the roles of prostanoids, leukotriens, and dietary fatty acids in cutaneous inflammatory diseases: Insights from pharmacological and genetic approaches

Prostanoids and leukotrienes (LTs) are representative of ω6 fatty acid-derived metabolites that exert their actions through specific receptors on the cell surface. These lipid mediators, being unstable in vivo, act locally at their production sites; thus, their physiological functions remain unclear. However, recent pharmacological and genetic approaches using experimental murine models have provided significant insights into the roles of these lipid mediators in various pathophysiological conditions, including cutaneous inflammatory diseases. These lipid mediators act not only through signaling by themselves but also by potentiating the signaling of other chemical mediators, such as cytokines and chemokines. For instance, prostaglandin E2 -EP4 and LTB4 -BLT1 signaling on cutaneous dendritic cells substantially facilitate their chemokine-induced migration ability into the skin and play critical roles in the priming and/or activation of antigen-specific effector T cells in the skin. In addition to these ω6 fatty acid-derived metabolites, various ω3 fatty acid-derived metabolites regulate skin immune cell functions, and some exert potent anti-inflammatory functions. Lipid mediators act as modulators of cutaneous immune responses, and manipulating the signaling from lipid mediators has the potential as a novel therapeutic approach for human skin diseases.

CD8+ tissue-resident memory T cells recruit neutrophils that are essential for flare-ups in contact dermatitis

BACKGROUND

Allergic contact dermatitis (ACD) is classically described as a delayed-type hypersensitivity reaction. However, patients often experience flare-ups characterized by itching erythema, edema, and often vesicles occurring within hours after re-exposure of previously sensitized skin to the specific contact allergen. Recent studies have indicated that skin-resident memory T (T_RM ) cells play a central role in ACD. However, the pathogenic role of T_RM cells in allergen-induced flare-ups is not known.

METHODS

By the use of various mouse models and cell depletion protocols, we investigated the role of epidermal T_RM cells in flare-up reactions to the experimental contact allergen 1-fluoro-2,4-dinitrobenzene. The inflammatory response was measured by changes in ear thickness, and the cellular composition in epidermis was determined by flow cytometry and confocal microscopy. Finally, adaptive transfer and inhibitors were used to determine the role of T_RM cells, neutrophils, and CXCL1/CXCL2 in the response.

RESULTS

We show that CD8⁺ T_RM cells initiate massive infiltration of neutrophils in the epidermis within 12 h after re-exposure to the contact allergen. Depletion of neutrophils before re-exposure to the allergen abrogated the flare-up reactions. Furthermore, we demonstrate that CD8⁺ T_RM cells mediate neutrophil recruitment by inducing CXCL1 and CXCL2 production in the skin, and that blockage of the C-X-C chemokine receptor type 1 and 2 inhibits flare-up reactions and neutrophil infiltration.

CONCLUSION

As the first, we show that epidermal CD8⁺ T_RM cells cause ACD flare-ups by rapid recruitment of neutrophils to the epidermis.

ω3 fatty acid metabolite, 12-hydroxyeicosapentaenoic acid, alleviates contact hypersensitivity by downregulation of CXCL1 and CXCL2 gene expression in keratinocytes via retinoid X receptor α

ω3 fatty acids show potent bioactivities via conversion into lipid mediators; therefore, metabolism of dietary lipids is a critical determinant in the properties of ω3 fatty acids in the control of allergic inflammatory diseases. However, metabolic progression of ω3 fatty acids in the skin and their roles in the regulation of skin inflammation remains to be clarified. In this study, we found that 12-hydroxyeicosapentaenoic acid (12-HEPE), which is a 12-lipoxygenase metabolite of eicosapentaenoic acid, was the prominent metabolite accumulated in the skin of mice fed ω3 fatty acid-rich linseed oil. Consistently, the gene expression levels of Alox12 and Alox12b, which encode proteins involved in the generation of 12-HEPE, were much higher in the skin than in the other tissues (eg, gut). We also found that the topical application of 12-HEPE inhibited the inflammation associated with contact hypersensitivity by inhibiting neutrophil infiltration into the skin. In human keratinocytes in vitro, 12-HEPE inhibited the expression of two genes encoding neutrophil chemoattractants, CXCL1 and CXCL2, via retinoid X receptor α. Together, the present results demonstrate that the metabolic progression of dietary ω3 fatty acids differs in different organs, and identify 12-HEPE as the dominant ω3 fatty acid metabolite in the skin.

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.

Animal Models of Contact Dermatitis: 2,4-Dinitrofluorobenzene-Induced Contact Hypersensitivity

Allergic contact dermatitis (ACD) is a common skin disease with high prevalence in work environments. Human allergic contact dermatitis is triggered by the exposure to haptens that leads to an initial phase known as sensitization. During this phase, hapten-protein complexes presented by antigen-presenting cells activate a T-cell-mediated response, leading to the generation of memory cells against the hapten. Upon re-exposure to the same hapten, the elicitation phase is initiated. This phase is characterized by a quicker acute inflammatory response involving activation and/or infiltration of a variety of immune cell populations. Human ACD can be studied through the use of animal models of contact hypersensitivity (CHS). The 2,4-dinitrofluorobenzene (DNFB)-induced CHS model is a commonly used mouse model that has been helpful in the study of the mechanisms as well as potential therapeutic interventions of ACD. In this chapter I will provide a detailed protocol to develop acute DNFB-induced CHS in mice in a period of 7 days. In addition, I will discuss several key considerations for experimental design including best controls, potential expected outcomes, and sample collection.

The Gastrointestinal Helminth Heligmosomoides bakeri Suppresses Inflammation in a Model of Contact Hypersensitivity

Helminths regulate host immune responses to ensure their own long-term survival. Numerous studies have demonstrated that these helminth-induced regulatory mechanisms can also limit host inflammatory responses in several disease models. We used the Heligmosomoides bakeri (Hb) infection model (also known as H. polygyrus or H. polygyrus bakeri in the literature) to test whether such immune regulation affects skin inflammatory responses induced by the model contact sensitiser dibutyl phthalate fluorescein isothiocynate (DBP-FITC). Skin lysates from DBP-FITC-sensitized, Hb-infected mice produced less neutrophil specific chemokines and had significantly reduced levels of skin thickening and cellular inflammatory responses in tissue and draining lymph nodes (LNs) compared to uninfected mice. Hb-induced suppression did not appear to be mediated by regulatory T cells, nor was it due to impaired dendritic cell (DC) activity. Mice cleared of infection remained unresponsive to DBP-FITC sensitization indicating that suppression was not via the secretion of Hb-derived short-lived regulatory molecules, although long-term effects on cells cannot be ruled out. Importantly, similar helminth-induced suppression of inflammation was also seen in the draining LN after intradermal injection of the ubiquitous allergen house dust mite (HDM). These findings demonstrate that Hb infection attenuates skin inflammatory responses by suppressing chemokine production and recruitment of innate cells. These findings further contribute to the growing body of evidence that helminth infection can modulate inflammatory and allergic responses via a number of mechanisms with potential to be exploited in therapeutic and preventative strategies in the future.

Oral administration of whole dihomo-γ-linolenic acid-producing yeast suppresses allergic contact dermatitis in mice

Dihomo-γ-linolenic acid (DGLA, C20: 3n-6) is known to have an anti-inflammatory activity, but its range of effects was not well studied because of its limited natural sources. We addressed these issues by constructing an yeast Saccharomyces cerevisiae strain having a complete metabolic pathway for DGLA synthesis by introducing two desaturase and one elongase genes to convert endogenous oleic acid to DGLA. Taking advantage of well-known safety of S. cerevisiae, we previously investigated the efficacy of heat-killed whole DGLA-producing yeast cells on irritant contact dermatitis, and showed that oral intake of this yeast significantly suppressed inflammatory reactions, whereas no such suppression was observed by the intake of 25 times the amount of purified DGLA. Since this method is considered to be a simple and efficient way to suppress inflammation, we examined its effectiveness against allergic contact dermatitis (ACD) in this study and showed that this method was also effective against ACD.

Dietary coconut oil ameliorates skin contact hypersensitivity through mead acid production in mice

Coconut oil is used as a dietary oil worldwide, and its healthy effects are recognized by the fact that coconut oil is easy to digest, helps in weight management, increases healthy cholesterol, and provides instant energy. Although topical application of coconut oil is known to reduce skin infection and inflammation, whether dietary coconut oil has any role in decreasing skin inflammation is unknown. In this study, we showed the impact of dietary coconut oil in allergic skin inflammation by using a mouse model of contact hypersensitivity (CHS). Mice maintained on coconut oil showed amelioration of skin inflammation and increased levels of cis-5, 8, 11-eicosatrienoic acid (mead acid) in serum. Intraperitoneal injection of mead acid inhibited CHS and reduced the number of neutrophils infiltrating to the skin. Detailed mechanistic studies unveiled that mead acid inhibited the directional migration of neutrophils by inhibiting the filamentous actin polymerization and leukotriene B₄ production required for secondary recruitment of neutrophils. Our findings provide valuable insights into the preventive roles of coconut oil and mead acid against skin inflammation, thereby offering attractive therapeutic possibilities.

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.

Amorphous silicon dioxide nanoparticles modulate immune responses in a model of allergic contact dermatitis

Amorphous silicon dioxide nanoparticles (SiNPs) are ubiquitous, and they are currently found in cosmetics, drugs, and foods. Biomedical research is also focused on using these nanoparticles as drug delivery and bio-sensing platforms. Due to the high potential for skin exposure to SiNPs, research into the effect of topical exposure on both healthy and inflammatory skin models is warranted. While we observe only minimal effects of SiNPs on healthy mouse skin, there is an immunomodulatory effect of these NPs in a model of allergic contact dermatitis. The effect appears to be mediated partly by keratinocytes and results in decreases in epidermal hyperplasia, inflammatory cytokine release, immune cell infiltration, and a subsequent reduction in skin swelling. Additional research is required to further our mechanistic understanding and to validate the extent of this immunomodulatory effect in human subjects in order to assess the potential prophylactic use of SiNPs for treating allergic skin conditions.

Multi-walled carbon nanotube oxidation dependent keratinocyte cytotoxicity and skin inflammation

BACKGROUND

The effects of carbon nanotubes on skin toxicity have not been extensively studied; however, our lab has previously shown that a carboxylated multi-walled carbon nanotube (MWCNT) exacerbates the 2, 4-dinitrofluorobenzene induced contact hypersensitivity response in mice. Here we examine the role of carboxylation in MWCNT skin toxicity.

RESULTS

MWCNTs were analyzed by transmission electron microscopy, zetasizer, and x-ray photoelectron spectroscopy to fully characterize the physical properties. Two MWCNTs with different levels of surface carboxylation were chosen for further testing. The MWCNTs with a high level of carboxylation displayed increased cytotoxicity in a HaCaT keratinocyte cell line, compared to the MWCNTs with intermediate levels of carboxylation. However, neither functionalized MWCNT increased the level of in vitro reactive oxygen species suggesting an alternative mechanism of cytotoxicity. Each MWCNT was tested in the contact hypersensitivity model, and only the MWCNTs with greater than 20% surface carboxylation exacerbated the ear swelling responses. Analysis of the skin after MWCNT exposure reveals that the same MWCNTs with a high level of carboxylation increase epidermal thickness, mast cell and basophil degranulation, and lead to increases in polymorphonuclear cell recruitment when co-administered with 2, 4-dinitrofluorobenzene.

CONCLUSIONS

The data presented here suggest that acute, topical application of low doses of MWCNTs can induce keratinocyte cytotoxicity and exacerbation of allergic skin conditions in a carboxylation dependent manner.

Neutrophil Cathepsin G Regulates Dendritic Cell Production of IL-12 during Development of CD4 T Cell Responses to Antigens in the Skin

Contact hypersensitivity (CHS) is a CD8 T cell-mediated response to hapten skin sensitization and challenge. Sensitization of wild-type (WT) mice induces hapten-reactive effector CD8 T cells producing IFN-γ and IL-17- and IL-4-producing CD4 T cells that cannot mediate CHS. Although CXCR2-dependent Ly6G⁺ (neutrophil) cell recruitment into hapten-challenged skin is required to direct effector CD8 T cell infiltration into the challenge site to elicit CHS, 2,4-dinitrofluorobenezene (DNFB) sensitization of CXCR2^-/- mice and neutrophil-depleted WT mice induced both hapten-reactive CD4 and CD8 T cells producing IFN-γ and IL-17. CD4 T cell-mediated CHS responses were not generated during DNFB sensitization of neutrophil-depleted WT mice treated with anti-IL-12 mAb or neutrophil-depleted IL-12^-/- mice. Neutrophil depletion during DNFB sensitization of WT mice markedly increased IL-12-producing hapten-primed dendritic cell numbers in the skin-draining lymph nodes. Sensitization of mice lacking the neutrophil serine protease cathepsin G (CG)-induced hapten-reactive CD4 and CD8 T cells producing IFN-γ and IL-17 with elevated and elongated CHS responses to DNFB challenge. Induction of CHS effector CD4 T cells producing IFN-γ in neutrophil-depleted WT mice was eliminated by s.c. injection of active, but not inactivated, CG during sensitization. Thus, hapten skin sensitization induces neutrophil release of CG that systemically inhibits hapten-presenting dendritic cell production of IL-12 and the development of hapten-reactive CD4 T cells to IFN-γ-producing CHS effector cells.

Inhibitory effects of dietary soyasaponin on 2,4-dinitrofluorobenzene-induced contact hypersensitivity in mice

Soyasaponins (SSs) abundant in soybean have anti-inflammatory activities; however, their therapeutic effects on allergic contact dermatitis (ACD) remain unknown. To assess the effects of SS-enriched diets on ACD, we used a mouse model of contact hypersensitivity (CHS). Mice were fed low-dose or high-dose SS-containing diets for 3 weeks prior to CHS induction with 2,4-dinitrofluorobenzene (DNFB). The low-dose SS diet attenuated DNFB-induced ear swelling and tissue oedema, and reduced the number of infiltrating Gr-1-positive myeloid cells. Low-dose, but not high-dose, SSs decreased chemokine (C-X-C motif) ligand 2 (CXCL2) and triggering receptor expressed on myeloid cells (TREM)-1 production in ear tissues, compared to a control. Taxonomic 16S rRNA analysis revealed significant alterations in faecal microbiota caused by CHS, which were reversed by low-dose SSs. The low-dose SS and non-CHS groups clustered together, while the high-dose SS group split between CHS and non-CHS clusters. Our results demonstrated that low-dose SSs alleviated CHS symptoms by attenuating inflammation and improving the intestinal microbiota composition, suggesting that dietary SSs may have beneficial effects on ACD.

Neutrophils are dispensable in the modulation of T cell immunity against cutaneous HSV-1 infection

Neutrophils rapidly infiltrate sites of inflammation during peripheral infection or tissue injury. In addition to their well described roles as pro-inflammatory phagocytes responsible for pathogen clearance, recent studies have demonstrated a broader functional repertoire including mediating crosstalk between innate and adaptive arms of the immune system. Specifically, neutrophils have been proposed to mediate antigen transport to lymph nodes (LN) to modulate T cell priming and to influence T cell migration to infected tissues. Using a mouse model of cutaneous herpes simplex virus type 1 (HSV-1) infection we explored potential contributions of neutrophils toward anti-viral immunity. While a transient, early influx of neutrophils was triggered by dermal scarification, we did not detect migration of neutrophils from the skin to LN. Furthermore, despite recruitment of neutrophils into LN from the blood, priming and expansion of CD4⁺ and CD8⁺ T cells was unaffected following neutrophil depletion. Finally, we found that neutrophils were dispensable for the migration of effector T cells into infected skin. Our study suggests that the immunomodulatory roles of neutrophils toward adaptive immunity may be context-dependent, and are likely determined by the type of pathogen and anatomical site of infection.

Aquaporin-9-expressing neutrophils are required for the establishment of contact hypersensitivity

Aquaporin-9 (AQP9), a water/glycerol channel protein, is expressed in several immune cells including neutrophils; however, its role in immune response remains unknown. Here we show the involvement of AQP9 in hapten-induced contact hypersensitivity (CHS), as a murine model of skin allergic contact dermatitis, using AQP9 knockout (AQP9^−/−) mice. First, the CHS response to hapten dinitrofluorobenzene (DNFB) was impaired in AQP9^−/− mice compared with wild-type (WT) mice. Adoptive transfer of sensitized AQP9^−/− draining lymph node (dLN) cells into WT recipients resulted in a reduced CHS response, indicating impaired sensitization in AQP9^−/− mice. Second, administration of WT neutrophils into AQP9^−/− mice during sensitization rescued the impaired CHS response. Neutrophil recruitment to dLNs upon hapten application was attenuated by AQP9 deficiency. Coincidentally, AQP9^−/− neutrophils showed a reduced CC-chemokine receptor 7 (CCR7) ligand-induced migration efficacy, which was attributed to the attenuated recruitment of neutrophils to dLNs. Furthermore, we found that neutrophil deficiency, observed in AQP9^−/− or neutrophil-depleted mice, decreased IL-17A production by dLN cells, which might be responsible for T cell activation during a subsequent CHS response. Taken together, these findings suggest that AQP9 is required for the development of sensitization during cutaneous acquired immune responses via regulating neutrophil function.

Leukotriene B₄-leukotriene B₄ receptor axis promotes oxazolone-induced contact dermatitis by directing skin homing of neutrophils and CD8⁺ T cells

Leukotriene B4 (LTB4 ) is a lipid mediator that is rapidly generated in inflammatory sites, and its functional receptor, BLT1, is mostly expressed on immune cells. Contact dermatitis is a common inflammatory skin disease characterized by skin oedema and abundant inflammatory infiltrates, primarily including neutrophils and CD8(+) T cells. The role of the LTB4 -BLT1 axis in contact dermatitis remains largely unknown. In this study, we found up-regulated gene expression of 5-lipoxygenase and leukotriene A4 hydrolase, two critical enzymes for LTB4 synthesis, BLT1 and elevated LTB4 levels in skin lesions of oxazolone (OXA)-induced contact dermatitis. BLT1 deficiency or blockade of LTB4 and BLT1 by the antagonists, bestatin and U-75302, respectively, in the elicitation phase caused significant decreases in ear swelling and skin-infiltrating neutrophils and CD8(+) T cells, which was accompanied by significantly reduced skin expression of CXCL1, CXCL2, interferon-γ and interleukin-1β. Furthermore, neutrophil depletion during the elicitation phase of OXA-induced contact dermatitis also caused significant decreases in ear swelling and CD8(+) T-cell infiltration accompanied by significantly decreased LTB4 synthesis and gene expression of CXCL2, interferon-γ and interleukin-1β. Importantly, subcutaneous injection of exogenous LTB4 restored the skin infiltration of CD8(+) T cells in neutrophil-depleted mice following OXA challenge. Collectively, our results demonstrate that the LTB4 -BLT1 axis contributes to OXA-induced contact dermatitis by mediating skin recruitment of neutrophils, which are a major source of LTB4 that sequentially direct CD8(+) T-cell homing to OXA-challenged skin. Hence, LTB4 and BLT1 could be potential therapeutic targets for the treatment of contact dermatitis.

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.

Sweet Is the Memory of Past Troubles: NK Cells Remember

Natural killer (NK) cells are important in host defense against tumors and microbial pathogens. Recent studies indicate that NK cells share many features with the adaptive immune system, and like B cells and T cells, NK cells can acquire immunological memory. Here, we review evidence for NK cell memory and the molecules involved in the generation and maintenance of these self-renewing NK cells that provide enhanced protection of the host.

Toll-like receptor 3 increases allergic and irritant contact dermatitis

There is increasing recognition of the role of Toll-like receptor 3 (TLR3) in noninfectious inflammatory diseases, but the function of TLR3 in inflammatory skin diseases is unclear. We investigated the functions of TLR3 in allergic and irritant contact dermatitis (ICD). The contact hypersensitivity (CHS) response was lower in Toll-like receptor 3 knockout (Tlr3 KO) mice, and was greater in TLR3 transgenic (Tg) mice than in wild-type (WT) mice after challenge with 2,4,6-trinitro-1-chlorobenzene. Adoptive transfer of immunized lymph node cells from Tlr3 KO mice induced CHS in WT recipients. In contrast, adoptive transfer of those from WT mice did not fully induce CHS in Tlr3 KO recipients. The ICD reaction following croton oil application was lower in Tlr3 KO mice, and was greater in TLR3 Tg mice than in WT mice. Maturation, migration, and antigen presentation of dendritic cells and proliferation of lymphocytes between WT mice and Tlr3 KO mice were comparable. These results show that TLR3 enhances antigen-independent skin inflammation in the elicitation phase of allergic contact dermatitis and in ICD.

The role of neutrophils and G-CSF in DNFB-induced contact hypersensitivity in mice

Neutrophils are thought to play an important role during contact hypersensitivity (CHS) in mice, a notion which is supported by studies in which neutrophils are depleted by monoclonal antibodies (mAb). Here, we show that administration of the commonly used anti-mouse Ly6G/C mAb (clone RB6.8C5) leads to depletion of not only neutrophils but also a population of monocytes and macrophages. In contrast, depletion using a Ly6G-specific mAb (clone 1A8) only leads to depletion of neutrophils. We demonstrate that the anti-Ly6G/C mAb suppresses the inflammatory response to a higher extent than the anti-Ly6G mAb suggesting that the impact of neutrophil-depletion in the CHS model may have been overstated when based on protocols using the anti-Ly6G/C mAb. Still, the role of neutrophils in CHS is substantiated as we demonstrate that G-CSF is an important regulator of neutrophil mobilization and effector function in CHS. Indeed, G-CSF was detectable both in the inflamed tissue and in serum during the immune response and we show that blocking G-CSF results in a reduced number of neutrophils in the blood and an attenuation of the ear-swelling response in the tissue. In conclusion, this study supports that neutrophils are important drivers of inflammation in the DNFB-induced CHS model and shows that G-CSF is a significant factor in mobilizing neutrophils during the response.

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.

Diverse novel functions of neutrophils in immunity, inflammation, and beyond

Neutrophils have long been considered simple suicide killers at the bottom of the hierarchy of the immune response. That view began to change 10-20 yr ago, when the sophisticated mechanisms behind how neutrophils locate and eliminate pathogens and regulate immunity and inflammation were discovered. The last few years witnessed a new wave of discoveries about additional novel and unexpected functions of these cells. Neutrophils have been proposed to participate in protection against intracellular pathogens such as viruses and mycobacteria. They have been shown to intimately shape the adaptive immune response at various levels, including marginal zone B cells, plasmacytoid dendritic cells and T cell populations, and even to control NK cell homeostasis. Neutrophils have been shown to mediate an alternative pathway of systemic anaphylaxis and to participate in allergic skin reactions. Finally, neutrophils were found to be involved in physiological and pathological processes beyond the immune system, such as diabetes, atherosclerosis, and thrombus formation. Many of those functions appear to be related to their unique ability to release neutrophil extracellular traps even in the absence of pathogens. This review summarizes those novel findings on versatile functions of neutrophils and how they change our view of neutrophil biology in health and disease.

Inflammatory and immune mechanisms in contact hypersensitivity (CHS) in rats

Contact hypersensitivity (CHS) is a T-cell-mediated skin inflammatory reaction to cutaneous exposure to small sensitizing chemicals, haptens. Majority of CHS studies were conducted in mice and there is paucity of data in other experimental animals. In this review, after a brief survey of murine CHS, hitherto known characteristics of CHS in rats were presented including inflammatory and immune mechanisms of both sensitization and elicitation phases. Survey of literature of rat CHS is presented, with our data concerning the importance of genetic background both in the induction and in the expression of reaction to dinitrochlorobenzene. The knowledge of CHS in rats, preferred animal in immunopharmacological studies, might help development of immunomodulatory intervention in contact allergy.

Update of immune events in the murine contact hypersensitivity model: toward the understanding of allergic contact dermatitis

Allergic contact dermatitis (ACD) is one of the most common skin diseases, consisting of sensitization and elicitation phases. With the advancement of technology and the discovery of new types of immune cells, our knowledge of the immunological mechanisms of contact hypersensitivity (CHS) as a murine model of ACD has expanded significantly in the past decade. For example, by introducing regulatory T cells, CD4(+) T-helper 17 cells, and Langerin-positive dermal dendritic cells, the initiation and termination mechanism of CHS has been revealed. In addition, the role of mast cells in CHS, long a matter of debate, has become apparent by developing conditional mast cell-deficient mice. Moreover, the role of the innate immunity system, such as that of Toll-like receptor signaling, has made a breakthrough in this field. In this review, we will integrate the recent advancement of immunological mechanisms of both the sensitization and elicitation phases of CHS into the classic view, and we will discuss updated mechanisms on its development and future directions.

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.

ONZIN deficiency attenuates contact hypersensitivity responses in mice

ONZIN is abundantly expressed in immune cells of both the myeloid and lymphoid lineage. Expression by lymphoid cells has been reported to further increase after cutaneous exposure of mice to antigens and haptens capable of inducing contact hypersensitivity (CHS), suggesting that ONZIN has a critical role in this response. Here, we report that indeed ONZIN-deficient mice develop attenuated CHS to a number of different haptens. Dampened CHS responses correlated with a significant reduction in pro-inflammatory IL-6 at the challenge site in ONZIN-deficient animals, compared with wild-type controls. Together the study of these animals indicates that loss of ONZIN impacts the effector phase of the CHS response through the regulation of pro-inflammatory factors.

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.

Percutaneous toxicity of dinitrochlorobenzene (DNCB) in rats

Contact hypersensitivity reaction (CHS) is a T-cell-mediated skin inflammatory reaction to cutaneous exposure to small sensitizing chemicals, haptens. While the significance of local inflammatory skin response to the hapten application in CHS induction and expression is known, there is paucity of data concerning systemic inflammation in CHS. In this study, changes in cellular (peripheral blood granulocytes) and humoral (plasma tumor necrosis factor (TNF)-α levels) components of inflammation during sensitization of rats with two consecutive applications of dinitrochlorobenzene (DNCB) were examined. The impact of sensitization on these parameters was determined by employing low (0.4%) and high (4%) hapten doses and by examining the dynamics (i.e. one and three days following the last application of DNCB) of these changes. Dose-dependent increase in relative numbers and priming (for respiratory burst and adhesion) effect of skin sensitization with DNCB on peripheral blood neutrophils in rats were noted. No changes in circulating TNF-α levels were observed following the sensitization. The increase in lung myeloperoxidase content and histologically evident presence of neutrophils was observed in lungs of the sensitized rats. The changes in granulocyte priming for adhesion might have accounted for the observed increase in lung neutrophil content in the sensitized rats.

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

Contact hypersensitivity is a CD8 T cell-mediated response to hapten sensitization and challenge of the skin. Effector CD8 T cell recruitment into the skin parenchyma to elicit the response to hapten challenge requires prior CXCL1/KC-directed neutrophil infiltration within 3-6 h after challenge and is dependent on IFN-γ and IL-17 produced by the hapten-primed CD8 T cells. Mechanisms directing hapten-primed CD8 T cell localization and activation in the Ag challenge site to induce this early CXCL1 production in response to 2,4-dinitrofluorobenzene were investigated. Both TNF-α and IL-17, but not IFN-γ, mRNA was detectable within 1 h of hapten challenge of sensitized mice and increased thereafter. Expression of ICAM-1 was observed by 1 h after challenge of sensitized and nonsensitized mice and was dependent on TNF-α. The induction of IL-17, IFN-γ, and CXCL1 in the challenge site was not observed when ICAM-1 was absent or neutralized by specific Ab. During the elicitation of the contact hypersensitivity response, endothelial cells expressed ICAM-1 and produced CXCL1 suggesting this as the site of CD8 T cell localization and activation. Endothelial cells isolated from challenged skin of naive and sensitized mice had acquired the hapten and the ability to activate hapten-primed CD8 T cell cytokine production. These results indicate that hapten application to the skin of sensitized animals initiates an inflammatory response promoting hapten-primed CD8 T cell localization to the challenge site through TNF-α-induced ICAM-1 expression and CD8 T cell activation to produce IFN-γ and IL-17 through endothelial cell presentation of hapten.

Contact allergic response to dinitrochlorobenzene (DNCB) in rats: insight from sensitization phase

Contact hypersensitivity (CHS) is a T-cell-mediated skin inflammatory reaction to cutaneous exposure to small sensitizing chemicals, haptens. Majority of CHS studies were conducted in mice and there is paucity of data in other experimental animals. In the present study, characteristics of contact hypersensitivity reaction to dinitrochlorobenzene (DNCB) were determined in Th1-prone Dark Agouti (DA) rats by evaluating sensitization phase as a function of time-dependent changes in draining lymph nodes (DLN). Apart from basic indices of DLN activity (cellularity and proliferation), the production of cytokines relevant for CHS induction, interleukin-6 (IL-6), interferon-γ (IFN-γ), interleukin-17 (IL-17) and interleukin-4 (IL-4) was analyzed. Anti-inflammatory cytokine interleukin-10 (IL-10) production by DLN cells was determined as well. Highest production of IL-6, IFN-γ and IL-17 in sensitized animals was observed at day 3 after DNCB application, with a decrease at day 5. Increased messages for IFN-γ and IL-17 were noted at this time point. In contrast to inflammatory cytokines, anti-inflammatory cytokine interleukin-4 (IL-4) was undetectable during the entire sensitization phase. Differential pattern (IL-6 and IFN-γ) and level (IFN-γ and IL-17) of inflammatory cytokine production was noted in sensitized Th2-prone Albino Oxford (AO) rats. Similarly to DA rats, no changes in IL-4 were noted in AO rats. Strain-dependent differences in inflammatory cytokine production seem to be based on anti-inflammatory cytokine interleukin-10 (IL-10). Production of IFN-γ concomitantly with undetectable IL-4 in both strains classify rat CHS to DNCB as Th1/type 1 reaction. Detection of IL-17 in sensitized DLN cells points to the involvement of T(IL-17) cells in rat contact hypersensitivity.

Elevated epidermal ornithine decarboxylase activity suppresses contact hypersensitivity

Previous reports have shown that elevated polyamine biosynthesis is sufficient to promote skin tumorigenesis in susceptible mouse strains. 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. Using an ODCER transgenic mouse model in which ODC is targeted to the epidermis, we examined the effect of ODC overexpression in keratinocytes on a classic contact hypersensitivity (CHS) response. Compared with normal littermate mice, ODCER transgenic mice showed reduced ear swelling, reduced neutrophil infiltration, and decreased migration of fluorescein isothiocyanate-loaded dendritic cells (DCs) to draining lymph nodes following hapten elicitation of CHS. In addition, elevated epidermal ODC activity suppressed the levels of cytokines keratinocyte-derived chemokine, monocyte chemoattractant protein-1, interleukin-6 (IL-6), and IL-10. Adoptive transfer of lymphocytes from sensitized ODCER transgenic or normal littermate mice to naive ODCER transgenic or wild-type mice indicated that elevated epidermal ODC activity suppresses both the sensitization and elicitation phases of CHS. The specific ODC inhibitor, α-difluoromethylornithine, abrogated all suppressive effects of ODC in CHS reactions. Collectively, these data suggest that the immunosuppression promoted by increased epidermal ODC is mediated by a reduction in cytokine levels, which suppresses DC migration and reduces immune cell infiltration to the site of hapten application.

Molecular mechanisms of leukocyte trafficking in T-cell-mediated skin inflammation: insights from intravital imaging

Infiltration of T cells is a key step in the pathogenesis of the inflammatory skin diseases atopic dermatitis, allergic contact dermatitis and psoriasis. Understanding the mechanisms of T cell recruitment to the skin is therefore of fundamental importance for the discovery and application of novel therapies for these conditions. Studies of both clinical samples and experimental models of skin inflammation have implicated specific adhesion molecules and chemokines in lymphocyte recruitment. In particular, recent studies using advanced in vivo imaging techniques have greatly increased our understanding of the kinetics and molecular basis of this process. In this review, we summarise the current understanding of the cellular immunology of antigen-driven dermal inflammation and the roles of adhesion molecules and chemokines. We focus on results obtained using intravital microscopy to examine the dermal microvasculature and interstitium to determine the mechanisms of T cell recruitment and migration in experimental models of T-cell-mediated skin inflammation.

Prostaglandin E(2)-EP(3) signaling suppresses skin inflammation in murine contact hypersensitivity

BACKGROUND

Prostaglandin (PG) E(2) exerts a variety of actions through 4 G protein-coupled receptors designated as EP(1), EP(2), EP(3), and EP(4). We have reported that PGE(2) acts on EP(3) in airway epithelial cells and exerts anti-inflammatory actions in ovalbumin-induced murine allergic asthma. Although EP(3) is also expressed in skin and PGE(2) is produced abundantly during skin allergic inflammation, the role of PGE(2)-EP(3) signaling in skin allergic inflammation remains unknown.

OBJECTIVE

We sought to investigate whether PGE(2)-EP(3) signaling exerts anti-inflammatory actions in skin allergic inflammation.

METHODS

We used a murine contact hypersensitivity (CHS) model and examined the role of EP(3) by using an EP(3)-selective agonist, ONO-AE-248 (AE248), and EP(3)-deficient mice. The inflammation was evaluated by the thickness and histology of the hapten-challenged ear. Inflammation-associated changes in gene expression and effects of AE248 were examined by means of microarray analysis of the skin. Localization of EP(3) was examined by staining for beta-galactosidase knocked in at the EP(3) locus in EP(3)-deficient mice. EP(3) action was also examined in cultured keratinocytes.

RESULTS

Administration of AE248 during the elicitation phase significantly suppressed CHS compared with that seen in vehicle-treated mice. Microarray analysis revealed that administration of AE248 inhibited the gene expression of neutrophil-recruiting chemokines, including CXCL1, at the elicitation site. X-gal staining in EP(3)-deficient mice revealed EP(3) expression in keratinocytes, which was further confirmed by anti-EP(3) antibody in wild-type mice. In cultured keratinocytes AE248 suppressed CXCL1 production induced by TNF-alpha.

CONCLUSION

PGE(2)-EP(3) signaling inhibits keratinocytes activation and exerts anti-inflammatory actions in murine CHS.

Thioredoxin suppresses the contact hypersensitivity response by inhibiting leukocyte recruitment during the elicitation phase

Thioredoxin, a redox-regulating protein that scavenges reactive oxygen species, appears to show an excellent antiinflammatory effect in treating animal models of various human inflammatory diseases. The aim of this study was to clarify whether thioredoxin is useful for treating inflammatory skin diseases, such as contact dermatitis, caused by epicutaneous exposure to environmental and occupational antigens. The allergic contact hypersensitivity response was suppressed in thioredoxin-transgenic mice. This suppressive effect of thioredoxin appeared to be via the inhibition of the efferent limb of contact hypersensitivity because administration of recombinant thioredoxin suppressed the inflammatory response in the elicitation phase but not in the induction phase. Adoptive-transfer studies revealed that the host environment, but not donor leukocytes, is critical in this suppressive effect. In thioredoxin-transgenic mice, the infiltration of neutrophils in the elicitation site was diminished, whereas the migratory function of cutaneous dendritic cells and hapten-specific cell proliferation were not disturbed. Thioredoxin-transgenic mice had also an attenuated inflammatory response to croton oil. These findings suggest that thioredoxin prevents skin inflammatory responses and could be a suitable candidate for the treatment of contact dermatitis.

CD8 T cells producing IL-17 and IFN-gamma initiate the innate immune response required for responses to antigen skin challenge

Effector CD8 T cell recruitment into the skin in response to Ag challenge requires prior CXCL1/KC-directed neutrophil infiltration. Mechanisms inducing CXCL1 production and the dynamics of neutrophil-CD8 T cell interactions during elicitation of Ag-specific responses in the skin were investigated. CXCL1 and CXCL2/MIP-2 were produced within 3-6 h of Ag challenge at 10-fold higher levels in skin challenge sites of Ag-sensitized vs nonsensitized mice. In the challenge sites of sensitized mice this production decreased at 6-9 h postchallenge to near the levels observed in skin challenge sites of nonsensitized mice but rose to a second peak 12 h after challenge. The elevated early neutrophil chemoattractant production at 3-6 h after skin challenge of sensitized animals required both IFN-gamma and IL-17, produced by distinct populations of Ag-primed CD8 T cells in response to Ag challenge. Although induced by the Ag-primed CD8 T cells, the early CXCL1 and CXCL2 production was accompanied by neutrophil but not CD8 T cell infiltration into the skin Ag challenge site. Infiltration of the CD8 T cells into the challenge site was not observed until 18-24 h after challenge. These results demonstrate an intricate series of early interactions between Ag-specific and innate immune components that regulate the sequential infiltration of neutrophils and then effector T cells into the skin to mediate an immune response.

A small molecule CRTH2 antagonist inhibits FITC-induced allergic cutaneous inflammation

A FITC-induced allergic contact hypersensitivity model was used to investigate the role that the prostaglandin D(2) receptor-chemoattractant receptor-homologous molecule expressed on T(h)2 cells (CRTH2) plays in modulating cutaneous inflammation. Our results show that inhibition of CRTH2, achieved via administration of a potent, small molecule antagonist, Compound A (Cmpd A), effectively blocked edema formation and greatly reduced the inflammatory infiltrate and skin pathology observed in drug vehicle-treated animals. Gene expression analysis revealed that Cmpd A administration down-regulated the transcription of a wide range of pro-inflammatory mediators. This correlated with decreases in cytokine and chemokine protein levels, notably IL-4, IL-1beta, tumor necrosis factor-alpha, transforming growth factor-beta, GRO-alpha, MIP-2 and thymic stromal lymphopoietin (TSLP) in FITC-challenged ears. The administration of an anti-TSLP-neutralizing antibody was only partially effective in lowering the FITC-induced inflammatory infiltrate and cytokine production compared with the CRTH2 antagonist. Taken together, these data suggest that blockade of CRTH2 inhibits multiple pathways leading to cutaneous inflammation in this model. This suggests that CRTH2 antagonism may be a viable route for therapeutic intervention in allergic skin diseases, such as atopic dermatitis.

MMP19 is essential for T cell development and T cell-mediated cutaneous immune responses

Matrix metalloproteinase-19 (MMP19) affects cell proliferation, adhesion, and migration in vitro but its physiological role in vivo is poorly understood. To determine the function of MMP19, we generated mice deficient for MMP19 by disrupting the catalytic domain of mmp19 gene. Although MMP19-deficient mice do not show overt developmental and morphological abnormalities they display a distinct physiological phenotype. In a model of contact hypersensitivity (CHS) MMP19-deficient mice showed impaired T cell-mediated immune reaction that was characterized by limited influx of inflammatory cells, low proliferation of keratinocytes, and reduced number of activated CD8(+) T cells in draining lymph nodes. In the inflamed tissue, the low number of CD8(+) T cells in MMP19-deficient mice correlated with low amounts of proinflammatory cytokines, especially lymphotactin and interferon-inducible T cell alpha chemoattractant (I-TAC). Further analyses showed that T cell populations in the blood of immature, unsensitized mice were diminished and that this alteration originated from an altered maturation of thymocytes. In the thymus, thymocytes exhibited low proliferation rates and the number of CD4(+)CD8(+) double-positive cells was remarkably augmented. Based on the phenotype of MMP19-deficient mice we propose that MMP19 is an important factor in cutaneous immune responses and influences the development of T cells.

The Th17-ELR+ CXC chemokine pathway is essential for the development of central nervous system autoimmune disease

The ELR⁺ CXC chemokines CXCL1 and CXCL2 are up-regulated in the central nervous system (CNS) during multiple sclerosis (MS) and its animal model, experimental autoimmune encephalomyelitis (EAE). However, their functional significance and the pathways regulating their expression are largely unknown. We show that transfer of encephalitogenic CD4⁺ Th17 cells is sufficient to induce CXCL1 and CXCL2 transcription in the spinal cords of naive, syngeneic recipients. Blockade or genetic silencing of CXCR2, a major receptor for these chemokines in mice, abrogates blood–brain barrier (BBB) breakdown, CNS infiltration by leukocytes, and the development of clinical deficits during the presentation as well as relapses of EAE. Depletion of circulating polymorphonuclear leukocytes (PMN) had a similar therapeutic effect. Furthermore, injection of CXCR2⁺ PMN into CXCR2^−/− mice was sufficient to restore susceptibility to EAE. Our findings reveal that a Th17–ELR⁺ CXC chemokine pathway is critical for granulocyte mobilization, BBB compromise, and the clinical manifestation of autoimmune demyelination in myelin peptide–sensitized mice, and suggest new therapeutic targets for diseases such as MS.

Signal transducer and activator of transcription 1 decoy oligodeoxynucleotide suppression of contact hypersensitivity

BACKGROUND

Cytokines play a pivotal role in allergy development through activating signaling mechanisms, such as the Janus kinase/signal transducer and activator of transcription (STAT) pathway, which controls the expression of numerous proinflammatory genes.

OBJECTIVE

In comparison with 2 different corticosteroids and a calcineurin inhibitor, the efficacy of a STAT1 decoy oligodeoxynucleotide (dODN)-containing ointment on hapten-induced contact hypersensitivity was examined in 3 different animal models.

METHODS

After sensitization, the test compounds were administered before hapten challenge, after hapten challenge, or both to different sites of the animal skin. Subsequent erythema and edema formation was scored macroscopically, microscopically, or by a shift in ear weight. Biopsy specimens were taken and processed for histopathology, immunohistochemistry, and real-time PCR analyses.

RESULTS

Treatment with the STAT1 dODN but not the corresponding control ODN markedly improved the clinical signs of inflammation in all 3 animal models in a dose-related manner. In guinea pig skin this was accompanied by a distinct decrease in leukocyte infiltration into the dermis after 24 hours. In addition, expression of CD40, IFN-gamma, IL-1beta, IL-8, IL-12, and TNF-alpha was strongly attenuated. The dODN was equally effective in the domestic pig model when administered therapeutically, and its preventive effect in the mouse model lasted for more than 48 hours.

CONCLUSIONS

Altogether, treatment with the dODN proved to be at least as effective as treatment with the reference compounds.

Macrophages and neutrophils are the targets for immune suppression by glucocorticoids in contact allergy

Glucocorticoids (GCs) are widely used in the treatment of allergic skin conditions despite having numerous side effects. Here we use Cre/loxP-engineered tissue- and cell-specific and function-selective GC receptor (GR) mutant mice to identify responsive cell types and molecular mechanisms underlying the antiinflammatory activity of GCs in contact hypersensitivity (CHS). CHS was repressed by GCs only at the challenge phase, i.e., during reexposure to the hapten. Inactivation of the GR gene in keratinocytes or T cells of mutant mice did not attenuate the effects of GCs, but its ablation in macrophages and neutrophils abolished downregulation of the inflammatory response. Moreover, mice expressing a DNA binding-defective GR were also resistant to GC treatment. The persistent infiltration of macrophages and neutrophils in these mice is explained by an impaired repression of inflammatory cytokines and chemokines such as IL-1beta, monocyte chemoattractant protein-1, macrophage inflammatory protein-2, and IFN-gamma-inducible protein 10. In contrast TNF-alpha repression remained intact. Consequently, injection of recombinant proteins of these cytokines and chemokines partially reversed suppression of CHS by GCs. These studies provide evidence that in contact allergy, therapeutic action of corticosteroids is in macrophages and neutrophils and that dimerization GR is required.

Deficient inflammatory response to UV radiation in neonatal mice

Mechanisms of juvenile susceptibility to cancer are not well understood. The immune response in neonates favors nonresponsiveness or T(H)2-dominant responses, raising the question of a role for neonatal immunity in this susceptibility. We have investigated the postulate that the inflammatory response differs in neonatal and adult skin. We found no inflammatory infiltrate into neonatal mouse skin in response to UV irradiation as a function of time, dose, or wavelength, although UV-induced DNA damage was readily detected. In contrast, UV irradiation of adult mice initiated a dose- and time-dependent influx of inflammatory cells, chiefly CD11b(+)Ly6G(+) neutrophils, into the skin, detected by immunohistochemistry and quantitated by FACS analysis. This inflammatory response was initiated by UVB (290-320 nm) but not by UVA (320-400 nm). Further, in neonates, in contrast to adults, neither topical trinitrochlorobenzene (TNCB) nor i.p. thioglycollate initiated an inflammatory infiltrate. Conversely, topical TNCB applied to neonates was tolerogenic, resulting in a subsequent antigen-specific decrease of the contact-hypersensitivity response in adults. Neonatal blood contained abundant neutrophils, which exhibited impaired chemotaxis to the chemokine growth-related oncogene-alpha but efficient chemotaxis to the bacterial product fMLP, concomitant with decreased expression of CXCR2 but normal levels of CD11b. We propose this neonatal deficiency in the inflammatory response is a significant, previously unrecognized factor in neonatal immune tolerance and may contribute to neonatal susceptibility to cancer, including melanoma and other UV-induced cancers.

Effects of the tumor microenvironment on the efficacy of tumor immunotherapy

Cancer immunotherapy utilizes vaccines targeting tumor antigens or tumor endothelium to prevent or regress tumors. Many cancer vaccines are designed to induce antigen-specific effector T cells that migrate to the tumor site. In an optimal situation, the effector T cells penetrate the tumor, release their effector molecules, induce tumor cell death and tumor regression. However, the tumor microenvironment is frequently immunosuppressive and contributes to a state of immune ignorance, impacting on the vaccine's ability to break tolerance to tumor antigen/s. This review discusses the factors in the tumor microenvironment that can affect the efficacy of cancer vaccines. In particular, the review focuses on pathways leading to effector T cell penetration of tumors or the inhibition of this process.

Accelerated dendritic-cell migration and T-cell priming in SPARC-deficient mice

On their path to draining lymph nodes, epidermal Langerhans cells traverse collagen-dense connective tissue before reaching lymphatic vessels. The matricellular protein SPARC (secreted protein, acidic and rich in cysteine), which is induced during inflammation and tissue repair, organizes collagen deposition in tissue stroma. We analyzed Langerhans cell and dendritic-cell migration and its impact on T-cell priming in SPARC-null (SPARC–/–) and SPARC-sufficient (SPARC+/+) mice. Although the same number of Langerhans cells populate the ear skin of SPARC–/– and SPARC+/+ mice, more Langerhans cells were found in the lymph nodes draining antigen-sensitized ears of SPARC–/– mice and significantly more Langerhans cells migrated from null-mice-derived ear skin explants. Such favored Langerhans cell migration is due to the host environment, as demonstrated by SPARC+/+>SPARC–/– and reciprocal chimeras, and have a profound influence on T-cell priming. Contact-, delayed type-hypersensitivity and naive T-cell receptor-transgenic T-cell priming, together indicate that the lack of SPARC in the environment accelerates the onset of T-cell priming by hastening Langerhans cell/dendritic-cell migration.

Fisiopatologia da dermatite de contato alérgica: papel das células T CD8 efetoras e das células T CD4 regulatórias

A dermatite de contato alérgica (DCA), também conhecida como hipersensibilidade de contato (HSC) é uma das dermatoses inflamatórias mais freqüentes, sendo caracterizada por eritema, pápulas e vesículas, seguidas de ressecamento e descamação. A DCA é induzida pelo contato da pele com substâncias químicas não protéicas denominadas haptenos, e corresponde a uma reação de hipersensibilidade cutânea do tipo tardio, mediada por células T hapteno-específicas. Durante a fase de sensibilização, tanto os precursores de células T CD4+ quanto os de CD8+ são ativados nos linfonodos de drenagem através da apresentação de peptídeos conjugados a haptenos pelas células dendríticas (CD) da pele. A subseqüente exposição de pele ao hapteno em um local a distância induz o recrutamento e ativação de células T específicas no local de provocação, levando à apoptose dos queratinócitos, recrutamento de células inflamatórias e desenvolvimento de sintomas clínicos. Estudos experimentais dos últimos 10 anos demonstraram que, em respostas normais de HSC a haptenos fortes, as células T CD8+ do tipo 1 são efetoras da HSC através de citotoxicidade e produção de IFNgama, enquanto que as células T CD4+ são dotadas de funções de regulação negativa. Estas últimas podem corresponder à população de células T regulatórias CD4+ CD25+ recentemente descritas. Entretanto, em algumas situações, especialmente naquelas em que há um pool deficiente de células T CD8, as células T CD4+ podem ser efetoras da HSC. Estudos em andamento deverão confirmar que a fisiopatologia da DCA em humanos é semelhante à HSC em camundongos, e que a resposta de HSC a haptenos fracos comuns, mais freqüentemente envolvidos na DCA em humanos, é semelhante à descrita para haptenos fortes.

A novel role for neutrophils as a source of T cell-recruiting chemokines IP-10 and Mig during the DTH response to HSV-1 antigen

Analogous to CD4+ T cells, neutrophils are essential participants in delayed-type hypersensitivity (DTH) to Herpes simplex virus type 1 antigen. However, what role they play in this cellular immune response is unclear. The recent recognition that neutrophils are potent producers of chemokines led us to hypothesize that they may help recruit CD4+ effector T cells. In the present study, we show that neutrophil depletion was accompanied by a marked decrease in the numbers of CD4+ and CXC receptor 3+ (CXCR3+)-expressing cells migrating to the DTH site and a sharp drop in the levels of interferon-inducible protein 10 (IP-10) and monokine induced by IFN-gamma (Mig). Purified mouse neutrophils were stimulated directly by IFN-gamma to secrete these chemokines, and neutrophils at the DTH site expressed IP-10. IFN-gamma knockout mice, which manifested depressed ear-swelling following DTH challenge, made little IP-10 and no Mig. Reconstitution of these mice with IFN-gamma induced CXCR3 ligand synthesis. Depletion of neutrophils or CD4+ T cells but not CD8+ T cells markedly reduced IFN-gamma levels, suggesting the former were direct (or indirect) cellular sources of this cytokine. Collectively, our results support the hypothesis that neutrophil production of T cell-recruiting chemokines contributes to the regulation and amplification of the DTH response.

The intensity of neutrophil infiltration controls the number of antigen-primed CD8 T cells recruited into cutaneous antigen challenge sites

Recruitment of antigen-specific T cells into the skin is a critical initiating event during immune responses to many parasites and tumors as well as T cell-mediated, cutaneous, allergic responses and autoimmune diseases. Mechanisms directing T cell trafficking into skin remain largely undefined. Here, we show that cutaneous contact with reactive antigen induces KC/CXC chemokine ligand 1 production and neutrophil infiltration in an antigen, dose-dependent manner. The intensity of neutrophil infiltration into cutaneous antigen challenge sites, in turn, controls the number of antigen-primed T cells recruited into the site and the magnitude of the immune response elicited. The absence of responses in immune animals challenged with suboptimal doses of antigen is overcome by manipulating neutrophil infiltration that then directs antigen-primed T cell infiltration into the challenge site. This inflammation also directs T cells primed to one antigen (dinitrofluorobenzene) into the site when challenged with a completely different antigen (oxazolone). These results identify the intensity of neutrophil infiltration into cutaneous, antigen-deposition sites as a critical parameter for the level of antigen-primed T cell recruitment to mediate the adaptive immune response. This interplay between the innate and adaptive responses suggests a strategy to modulate, in a positive or negative manner, antigen-primed T cell infiltration into cutaneous inflammation sites.

Neutrophil chemoattractant genes KC and MIP-2 are expressed in different cell populations at sites of surgical injury

KC and macrophage-inflammatory protein-2 (MIP-2) are CXC chemokines that exhibit distinct temporal patterns of expression in the skin following surgical injury. In situ hybridization analysis demonstrates that these two chemokines are expressed by distinct cell types at different times following injury. Dermal fibroblasts and endothelial cells are primarily responsible for KC expression in the skin 6 h following surgery. In contrast, MIP-2 production appears to be restricted to infiltrating inflammatory leukocytes including neutrophils and monocytes, which appear later in the response. This cell type-specific pattern of chemokine expression is recapitulated in vitro using isolated primary- and long-term-cultured cell types. Primary dermal fibroblasts stimulated with interleukin-1alpha express predominantly KC and very little MIP-2, and peritoneal exudate neutrophils produce as much or more MIP-2 as KC following stimulation in vitro. Although a collection of exogenous stimuli can induce expression of KC and MIP-2, the quantitative ratio for expression reflects the cell type and not the stimulus. The selective expression of KC over MIP-2 in endothelial cells results from markedly greater KC gene transcription and not from alterations in the rate of mRNA decay. These results demonstrate that distinct CXC chemokines show restricted expression in myeloid versus nonmyeloid cell types and that patterns of chemokine expression at sites of inflammation in vivo reflect the temporally ordered contribution of these distinct cell types.